AU2010202597B2

AU2010202597B2 - Method for operating a steam turbine power plant and also device for generating steam

Info

Publication number: AU2010202597B2
Application number: AU2010202597A
Authority: AU
Inventors: Martin Belting; Georg Berger; Christian Fielenbach; Toni Rupprecht
Original assignee: RWE Power AG
Current assignee: RWE Power AG
Priority date: 2009-07-28
Filing date: 2010-06-22
Publication date: 2014-09-11
Anticipated expiration: 2030-06-22
Also published as: EP2423465A2; AU2010202597A1; DE102009035062A1; EP2423465A3

Abstract

METHOD FOR OPERATING A STEAM TURBINE POWER PLANT AND ALSO DEVICE FOR GENERATING STEAM Abstract 5 The invention refers to a method for operating a steam turbine power plant with a steam generator (4) which is fired with brown coal, in which the brown coal is first subjected to indirect drying, preferably in a fluidized bed dryer (8). The fluidized bed dryer (8) is at least partially heated by steam from the water/steam cycle of the steam generator (4). The method according to the invention is characterized in that the energy of 1o the vapour which results from the drying of the brown coal is at least partially used for preheating the combustion air. Fig.1

Description

S&F Ref: 956540 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address RWE Power Aktiengesellschaft, of Huyssenallee 2, of Applicant : 45128, Essen, Germany Actual Inventor(s): Martin Belting Georg Berger Christian Fielenbach Toni Rupprecht Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Method for operating a steam turbine power plant and also device for generating steam The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(2787197_1) 1 METHOD FOR OPERATING STEAM PLANT AND ALSO DEVICE FOR GENERATING Field The invention refers to a method for operating a steam turbine power plant with a steam generator which is fired with brown coal, in which the brown coal is first subjected to indirect drying in a fluidized bed dryer, wherein the fluidized bed dryer is at least partially heat generator. Background A method of the type which is referred to the introduction is known for example from DE 10319477 Al. The combustion of brown coal is generally known, particularly insofar as the pit-wet brown coal contains up to 65% water, from which higher specific C0 2 emissions result during the generation of electric current from brown coal in comparison to electric current generation from hard coal. As a result of corresponding drying of the brown coal before firing in the steam generator of a power plant, a significant increase of efficiency can be achieved, as a result of which the specific C0 2 emission is reduced. The pit-wet brown coal has a water content of about 45 to 65%, which as a result of drying is reduced to about 10 to 25%. The so-called WTA process (fluidized bed drying with internal waste heat utilization) has been proved to be a particularly efficient drying process. With such a drying process, which is known for example from DE 195 18 644 C2, the efficiency of a brown coal power plant can be improved by about 4 to 5 per cent compared with conventional brown coal power plant technology. In the fluidized bed dryer, precrushed raw brown coal is introduced into the stationary fluidized bed of a dryer, which operates with a slight overpressure. In the dryer/reactor there is an arrangement of heating coils, the heating steam of which condenses at a temperature level of about 130 0 C. The water which issues from the raw brown coal during drying in the fluidized bed dryer arrangement is present in a slightly superheated state and vaporous form as a separate substance flow which is referred to as vapour. Some of the vapour is fed back via a fan into the dryer for the purpose of fluidizing the fluidized bed.

2 In DE 195 18 644 C2, for example, it is proposed to compress a partial stream of the vapour and to feed it to the heat exchanger as heating medium so that the vapour at least partially condenses so that the evaporation heat of the vapour can be utilized in part for the desired drying of the fuel. With such an arrangement or such a procedure, a more intense energetic utilization of the vapour which issues from the dryer is possible so that overall the efficiency of the power plant is increased and the emissions are lowered. Alternatively, it is possible to utilize the energy of the vapour for preheating the feed water. This method variant is described for example in DE 103 19 477 Al. According to the method which is described there, provision is made for the energy of the vapour which results from the drying of the brown coal to be utilized for multistage preheating of the cold feed water from the water/steam cycle. Preheating of the feed water in the water/steam cycle, however, does not allow complete utilization of the vapour heat since the feed water does not constitute a sufficiently large heat sink. In DE 103 19 477 Al, it is proposed to compress a partial stream of the vapour and with the compressed vapour to preheat feed water to a higher temperature level. Also in this variant of the energetic utilization of the vapour, some of the heat content of the vapour is not optimally utilized. There is a need to provide a method and also a device of the type referred to in the introduction or of the energetic utilization of the vapour which results during the drying. Object of the Invention It is an object of the present invention to substantially overcome or at least ameliorate one or more of the disadvantages of the prior art, or to at least provide a useful alternative. Summary of the Invention The present invention provides a method for operating a steam turbine power plant with a steam generator which is fired with brown coal, in which the brown coal is first subjected to indirect drying in a dryer, wherein energy of vapour which results from the drying of the brown coal is at least partially used for preheating combustion air, and wherein injection of the energy 3 of the vapour into the combustion air is carried out by means of at least one heat exchanger which is connected upstream to an air preheater which is heated by a flue gas. The present invention also provides a device for generating steam, comprising at least one dryer for predrying pit-wet brown coal, at least one steam generator which is fired with the brown coal, at least one steam turbine which is connected downstream to the steam generator, at least one feed-water supply line to the steam generator, at least one device for preheating feed water, and at least one air preheater for combustion air, wherein at least one heat exchanger, which is connected to a vapour outlet of the dryer, is connected upstream to the air preheater, wherein energy of vapour which results from the drying of the brown coal is at least partially used for preheating the combustion air, wherein the air preheater is operated/heated by a flue gas, and wherein the dryer is formed as a fluidized bed dryer. It is basically practical to raise the temperature of the combustion air to a higher level by regenerative air preheating, specifically with regard to the carnotization of the power plant process. In any case, it is wise and desirable to inject sufficient heat into the combustion air for the air temperature upstream of the combustion chamber inlet to correspond approximately to the flue gas temperature downstream of the economizer, less terminal temperature difference. Since, however, a conventional regenerative air preheater- subsequently referred to as a Luvo for the sake of simplicity - has a large lower terminal temperature difference, and therefore creates large energy losses, it is wise and expedient to preheat the fresh air which is fed to the Luvo by means of a heat exchanger. If in the following text "downstream" or "upstream" is mentioned with regard to the parts of the steam turbine power plant, this expression always relates to the flow direction of the substance flow which is to be considered in the respective branch of the method. For such preheating of the combustion air, according to the prior art energy is customarily extracted either in the form of low-temperature heat from the water/steam cycle or from the flue gas stream leaving the Luvo. The procedure according to an aspect of the invention has the advantage that the amount of heat which has been injected into the combustion air no longer has to be extracted from the flue gas via the Luvo. Therefore, a specific amount of heat is shifted from a low temperature level to a higher temperature level and then made available to the water/steam cycle. A regenerative heat exchanger is not necessarily to be understood by Luvo in the sense of the invention, rather this for example can also be a Luvo which is heated by flue gas.

4 With an aspect of the invention therefore, two advantages are achieved in equal measure, specifically the greater energetic utilization of the vapour as result of heat exchange with a larger heat sink on the one hand, and also a shift of the amount of heat, which is liberated in the sense of usability, to a higher temperature level, which can ultimately be utilized in the feed water supply. In an advantageous variant of aspects of the invention, injection of the energy of the vapour into the combustion air is carried out by means of at least one heat exchanger which is connected upstream to a Luvo which is heated by flue gas. This is carried out especially by means of a condensation heat exchanger. In a further variant of the method, provision is made for heat from the flue gas stream, which is already partially cooled by means of the Luvo, to be additionally yielded to the Luvo. In this case, the heat can be extracted from the flue gas downstream of the air preheater by means of a heat transfer medium, for example by means of water. In an especially advantageous variant of the method according to an aspect of the invention, provision is made for at least a partial flow of the vapour, after discharging from the fluidized bed dryer, to be compressed in a vapour compressor and to be fed to at least one condensation heat exchanger. In this way, the liberated condensation heat of the vapour is additionally utilized. As a result of the compression, the temperature level at which the vapours condense is increased, and therefore a higher air preheating can be achieved. In this case, such amounts of energy can be injected into the combustion air that extraction of heat from the flue gas for the purpose of preheating the combustion air is possibly completely superfluous. A partial stream of the flue gas is expediently branched off upstream of the air pre heater and used for preheating the boiler feed water, specifically bypassing the air preheater. In an especially advantageous variant of the method according to an aspect of the invention, provision is made for flue gas to be branched off upstream of the air pre heater in such quantity as to correspond to the energy from the vapour which is injected into the combustion air.

5 It is especially advantageous if injection of the energy of the vapour into the combustion air is carried out in a multi-staged manner, wherein a partial amount of the vapour is compressed in a vapour compressor and condensed in a condensation heat exchanger. There is also provided a device for generating steam, comprising at least one dryer for predrying pitwet brown coal, at least one steam boiler which is fired with the predried brown coal, at least one steam turbine which is connected downstream to the steam generator, at least one feed-water supply line to the steam generator, at least one device for preheating the feed water, and also at least one air preheater for the combustion air, wherein the device according to the invention is characterized in that at least one heat exchanger is connected upstream to the air preheater in the fresh air feed line and is connected to the vapour outlet of the dryer. The dryer is expediently formed as a fluidized bed dryer. The dryer does not necessarily have to be formed as a fluidized bed dryer, rather the drying can also be carried out in other indirectly heated reactors, in which energy-rich vapours/fumes accumulate. In an advantageous variant of the device according to an aspect of the invention, provision is made for the flue gas line which is led to the air pre heater to be provided with a branch which bypasses the air preheater and is connected to the feed-water preheating facility. In this way, the energy from the dryer which is injected into the combustion air can be completely "shifted" into the feed-water preheating facility. Downstream of the air preheater, provision can be made for at least one further flue-gas cooler which interacts with the combustion air feed upstream of the air preheater. According to an especially advantageous development of the device according to an aspect of the invention, provision is made for at least one vapour compressor to be provided, which is connected upstream to at least one condensation heat exchanger in the combustion air feed line upstream of the air preheater. The air preheater is expediently formed as a regenerative air preheater.

6 Brief Description of the Drawings The invention is explained below, based on two method variants with reference to the attached figures. In the drawing: Figure 1 shows the method scheme of a first interconnection variant of the device of the invention, and Figure 2 shows the method scheme of a second interconnection variant of the device of the invention. Detailed Description of the Drawings In the figures, parts of a steam turbine power plant and their interconnection are schematically shown, wherein for reasons of simplicity only the mass flows of vapour 1, combustion air 2 and flue gas 3 are essentially shown. The water/steam cycle of the steam turbine power plant is shown only partially and in a greatly simplified manner.

7 The steam generator of the steam turbine power plant is identified by the designation 4. The steam generator 4 is formed as a boiler which is fired with brown coal. In this, water is vaporized in a known manner and expanded in a downstream steam turbine 5. The steam turbine 5 comprises a high-pressure 5 section, an intermediate-pressure section and a low-pressure section, which are not identified more specifically in the method scheme. The steam turbine 5 drives a generator 6 which in turn feeds electric energy to an electricity network. A condenser 7, in which the low-pressure steam is condensed, is connected 10 downstream to the steam turbine 5. By means of the boiler feed-water pump, the condensate is fed back again to the steam generator 4. 15 The steam generator 4 is charged with dry brown coal as fuel, which has been subjected to indirect drying in a fluidized bed dryer 8. The fluidized bed dryer 8 is heated by steam from the low-pressure section of the steam turbine 5. Some of the vapour 1 which results during drying of the brown coal is first of all dedusted in a dust separator 9 and by a fan 10 fed back again to the fluidized bed dryer 8 as 20 fluidizing medium. Further partial streams of the vapour 1, as is described again below, are used for preheating the combustion air 2. The combustion air 2 is fed back in a known manner to a regenerative air preheater 11 in which the combustion air is preheated in counterflow with the flue 25 gas 3. As is provided both in the method scheme according to Figure 1 and in the method scheme according to the Figure 2, a partial stream of flue gas 3 is guided past the air preheater 11 via a bypass line 12. This is achieved initially via a first 30 high-pressure air-bypass economizer 13 (HP Lubeco) and then via a low-pressure air-bypass economizer 14 (LP Lubeco), which are connected in series with regard to the flue gas stream 3. The heat content of the flue gas 3 is injected via the HP Lubeco 13 into the high-pressure section of the feed water cycle, the remaining 8 heat of the flue gas being injected in the next stage into the low-pressure section of the boiler feed water cycle. In the flow direction downstream of the air preheater 11 and to the economizers 5 13, 14 provision is made in the method variant which is shown in Figure 1 for a further flue-gas cooler 15 which discharges its heat load via a water/air preheater 16 which is provided in the combustion air feed line. The flue-gas cooler 15 and the water/air preheater 16 intercommunicate via water as the heat transfer medium in a closed cycle. 10 At an assumed environmental temperature of about 10' C, the combustion air 2, in the method variant 1 according to Figure 1, at a temperature of about 10* C, reaches a vaporous-air preheater 17 where this is heated up to about 95 C. The vaporous-air preheater 17 is exposed to admission of a partial stream of vapour 1 15 from the fluidized bed dryer 8. The water/air preheater 16, in which the combustion air 2 can be raised to a temperature of about 140 C, is connected downstream to the vaporous-air preheater 17, as seen in the flow direction of the combustion air 2. The combustion air 2 then flows through the regenerative air preheater 11 where this, in counterflow with the approximately 360 C hot flue 20 gas, is heated up to about 330 C. The flue gas, which enters the air preheater 11 at 360 C, can leave this for example at about 160 C. In practice, the preheating of the air with the vapour heat is carried out in all probability indirectly, i.e. via a further heat exchanger with water cycle (or another 25 liquid). The reason for this is that high volumetric flows occur both in the case of vapour and in the case of air. Since the fluidized bed drying is arranged remotely, corresponding systems would have to be provided for the high volumetric flows over the distance in the case of direct preheating of the air. As a result of the indirect preheating, these systems can be designed considerably smaller. 30 In the method variant which is shown in Figure 2, a partial stream of the vapour 1 which leaves the dust separator 9 of the fluidized bed dryer 8 is fed to a vapour compressor 18, to which a second vaporous-air preheater 19 is connected downstream.

9 A first partial stream of the vapour 1 is fed to the vaporous-air preheater 17, this being connected upstream to the condensation heat exchanger 19 in the flow direction of the combustion air 2. In this way, the energy of the vapour 1 is 5 injected into the combustion air 2 in a multistaged manner, wherein a further part of the liberated condensation heat of the vapour 1 is additionally utilized in the condensation heat exchanger 19. As a result, the air can be preheated to a higher temperature compared with the method according to Figure 1. 10 In the method variant which is shown in Figure 2, it is possible to inject the predominant part of the energy of the vapour 1 into the combustion air 2 so that this total heat can be injected into the boiler feed water by means of the HP Lubeco 13 and the LP Lubeco 14. 15 The flue-gas cooler 20, which is connected downstream in the flue gas stream, can also inject the quantity of heat which is extracted from the flue gas into the boiler feed water. A flue-gas desulphurization plant is designated 21, a cooling tower 22 being able 20 to be connected downstream to this, which primarily serves for cooling the condensate from the condenser 7. An introduction of flue gas from the flue gas desulphurization plant 21 into the cooling tower 22 can be carried out.

10 List of designations: 1 Vapour 2 Combustion air 3 Flue gas 4 Steam generator 5 Steam turbine 6 Generator 7 Condenser 8 Fluidized bed dryer 9 Dust separator 10 Fan 11 Air preheater (Luvo) 12 Bypass line 13 High-pressure air-bypass economizer (HP Lubeco) 14 Low-pressure air-bypass economizer (LP Lubeco) 15 Flue-gas cooler 16 Water/air preheater 17 Vaporous-air preheater 18 Vapour compressor 19 Vaporous-air preheater 20 Flue-gas cooler 21 Flue-gas desulphurization plant 22 Cooling tower

Claims

1. Method for operating a steam turbine power plant with a steam generator which is fired with brown coal, in which the brown coal is first subjected to indirect drying in a dryer, wherein energy of vapour which results from the drying of the brown coal is at least partially used for preheating combustion air, and wherein injection of the energy of the vapour into the combustion air is carried out by means of at least one heat exchanger which is connected upstream to an air preheater which is heated by a flue gas.

2. Method according to claim 1, wherein the brown coal is subjected to indirect drying in a fluidised bed dryer, and wherein the fluidized bed dryer is at least partially heated by steam from a water/steam cycle of the steam generator.

3. Method according to claim 1 or 2, wherein heat from the flue gas, which is already partially cooled by means of the air preheater, is additionally yielded to the combustion air upstream of the air preheater.

4. Method according to claim 3, wherein the heat is extracted from the flue gas downstream of the air preheater by means of a heat transfer medium.

5. Method according to claim 2, wherein at least a partial stream of vapour, after discharging from the fluidized bed dryer, is compressed in a vapour compressor and fed to at least one condensation heat exchanger.

6. Method according to claim 2, wherein a partial flow of flue gas is branched off upstream of the air preheater and used for preheating boiler feed water.

7. Method according to claim 6, wherein flue gas is branched off upstream of the air preheater in such quantity as to correspond to the energy from the vapour which is injected into the combustion air.

8. Method according to claim 7, wherein injection of the energy of the vapour into the combustion air is carried out in a multistaged manner, wherein at least a partial quantity of vapour is compressed in a vapour compressor and condensed in a condensation heat exchanger. 12

9. Device for generating steam, comprising at least one dryer for predrying pit-wet brown coal, at least one steam generator which is fired with the brown coal, at least one steam turbine which is connected downstream to the steam generator, at least one feed-water supply line to the steam generator, at least one device for preheating feed water, and at least one air preheater for combustion air, wherein at least one heat exchanger, which is connected to a vapour outlet of the dryer, is connected upstream to the air preheater, wherein energy of vapour which results from the drying of the brown coal is at least partially used for preheating the combustion air, wherein the air preheater is operated/heated by a flue gas, and wherein the dryer is formed as a fluidized bed dryer.

10. Device according to claim 9, wherein a flue gas line leading to the air preheater is provided with a branch which bypasses the air preheater and is connected to a feed-water preheating facility.

11. Device according to any one of claims 9 or 10, wherein in the flue gas stream, downstream of the air preheater, provision is made for at least one further flue-gas cooler which interacts with a combustion air feed line upstream of the air preheater.

12. Device according to claim 11, wherein at least one vapour compressor is connected upstream to at least one condensation heat exchanger in the combustion air feed line upstream of the air preheater.

13. Device according to any one of claims 9 to 12, wherein the air preheater is formed as a regenerative air preheater.

14. Method for operating a steam turbine power plant substantially as hereinbefore described with reference to the accompanying drawings.

15. Device for generating steam substantially as hereinbefore described with reference to the accompanying drawings. RWE Power Aktiengesellschaft Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON