CA1152759A - Method of and system for controlling drain water level of feed-water heater - Google Patents
Method of and system for controlling drain water level of feed-water heaterInfo
- Publication number
- CA1152759A CA1152759A CA000373749A CA373749A CA1152759A CA 1152759 A CA1152759 A CA 1152759A CA 000373749 A CA000373749 A CA 000373749A CA 373749 A CA373749 A CA 373749A CA 1152759 A CA1152759 A CA 1152759A
- Authority
- CA
- Canada
- Prior art keywords
- water level
- drain
- level control
- opening
- instruction
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Control Of Non-Electrical Variables (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed are improvements in a method of controlling the drain water level of a high pressure feed water heater for heating feed water with steam extracted from a turbine through the control of the opening of first and second water level control valves respectively provided in a first drain duct leading from the heater to a deaerator and a second drain duct leading from the heater to a low pressure feed water heater according to the detected drain water level and also a system for carrying out the control method.
The state of drain in the neighborhood of the drain outlet of the high pressure feed water heater and the state of drain in the neighborhood of the drain inlet of the deaerator are detected, and the drain led to the high pressure feed water heater from a preceding stage or drain led out from the high pressure feed water heater is led to the deaerator prior to being subject to the effect of flashing according to the detected drain states, thus ensuring reliable control of the drain water level even at the time of the flashing in the neighborhood of the inlet of the first water level control valve and suppressing abnormal drain water level changes even in the case of a sudden change of the load or in the case of switching drain paths.
Disclosed are improvements in a method of controlling the drain water level of a high pressure feed water heater for heating feed water with steam extracted from a turbine through the control of the opening of first and second water level control valves respectively provided in a first drain duct leading from the heater to a deaerator and a second drain duct leading from the heater to a low pressure feed water heater according to the detected drain water level and also a system for carrying out the control method.
The state of drain in the neighborhood of the drain outlet of the high pressure feed water heater and the state of drain in the neighborhood of the drain inlet of the deaerator are detected, and the drain led to the high pressure feed water heater from a preceding stage or drain led out from the high pressure feed water heater is led to the deaerator prior to being subject to the effect of flashing according to the detected drain states, thus ensuring reliable control of the drain water level even at the time of the flashing in the neighborhood of the inlet of the first water level control valve and suppressing abnormal drain water level changes even in the case of a sudden change of the load or in the case of switching drain paths.
Description
,Z~59 1 This invention relates to a method of and a system for controlling the drain water level of a feed water heater in a steam-power plant or a nuclear power plant.
In the steam-power plant or nuclear power plant, generally a plurality of feed water heaters are provided for elevating the heat efficiency of the plant, and steam extracted from a turbine is used as a heat source for preheating the feed water supplied to a steam generator.
As the extracted steam is sub~ected to heat exchange with the feed water, it is condensed into drain, and drains from high pressure feed water heaters progressively ~oin together and are directed to low pressure feed water heaters or an air separator. In the high pressure feed water heaters, constant drain level control is effected in order to prevent damage to the turbine due to reverse drain flow or prevent reduction of the heat exchange efficiency.
Generally, the drain path from each feed water heater is changed according to the load of the plant, and with the prior art control system in which the switching of drain paths (hereinafter referred to as drain switching) i3 effected through continuous operation of individual water level controi valves with continuous load change, great variations of the drain level are ~.
'3~; 7~9 liable to result from the delay in the flow i.n the individual drain ducts and also differences in the control.
signal level. Also, in case where the load decreases, abnormal drain level increase is liable. Therefore, with the prior art drain level control method it has been difficult to obtain steady and stable drain level control.
This invention is contemplated in the light of the afore-mentioned problems in the prior art drain level control techniques, and it has for its object to provide a method of and a system for controlling the feed water heater drain level, with which water level control valves are properly operated to obtain steady and reliable control of the high pressure feed water heater drain level free from abnormal variations of the level even in the case of the drain switching or a sudden load change.
In accordance with an aspect of the invention there is provided a method of controlling the drain level of a high pressure feed water heater for heating the feed water with steam extracted from a turbine comprising the steps of detecting said drain level, generating a control signal to be applied to a control valve in such a manner that the detected value is coincident with a predetermined value, and controlling the openings of first and second water leve; control valves respectively provided in a first drain duct leading from said high pressure feed water heater to a deaerator and a second drain duct leading from said high pressure feed water heater to a low pressure feed water heater according to the detected water level, wherein said method further comprises the steps of detecting a first state of drain in the
In the steam-power plant or nuclear power plant, generally a plurality of feed water heaters are provided for elevating the heat efficiency of the plant, and steam extracted from a turbine is used as a heat source for preheating the feed water supplied to a steam generator.
As the extracted steam is sub~ected to heat exchange with the feed water, it is condensed into drain, and drains from high pressure feed water heaters progressively ~oin together and are directed to low pressure feed water heaters or an air separator. In the high pressure feed water heaters, constant drain level control is effected in order to prevent damage to the turbine due to reverse drain flow or prevent reduction of the heat exchange efficiency.
Generally, the drain path from each feed water heater is changed according to the load of the plant, and with the prior art control system in which the switching of drain paths (hereinafter referred to as drain switching) i3 effected through continuous operation of individual water level controi valves with continuous load change, great variations of the drain level are ~.
'3~; 7~9 liable to result from the delay in the flow i.n the individual drain ducts and also differences in the control.
signal level. Also, in case where the load decreases, abnormal drain level increase is liable. Therefore, with the prior art drain level control method it has been difficult to obtain steady and stable drain level control.
This invention is contemplated in the light of the afore-mentioned problems in the prior art drain level control techniques, and it has for its object to provide a method of and a system for controlling the feed water heater drain level, with which water level control valves are properly operated to obtain steady and reliable control of the high pressure feed water heater drain level free from abnormal variations of the level even in the case of the drain switching or a sudden load change.
In accordance with an aspect of the invention there is provided a method of controlling the drain level of a high pressure feed water heater for heating the feed water with steam extracted from a turbine comprising the steps of detecting said drain level, generating a control signal to be applied to a control valve in such a manner that the detected value is coincident with a predetermined value, and controlling the openings of first and second water leve; control valves respectively provided in a first drain duct leading from said high pressure feed water heater to a deaerator and a second drain duct leading from said high pressure feed water heater to a low pressure feed water heater according to the detected water level, wherein said method further comprises the steps of detecting a first state of drain in the
- 2 -. ~
~ 2 ~S9 1 neighborhood of a drain outlet of the high pressure feed water heater and a second state of drain in the neighbor-hood of a drain inlet of the deaerator, and selectively directing one of the drain to be led to the high pres-sure feed water heater from a preceding state and thedrain from the high pressure feed r~ater heater toward the deaerator prior to the occurrence of flashing in the neighborhood of the inlet of the first water level control valve are provided, thereby ensuring steady and reliable drain level control at the time of the flashing.
In another aspect of the inventian, there is provided a system for controlling the drain water level of a high pressure feed water heater, which comprises a high pressure feed water heater for heating feed water with steam extracted from a turbine, first and second water level control valves respectively provided in a first drain duct leading from the high pressure feed water heater to a deaerator and a second drain duct leading from the high pressure feed water heater to a low pressure feed water heater, a detector for detectlng the openings of the first and second water level control valves, and a detector for detecting the drain level of the high pressure feed water heater, and in which the drain level is controlled through the control of the openings of the first and second water level control valves in accordance with the detected drain water level and openings of the first and second s9 1 water level control valves. The system mentioned further comprises a detectof for detecting a first state of drain in the neighborhood of the drain outlet of the high pressure feed water heater, a detector for detecting a second state of drain in the neighborhood of the drain inlet of the deaerator, and a selector for selectively directing either the drain led to the high pressure feed water heater from a preceding stage or the drain from the high pressure feed water heater prior to the occurrence of the flashing in the neighborhood of the inlet of the first water level control valve, thereby ensuring steady and reliable drain water level control.
The invention will become apparent from the preceding description of the prior art and the description of the preferred embodiments of the invention with reference to the accompanying drawings, in which:
Fig. l is a schematic representation of a prior art feed water heater drain level control system;
Fig. 2 is a graph showing the load character-istics of the same system;
Fig. 3 is a graph showing the drain level control charactersitics of the same system;
Fig. 4 is a graph showing a control valve characteristic;
Fig. 5 is a schematic representation of a feed water heater drain level control system embodying the invention;
Figs. 6 and 7 are block diagram showing the control valve operation signal generator and in-advance control valve operation signal generator in the embodiment of Fig. 5;
Figs. 8 and 9 are flow charts illustrating the embodiment of Fig. 5;
Figs. 10 and 11 are graphs showing the control characteristics of t'ne embodiment of Fig. 5;
Fig. 12 is a schematic representation of another embodiment of the invention applied to a digital water level control system;
Fig. 13 is a view illustrating the function of a study control system incorporated in the embodiment of Fig. 12;
Figs. 14A, 14B, 14C and 14D illustrate an example lS of producing basic data from fetched data;
Fig. 15 is a schematic representation of a further embodiment of the feed water heater drain level control system according to the invention;
Fig. 16 is a block diagram showing the con-struction of a feed forward water level adjuster in the embodiment of Fig. lS;
Fig. 17 is a block diagram showing the con-struction of an opening difficiency compensation mechanism in the feed forward water level adjuster shown in Fig. 16;
Fig. 18 is a flow chart showing the method of calculation of the flash factor;
Fig. 19 is a block diagram showing the con-struction of an in-advance drain switching valve gradual . .. ~
- ' `3~7J59 1 opening operation signal generator;
Fig. 20 is a flow chart showing the construction of a drain switching signal selector;
Fig. 21 is a flow chart showing the construction of gradual opening signal starter;
Fig. 22 is a flow chart showing the construction of a drain switch circuit; and Fig. 23 is a graph showing the drain level control characteristics of the embodiment of Fig. 15.
For the sake of facilitating the understanding of the invention, a prior art drain level control method will first be described with reference to Fig. 1 prior to the description of the preferred embodiments of the inven-tion.
Referring to the figure, the feed water to be heated is forced by a feed water pump 2 through a feed water duct 1, and first and second high pressure feed water heaters (hereinafter referred to as first and second heaters) 3 and 4 and further a prestage high pressure feed water heater (not shown) are provided on the feed water duct 1 in the mentioned order from the upstream side with respect to the pump. First and second extracted steam ducts 5 and 6, to which steam extracted from a turbine (not shown) is led, are connected to the respective first and second heaters
~ 2 ~S9 1 neighborhood of a drain outlet of the high pressure feed water heater and a second state of drain in the neighbor-hood of a drain inlet of the deaerator, and selectively directing one of the drain to be led to the high pres-sure feed water heater from a preceding state and thedrain from the high pressure feed r~ater heater toward the deaerator prior to the occurrence of flashing in the neighborhood of the inlet of the first water level control valve are provided, thereby ensuring steady and reliable drain level control at the time of the flashing.
In another aspect of the inventian, there is provided a system for controlling the drain water level of a high pressure feed water heater, which comprises a high pressure feed water heater for heating feed water with steam extracted from a turbine, first and second water level control valves respectively provided in a first drain duct leading from the high pressure feed water heater to a deaerator and a second drain duct leading from the high pressure feed water heater to a low pressure feed water heater, a detector for detectlng the openings of the first and second water level control valves, and a detector for detecting the drain level of the high pressure feed water heater, and in which the drain level is controlled through the control of the openings of the first and second water level control valves in accordance with the detected drain water level and openings of the first and second s9 1 water level control valves. The system mentioned further comprises a detectof for detecting a first state of drain in the neighborhood of the drain outlet of the high pressure feed water heater, a detector for detecting a second state of drain in the neighborhood of the drain inlet of the deaerator, and a selector for selectively directing either the drain led to the high pressure feed water heater from a preceding stage or the drain from the high pressure feed water heater prior to the occurrence of the flashing in the neighborhood of the inlet of the first water level control valve, thereby ensuring steady and reliable drain water level control.
The invention will become apparent from the preceding description of the prior art and the description of the preferred embodiments of the invention with reference to the accompanying drawings, in which:
Fig. l is a schematic representation of a prior art feed water heater drain level control system;
Fig. 2 is a graph showing the load character-istics of the same system;
Fig. 3 is a graph showing the drain level control charactersitics of the same system;
Fig. 4 is a graph showing a control valve characteristic;
Fig. 5 is a schematic representation of a feed water heater drain level control system embodying the invention;
Figs. 6 and 7 are block diagram showing the control valve operation signal generator and in-advance control valve operation signal generator in the embodiment of Fig. 5;
Figs. 8 and 9 are flow charts illustrating the embodiment of Fig. 5;
Figs. 10 and 11 are graphs showing the control characteristics of t'ne embodiment of Fig. 5;
Fig. 12 is a schematic representation of another embodiment of the invention applied to a digital water level control system;
Fig. 13 is a view illustrating the function of a study control system incorporated in the embodiment of Fig. 12;
Figs. 14A, 14B, 14C and 14D illustrate an example lS of producing basic data from fetched data;
Fig. 15 is a schematic representation of a further embodiment of the feed water heater drain level control system according to the invention;
Fig. 16 is a block diagram showing the con-struction of a feed forward water level adjuster in the embodiment of Fig. lS;
Fig. 17 is a block diagram showing the con-struction of an opening difficiency compensation mechanism in the feed forward water level adjuster shown in Fig. 16;
Fig. 18 is a flow chart showing the method of calculation of the flash factor;
Fig. 19 is a block diagram showing the con-struction of an in-advance drain switching valve gradual . .. ~
- ' `3~7J59 1 opening operation signal generator;
Fig. 20 is a flow chart showing the construction of a drain switching signal selector;
Fig. 21 is a flow chart showing the construction of gradual opening signal starter;
Fig. 22 is a flow chart showing the construction of a drain switch circuit; and Fig. 23 is a graph showing the drain level control characteristics of the embodiment of Fig. 15.
For the sake of facilitating the understanding of the invention, a prior art drain level control method will first be described with reference to Fig. 1 prior to the description of the preferred embodiments of the inven-tion.
Referring to the figure, the feed water to be heated is forced by a feed water pump 2 through a feed water duct 1, and first and second high pressure feed water heaters (hereinafter referred to as first and second heaters) 3 and 4 and further a prestage high pressure feed water heater (not shown) are provided on the feed water duct 1 in the mentioned order from the upstream side with respect to the pump. First and second extracted steam ducts 5 and 6, to which steam extracted from a turbine (not shown) is led, are connected to the respective first and second heaters
3 and 4 for supplying the steam thereto for heat exchange with the feed water. The extracted steam ducts 5 and 6 are provided with respect to the turbine such 1 that the pressure of the extracted steam is higher for the downstream side with respect to the feed water. In other words, the pressure of steam supplied to the down-steam side second heater 4 is higher than that supplied to the first heater 3. In these heaters 3 and 4, the extracted steam is condenced to drain as it effects heat exchange with the feed water, so that the individual hèaters 3 and 4 are provided with respective drain ducts.
To the downstream side second heater 4 connected is a drain duct 7 leading from the prestage heater (not shown), and a drain duct 8 for leading the combination of the drain from the prestage heater and the drain produced in the second heater 4 to the first heater 3 is connected to the second heater 4. To the last stage first heater 3 is connected, in addition to the afore-mentioned drain duct 8, a drain duct 9 for leading the combination of the drain led from the second heater 4 and the drain produced in the first heater 4. The drain duct 9 is connected to an air separator 10, which is provided at a position several ten meters higher in level than the first heater 3, and through which the drain is converted to feed water for reuse.
In this system, in case when the operation condltion gets out of the normal high pressure load state so that the turbine load is extremely reduced, the drain from the first heater 3 can no longer be led to the deaerator 10. In this case, the drain level in the first and second heaters 3 and 4 is increased, l thus posing the afore-mentioned problems. Accordingly, the system is provided with a drain level controller.
More particularly, a drain duct 12 branching from the drain duct 9 is provided so that in case oP the reduction of the drain exhausting capacity of the first heater 3 the drain therefrom can be led to a low pressure feed water heater (hereinafter referred to as low pressure heater) which is provided downstream the heater 3 with respect to the drain, and water level control valves 13 and 14 are provided on the respective drain ducts 9 and 12. Also, a drain duct 15 branching from the drain duct 8 leading from the second heater 4 is connected to the deaerator lO, and water level control valves 16 and 17 are provided on the respective drain ducts 8 and 15. When the water level of the first heater 3 is increased at the time of the low load condition, it is controlled by operating the valves 13, 14, 16 and 17 such that the drain from the second heater 4 is led to the deaerator 10 while the drain from the first heater 3 is led to the low pressure heater 11. More specifically, the control of the water level of the first heater 3 is effected by operating the valve 13 through a water level setter 19 for producing a signal representing the difference between t~e detected water level detected by a water level detector 18 provided in the first heater 3 and a reference water level (hereinafter abbreviated as NWL) and a water level ad~uster 20 operated according to the difference signal ^l.~l~Z~59 1 or operating the valve 14 through a water level setter 21 for generating a signal representing the difference between the detected water level detected by the water level detector 18 and a high reference water level (hereinafter abbreviated as HNWL) and a water level adjuster 22 operated by the difference signal. ~he control of the water level of the second heater 4 is effected by operating the valve 16 through a water level setter 24 for generating a signal representing the difference of the detected water level detected by a water level detector 23 providedlin the second heater 4 and the NWL and a water level adjuster 25 operated by the difference signal or operating the valve 17 through a water level setter 26 for generating a deviation signal representing the difference between the detected water level detected by the detector 23 and the HNWL and a water level adjuster 27 actuated by this deviation signal.
Thus, in case when the turbine load is at the rated load level (i.e., high load), the drain G2 from the second heater 4 is led through the duct 8 to the first heater 3, and the combination drain Gl therefrom is led through the duct 9 to the deaerator 10, and the individual drain levels are controlled to the rererence level NWL by the valves 16 and 13. In this case, the valves 17 and 14 are held fully closed. Since the valves 13 and 16 are normally operated to control the drain level of each heater, they are respectively called first 7S~
1 and second N valves here for the sake of facilitating the description.
When the turbine load is low, the difference E between the internal pressure in the first heater 3 and deaerator 10 is substantially equal to or less than the static head F of these units, and the discharge capacity is thus lost. In this case, the drain G2 from the second heater 4 is led through the duct 15 to the deaerator 10, while the drain Gl from the first heater 3 is led through the duct 12 to the next stage low pressure heater 11. The water levels at this time are controlled by the valves 14 and 17 for maintaining the HNWL. Also at this time the other valves 16 and 13 are held fully closed. Since the valves 14 and 17 are operated for the water level control in the case where the load is low, they are respectively called first and second X valves here for the sake of facilltating the description.
As is shown, the switching of the drain paths is done with respect to a predetermined load level X as shown in Fig. 2. More particularly, in the case when the load is increased from a low level to a high level, upon reaching of the drain switching point X a forced full closure signal (hereinafter referred to as full closure signal) which has been given from the ad~usters 20 and 25 to the first and second N valves 13 and 16 is switched to a wa~er level control signal for permitting the N valves 13 and 16 to effect the water level control while the fu;l '7S9 1 closure signal is given from the ad~usters 22 and 27 to the first and second X valves 14 and 17. On the other hand, in the case when the load is reduced from a high level to a low level, the full closure signal is given from the adjusters 20 and 25 to the N valves 13 and 16, while the water level control signal is given from the water level adjusters 22 and 27 to the X valves 14 and 17 to permit these valves to control the water levels of the heaters 3 and 4.
With the prior art water level control system described above, however, at the time of the drain switching great water level variations resulted from the delay in the control air signals for the valves 13, 14, 16 and 17 and also the differences in the water level settings; particularly in case of the load reduc-tion it is liable that an abnormal increase of the drain level of the first heater 3 is caused due to the phenomenon of flashing in the neighborhood of the inlet of the first N valve 13 (which will be discussed later in detail).
When this occurs, steady and reliable water level control can no longer be obtained.
In Fig. 1, desi~nated at 28 and 29 are electro-magnetic valves for cutting off steam from boilers (not shown), and at 32 and 33 reverse drain flow check valves.
Referring now to Fig. 3, when the turbine load is at the rated level (high load), the drain level (curve B) of the first heater 3 is controlled to .' ' , - ~ :
, . ' .
1 NWL by the flrst N valve 13, and the first X valve 14, which is set to HNWL, is held fully closed by the deviation signal representing the difference between the reference level HNWL and detected water level detected by the detector 18. With gradual decrease of the load in this state (as shown by curve A), the drain flow rates in the heaters 3 and 4-are reduced, so that the first N
valve 13 is controlled such that its opening is reduced (as shown by curve C). With further decrease of the load, the pressure at the inlet of the first M valve 13 (hereinafter referred to as inlet pressure) becomes lower than the steam pressure in the drain. As a result, the phenomenon of flashing is caused in the neighborhood of the inlet of the valve 13 with the boiling of the drain under reduced pressure in the duct 9. When this phenomenon occurs, the drain flows as a two-phase stream consisting of gas and liquid streams, so that the volume of the stream is increased. Consequenlty~ although the first N valve 13 is opened (at an instant tl) in order to maintain the drain level of the first heater 3 (curve B) at NWL, depending upon the range of decrease of the load the drain level cannot be held at NWL even with the first N valve 13 being fully opened. In such a case, the drain level of the first heater 3 is extra-ordinarily increased. When the drain level exceedsNHWL, the first X valve 14 provided on the duct 12 begins to be opened (at an instant t2) as shown by the curve D and acts to suppress the extraordinary drain level ~a~7ss 1 increase. However, the response of the first X valve 14 is not good because of the delay in the valve control air signal and of the presence of an insensitive region in the control valve opening versus valve operating air pressure characteristic as shown in Fig.
To the downstream side second heater 4 connected is a drain duct 7 leading from the prestage heater (not shown), and a drain duct 8 for leading the combination of the drain from the prestage heater and the drain produced in the second heater 4 to the first heater 3 is connected to the second heater 4. To the last stage first heater 3 is connected, in addition to the afore-mentioned drain duct 8, a drain duct 9 for leading the combination of the drain led from the second heater 4 and the drain produced in the first heater 4. The drain duct 9 is connected to an air separator 10, which is provided at a position several ten meters higher in level than the first heater 3, and through which the drain is converted to feed water for reuse.
In this system, in case when the operation condltion gets out of the normal high pressure load state so that the turbine load is extremely reduced, the drain from the first heater 3 can no longer be led to the deaerator 10. In this case, the drain level in the first and second heaters 3 and 4 is increased, l thus posing the afore-mentioned problems. Accordingly, the system is provided with a drain level controller.
More particularly, a drain duct 12 branching from the drain duct 9 is provided so that in case oP the reduction of the drain exhausting capacity of the first heater 3 the drain therefrom can be led to a low pressure feed water heater (hereinafter referred to as low pressure heater) which is provided downstream the heater 3 with respect to the drain, and water level control valves 13 and 14 are provided on the respective drain ducts 9 and 12. Also, a drain duct 15 branching from the drain duct 8 leading from the second heater 4 is connected to the deaerator lO, and water level control valves 16 and 17 are provided on the respective drain ducts 8 and 15. When the water level of the first heater 3 is increased at the time of the low load condition, it is controlled by operating the valves 13, 14, 16 and 17 such that the drain from the second heater 4 is led to the deaerator 10 while the drain from the first heater 3 is led to the low pressure heater 11. More specifically, the control of the water level of the first heater 3 is effected by operating the valve 13 through a water level setter 19 for producing a signal representing the difference between t~e detected water level detected by a water level detector 18 provided in the first heater 3 and a reference water level (hereinafter abbreviated as NWL) and a water level ad~uster 20 operated according to the difference signal ^l.~l~Z~59 1 or operating the valve 14 through a water level setter 21 for generating a signal representing the difference between the detected water level detected by the water level detector 18 and a high reference water level (hereinafter abbreviated as HNWL) and a water level adjuster 22 operated by the difference signal. ~he control of the water level of the second heater 4 is effected by operating the valve 16 through a water level setter 24 for generating a signal representing the difference of the detected water level detected by a water level detector 23 providedlin the second heater 4 and the NWL and a water level adjuster 25 operated by the difference signal or operating the valve 17 through a water level setter 26 for generating a deviation signal representing the difference between the detected water level detected by the detector 23 and the HNWL and a water level adjuster 27 actuated by this deviation signal.
Thus, in case when the turbine load is at the rated load level (i.e., high load), the drain G2 from the second heater 4 is led through the duct 8 to the first heater 3, and the combination drain Gl therefrom is led through the duct 9 to the deaerator 10, and the individual drain levels are controlled to the rererence level NWL by the valves 16 and 13. In this case, the valves 17 and 14 are held fully closed. Since the valves 13 and 16 are normally operated to control the drain level of each heater, they are respectively called first 7S~
1 and second N valves here for the sake of facilitating the description.
When the turbine load is low, the difference E between the internal pressure in the first heater 3 and deaerator 10 is substantially equal to or less than the static head F of these units, and the discharge capacity is thus lost. In this case, the drain G2 from the second heater 4 is led through the duct 15 to the deaerator 10, while the drain Gl from the first heater 3 is led through the duct 12 to the next stage low pressure heater 11. The water levels at this time are controlled by the valves 14 and 17 for maintaining the HNWL. Also at this time the other valves 16 and 13 are held fully closed. Since the valves 14 and 17 are operated for the water level control in the case where the load is low, they are respectively called first and second X valves here for the sake of facilltating the description.
As is shown, the switching of the drain paths is done with respect to a predetermined load level X as shown in Fig. 2. More particularly, in the case when the load is increased from a low level to a high level, upon reaching of the drain switching point X a forced full closure signal (hereinafter referred to as full closure signal) which has been given from the ad~usters 20 and 25 to the first and second N valves 13 and 16 is switched to a wa~er level control signal for permitting the N valves 13 and 16 to effect the water level control while the fu;l '7S9 1 closure signal is given from the ad~usters 22 and 27 to the first and second X valves 14 and 17. On the other hand, in the case when the load is reduced from a high level to a low level, the full closure signal is given from the adjusters 20 and 25 to the N valves 13 and 16, while the water level control signal is given from the water level adjusters 22 and 27 to the X valves 14 and 17 to permit these valves to control the water levels of the heaters 3 and 4.
With the prior art water level control system described above, however, at the time of the drain switching great water level variations resulted from the delay in the control air signals for the valves 13, 14, 16 and 17 and also the differences in the water level settings; particularly in case of the load reduc-tion it is liable that an abnormal increase of the drain level of the first heater 3 is caused due to the phenomenon of flashing in the neighborhood of the inlet of the first N valve 13 (which will be discussed later in detail).
When this occurs, steady and reliable water level control can no longer be obtained.
In Fig. 1, desi~nated at 28 and 29 are electro-magnetic valves for cutting off steam from boilers (not shown), and at 32 and 33 reverse drain flow check valves.
Referring now to Fig. 3, when the turbine load is at the rated level (high load), the drain level (curve B) of the first heater 3 is controlled to .' ' , - ~ :
, . ' .
1 NWL by the flrst N valve 13, and the first X valve 14, which is set to HNWL, is held fully closed by the deviation signal representing the difference between the reference level HNWL and detected water level detected by the detector 18. With gradual decrease of the load in this state (as shown by curve A), the drain flow rates in the heaters 3 and 4-are reduced, so that the first N
valve 13 is controlled such that its opening is reduced (as shown by curve C). With further decrease of the load, the pressure at the inlet of the first M valve 13 (hereinafter referred to as inlet pressure) becomes lower than the steam pressure in the drain. As a result, the phenomenon of flashing is caused in the neighborhood of the inlet of the valve 13 with the boiling of the drain under reduced pressure in the duct 9. When this phenomenon occurs, the drain flows as a two-phase stream consisting of gas and liquid streams, so that the volume of the stream is increased. Consequenlty~ although the first N valve 13 is opened (at an instant tl) in order to maintain the drain level of the first heater 3 (curve B) at NWL, depending upon the range of decrease of the load the drain level cannot be held at NWL even with the first N valve 13 being fully opened. In such a case, the drain level of the first heater 3 is extra-ordinarily increased. When the drain level exceedsNHWL, the first X valve 14 provided on the duct 12 begins to be opened (at an instant t2) as shown by the curve D and acts to suppress the extraordinary drain level ~a~7ss 1 increase. However, the response of the first X valve 14 is not good because of the delay in the valve control air signal and of the presence of an insensitive region in the control valve opening versus valve operating air pressure characteristic as shown in Fig.
4, and great water level increases are casued a~ the instants tl and t2 in Fig. 3. ~his phenomenon is pronounced the more the greater the rate of change of the load.
When the load (shown as the curve A) reaches a preset level (X) in this state, the switching of drain paths is effected. With this prior art methos of the drain switching, however, great water level increase is liable depending upon the timing of closing the N
valves 13 and 16. Accordingly, at a drain switching point t3 the full closure signal is given from the ad~uster 25 to the second N valve 16 to fully close it, and then at an instant t4 slightly after the drain switch-ing point t3 the full closure signal is given from the adJuster 20 to the first N valve 13 to fully close it.
By this method of drain switching, the increase of the drain level of the first heater 3 is prevented. At this time, the rate of drain flow into the first heater 3 is first reduced to reduce the water level thereof.
Besides, although the first X valve 14 is fully closed by the water level control signal provided with the reduction of the water level, the first N valve 13 is still fully open at this moment, so that the water level .
~ ' ' ', ~
.
...
p~s9 1 tends to be further reduced. However, after the instantt4, at which the first N valve 13 is fully closed, at an instant t5 of taking measures for recovering the drain level the flrst X valve 14 is in the fully closed state, and also the response of the first X valve 14 is deterio-rated due to such causes as the delay in the valve control air signals and the presence of the control valve action insensitive element. Therefore, great water level variations occur after the drain switching.
At this time, the greater the reduction of the water level immediately after the drain switching point t3, the greater is the water level increase immediately after the water level recovery point t5, and also the longer is the period of the subsequent instable state.
In this case, if the proportion gain of the ad~uster 20 and 22 is increased or the integration period is reduced to improve the control response in order to prevent the water level increase at the time points tl and t2, the water level becomes unstable in the low flow rate region after the drain switching. Further, there is such a tendency that the larger the difference between the value NWL before the drain switching and the value NHWL after the drain switching is the more the unstable state increases.
Further, while in the heaters 3 and 4 an alarm is produced when the drain level departs by more than several 100 mm above or below NW~, the electromagnetic valves 28 and 29 provided on the extracted steam ducts ~5~'~59 l 5 and 6 are forcibly fully closed when the water level exceeds the alarm level and reaches a certain level at the time of the water level increase. This is done so for the purpose of preventing the damage to the turbine due to reverse drain flow. ~herefore, when the water level is extraordinarily increased due to the water level variation caused by the valve inlet flashing or drain switching as mentioned above, the electromagnetic valve 28 is closed, and the supply of steam is cut off to reduce the internal pressure in the first heater.
Therefore, it becomes still further difficult to provide for the drain flow. Furhter, the drain from the second heater 4 cannot be led to the first heater 3. ~hus, the drain levels of the individual heaters are abnormally increased in a fashion like the chain reaction.
~ he problems discussed above are present in the prior art water level control.
Now, a preferred embodiment of the invention will be described in detail with reference to Figs. 5 to ll.
Fig. 5 shows a heater drain level control system embodying the invention. In the Figure, the same parts as those in the prior art example described above are deslgnated by like reference numerals, and their description is omitted. Designated at 34 and 35 in Fig. 5 are control valve operation signal generators.
The generator 34 receives the signal 36 representing the water level of the first heater 3 detected by the J?~7~5~
1 detector 18 and compares the detected water level with NWL and HNWL to generate valve operation signals 37 and 38 for controlling the openings of the valves 13 and 14 as mentioned previously in connection with the prior art example shown in Fig. 1. The generator 35 receives the signal 39 representing the water level of the second heater 4 detected by the detector 23 and compares the detected water level with NWL and HNWL to gençrate valve operation signals 40 and 41 for controlling the openings of the valves 16 and 17 as mentioned previously in connection with the prior art example shown in Fig. 1.
According to the embodiment, the following control is provided in addition to the water level control valve control in the prior art techniques described above. The pressure of the extracted steam flowing through the extracted steam duct 5 into the first heater 3 is detected as the plant load state by a plant load detector 24 to generate a detected load signal 43 which is coupled to the generators 34 and 35.
The detector 42 m~y not necessarily detect the extracted steam pressure, but it may detect turbine load output, turbine flrst stage pressure, heater pressure, etc. as well.
Further, a pressure detector 44 for detecting the pressure in the neighborhood of the inlet to the first N valve 13 is provided upstream the valve 13, and a temperature detector 45 for detecting the temperature of the drain in the neighborhood of the 27~9 1 drain outlet of the first heater 3 is provided downstream the heater 3. The control valve operation signal generator 34 is so constructed as to produce a valve operation signal for making up for the difficiency of the opening of the first N valve 13 due to the flashing at the inlet thereof from a pressure signal 46 provided from the pressure detector 44, a temperature signal 47 provided from the temperature detector 45, a pressure signal 47 ~ provided from the pressure detector 42, and opening signals 50 and 51 provided from opening detectors 48 and 49 which are provided on the respective valves 13 and 14. The construction, operation and , effects of the control valve operation signal generator will be described hereinunder.
Fig. 6 shows the construction of the generator 34. The generator 34 includes a water level control signal generator 52, a full closure signal generator 53 and a gradual opening signal generator 54. For the gradual opening signal generator 54, a gradual 20 opening signal start setter 55, an opening setter 56 and a valve operation period setter 57 are provided.
The generator 34 further includes a high reference load level setter 58, a low reference load level setter 59, a control valve operation signal selector 60. The signal 25 generator 52 receives the water level signal 36 and provides a water level control signal 63 for controlling the water level control valve opening according to the detected water level. The signal generator 53 provides 2'7S9 1 a full closure signal 64 for forcibly closing the water level control valve. The setter 55 determines the timing of generation of the gradual opening signal, and its output is supplied to the signal generator 54 for operating it. The signal generator 54 receives the output signals from the opening setter 56 and valve operation period setter 57 and also the plant load signal 43 and generate the gradual opening signal for permitting smooth drain switching according to the input signals. The selector 60 receives the water level control signal 63, full closure signal 64, gradual opening signal 68, load signal 43, HL signal 69 provided from the setter 58 and representing a high reference load level (hereinafter referred to as HL) during the drain swltching operation period (see Fig. 3)~ LL
signal 70 provided from the setter 59 and representir.g a low reference load level (hereinafter referred to as LL) (see Fig. 3) during the drain switching operation period and valve opening signals 50 and 50, and it selectively couples either the water level control signal 63, full closure signal 64 or gradual opening signal 68 as its output signal 71 to the first N valve 13 and also selectively couples one of the remaining two signals as its output signal 72 to the first X
valve 14 in accordance with a method to be described hereinafter. ~he output signals 71 and 72 are coupled to the first N and X valves 13 and 14 as their operation signals 37 and 38. In practical, there is additionally s~
1 provided a device for producing a control valve in-advance operation signal (shown in Fig. 7) so that in a first embodiment a sum signal obtained by adding the control valve in-advance operation signal to the signal 72 is applied to the second X valve 17 and alterna~ively in a second embodiment a sum si~nal obtained by adding the control valve in-advance opera-tion signal to the signal 71 is applied to the first N valve 13. Description will be made hereunder about only the latter or second embodiment by way of example, while eliminating the description about the former embodiment. Fig. 7 shows the control valve in-advance operation signal generator 61, which includes an enthalpy calculator 75, a forecast inlet flash factor calculator 76 and an opening difficiency calculator 78. The enthalpy calculator 75 receives the pressure signal 47' from the pressure detector 42 and the temperature signal 47 from the temperature detector 45 and calculates the enthalpy of the drain at the inlet Of the valve 13. The forecast inlet flash factor forecasting calculator 76 calculates the forecast inlet flash factor at the inlet of the valve 13. The calculation methods will be described later in detail with reference to Fig. 18. The opening difficiency calculator 78 calculates the opening of the first N valve 13 from the calculated forecast inlet flash factor and derives the opening difficiency through comparison of the calculated opening and the actual opening represented by the opening ~R~'7S9 1 signal 50 for providing the derived opening difficiency as the first N valve in-advance operation signal 73.
The method of the opening difficiency derivation will be described later with reference to Fig. 17.
Now, an example of the afore-mentioned generator 34, which is realized with a mini-computor or a microcomputor, will now be described with reference to Figs. 5 through 11.
First, the method of drain switching in the case where the load increases from low to high level will be described. In this case, while the load is still lower than LL, in steps 80 to 88 in the flow diagram of Fig. 8, the step 80 yields a decision "yes" while the step 81 yields a decision "no". Thus, the start signal, i.e., a key-on signal, is led through signal routes 89 and 90 to select the full closure slgnal 64 for the first N valve 13, while it is also led through slgnal routes 89 and 91 to select the water le~el control signal 63 for the first X valve 14. In other words, although the drain switching is effected during the increase of the load, before the reaching of LL by the load the water level control signal 63 is given to the first X valve 14 to permit passage of the drain through the valve 14, while the full closure signal 68 is given to the first N valve 13 to hold the valve 13 fully clo~ed so as to prevent the drain from entering the deaerator 10. In respect of the flow chart of Fig. 8, the water level control signal 63, full closure signal , 13L~;.;~'759 1 64 and gradual opening signal 68 for the system involving the first X valve 14 are respectively labeled A, B and C, and their presence is shown by a logic level "1" and their absence by a level "0". Thus, the instant situa-tion is expressed as A = 1, B = 0 and C = 0. Likewise,by label~ng the signals 68, 64 and 63 for the system - involving the first N valve 13 respectively A, B and C, the instant situation is expressed as A = 0, B = 1 and C = 0. Further, for the first X valve 14 the state A = 1, B = 0 and C = 0 is expressed as D = 1, the state A = 0, B = 1 and C = 0 as D = 3, and the state A = 0, B = 0 and C = 1 as D = 5. Likewise, for the first N valve 13 the state A = 0, B = 0 and C = 1 is expressed as D = 2, the state A = 0, B = 1 and C = 0 is expressed as D = 4, and the state A = 1, B = 0 and C = 0 as D = 6. With the water level control signal 63 selected for the first X valve 14, a signal representing the selection state D = 1 is provided as the selection signal 72. Also, wlth the full closure signal 64 selected for the ~irst N valve 13, a signal representing the selection state D = 4 is provided as the selection signal 71. Thus, in Fig. 9 only steps D = 1 and D = 4 of steps D = 1 to D = 6 yield a "yes" while all the other steps yield a "no".
In other words, the full closure signal 64 from the signal generator 53 is transmitted through routes 92 and 93 to the first X valve 14, while the water level control signal 63 is transmitted from the signal generator 52 through a route 94 to the first N valve 13. If the ~z~s9 1 control signal generator 35 is constructed such that it gives the full closure signal 64 to the second N
valve 16 and the water level control signal 63 to the second X valve 17, the drain of the second heater 4 at this time is all led to the deaerator 10 while the drain of ~ the first heater 3 is all led to the low pressure heater :; 11.
When the load is increased to exceed LL, the steps 81, 86, 87 and 88 of the steps 80 to 88 in Fig. 8 yield a l'yes" while the steps 82 and 84 yield a "no", so that i~ the step 83 becomes to yield a "no" the key-on signal is led through routes 89, 95, 96 and 97 to select the gradual opening signal 68 for the first N valve 13 while it is also led through routes 15 89, 95, 96, 98 and 91 to select the water level control signal 63 for the first X valve 14. In other words, at this time the first X valve operation signal 72 represents the state D - 1 while the first N valve operation signal 71 represents the state D = 6. ~his means that only the steps D = 1 and D = 6 among the steps D = 1 to D = 6 in Fig. 9 provide a "yes" while the other steps all provide a "no". In other words, the water level control signal 63 from the signal generator 52 is given through a route 94 to the first X valve 14 while the gradual opening signal 65 from the signal generator 57 is given through routes 99 and 100 to the first N valve 13. At this time, the signal generator 57 produces the gradual opening signal 65 in response to a start signal coupled ~ , , .
. ~
1 to it through a route 101, and the signal 65 dictates the control of the first N valve 13 such that it is gradually opened according to output signals 66 and 67 from signal generators 55 and 56. On the other hand, since the
When the load (shown as the curve A) reaches a preset level (X) in this state, the switching of drain paths is effected. With this prior art methos of the drain switching, however, great water level increase is liable depending upon the timing of closing the N
valves 13 and 16. Accordingly, at a drain switching point t3 the full closure signal is given from the ad~uster 25 to the second N valve 16 to fully close it, and then at an instant t4 slightly after the drain switch-ing point t3 the full closure signal is given from the adJuster 20 to the first N valve 13 to fully close it.
By this method of drain switching, the increase of the drain level of the first heater 3 is prevented. At this time, the rate of drain flow into the first heater 3 is first reduced to reduce the water level thereof.
Besides, although the first X valve 14 is fully closed by the water level control signal provided with the reduction of the water level, the first N valve 13 is still fully open at this moment, so that the water level .
~ ' ' ', ~
.
...
p~s9 1 tends to be further reduced. However, after the instantt4, at which the first N valve 13 is fully closed, at an instant t5 of taking measures for recovering the drain level the flrst X valve 14 is in the fully closed state, and also the response of the first X valve 14 is deterio-rated due to such causes as the delay in the valve control air signals and the presence of the control valve action insensitive element. Therefore, great water level variations occur after the drain switching.
At this time, the greater the reduction of the water level immediately after the drain switching point t3, the greater is the water level increase immediately after the water level recovery point t5, and also the longer is the period of the subsequent instable state.
In this case, if the proportion gain of the ad~uster 20 and 22 is increased or the integration period is reduced to improve the control response in order to prevent the water level increase at the time points tl and t2, the water level becomes unstable in the low flow rate region after the drain switching. Further, there is such a tendency that the larger the difference between the value NWL before the drain switching and the value NHWL after the drain switching is the more the unstable state increases.
Further, while in the heaters 3 and 4 an alarm is produced when the drain level departs by more than several 100 mm above or below NW~, the electromagnetic valves 28 and 29 provided on the extracted steam ducts ~5~'~59 l 5 and 6 are forcibly fully closed when the water level exceeds the alarm level and reaches a certain level at the time of the water level increase. This is done so for the purpose of preventing the damage to the turbine due to reverse drain flow. ~herefore, when the water level is extraordinarily increased due to the water level variation caused by the valve inlet flashing or drain switching as mentioned above, the electromagnetic valve 28 is closed, and the supply of steam is cut off to reduce the internal pressure in the first heater.
Therefore, it becomes still further difficult to provide for the drain flow. Furhter, the drain from the second heater 4 cannot be led to the first heater 3. ~hus, the drain levels of the individual heaters are abnormally increased in a fashion like the chain reaction.
~ he problems discussed above are present in the prior art water level control.
Now, a preferred embodiment of the invention will be described in detail with reference to Figs. 5 to ll.
Fig. 5 shows a heater drain level control system embodying the invention. In the Figure, the same parts as those in the prior art example described above are deslgnated by like reference numerals, and their description is omitted. Designated at 34 and 35 in Fig. 5 are control valve operation signal generators.
The generator 34 receives the signal 36 representing the water level of the first heater 3 detected by the J?~7~5~
1 detector 18 and compares the detected water level with NWL and HNWL to generate valve operation signals 37 and 38 for controlling the openings of the valves 13 and 14 as mentioned previously in connection with the prior art example shown in Fig. 1. The generator 35 receives the signal 39 representing the water level of the second heater 4 detected by the detector 23 and compares the detected water level with NWL and HNWL to gençrate valve operation signals 40 and 41 for controlling the openings of the valves 16 and 17 as mentioned previously in connection with the prior art example shown in Fig. 1.
According to the embodiment, the following control is provided in addition to the water level control valve control in the prior art techniques described above. The pressure of the extracted steam flowing through the extracted steam duct 5 into the first heater 3 is detected as the plant load state by a plant load detector 24 to generate a detected load signal 43 which is coupled to the generators 34 and 35.
The detector 42 m~y not necessarily detect the extracted steam pressure, but it may detect turbine load output, turbine flrst stage pressure, heater pressure, etc. as well.
Further, a pressure detector 44 for detecting the pressure in the neighborhood of the inlet to the first N valve 13 is provided upstream the valve 13, and a temperature detector 45 for detecting the temperature of the drain in the neighborhood of the 27~9 1 drain outlet of the first heater 3 is provided downstream the heater 3. The control valve operation signal generator 34 is so constructed as to produce a valve operation signal for making up for the difficiency of the opening of the first N valve 13 due to the flashing at the inlet thereof from a pressure signal 46 provided from the pressure detector 44, a temperature signal 47 provided from the temperature detector 45, a pressure signal 47 ~ provided from the pressure detector 42, and opening signals 50 and 51 provided from opening detectors 48 and 49 which are provided on the respective valves 13 and 14. The construction, operation and , effects of the control valve operation signal generator will be described hereinunder.
Fig. 6 shows the construction of the generator 34. The generator 34 includes a water level control signal generator 52, a full closure signal generator 53 and a gradual opening signal generator 54. For the gradual opening signal generator 54, a gradual 20 opening signal start setter 55, an opening setter 56 and a valve operation period setter 57 are provided.
The generator 34 further includes a high reference load level setter 58, a low reference load level setter 59, a control valve operation signal selector 60. The signal 25 generator 52 receives the water level signal 36 and provides a water level control signal 63 for controlling the water level control valve opening according to the detected water level. The signal generator 53 provides 2'7S9 1 a full closure signal 64 for forcibly closing the water level control valve. The setter 55 determines the timing of generation of the gradual opening signal, and its output is supplied to the signal generator 54 for operating it. The signal generator 54 receives the output signals from the opening setter 56 and valve operation period setter 57 and also the plant load signal 43 and generate the gradual opening signal for permitting smooth drain switching according to the input signals. The selector 60 receives the water level control signal 63, full closure signal 64, gradual opening signal 68, load signal 43, HL signal 69 provided from the setter 58 and representing a high reference load level (hereinafter referred to as HL) during the drain swltching operation period (see Fig. 3)~ LL
signal 70 provided from the setter 59 and representir.g a low reference load level (hereinafter referred to as LL) (see Fig. 3) during the drain switching operation period and valve opening signals 50 and 50, and it selectively couples either the water level control signal 63, full closure signal 64 or gradual opening signal 68 as its output signal 71 to the first N valve 13 and also selectively couples one of the remaining two signals as its output signal 72 to the first X
valve 14 in accordance with a method to be described hereinafter. ~he output signals 71 and 72 are coupled to the first N and X valves 13 and 14 as their operation signals 37 and 38. In practical, there is additionally s~
1 provided a device for producing a control valve in-advance operation signal (shown in Fig. 7) so that in a first embodiment a sum signal obtained by adding the control valve in-advance operation signal to the signal 72 is applied to the second X valve 17 and alterna~ively in a second embodiment a sum si~nal obtained by adding the control valve in-advance opera-tion signal to the signal 71 is applied to the first N valve 13. Description will be made hereunder about only the latter or second embodiment by way of example, while eliminating the description about the former embodiment. Fig. 7 shows the control valve in-advance operation signal generator 61, which includes an enthalpy calculator 75, a forecast inlet flash factor calculator 76 and an opening difficiency calculator 78. The enthalpy calculator 75 receives the pressure signal 47' from the pressure detector 42 and the temperature signal 47 from the temperature detector 45 and calculates the enthalpy of the drain at the inlet Of the valve 13. The forecast inlet flash factor forecasting calculator 76 calculates the forecast inlet flash factor at the inlet of the valve 13. The calculation methods will be described later in detail with reference to Fig. 18. The opening difficiency calculator 78 calculates the opening of the first N valve 13 from the calculated forecast inlet flash factor and derives the opening difficiency through comparison of the calculated opening and the actual opening represented by the opening ~R~'7S9 1 signal 50 for providing the derived opening difficiency as the first N valve in-advance operation signal 73.
The method of the opening difficiency derivation will be described later with reference to Fig. 17.
Now, an example of the afore-mentioned generator 34, which is realized with a mini-computor or a microcomputor, will now be described with reference to Figs. 5 through 11.
First, the method of drain switching in the case where the load increases from low to high level will be described. In this case, while the load is still lower than LL, in steps 80 to 88 in the flow diagram of Fig. 8, the step 80 yields a decision "yes" while the step 81 yields a decision "no". Thus, the start signal, i.e., a key-on signal, is led through signal routes 89 and 90 to select the full closure slgnal 64 for the first N valve 13, while it is also led through slgnal routes 89 and 91 to select the water le~el control signal 63 for the first X valve 14. In other words, although the drain switching is effected during the increase of the load, before the reaching of LL by the load the water level control signal 63 is given to the first X valve 14 to permit passage of the drain through the valve 14, while the full closure signal 68 is given to the first N valve 13 to hold the valve 13 fully clo~ed so as to prevent the drain from entering the deaerator 10. In respect of the flow chart of Fig. 8, the water level control signal 63, full closure signal , 13L~;.;~'759 1 64 and gradual opening signal 68 for the system involving the first X valve 14 are respectively labeled A, B and C, and their presence is shown by a logic level "1" and their absence by a level "0". Thus, the instant situa-tion is expressed as A = 1, B = 0 and C = 0. Likewise,by label~ng the signals 68, 64 and 63 for the system - involving the first N valve 13 respectively A, B and C, the instant situation is expressed as A = 0, B = 1 and C = 0. Further, for the first X valve 14 the state A = 1, B = 0 and C = 0 is expressed as D = 1, the state A = 0, B = 1 and C = 0 as D = 3, and the state A = 0, B = 0 and C = 1 as D = 5. Likewise, for the first N valve 13 the state A = 0, B = 0 and C = 1 is expressed as D = 2, the state A = 0, B = 1 and C = 0 is expressed as D = 4, and the state A = 1, B = 0 and C = 0 as D = 6. With the water level control signal 63 selected for the first X valve 14, a signal representing the selection state D = 1 is provided as the selection signal 72. Also, wlth the full closure signal 64 selected for the ~irst N valve 13, a signal representing the selection state D = 4 is provided as the selection signal 71. Thus, in Fig. 9 only steps D = 1 and D = 4 of steps D = 1 to D = 6 yield a "yes" while all the other steps yield a "no".
In other words, the full closure signal 64 from the signal generator 53 is transmitted through routes 92 and 93 to the first X valve 14, while the water level control signal 63 is transmitted from the signal generator 52 through a route 94 to the first N valve 13. If the ~z~s9 1 control signal generator 35 is constructed such that it gives the full closure signal 64 to the second N
valve 16 and the water level control signal 63 to the second X valve 17, the drain of the second heater 4 at this time is all led to the deaerator 10 while the drain of ~ the first heater 3 is all led to the low pressure heater :; 11.
When the load is increased to exceed LL, the steps 81, 86, 87 and 88 of the steps 80 to 88 in Fig. 8 yield a l'yes" while the steps 82 and 84 yield a "no", so that i~ the step 83 becomes to yield a "no" the key-on signal is led through routes 89, 95, 96 and 97 to select the gradual opening signal 68 for the first N valve 13 while it is also led through routes 15 89, 95, 96, 98 and 91 to select the water level control signal 63 for the first X valve 14. In other words, at this time the first X valve operation signal 72 represents the state D - 1 while the first N valve operation signal 71 represents the state D = 6. ~his means that only the steps D = 1 and D = 6 among the steps D = 1 to D = 6 in Fig. 9 provide a "yes" while the other steps all provide a "no". In other words, the water level control signal 63 from the signal generator 52 is given through a route 94 to the first X valve 14 while the gradual opening signal 65 from the signal generator 57 is given through routes 99 and 100 to the first N valve 13. At this time, the signal generator 57 produces the gradual opening signal 65 in response to a start signal coupled ~ , , .
. ~
1 to it through a route 101, and the signal 65 dictates the control of the first N valve 13 such that it is gradually opened according to output signals 66 and 67 from signal generators 55 and 56. On the other hand, since the
- 5 opening of the first N valve 14 is controlled so as to cause the heater water level to be constant by the water level control signal 63, the opening is gradually closed by this control signal 63 with the gradual opening of the first N valve 13. In the load state higher than LL but lower than HL, i.e., in the state before the completion of the drain switching, if the first X valve 14 becomes its full closed state or reaches its lower limit value as shown in Fig. 10, the step 83 in Fig. 8 yields a "yes", and as a result the key-on signal is led through routes 89, 95, 96, 102 and 103 to select the full closure signal 64 for the first X valve 14 while it is led through routes 102, 103 and 104 to select the water level control signal for the N valve 13. Thus, the first X valve operation signal 72 represents the state D = 3 while the first N valve operation signal 71 represents the state D = 2. It is to be understood that the water level of the first heater 3 is controlled either by the first X valve 14 or first N valve 13 alone, and thus it is possible to prevent the reduction of the control performance due to the interaction of the two control valves with each other. Reviewing this state with reference to Fig. 9, the steps D = 2 and D = 3 are providing a "yes" while the steps D = 1, D = 4, .
Z'7S9 1 D = 5 and D = 6 are pvoding "no", and a reset signal is thus given through routes 105, 106 and 107 to the signal generator 57 to reset the generator 57, thus bringing the gradual opening signal 65 to a "0" level. Also, it will be readily understood that the full closure signal 64 is given from the signal generator 53 through routes 108 and 94 to the first X valve 14 and the water level control signal 63 is given from the signal generator 52 through routes 109 and 110 to the first N valve 13.
When the load is increased to exceed HL, all the steps except for the step 87 in Fig. 8 yield a "yes"
~hus, the key-on signal is led through routes 89, 95 and 103 to select the full closure signal 64 for the first X valve 14 while it is led through routes 89, 95 and 104 for giving the water level control signal 63 to the first N valve 13. This means that the operation signals 71 and 72 represent the respective states D = 3 and D = 2, that is, the previous control state mentioned above is maintained. In the above way, the drain switching in the case when the load is increasing is completed. It will be understood that the drain switching for the second heater by the generator 35 is effected in the same manner as described above.
Fig. 11 shows the changes in load and changes in valve openings in the case when the load decreases from high to low level. In this case, the drain switching is effected in a manner similar to that in the case of the increasing load. Further, even in case 7~;g 1 when the valve inlet flashing phenomenon occurs the output signal 73 from the control valve in-advance operation signal generator 61 in the signal generator 34 is additionally applied to the second X valve 17 in advance through the signal generator 35, so that the opening of the first N valve 13 is not so increased compared to the case of the prior art, and it is possible to alleviate the sudden change of the water legel caused by the reduction of the drain exhaust capacity of the first N valve due to the valve inlet flashing phenomenon.
Now, a different preferred embodiment of the invention will be described with reference to Figs. 12 to 14. In the figures, like component parts as those already described are designated by like reference numerals, and their detailed description is omitted.
In the system shown in Fig. 12, a digital water level control unit 120 of a study control system ls used for the water level control of the first heater 3. The control unit 120 receives, as signals having dlrect bearing upon the water level of the first heater 3, opening signals 50, 51, 121 and 123 respectively provided from opening detectors 48, 49, 31 and 122 for detecting the openings of water level control valves 13, 14 and 16 and an extracted steam check valve 30, a water level signal 124 provi~ed as a plant state signal from a water level detector 18, a signal 43 representing the plant load state provided from a plant load detector 42, a load change rate signal 125 representing the t,~Z 7S9 1 transient running state of the plant and a pressure signal 127 provided from a pressure detector 126 for detecting the pressure in the deaerator 10. ~hese input signals are processed in a manner as will be described hereinafter with reference to Fig. 13 to generate a water level control signal 63 which is coupled to the first N valve 13 and first X valve 14 for the opening control thereof.
Now, the study control system of the digital water level control unit 120 will be descri~ed with reference to Fig. 13. The control unit 120 may be realized as a computor, and it fetches the signals from the individual detectors as mentioned previously with reference to Fig. 12 for each predetermined sampling cycle period ~T. The water level signal 124 is compared with a preset level, and the difference is sub~ect to a proportlonal integrating differentiating (PID) proces-slng to provide a water level control valve feedback signal 128. When the initial basic data for determining the control valve operation signals from the fetched data are not prepared yet, these data are prepared through a data logger. That is, before the preparation of the initial basic data is completed, the signal 128 is provided as the water level control signal 63, and the water level control depends only upon the feedback control through the PIC control. However, where the plant characteristics are forecastable and it is possible to prepare the initial basic data in advance, ' - 2~ -., .
; , .
s9 1 the initial basic data may be coupled as input data as well. The data logger is progressively renewed.
When the preparation of the initial basic data is completed, the fetched data are compared with the basic data before the calculation processing to determine a water level control valve forecast control signal 129.
Concurrently with this signal processing, whether the water level is within a predetermined control range is checked. If it is not within the control range, it means that the water level control valve control signal determined on the basis of the data fetched at an instant (T - ~T) one sampling cycle before the instant time (T) has been unsatisfactory. In this case, the correction of the basic data is made by using values fetched at the present instant (time T) as the opening slgnals 50 and 51 while using the values at the instant (T - ~T) one cycle before as the other fetched data. If the water level is within the control range, no correction of the basic data is made.
In the above way, when the preparation of the initial basic data is completed, the water level control valve forecast operation control signal 129 obtained through the calculation with the fetched data as mentioned ; serves as the basic valve control signal, and to this signal the afore mentioned water level control valve i feedback control signal 128 is added to produce the water level control signal 63 for controlling the valves 13 and 14.
,~, ., .
1 Now, an example of the method o~ preparing the basic data ~ill be briefly explained referring to Fig.
14. ~he fetched data are put in order with respect to the load as shown in Figs. 14A, 14B and 14C, and the basic charactersitics of the individual fetched data corresponding to the load are grasped as respective patterns. On the basis of these patterns the openings of the water level control valves 13, 14 and 16 are determined according to the load while also making it possible to make correction of the water level control valve openings by using deviations of the individual fetched data from the basic characteristics as shown in Fig. 14D. As is seen from Fig.14D, this correction of the opening of the first N valve 13 is made by fore-casting the inlet flashing phenomenon that occurs whenthe laod change rate takes a negative value as is apparent from Fig. 3.
As has been shown, by carrying out the feed water heater water level control with the study control system as according to the embodiment, it is possible to prevent abnormal variations of the drain level of the feed water heater at the time of the afore-mentioned drain switching and sudden load change.
A further preferred embodiment of the invention will now be described with reference to Fig. 15 and following figures. In the figures, like component parts as those already described are designated by like reference numerals, and their detailed description is omitted.
,.
'7S~
1 In this embodiment, a feed forward water level adjuster 129 is provided. The water level adjuster 129 receives opening signals 50 and 51, a water level signal 36, a plant load signal 43, a drain temperature signal 132 provided from a drain temperature detector 130 connected to the drain duct 9, a drain pressure signal 133 provided from a drain pressure detector 131 also connected to the drain duct 9, an inlet drain pressure signal 46 provided from the drain pressure detector 44 connected to the drain duct 9 and a flow rate signal 135 provided from a flow rate detector 134 for detecting the flow rate of drain through the drain duct 9, and it provides valve operation signals 37 and 38 to the water level control valves 13 and 14 respectively.
Fig. 16 shows the construction of the feecback water level adjuster 129. It includes an opening dlfficiency compensation mechanism, an in-advance drain switching valve gradual opening mechanism and a drain switching mechanism.
The opening difficiency compensation mechanism includes an inlet flash factor forecaster 136, which forecasts the flash factor at the inlet of the first N
valve 13 by fetching the drain temperature signal 132, a drain pressure signal 133, an inlet drain pressure signal 46 and a drain flow rate signal 135, and an opening difficiency in-advance compensator 138, which calculates the opening difficiency corresponding to the inlet flashing from the output signal 137 of the forecaster ~tljz~7s9 1 136 and the valve opening signal 50 and providing an output signal 139 representing the result of the calcula-tion. Fig. 17 shows the detailed construction of the forecaster 136 and compensator 138.
The iniet flash factor forecaster 136 includes an enthalpy claculator 140, which calculates the enthalpy of the drain at the outlet of the first heater 3 from the drain temperature signal 132 and drain pressure signal 133. The forecaster 136 also includes a drain flow delay calculator 141, which receives the drain flow rate signal 135 and calculates the delay of the drain from the outlet of the heater 3 before reaching the inlet of the first N valve 13 from the drain flow rate, the length and diameter of the duct 9, etc. The outputs of the enthalpy calculator 140 and drain flow delay calculator 141 are coupled to an inlet enthalpy calculator 142, whlch calculates the enthalpy of the drain at the inlet of the first N valve 13. The output of the inlet enthalpy calculator 142 is coupled together with the output of the inlet drain pressure signal 46 to an inlet flash factor calculator 143. The inlet flash factor calculator 143 calculates the dryness and volume factor which are physical properties of the drain and also calculates by using these parameters the inlet flash factor and bu~ble ratio (i.e., void factor Vr), and the calculated data are provided as an output signal 137 of the forecaster 136.
The construction of the inlet flash factor .' , .
' ' , ~3~ ~59 1 calculator 143 will now be described with reference to the flow chart of Fig. 18.
The calculator 143 fetches the inlet drain enthalpy iH calculated in the calculator 142 and derives the saturation pressure PlV corresponding to the enthalpy iH. The saturation pressure PlV is compared with the inlet drain pressure Pl represented by the input signal 46, and if P1 > PlV it means the flash state, so that the following calculation is made. If P1 < PlV, it means the single phase stream, so that no correction of the valve opening is made. If P1 > PlV, decided that the inlet flash state is in force, the enthalpy ilg and volume ratio Vlg of the saturated steam with respect to the inlet pressure Pl and the enthalpy ilQ and volume ratio VlQ of the saturated water are derived from approximate functions stored. The void factor Vr is calculated form these values and the afore-mentioned inlet enthalpy iH by using an equation Vr V r V (l~X~ ~~~~~~~~~~ (1) where X is the flash factor given as ~' X = H iQ ~~~~~~~~~~~~~~~~ (2) , lg lQ
,j 20 When the pressure of the saturated water of the ' drain at the inlet of the first N valve 13 becomes lower $:
than the saturated steam pressure, the flashing occurs ~;
.', ~ -.. . .
.~.
7S~
1 to reduce the drain exhausting capacity of the first N
valve 13. The reduction is pronounced the more the higher the flash factor. In the neighborhood of the inlet of the N valve 13, the flash factor is about 80%
even when the dryness of the drain saturated water is about 0.5%, and the corresponding control valve Cv (velocity coefficient) value correction coefficient which has close bearing upon the flash factor is large.
This means that under the ~lashing phenomenon the drain in the case when there is no flashing cannot be e~hausted with the same valve opening.
Accordingly, the compensator 138 includes calculators 144, 145 and 146 and a subtractor 147 and has the following function. The calculator 144 receives the output signal 137 of the inlet flash factor forecaster 136 and calculates the opening Cv value correction coefficient which is proportlonal to the inlet flash factor Vr. The calculator 145 receives the first N
valve opening signal 50 and calculates the present Cv value of the first N valve 13 from the input signal.
The outputs of the calculators 144 and 145 are coupled to the calculator 146, which calculates the necessary opening of the first N valve 13 compensated for the 1, reductlon of the valve capacity due to the inlet flashing. The output signal of the calculator 146 is coupled to the subtractor 147, which also receives the opening signal 50 and subtracts the present opening from the necessary opening to derive the opening /
!
., .
~ 7S9 l difficiency and provide a signal 139 representing the difficiency as the output of the compensator 138. The output signal 139 is coupled to an adder 149 shown in Fig. 16, which provides the operation signal 37 to the 5 first N valve 13.
The in-advance drain switching valve gradual opening mechanism, which serves to cause gradual opening of the first X valve 14 in advance to make up for the transient capacity difficiency of the first N
lO valve 13, includes an in-advance drain switching valve gradual opening operation signal generator 150 which receives the first N valve opening signal 50 and forecast inlet flash factor signal 137. Fig. 19 shows the detailed construction of the signal generator 150.
15 The inlet flash factor signal 137 from the inlet flash factor forecaster 136 and a reference valve set in a drain flash factor setter 125 are coupled to a subtractor 151, and when the signal 137 exceeds the reference value, i.e., when the forecast flash factor exceeds the 20 preset reference flash factor, the difference signal is provided from the subtractor 151. Also, the first N valve opening signal 50 and a reference value set in an opening setter 154 are coupled to a subtractor 153, and when the signal 50 exceeds the reference value, s 25 i.e., when the opening of the first N valve 13 exceeds the preset opening, the difference signal is provided , from the subtractor 153. The difference signals from , the subtractors 151 and 153 are coupled to an in-advance ..
,, ~
., .
:
,, 1 gradual opening start signal generator 55, which generates a start signal according to the input difference signals.
The start signal is coupled together with gradual opening period and gradual opening upper limit data preset in respective setters 156 and 157 to a gradual opening signal program setter 158, and the output signal of the setter 158 is coupled to a non-linear signal converter 159, which converts the input signal into a non-s linear signal. Thus, when the opening of the first N
', 10 valve 13 exceeds a predetermined value or when the iniet flash factor exceeds a preset flash factor, the signal generator 150 generates a gradual opening signal 160 based upon the program in accordance with the opening , signal 50 and forecast inlet flash factor signal 137.
s 15 This gradual opening signal 160 is coupled to an adder 161, whlch provides the operation signal 38 for the first X valve 14, whereby the first X valve 14 is gradually ~, opened in advance so as to make up for the difficiency of the opening of the first N valve 13 and prevent the 20 loss of control due to otherwise liable full opening of the first N valve 13.
The drain switching mechanism in the feed forward water level adjuster 129 has the following construction. The signal provided from the load detector 25 42 provided on the extracted steam duct 5 is converted '~ by a load converter 163 into a turbine load signal. The output signal of the load converter 163 is coupled to a .
load change rate calculator 164, which converts the rate :
, . .
., ~
1 of change of the turbine load. A load conversion signal 165 provided from the converter 163 and a load change rate signal 166 provided from the calculator 164 are coupled together with the opening signals 50 and 51 to a drain switching signal selector 167. The selector 167 compares the preset value of load with HL and LL according to the input signals mentioned above for switching the paths, , through which the full closure signal, gradual opening s signl and water level control signal for controlling 10 the water level according to the drain level are transmitted to the first N valve 13 and first X valve 14.
s Fig. 20 shows the construction of the signal ~ selector 167 as a flow chart. In the drain switching i~ signal selector 167, the selection of switching as to 15 which one of the valves 13 and 14 the water level control signal 63 is to be given to is effected by providing a signal D which has either content "1" or "2" depending upon the load conversion signal 165 and opening signals , 50 and 51 coupled to a signal receiving section 168.
20 The signal D has the same meaning as described earlier in connection with Fig. 8. That is, like the case of Fig. 8, if D = 1 the coupling of the water level control s signal to the first X valve 14 is selected, and if D = 2 'si the coupling of the water level control signal to the 25 first N valve 13 is selected. The selection of the coupling path of the gradual opening signal 68 is effected by providing a signal D which has either content , "5" or "6" depending upon the load conversion signal 165 s ~ ~ 35 -:.
,,.
~ Z ~ 5 9 and opening signals 50 and 51 coupled to a signal receiv-ing section 169. If D = 5 the coupling of the gradual opening signal to the first X valve 14 is selected, and if D = 6 the coupling of the gradual opening signal to the first N valve 13 is selected. The selection of the coupling path of the full closure signal 64 is effected by providing a signal D which has either content "3" or "4" depending upon the load conversion signal 165 and oepning signals 50 and 51 coupled to a signal receiving section 170. If D = 3 the route to the valve 14 is selected, and if D = 4 the route to the valve 13 is selected. Thus, in the normal turbine load state in excess of the preset value HL, the output signal D of the drain switching signal selector 167 has the content (D = 3) of dictating the coupling of the full closure signal to the first X valve 14 and also the content (D = 2) of dictating the coupling of the water level control signal for the feedback control of the water level according to the detected drain level to the first N
s, 20 valve 13. In the case where the turbine load is lower than the preset level LL, the output signal D has contents (D - 4 and D = 1) of dictating the coupling of the full closure signal to the first N valve 13 and the water level control slgnal to the first X valve 14. In the case where the turbine load is between the preset levels HL and HL, the output signal D has the contetnt (D = 3 or D = 4) of dictating the continual coupling of full closure signal to the water control valve in the fully closed , ~
i ,, :
.;: . .
....
~.~t'.~ S9 1 state to maintain this state and the content (D = 2 or D = 1) of dictating the coupling of coupling the water control signal to the water control valve which is not fully closed. Further, when the rate of change of 5 the load is positive, the signal D has the content (D =
Z'7S9 1 D = 5 and D = 6 are pvoding "no", and a reset signal is thus given through routes 105, 106 and 107 to the signal generator 57 to reset the generator 57, thus bringing the gradual opening signal 65 to a "0" level. Also, it will be readily understood that the full closure signal 64 is given from the signal generator 53 through routes 108 and 94 to the first X valve 14 and the water level control signal 63 is given from the signal generator 52 through routes 109 and 110 to the first N valve 13.
When the load is increased to exceed HL, all the steps except for the step 87 in Fig. 8 yield a "yes"
~hus, the key-on signal is led through routes 89, 95 and 103 to select the full closure signal 64 for the first X valve 14 while it is led through routes 89, 95 and 104 for giving the water level control signal 63 to the first N valve 13. This means that the operation signals 71 and 72 represent the respective states D = 3 and D = 2, that is, the previous control state mentioned above is maintained. In the above way, the drain switching in the case when the load is increasing is completed. It will be understood that the drain switching for the second heater by the generator 35 is effected in the same manner as described above.
Fig. 11 shows the changes in load and changes in valve openings in the case when the load decreases from high to low level. In this case, the drain switching is effected in a manner similar to that in the case of the increasing load. Further, even in case 7~;g 1 when the valve inlet flashing phenomenon occurs the output signal 73 from the control valve in-advance operation signal generator 61 in the signal generator 34 is additionally applied to the second X valve 17 in advance through the signal generator 35, so that the opening of the first N valve 13 is not so increased compared to the case of the prior art, and it is possible to alleviate the sudden change of the water legel caused by the reduction of the drain exhaust capacity of the first N valve due to the valve inlet flashing phenomenon.
Now, a different preferred embodiment of the invention will be described with reference to Figs. 12 to 14. In the figures, like component parts as those already described are designated by like reference numerals, and their detailed description is omitted.
In the system shown in Fig. 12, a digital water level control unit 120 of a study control system ls used for the water level control of the first heater 3. The control unit 120 receives, as signals having dlrect bearing upon the water level of the first heater 3, opening signals 50, 51, 121 and 123 respectively provided from opening detectors 48, 49, 31 and 122 for detecting the openings of water level control valves 13, 14 and 16 and an extracted steam check valve 30, a water level signal 124 provi~ed as a plant state signal from a water level detector 18, a signal 43 representing the plant load state provided from a plant load detector 42, a load change rate signal 125 representing the t,~Z 7S9 1 transient running state of the plant and a pressure signal 127 provided from a pressure detector 126 for detecting the pressure in the deaerator 10. ~hese input signals are processed in a manner as will be described hereinafter with reference to Fig. 13 to generate a water level control signal 63 which is coupled to the first N valve 13 and first X valve 14 for the opening control thereof.
Now, the study control system of the digital water level control unit 120 will be descri~ed with reference to Fig. 13. The control unit 120 may be realized as a computor, and it fetches the signals from the individual detectors as mentioned previously with reference to Fig. 12 for each predetermined sampling cycle period ~T. The water level signal 124 is compared with a preset level, and the difference is sub~ect to a proportlonal integrating differentiating (PID) proces-slng to provide a water level control valve feedback signal 128. When the initial basic data for determining the control valve operation signals from the fetched data are not prepared yet, these data are prepared through a data logger. That is, before the preparation of the initial basic data is completed, the signal 128 is provided as the water level control signal 63, and the water level control depends only upon the feedback control through the PIC control. However, where the plant characteristics are forecastable and it is possible to prepare the initial basic data in advance, ' - 2~ -., .
; , .
s9 1 the initial basic data may be coupled as input data as well. The data logger is progressively renewed.
When the preparation of the initial basic data is completed, the fetched data are compared with the basic data before the calculation processing to determine a water level control valve forecast control signal 129.
Concurrently with this signal processing, whether the water level is within a predetermined control range is checked. If it is not within the control range, it means that the water level control valve control signal determined on the basis of the data fetched at an instant (T - ~T) one sampling cycle before the instant time (T) has been unsatisfactory. In this case, the correction of the basic data is made by using values fetched at the present instant (time T) as the opening slgnals 50 and 51 while using the values at the instant (T - ~T) one cycle before as the other fetched data. If the water level is within the control range, no correction of the basic data is made.
In the above way, when the preparation of the initial basic data is completed, the water level control valve forecast operation control signal 129 obtained through the calculation with the fetched data as mentioned ; serves as the basic valve control signal, and to this signal the afore mentioned water level control valve i feedback control signal 128 is added to produce the water level control signal 63 for controlling the valves 13 and 14.
,~, ., .
1 Now, an example of the method o~ preparing the basic data ~ill be briefly explained referring to Fig.
14. ~he fetched data are put in order with respect to the load as shown in Figs. 14A, 14B and 14C, and the basic charactersitics of the individual fetched data corresponding to the load are grasped as respective patterns. On the basis of these patterns the openings of the water level control valves 13, 14 and 16 are determined according to the load while also making it possible to make correction of the water level control valve openings by using deviations of the individual fetched data from the basic characteristics as shown in Fig. 14D. As is seen from Fig.14D, this correction of the opening of the first N valve 13 is made by fore-casting the inlet flashing phenomenon that occurs whenthe laod change rate takes a negative value as is apparent from Fig. 3.
As has been shown, by carrying out the feed water heater water level control with the study control system as according to the embodiment, it is possible to prevent abnormal variations of the drain level of the feed water heater at the time of the afore-mentioned drain switching and sudden load change.
A further preferred embodiment of the invention will now be described with reference to Fig. 15 and following figures. In the figures, like component parts as those already described are designated by like reference numerals, and their detailed description is omitted.
,.
'7S~
1 In this embodiment, a feed forward water level adjuster 129 is provided. The water level adjuster 129 receives opening signals 50 and 51, a water level signal 36, a plant load signal 43, a drain temperature signal 132 provided from a drain temperature detector 130 connected to the drain duct 9, a drain pressure signal 133 provided from a drain pressure detector 131 also connected to the drain duct 9, an inlet drain pressure signal 46 provided from the drain pressure detector 44 connected to the drain duct 9 and a flow rate signal 135 provided from a flow rate detector 134 for detecting the flow rate of drain through the drain duct 9, and it provides valve operation signals 37 and 38 to the water level control valves 13 and 14 respectively.
Fig. 16 shows the construction of the feecback water level adjuster 129. It includes an opening dlfficiency compensation mechanism, an in-advance drain switching valve gradual opening mechanism and a drain switching mechanism.
The opening difficiency compensation mechanism includes an inlet flash factor forecaster 136, which forecasts the flash factor at the inlet of the first N
valve 13 by fetching the drain temperature signal 132, a drain pressure signal 133, an inlet drain pressure signal 46 and a drain flow rate signal 135, and an opening difficiency in-advance compensator 138, which calculates the opening difficiency corresponding to the inlet flashing from the output signal 137 of the forecaster ~tljz~7s9 1 136 and the valve opening signal 50 and providing an output signal 139 representing the result of the calcula-tion. Fig. 17 shows the detailed construction of the forecaster 136 and compensator 138.
The iniet flash factor forecaster 136 includes an enthalpy claculator 140, which calculates the enthalpy of the drain at the outlet of the first heater 3 from the drain temperature signal 132 and drain pressure signal 133. The forecaster 136 also includes a drain flow delay calculator 141, which receives the drain flow rate signal 135 and calculates the delay of the drain from the outlet of the heater 3 before reaching the inlet of the first N valve 13 from the drain flow rate, the length and diameter of the duct 9, etc. The outputs of the enthalpy calculator 140 and drain flow delay calculator 141 are coupled to an inlet enthalpy calculator 142, whlch calculates the enthalpy of the drain at the inlet of the first N valve 13. The output of the inlet enthalpy calculator 142 is coupled together with the output of the inlet drain pressure signal 46 to an inlet flash factor calculator 143. The inlet flash factor calculator 143 calculates the dryness and volume factor which are physical properties of the drain and also calculates by using these parameters the inlet flash factor and bu~ble ratio (i.e., void factor Vr), and the calculated data are provided as an output signal 137 of the forecaster 136.
The construction of the inlet flash factor .' , .
' ' , ~3~ ~59 1 calculator 143 will now be described with reference to the flow chart of Fig. 18.
The calculator 143 fetches the inlet drain enthalpy iH calculated in the calculator 142 and derives the saturation pressure PlV corresponding to the enthalpy iH. The saturation pressure PlV is compared with the inlet drain pressure Pl represented by the input signal 46, and if P1 > PlV it means the flash state, so that the following calculation is made. If P1 < PlV, it means the single phase stream, so that no correction of the valve opening is made. If P1 > PlV, decided that the inlet flash state is in force, the enthalpy ilg and volume ratio Vlg of the saturated steam with respect to the inlet pressure Pl and the enthalpy ilQ and volume ratio VlQ of the saturated water are derived from approximate functions stored. The void factor Vr is calculated form these values and the afore-mentioned inlet enthalpy iH by using an equation Vr V r V (l~X~ ~~~~~~~~~~ (1) where X is the flash factor given as ~' X = H iQ ~~~~~~~~~~~~~~~~ (2) , lg lQ
,j 20 When the pressure of the saturated water of the ' drain at the inlet of the first N valve 13 becomes lower $:
than the saturated steam pressure, the flashing occurs ~;
.', ~ -.. . .
.~.
7S~
1 to reduce the drain exhausting capacity of the first N
valve 13. The reduction is pronounced the more the higher the flash factor. In the neighborhood of the inlet of the N valve 13, the flash factor is about 80%
even when the dryness of the drain saturated water is about 0.5%, and the corresponding control valve Cv (velocity coefficient) value correction coefficient which has close bearing upon the flash factor is large.
This means that under the ~lashing phenomenon the drain in the case when there is no flashing cannot be e~hausted with the same valve opening.
Accordingly, the compensator 138 includes calculators 144, 145 and 146 and a subtractor 147 and has the following function. The calculator 144 receives the output signal 137 of the inlet flash factor forecaster 136 and calculates the opening Cv value correction coefficient which is proportlonal to the inlet flash factor Vr. The calculator 145 receives the first N
valve opening signal 50 and calculates the present Cv value of the first N valve 13 from the input signal.
The outputs of the calculators 144 and 145 are coupled to the calculator 146, which calculates the necessary opening of the first N valve 13 compensated for the 1, reductlon of the valve capacity due to the inlet flashing. The output signal of the calculator 146 is coupled to the subtractor 147, which also receives the opening signal 50 and subtracts the present opening from the necessary opening to derive the opening /
!
., .
~ 7S9 l difficiency and provide a signal 139 representing the difficiency as the output of the compensator 138. The output signal 139 is coupled to an adder 149 shown in Fig. 16, which provides the operation signal 37 to the 5 first N valve 13.
The in-advance drain switching valve gradual opening mechanism, which serves to cause gradual opening of the first X valve 14 in advance to make up for the transient capacity difficiency of the first N
lO valve 13, includes an in-advance drain switching valve gradual opening operation signal generator 150 which receives the first N valve opening signal 50 and forecast inlet flash factor signal 137. Fig. 19 shows the detailed construction of the signal generator 150.
15 The inlet flash factor signal 137 from the inlet flash factor forecaster 136 and a reference valve set in a drain flash factor setter 125 are coupled to a subtractor 151, and when the signal 137 exceeds the reference value, i.e., when the forecast flash factor exceeds the 20 preset reference flash factor, the difference signal is provided from the subtractor 151. Also, the first N valve opening signal 50 and a reference value set in an opening setter 154 are coupled to a subtractor 153, and when the signal 50 exceeds the reference value, s 25 i.e., when the opening of the first N valve 13 exceeds the preset opening, the difference signal is provided , from the subtractor 153. The difference signals from , the subtractors 151 and 153 are coupled to an in-advance ..
,, ~
., .
:
,, 1 gradual opening start signal generator 55, which generates a start signal according to the input difference signals.
The start signal is coupled together with gradual opening period and gradual opening upper limit data preset in respective setters 156 and 157 to a gradual opening signal program setter 158, and the output signal of the setter 158 is coupled to a non-linear signal converter 159, which converts the input signal into a non-s linear signal. Thus, when the opening of the first N
', 10 valve 13 exceeds a predetermined value or when the iniet flash factor exceeds a preset flash factor, the signal generator 150 generates a gradual opening signal 160 based upon the program in accordance with the opening , signal 50 and forecast inlet flash factor signal 137.
s 15 This gradual opening signal 160 is coupled to an adder 161, whlch provides the operation signal 38 for the first X valve 14, whereby the first X valve 14 is gradually ~, opened in advance so as to make up for the difficiency of the opening of the first N valve 13 and prevent the 20 loss of control due to otherwise liable full opening of the first N valve 13.
The drain switching mechanism in the feed forward water level adjuster 129 has the following construction. The signal provided from the load detector 25 42 provided on the extracted steam duct 5 is converted '~ by a load converter 163 into a turbine load signal. The output signal of the load converter 163 is coupled to a .
load change rate calculator 164, which converts the rate :
, . .
., ~
1 of change of the turbine load. A load conversion signal 165 provided from the converter 163 and a load change rate signal 166 provided from the calculator 164 are coupled together with the opening signals 50 and 51 to a drain switching signal selector 167. The selector 167 compares the preset value of load with HL and LL according to the input signals mentioned above for switching the paths, , through which the full closure signal, gradual opening s signl and water level control signal for controlling 10 the water level according to the drain level are transmitted to the first N valve 13 and first X valve 14.
s Fig. 20 shows the construction of the signal ~ selector 167 as a flow chart. In the drain switching i~ signal selector 167, the selection of switching as to 15 which one of the valves 13 and 14 the water level control signal 63 is to be given to is effected by providing a signal D which has either content "1" or "2" depending upon the load conversion signal 165 and opening signals , 50 and 51 coupled to a signal receiving section 168.
20 The signal D has the same meaning as described earlier in connection with Fig. 8. That is, like the case of Fig. 8, if D = 1 the coupling of the water level control s signal to the first X valve 14 is selected, and if D = 2 'si the coupling of the water level control signal to the 25 first N valve 13 is selected. The selection of the coupling path of the gradual opening signal 68 is effected by providing a signal D which has either content , "5" or "6" depending upon the load conversion signal 165 s ~ ~ 35 -:.
,,.
~ Z ~ 5 9 and opening signals 50 and 51 coupled to a signal receiv-ing section 169. If D = 5 the coupling of the gradual opening signal to the first X valve 14 is selected, and if D = 6 the coupling of the gradual opening signal to the first N valve 13 is selected. The selection of the coupling path of the full closure signal 64 is effected by providing a signal D which has either content "3" or "4" depending upon the load conversion signal 165 and oepning signals 50 and 51 coupled to a signal receiving section 170. If D = 3 the route to the valve 14 is selected, and if D = 4 the route to the valve 13 is selected. Thus, in the normal turbine load state in excess of the preset value HL, the output signal D of the drain switching signal selector 167 has the content (D = 3) of dictating the coupling of the full closure signal to the first X valve 14 and also the content (D = 2) of dictating the coupling of the water level control signal for the feedback control of the water level according to the detected drain level to the first N
s, 20 valve 13. In the case where the turbine load is lower than the preset level LL, the output signal D has contents (D - 4 and D = 1) of dictating the coupling of the full closure signal to the first N valve 13 and the water level control slgnal to the first X valve 14. In the case where the turbine load is between the preset levels HL and HL, the output signal D has the contetnt (D = 3 or D = 4) of dictating the continual coupling of full closure signal to the water control valve in the fully closed , ~
i ,, :
.;: . .
....
~.~t'.~ S9 1 state to maintain this state and the content (D = 2 or D = 1) of dictating the coupling of coupling the water control signal to the water control valve which is not fully closed. Further, when the rate of change of 5 the load is positive, the signal D has the content (D =
6) of dictating the coupling of the gradual opening signal to the valve 13 after the confirmation of the fact that the valve 14 is not fully closed, and in the case of a negative load change rate the signal D has the content 10 (D = 5) of dictating the coupling of the gradual opening signal to the valve 14 after the confirmation of the fact that the valve 13 is not fully closed. These output signals D of the drain switching signal selector 167 are transmitted to a drain switch circuit 171 (shown 15 ln Fig. 16).
Referring again to Fig. 16, the signals 165 and 166 from the converter 163 and calculator 164 are also coupled to a gradual opening signal start selector 172. When the load conversion signal 165 and load change rate signal 166 are coupled to the selector 172, whether the rate of change of the load is positive or negative is first checked, and then whether the load is ~ increasing from low to high level or decreasin~ from s high to low level is checked. If the rate of change of 25 the load is negative, a gradual opening signal starter 155 !, iS rendered operative upon detection of the reaching of the preset level HL by the load. If the rate of change of the load is positive, the starter 155 is rendered ;~
~:~ C,~;~'7S9 1 operative upon detection of the reaching of the preset level LL by the load.
When the starter 155 is rendered operative upon reaching of the preset level ~L or LL depending upon 5 whether the rate of change of the load is positive or negative, it provides an output signal to a gradual opening signal generator 173. As a result, the generator 173 generates the gradual opening signal 68 which is coupled to the drain swtich circuit 17I mentioned above.
To the drain switch circuit 171 are coupled the gradual opening signal 68 from the signal generator 173, the signal D from the selector 167, the full closure signal 64 from the signal generator 174, and the water level control signal 63 provided from the feedback 15 water level controller 175 according to the water ~; level signal 36. The function of the drain switch circuit 171 will now be described in detail with reference to Fig. 22. It will be readily seen from the figure that the water level control signal 63, full closure signal 64 and gradual opening signal 68 are selectively provided as signal 177 to be coupled to the valve 13 and also signal 177 to be coupled to the valve 14 in accordance with the content of the signal D. The content of the signal D and the selection of the valves are as has been described previously in connection with Fig. 19.
The operation signal 176 for operating the first N valve 13, provided from the drain switch circuit 171, is added in an adder 149 to the output signal 139 from , - 38 -. . .
. .
-. ,.
5~
1 the opening difficiency compensation mechanism (i.e., the signal representing the difficiency of the opening of the first N valve 13) to provide the first N valve operation signal 37. On the other hand, the operation signal 177 for the first X valve 14 is added in an adder ' 161 to the output signal 160 from the in-advance drain I switching valve gradual opening mechanism (i.e., the gradual opening signal for making up for the difficiency of the capacity of the N valve 13) to provide the first X valve operation signal 38. ~he signals 37 and 38 are given as the output of the feed forward water level ad~uster 129 to the first N valve 13 and first X
valve 14 respectively.
As has been shown, with this embodiment the gradual opening signal generator 173 is rendered operative by the load conversion signal 165 and load change rate ~ignal 166, and even during the drain switching state i the water level control signal 63 based upon the drain water level is always transmitted to either the first N valve 13 or the first X valve 14 for the opening ,' control while the forced closure signal 64 or gradual opening signal 68 is always transmitted to the other ~; water level control valve for operating it in accordance $ with the signals 165 and 166 and also the opening signals , 25 50 and 51 representing the openings of the valves 13 and 14. Further, before the drain led out from the outlet of the first heater 3 with a constant flash factor reaches the neighborhood of the inlet of the first N valve ,,.
~ - 39 -.
'$
7S~
1 13 with a flow delay, a sum control instruction is transmitted to the control valves, to which the afore-mentioned instructions have been given, in correspon-, dence to the detected flash factor in order that the 5 difficiency of the exhausting capacity will not result.
More particularly, the flashing phenomenon occurring due to the decrease o~ the load is preliminarily detected f at the outlet of the first heater 3, and the first N
valve 13 is opened in advance with respect to the delay 10 in flow rate the difficiency of capacity should not result in correspondence to the flash factor, while the , first X valve 14 is gradually opened in advance according to a program in the case where a difflciency of the capacity is going to result with the sole first N valve 13 being 15 open. The situation that the dlfflciency of capacity is going to result with the sole first N valve 13 being open is grasped as a case when the flash factor exceeds a predetermined level or as a case when the opening of the first N valve 13 exceeds a predetermined 20 value. Further, through the control of the first N
valve 13 and first X valve 14 in advance in the manner as has been shown, it is possible to absorb the deteriora-tion of the response due to the delay in the control air signals for the indivldual valves and ellminate the 25 likelihood of the delay of the control.
Fig. 23 shows experimental data obtained when the drain water level control is made by using the system and method as in the above embodiment. According l. ~ "
J - ~0 _ 'k , ., ;:
.,~, 1 to the embodiment, no great water level variation is caused even in case of occurrence of the inlet flashing, and also water level variations accompanying the drain ~ switching can be avoided.
As has been described in the foregoing, accord-ing to the invention it is possible to obtain satis-factory water level control even in the case of the drain switchlng or in the case of a sudden load change and avoid abnormal varlat~ons of the drain level.
~, i .
, :, i .
,;~.
... .
.~.
Referring again to Fig. 16, the signals 165 and 166 from the converter 163 and calculator 164 are also coupled to a gradual opening signal start selector 172. When the load conversion signal 165 and load change rate signal 166 are coupled to the selector 172, whether the rate of change of the load is positive or negative is first checked, and then whether the load is ~ increasing from low to high level or decreasin~ from s high to low level is checked. If the rate of change of 25 the load is negative, a gradual opening signal starter 155 !, iS rendered operative upon detection of the reaching of the preset level HL by the load. If the rate of change of the load is positive, the starter 155 is rendered ;~
~:~ C,~;~'7S9 1 operative upon detection of the reaching of the preset level LL by the load.
When the starter 155 is rendered operative upon reaching of the preset level ~L or LL depending upon 5 whether the rate of change of the load is positive or negative, it provides an output signal to a gradual opening signal generator 173. As a result, the generator 173 generates the gradual opening signal 68 which is coupled to the drain swtich circuit 17I mentioned above.
To the drain switch circuit 171 are coupled the gradual opening signal 68 from the signal generator 173, the signal D from the selector 167, the full closure signal 64 from the signal generator 174, and the water level control signal 63 provided from the feedback 15 water level controller 175 according to the water ~; level signal 36. The function of the drain switch circuit 171 will now be described in detail with reference to Fig. 22. It will be readily seen from the figure that the water level control signal 63, full closure signal 64 and gradual opening signal 68 are selectively provided as signal 177 to be coupled to the valve 13 and also signal 177 to be coupled to the valve 14 in accordance with the content of the signal D. The content of the signal D and the selection of the valves are as has been described previously in connection with Fig. 19.
The operation signal 176 for operating the first N valve 13, provided from the drain switch circuit 171, is added in an adder 149 to the output signal 139 from , - 38 -. . .
. .
-. ,.
5~
1 the opening difficiency compensation mechanism (i.e., the signal representing the difficiency of the opening of the first N valve 13) to provide the first N valve operation signal 37. On the other hand, the operation signal 177 for the first X valve 14 is added in an adder ' 161 to the output signal 160 from the in-advance drain I switching valve gradual opening mechanism (i.e., the gradual opening signal for making up for the difficiency of the capacity of the N valve 13) to provide the first X valve operation signal 38. ~he signals 37 and 38 are given as the output of the feed forward water level ad~uster 129 to the first N valve 13 and first X
valve 14 respectively.
As has been shown, with this embodiment the gradual opening signal generator 173 is rendered operative by the load conversion signal 165 and load change rate ~ignal 166, and even during the drain switching state i the water level control signal 63 based upon the drain water level is always transmitted to either the first N valve 13 or the first X valve 14 for the opening ,' control while the forced closure signal 64 or gradual opening signal 68 is always transmitted to the other ~; water level control valve for operating it in accordance $ with the signals 165 and 166 and also the opening signals , 25 50 and 51 representing the openings of the valves 13 and 14. Further, before the drain led out from the outlet of the first heater 3 with a constant flash factor reaches the neighborhood of the inlet of the first N valve ,,.
~ - 39 -.
'$
7S~
1 13 with a flow delay, a sum control instruction is transmitted to the control valves, to which the afore-mentioned instructions have been given, in correspon-, dence to the detected flash factor in order that the 5 difficiency of the exhausting capacity will not result.
More particularly, the flashing phenomenon occurring due to the decrease o~ the load is preliminarily detected f at the outlet of the first heater 3, and the first N
valve 13 is opened in advance with respect to the delay 10 in flow rate the difficiency of capacity should not result in correspondence to the flash factor, while the , first X valve 14 is gradually opened in advance according to a program in the case where a difflciency of the capacity is going to result with the sole first N valve 13 being 15 open. The situation that the dlfflciency of capacity is going to result with the sole first N valve 13 being open is grasped as a case when the flash factor exceeds a predetermined level or as a case when the opening of the first N valve 13 exceeds a predetermined 20 value. Further, through the control of the first N
valve 13 and first X valve 14 in advance in the manner as has been shown, it is possible to absorb the deteriora-tion of the response due to the delay in the control air signals for the indivldual valves and ellminate the 25 likelihood of the delay of the control.
Fig. 23 shows experimental data obtained when the drain water level control is made by using the system and method as in the above embodiment. According l. ~ "
J - ~0 _ 'k , ., ;:
.,~, 1 to the embodiment, no great water level variation is caused even in case of occurrence of the inlet flashing, and also water level variations accompanying the drain ~ switching can be avoided.
As has been described in the foregoing, accord-ing to the invention it is possible to obtain satis-factory water level control even in the case of the drain switchlng or in the case of a sudden load change and avoid abnormal varlat~ons of the drain level.
~, i .
, :, i .
,;~.
... .
.~.
Claims (30)
1. A method of controlling the drain level of a high pressure feed water heater for heating the feed water with steam extracted from a turbine comprising the steps of detecting said drain level, generating a control signal to be applied to a control valve in such a manner that the detected value is coincident with a predetermined value, and controlling the openings of first and second water level control valves respectively provided in a first drain duct leading from said high pressure feed water heater to a deaerator and a second drain duct leading from said high pressure feed water heater to a low pressure feed water heater according to the detected water level, wherein said method further comprises the steps of detecting a first state of drain in the neighborhood of a drain outlet of said high pressure feed water heater and a second state of drain in the neighborhood of a drain inlet of said deaerator, and selectively directing one of the drain to be led to said high pressure supply water heater from a preceding stage and the drain from said high pressure feed water heater toward said deaerator prior to the occurrence of flashing in the neighborhood of the inlet of said first water level control valve thereby ensuring steady and reliable drain level control at the time of the flashing.
2. The method according to claim 1, wherein said method further comprises the steps of detecting the plant load state, selectively giving a forced full closure instruction, a gradual opening instruction and an opening control instruction to said first and second water level control valves in accordance with said detected plant load state and detected drain level, detecting the enthaply of the drain in the neighborhood of the drain outlet of said high pressure feed water heater, detecting the opening of said first water level control valve and pressure exerted thereto, and forecasting the difficiency of the opening of said first water level control valve due to the flashing in the neighborhood of the inlet thereof from said detected enthalpy and said detected opening of said first water level control valve and said detected pressure in the neighborhood of the inlet of said first water level control valve and giving a valve opening increase instruction to said first water level control valve for increasing the opening thereof by an amount corresponding to said difficiency.
3. The method according to claim 2, wherein said opening control instruction and forced full closure instruction are respectively given to said first and second water level control valves when the plant load is at its rated load level higher than a high reference load level while said forced full closure instruction and opening control instruction are given to said respective first and second water level control valves when the plant load is at a low load level lower than a low reference level.
4. The method according to claim 3, wherein in the case where said plant load increases from said low level to said rated load level, when said plant load level exceeds said low reference load level, said gradual opening instruction is given to said first water level control valve for gradually opening it while giving said opening control instruction to said second water level control valve for the water level control and when said plant load level reaches said rated load level, said opening control instruction is given to said first water level control valve while giving said full closure instruction to said second water level control valve, and in the case where said plant load decreases from said rated load level toward said low load level instructions are given to said first and second water level control valves in the order converse to the case of the load increase, thereby suppressing a sudden change of said drain level at the time of switch-ing of drain paths in the case of the plant load increase and also in the case of the plant load decrease.
5. The method according to claim 1, wherein said method further comprises the steps of controlling the opening of third and fourth water level control valves respectively provided in a third drain duct leading from a prestage feed water heater to said deaerator and a fourth drain duct leading from said prestage high pressure feed water heater to said first-mentioned high pressure feed water heater for controlling the drain water level of said first-mentioned high pressure feed water heater, detecting the plant load state, selectively giving a forced full closure instruction, a gradual opening instruction and an opening control instruction to said first to fourth water level control valves in accordance with said detected plant load state and said detected drain water level, detecting the enthalpy of the drain in the neighborhood of the outlet of said first-mentioned high pressure feed water heater, detecting the opening of said first water level control valve and the pressure in the neighborhood of the inlet thereof, and forecasting the difficiency of the opening of said first water level control valve due to the flashing in the neighborhood of the inlet thereof from said detected enthalpy, said detected opening of said first water level control valve and said detected pressure in the neighborhood of the inlet of said first water level control valve and giving a valve opening increase instruction to a selected one of said first to third water level control valves for increasing the opening thereof by an amount correspond-ing to said difficiency.
6. The method according to claim 5, wherein in the case where the plant load is at its rated load level higher than a high reference load level said opening control instruction is given to said first and fourth water level control valves while giving said forced full closure instruction to said second and third water level control valves, and in the case where the plant load is at its low load level lower than a low reference load level said full closure instruction is given to said first and fourth water level control valves while giving said opening control instruction to said second and third water level control valves.
7. The method according to claim 6, wherein in the case where said plant load increases from said low load level to said rated load level, when said plant load level exceeds said low reference load level, said gradual opening instruction is given to said first and fourth water level control valves for gradually opening these valves while giving said opening control instruction to said second and third water level control valves for the water level control and when said plant load level reaches said high reference load level, said opening control instruction is given to said first and fourth water level control valves while giving said full closure instruction to said second and third water level control valves, and in the case where said plant load decreases from said rated load level toward said low load level the instructions are given to said first to fourth water level control valves in the order converse to the case of the load increase, thereby suppressing a sudden change of said drain water level at the time of switching of drain paths in the case of the plant load increase and also in the case of the plant load decrease.
8. Method according to claim 1, wherein said method further comprises the steps of detecting the plant load and the rate of change thereof, detecting the respective openings of said first and second water level control valves and a reverse flow checking valve of the steam extracted from said turbine, sampling said detected plant load, said detected rate of change of said plant load, said detected openings of said valves and said detected drain water level to thereby provide sample data with a predetermined sampling cycle period, deriving the difference between the sampled rain water level data and a reference drain water level and generating a water level feedback control signal through digital proportional integrating differentiating processings of the derived water level difference, producing basic water level control data from said sampled data, deriving a water level control valve forecast control signal from said sampled data and basic water level control data, and adding said water level feedback control signal and water level control valve forecast control signal and giving the resultant sum signal to said first and second water level control valves for the drain water level control, said water level feedback control signal alone being given to each of said first and second water level control valves for the drain water level control during the period until said basic water level control signal is produced.
9. The method according to claim 8, wherein said feedback control signal or said sum signal is given to a third water level control value provided in a third drain duct leading from a prestage high pressure feed water heater to said first-mentioned high pressure feed water heater.
10. The method according to claim 8 or 9, wherein whether the detected drain water level is within a predetermined water level control range is checked and said basic water level control data is renewed if the checked drain water level is outside said control range.
11. The method according to claim 1, wherein said method further comprises the steps of detecting the plant load, the openings of said first and second water level control valves, the enthalpy of the drain at the outlet of said high pressure feed water heater, the drain flow rate in said first drain duct and the pressure in the neighborhood of the inlet of said first water level control valve, selectively giving either said full closure instruction, said gradual opening instruction or said opening control instructin to said first and second water level control valves in accordance with said detected plant load, said detected openings of said valves and said detected drain water level, deriving the flash factor in the neightborhood of said first water level control valve inlet in accordance with said detected drain enthalpy, said detected drain flow rate and pressure in the neighborhood of said first water level control valve inlet, and forecasting the optimum openings of said first and second water level control valves from said derived flash factor and detected first water level control valve opening so as to transmit an in-advance operation instruction to each of said first and second water level control valves for operating each said valve in combination with the instruction having been already given.
12. The method according to claim 11, wherein said method further comprises a step of calculating the dif-ficiency of the opening of said first water level control valve due to the forecast flashing in the neighborhood of the inlet of said first water level control valve from said derived flash factor and detected opening of said first water level control valve, said in-advance operation instruction given to said first water level control valve dictating the increase of the opening of said first water level control valve by an amount corresponding to the calculated difficiency of opening.
13. The method according to claim 11 or 12, wherein said in-advance operation instruction given to said second water level control valve dictates the valve opening gradual increase from the value specified by the instruction having already been given to said second water level control valve prior to the effect of flashing when said calculated flash factor exceeds a preset flash factor.
14. The method according to claim 11 or 12, wherein said in-advance operation instruction given to said second water level control valve dictates the valve opening gradual increase from the value sepcified by the instruc-tion having already been given to said second water level control valve prior to the effect of flashing when the detected first water level control valve opening exceeds a preset opening.
15. The method according to claim 11, wherein said gradual opening instruction is produced in accordance with the detected values of said plant load and said rate of change of said plant load, and said opening control signal is transmitted to either one of said first and second water level control valves for operating it while transmitting either said full closure instruction or said gradual opening instruction to the other water level control valve in accordance with the detected values of said plant load, said rate of change of said plant load and said first and second water level control valve openings.
16. A system for controlling the drain water level of a high pressure feed water heater comprising a high pressure feed water heater for heating feed water with steam extracted from a turbine, first and second water level control valves respectively provided in a first drain duct leading from said high pressure feed water heater to a deaerator and a second drain duct leading from said high pressure feed water heater to a low pressure feed water heater, means for detecting the openings of said first and second water level control valves, means for detecting the drain level of said high pressure feed water heater, said drain level being controlled through the control of the openings of said first and second water level control valves in accordance with the detected drain water level and the detected openings of said first and second water level control valves, wherein said system further comprises means for detecting a first state of drain in the neighborhood of the drain outlet of said high pressure feed water heater, means for detecting a second stage of drain in the nighborhood of the drain inlet of said deaerator, and means for selectively directing one of the drain to be led to said high pressure feed water heater from a preceding stage and the drain from said high pressure feed water heater prior to the occurrence of the flashing in the neighborhood of the inlet of said first water level control valve thereby ensuring steady and reliable drain water level control.
17. The system according to claim 16, wherein said system further comprises means for detecting the state of plant load, means for generating a forced full closure instruction, means for generating a gradual opening instruction, means for generating an opening control instruction for controlling the valve opening according to the detected drain water level, means for detecting the enthalpy of drain in the neighborhood of the outlet of said high pressure feed water heater, means for detecting the pressure in the neighborhood of the inlet of said first water level control valve, means for selectively giving either said forced full closure instruction, gradually opening instruction or open-ing control instruction to said first and second water level control valves in accordance with said detected plant load state and drain water level, means for forecasting the difficiency of the opening of said first water level control valve due to flashing in the neighborhood of the inlet thereof in accordance with said detected enthalpy and the opening of said pressure in the neighborhood of the inlet of said first water level control valve, and means for transmitting a valve opening increase instruction to said first water level control valve for increasing the opening thereof by an amount corresponding to said difficiency.
18. The system according to claim 17, wherein said instruction selecting means gives said opening control instruction and forced full closure instruction respectively to said first and second water level control valves when the detected plant load is at a rated level higher than a high reference load level and gives said forced full closure instruction and opening control instruction respectively to said first and second water level control valves when the detected plant load is its low load level lower than a low reference load level.
19. The system according to claim 18, wherein in the case where said plant load increases from said low level to said rated load level, when said plant load level exceeds said low reference load said instruction selecting means gives said gradual opening instruction to said first water level control valve for gradually opening it and said opening control instruction to said second water level control valve for the water level control and, when the plant load reaches said high reference load level, gives said opening control instruc-tion to said first water level control valve and said full closure instruction to said second water level control valve, and in the case where said plant load decreases from said rated load level toward said low load level said instruction selecting means gives instruc-tions to said first and second water level control valves in the order converse to the case of the load increase, thereby suppressing a sudden change of said drain water level at the time of switching of drain paths in the case of the plant load increase and also in the case of the plant load decrease.
20. The system according to claim 17, wherein said instruction selecting means also selectively gives one of said three instructions to third and fourth water level control valves respectively provided in a third drain duct leading from a prestage high pressure feed water heater to said deaerator and in a fourth drain duct leading from said prestage high pressure feed water heater to said first-mentioned high pressure feed water heater, and wherein said valve opening increase instruction transmitting means also selectively transmits said valve opening increase instruction to either one of said first to third water level control valves.
21. The system according to claim 20, wherein in the case where the plant load is at its rated load level higher than a high reference load level said instruction selecting means gives said opening control instruction to said first and fourth water level control valves and said forced full closure instruction to said second and third water level control valves, and in the case where the plant load is at its low load level lower than a low reference load level said instruction giving means gives said forced full closure instruction to said first and fourth water level control valves and said opening control instruction to said second and third water level control valves.
22. The system according to claim 21, wherein in the case where said plant load increases from said low load level to said rated load level, when said plant load exceeds said low reference load level, said instruction giving means gives said gradual opening instruction to said first and fourth water level control valves for gradually opening these valves and said opening control instruction to said second and third water level control valves for the water level control, when said plant load reaches said high reference load level, gives said opening control instruction to said first and fourth water level control valves and said full closure instruction to said second and third water level control valves, and in the case where said plant load decreases from said rated load level toward said low load level said instruction givening means gives the instructions to said first to fourth water level control valves in the order converse to the case of the load increase, thereby suppressing a sudden change of said drain water level at the time of switching paths in the case of the plant load increase and also in the case of the plant load decrease.
23. The system according to claim 16, wherein said system further comrpsies means for detecting the plant load and the rate of change of the plant load, means for detecting the openings of said first and second water level control valves and a check valve for checking the reverse flow of steam extracted from said turbine, means for sampling said detected values of said plant load, said rate of change of said load, said valve openings and said drain water level with a predetermined sampling cycle period, means for deriving the difference between the sampled drain water level data and a reference drain water level, means for generating a water level feedback control signal through digital proportional integrating differentiating processing of the derived water level difference, means for producing basic water level data from said sampled data, means for deriving a water level control valve forecast control signal from said sampled data and basic water level control data, and means for adding said water level feedback control signal and forecast water level control valve control signal so as to give the resultant sum signal to said first and second water level control valves for the drain water level control, said adding means being adapted to give said water level feedback control signal alone to each of said first and second water level control valves for the drain water level control during the period until said basic water level control signal is produced.
24. The system according to claim 23, wherein said feedback control signal or said sum signal are also given to a third water level control valve provided in a third drain duct leading from said prestage high pressure feed water heater to said first-mentioned high pressure feed water heater.
25. The system according to claim 23 or 24, wherein said system further comprises means for checking whether the detected drain water level is within a predetermined water level control range and renewing said basic water level control data if the checked drain water level is outside said control range.
26. The system according to claim 16, wherein said system further comprises means for detecting the plant load, means for detecting the openings of said first and second water level control valves, means for detecting the enthalpy of drain at the outlet of said high pressure feed water heater, means for detecting the flow rate of drain in said first drain duct, means for detecting the pressure in the neighborhood of the inlet of said first water level control valve, means for generating a forced full closure instruction, means for generating a gradual opening instruction, means for generating an instruction for opening control according to the water level changes, means for selectively giving either said full closure instruction, gradual opening instruction or opening control instruction to said first and second water level control valves in accordance with said detect-ed values of said plant load, said openings of said valves and said drain water level, means for deriving the flash factor in the neighborhood of said first water level control valve inlet in accordance with said detected values of said drain enthalpy, said drain flow rate and said pressure in the neighborhood of said first water level control valve inlet, and means for forecasting the optimum openings of said first and second water level control valves from said derived flash factor and detected first water level control valve opening to thereby transmit an in-advance operation inst-ruction to each of said first and second water level control valves for operating each said valve in combina-tion with the instruction having been already given.
27. The systm according to claim 26, wherein said forecasting means includes means for calculating the difficiency of opening of said first water level control valve due to the forecast flashing in the neighborhood of the inlet of said first water level control valve from said derived flash factor and detected opening of said first water level control valve, said in-advance operation instruction given to said first water level control valve dictating the increase of the opening of said first water level control valve by the amount corresponding to the calculated difficiency of opening.
28. The system according to claim 26 or 27, wherein said in-advance operation instruction given to said second water level control valve dictates the valve opening gradual increase from the value specified by the instruction having already been given to said second water level control valve prior to the effect of flashing when said calculated flash factor exceeds a preset flash factor.
29. The system according to claim 26 or 27, wherein said in-advance operation instruction given to said second water level control valve dictates the valve opening gradual increase from the value specified by the instruction having already been given to said second water level control valve prior to the effect of flashing when the detected first water level control valve opening exceeds a preset value.
30. The system according to claim 26, wherein said means for generating a gradual opening instruction generates said gradual opening instruction in accordance with the detected values of said plant load and said rate of change of said plant load, and wherein said instruction selecting means transmits said opening control instruction to either said first or second water level control valve and either said full closure instruc-tion or gradual opening instruction to the other water level control valve in accordance with the detected values of said plant load, said rate of change of said load and said first and second water level control valve openings.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP37597/1980 | 1980-03-26 | ||
| JP3759780A JPS56137004A (en) | 1980-03-26 | 1980-03-26 | Method of and apparatus for controlling drain level |
| JP51639/1980 | 1980-04-21 | ||
| JP5163980A JPS56149504A (en) | 1980-04-21 | 1980-04-21 | Water level control of water feed heater |
| JP17454580A JPS5798704A (en) | 1980-12-12 | 1980-12-12 | Method of and apparatus for controlling drain level of feed water heater |
| JP174545/1980 | 1980-12-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1152759A true CA1152759A (en) | 1983-08-30 |
Family
ID=27289520
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000373749A Expired CA1152759A (en) | 1980-03-26 | 1981-03-24 | Method of and system for controlling drain water level of feed-water heater |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU528466B2 (en) |
| CA (1) | CA1152759A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113900463A (en) * | 2021-09-17 | 2022-01-07 | 陕西省计量科学研究院 | Cold and hot water tank water level balancing method based on incremental PID control algorithm |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113154360A (en) * | 2021-05-13 | 2021-07-23 | 镇江裕太防爆电加热器有限公司 | Water level switching method of intelligent high-pressure heater for nuclear power |
-
1981
- 1981-03-24 CA CA000373749A patent/CA1152759A/en not_active Expired
- 1981-03-25 AU AU68717/81A patent/AU528466B2/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113900463A (en) * | 2021-09-17 | 2022-01-07 | 陕西省计量科学研究院 | Cold and hot water tank water level balancing method based on incremental PID control algorithm |
Also Published As
| Publication number | Publication date |
|---|---|
| AU6871781A (en) | 1981-10-01 |
| AU528466B2 (en) | 1983-04-28 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4578944A (en) | Heat recovery steam generator outlet temperature control system for a combined cycle power plant | |
| US7053341B2 (en) | Method and apparatus for drum level control for drum-type boilers | |
| US20100139392A1 (en) | System and method for controlling liquid level in a vessel | |
| US4550565A (en) | Gas turbine control systems | |
| EP0933505B1 (en) | Steam cooled system in combined cycle power plant | |
| US4561254A (en) | Initial steam flow regulator for steam turbine start-up | |
| EP0411013A1 (en) | Automatic steam generator control at low power | |
| CA1152759A (en) | Method of and system for controlling drain water level of feed-water heater | |
| CA1057065A (en) | Control systems for steam turbine plants including turbine bypass systems | |
| JPH01248098A (en) | Operating device for small and short ranged load following of boiling water nuclear reactor | |
| US4840766A (en) | Method of and apparatus for controlling steam vent volume of moisture separator reheaters | |
| JPH0368278B2 (en) | ||
| JPS63117106A (en) | Stoppage controlling method and device for turbine plant | |
| JPS6138763B2 (en) | ||
| JP2504939Y2 (en) | Boiler level controller | |
| KR840002451B1 (en) | Method for regulating the power supplied to a steam turbine pressurized water nuclear reactor | |
| JPS6218803B2 (en) | ||
| JP2574779B2 (en) | Water level control device for feed water heater | |
| JPS63162907A (en) | Control for combined power generation plant | |
| JPH0861605A (en) | Turbine bypass steam temperature controller | |
| JPS6250756B2 (en) | ||
| JPS6228362B2 (en) | ||
| JP2523493B2 (en) | Turbin bypass system | |
| JPS5934406A (en) | Controller of steam pressure in steam turbine | |
| JPH0743084B2 (en) | Main steam pressure controller |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |