DE3817690A1 - Combined gas- and steam-turbine power station having coal gasification - Google Patents

Abstract

In a combined gas- and steam-turbine power station having an integrated coal gasification system, the problem arises of incorporating the sensible waste heat from the coal gasification, which results during the cooling of the raw gas, into the power-station process in such a manner that as high as possible an efficiency for the entire process results. The novel method functions with a combined gas- and steam-turbine process, the fuel gas for the gas turbine being generated in a coal-gasification system (50-56). The carbon-containing gasification residue (63) is burned in an atmospheric fluidised-bed combustion system (8) which is arranged in the exhaust gas flow of the gas turbine (2). Optimal utilisation of the waste heat from the coal gasification is achieved in that the said heat (52) is incorporated, with the aid of a heat-transfer circuit (20) having a liquid heat carrier, such as sodium, into the steam process and is used there for superheating (23) or reheating (24) of steam. Furthermore, the heat-transfer circuit is used to preheat (22) compressed air from the gas turbine to approximately 600@C. The method is used for generating electrical energy from solid fuel with a high degree of conversion. <IMAGE>

Description

The invention relates to a method for operating a combined gas and steam turbine power plant, in which the fuel gas for the gas turbine process in a coal mine solution and the feeling that arises from coal gasification bare waste heat to improve efficiency with the help a heat transfer circuit in the steam process is bound.

Various methods are known, combined gas and To operate steam turbine power plants with coal gasification ben. In these processes, the coal is made using Oxygen or air as a gasifying agent in a gas gasification solution reactor and the coal gas thus generated after a Cleaning burned in the combustion chamber of a gas turbine. The Residual heat in the exhaust gas of the gas turbine is used for steam to generate, with which a steam turbine is driven.

With some concepts, the coal used becomes an education the most complete carbon conversion possible Use of pure oxygen gasified. For deployment of oxygen, however, an air separation plant is required the effect of which increases the plant costs just worsened by self-consumption and the load the behavior of the power plant is restricted.

In order to avoid these problems, some were asked whose concepts suggested using coal Air only partially gasified and the remaining coal substance in a dust or fluidized bed firing under on Complete set of exhaust gases from the gas turbine containing oxygen  dig to burn. Such methods are e.g. in the open legend DE 36 12 888 or the magazine VGB-Kraft werkstechnik 62 (1982), No. 5, described from page 365 onwards ben. Some special concepts also provide part of the heat released in the furnace, directly or with the help of a heat transfer circuit to the To transfer gas turbine process and to preheat the Compressor air to use the required Brenn amount of gas and thus the plant costs for coal gasification to be reduced (OS-DE 36 05 408 or OS-DE 36 03 095).

The main problem with the different concepts for a gas and steam turbine power plant with integrated coal gasification is the achievement of the highest possible effect degree with simultaneous limitation of the plant expenditure, to achieve good economy.

The operation of coal gasification results from the emergency agile cooling of the raw gas a relatively large amount of waste heat amount. The problem arises, this sensible warmth so involved in the power plant process that overall results in a favorable efficiency.

In previous concepts, the waste heat is usually Coal gas used to generate high pressure steam, which then together with steam from the waste heat boiler or the furnace is relaxed in a steam turbine. This results in Problems caused by high thermal and mechanical loads heating pipes due to a relatively good heat transfer gangs in the area of raw gas heating pipe and a less cheap Heat transfer in the area of the heating tube steam, which leads to a rela tiv high heating tube temperature leads. The chemical together Settlement of the raw gas also leads to a heating pipe high risk of corrosion and material decomposition with increasing pipe wall temperature increases. To these problems In many concepts, it is intended to meet the  Limit the maximum pipe wall temperature to around 400 ° C. However, this results in a relatively low steam temperature rature and thus a significant deterioration in Efficiency.

The object of the invention is that in coal gasification accumulating sensible heat in the power plant process bind that the highest possible efficiency for the Overall process results and the load on the heating pipes in coal gasification versus generating over heated high pressure steam is reduced.

This object is achieved in that a larger part of the in the case of raw gas cooling in coal gasification sensible heat by means of a heat transfer circuit turned into the steam process with a liquid heat transfer medium bound and there together with heat from a furnace Overheating and / or intermediate overheating of steam turned on is set. The corresponding heat exchangers from the coal company The solution and the furnace are formulated in this way tet that the liquid heat transfer medium of heat transfer circuit first preheated in coal gasification and then continue to open in a heat exchanger of the furnace the full flow temperature of e.g. 600 ° C is heated. Because of this series connection and because of the good warmth transition in the area of the heating tube heat transfer medium, the maxi Male pipe wall temperature of the heating pipes in the heat exchangers coal gasification is limited to approx. 500 ° C and thereby the Danger of high temperature corrosion and material decomposition be significantly reduced. In addition, due to the low operating pressure of the heat transfer circuit a lower mechanical load on the heating pipes and on due to the relatively low volume flow of the liquid Heat transfer medium and the elimination of desuperheaters Steam temperature control a simplified structure of this Heat exchanger in coal gasification.  

Salts or liquids are suitable as the liquid heat transfer medium Metals like sodium, potassium or a mixture of both. The one heated in coal gasification and the furnace The heat transfer medium then becomes the heat exchanger of the Dampfpro fed and there for overheating or intermediate Overheating of steam and possibly also evaporation of water and thereby to a return temperature cooled from about 400 ° C.

By using a heat transfer circuit also the construction of the heat exchanger for overheating or Reheating steam, including the pipes and the regulation of the upper temperature of the steam or Intermediate steam significantly simplified.

The further heating of the liquid heat carrier in one If necessary, the heat exchanger of the furnace can also be omitted, if the steam or intermediate steam is also in a heat Exchanger of the furnace overheated to full temperature or the heat transfer medium in coal gasification is increased is heated, but this places a higher load on the heating pipes in coal gasification.

The further cooling of the coal gas to the necessary Rei cleaning temperature can be in a raw gas-clean gas heat exchanger and a feed water preheater or evaporator.

The heat transfer circuit can still be used the compressor air of the gas turbine, the Pro Zeßluft the coal gasification and possibly also the gerei preheat coal gas so as to produce the necessary amount of coal gas for the gas turbine process and thus the plant expenditure for to reduce coal gasification.

The furnace can act as a circulating, atmospheric vortex layered fire designed and with the oxygen-containing  Exhaust gas from the gas turbine are operated. The coal gasification can be used as partial coal gasification when using compressed gas Air can be interpreted as a gasifying agent, the koh Gasification residue in the fluidized bed fire containing fuel can be fired. Desulphurization of coal gases can be absorbed in a hot gas sulfurization, in a wet desulfurization or also, at Desulphurization in the coal gas path, in one of the Gas turbine downstream desulfurization, especially in a fluidized bed combustion by means of an absorbent respectively.

The advantage achieved by the invention is in particular the fact that through the use of heat transfer the sensible waste heat from the raw gas cooling used at a higher temperature level and more optimal in the Overall process can be integrated as in the direct Generation of high pressure steam. This results in opposite known concepts a significant improvement of the we degree of efficiency and thus the overall economy investment. In addition, there is for the heat exchanger in the Coal gasification is simplified and less Burden.

When combining partial coal gasification with a secondary switched atmospheric fluidized bed firing results also a simplified structure of the entire coal contract solution, since these are operated with air as a gasifying agent and the carbonaceous gasification residues in the vortex stratified combustion can be fully implemented. As In addition to all types of coal, fuel is also other solid fuels, such as biomass.  

The invention is explained in more detail using an exemplary embodiment. The combined gas and steam turbine power plant consists essentially of a gas turbine group 1 to 3 , a coal gasification system 50 to 63 and a fluidized bed combustion 8 to 13 .

With the help of a compressor 1 , which is coupled to a gas turbine 2 and a generator 3 via a shaft, intake air is compressed to 15 bar and then fed to a heat exchanger 22 . The gas turbine 1 , 2 is a modified series gas turbine with an air throughput of 500 kg / s, a turbine inlet temperature of 1100 ° C and an output of 150 MW. In the heat exchanger 22 , the compressed air is preheated to approximately 600 ° C. with the aid of heat from a heat transfer circuit 20 , then further heated to 1100 ° C. in a gas turbine combustion chamber 6 by burning coal gas and then expanded in the gas turbine 2 with energy being released .

The coal gasification 50 is designed as partial gasification and works on the principle of the circulating fluidized bed. The gasification air for coal gasification is branched off from a line 5 for the preheated compressor air, post-compressed in a compressor 59 by 2 bar and supplied to a gasification reactor 50 via a hot gas line 60 . The ground coal 62 is partially gasified in the fluidized bed gasification reactor 50 with the aid of the gasification air 60 and possibly additional steam 61 at a temperature of approximately 1100 ° C. to 50 to 80%. The gasification residue, consisting of fine coke and ash, is withdrawn from the gasification reactor and fed to a fluidized bed furnace 8 for complete combustion. Desulphurization of the coal gas is dispensed with to simplify the coal gasification plant. The separation of the sulfur dioxide formed during the combustion of the coal gas is carried out in a fluidized bed furnace connected downstream of the gas turbine.

The raw gas emerging from the gasification reactor 50 is after dedusting in a cyclone 51 in a heat exchanger 52 , which serves to preheat a liquid heat transfer medium, to about 500 ° C., in a raw gas clean gas heat exchanger 53 to about 300 ° C. and one Feed water preheater 54 cooled to 250 ° C. In a bag filter system 55 , the remaining fine coke and other fine dust is separated down to a residual dust content of less than 5 ppm and likewise fed to the fluidized bed combustion 8 . In a further gas cleaning stage 56 , which operates according to the dry absorption process, chlorides and fluorides are separated off. The clean gas is post-sealed in an adjustable compressor 57, preheated in the raw gas-clean gas heat exchanger 53 to 450 ° C. and then fed to the gas turbine combustion chamber 6 and burned there.

The carbon-containing gasification residue 63 and additional coal 62 are burned in a circulating fluidized bed furnace 8 operated at atmospheric pressure. For this purpose, the exhaust gas 7 from the gas turbine is predominantly used as combustion air, which still has an oxygen content of over 10%. The separation of the sulfur dioxide, which is formed during the combustion of the gasification residue and the coal and is contained in the exhaust gas 7 of the gas turbine, takes place in the fluidized bed furnace 8 by adding limestone 10 as an absorbent. The calcium sulfate (CaSO ₄ ) that forms during the desulphurization process is extracted together with the ash from the fluidized bed furnace. The heat released in the fluidized bed furnace is used for evaporation and for pre-overheating of the steam and for further heating of a liquid heat transfer medium. The exhaust gas from the fluidized bed combustion is after a dedusting in a recycle cyclone 13 , shear 35 , 34 , 31 in Wärmetau further cooled to about 100 ° C, then cleaned in a filter system 14 and then released via a chimney 43 to the environment.

The falling in the cooling of the raw gas in the coal gasification to heat is mostly integrated with the help of a heat transfer circuit 20 with liquid sodium as a heat carrier together with heat from the fluidized bed combustion 8 in the steam process and used to preheat the compressor air. For this purpose, the sodium is pumped by means of a circulation pump 21 to the heat exchanger 52 of the raw gas cooling, preheated there to about 500 ° C. and then further heated to 650 ° C. in a heat exchanger 12 of the fluidized bed furnace. The sodium is then fed to the heat exchangers 23 , 24 for superheating and intermediate superheating of the steam and is then cooled again to 400 ° C. while releasing energy. A partial stream of sodium is fed to a heat exchanger 22 for preheating the compressor air.

The condensate water is fed by means of a condensate pump 30 to a waste heat boiler 31 and a multi-stage, regenerative feed water preheating 36 , where it is preheated to 150 ° C. and then fed to a feed water tank and degasser 32 . With feed water pumps 33 , the feed water is compressed to 280 bar and, divided into partial streams, is fed to a waste heat boiler 34 , a multi-stage, regenerative high pressure feed water preheater 37 and a coal gas heat exchanger 54 , where it is preheated to 250 ° C. and then further in a full flow waste heat boiler 35 preheated and partially evaporated.

Then the water-steam mixture in a vaporizer and superheater 11 of the fluidized bed furnace 8 is completely evaporated and partially overheated. In a heat exchanger 23 , which is heated via the sodium circuit 20 , the steam is further overheated and then fed to a high-pressure turbine at a temperature of 540 ° C. and a pressure of 250 bar, and in this is relieved to 40 bar, giving off energy. The intermediate steam is reheated to 540 ° C. in an intermediate superheater 24 , which is also heated via the sodium circuit, expanded to 0.05 bar in a low-pressure turbine and condensed in a condenser 41 . The condensate heat is released to the environment via a cooling circuit 42 . The steam turbine 39 has an output of 250 MW and drives a generator 40 .

The thermal power of the combined cycle power plant is 760 MW (supplied fuel flow), the electrical output Power is 350 MW. The efficiency is 46%.

With partial load operation, only the steam output is initially reduced and first the feed water flow through the steam-heated one Feed water preheating reduced. This increases up to one Partial load of approx. 85% the efficiency initially over 47%, so that the power plant is also good for the Part load operation is suitable.

Claims (5)

1. Combined gas and steam turbine power plant, with a gas turbine group ( 1 to 3 ) with combustion chamber ( 6 ), with a gasification system ( 50 to 63 ) for the gasification of a solid fuel, the fuel gas generated in the gas turbine combustion chamber ( 6 ) being burned and with a steam generator system for operating a steam turbine, characterized in that waste heat ( 52 ) from the gasification system ( 50 ) with the aid of a heat transfer circuit ( 20 ) with a liquid heat carrier on the heat exchanger ( 23 , 24 ) of the steam generator system for overheating and / or reheating is carried by steam. 2. The method according to claim 1, characterized in that waste heat from the gasification system ( 50 ) and heat from a furnace ( 8 ) with the aid of a heat transfer circuit ( 20 ) is transferred to heat exchangers ( 23 , 24 ) for overheating and / or reheating steam and the heat exchangers ( 52 , 12 ) for heating the liquid heat carrier are connected in series in such a way that the liquid heat carrier is first preheated in the gasification and then further heated in the furnace. 3. The method according to claim 1 or 2, characterized in that the furnace ( 8 ) is a fluidized bed and with carbon-containing gasification residue ( 63 ) and / or solid fuel ( 62 ), using the oxygen-containing Abga ses ( 7 ) of the gas turbine, fired becomes. 4. The method according to claim 1 to 3, characterized in that the compressor air ( 4 ) of the gas turbine and / or the Ver gassing air ( 60 ) with the help of heat from the heat transfer circuit ( 20 ) are preheated. 5. The method according to claim 1 to 4, characterized in that the evaporation of the feed water in heat exchangers ( 35 , 11 ) of the waste heat boiler or the furnace ( 8 ).