GB2357551A

GB2357551A - Method of operating a power station

Info

Publication number: GB2357551A
Application number: GB0031116A
Authority: GB
Inventors: Hans Ulrich Frutschi
Original assignee: Alstom Power Inc
Current assignee: Alstom Power Inc
Priority date: 1999-12-20
Filing date: 2000-12-20
Publication date: 2001-06-27
Also published as: DE19961385A1; GB0031116D0

Abstract

A method of operating a power station comprising a compressor 1, a combustion chamber 2, a gas turbine 3, a cooling-air re-cooler 4, a generator 8 or a load, a waste-heat steam generator 5 arranged downstream of the gas-turbine, and a steam circuit arranged downstream of the waste-heat steam generator 5, wherein the re-cooler cools compressed air 15 of the compressor 1 before feeding it into the gas turbine 3 as cooling air 17, the waste gases flow out of the gas turbine 3 through the waste-heat steam generator 5 in which the generation of steam takes place in order to drive at least one steam turbine 7 belonging to the steam circuit, and saturated steam from a steam-collecting drum 6 connected to the waste-heat steam generator 5 is superheated in the cooling-air re-cooler 4 and is supplied to the steam turbine 7, as illustrated, or to the combustion chamber 2 (see Figure 2).

Description

2357551 M&C Folio: GBP 83150 Document #: 625289 "Method of Operating a

Power Station"

Technical Field

The invention relates to a method of operating a power station according to the preamble of Claim 1.

Prior Art

In a power station which comprises a gas-turbine group, a waste-heat steam generator arranged downstream and an adjoining steam circuit, in order to achieve maximum efficiency it is advantageous to provide a supercritical steam process in the steam circuit. A cooling-air re-cooler, which cools the air compressed in the compressor before it is supplied as cooling air to the gas turbine, is usually arranged between the compressor and the gas turbine. Until now it has generally been customary for this cooling-air re-cooler to be operated with water. This has the drawback, however, that a jump in temperature occurs between the air to be cooled and the water, since the evaporation procedure is isothermic. This represents a major drawback in exergetic tenns.

Presentation of the Invention The object of the invention is to overcome the drawbacks named above and to provide a method of operating a power station which is characterized by an improved level of efficiency or by an increase in output.

Claims

This is attained according to the invention by a method of Claim 1 in that saturated steam from the steam-collecting drum is superheated in the cooling-air re-cooler, and is supplied together with the compressed air to a suitable point in the power station, prefer- 2 ably the steam turbine or the combustion chamber of the gas turbine. The use of saturated steam in the cooling-air re-cooler has the advantage of preventing an exergetically disadvantageous jump in temperature between the cooling air and the steam to be heated. This has occurred until now when using water, since the evaporation procedure is isothermic. The cooling-air re-cooler is advantageously operated in counter-flow to the cooling air. Brief Description of the Drawings A specific embodiment of the invention will now be described with reference to the accompanying drawings, in which:- Fig. 1 is a diagrammatic illustration of a gas and steam combination plant according to the invention with superheating of steam in the cooling-air re-cooler of the gas turbine and subsequent feeding of the superheated steam into the steam turbine, and Fig. 2 is a diagrammatic illustration of a gas and steam combination plant according to the invention with superheating of steam in the cooling-air re-cooler of the gas turbine and subsequent feeding of the superheated steam into the compressed air upstream of the burner of the gas turbine. Only the elements essential to the invention are illustrated. The same elements are designated in the same way in the different drawings. Manner of Performing an embodiment of the Invention Fig. 1 shows a power station which comprises a gas-turbine group, a waste- heat steam generator arranged downstream of the gas-turbine group, and a steam circuit arranged downstream of the said waste-heat steam generator. The present gas-turbine group is provided with an individual gas turbine, but the in- 3 vention is not limited thereto, and the use of a gas-turbine group with a so-called sequential combustion is possible. The present gas-turbine group comprises a compressor 1, a combustion chamber 2 arranged downstream of the compressor 1, and a gas turbine 3 arranged downstream of the said combustion chamber 2. Compressed air 15 is led from the compressor 1 by way of a cooling-air re-cooler 4, is cooled and fed to the gas turbine 3 as cooling air 17. The compressor 1 and the gas turbine 3 have a common shaft 12 to which a generator 8 - which can also act as a starting motor - or another load is attached. This shaft 12 is preferably mounted on two bearings (not visible in detail in Fig. 1) which are preferably positioned at the head of the compressor 1 and downstream of the gas turbine 3. Air 13 drawn in is compressed in the compressor 1 and part then flows as compressed air 14 into a housing (not shown in detail). The combustion chamber 2, which is preferably designed as a continuous annular combustion chamber, is also arranged in this housing. The compressed air 14 can also of course be supplied to the combustion chamber 2 from an air reservoir (not shown). The head end of the combustion chamber 2 is provided with a plurality of burners (not shown in detail) distributed around the periphery and preferably designed, as pre-mixing burners. It is also possible per se for diffusion burners to be used here. In order to reduce the emission of pollutants from this combustion, in particular with respect to NO, emissions, it is advantageous to provide an arrangement of pre-mixing burners according to EP-A-0 321809, the subject of the invention of the said publication being an integral component of this description, and, in addition, also the manner of supplying a fuel 16 as described there. With respect to the arrangement of the pre-mixing burners in the peripheral direction of the combustion chamber 2, such an arrangement can if necessary deviate from the customary configuration of similar burners, and, instead, pre-mixing burners of different sizes can be used. This is preferably carried out in such a way that two large pre-mixing burners have one small pre-mixing burner of the same configuration arranged between them in each case. The large pre-mixing burners, which have to perform the function of main burners, are in a size ratio - which is fixed in accordance with the case in question - to the small pre-mixing burners, which are the pilot burners of the said combustion chamber 2, with respect to the burner air flowing through them, i.e. the compressed air 14 from the compressor 1. In the entire load region of the combustion chamber 2 the 4 pilot burners operate as self-feeding pre-mixing burners, in which case the air ratio remains virtually constant. The main burners are switched on or off in accordance with defined guidelines specific to the plant. Since the pilot burners can be run in the entire load range with an ideal mixture, the NO, emissions even with a partial load are very low. With an arrangement of this type, the circulating flow lines in the front region of the combustion chamber 2 come very close to the vortex centres of the pilot burners, so that ignition is possible per se only with these pilot burners. During running up, the quantity of fuel supplied by way of the pilot burners is increased until the latter are balanced out, i.e. until the entire quantity of fuel is available. The configuration is selected in such a way that this point corresponds to the respective load-shedding conditions of the gas-turbine group. The further increase in output then takes place by way of the main burners. At the peak load of the gasturbine group the main burners are also balanced out accordingly. Since the configuration of "small" hot vortex centres initiated by the pilot burners between the "large" cooler vortex centres originating from the main burners is extremely unstable, even with lean-operated main burners in the partial-load range a very good burning is achieved with low CO and UHC emissions in addition to the low NQ, emissions, i.e. the hot vortices of the pilot burners immediately penetrate into the small vortices of the main burners. The combustion chamber 2 can of course comprise a plurality of individual tubular combustion spaces which are likewise arranged in the form of an oblique ring, and sometimes also in the forTn of a helix, around the rotor axis. This combustion chamber 2, irrespective of its design, is and can be arranged geometrically in such a way that it has practically no effect upon the rotor length. The provision (not visible in Fig. 1) of the fuel required for operating the combustion chamber 2 may be made for example by a coal gasification plant cooperating with the gas-turbine group. It is also possible, of course, to draw the fuel used from a primary supply system. If the supply of a gaseous fuel for operating the gas-turbine group is provided by way of a pipeline, the potential can be recovered from the pressure and/or temperature difference between the primary supply system and the consumer supply system with respect to the gas-turbine group or the circuit generally. After pressure release in the gas turbine 3, the waste gases 19 still having a high calorific potential flow through a waste-heat steam generator 5 in which steam is generated in the heat-exchange process and then forms the operating medium of the steam circuit arranged downstream. The waste gases used up calorifically then flow as flue gases 20 into the open air. The waste-heat steam generator 5 has an economizer 24, an evaporator 25 and a superheater 26. The economizer 24 is connected to a steamcollecting drum 6 which feeds the evaporator 25 and receives the steam generated in the evaporator 25 in order to pass it on to the superheater 26. The steam generated in the superheater 26 is fed to a steam turbine 7 by way of a live-steam line 27. The steam turbine 7 is connected to a generator 9 or another load by way of a shaft 12a. It is also possible to mount the gas turbine 3 and the steam turbine 7 jointly on a shaft and to connect a common generator to this shaft. A condenser 10 is connected downstreani of the steam turbine 7 by way of an exhaust-steam line 2 1. The condenser 10 is fed by a cooling medium 22. The condenser 10 is connected to the economizer 24 by way of a line 23 and a pump 11. In accordance with the invention, as illustrated in Fig. 1, in the case of a combination plant of this type it has been found to be exergetically advantageous, not to heat water in the cooling-air re-cooler 4 as known from the prior art, but instead to use steam close to the saturation point. This steam, which has been generated by the economizer 24 and the evaporator 25, is removed from the steam-collecting drum 6 and is fed to the cooling-air re-cooler 4 by way of the line 28. It has been found to be particularly advantageous to operate the cooling-air re-cooler 4 in counter-flow to the cooling air 17. The superheated steam downstream of the cooling-air re-cooler 4 can be used at different points in the power station. In Fig. 1, the superheated steam is supplied to a suitable point in the steam turbine 7 by way of the line 29. In order to increase the output of the gas turbine 3 it is also possible, however, for the steam generated in the cooling-air re-cooler 4 to be supplied together with the compressed air 14 to the combustion chamber 2 by way of the line 30. This connexion variant is illustrated in Fig. 2. The water consumption for injection into the combustion 6 chamber 2 and into the gas turbine 3 is compensated by a water supply device 3 1. The use of saturated steam in the cooling-air re-cooler has the advantage that an exergetically disadvantageous jump in temperature between the cooling air and the water to be evaporated - as hitherto in the prior art by the use of water - is prevented. This jump occurred hitherto when using water, since the evaporation process is isothermic. 7 List of References: 1 compressor 2 combustion chamber 3 gas turbine 4 cooling-air re-cooler waste-heat steam generator 6 steam-collecting drum 7 steam turbine 8 generator 9 generator condenser 11 PUMP 12, 12a shaft 13 air to be compressed, upstream of the compressor 1 14 compressed air, upstream of the combustion chamber 2 compressed air, upstream of the cooling-air re-cooler 4 16 fuel-supply device 17 cooling air from the gas turbine 3 18 hot gases 19 waste gases flue gases 21 exhaust-steam line 22 cooling medium for the condensor 10 23 line 24 economizer evaporator 26 superheater 27 live-steam line 28 line for removing cooled steam 29 line from the cooling-air re-cooler 4 to the steam turbine 7 line from the cooling-air re-cooler 4 to the combustion chamber 2 31 water supply 8 CLAIMS:

1. A method of operating a power station, essentially comprising a gasturbine group, a waste-heat steam generator (5) arranged downstream of the gas-turbine group, and a steam circuit arranged downstream of the waste-heat steam generator (5), wherein the gas-turbine group comprises a compressor (1), a combustion chamber (2), a gas turbine (3), a coolingair re-cooler (4), which cools compressed air (15) of the compressor (1) before feeding into the gas turbine (3) as cooling air (17), and a generator (8) or a load, wherein the waste gases flow out of the gas turbine (3) through the waste-heat steam generator (5) in which the generation of steam takes place in order to drive at least one steam turbine (7) belonging to the steam circuit, and a steam-collecting drum (6) connected to the waste-heat steam generator (5), characterized in that saturated steam from the steam-collecting drum (6) is superheated in the cooling-air re-cooler (4), and is supplied to a suitable point in the power station.

2. A method of operating a power station according to Claim 1, characterized in that the steam of the steam turbine (7) superheated in the cooling-air re-cooler (4) is supplied to a suitable point.

3. A method of operating a power station according to Claim 1, characterized in that the steam of the combustion chamber (2) superheated in the cooling-air re-cooler (4) is supplied together with the compressed air of the compressor (1) to the gas turbine (3).

4. A method of operating a power station according to Claim 2 or 3, characterized in that the superheated steam of the steam-collecting drum (6) in the cooling-air re-cooler (4) is conveyed in counter-flow to the cooling air (17) of the gas turbine (3).

5. A method of operating a power station substantially as herein described with reference to the accompanying drawings.