EP1969285B1 - Steam cycle of a power plant - Google Patents

Description

The present invention relates to a steam cycle of a power plant with at least one steam generator and at least one superheater. Such a steam cycle is eg in document US-B1-6,237,542 disclosed.

Such water vapor circuits are known from steam power plants and combined gas and steam power plants, in which the thermal energy of water vapor in a steam turbine is converted into kinetic energy. The steam required to operate the steam turbine is generated in a steam generator from previously purified and desalinated water and superheated in a superheater. From the superheater, the steam is fed to the steam turbine, where it gives off part of its previously recorded heat energy in the form of kinetic energy to the turbine. To the turbine, a generator is coupled, which converts the movement of the turbine into electrical energy. After flowing through the steam turbine, the expanded and cooled steam is passed into a condenser, where it continues to cool while releasing heat and collects in liquid form as water in the so-called hotwell. From there it is pumped via appropriate pumps into a feed water tank and temporarily stored there. Finally, the condensate is fed via a feed pump again to the steam generator. The steam generator itself can be heated both with conventional fuels, such as oil, gas or coal, but also nuclear.

During operation of the steam cycle, contaminants enter the circulating water which, over time, can damage the steam cycle components. Accordingly, it is necessary to ensure the chemical nature of the circulation medium (water, steam) within certain limits. In boilers with boiler drums (natural or forced circulation), this happens, for example, by the fact that constantly or in Intervals of water are drained from the drum. In addition, during startup and shutdown, water also accumulates in the superheater heating surfaces. These waters are discharged as wastewater and must be replaced with treated water (demineralised water). From a business point of view, it is desirable to reduce the amount of wastewater generated and to increase the proportion of reused wastewater from operations. However, this is offset by very high costs in the construction of the power plant, so that a minimization of the wastewater was based on the cost of the entire power plant with the previously known technical possibilities in the rule was not useful. The accumulated operating waste water of the steam cycle are therefore usually only collected and then completely discarded, so ultimately fed to the general sewer system. Usually, the wastewater must undergo a predetermined treatment in accordance with the legal conditions.

In the future, due to a foreseeable further tightening of the environmental protection conditions, it can be assumed that a reduction of the waste water quantity will be enforced by law or the wastewater discharge, including the treatment, will become more expensive, so that a reduction of the wastewater volume will be economically viable.

In a steam cycle, the wastewater can generally be divided into two groups. Dewatering in the steam zone of the steam cycle, such as dewatering the superheater, provides "clean" wastewater, that is, the chemical nature of the waste water allows direct reuse in the steam cycle. Dewatering in the water area of the steam cycle, such as the emergency drainage on the boiler drum, on the other hand, results in "contaminated" wastewater, which means that the chemical nature of the wastewater does not permit direct reuse in the steam cycle. The cleanliness of the sewage from the drainage In the steam sector, this is due to the fact that during the separation in the steam generator in water and vapor phase any impurities remain in the water phase and the steam leaves the steam generator clean.
If it is possible to collect the clean wastewater separately, so that a return to the steam cycle is possible, in addition to an up to 60% reduction in wastewater discharge and the associated expenses and corresponding expenses in connection with the generation and subsequent conditioning of demineralized Saved water that would have to replace the discarded water in the circulation.

The largest proportion of clean wastewater is generated when the power plant starts and, above all, shuts down at the superheater. This fact makes use of a known concept for minimizing wastewater from a steam cycle in which superheater drain lines lead to a separate collection tank. The condensate is then pumped from the collection tank using a pump into a condensate collection tank and from there to the condenser of the water vapor cycle. The known concept will be described in more detail below with reference to Fig. 1 described.

It is an object of the present invention to provide an alternative steam cycle of a power plant.

This object is achieved according to the present invention by a steam circuit according to claim 1. The dependent claims relate to individual embodiments of the water vapor cycle according to the invention.
The steam cycle according to the present invention comprises at least one steam generator and at least one superheater. According to the invention is between the superheater and the steam generator for collecting condensate present in the superheater and for returning the condensate in the evaporator a condensate collection and return line including small pumps provided. The corresponding drainage pipes from the steam area, which are located in front of the boiler slide, are integrated into this condensate collection and return line. This condensate collection and return line is constantly under pressure, since at least one, advantageously all drainage pipes are connected directly to this, ie it is dispensed with motorized shut-off valves.
In contrast to the prior art, the condensate possibly collecting in the superheater is therefore not pumped via a collection tank and a condensate collection tank to the condenser and fed back to the actual steam circuit of the power plant, but the condensate is collected only in a condensate collection and return line and the Evaporator fed directly back. In addition to the motorized shut-off valves, it is also possible to dispense with the collecting tank (s) including associated secondary components, such as, for example, pumps, heat exchangers, connecting pipelines, etc. Preferably, a water lock is provided between the drainage line and the condensate collection and return line to minimize any crossflows. Further, the diameter of a superheater pipe should be larger than the diameter of the drainage pipe. If necessary, several drain lines with a smaller diameter can lead to the condensate collection and return line. This serves to minimize those cross flows that might occur despite the water lock. To control these possible cross flows due to different pressure at the individual drainage points, the lower pressure drainage lines should also be designed with a larger diameter than the higher pressure drainage lines. It would also be possible to lead the individual drainage pipes except for a drainage line, via which a constantly open connection is ensured, so that the condensate collection and return line is always under pressure, in each case via a motorized valve in the condensate collection and return line, rather than directly on the condensate collector. However, this alternative would be more costly.
With the condensate collection and return line, a pump is advantageously operatively connected, with the aid of which the condensate collected in the condensate collection and return line of the superheater can be pumped back into the steam generator. The operation of the pump is preferably controllable in dependence on the amount of condensate present in the condensate collection and return line. For example, a 2-point level detector is provided which detects upper and lower condensate level limits in the condensate manifold. When the upper limit is reached, the pump is operated to pump the condensate from the condensate collection and return line into the evaporator. If then the lower limit level is reached, the pump is switched off accordingly, in order to promote any further condensate in the steam generator. If the condensate reaches the upper limit level of the condensate collector without the operation of the pump, this is an indication that the pump and / or the controller is defective. In this case, the condensate header preferably comprises a discharge valve provided with an emergency valve, which branches off from the condensate collecting and return line, wherein the discharge line is connected to a waste water tank. In this way, the condensate collection and return line can be emptied poorly in case of failure of the pump or pump control.

According to a further embodiment of the present invention, the condensate collection and return line comprises at least one shut-off valve, better still two shut-off valves, which are respectively provided downstream and upstream of the pump. Accordingly, during the operation of the steam cycle maintenance and repair work on the pump can be made.

According to a further embodiment of the present invention, at least one drainage line is arranged between the superheater and the condensate collecting line, which is the superheater connects to the condensate collector. Preferably, a water lock is provided between the drainage line and the condensate collecting line in order to minimize any crossflows. Further, the diameter of a superheater pipe from which the drainage pipe branches off should be larger than the diameter of the drainage pipe. Optionally, several drain lines with a smaller diameter lead to the condensate collecting line. This serves to minimize those cross flows that might occur despite the water lock. To control these possible cross flows due to different pressure at the individual drainage points, the lower pressure drainage lines should also be designed with a larger diameter than the higher pressure drainage lines. It would also be possible to route the individual drainage conduits, except for a drainage line, through which a constantly open connection is made, so that the condensate collecting line is always under pressure, via a motorized valve into the condensate collecting line, rather than directly to the condensate collecting line. However, this alternative would be more costly.

According to a further embodiment of the present invention, the evaporator for discharging the condensate present in this via further drainage lines is also preferred. connectable to the condensate collecting and return line, wherein a condensate collecting and return line branches off a valve provided with a discharge line, which is connected to a waste water collection tank. Accordingly, the water present in the evaporator can be dewatered via the condensate collecting line according to the invention in the waste water tank. This has the advantage that the wastewater container does not have to be placed in a correspondingly large pit (to increase the geodetic height), but can be arranged at ground level.

Fig. 1

eine schematische Ansicht eines bekannten Konzeptes eines Wasserdampfkreislaufs einer Kraftwerksanlage;

Fig. 2

eine schematische Ansicht einer Ausführungsform des erfindungsgemäßen Wasserdampfkreislaufs; und

Fig. 3

eine schematische Ansicht einer Ausführungsform einer Kondensatsammelleitung des erfindungsgemäßen Wasserdampfkreislaufs.

Hereinafter, the present invention will be described in detail with reference to the drawings. That's it

Fig. 1

a schematic view of a known concept of a steam cycle of a power plant;

Fig. 2

a schematic view of an embodiment of the steam cycle according to the invention; and

Fig. 3

a schematic view of an embodiment of a condensate collecting line of the steam cycle according to the invention.

Like reference numerals refer to similar components below.

Fig. 1 is a schematic representation and shows a known concept for minimizing waste water from a steam cycle 10. The steam circuit 10 includes three steam generators 12, 14 and 16, which evaporate preheated in the economizers water vapor, wherein Fig. 1 only the corresponding inlets 17a, 17b and 17c are shown by the economizers in the drums of the evaporators 12, 14 and 16. The water vapor is passed from the steam generators 12, 14 and 16 via lines 18, 20 and 22 to superheaters 24, 26 and 28, where it is superheated and then passed via respective lines 30, 32 and 34 to corresponding stages of a steam turbine 36. In the steam turbine 36, a large part of the heat energy of the superheated steam is converted into kinetic energy. The cooled water vapor leaves the steam turbine 36 via a line 38 and is supplied to a condenser 40 in which it is further cooled and condensed. The condensate enters the hotwell 42 arranged below the condenser 40, from where it is conveyed again in the direction of the steam generators 12, 14 and 16 by means of a pump 44. Between the pump 44 and the steam generators 12, 14 and 16, the condensate by not shown Preheater be brought to a predetermined temperature. In this way, a closed water vapor cycle results.

At a drainage of the steam cycle 10, the "clean" wastewater in the steam region of the steam cycle 10, so that waste water that allows direct reuse in the steam cycle 10, from the "contaminated" wastewater in the water area of the steam circuit 10, for direct reuse in the steam cycle 10 is not suitable, without this previously prepare to separate, the steam circuit 10 includes a special drainage system, which will be described in more detail below.

For dewatering the lines 30, 32 and 34, in which there is steam at the time of switching off the power plant, drainage lines 46, 48 and 50 are provided which direct the condensate located in the lines 30, 32 and 34 in a collecting container 52, in the remaining vapor condenses. The resulting in the superheaters 24, 26 and 28 condensate is passed through drainage lines 54, 46 and 58 in a further collecting container 60, in which the remaining water vapor is also condensed. The containers 52 and 60 are connected to the condenser. Due to the correspondingly low pressure, the incoming condensate will partially evaporate and pass via the connecting line 61 into the condenser 40. The residual condensate collected in the reservoirs 52 and 60 is pumped via lines 62 and 64 into a condensate receiver 70 using pumps 66 and 68 and stored there. If necessary, the condensate stored in the condensate collecting tank 70 can then be fed again via a line 72 to the condenser 40 and in this way the actual water vapor cycle. By separating the clean wastewater and feeding back into the steam cycle 10, the amount of wastewater generated can be reduced by up to 60%, which saves costs in the long term. In addition, due to the reduction in the amount of wastewater generated, expenses associated with the generation and subsequent conditioning of demineralised water are reduced.

The "polluted" wastewater in the water area of the Fig. 1 illustrated steam circuit 10, which is obtained in particular during the dewatering of the steam generator 12, 14 and 16, is fed via drainage lines 74, 76 and 78 to a wastewater collection tank 80. Since the container 80 is indirectly connected to the condenser 40, the incoming contaminated condensate will partially evaporate and enter the condenser 40 via the connection line 61. This is permissible because, due to the separation in water and vapor phase, the chemical quality in the steam cycle is not impaired. The contaminated residual condensate collected in the waste water collection tank 80 can be supplied via a line 82 by means of a pump 84 to a heat exchanger 86, where it is cooled accordingly. Subsequently, the cooled condensate can be discarded via a line 88 and supplied to the general sewer system, which can be connected to the line 88 a wastewater treatment plant, not shown, which processes the wastewater so that it complies with the legal requirements. Alternatively, the condensate from the heat exchanger 86 can be supplied via a line 90 to a collecting container 92 and stored therein. The condensate contained in the collecting container 92 can then be supplied via a line 94 by means of a pump 96 to a condensate treatment device 98, in which it is prepared so that it meets the requirements that are placed on the water used in the steam circuit 10. The condensate treated in this way can then be supplied to the condenser 40 in order to feed the condensate back into the actual water vapor circuit 10.

A disadvantage of in Fig. 1 shown Wasserdämpfkreislaufes 10 is that in particular the drainage of the Superheater 24, 26 and 28 is very expensive and expensive. Firstly, the drainage lines 54, 56 and 58, which lead from the superheaters 24, 26 and 28 to the sump 60, have a relatively large length to bridge the distance between the superheaters 24, 26 and 28 to the sump 60. Furthermore, it requires a separate collection container 60, which is also associated with costs. Finally, the pump 68 must have a relatively high capacity to pump the condensate contained in the sump 60 into the flash tank 70.

Fig. 2 shows a schematic view of an embodiment of the steam cycle 110 according to the invention. Components which are similar to those of in Fig. 1 correspond to the illustrated steam cycle 10, are identified by the same reference numerals. The in Fig. 2 shown steam circuit 110 substantially corresponds to the steam circuit 10 in Fig. 1 , However, the steam circuit 110 differs from the steam circuit 10 by the dehydration of the superheater 24, 26 and 28 and the management of the residual dewatering of the evaporators 12, 14 and 16, which is described in more detail below.
Of the superheaters 24, 26 and 28 branch off corresponding drainage lines 112, 114 and 116, each leading to a condensate collection and return line, with reference to Fig. 3 is explained in more detail. The condensate collected in the condensate collection lines can be pumped via return lines 118, 120 and 122 directly back into the associated evaporator 12, 14 and 16 using appropriate pumps 124, 126 and 128. Optionally, the wastewater contained in the evaporators 12, 14 and 16 can be fed via drainage lines 130, 132 and 134 to the condensate collecting lines and conveyed via lines 136, 138 and 140 into the waste water collecting tank 80.
The detailed structure of a superheater and steam generator drainage system is schematically shown in FIG Fig. 3 shown, where Fig. 3 exemplifies the drainage system of the superheater 24 and the evaporator 12. The drainage systems for the superheater 26 and the evaporator 14 and for the superheater 28 and the evaporator 16 correspond to the in Fig. 3 illustrated system.

Fig. 3 shows the superheater 24 having three manifolds 142a, 142b and 142c. In these headers 142a, 142b and 142c bind the individual superheater tubes. Hot exhaust of the power plant flows in the direction of arrow 144 past the three superheater tubes, so that the manifold 142c is heated more than the manifold 142b, which in turn is stronger than the manifold 142a. From the respective headers 142a, 142b and 142c drain drainage lines 112a, 112b and 112c, which open into a just over 0 m condensate collection and return line 146. The individual pipe diameter of each superheater pipe, which opens into a collecting pipe 142a, 142b and 142c, is greater than the pipe diameter of the corresponding drainage pipe 112a, 112b and 112c. In this way it should be ensured that superheated steam flows in the direction of the collecting pipes 142a, 142b and 142c and does not reach the drainage pipes 112a, 112b and 112c. The drainage lines 112a, 112b and 112c are intended only to dewater condensate contained in the headers 142a, 142b and 142c. At the junction between the drainage lines 112a, 112b and 112c and the condensate collection and return line 146, there are provided water locks 148, 150 and 162 which are also intended to prevent the entry of water vapor into the condensate collection and return line 146. The water locks 148, 150 and 152 are presently designed as U-shaped lines in which collects condensate, which is intended to prevent ingress of water vapor into the condensate collection and return line 146. The condensate collection and return line 146 is presently substantially L-shaped, wherein a substantially vertically downwardly extending portion of the condensate collection and return line 146 extends into a pit 154. In this substantially vertically downwardly extending portion of the condensate collection and return line 146 collects the condensate that has been removed via the drainage lines 112a, 112b and 112c the headers 142a, 142b and 142c. The level of the condensate collected in the condensate collection and return line 146 is designated by the reference numeral 156. The condensate collection and return line 146 further includes a level detector, not shown, which detects a maximum level 158 and a minimum level 160 of condensate accumulated in the condensate collection and return line 146. Connected to the Kohdensatsammel- and return line 146, a line 162 which includes a valve 164 and a pump 166 arranged at about -2 m. With the valve 164 open, condensate from the condensate collection and return line 146 can be pumped through line 162 using the pump 166. Behind the pump 166, the line 162 branches into the return line 118, which is provided with a valve 168, and into the line 136, which is also provided with a valve 170. The operation of the condensate collecting line 146 will be described in more detail below.

If the condensate level 156 reaches the maximum level 158, which is detected by the level detection device, not shown, the pump 166 is turned on, the valves 164 and 168 are opened and the valve 170 is closed. In this way, the condensate collected in the condensate collection and return line 146 is pumped back into the evaporator 12. If the level detector detects that the condensate level 156 has reached the minimum level 160, the pump 166 is stopped, so that no further condensate from the condensate collection and return line 146 is conveyed via the lines 162 and 118 into the evaporator 12. This scenario repeats as soon as the maximum level 158 is reached again. When the condensate level 156 reaches the maximum level 158 without the pump 166 starting, an alarm is triggered because of a pump 166 or pump control fault. If the pump 166 is defective, the valve 170 of the line 156 can be opened and the condensate is discharged into the sewage tank 80.

For dewatering the evaporator 12, the evaporator 12 and the condensate collection and return line 146 are connected to each other via the drainage line 130, wherein the drainage line 130 has a valve 172. If now the condensate contained in the evaporator 12 are emptied, the valve 168 of the return line 118 are closed and the valve 170 of the line 136 and the valve 172 of the drainage line 130 is opened. The pressurized condensate contained in the evaporator 112 may thus flow to the sewage sump 80 via the drainage line 130, the condensate header 146 and the line 136 using the pump 166.

For maintenance or repair of the pump 166, the valves 164, 170 and 168 can be closed, so that it is easy to work on the pump 166.

This in Fig. 3 shown drainage system is designed to be mobile, to counteract a buildup of tension by the cyclic heating and cooling.

A significant advantage of the previously described drainage system for the superheaters 24, 26 and 28 and the evaporators 12, 14 and 16 is its simple construction. Furthermore, compared with the in Fig. 1 illustrated steam circuit 10 on the (motorized) shut-off valves, to the collecting container 60, the pump 68 and the line 64 are dispensed with, whereby considerable costs can be saved. In addition, the subscript of the waste water tank 80 can be dispensed with, thus reducing the cost of the pits. It should be noted that the pump 166 compared to the pump 68 must have a much lower performance.

It should be understood that the present invention is not limited to the embodiment described above. Rather, modifications and changes are possible without departing from the scope of the present invention, which is defined by the appended claims.

Claims (10)

1. Steam circuit (110) in a power station comprising at least one evaporator (12; 14; 16) and at least one overheater (24; 26; 28),
   characterised in that
   a condensate collector and return line (146) is provided between the overheater (24; 26; 28) and the evaporator (12; 14; 16) in order to trap condensate present in the overheater (24; 26; 28) and to return the condensate to the evaporator (12; 14; 16).
2. Steam circuit (110) according to one of the previous claims,
   wherein the volume of the evaporator (12; 14; 16) is greater than the volume of the overheater (24; 26; 28).
3. Steam circuit (110) according to one of the previous claims,
   wherein the condensate collector and return line (146) has a pump (166).
4. Steam circuit (110) according to claim 3,
   wherein the operation of the pump (166) can be controlled as a function of the amount of condensate present in the condensate collector and return line (146).
5. Steam circuit (110) according to one of the previous claims,
   wherein the condensate collector and return line (146) has at least one flow control device (164; 168; 170).
6. Steam circuit (110) according to claim 5,
   wherein there is a flow control device (164; 168; 170) upstream and downstream respectively of the pump (166).
7. Steam circuit (110) according to one of the previous claims,
   wherein at least one drain line (112; 114; 116) is arranged between the overheater (24; 26; 28) and the condensate collector and return line (146).
8. Steam circuit (110) according to claim 7,
   wherein the diameter of a manifold (142a; 142b; 142c), from which the drain line (112a; 112b; 112c) branches off, is greater than the diameter of the drain line (112a; 112b; 112c).
9. Steam circuit (110) according to one of claims 3 to 8, wherein a line (136) provided with an emergency valve (170) and connected to a waste water tank (80) branches off from the condensate collector and return line (146).
10. Steam circuit (110) according to one of the previous claims,
    wherein the evaporator (12; 14; 16) for removing the condensate present in it can be connected to the condensate collector and return line (146) via additional drain lines (130) and a line (136) with a valve (170) branches off from the condensate collector and return line (146) and is connected to a waste water tank (80).

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