Gas turbine plant with exhaust gas recirculation and also method for operating such a plant

Abstract

A gas turbine plant is provided with exhaust gas recirculation and includes a main gas turbine having a main compressor and main turbine driving a main generator, and a combustion chamber, with an outlet connected to the inlet of the main gas turbine, has a fuel feed, and via the recuperator's high-pressure side obtains combustion air from the main gas turbine's compressor outlet. The outlet of the main turbine and the inlet of the main compressor are connected via the recuperator's low-pressure side and a cooler for exhaust gas recirculation. On the recuperator's low-pressure side, a charging unit, with a compressor and a turbine is arranged, and draws in air via an air intake and by the outlet of its compressor is connected to the recuperator's low-pressure side outlet and by the inlet of its turbine is connected to a surplus-gas extraction line on the recuperator's low-pressure side.

What is claimed is: 
     
         1 . A method for operating a gas turbine plant in a partially closed, charged gas turbine cycle, the method comprising:
 combusting fuel in a combustion chamber, feeding a gaseous compressed operating medium which contains combustion air;   expanding the operating medium, which contains hot combustion gases, in a main turbine of a main gas turbine, thereby performing work;   extracting heat from the operating medium in a subsequent recuperator and in a cooler;   compressing the operating medium in a compressor of the main gas turbine, and heat is fed to the compressed operating medium in the recuperator before re-entry into the combustion chamber;   extracting on the low-pressure side of the recuperator a partial flow of the operating medium at an extraction point which is at a suitable first temperature level, and further expanded in a turbine of a charging unit; drawing in and compressing air by a compressor of the charging unit; and   feeding the air to the operating medium on a low-pressure side of the recuperator.   
     
     
         2 . The method as claimed in  claim 1 , wherein CO 2  is separated from recirculated exhaust gases of the main turbine and/or from exhaust gases of the turbine of the charging unit. 
     
     
         3 . The method as claimed in  claim 1 , wherein the compressor and turbine of the charging unit are connected to separate motor/generator units which are operated at different controlled speeds. 
     
     
         4 . The method as claimed in  claim 1 , wherein for cooling the main turbine or a hot-gas liner, a partial flow is extracted from the recuperator via a supply line. 
     
     
         5 . The method as claimed in  claim 4 , wherein the partial flow of cooling medium is extracted at a temperature of 300°-500° C. 
     
     
         6 . The method as claimed in  claim 4 , wherein for cooling the units, a plurality of partial flows are extracted at different temperature levels. 
     
     
         7 . The method as claimed in  claim 1 , wherein the main turbine has a closed cooling system which is supplied, via a booster compressor, with cooling fluid which is extracted downstream of the compressor of the main gas turbine, and the heated cooling fluid flows back into the main cycle upstream of the combustion chamber. 
     
     
         8 . The method as claimed in  claim 1 , wherein pure oxygen or an oxygenous fluid is added into the cycle upstream of the combustion chamber via at least one control element. 
     
     
         9 . The method as claimed in  claim 8 , wherein for a temporary quick power increase of the plant, the addition is carried out between a supply line in the recuperator and the combustion chamber. 
     
     
         10 . The method as claimed in  claim 1 , wherein the gas turbine plant is subjected to a purging cycle before each start. 
     
     
         11 . The method as claimed in  claim 1 , wherein the main gas turbine is started together with the charging unit either by generators, which are operated as starter motors, by a motor, or by other independent starting machines. 
     
     
         12 . The method as claimed in  claim 1 , wherein the compressor of the charging unit compresses air which is drawn in at atmospheric pressure exactly to a pressure at an inlet into the cooler. 
     
     
         13 . The method as claimed in  claim 1 , wherein the fuel is preheated, and the heat for preheating the fuel comes from one or more integrated coolers. 
     
     
         14 . The method as claimed in  claim 1 , wherein the heat which is not required for CO 2  separation and/or fuel preheating is used for operating a bottoming cycle. 
     
     
         15 . The method as claimed in  claim 14 , wherein the bottoming cycle is a Rankine cycle or Kalina cycle. 
     
     
         16 . The method as claimed in  claim 2 , wherein the operating medium is extracted from a cold end of the low-pressure side of the recuperator before admixing of fresh air, the operating medium, after separate cooling and compression, is used as a low-oxygenic and CO 2 -rich alternative cooling fluid supply. 
     
     
         17 . The method as claimed in  claim 1 , wherein average residual oxygen content at an outlet of the combustion chamber is at least 0.5%. 
     
     
         18 . The method as claimed in  claim 1 , wherein output of the gas turbine plant is controlled by controlling charging pressure, which is built up by the compressor of the charging unit. 
     
     
         19 . The method as claimed in  claim 18 , wherein a gas flow which flows through the compressor of the charging unit and a gas flow which flows through the turbine of the charging unit are controlled separately, either by a variable speed of a common shaft or a variable speed in a case of individual drive with two motors/generators and/or by movable guide vane rows in the compressor and/or turbine. 
     
     
         20 . The method as claimed in  claim 18 , wherein for the charging unit a pressure ratio between a minimum value and a maximum design specification of between 4 and 10 is used, and wherein partial-load operation is carried out with a charging pressure ratio between the minimum value and the maximum design specification. 
     
     
         21 . The method as claimed in  claim 20 , wherein the charging unit is operated with a compressor pressure ratio of approximately 1 or lower by switchable bypass lines, with or without restrictors, instead of charging compressor and charging turbine, and wherein shifted interfaces to a process of the main gas turbine are provided. 
     
     
         22 . The method as claimed in  claim 1 , wherein a power increase is brought about by feeding an atomized liquid fluid into at least one of the compressors. 
     
     
         23 . The method as claimed in  claim 1 , wherein opening of a fuel valve, or fuel valves, and ignition remain disabled unless a purging cycle with air has expired within a retention period. 
     
     
         24 . The method as claimed in  claim 1 , wherein the method is used as an alternative to CODOG drives (Combined Diesel or Gas Turbines), using useful power for propulsion and/or power supply of ships.