US20160208658A1

US20160208658A1 - Method for the recovery of process wastewaters of a fossil-fueled steam power plant and fossil-fueled steam power plant

Info

Publication number: US20160208658A1
Application number: US14/913,109
Authority: US
Inventors: Ute Amslinger; Anke Söllner; Wolfgang Glück; Peter Widmann; Werner Spies
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2013-08-30
Filing date: 2014-08-21
Publication date: 2016-07-21
Also published as: KR20160047548A; WO2015028387A2; JP2016536518A; WO2015028387A3; EP3004570A2

Abstract

A fossil-fueled steam power plant and method, the plant has a water-steam circuit, cooling water circuit, flue gas cleaning system and cooling tower. A fossil-fueled steam generator, steam turbine and condenser are connected to the water-steam circuit. In the cooling water circuit, a cooling tower and condenser are connected such that expanded steam is condensed by the exchange of heat with the cooling water circuit. The flue gas from the generator is cleaned in the flue gas cleaning system, and the cleaning system is supplied with process water. Process wastewater leaves the cleaning system. The cleaning system is connected to the cooling water circuit such that process water required for cleaning system is drawn from the cooling water circuit. To remove contaminated process wastewater, the cleaning system is connected to a wastewater treatment system having an evaporator, where system purified process wastewater is generated.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2014/067824 filed Aug. 21, 2014, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 102013217335.0 filed Aug. 30, 2013. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates to a steam power plant with cooling tower and flue gas purification plant and with a wastewater treatment plant for process wastewater and in particular for recovering process water. The invention furthermore relates to a method for operating a steam power plant with cooling tower and flue gas purification plant.

BACKGROUND OF INVENTION

Steam power plants serve to generate electrical energy. A steam power plant substantially comprises a fired boiler, a steam turbine, a water-steam circuit, a condenser, a cooling tower and a flue gas purification plant.
The working medium used in the water-steam circuit in steam power plants is deionized water which is produced in a deionization plant using ion-exchange resins. The deionized water is evaporated in the steam generator and passed into the steam turbine where it is expanded. The energy released during expansion is transferred via a shaft to the generator. The expanded steam is then fed to a condenser, and the liquid phase is condensed. To assist the condensation process, an evacuation system is connected to the condenser, which system produces a vacuum in the condenser when the steam power plant is started up, and maintains it during operation. The vacuum increases steam turbine efficiency and removes non-condensable gases from the liquid stream.
During the energy generation process, various contaminants may be introduced into the working medium. In addition, various substances are added to the working medium for conditioning or purification.
The contaminants and additives in particular include ammonia, calcium, magnesium, sodium, potassium, chlorides, nitrates, sulfates (sulfuric acid) and silicon dioxide. The working medium contaminated by contaminants or additives must be discharged from the water-steam circuit as process wastewater, since the contaminants stand in the way of direct reuse as a working medium in the water-steam circuit.
Ammonia serves as an alkalizing agent for conditioning the feed water. Through the addition of ammonia, an increase in the pH value of the working medium may be achieved, whereby the relative corrosion rate of the feed water is reduced. Since the distribution coefficient of ammonia in liquids and steam is different, locally markedly elevated ammonia concentrations may occur in system parts involving evaporation and condensation processes.
Process wastewaters arise at various points in the steam power plant. A large proportion of contaminated water arises in the form of the desalination stream from the boiler drums in the evacuation system. On startup and shutdown, deficiencies (due to additional feeding of working medium) and excesses (due to discharge of working medium) of the working medium must be compensated. Moreover, process wastewaters arise due to water samples being taken and leaks in the water-steam circuit. As a result of the above-stated water losses, the water-steam circuit must be continuously additionally fed with deionized water (DIW). Backwashing and regeneration processes in the deionization plant and condensate purification also result in process wastewaters.
Further process wastewaters arise through drainage. Drainage is performed for example during ongoing operation from pipes in which condensate has collected and which have been closed for an extended period. To this end, the pipes are opened briefly and thus drained. Water is then lost from the water circuit, which has to be replaced by make-up water (DIW). Drainage also in particular arises to a greater extent on startup and shutdown of the steam power plant, since for example on shutdown of the steam power plant the steam in the water circuit gradually condenses and the resultant liquid water must not be allowed to stand in the plant parts, in particular in the heating surfaces. On shutdown, more water is drained from the water circuit than is replenished, until ultimately no more water is replenished.
According to the current prior art, the process wastewaters from the water-steam circuit are, depending on quality, returned to the water-steam circuit or discharged into the cooling tower or the industrial wastewater system.
Further highly contaminated process wastewaters arise from the flue gas purification plant, wherein large volumes of process wastewater with a high pollutant load arise from flue gas desulfurization in coal-fired steam power plants. In steam power plants with a cooling tower, however, the majority of the process wastewater arises in the form of blowdowns from the cooling tower (cooling tower blowdown) in the open cooling water circuit. Cooling tower blowdowns have in the past been discharged into public watercourses via a receiving stream.
An exemplary 2×1050 MW fossil fuel-fired steam power plant according to the prior art with natural draft cooling tower and a wet limestone flue gas purification plant produces up to 100,000 tonnes of process wastewater per year in base-load operation, which has to be discharged into public watercourses. Just about half of this amount is accounted for by the cooling tower.
Due to ever more stringent environmental legislation, and in those countries suffering water shortages, it is becoming increasingly important to reduce water consumption and thus reuse wastewaters and process waters within the water-steam circuit. In particular, the guidelines for discharging wastewaters into public watercourses are becoming ever more stringent. The water consumption of a steam power plant should therefore be reduced as much as possible.

SUMMARY OF INVENTION

The object of the invention is therefore that of providing a steam power plant in which the total water consumption of a steam power plant, the pollutant load in the remaining wastewater, in particular the wastewater from the flue gas purification plant, and the consumption of deionized water are minimized. The object of the invention is furthermore that of providing a method for operating a steam power plant in which total water consumption is minimized.
The apparatus-related object of the invention is achieved by the features in the independent apparatus claim.
The fossil fuel-fired steam power plant here comprises a water-steam circuit, a cooling water circuit, a cooling tower and a flue gas purification plant. A fossil fuel-fired steam generator, a steam turbine, and a condenser are connected into the cooling water circuit. A cooling tower and the condenser are interconnected in the cooling water circuit in such a manner that expanded steam from the water-steam circuit is condensable in the condenser by heat exchange with the cooling water circuit. The flue gas from the fossil fuel-fired steam generator may be purified, for example of carbon dioxide (CO₂), in the flue gas purification plant. To this end, process water may be supplied to the flue gas purification plant and process wastewater may be discharged therefrom. According to the invention, the flue gas purification plant is connected to the cooling water circuit in such a manner that the process water required for flue gas purification may be drawn from the cooling water circuit. In addition, the flue gas purification plant is connected to a wastewater treatment plant comprising an evaporator for discharge of process wastewater. Purified process wastewater may be produced by the wastewater treatment plant.
The invention is here based on the consideration, on the one hand, of using water from the cooling water circuit for flue gas purification and, on the other hand, of purifying the process wastewater contaminated by the flue gas purification by evaporation in the wastewater treatment plant, so giving rise to cleaner process wastewater. As a consequence, the raw water requirement of the steam power plant may be reduced by the amount of the additional water requirement of the flue gas purification plant.
As a result of lower water usage or optimized water treatment, the consumption of chemicals may also be lowered, whereby the environmental balance of the power plant may be made more resource-efficient.
Various technologies are available for concentrating the wastewaters from flue gas desulfurization by evaporation. Theoretically, all dissolved constituents are removed from the wastewater by evaporation and crystallization. These constituents may then be disposed of as a solid. The distillate is of high purity and may be reused in the power plant. It is possible to introduce the distillate into the raw water tank or into the permeate tank of the deionization plant. The wastewaters with their high pollutant loads from flue gas purification are completely processed by evaporation. The raw water requirement and the wastewater volume of the power plant are thus reduced.
In a corresponding embodiment of the fossil fuel-fired steam power plant, the flue gas purification plant is connected to the cooling water circuit downstream of the cooling tower in such a manner that cooling tower blowdown water may be used as process water for flue gas purification. Cooling tower blowdown is wastewater which necessarily occurs in large volumes as contaminated process water in a power station with a cooling tower and is thus always available. The total wastewater volume is reduced as a consequence since the process water is additionally concentrated in the flue gas purification plant.
Depending on local guidelines and specifications or prerequisites, concentration may however also be considered disadvantageous since the process wastewater is repeatedly concentrated in the flue gas purification plant. The salt and heavy metal loading and the input of pollutants by flue gas purification into the process wastewater may reach very high levels as a consequence. An improved and particular embodiment of the fossil fuel-fired steam power plant therefore proposes supplying the flue gas purification plant with a process water which is connected from the cooling water circuit upstream of the cooling tower and upstream of a cooling tower make-up water treatment plant. Said process water has not yet been treated in the cooling tower make-up water treatment plant and is thus untreated.
It is advantageous here that the water is in each case concentrated only once in the flue gas purification plant and it is therefore easier to comply with limit values for chloride, sulfate and heavy metals. Furthermore, the additional input of chloride into the process wastewater due to precipitation with FeCl₃during cooling tower make-up water treatment also does not occur. Since the cooling tower blowdown is not put to any further use in this case, it can be more highly concentrated. The volume of make-up water for the cooling tower falls because the level of blowdown is lower. As a consequence, the water consumption of the steam power plant is reduced. Depending on the required purity of the gypsum arising in the cooling water circuit during operation of the steam power plant (gypsum purity/degree of whiteness) and the quality of the raw water, any solids may however have to be removed from the untreated cooling tower make-up water, for example by a settling tank.
In a further alternative embodiment of the fossil fuel-fired steam power plant, the flue gas purification plant is connected to the cooling water circuit upstream of the cooling tower and to a cooling tower make-up water treatment plant, such that cooling tower water treated for use in the cooling tower may be used as process water for flue gas purification. If treated cooling tower make-up water is used as process water, said water is concentrated only once, whereby it is easier to comply with limit values. As a result of precipitation with FeCl₃in the cooling tower make-up water, the chloride content of the water is slightly raised. Since the cooling tower blowdown is not put to any further use, it can be more highly concentrated. As a consequence, the volume of make-up water for the cooling tower falls because the level of blowdown is lower. As a consequence, the water consumption of the power plant is reduced. This measure may also be necessary if the total discharge volume for wastewater into the receiving stream is fixed.
In one further development of the embodiment of the fossil fuel-fired steam power plant, the wastewater treatment plant is connected to a deionization plant included in the water-steam circuit. As a consequence, purified process wastewater from the wastewater treatment plant may be introduced into the deionization plant. The purified process wastewater thus contributes to additionally feeding the water-steam circuit, thereby on the one hand saving raw water for additional feeding and on the other hand reducing the load on the deionization plant since less deionized water (DIW) need be produced.
In an alternative further development of the embodiment of the fossil fuel-fired steam power plant, the wastewater treatment plant is connected to a cooling tower make-up water treatment plant included in the water-steam circuit. As a consequence, purified process wastewater from the wastewater treatment plant may be introduced into the cooling tower make-up water treatment plant.
The wastewater treatment plant is advantageously furthermore also connected to the condensate purification plant, the evacuation system and sampling point for introduction of contaminated process wastewaters from the water-steam circuit into the wastewater treatment plant.
All the process wastewaters from the condensate purification plant are recirculated into the water-steam circuit via the wastewater treatment plant. The process wastewaters which arise during startup for boiler flushing are recovered as a consequence. Since boiler flushing is performed with DIW, the discarded process wastewaters are of good quality. The auxiliary boiler is likewise fed with DIW, for which reason the process wastewater (blowdown) is of high quality. The process wastewater from the auxiliary boiler must be expected to have elevated ion concentrations and to be contaminated with iron particles.
By recirculating the condensate arising in the wastewater treatment plant by evaporation into the deionization plant, up to 75,200 tonnes per year less DIW have to be treated by the deionization plant in the steam power plant mentioned by way of example. Around 15,000 tonnes per year of this is accounted for by the recoverable process wastewaters from boiler flushing and startup, around 4,300 tonnes per year by recoverable blowdowns from the auxiliary boiler, up to 6,000 tonnes per year by process wastewater from the sampling point and around 50,000 tonnes per year by condenser recovery.
The streams which may be recirculated into the water-steam circuit comprise low levels of contaminants (for example iron particles and ammonia). Before recirculation into the water-steam circuit, these streams must therefore be purified using the condensate purification plant. This may proceed by feeding into the riser tube of the condenser upstream of the condensate purification plant. In the case of recirculation upstream of the condensate purification plant, the maximum operating temperature of the ion exchangers in the condensate purification plant must be borne in mind. Under certain circumstances, the recirculated streams must firstly be cooled. The service life of the condensate purification plant is reduced by the higher ion loading. The volume of DIW which has to be provided by the deionization plant is lower, since less make-up water is required.
The method-related object of the invention is achieved by the features of the independent method claim.
The method for operating a fossil fuel-fired steam power plant comprises a steam power plant with a water-steam circuit, a cooling water circuit, a flue gas purification plant and a cooling tower. A fossil fuel-fired steam generator, a steam turbine, and a condenser are connected into the water-steam circuit, wherein steam is generated in the steam generator, and said steam is expanded in the steam turbine, and passed into the condenser. A cooling tower and the condenser are interconnected in the cooling water circuit in such a manner that the expanded steam from the water-steam circuit is condensed in the condenser by heat exchange with the cooling water circuit. Flue gas from the fossil fuel-fired steam generator is purified in the flue gas purification plant. The process water required for the flue gas purification plant is here drawn from the cooling water circuit. Said water is contaminated by flue gas purification, wherein contaminated process wastewater is formed. The contaminated process wastewater is supplied to a wastewater treatment plant comprising an evaporator, in which a purified process wastewater is formed by evaporation.
The advantages of the method according to the invention correspond to those of the apparatus according to the invention.
In a corresponding embodiment of the method, the flue gas purification plant is supplied with a cooling tower blowdown water as process water which is drawn from the cooling water circuit downstream of the cooling tower.
In a particular embodiment of the method, the flue gas purification plant is supplied with an as yet untreated cooling tower water as process water which is drawn from the cooling water circuit upstream of the cooling tower and upstream of a cooling tower make-up water treatment plant.
In an alternative embodiment of the method, the flue gas purification plant is supplied with a treated cooling tower water as process water which is drawn from the cooling water circuit upstream of the cooling tower of a cooling tower make-up water treatment plant.
In a further development of the method, the purified process wastewater is passed out of the wastewater treatment plant into a deionization plant included in the water-steam circuit.
In an alternative development of the method, the purified process wastewater is passed out of the wastewater treatment plant into a cooling tower make-up water treatment plant included in the cooling water circuit.
In another further development of the method, contaminated process wastewaters from the water-steam circuit, from the condensate purification plant, from the evacuation system and the sampling point are furthermore additionally introduced into the wastewater treatment plant.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are explained below in greater detail with reference to figures in which:

FIG. 1 shows a fossil fuel-fired steam power plant with cooling tower and flue gas purification plant according to the prior art,

FIG. 2 shows a first embodiment of the fossil fuel-fired steam power plant according to the invention with use of cooling tower blowdown water as process water for flue gas purification,

FIG. 3 shows a second embodiment of the fossil fuel-fired steam power plant according to the invention with use of untreated cooling tower water as process water for flue gas purification,

FIG. 4 shows a third embodiment of the fossil fuel-fired steam power plant according to the invention with use of treated cooling tower water as process water for flue gas purification

FIG. 5 shows a fossil fuel-fired steam power plant with cooling tower and flue gas purification plant with process wastewater recovery.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 is a schematic diagram of a fossil fuel-fired steam power plant 1 with cooling tower 7 and flue gas purification plant 8 according to the prior art. The fossil fuel-fired steam power plant 1 comprises a largely closed water-steam circuit 2 and an open cooling water circuit 6.
Raw water 25, for example from a public watercourse, is supplied to a raw water tank 24 where it is held in intermediate storage. The raw water 25 is conveyed from the raw water tank 24 into a cooling tower make-up water treatment plant 16. The raw water 25 is filtered and purified in the cooling tower make-up water treatment plant 16.
Water from the cooling tower make-up water treatment plant 16 is deionized for the water-steam circuit 2 in a deionization plant 19 using ion-exchange resins. A process wastewater 26 contaminated by reverse osmosis is passed via a receiving stream 27 back into the public watercourse. DIW 28 formed in the deionization plant 19 is supplied to the water-steam circuit 2. In the water-steam circuit 2, the DIW 28 is evaporated in a fossil fuel-fired steam generator 3. The resultant steam is expanded in a steam turbine which is not explained in greater detail.
The expanded steam is then condensed in a condenser 5. In order to assist the condensation process, the water-steam circuit 2 comprises an evacuation system 21. The condensate is supplied to a condensate purification plant 20 and subjected to mechanical purification. In order to enable ongoing monitoring of water quality during operation of the steam power plant 1, a sampling point 22 is provided from which water samples may be taken on an ongoing basis from the water-steam circuit 2. Some of the water samples are here mixed with chemicals.
Slightly contaminated process wastewaters 30 and severely contaminated process wastewaters 23 are discharged from the water-steam circuit 2.
The process wastewater 23 from the condensate purification plant 20 is particularly highly contaminated and must be sent for external disposal. The highly contaminated process wastewaters 23 from the evacuation system 21, the highly contaminated samples from the sampling point 22, and the severely contaminated process wastewaters 23 arising from flushing the steam generator 3 on startup of the steam generator 3 are passed back into the raw water tank 24.
The slightly contaminated process wastewaters 30 from the auxiliary steam generator 29 and the condensate formed on startup in the condenser 5 are passed into the cooling tower 7. Recirculation of relatively clean condensate from the condenser 5 into the steam generator 3 is not shown.
For the cooling water circuit 6, the water purified in the cooling tower make-up water treatment plant 16 is passed into the condenser 5 where it undergoes indirect heat exchange with the expanded steam. As a result, the steam condenses and the water in the cooling water circuit 6 is heated. The heated water from the cooling water circuit is supplied to the cooling tower 7, where it is atomized and releases heat to the ambient air by evaporation and convection with the air.
Cooled cooling water leaves the cooling tower 7 and is discharged via the receiving stream 27 into the public watercourse.
Process water 9 for the flue gas purification plant 8 is also drawn from the cooling tower make-up water treatment plant 16. The process water 9 contaminated in the flue gas purification plant 8 by input of flue gas residues is likewise discharged into the receiving stream 27 as process wastewater 10.
FIGS. 2 to 4 each show inventive embodiments of the invention respectively having a raw water tank 24, a cooling tower make-up water treatment plant 16, a cooling tower 7, a flue gas purification plant 8, a wastewater treatment plant 13 comprising an evaporator 12, and a receiving stream 27.
Raw water 25 from a public watercourse is supplied to the raw water tank 24 and stored therein. From the raw water tank 24, the raw water 25 is then passed into the cooling tower make-up water treatment plant 16 where it is treated. The treated water thereafter undergoes heat exchange with the expanded steam in the condenser via the cooling water circuit 6, but this is not explained in greater detail here. The cooling water which is heated as a consequence is then supplied to the cooling tower 7. Cooled cooling tower blowdown water leaves the cooling tower and is discharged into the receiving stream 27.
FIG. 2 shows an inventive embodiment of the invention, wherein the flue gas purification plant 8 is supplied with the cooling tower blowdown water as process water 9 which is drawn from the cooling water circuit 6 downstream of the cooling tower 7. The contaminated process wastewater 10 leaving the flue gas purification plant 8 is supplied to the wastewater treatment plant 13. The remaining cooling tower blowdown water from the cooling tower 7 is passed into the receiving stream 27.
FIG. 3 shows a particular embodiment of the invention, wherein the flue gas purification plant 8 is supplied with an as yet untreated cooling tower water 17 as process water 9 which is drawn from the cooling water circuit 6 upstream of the cooling tower 7 and upstream of a cooling tower make-up water treatment plant 16.
FIG. 4 shows a further alternative embodiment of the invention, wherein the flue gas purification plant 8 is supplied with a treated cooling tower water 18 as process water 9 which is drawn from the cooling water circuit 6 upstream of the cooling tower 7 of a cooling tower make-up water treatment plant 16.
FIG. 5 shows a fossil fuel-fired steam power plant 1 with cooling tower 7 and flue gas purification plant 8 with process wastewater recovery.
In contrast with the fossil fuel-fired steam power plant 1 according to the prior art shown in FIG. 1, in this case a wastewater treatment plant 13 is provided which, in addition to the contaminated process wastewaters from the cooling water circuit 11, also purifies the severely contaminated process wastewaters from the water-steam circuit 23.
The wastewater treatment plant 13 is accordingly supplied with the contaminated process wastewater 10 from the flue gas purification plant 8.
The wastewater treatment plant 13 is furthermore supplied with the severely contaminated process wastewaters 23 from the water-steam circuit 2, from the condensate purification plant 20, from the evacuation system 21, the sampling point 22, and the severely contaminated process wastewaters 23 arising from flushing the steam generator 3 on startup of the steam generator 3. The wastewater treatment plant 13 is furthermore supplied in a separate waste water stream with the slightly contaminated process wastewaters 30 from the water-steam circuit 2 and the condensate formed on startup in the condenser 5. Recirculation of relatively clean condensate from the condenser 5 into the steam generator 3 is not shown.
The contaminated process wastewaters are evaporated in the wastewater treatment plant 13, wherein a condensate 32 and a solid 31 are formed. Depending on requirements or mode of operation, the condensate 32 is recirculated either into the cooling tower make-up water treatment plant 16 or into the deionization plant 19.

Claims

1. A fossil fuel-fired steam power plant, comprising

a water-steam circuit into which are connected a fossil fuel-fired steam generator, a steam turbine, and a condenser,

a cooling water circuit, into which are connected a cooling tower and the condenser, wherein expanded steam from the water-steam circuit is condensable in the condenser by heat exchange with the cooling water circuit, and

a flue gas purification plant, in which flue gas from the fossil fuel-fired steam generator is purified, wherein the flue gas purification plant is supplied with a process water and a process wastewater is discharged therefrom,

wherein the flue gas purification plant is connected to the cooling water circuit, such that the process water required for the flue gas purification plant is drawn from the cooling water circuit, and the flue gas purification plant is connected for discharge of contaminated process wastewater to a wastewater treatment plant comprising an evaporator and by which a purified process wastewater is produced.

2. The fossil fuel-fired steam power plant as claimed in claim 1,

wherein the flue gas purification plant is connected to the cooling water circuit downstream of the cooling tower, such that cooling tower blowdown water is used as process water for the flue gas purification plant.

3. The fossil fuel-fired steam power plant as claimed in claim 1,

wherein the flue gas purification plant is connected to the cooling water circuit upstream of the cooling tower and upstream of a cooling tower make-up water treatment plant, such that an as yet untreated cooling tower water for use in the cooling tower is used as process water for the flue gas purification plant.

4. The fossil fuel-fired steam power plant as claimed in claim 1,

wherein the flue gas purification plant is connected to the cooling water circuit upstream of the cooling tower and to a cooling tower make-up water treatment plant, such that a cooling tower water treated for use in the cooling tower is used as process water for the flue gas purification plant.

5. The fossil fuel-fired steam power plant as claimed in claim 1,

wherein the wastewater treatment plant is connected to a deionization plant connected into the water-steam circuit, such that a purified process wastewater from the wastewater treatment plant is passed into the deionization plant.

6. The fossil fuel-fired steam power plant as claimed in claim 1,

wherein the wastewater treatment plant is connected to a cooling tower make-up water treatment plant connected into the water-steam circuit, such that a purified process wastewater from the wastewater treatment plant is passed into the cooling tower make-up water treatment plant.

7. The fossil fuel-fired steam power plant as claimed in claim 1,

wherein the wastewater treatment plant is furthermore additionally connected to the condensate purification plant, the evacuation system and the sampling point for introduction of contaminated process wastewaters from the water-steam circuit into the wastewater treatment plant.

8. A method for operating a fossil fuel-fired steam power plant, comprising

a water-steam circuit, into which are connected a fossil fuel-fired steam generator, a steam turbine, and a condenser, wherein steam is generated in the steam generator, and said steam is expanded in the steam turbine, and passed into the condenser,

a cooling water circuit, into which are connected a cooling tower and the condenser, wherein the expanded steam from the water-steam circuit is condensed in the condenser by heat exchange with the cooling water circuit, and

a flue gas purification plant, in which flue gas from the fossil fuel-fired steam generator is purified,

the method comprising:

drawing the process water required for the flue gas purification plant from the cooling water circuit, which water is contaminated by flue gas purification, wherein contaminated process wastewater is formed, and

supplying the contaminated process wastewater to a wastewater treatment plant comprising an evaporator, in which a purified process wastewater is formed by evaporation.

9. The method for operating a fossil fuel-fired steam power plant as claimed in claim 8,

wherein the flue gas purification plant is supplied with a cooling tower blowdown water as process water which is drawn from the cooling water circuit downstream of the cooling tower.

10. The method for operating a fossil fuel-fired steam power plant as claimed in claim 8,

wherein the flue gas purification plant is supplied with an as yet untreated cooling tower water as process water which is drawn from the cooling water circuit upstream of the cooling tower and upstream of a cooling tower make-up water treatment plant.

11. The method for operating a fossil fuel-fired steam power plant as claimed in claim 8,

wherein the flue gas purification plant is supplied with a treated cooling tower water as process water which is drawn from the cooling water circuit upstream of the cooling tower of a cooling tower make-up water treatment plant.

12. The method for operating a fossil fuel-fired steam power plant as claimed in claim 8,

wherein the purified process wastewater from the wastewater treatment plant is passed into a deionization plant connected into the water-steam circuit.

13. The method for operating a fossil fuel-fired steam power plant as claimed in claim 8,

wherein the purified process wastewater from the wastewater treatment plant is passed into a cooling tower make-up water treatment plant connected into the water-steam circuit.

14. The method for operating a fossil fuel-fired steam power plant as claimed in claim 8,

wherein contaminated process wastewaters from the water-steam circuit, from the condensate purification plant, from the evacuation system and the sampling point are furthermore additionally introduced into the wastewater treatment plant.