Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
  • F01K23/00—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids
  • F01K23/02—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled
  • F01K23/06—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle
  • F01K23/10—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle with exhaust fluid of one cycle heating the fluid in another cycle
  • F01K23/103—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle with exhaust fluid of one cycle heating the fluid in another cycle with afterburner in exhaust boiler
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
  • F01K23/00—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids
  • F01K23/02—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled
  • F01K23/06—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle
  • F01K23/10—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle with exhaust fluid of one cycle heating the fluid in another cycle
  • F01K23/106—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle with exhaust fluid of one cycle heating the fluid in another cycle with water evaporated or preheated at different pressures in exhaust boiler
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E20/00—Combustion technologies with mitigation potential
  • Y02E20/16—Combined cycle power plant [CCPP], or combined cycle gas turbine [CCGT]

Definitions

• This invention concerns a steam turbine in which heat is extracted from hot exhaust gases from a gas turbine, and the extracted heat used to heat steam to drive the steam turbine.
• the invention is particularly, but not exclusively, applicable to combined cycle gas turbine (CCGT) electrical power generation.
• CCGT combined cycle gas turbine
• a conventional CCGT power generation unit comprises a gas turbine which drives an electrical generator to produce electrical power. Hot exhaust gases from the gas turbine are ducted into a heat recovery steam generator (HRSG) and steam raised in the HRSG is supplied to a steam turbine which also drives an electrical generator to produce further electrical power.
• HRSG heat recovery steam generator
• the ratio of steam turbine power to gas turbine power is about 0.6.
• a burner in the exhaust duct at a position therein between the gas turbine and the first part of any superheater arrangement encountered by the exhaust gases in the HRSG; the superheater arrangement being to heat high pressure steam for driving a high pressure cylinder of the steam turbine, and, in respect of the direction of exhaust gas flow along the duct, the burner being upstream of said first part of the superheater arrangement.
• the burner burns fluid fuel, for example fuel gas, and provides supplementary heat to increase steam production, but the amount of fuel used is relatively small compared with the amount used in the gas turbine. Supplementary firing in this manner is used mainly in combined heat and power plants to raise additional steam for process or heating use.
• An object of the invention is to provide a steam turbine in which the need to raise steam at a multiplicity of pressure levels can be avoided, and in which steam at optimum conditions of high pressure and temperature can be raised in an HRSG using heat from exhaust gases from a gas turbine, the steam turbine comprising a first cylinder arrangement and a second cylinder arrangement, the first cylinder arrangement being arranged to be driven by steam supplied thereto at a first pressure, the second cylinder arrangement being arranged to be driven by steam supplied thereto at a second pressure, the first pressure being greater than the second pressure, and the HRSG having a flexibility of heat input thereto enabling steam for driving the second cylinder arrangement to be produced to have a temperature and a second pressure which more closely approach an optimum for driving the second cylinder arrangement.
• a steam turbine comprises a first cylinder arrangement and a second cylinder arrangement,said first cylinder arrangement being provided to be driven by steam supplied to the first cylinder arrangement at higher pressure than steam supplied to said second cylinder arrangement to drive the second cylinder arrangement whereby said steam supplied to the second cylinder arrangement is at a lower pressure relative to said higher pressure, a superheater arrangement to heat the higher pressure steam to be supplied to said first cylinder arrangement, a reheater arrangement to heat the lower pressure steam to be supplied to said second cylinder arrangement and said reheater arrangement being arranged to receive steam from said first cylinder arrangement to be supplied as steam at said lower pressure to said second cylinder arrangement, said superheater arrangement comprising at least one superheater heat exchanger in which the steam is to be heated, a gas turbine and passage means to convey away from the gas turbine hot exhaust gases, said superheater heat exchanger and said reheater heat exchanger being each disposed in said passage means to receive heat from said exhaust gases, and, with respect to the direction of flow of the exhaust gases along the
• the heat source means may comprise burner means for burning fluid fuel.
• Additional burner means may be provided in the passage means at a position or positions upstream and/or downstream of the first mentioned burner means.
• the fluid fuel may be fuel gas.
• Figure 1 is a diagrammatic representation of a first embodiment of a steam turbine formed according to the invention
• Figure 2 is a diagrammatic representation of a variation of a part of the embodiment shown in Figure l;
• Figure 3 is a diagrammatic representation of part of a second embodiment of a steam turbine formed according to the invention.
• Figure 4 is a diagrammatic representation of part of a third embodiment of a steam turbine formed according to the invention.
• FIG. 1 illustrates a combined cycle gas turbine (CCGT) in which a gas turbine 2 drives an electric power generator 4, and a steam turbine 6, driven by steam raised in a heat recovery steam generator (HRSG) 8, drives an electric power generator 10.
• Gas turbine 2 comprises an air compressor 12, a combustion chamber 14 supplied with fluid fuel by a supply 16, and a turbine section 18 from which the hot exhaust gases leave along the direction of arrow A and flow along a passage or duct to leave in the direction of arrow B, ultimately to atmosphere.
• the generator 4 can be driven by drive taken off from the other end of the gas turbine 2 i.e. the end comprising the turbine section 18.
• Various tubular coils or heat exchangers 22, 24, 26, 28, 30 and 32 of the heat recovery steam generator 8 are mounted in the duct 20 to receive heat from the hot exhaust gases from the gas turbine 2 to heat water and steam in the heat recovery steam generator to drive the steam turbine 6 which comprises a high pressure cylinder arrangement 34 to be driven by steam at high pressure, an intermediate pressure cylinder arrangement 36 to be driven by intermediate pressure steam, and a low pressure cylinder arrangement 38 to be driven by steam at low pressure.
• the expressions "high pressure steam”, “intermediate pressure steam”, and "low pressure steam” are well understood by those skilled in the art.
• steam exhausting from the low pressure cylinder arrangement 38 passes to a condenser 40 and the resultant water is pumped along the system by a pump 42. Downstream of the pump 42 make-up water may be added through a water supply 44 to compensate for water or steam loss. Then the water passes through a boiler feed water heater 22 and is supplied to a deaerator 46 comprising in known manner a heat exchanger (not shown) supplied with low pressure steam from a low pressure boiler or low pressure steam and water drum 48 from which water is converted into steam in a low pressure evaporator 24. From the deaerator 46 the boiler feed water is pumped by a pump 49 to an economiser 26 and passes to be converted to steam in a high pressure evaporator 28.
• the steam and any liquid water therein passes to a high pressure boiler or high pressure steam and water drum 50 (known per se) which has known means for monitoring a predetermined water level in the drum 50.
• a pump 52 is used to recirculate water from drum 50 to the inlet side of the high pressure evaporator 28.
• the drum 50 also includes a blowdown valve and outlet 54.
• At least one burner 56 arranged to be supplied with fluid fuel is mounted in the duct 20 in a position between the superheater 32 and the reheater 30.
• the burner 56 is upstream of the reheater 30 and downstream of the superheater 32.
• At least one other fluid fuel burner 58 is provided in the duct 20 between the reheater 30 and the high pressure evaporator 28 to inject further heat into the gas turbine exhaust gases to ensure enough heat is imparted to at least the high pressure evaporator 28 to raise the steam supplied to the drum 50 to a desired temperature to improve the chances of the steam from the superheater 32 and reheater 30 having the desired characteristics of temperature and pressure to drive the steam turbine in the desired manner.
• At least one further fluid fuel burner 60 can be provided in the duct 20 between the gas turbine 6 and the superheater 32.
• the burner 60 may be used to inject heat into the exhaust gases to ensure that the high pressure steam generated has the desired characteristics of temperature and pressure to substantially match the design requirements of the steam turbine 6. But the amount of heat needed to be supplied by the burner 60 will usually be small if it is required at all.
• the temperature of the exhaust gases leaving the gas turbine 2 may be of the order of 540°C and it may be desired to raise the steam in the superheater 32 to a temperature of substantially 538°C, which is somewhat close to the exhaust temperature.
• the temperature of the exhaust gases at the superheater 32 may not be quite sufficient to ensure that the high pressure steam temperature has the desired value. Therefore it may be necessary to use the burner 60 to provide a small amount of "top-up" heat. After the exhaust gases have passed the superheater 32 and are about to reach the reheater 30 the temperature drop in the exhaust gases may be of the order of 100° or 200°C. If it is desired that the temperature of the intermediate pressure from the reheater also have a temperature of 538°C, the provision of the burner 56 is a necessity to ensure that enough heat be injected into the exhaust gases to ensure that the reheater 30 is at the appropriate desired temperature.
• the burner 58 can be used to impart heat to the exhaust gases passing the high pressure evaporator 28 and the economiser 26 to meet their heat requirements so as to produce steam at a temperature and pressure which are sufficiently high to ensure that the step-up to the high pressure and temperature desired for the steam output from the superheater 32 can be attained at the superheater.
• the system in Figure 1 may be designed to give a steam turbine electrical power output to gas turbine electrical power output ratio of substantially 1.0, with steam leaving the superheater 32 at a pressure of substantially 165 bar and a temperature of substantially 538°C and the steam leaving the reheater 30 at a temperature of substantially 538°C.
• the temperatures in the duct 20 are not excessive, for example below 700°C.
• a relatively inexpensive heat withstanding duct 20 can be used, because the cost of high temperature resistant materials for the duct need not be incurred. If, for example,only the burner 60 were present, it would be necessary to raise the temperature of the gas turbine exhaust gases at the burner 60 and superheater 32 to some hundreds of degrees Celsius above the temperature of the exhaust gases leaving the gas turbine 2. That is because it is desirable to ensure that the exhaust gases are still sufficiently hot when they reach the reheater 30 (and preferably the high pressure evaporator 28 and economiser 26) . Thus in the region of the burner 60 and superheater 32 the duct would have to be made from very high temperature resistant material.
• the burner 56 is present it is only required to raise the temperature of the exhaust gases to a value sufficient to meet the needs of the reheater 30, which are not excessively high, e.g. below 700°C and when the burner 58 is present it too does not need to raise the temperature of the exhaust gases to an excessive value to match the heating needs of the high pressure evaporator 28 or the economiser 26.
• boiler feed water heater 22 in Figure 1 is omitted. Instead, boiler feed water is initially heated by one or more preheaters 62 each comprising a heat exchanger in which the water is heated by heat transferred thereto from steam taken off from either or both the intermediate pressure cylinder arrangement 36 and the low pressure cylinder arrangement 38 and after the preheater(s) sent to the deaerator 46 via pipe 64.
• preheaters 62 each comprising a heat exchanger in which the water is heated by heat transferred thereto from steam taken off from either or both the intermediate pressure cylinder arrangement 36 and the low pressure cylinder arrangement 38 and after the preheater(s) sent to the deaerator 46 via pipe 64.
• the high pressure evaporator arrangement 28 comprises, in relation to the direction of exhaust gases flow A, a downstream high pressure evaporator 28a and in parallel therewith an upstream high pressure evaporator 28b, with the burner 58 disposed between them.
• the superheater arrangement 32 comprises a downstream superheater 32a and in series therewith an upstream superheater 32b.
• the downstream superheater 32a is downstream of the reheater 30 and upstream of the upstream evaporator 28b.
• At least one fourth fluid fuel burner 66 is disposed in the duct between the reheater 30 and the downstream superheater 32a.
• the burner 66 imparting heat to the exhaust gases to replace that extracted by the reheater 30 and bring the temperature of the exhaust gases at the downstream superheater 32a up to a value meeting the requirements of the superheater 32a.
• the system in Figure 3 may be designed, due at least in part to the supplementary firing provided by the burner 66, to give a steam turbine electrical power output to gas turbine electrical power output ratio of substantially 1.5 with the steam leaving the upstream superheater 32b at a pressure of substantially 165 bar and a temperature of substantially 538°C and the steam leaving the reheater 30 at a temperature of substantially 538°C.
• the embodiment shown in Figure 4 uses supercritical steam from the superheater arrangement 32 to drive the steam turbine 6.
• feed water at a pressure greater than a critical pressure of about 210 bar is passed through heat exchanger 68 disposed in the duct 20.
• That heat exchanger 68 forms a convective heater in which the water flashes into steam without the need of latent heat.
• This supercritical steam passes to a separator 70 in which water droplets carried over separate from the steam, and the separated water is returned to the deaerator 46.
• the reheater arrangement comprises an intermediate pressure reheater 30a and a low pressure reheater 30b both at substantially the same position along the duct 20. Whilst reheater 30a heats steam from the high pressure cylinder arrangement 34 and feeds it to the intermediate pressure cylinder arrangement 36, the low pressure reheater 30b heats steam from the intermediate pressure cylinder arrangement and feeds that steam to the low pressure cylinder arrangement 38.
• Separator 70 supplies steam to the superheater arrangement 32 comprising the superheaters 32a and 32b in series, the downstream superheater 32a being downstream of the reheaters 30a and 30b, and the upstream superheater 32b being upstream of the reheaters, with the burner 56 being between the reheaters and the upstream superheater 32b.
• the system in Figure 4 may be designed to give a steam turbine electrical power output to gas turbine electrical power output ratio of substantially 1.0, with steam leaving the upstream superheater 32b at a pressure of substantially 310 bar and at a temperature of substantially 566°C which is substantially the same temperature at which steam is supplied from each of the reheaters 30a and 30b.
• the amount of air in the exhaust gases emerging from the gas turbine 6 may provide sufficient oxygen to support combustion of the fluid fuel at each of the burners 56, 58, 60 and 66 referred to above. Or if extra oxygen is required additional air may be introduced into the duct 20, for example in the vicinity of any of the burners, or air may be pre-mixed with the fluid fuel supplied to any burner.
• the fluid fuel referred to above supplied to the gas turbine 6 and each or any of the burners 56, 58, 60 or 66 may be a liquid fuel, or a fuel gas, for example natural gas.
• the gas turbine 2 and the steam turbine 6 drive electric generators 4 and 10, as described above, which may generate electric power in a power station for transmission therefrom.
• an existing steam turbine (say for example in an existing power station which may have originally been fired by coal or oil) having already defined operating steam characteristics can be adapted by substituting gas turbine exhaust gas firing as described for the original form of firing.
• an existing steam turbine can have the combination of the gas turbine 2 and an above described heat recovery steam generator 8 (with at least burner 56) retrofitted to provide steam of the appropriate characteristics with which the steam turbine 10 was originally designed to work. From the above disclosure it will be appreciated that the application of the invention overcomes many of the limitations of the conventional combined cycle gas turbine arrangement and provides:
• the ways in which the invention may be utilised as described above permits the selection of optimum steam conditions,including multiple reheat, for a wide variety of situations and give high efficiency without the need for a complex multiplicity of steam raising pressure levels.
• Application to the retrofitting to existing power stations may be particularly beneficial as the steam conditions required by the existing steam turbine can be met and thus full advantage taken of the performance the steam turbine was originally designed to attain.
• a range of possible steam generator arrangements have been investigated and the results suggest that any gas turbine can be matched with any required steam conditions and arrangement of steam circuits using the burner 56 and possibly one or more other burners firing at various locations along the gas turbine exhaust gases duct.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Engine Equipment That Uses Special Cycles (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 1993
  • 1993-05-12 GB GB939309735A patent/GB9309735D0/en active Pending
• 1994
  • 1994-04-29 IN IN352MA1994 patent/IN183919B/en unknown
  • 1994-05-11 GB GB9409415A patent/GB2277965B/en not_active Expired - Fee Related
  • 1994-05-11 AU AU66858/94A patent/AU674751B2/en not_active Ceased
  • 1994-05-11 EP EP94914510A patent/EP0698177A1/en not_active Withdrawn
  • 1994-05-11 WO PCT/GB1994/001013 patent/WO1994027034A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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