Combined cycle gas turbine unit with heat pump

Abstract

FIELD: thermal power engineering.SUBSTANCE: used in combined cycle power plants. The combined cycle power plant contains a gas turbine and a steam turbine unit, a waste heat boiler, a circulating water supply system with a cooling tower, as well as a circulating water flow controller connected to a pressure sensor in the condenser, a regulating element on the pressure pipeline and a regulating valve of the recirculation pipeline. The unit is equipped with a heat pump, including an evaporator, compressor, condenser and expansion valve, as well as a bypass pipeline for circulating water with a flow regulator for water directed to the evaporator and bypass. The flow regulator is connected to a refrigerant vapor dryness sensor at the evaporator outlet, a control valve on the water supply pipeline to the evaporator, and a control valve on the bypass pipeline. The evaporator is connected via a heat source to a pressure pipeline to the condenser of a steam turbine, and the condenser of the heat pump is connected via a heated path to the condensate pipeline of the steam turbine plant.EFFECT: increasing the generation of electric power due to additional cooling of the circulating water before the steam turbine condenser and reducing the energy costs for driving the turbine condensate recirculation pump.1 cl, 1 dwg

Description

[0001] Field of technology to which the invention relates

[0002] The invention relates to the field of energy and can be used in combined-cycle plants of thermal power plants to increase the generation of electrical energy.

[0003] Technology Level

[0004] A combined cycle power plant is known (see Tsanev S.V., Burov V.D., Remezov A.N. Gas turbine and combined cycle power plants of thermal power plants: a textbook for universities. - M.: MPEI Publishing House, 2009, Fig. 8.8, p. 278), containing a gas turbine plant including a turbocompressor, a combustion chamber, a gas turbine and an electric generator, a waste heat boiler in which superheater and evaporator heat exchange surfaces and a heat exchange surface of a gas condensate heater are placed sequentially along the flow of gases, a steam turbine plant including a steam turbine with a condenser, a condensate pump, a condensate line, a deaerator and a feed pump, a turbine condensate recirculation pump, an electric generator.

[0005] A disadvantage of the current technical solution is low power generation due to significant heat losses with exhaust steam in the steam turbine. This is due to the lack of a pressure control system in the steam turbine condenser when the circulating water temperature in the circulating water system changes. This is especially significant during the summer, when the circulating water temperature rises. Furthermore, to prevent hydrate corrosion of the heat-exchange surface of the gas condensate heater, the turbine condensate is heated before being fed to the waste heat boiler by recirculating a portion of the turbine condensate heated in the waste heat boiler via a recirculation pump. Driving the recirculation pump consumes electrical energy, which further reduces the efficiency of the combined cycle gas turbine.

[0006] A system for circulating water supply for a power plant with a cooling tower is known (see Russian Federation Patent 2350715, Bulletin No. 9, 2009), comprising a circulation pump, a recirculation pipeline with a control valve connecting a pressure pipeline to a steam turbine condenser with a discharge pressure pipeline to a cooling tower consisting of an exhaust tower and a collection basin, a circulating water flow controller connected to a pressure sensor in the condenser and a circulating water flow controller installed on the pressure pipeline to the steam turbine condenser.

[0007] The disadvantage of this technical solution is the low thermal efficiency of the power plant in the summer due to the low cooling of the circulating water heated in the condenser of the steam turbine in the cooling tower and the lack of additional cooling of the circulating water sent to the condenser of the steam turbine, which causes an increase in the pressure in the condenser of the steam turbine and a decrease in the efficiency of the thermal power plant.

[0008] The proposed invention eliminates these disadvantages.

[0009] Disclosure of the essence of the invention

[0010] The essence of the invention is as follows.

[0011] To increase the power generation of a combined-cycle gas turbine (CCGT) plant, it is advisable to additionally cool the circulating water sent to the steam turbine condenser. To reduce energy costs for driving the turbine condensate recirculation pump, it is necessary to heat the turbine condensate before feeding it to the waste heat boiler. For this purpose, it is proposed to additionally install a heat pump, including an evaporator, compressor, heat pump condenser, and a regulating valve, as well as a bypass line for the circulating water sent to the steam turbine condenser. The evaporator should be connected via the heat source to the pressure line leading to the steam turbine condenser, and the heat pump condenser should be connected via the heated line to the condensate line to heat the turbine condensate before feeding it to the waste heat boiler.

[0012] The flow rate of water directed to the evaporator and passed through the circulating water bypass line is regulated by a water flow controller connected to a refrigerant vapor dryness sensor at the evaporator outlet, a control valve installed on the water supply line to the evaporator, and a regulating electric valve installed on the circulating water bypass line. It is also advisable to regulate the flow rate of circulating water directed to the steam turbine condenser and passed through the recirculation line. For this purpose, it is proposed to connect the circulating water flow controller, connected to a pressure sensor in the condenser and a regulating element installed on the discharge line to the steam turbine condenser, to a regulating valve installed on the recirculation line.

[0013] The technical result of the invention is an increase in the production of electrical energy by a combined cycle plant by implementing additional cooling of the circulating water sent to the condenser of the steam turbine, and a reduction in the cost of electrical energy for driving the turbine condensate recirculation pump by installing a heat pump and a bypass pipeline for circulating water.

[0014] The said technical result in carrying out the invention is achieved in that the known combined cycle gas turbine plant comprises a gas turbine plant including a turbocompressor, a combustion chamber, a gas turbine and an electric generator, a waste heat boiler in which superheating and evaporative heat exchange surfaces and a heat exchange surface of a gas condensate heater are arranged sequentially along the flow of gases, a steam turbine plant including a steam turbine with a condenser, a condensate pump, a condensate line, a deaerator and a feed pump, a turbine condensate recirculation pump, an electric generator, a circulating water supply system including a circulation pump, a recirculation pipeline with a control valve connecting the pressure pipeline to the steam turbine condenser with a drain pressure pipeline to a cooling tower consisting of an exhaust tower and a collection basin, a circulating water flow controller,connected to the pressure sensor in the condenser and the regulating element installed on the pressure pipeline to the condenser of the steam turbine. The peculiarity of the combined cycle power plant is that the combined cycle power plant is made with a heat pump, including an evaporator, a compressor, a heat pump condenser and a regulating valve, and is equipped with a bypass pipeline of circulating water and a flow regulator of water directed to the evaporator and passed through the bypass pipeline of circulating water, connected to a sensor of refrigerant vapor dryness at the outlet of the evaporator, a regulating valve installed on the pipeline for supplying water to the evaporator, and a regulating electric valve installed on the bypass pipeline of circulating water, wherein the circulating water flow regulator, connected to the pressure sensor in the condenser and the regulating element installed on the pressure pipeline to the condenser of the steam turbine, is additionally connected to the regulating valve,installed on the recirculation pipeline, in addition, the evaporator is connected via a heat source to the pressure pipeline to the condenser of the steam turbine, and the condenser of the heat pump is connected via a heated path to the condensate pipeline of the steam turbine plant.

[0015] Brief description of drawings

[0016] Fig. 1 shows a diagram of a combined cycle plant with a heat pump.

[0017] A combined cycle power plant with a heat pump comprises a gas turbine plant including a turbocompressor 1, a combustion chamber 2, a gas turbine 3 and an electric generator 4, a waste heat boiler in which a superheating and evaporative heat exchange surface 5 and a heat exchange surface of a gas condensate heater 6 are arranged sequentially along the flow of gases, a steam turbine plant including a steam turbine 7 with a condenser 8, a condensate pump 9, a condensate line 10, a deaerator 11 and a feed pump 12, a turbine condensate recirculation pump 13, an electric generator 14, a circulating water supply system including a circulation pump 15, a recirculation pipeline 16 connecting a pressure pipeline 17 to a condenser 8 of a steam turbine 7 with a drain pressure pipeline 18 to a cooling tower, consisting of an exhaust tower 19 and a collection basin 20, a heat pump including an evaporator 21, a compressor 22, a heat pump condenser 23 and a regulating valve 24,a bypass pipeline 25 of circulating water, a flow controller 26 of circulating water directed to the condenser 8 and passed through the recirculation pipeline 16, connected to a pressure sensor 27 in the condenser 8, a regulating element 28 installed on the pressure pipeline 17, and a regulating valve 29 installed on the recirculation pipeline 16, a flow controller 30 of water directed to the evaporator 21 and passed through the bypass pipeline 25, connected to a sensor 31 of dryness of refrigerant vapor at the outlet of the evaporator 21, a regulating valve 32 installed on the pipeline for supplying water to the evaporator 21 and a regulating electric valve 33 installed on the bypass pipeline 25.

[0018] Implementation of the invention

[0019] The operation of the combined cycle plant with a heat pump is carried out as follows.

[0020] Turbocharger 1 receives atmospheric air, where it is compressed to the required pressure. The compressed air is then directed into combustion chamber 2, where organic fuel is also supplied. In combustion chamber 2, the organic fuel is combusted, producing highly heated combustion products. The combustion products are mixed with secondary air, forming gases. The resulting gases are directed into gas turbine 3, where they perform the work of the gas turbine cycle, driving turbocharger 1 and electric generator 4. Electric generator 4 generates electrical energy, which is transmitted to the consumer.

[0021] The exhaust gases from the gas turbine 3 are discharged into the heating path of the waste heat boiler, in which the superheating and evaporative heat exchange surfaces 5 and the heat exchange surface of the gas condensate heater 6 are located sequentially along the flow of gases. In the waste heat boiler, heat exchange occurs between the gases, feed water and turbine condensate, while the gases are cooled and discharged into the atmosphere. In the heat-exchange surface of the gas condensate heater 6, the turbine condensate is heated and its main portion is fed to the deaerator 11. To prevent hydrate corrosion of the heat-exchange surface of the gas condensate heater 6, the turbine condensate is heated before being fed to the waste heat boiler by recirculating a portion of the turbine condensate heated in the waste heat boiler using the recirculation pump 13. In the waste heat boiler, the feed water evaporates, generating water vapor, which is superheated.Superheated water vapor is directed to steam turbine 7.

[0022] The steam turbine 7 performs the expansion of water vapor, performing useful work of the steam power cycle, which is spent on driving the electric generator 14. The electric generator 14 generates electrical energy, which is transmitted to the consumer. The water vapor exhausted in the steam turbine 7 is directed to the condenser 8, where circulating water is simultaneously supplied through the pressure pipeline 17 by the circulation pump 15. Heat exchange occurs in the condenser 8, whereby the water vapor condenses, and the circulating water is heated and discharged through the discharge pressure pipeline 18 into the exhaust tower 19 of the cooling tower, where, during the process of heat exchange with the atmospheric air, the circulating water is cooled and discharged into the collection basin 20, and the atmospheric air is heated and discharged into the atmosphere.

[0023] A portion of the circulating water cooled in the exhaust tower 19 of the cooling tower from the collection basin 20 is fed by the circulation pump 15 through the pressure pipeline 17 to the evaporator 21 of the heat pump, while the remaining water passes through the bypass pipeline 25. An intermediate heat transfer fluid (refrigerant) in a liquid state enters the evaporation path of the evaporator 21 under a certain pressure. The saturation temperature of the refrigerant at this pressure is lower than the temperature of the circulating water. This condition allows the refrigerant to evaporate (boil), removing thermal energy from the water. This cools the water. In the evaporator 21, the refrigerant and water are separated by a wall. At the outlet of evaporator 21, the refrigerant is in a gaseous aggregate (vapor) state; the dryness of the refrigerant vapor at the outlet of evaporator 21 is 100%. From evaporator 21, the refrigerant in a vapor state is directed to compressor 22, where the pressure and temperature of the refrigerant vapor increase during the compression process.After compressor 22, refrigerant vapor at elevated pressure and temperature is directed to the condenser of heat pump 23, into the heated tract of which turbine condensate is fed via condensate line 10. In the condenser of heat pump 23, condensation of refrigerant vapor occurs during heat exchange, and the heat of condensation is expended on heating the turbine condensate. In the condenser of heat pump 23, the refrigerant and turbine condensate are separated by a wall. The refrigerant pressure in the condenser of heat pump 23 is maintained by compressor 22 at a constant level, at which the saturation temperature of the refrigerant is higher than the temperature of the heated turbine condensate at the outlet of the condenser of heat pump 23. The turbine condensate heated in the condenser of heat pump 23 is directed to the heat exchange surface of the gas condensate heater 6.After passing through heat pump condenser 23, the refrigerant is in a liquid state and is directed to a pressure-reducing device—regulating valve 24. In regulating valve 24, the refrigerant pressure is reduced to the pressure level in evaporator 21. Thus, the cycle of thermal energy transfer from water to refrigerant and from refrigerant to turbine condensate in the heat pump is closed. The water cooled in evaporator 21 is mixed with circulating water passing through bypass pipe 25.

[0024] The amount of heat q0, kW, spent on evaporation of the refrigerant (the supplied amount of heat q0), is calculated from the heat balance equation of the evaporator:

[0025] q0= G хл ·r= G в ·c в (t1-t2),

[0026] where G хл , r is the flow rate, kg / s, and the heat of vaporization of the refrigerant, kJ / kg; G в , c в- water flow rate into the evaporator, kg / s, and heat capacity of water, kJ / (kg K); t1, t2 - water temperature at the inlet and outlet of the evaporator, °C.

[0027] The temperature t2 of the water at the outlet of the evaporator is calculated from the heat balance equation at known G хл , r, t1, G в and c в .

[0028] During the operation of the combined cycle heat pump unit, the water flow rate at the inlet of the evaporator 21 is maintained at a predetermined level by the controller 30 in accordance with the predetermined dryness value of the refrigerant vapor at the outlet of the evaporator 21, continuously measured by the sensor 31. The signal from the sensor 31 for the dryness of the refrigerant vapor is fed to the input of the controller 30 for the water flow rate directed into the evaporator 21 and passed through the bypass pipeline 25. The controller 30 has two outputs, one output is connected to the regulating valve 32, and the second to the regulating electric valve 33 for the water flow rate, respectively, into the evaporator 21 and passed through the bypass pipeline 25.

[0029] The pressure in the condenser 8 of the steam turbine 7 is maintained at a given level by changing the flow rate of circulating water at the inlet of the condenser 8. During the operation of the combined cycle plant with a heat pump, the pressure in the condenser 8 is continuously measured by the pressure sensor 27. The signal from the pressure sensor 27 is fed to the input of the flow controller 26 of the circulating water directed to the condenser 8 and passed through the recirculation pipeline 16. The flow controller 26 has two outputs, one output is connected to the regulating element 28, and the second - to the regulating valve 29 of the flow rate of circulating water, respectively, into the condenser 8 and passed through the recirculation pipeline 16.

[0030] When a situation arises where the dryness of the refrigerant vapor at the outlet of the evaporator 21 deviates from the set value, the controller 30, based on the signal from the sensor 31, generates command signals to change the flow rate of water supplied to the evaporator 21 and passed through the bypass pipeline 25. In this case, the flow rate of water supplied to the evaporator 21 is set such that the dryness of the refrigerant vapor at the outlet of the evaporator 21, the value of which is continuously measured by the sensor 31, is equal to 100% in all operating modes of the combined cycle plant. That is, during the heat exchange process in the evaporator 21, the entire flow of refrigerant from the liquid state of aggregation will be converted to the vapor state, which ensures maximum cooling of the water in the evaporator 21 and the operation of the heat pump with the maximum value of the conversion coefficient ε:

[0031] ε = q к / P = (q0+ P) / P,

[0032] where q к- the amount of heat, kW, spent on heating the turbine condensate in the condenser of the heat pump; P is the power, kW, spent on driving the compressor (see Heinrich G., Nayork H., Nestler V. Heat pump units for heating and hot water supply: Translated from German by N. L. Korableva, E. Sh. Feldman. Ed. by B. K. Yavnel. - Moscow: Stroyizdat, 1985. pp. 12-13).

[0033] The water cooled in the evaporator 21 is mixed with the flow of circulating water passed through the bypass pipeline 25, the total flow of circulating water at a reduced temperature is directed through the pressure pipeline 17 to the condenser 8 of the steam turbine 7. The supply of circulating water at a reduced temperature to the condenser 8 allows for a decrease in the pressure in the condenser 8, an increase in the heat drop of the water vapor and the useful work performed by the water vapor in the steam turbine 7, which ensures an increase in the electricity generation of the electric generator 14, including reduced (partial) power loads. This makes it possible to reduce the impact of changes in the outside air temperature on the operating parameters of the steam turbine 7 by regulating the temperature of the circulating water at the inlet of the condenser 8 by changing the load of the heat pump.

[0034] At the same time, when there is a deviation from the set value of the pressure in the condenser 8 of the steam turbine 7, according to the signal from the pressure sensor 27, the flow controller 26 generates command signals to change the flow rate of the circulating water supplied to the condenser 8 of the steam turbine 7 and passed through the recirculation pipeline 16. The command signals generated by the flow controller 26 act on the regulating element 28 and the regulating valve 29, which change the flow rate of the circulating water sent to the condenser 8 and passed through the recirculation pipeline 16. The new values ​​of the circulating water flow rates correspond to the set value of the pressure in the condenser 8, the value of which is continuously measured by the pressure sensor 27. By changing the flow rate of the circulating water through the recirculation pipeline 16, the required value of the temperature of the circulating water at the outlet of the cooling tower is achieved, then is at the entrance to the evaporator 21.

[0035] Thus, supplying a combined cycle power plant with a heat pump, including an evaporator, a compressor, a heat pump condenser and a regulating valve, a bypass pipeline of circulating water, a water flow controller connected to a refrigerant vapor dryness sensor at the outlet of the evaporator, a regulating valve installed on the pipeline for supplying water to the evaporator, and a regulating electric valve installed on the bypass pipeline of circulating water, and a circulating water flow controller connected to a pressure sensor in the condenser, a regulating element installed on the pressure pipeline to the condenser of the steam turbine, and a regulating valve installed on the recirculation pipeline, makes it possible to carry out additional cooling of the circulating water sent to the condenser of the steam turbine.This reduces the pressure in the steam turbine condenser, increases the heat drop of the steam, and increases the useful work performed by the steam in the steam turbine. This results in increased power generation by the electric generator, even at reduced (partial) power loads. Furthermore, the turbine condensate is heated in the heat pump condenser before being fed to the heat-exchange surface of the gas condensate heater, further increasing the efficiency of the combined cycle plant by reducing the electrical energy consumption for driving the turbine condensate recirculation pump.

Claims

A combined cycle gas turbine unit comprising a gas turbine unit including a turbocompressor, a combustion chamber, a gas turbine and an electric generator, a waste heat boiler in which a superheater and an evaporator heat exchange surface and a heat exchange surface of a gas condensate heater are arranged sequentially along the flow of gases, a steam turbine unit including a steam turbine with a condenser, a condensate pump, a condensate line, a deaerator and a feed pump, a turbine condensate recirculation pump, an electric generator, a circulating water supply system including a circulation pump, a recirculation pipeline with a control valve connecting the pressure pipeline to the steam turbine condenser with a drain pressure pipeline to a cooling tower consisting of an exhaust tower and a collection basin, a circulating water flow controller connected to a pressure sensor in the condenser and a regulating element,installed on the pressure pipeline to the condenser of the steam turbine, characterized in that the combined cycle plant is made with a heat pump, including an evaporator, a compressor, a condenser of the heat pump and a regulating valve, and is equipped with a bypass pipeline of circulating water and a flow regulator of water directed to the evaporator and passed through the bypass pipeline of circulating water, connected to a sensor of dryness of refrigerant vapor at the outlet of the evaporator, a regulating valve installed on the pipeline of water supply to the evaporator, and a regulating electric valve installed on the bypass pipeline of circulating water, wherein the flow regulator of circulating water, connected to the pressure sensor in the condenser and the regulating element installed on the pressure pipeline to the condenser of the steam turbine, is additionally connected to the regulating valve installed on the recirculation pipeline, in addition,the evaporator is connected via a heat source to the pressure pipeline to the condenser of the steam turbine, and the condenser of the heat pump is connected via a heated path to the condensate pipeline of the steam turbine plant.

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