KR100249721B1 - Method for the operation of a once-through steam generator with low load recirculation - Google Patents

Abstract

The steam generator of the present invention is connected to a feed pump (5), economizer (1), vaporizer (2), water separator (3) and at least one super heater (4), and also to the water outlet of the water separator (3). At the same time there is provided a circulation line 20 for discharging the flow of the working medium between the feed pump and the economizer. Between the discharge point 19 of the circulation line 20 and the economizer 1, the circulation pump 23 and the level control valve 24 thereafter are arranged. The method of operating such a steam generator is to adjust the water supply above the minimum flow rate of the economizer 1 in accordance with the steam temperature downstream of the water separator 3, and disposed between the circulation pump 23 and the economizer 1 By driving the level control valve 24, the water level of the water separator 3 is controlled to be equal to or less than the minimum flow rate of the economizer 1.

Therefore, the water level control for supplying water in the steam temperature control does not require the normal switching of the steam temperature control or the reverse switching thereof.

Description

How to operate the once-through flow steam generator with low load recirculation

1 is a connection diagram showing a steam generator for carrying out the method according to the invention.

FIG. 2 (a) is a diagram showing water separators having various water levels and the position of the associated valve in percentage relative to the open end of the valve.

Figure 2 (b) is a diagram showing the transition from dry operation to wet operation of the water separator.

FIG. 2 (c) is a diagram showing the transition from wet to dry operation of the water separator under certain circumstances.

3 is a control diagram in which the level control mechanism of FIG. 1 is modified.

The present invention provides a feed pump, an economizer, a vaporizer, a water separator and at least one super heater connected in series according to a flow path of a working medium, a circulation line connected to the water outlet of the water separator, and a feed pump. A method of operating a once through flow steam generator with low load recirculation having a circulation pump disposed between economizers.

In the conventional operation method of the steam generator having the above components, the amount of water supplied to the steam generator is adjusted in accordance with the steam temperature in the high load region and the water level of the water separator in the low load region. That is, the amount of water supplied to the steam generator is adjusted by changing the rotational speed of the feed pump or adjusting the opening and closing of the feed valve. A switching device is arranged behind the steam temperature control device or the water level control device in accordance with the signal line in order to switch to the water level or the reverse direction depending on the steam temperature. Superheating measured at the inlet of the first superheater can be used as a standard for marking for conversion (Swiss patent 667 697). As a standard of indication for switching for pure load control, for example, the discharge pressure of a feed pump can be mentioned (Swiss Patent No. 571 266). Switching of the control device is not always desirable in that large changes can occur in the supply of the working medium to the economizer during the conversion. In the supply of the working medium, a large change can occur due to whether the water level of the water separator rises or falls during the changeover, or whether it is actually located at a certain height from the temperature control device and the water level control device. This is because the magnitudes of the signals are different and they may not have the same digit signal.

It is an object of the present invention to provide an improved operating method which does not require switching by the above method for a steam generator having the components described at the outset.

The above object of the present invention can be achieved by the method described in claim 1 of the claims. By this method, the water supply is basically regulated according to the steam temperature and never falls below the fixed minimum flow rate of the economizer. The water level in the water separator is not affected by the change in the water supply as in the prior art, but is influenced by the valve disposed behind the circulation pump according to the flow path of the working medium. By this method, the conventional switching operation can be avoided without compromising the advantages of Swiss Patent No. 673697, for example, as compared with conventional methods such as Swiss Patent No. 59266. According to the circulation line, the valve disposed between the water separator and the circulation pump is generally not a throttle valve for level control. As a result, no steam gap is formed in the mixing area of the circulation water and the supply water, and as a result, Cavitation does not occur.

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the steam generator has an eco-nomizer 1, a vaporizer 2, a water separator 3 and a super heater 4, which are in series according to the flow path of the working medium. Is connected. The feed pump 5 for supplying the steam generator is connected to the inlet of the economizer 1 via the feed pipe 6, and the pipe 6 adjacent to the inlet is a flow meter for measuring the quantity of water flowing into the economizer. The measuring device 7 is arranged. The measuring device 7 is connected to the checkpoint 9 via a signal line 8, which is connected to the outlet of the feed control mechanism 11 via a signal line 16. The control mechanism 11 is designed as a state controller with an observer as described in Korean Patent Application No. 92-5479 by the applicant. The feed control mechanism 11 receives the temperature measurement signal through the signal line 12, and this measurement signal represents the actual value of the steam temperature, and is a value taken through the measuring device 13 located at the outlet of the super heater 4. to be. In the stage before steam is supplied to the consumer (not shown), several super heaters may be further disposed downstream of the measuring device 13, and the measuring device between the water separator 3 and the super heater 4 is (13) may be excreted. The feed control mechanism 11 receives a set value of the steam temperature via the signal line 14 and receives a signal indicating the minimum amount of working medium flowing into the economizer 1 via the signal line 15.

The minimum amount signal is used when the quantity of water flowing into the economizer 1 is reduced to a minimum amount of about 30% of the total load. The checkpoint 9 is included in the control device 17, and the output of the control device 17 is connected to the feed pump 5 via the signal line 18, which feed pump 5 is connected to the feed control loop. It forms one component. The control device 17 may for example be configured as a PI controller.

The circulation line 20 is connected to the outlet of the water separator 3, and this line 20 has a check valve 21 and a shutoff valve 22 which are sequentially positioned along the flow path. The line 20 discharges from the pit pump 5 to the downstream feed pipe 6 at the discharge point 19, and downstream from the discharge point 19, the circulation pump 23 and the level control valve 24. Is located. Thus, the circulating water from the water separator 3, except for the feed water, during operation to the water separator is passed through the portion 6 'of the feed pipe 6 including the circulation pump 23 and the level control valve 24. The amount of water supplied by the feed pump through the line 25 when the stream 25 has a large load and flows, in parallel with the part 6 'of the pipe, with a check valve 26 Part of will flow. The water supply line 27 is connected to the super heater 4, and alternatively, this line 27 may be connected to various super heaters (not shown) interposed behind the super heater 4, as is known.

A line 30 having a drain valve 31 is connected between the check valve 21 and the shutoff valve 22 of the circulation line 30, and this line 30 is a water supply tank (not shown) of the steam generating plant. May be connected to a specific tank of the condenser or plant.

The level control mechanism 33 is arranged to operate the level control valve 24, which is configured as a state controller having an observer like the feed control mechanism 11. The level control mechanism 33 receives the measurement signal via the signal line 34, which represents the actual value of the water level in the water separator 3. The set value for the water level is supplied to the level control mechanism 33 via the signal line 35, and the shutoff valve 22 operates according to the control signal transmitted from the level control mechanism 33 via the signal line 29. The function of this control signal will be described in detail later. The drain valve 31 operates in accordance with the level measurement signal transmitted from the signal line 34 via the signal line 32, the function of which is also described in detail below.

In Fig. 2 (a), the water separator 3 shows five different water level levels consisting of 1 m, 3 m, 7.7 m, 10.7 m and 14.2 m, of which the 7.7 m water level indicates that the steam generating plant is normally When operated, it is the set quantity level of the level control mechanism 33, and the 1m and 3m quantity levels are related to the transition from the operation of the wet separator to the operation of the dry separator, or the reverse thereof, and the 10.7 m and 14.2 The quantity level is related to the first startup stage of the steam generator. At this stage, a large quantity is available in the water separator 3, and if it exceeds the 10.7 m mark, the drain valve 31 starts to open according to the result of the level measurement signal of the line 32 to the 14.2 m mark. When it reaches as early as 100%, it is as shown by the solid line B in the center part of FIG.2 (a). In the 1m water level mark, the shutoff valve 22 moves from the 100% open position to the 0% closed position, and when it reaches the 3m water level mark, it opens from 0% to 100%, which is the second (a). As shown by two horizontal lines C in the figure. The valve movement of the level control valve 24 at the water level of 1m and 3m is shown on the right side of the second (a) diagram by two horizontal lines D, where the dashed line is fully automatic when the wet separator is operating. Indicates the result of the control.

The operation of the plant described above is as follows. In normal operation, that is, when the minimum flow rate of the economizer 1 is higher, that is, about 30% or more of the total load, the amount of water supplied to the steam generator is supplied by the feed pump 5 according to the steam temperature measured by the measuring device 13. Supplied. In the feed control mechanism 11, the actual measured value of the temperature is compared with the set value of the temperature supplied through the signal line 14, and the checkpoint 9 is set as the flow rate set value of the economizer 1 through the signal line 16. To generate an output signal. Measurements for the flow rate are supplied to the checkpoint 9 via the signal line 8 as measured values. An error signal for adjusting the speed of the feed pump 5 through the signal line 18 to supply a larger amount of water supply when the steam temperature rises, and to supply a smaller amount of water supply when the steam temperature falls, is set to the set value of the flow rate and According to the result of comparing the measured value, it is produced | generated by the control apparatus 17 which depends on the mechanism 11. As shown in FIG.

During this normal operation, a pure control passage of the working medium exists in the steam generator, and superheated steam flows into the water separator 3, so that saturated water returns to the economizer 1 through the circulation line 20. I never do that. Since the water separator is subjected to dry operation due to the overheated state of the steam, the water level of the water separator is very deep and the level control mechanism 33 must maintain the level control valve 24 in a substantially completely closed position. But. According to the present invention, there is always a flow state through the circulation pump 23, and therefore, when resuming the circulation operation, it is possible to avoid the temperature shock occurring in the pump after a long shutdown. For this reason, the level control valve 24 is kept completely open in the above-described operating stage and the circulation pump 23, and the circulation pump 23, which is switched off when the load is 50% or more, is the feed pump 5 Receive a portion of the water supply is supplied by, the remaining water supply is supplied to the economizer (1) through the line (25). No-load operation of the water separator 3 is prevented by the shutoff valve 22, in which case the shutoff valve 22 is in the fully closed position as the drain valve 31.

The transition from the dry operation to the wet operation of the water separator as shown in FIG. 2 (b) is as follows. The level control valve 24 and the shutoff valve 22 are in the preparation position (region E in FIG. 2 (b)), and the water level of the water separator 3 is 3 m or less. As the load of the steam generator decreases, saturated steam flows into the water separator 3, and accordingly, the water level of the water separator 3 rises (see curve H in FIG. 2 (b)). When the water level reaches 3m in height, the open end of the level control valve 24 is reduced by the first sequence of control commands programmed in the level control mechanism 33 (see area F in Fig. 2 (b)). As soon as the open cross section reaches 31%, the shutoff valve 22 moves to the fully open cross section by the control command (the end point of the area F), and accordingly switches the level control mechanism 33 to the automatic control operation. Region G in Figure 2 (b). That is, the level control mechanism 33 adjusts the level control valve 24 to measure a set value of 7.7 m for the water level.

There is no need to intervene any particular task in the transition from wet or cyclic to dry or controlled flow, and the level control valve (24) is proportional to the reduction rate of the saturated flow of water flowing into the water separator (3). ), The level control mechanism 33 reduces the open end surface. As a result, the circulation amount is timely reduced in accordance with the saturated flow of water to the water separator 3 so that the level of the water separator is kept constant. Therefore, the circulation amount is reduced to zero completely by the automatic control means, and when a reliable control flow operation is obtained, the serviceman switches off the circulation pump 23 as 50% of the full load, for example. Then, the control logic of the control mechanism 33 closes the shutoff valve 22 and fully opens the level control valve 24, whereby the circulation pump 23 receives a small flow rate manually enough to keep the water warm. do.

The sequence of FIG. 2 (c) forms a safety circuit that ensures the non-circulation of steam. If an unexpected transient transition occurs, the level control mechanism 33 may react too late, and the level of the water separator 3 may temporarily drop below 1 m mark. In order to prepare for such an accident, a second sequence of control commands is programmed in the control mechanism, and by this control command the shutoff valve 22 is immediately closed (area I in FIG. 2 (c)). When the shutoff valve 22 is closed, the level control mechanism 33 is out of automatic control operation, and the level control valve 24 is opened to the maximum allowable value by a control command (area K in Fig. 2 (c)). Therefore, the plant automatically takes an automatic control operation when the water level in the water separator 3 increases.

The circulation of water is suppressed due to an increase in the water supply pressure during operation of the wet water separator, that is, during the circulation operation, thereby causing the closing of the check valve 21. This phenomenon may occur for safety reasons, for example, when the minimum demand flow rate flowing through the economizer 1 increases due to a small load corresponding to about 15% of the total load. In this case, the level control mechanism 33 cannot perform the control function satisfactorily. In order to avoid such a phenomenon, as shown in FIG. 3, the level control mechanism 33 modified so that the input signal PE and the pilot signal FF flows in is provided. In Fig. 3, the drain valve 31 having the line 25, the line 30, the check valve 21, the shut-off valve 22 and the signal line 29 is omitted in clarity.

The input signal PE is formed by the difference between the pressure PA of the water separator 3 and the discharge pressure PS of the feed pump 5, and the increase in the discharge pressure PS is a signal in the pressure circuit of the level control mechanism 33. Before the change of PE occurs and the level of the water separator 3 increases, the open section of the level control valve 24 is immediately increased in response to this change. The pilot signal FF is formed in the function generator 38 and the multiplier 39 interposed after the generator 38, and as shown in the diagram of the function generator 38, this signal is the minimum flow rate of the economizer 1. Proportional to and multiplied by multiplier 39 having a multiplier L, the multiplier L requires a constant level state in the water separator 3 when the minimum flow rate flowing through the economizer 1 increases, and a level control valve ( 24 is opened.

As a variant of the above-described embodiment, the feed control mechanism 11 may be configured as a classical PID controller in which the output signal is limited and the PI controller is connected to a cascade, and the same modification is also possible in the level control mechanism 33. Do.

Claims (6)

Feed pump 5, economizer 1, vaporizer 2, water separator 3 and at least one super heater 4 and also water flow of water separator 3 connected in series along the flow path of the working medium A circulation line 20 connected to the outlet and simultaneously open to the flow path of the work medium between the feed pump 5 and the economizer 1, and the discharge point 19 and the economizer of the circulation line 20 in the flow path of the work medium. A circulation pump 23 disposed between (1) and a valve 24 disposed between the circulation pump 23 and the economizer 1, and the steam temperature downstream of the water separator 3 And measuring the flow level of the water separator 3 and adjusting the flow rate to the minimum flow rate of the economizer 1 through the control mechanism 11 according to the measured steam temperature (operating with a dry separator), and circulating pump ( By driving the valve 24 disposed between the economizer 23 and the economizer 1, the economizer ( A method of operating a once through flow steam generator for low load recirculation, characterized by controlling the water level of the water separator 3 under the minimum flow rate of 1) (operating with a wet separator). The shut-off valve (22) is disposed in the circulation line (20) upstream of the discharge point (19) connected to the flow path of the working medium, and the circulation pump during the operation with the minimum flow rate (operating with the dry separator). The operation method of the steam generator characterized in that the valve (24) disposed between the (23) and the economizer (1) is switched to the fully open end position, and the shutoff valve (22) is switched to the closed position. 3. The load reducing course in which the water level of the water separator 3 rises above a predetermined mark, according to claim 1, is first opened in an open section suitable for the level control operation of the water separator 3 by the control command of the first sequence. By setting the valve 24 disposed between the circulation pump 23 and the economizer 1, the shutoff valve 22 is completely opened, and the level control device is smoothly switched to the automatic control operation in order. A method of operating a steam generator, characterized in that the water separator (3) transitions to a level control operator. 4. The method according to claim 3, wherein when the water level drops rapidly below a predetermined mark, a second sequence of control commands is triggered, which first closes the shutoff valve 22, and then the level control mechanism. The operation method of the steam generator characterized by switching (33) to manual operation, and automatically opening the valve 24 disposed between the circulation pump 23 and the economizer 1 automatically. The steam generator according to claim 1, characterized in that the level control mechanism (33) is designed as a cascade having a difference between the pressure of the water separator (3) and the discharge pressure of the feed pipe (6) used in the subloop. How to operate. 6. The pilot control (38, 39) according to claim 5, wherein the pilot control (38, 39) acts on the level control mechanism (33), so that when there is a change in the minimum flow rate of the economizer (1), it is disposed between the circulation pump (23) and the economizer (1). A method of operating a steam generator, characterized in that the open end of the valve 24 is immediately adjusted to a new flow rate.