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
  • F01K23/106—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
  • F01K23/108—Regulating means specially adapted therefor
• • 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
  • F01K7/00—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating
  • F01K7/16—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating the engines being only of turbine type
  • F01K7/18—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating the engines being only of turbine type the turbine being of multiple-inlet-pressure type
  • F01K7/20—Control means specially adapted therefor
• • 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
  • F01K7/00—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating
  • F01K7/34—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating the engines being of extraction or non-condensing type; Use of steam for feed-water heating
  • F01K7/44—Use of steam for feed-water heating and another purpose
• • 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 is directed in general to control systems for steam turbine power plants and in particular this invention is applicable to a power plant which includes a flash tank upstream from a turbine pressure stage.
• the combined cycle power plant typically includes at least one gas turbine power plant, one steam turbine power plant and a heat recovery steam generator (HRSG) which thermally couples the two individual power plants to form a combined cycle power plant.
• the HRSG produces steam for the steam turbine by utilizing gas turbine exhaust gases in a heat exchange relation with turbine feedwater.
• the HRSG is a stack structure which includes serially arranged heating sections, which include a superheater, an evaporator and a high pressure economizer
• the HRSG also includes a steam drum which is connected to the aforementioned heat exchange sections.
• a feedwater preheating cycle which is used as a means for preheating and otherwise conditioning (deaerating) turbine condensate feedwater.
• a flash tank is included in this feedwater preheating circuit in order to provide steam to the deaerator for maintaining deaerator pressure to heat the feedwater to a level such that dew point corrosive chemical reactions cannot damage the heat recovery steam generator and to remove noncondensibles which can cause oxidation within piping and heat recovery steam generator tubing.
• the deaerator is operated at a* constant pressure which is maintained by a pressure' control valve located upstream from the deaerator.
• the flash tank also drains nto the deaerator to provide direct contact heating of the turbine feedwater.
• Excess steam from the flash tank is directed to a low pressure admission and bypass system associated with the steam turbine.
• the low pressure admission and bypass system provides regulation of the flash tank pressure while directing the steam flow either to the condenser through the bypass valve or to a turbine low pressure section through the low pressure admission valve.
• the flash tank pressure set point is a constant established by the value of the crossover steam pressure at peak steam turbine load. Mechanical design of the steam turbine in a tandem compound arrangement makes the crossover piping a convenient steam admission point.
• the invention as proposed will provide a means for relieving the excess energy problem by promoting the increased production of steam which is the input into the low pressure admission section of the steam turbine.
• the benefit obtained is higher efficiency in the cycle while solving tne problem of excess energy during less than peak operation.
• the steam admission valve for the turbine can be maintained at constant position for most operating conditions to admit whatever excess steam that is generated by the flash tank without system upset.
• the admission and bypass valve logic is such that these valves will modulate to maintain stable system operation at a minimum prescribed pressure while under low load conditions.
• Fig. 1 is an overall view of a combined cycle power plant.
• Fig. 2 is a schematic view of a preheater circuit and controls according to the present invention.
• Figs. 3A, 3B, 3C and 3D are flow charts in accordance with the method practiced in the present invention.
• Fig. 1 shows a line diagram of a ccmbined cycle power plant 10 which includes a gas turbine power plant 20, a steam turbine power plant 30 thermally interconnected by a heat recovery steam generator (HRSG) 40.
• the gas turbine power plant includes a compressor 22 which is driven by a gas turbine 24 and an electrical generator 26 also driven by the gas turbine.
• the steam turbine power plant includes a steam turbine including a high pressure section 32, a low pressure section 34 and an electrical generator 36.
• the low pressure section and the high pressure section are interconnected by crossover piping 35.
• the HRSG comprises several heat exchange sections including in ascending order with respect to the direction of gas turbine exhaust gas flow, a superheater 42, an evaporator 44 and a high pressure economizer 46. These heat exchangers are in communication through a steam drum 48.
• This feedwater preheater loop 50 includes a low pressure economizer 52, a flash tank.54 and a deaeratorpreheater 56.
• Condensate pump 60 delivers water from the turbine condenser 38 to the deaerator 56 where it is deaerated and preheated.
• a pump 70 circulates the feedwater from the deaerator to the low pressure economizer 52 whereupon the heated feedwater is introduced into the flash tank 54.
• Boiler feedwater pump 80 circulates heated feedwater from the deaerator holding tank to the high pressure economizer 46.
• the flash tank 54 receives heater water from the HRSG low pressure economizer (not shown) through conduit 53. As this heated water is dumped into the flash tank, a drop in pressure occurs which causes flashing or the production of steam. A portion of this steam is used to pressurize the deaerator through conduit 102 with control valve 104 being positioned by an input from pressure transducer 106 for holding the pressure in the deaerator at a constant pressure.
• Conduit 112 is a water line interconnecting the flash tank with the deaerator holding tank through level control valve 114.
• the control system of the present invention is shown in functional-schematic form indicated by control boxes, arrows and dashed lines representing signal processing and signal, flow.
• P s the pressure setpoint
• P FT the actual flash tank pressure. The latter is obtained from a pressure transducer 122 connected to the flash tank.
• the pressure set point P s is obtained as the output of high value gate (HVG) 124 and may either be a floor pressure or minimum pressure limit; or, a sliding pressure based upon the turbine crossover pressure.
• the floor pressure is based upon the minimum flash tank pressure at which the low pressure bypass valve will be allowed to open. This value in turn is based upon the deaerator sizing, turbine conditions and quantitative expectations of excess energy available from the combined cycle operation. For a steam turbine wherein the crossover pressure may ultimately rise to 130 psia, a floor pressure of
• a second input into the high value gate 124 is the pressure set point integrator P ST derived in the following manner.
• Pressure transducer 123 provides a signal output P CR which when processed is indicative of turbine crossover pressure.
• This signal P CR is supdemented by an offset signal P B from offset signal generator 130 which accounts for system losses such as pipe losses and pressure drops across valves in order to assure that the pressure set point P S based on the crossover pressure will in fact exceed the crossover pressure.
• the two signals are input into a signal summing junction 132 with the output P R representing a pressure reference.
• the pressure reference P R is then input into a setpoint integrator 134 to provide an output signal P SI proportional to the time integral of the pressure change occurring in the turbine crossover.
• This signal is rate limited in the pressure falling direction in order to avoid flash tank upset which could cause boiling and surge in the flash tank water level.
• Maximum limit function 136 in combination with low value gate 138 assures that the pressure set point P S does not exceed flash tank limitations.
• the output of summing junction 120 is a positive or negative signal P E representing the pressure error between the pressure set point P S and the flash tank pressure P FT .
• the pressure error signal is input into proportional plus integral function 140 to produce a pressure control signal P CS .
• the pressure control signal is utilized in a split pressure control circuit similar to the split range controller described in U. S. Patent Application Serial No. 187,153 filed September 15, 1980, for a Steam Turbine Control to Wagner and Priluck, assigned to the assignee of the present invention and incorporated herein by reference.
• Summing junction 150 combines the load control 160 load reference signal L R with the pressure control signal P CS to provide an adjusted load signal L A , Signals L A and L R are gated in a low value gate 162 with the resultant output L C or load control signal for the admission control valve 108.
• the concept of a load reference signal is familiar to those having ordinary skill in the art and represents a computer generated load target based upon thermal and material considerations. This concept is disclosed in the aforementioned Wagner/Priluck patent application as well as in U. S. Patents 4,104,908 and 4,046,002, all assigned to the assignee of the present invention and incorporated herein by reference.
• the low pressure bypass valve will receive a decreasing positive control signal P CS calling for a more closed valve position to maintain flashtank pressure which is being depleted by the increased flow to the turbine crossover through the admission control valve 108.
• P CS positive control signal
• the low pressure bypass valve 110 is completely closed, pressure control of the flash tank is transferred to the admission control valve. This occurs because the pressure control signal P CS goes negative causing the load reference to be ramped full positive which then means the load adjust signal L A will be passed through low value gate 162 to provide a load control signal L C .
• a ramp signal 163 is responsible for uprating the speed/load signal whenever the output from summing junction 150 L A is less than the speed/load signal L R or (A ⁇ R).
• FIGs. 3A, 3B, 3C and 3D are flow diagrams illustrative of the method of the present invention and capable of being transformed into computer software by those persons having a skill in the computer arts.
• the program is called out as a low pressure pressure load (LPPL) and commences by reading the turbine crossover pressure P CR which is then offset by a pressure bias P B in order to assure that the pressure reference P R will exceed the actual crossover pressure.
• the set point integrator is updated with the new pressure reference to produce a new pressure set point integrator P SI output which is then compared with maximum and minimum set point values.
• the appropriate pressure set point P S is chosen depending on whether P SI is above or below or between the rainimum-maximum limits.
• the G SI term in the set point integrator equation determines the maximum integrator reset rate which is chosen so as to avoid unacceptable surge conditions in the flash tank under rapid system depressurization.
• the program between states L 1 and L 2 (Fig. 3B) is used to derive a pressure error signal P E .
• the involved steps include reading the flash tank pressure P FT and subtracting the pressure set point P S from the flash tank pressure P FT .
• the error signal limited to a value between +1 low pressure bypass full open and -1 admission control valve full closed.
• the program between states L 2 and L 3 calculates a control signal P CS on the basis of the error signal.
• the P CS value is applied to the low pressure bypass valve actuator and if positive will position the valve proportionately. If P CS is negative, the valve remains closed.
• the same signal P CS is used to calculate a load adjust signal L A by adding it to the load reference L R .
• the program at L 3 (Fig. 3D) completes the control system by determining whether the load adjust L A or L R will apply to the admission control valve as a load control signal L C . The lower of the two signal dominates and if the pressure control signal P CS is negative, the load adjust signal L A will dominate to position the admission control valve.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Control Of Turbines (AREA)
• Engine Equipment That Uses Special Cycles (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=23257308

Family Applications (1)

Country Status (7)

Cited By (4)

Families Citing this family (13)

Citations (2)

Family Cites Families (6)

• 1981
  • 1981-11-19 US US06/322,988 patent/US4402183A/en not_active Expired - Fee Related
• 1982
  • 1982-07-06 WO PCT/US1982/000902 patent/WO1983001812A1/en active IP Right Grant
  • 1982-07-06 EP EP82902491A patent/EP0093724B1/en not_active Expired
  • 1982-07-06 JP JP82502455A patent/JPS58501953A/ja active Granted
  • 1982-07-06 DE DE8282902491T patent/DE3277316D1/de not_active Expired
  • 1982-09-21 MX MX194475A patent/MX158938A/es unknown
  • 1982-11-18 KR KR8205206A patent/KR890001170B1/ko not_active Expired

Patent Citations (2)

Also Published As

Similar Documents

Legal Events