WO2011107187A1

WO2011107187A1 - Method for operating a steam turbine power plant having at least one steam generator fired with brown coal

Info

Publication number: WO2011107187A1
Application number: PCT/EP2011/000263
Authority: WO
Inventors: Kamil Marcak; Peter Moser; Toni Rupprecht; Sandra Schmidt; Knut Stahl
Original assignee: Rwe Power Aktiengesellschaft
Priority date: 2010-03-05
Filing date: 2011-01-22
Publication date: 2011-09-09
Also published as: DE102010010540A1

Abstract

The invention relates to a method for operating a steam turbine power plant having at least one steam generator fired with brown coal, in such a manner that the flue gas from the steam generator is subjected to gas scrubbing for removing CO₂, and the brown coal is predried in a dryer. In this process the energy required for the gas scrubbing is at least partially diverted from the drying of the brown coal and the waste heat produced in the gas scrubbing is at least partially utilized for preheating the boiler feed water and/or the combustion air of the steam generator.

Description

A method of operating a steam turbine power plant having at least one lignite-fired steam generator

The invention relates to a method for operating a steam turbine power plant with at least one lignite-fired steam generator, such that the flue gas from the steam generator is subjected to a gas scrubber for the separation of carbon dioxide (CO2).

A similar process is known, for example, from EP 1 473 072 B1. There, a process for the recovery of carbon dioxide is described.

With modern power plant technology, reduced CO2 release is increasingly playing a role. The decreased C02 release of fossil-fired

Power plants not only serve to protect the climate, they also increase the profitability of power generation against the background of existing C02 certificates trading.

A suitable method for the separation of CO2 from industrial waste gases is known, for example, from EP 1 967 249 A1, in which the CO ₂ scrubbing for the purification of flue gases from power plant processes is described. The washing process disclosed therein includes the gas scrubbing (CO2 scrubbing) of the

Flue gas in an absorber with an aqueous solution of a CO2-binding component (absorbent), and the so-called. "Regeneration" of the CO2-laden absorbent in a desorber, in which the

Absorbent is passed in countercurrent to hot steam and thereby releases the C0 ₂ again. This steam is generated in a so-called "reboiler" by heating a partial flow of the absorbent by means of low-pressure steam, whereby the low-pressure steam is taken from the steam turbine for power generation In a non-optimized washing process, up to 70% of the low-pressure steam produced by a power plant block can only be used to regenerate the C0 _2- laden absorbent Low-pressure steam can reduce the electrical efficiency of a power plant by up to 11%.

To improve this energy balance, it is proposed in EP 1 473 072 B1 to use the unused waste heat from the CO 2 scrubbing for preheating the cold feed water from the water-steam cycle (boiler feed water). This can increase the efficiency of a power plant with CO2 scrubbing. Still, however, here is a significant amount

Low-pressure steam is needed to regenerate the CO2-laden absorbent.

While the reduction of C02 release plays a prominent role in fossil-fired power plants in general, this is particularly important in lignite-fired power plants. Compared to power generation from z. As hard coal is the combustion of lignite associated with a higher CO 2 emission. This is mainly caused by the higher water content of lignite. The pit-wet lignite has a water content of about 45 to 65%, which is reduced by drying to about 10 to 25%. In order to achieve a more efficient brown coal power conversion, it is known, for example, that the brown coal is first subjected to indirect drying in one

To undergo fluidized bed dryer, wherein the fluidized bed dryer is at least partially heated with steam from the water-steam cycle of the steam generator and the energy of the resulting from the drying of lignite vapor for preheating the boiler feed water or the combustion air of the steam generator is used. This known process is also referred to as "WTA (Fluid Bed Drying with Internal Waste Heat Utilization)." Through this fluidized bed drying process utilizing the process known from US Pat

Drying system exiting high - energy vapor in the dryer and using low pressure steam from the steam cycle of the

Steam generator, an efficiency increase of 4 to 5 percentage points compared to conventional lignite-fired power plant techniques can be achieved. The WTA technique is known for example from DE 195 18 644 C2. The invention has for its object to provide a method for operating a dry lignite-fired steam turbine power plant with CO ₂ scrubbing of the exhaust gas, which reduces the necessary for the process low-pressure steam quantity and so the efficiency and controllability of such steam turbine power plant in principle, the means in particular in every load condition is improved.

The object is achieved by a method for operating a steam turbine power plant with at least one fired lignite steam generator, such that the flue gas from the steam generator is subjected to a CO ₂ scrubbing and the lignite is predried in a dryer, wherein for the C0 ₂ - Laundry required energy is at least partially decoupled from the drying of lignite and the resulting in CO ₂ scrubbing waste heat is used at least partially for preheating the boiler feed water and / or the combustion air of the steam generator. Waste heat in CO2 scrubbing can be generated, for example, in the form of heated CO 2 -containing desorber head scraps, which is produced during the regeneration of the absorber agent.

Suitable drying processes in the context of the invention are those in which vapor is produced, for example also the mechanical-thermal dehydration. The heat content of this vapor can be used further, which is realized in conventional methods by the preheating of the boiler feed water and / or the combustion air of the steam generator with the aid of the vapor. But as in conventional methods for operating a

Steam turbine power plant with CO2 scrubbing a relatively large amount

Low pressure steam is used for gas scrubbing, the inventive method has the advantage that instead of the vapors from the brown coal drying can be used for gas scrubbing. In an advantageous embodiment of the invention, a partial stream of the obtained during lignite drying vapor for gas scrubbing, while another partial flow continues to be used for preheating the

Boiler feed water and / or the combustion air of the steam generator is being used. Thus, the amount of heat energy used can be optimized from the vapors produced during lignite drying within the power plant process, while minimizing the amount of low-pressure steam consumed during this process. In this case, the proportion for the respective partial flows can be variable and, for example, with priority for the

Heat transfer be controlled within the C02 gas scrubbing process. In another embodiment of the invention, the entire vapors from brown coal drying is used for CO2 scrubbing. According to the invention, the preheating of the combustion air and / or the boiler feed water takes place by using the costs incurred in the gas scrubbing

Waste heat. This ensures optimum utilization of the available waste heat sources and heat sinks in the coupled processes. By inventively considerably cheaper use of the heat content of the vapor from brown coal drying instead of low-pressure steam in gas scrubbing, correspondingly less low-pressure steam is withdrawn from the steam turbine and thus increases the efficiency of the steam turbine power plant. In a preferred variant of the method according to the invention, the gas scrubbing of the exhaust steam takes place in at least one absorber or one

Absorber column with the aid of a CO2 absorbing absorbent, wherein the regeneration of the CO2-loaded absorbent in

at least one desorber or a desorber column is carried out by heating. Under "absorbents" in the context of the invention may be both a

Solvent, as well as a solvent mixture for the absorption of CO2 to be understood. For heating the absorption solution, for example, it can be passed in countercurrent to hot steam at 110 ° C. to 130 ° C., whereby the absorption solution releases the CO 2 to the steam. The C02 / water-vapor mixture produced in this process is also referred to as desorber vapors or desorber head vapors.

In a preferred variant of the method according to the invention, the absorbent in the desorber with the aid of the residual heat of at least part of the heated during the drying of brown coal resulting vapor. For this purpose, at least one condensation heat exchanger find application, which is acted upon by at least a partial flow of the vapor from the drying. Advantageously, takes place for the C0 ₂ separation from the flue gas of the

Steam generator, the method described in EP 1 967 249 application, in which in the regeneration of the CO 2 -loaded absorbent strip component is used, but with the difference that in the inventive method, the energy required for this at least partially from the drying of lignite is decoupled.

In order to ensure condensation of the vapor from brown coal drying in the heat exchanger required for this purpose, the vapor is preferably pre-compressed to a pressure of between 3 and 5 bar (vapor compression). That is, the pressure of the vapor is raised by means of the vapor compression to a level corresponding to a condensation temperature of about 130 ° C. As a condensation heat exchanger, for example, a "reboiler" can be used, which is connected to the bottom of the desorber or the desorber, wherein in the reboiler, the hot, about 4 bar pre-compressed vapors from brown coal drying, condensed at about 130 ° C and its Heat to the preheated C02-loaded absorbent, resulting in C02 release from the absorbent.

The vapor compression can preferably take place in one or more compressors or single-stage or multi-stage vapor compressor trains with injections for intermediate cooling. Preferably, the drive for the compression of the vapor with the aid of low-pressure steam from the steam cycle of the

Steam generation process. Alternatively, one or more vapor compressors can also be operated with electrical energy. In a preferred variant of the method according to the invention, it is provided that a subset of the energy required for the regeneration of the CO 2 absorption solution in the form of low-pressure steam is decoupled from the water-steam cycle of the steam turbine process. For example, about 50% of the energy required from the residual heat of the drying of the Lignite accumulating vapors are used. The remaining 50% can be obtained in the form of low-pressure steam from the overflow from the medium-pressure part in the low-pressure part of the steam turbine. In a further embodiment of the invention, for example, the unused during gas scrubbing heat content of the Brüdens for preheating the

Combustion air and / or the boiler feed water used. For example, the vapor from the coal drying can be used to provide a reboiler for the desorber with heat energy, in which case the vapor condensate at the outlet of the reboiler according to preheat the

Combustion air and / or the boiler feed water can be used.

In a particularly preferred embodiment of the invention is the

Heat content from the Desorberkopfbrüden used for preheating the combustion air of the steam generator and / or the boiler feed water. In this case, the waste heat contained within the Desorberkopfbrüden, compared to the used in one embodiment of the invention also heat content of the vapor from the coal drying, provide the essential part of the heat energy used for preheating. In another embodiment of the invention, the combustion air of the steam generator and / or the boiler feed water is preheated only with the heat content from the Desorberkopfbrüden.

In an expedient variant of the method, it is provided that the resulting in the regeneration of C02-applied absorption solution

Desorberkopfbrüden example, divided into two streams, with a portion of the Desorberkopfbrüdens is used to preheat the combustion air and another part of the Desorberkopfbrüdens for preheating the boiler feed water of the steam generator. For example, the heat content of Desorberkopfbrüdens be transferred using two Kondensationswärmetauschern in the respective media. Preferably, the heat content of the Desorberkopfbrüden transferred to the combustion air or the boiler feed water in a ratio of 2: 3. The inventive use of Desorberkopfbrüden for preheating the boiler feed water and / or the combustion air and the use of incurred in the drying of lignite vapor for the regeneration of C02-containing absorption solution, a much cheaper

Energy distribution causes.

Overall, the consumption of low-pressure steam can be significantly reduced by the invention and the efficiency of the overall process by about

0.5 percentage points can be improved.

In a further embodiment of the method according to the invention is used to increase the operating flexibility and to further reduce the low-pressure steam mass flow for the absorbent regeneration higher-value medium-pressure steam for compression of the washed out of the flue gas CO2. In order to limit the loss of efficiency of the steam turbine power plant, the medium-pressure steam can be expanded by means of a steam turbine driving the C02 compressor, in order then to be used as low-pressure steam in an additional reboiler of the C0 ₂ -separation plant. Compared to an electric drive of the C02 compressor and the use of low-pressure steam for regeneration, the use of medium-pressure steam described here has the advantage that as a result the net output of the power plant is increased, as the use of a steam-driven compressor is not the power plant's own needs electric power, but only increases the steam demand.

An advantageous embodiment of the method according to the invention for

Operating a steam turbine power plant with at least one lignite-fired steam generator will be explained with reference to the embodiment shown in the drawings. Show it:

Figure 1 is a process diagram for operating a

Steam turbine power plant with at least one lignite-fired steam generator according to the invention.

Figure 2 is a schematic representation of the heat transfer between

Heat sinks and heat sources when operating a steam turbine power plant with at least one fired lignite steam generator according to the invention

The invention will be described below with reference to FIG

Plant Schemes explained in more detail. For reasons of simplification, only brown coal drying and CO 2 gas scrubbing are shown. In addition, essential parts of the steam turbine power plant, such as the steam generator, the steam turbine, the regenerator and the water-steam cycle, not shown. These parts of a steam turbine power plant are known per se, as well as their interconnection is known.

The inventive method relates to the operation of a steam turbine power plant, which comprises a lignite-fired steam generator.

Mine moisture Lignite has a water content of about 45 to 65%, which is reduced by drying to about 10 to 25%. In the process according to the invention, the drying takes place with the aid of a fluidized-bed dryer, which is denoted by 1 in FIG. At the bottom of the

Fluidized bed dryer 1, the pre-dried lignite 4 is withdrawn, cooled and comminuted again by means of one or more mills before it is supplied to the steam generator for the purpose of combustion. These

Process steps concerning the brown coal are not shown in the figure. The process described here uses the drying of lignite in a stationary fluidized bed, wherein water vapor or the vaporized hydrocarbon is used as a fluidizing agent. The required drying energy is coupled via a heat exchanger 2 in the fluidized bed. The heat Exchanger 2 is acted on the bleed steam line 3 with bleed steam from the turbine. The resulting in the drying in the fluidized bed dryer 1 vapors is in a vapor compressor 6 to a pressure of about 4 bar

(Absolute) compressed and one of the desorber 8 associated first reboiler 7 supplied.

The desorber column 8 is part of the C0 ₂ scrubbing of the steam generator described below. The flue gas scrubbing system used for the C0 ₂ scrubbing comprises at least one absorber column 11, the desorber column 8, one provided between the absorber column 11 and the desorber column 8

Heat exchanger 12, which is preferably designed as a countercurrent heat exchanger, two connected to the head of the Desorberkolonne 8 capacitors 17 and 16, and also connected to the bottom of the Desorberkolonne 8 second reboiler 28th

The flue gas 9 from the steam generator is washed in the absorber column 11 at low temperature (for example 40 ° C to 60 ° C) with an aqueous solution of a CO2-binding component (absorber). Such an absorbent may, for example, a mixture of water with

Monoethanolamine. The purified flue gas is 10 in the figure

designated.

After the CO2-laden absorbent on the

Preheated countercurrent heat exchanger 12, the preheated CO2-laden absorbent is introduced into the desorber 8. Here, the liquid CO2-laden absorbent medium flows from below near the bottom of the swamp

Desorber column 8 about 110 ° C to 130 ° C hot steam opposite, which is generated in one of the reboiler 7, 28 by heating a partial flow of the absorber means. At these elevated temperatures, the absorbent releases the CO2 again. Behind the desorber column 8, the hot C02 / water-steam mixture (Desorberkopfbrüden) is divided into two partial streams 15, 14 and each supplied to a capacitor 17, 16. In the first of the two capacitors 16 boiler feed water 19 is preheated, while the second of the two capacitors 17, the combustion air 18 of the steam generator using a not shown heat exchanger is preheated. The water obtained in the two condensers 16, 17 is separated and fed back to the desorber column 8. The CO2 22 is available for storage or use. The hot C02-poor absorbent is used to cool over the

Countercurrent heat exchanger 12 out, to then be available as a cooled low-CO2 absorbent the laundry cycle again. The flue gas 10 freed from the CO 2 leaves the absorber column 11 at its upper end.

In the case of CO 2 scrubbing, for example, the process described in EP 1 967 249 can be used using a strip component. As a strip component, a commercially available chemical can be used which is substantially immiscible with the wash liquor, virtually unreacted with it, and which should have a higher vapor pressure, ie a lower boiling temperature than this. Examples of suitable strip components are alkalis, for example fluoroalkanes. This measure serves to lower the boiling point of the absorbent, thereby reducing the energy consumption for the regeneration of the absorbent. As a strip-steam, the heated in the desorber 8 (stripper) is guided

Partial flow of the absorbent referred to. This partial flow of the heated absorbent is generated by means of the reboiler 7, 28. The invention is not limited to the illustrated interconnection of the flue gas scrubbing according to the exemplary embodiment, but other interconnections are also possible, for example those described in EP 1 967 249.

Is, as described in this embodiment, the vapor 5 from the drying of lignite completely for the regeneration of

Used absorbent, for example, the vapor condensate from the reboiler 7 continue to serve for preheating the boiler feed water or the combustion air. Depending on the design, about 50% of the energy required for absorption medium regeneration can be extracted from the vapors produced during fluidized-bed drying. The remaining amount of energy can be applied according to the invention via a second reboiler 28 which, as described in this example, is operated with low-pressure steam 27.

As shown in the figure, in this embodiment, medium-pressure steam 26 is passed to a turbine, wherein the steam outlet stream as

Low-pressure steam 27 is guided in the reboiler 28. The turbine 24, driven by the center-side steam 26, in turn drives a CO 2 compressor 23, the compressed CO 2 available then being 25 more

Can be used.

The first and second reboilers 7, 28 are operated in parallel under approximately the same conditions. In the embodiment shown here, the two reboiler are connected in parallel. The proportion of the strip steam provided by the reboilers 7, 28 is preferably controllable.

It is particularly advantageous if both reboiler 7, 28 work at the same condensation temperature.

Figure 2 shows the heat transfer between heat sinks and heat sources as it is according to an exemplary method according to the invention for operating a steam turbine power plant. At first you can

Identify heat sources and heat sinks that are present according to the above embodiment, the actual operation of a conventional steam turbine power plant. The operation of such

Steam turbine power plant generated low-pressure steam, for example, represents a heat source. On the other hand, the boiler feed water 19, and the combustion air 18 must be preheated for efficient operation and therefore represent heat sinks

Heat sinks in the fluidized bed drying 1 and the CO 2 scrubbing 29 ago. All of these heat sources and heat sinks are shown by way of example in FIG. For optimal operation of a steam turbine power plant, it makes sense to efficient heat transfer between the existing heat sources and

To ensure heat sinks.

The fluidized bed drying 1 is operated by means of low-pressure steam 3 via a heat exchanger 2. The heat exchange realized thereby is represented in FIG. 2 by the arrow marked with the reference numeral 3. According to the embodiment of the illustrated here

The method according to the invention is the compressed vapor 5 from the

Coal drying 1 used for the regeneration of the absorber. The heat transfer realized in this way is shown in FIG. 2 by the arrow between the

Heat source from the vapors of brown coal drying with vapor compression and during the absorber agent regeneration (detergent regeneration)

present heat sink shown.

The C02 laundry in turn provides a heat source due to the

Desorberkopfbrüden 13 ready. The Desorberkopfbrüden 13 is used according to the inventive method to heat the combustion air 18 of the steam generator and / or the boiler feed water 19. It is implemented as a heat transport, which are indicated by the arrows by the reference numerals 13, 14 and 15. The embodiment described above and shown in Figure 1 further includes a second reboiler 28 for heating the absorber means. This reboiler is by means of low pressure steam 27 from a turbine 24 for

Driving a compressor 23 operated. The realized thereby

Heat transfer is indicated in Figure 2 by the reference numeral 27.

The optional use according to the invention of uncompressed vapors from lignite drying for preheating the boiler feed water 19 and / or the combustion air 18 is represented in FIG. 2 by the dashed arrow. This heat transfer shown in this way corresponds to the use of the vapor from the coal drying, as is the case with conventional methods.

LIST OF REFERENCE NUMBERS

1 fluid bed dryer

2 heat exchangers

3 tap steam line

4 pre-dried coal

5 vapors from the coal drying

6 vapor compressors

7 first reboiler

8 desorber column

9 flue gas

10 filtered flue gas

11 absorber column

12 countercurrent heat exchanger

13 Desorberkopfb males

14 first part of the desorber Kopfbrüdens

15 second part of the desorber Kopfbrüdens

16 heat exchangers

17 heat exchangers

18 combustion air for the steam generator

19 boiler feed water

20 water separators

21 condensed water

22 filtered C0 ₂ stream

23 compressor

24 turbine

25 compressed CO2

26 medium pressure steam

27 low-pressure steam

28 second reboiler

29 C0 ₂ scrubbing (Post Combustion Capture (PCC))

Claims

claims

A method of operating a steam turbine power plant having at least one lignite fired steam generator, such that the

Flue gas from the steam generator is subjected to a gas scrubbing to remove CO ₂ and the lignite in a dryer (1)

is pre-dried, wherein the energy required for the gas scrubbing is at least partially decoupled from the drying of lignite and the resulting waste gas during scrubbing (13) is at least partially used for preheating the boiler feed water (19) and / or the combustion air (18) of the steam generator ,

2. The method according to claim 1, characterized in that the drying of the brown coal takes place indirectly in a fluidized bed dryer (1).

3. The method according to any one of the preceding claims, characterized

in that the gas scrubbing in an absorber (11) by means of a carried out, the CO ₂ absorbing absorption solution, the C0 ₂ is acted upon absorbing solution in a desorber (8) by heating using the residual heat of at least part of the accumulated during the drying of brown coal the vapor (5) is regenerated and the Desorberkopfbrüden (13) generated in this process is at least partially used for preheating the boiler feed water (19) and / or the combustion air (18) of the steam generator.

4. The method according to claim 3, characterized in that by

at least partial condensation of the Desorberkopfbrüden (13), using at least one condensation heat exchanger (16, 17), a portion of the heat content of Desorberkopfbrüdens (13) in the combustion air (18) and / or the boiler feed water (19) of the steam generator is transmitted.

5. The method according to any one of claims 3 or 4, characterized in that the vapor (5) acted upon to heat the CO ₂ Absorbing solution is at least partially compressed so that the

Condensation temperature of the vapor is large enough to

Regeneration of the absorption solution can be used.

6. The method according to claim 5, characterized in that the vapor (5) is compressed to a level corresponding to a condensation temperature of about 130 ° C.

7. The method according to any one of claims 5 or 6, characterized in that the vapor recompression in one or more multi-stage

Brüdenverdichter-Strängen (6), consisting of compressors and

Injections for intercooling, takes place.

8. The method according to any one of the preceding claims, characterized

characterized in that the heating of the CO ₂ acted upon

Absorption solution using a reboiler (7).

9. The method according to any one of the preceding claims, characterized

in that the CO ₂ (22) separated from the absorbent is compressed by a compressor (23) for further use, the compressor (23) being compressed by means of a steam, preferably

Medium pressure steam, driven turbine (24) is driven, wherein the steam outlet stream (27) from this turbine (24) is used to heat the CO ₂ acted upon absorption solution.

10. The method according to claim 9, characterized in that the heating of the CO ₂ acted upon absorption solution using a reboiler (28).