Operation of combined cycle plant with heat pump

Abstract

FIELD: thermal power engineering.SUBSTANCE: used in the operation of combined cycle power plants. The method involves feeding fuel and compressed air into a combustion chamber, expanding the resulting gases in a gas turbine to generate electricity, and discharging them into a waste heat boiler. The steam generated in the boiler is sent to a steam turbine, and the exhaust steam is condensed in a condenser through heat exchange with circulating water, which is cooled in a cooling tower. In this case, the pressure in the condenser is measured and the flow rate of circulating water at its inlet is regulated using a flow regulator. Part of the circulating water is passed through a recirculation pipeline with a control valve into the discharge pressure pipeline to the cooling tower. A distinctive feature is that the circulating cooling water is divided into two streams before being fed to the condenser. One flow is directed to the heat pump evaporator, and the second is passed through the bypass pipeline. In this case, the dryness of the refrigerant vapor at the outlet of the evaporator is measured and the ratio of the flow rates of the specified flows is regulated by changing the degree of opening of the control valve at the inlet to the evaporator and the electric valve on the bypass. In the evaporator, the circulating water is cooled by boiling the refrigerant, the vapor of which is compressed by the compressor and sent to the condenser of the heat pump, where the turbine condensate is heated before being fed to the waste heat boiler. When regulating the pressure in the condenser, the degree of opening of the control valve on the recirculation pipeline of the cooling tower is additionally changed.EFFECT: increasing the generation of electric power due to additional cooling of the circulating water before the 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 known method of operation of a combined-cycle plant (see Tsanev S.V., Burov V.D., Remezov A.N. Gas turbine and combined-cycle plants of thermal power plants: a textbook for universities. - M.: MPEI Publishing House, 2009, Fig. 8.8, p. 278), according to which organic fuel and atmospheric air compressed in a turbocompressor are fed into the combustion chamber of a gas turbine plant, where the process of combustion of organic fuel takes place with the formation of combustion products heated to a high temperature, the combustion products are mixed with secondary air, the gases formed during the mixing process are sent to a gas turbine, in the gas turbine the process of expansion of gases takes place and the work of the gas turbine cycle is performed, spent on driving the turbocompressor and electric generator, the exhaust gases in the gas turbine are discharged into the heating tract waste heat boiler,in which, in sequence along the flow of gases, a steam superheater and an evaporator heat exchange surface and a heat exchange surface of a gas condensate heater are placed, turbine condensate and feed water are fed into the heated path of the waste heat boiler, a recirculation of a portion of the turbine condensate heated in the waste heat boiler is carried out by means of a recirculation pump, in the waste heat boiler, in the process of heat exchange between gases and feed water, water vapor is generated, which is superheated and sent to a steam turbine, and the exhaust gases are discharged into the atmosphere, in the steam turbine, the process of expansion of water vapor takes place and useful work of the steam power cycle is performed, spent on driving an electric generator, the water vapor exhausted in the steam turbine is discharged into a condenser, where, in the process of heat exchange with circulating water, condensation of water vapor and heating of circulating water are carried out.

[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 method for operating a power plant's circulating water supply system with a cooling tower is known (see Russian Patent 2350715, Bull.No. 9, 2009), through which the water vapor exhausted in the steam turbine is discharged into a condenser, where, in the process of heat exchange with circulating water, condensation of water vapor and heating of the circulating water are carried out, which is discharged through a drain pressure pipeline into the exhaust tower of the cooling tower, where, in the process of heat exchange with atmospheric air, the circulating water is cooled and drained into a collection basin, and the heated atmospheric air is discharged into the atmosphere, continuous monitoring is carried out and maintained at a given level in accordance with the pressure in the condenser of the steam turbine, the flow rate of circulating water at the inlet to the condenser by means of a circulating water flow regulator connected to a pressure sensor in the condenser and a regulating element installed on a pressure pipeline to the condenser of the steam turbine, part of the circulating water is passed through a recirculation pipeline with a regulating valve.

[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 the implementation of the invention is achieved by the fact that in the known method of operation of a combined cycle plant, according to which organic fuel and atmospheric air compressed in a turbocompressor are supplied to the combustion chamber of a gas turbine plant, where the process of combustion of organic fuel is carried out with the formation of combustion products heated to a high temperature, the combustion products are mixed with secondary air, the gases formed in the mixing process are sent to a gas turbine, in the gas turbine the process of expansion of gases is carried out and the work of the gas turbine cycle is performed, spent on driving the turbocompressor and the electric generator, the exhaust gases in the gas turbine are discharged into the heating tract of the waste heat boiler, in which the steam superheater and evaporative heat exchange surfaces and the heat exchange surface of the gas condensate heater are placed sequentially along the flow of gases,turbine condensate and feedwater are fed into the heated path of the waste heat boiler, a portion of the turbine condensate heated in the waste heat boiler is recirculated by means of a recirculation pump, in the waste heat boiler, during the process of heat exchange between gases and feedwater, water vapor is generated, which is superheated and sent to the steam turbine, and the exhaust gases are discharged into the atmosphere, in the steam turbine, the process of expansion of water vapor occurs and useful work of the steam power cycle is performed, spent on driving an electric generator, the water vapor exhausted in the steam turbine is discharged into a condenser, where, in the process of heat exchange with circulating water, condensation of water vapor and heating of circulating water are carried out, which is discharged through a drain pressure pipeline into the exhaust tower of the cooling tower, where, during the process of heat exchange with atmospheric air, the circulating water is cooled and drained into a collection basin, and the heated atmospheric air are released into the atmosphere,The flow rate of circulating water at the condenser inlet is continuously monitored and maintained at a predetermined level in accordance with the pressure in the steam turbine condenser by means of a circulating water flow controller connected to a pressure sensor in the condenser and a regulating element installed on the pressure pipeline to the steam turbine condenser, a portion of the circulating water is passed through a recirculation pipeline with a regulating valve. The peculiarity lies in the fact that the combined cycle power plant is implemented with a heat pump, including an evaporator, a compressor, a heat pump condenser and a regulating valve, and is supplied with a bypass pipeline of circulating water and the flow rate of water into the evaporator is continuously monitored and maintained at a predetermined level in accordance with the predetermined dryness of the refrigerant vapor at the outlet of the evaporator by means of a flow controller of water directed to the evaporator and passed through the bypass pipeline of circulating water,connected to a refrigerant vapor dryness sensor at the outlet of the evaporator, a regulating valve installed on the water supply pipeline to the evaporator, and a regulating electric valve installed on the bypass pipeline of the circulating water, while in order to maintain the pressure in the condenser of the steam turbine at a given level, the circulating water flow regulator is additionally connected to a regulating valve installed on the recirculation pipeline, in addition, in the condenser of the heat pump, the turbine condensate is heated before being fed to the heat exchange surface of the gas condensate heater.

[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 method is implemented 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 gas condensate heater 6, turbine condensate is heated, and the bulk of it is fed to deaerator 11. To prevent hydrate corrosion of the heat-exchange surface of gas condensate heater 6, turbine condensate is preheated before being fed to the waste-heat boiler by recirculating a portion of the turbine condensate heated in the waste-heat boiler via recirculation pump 13. In the waste-heat boiler, feedwater evaporates, generating superheated steam. The superheated steam is fed to steam turbine 7.

[0022] The steam turbine 7 expands water vapor, performing useful work in the steam power cycle, which is expended 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 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 sent 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, refrigerant vapor condenses 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 refrigerant saturation temperature 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 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 line 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 given level by the controller 30 in accordance with the given value of the refrigerant vapor dryness at the outlet of the evaporator 21, continuously measured by the sensor 31. The signal from the sensor 31 of the refrigerant vapor dryness is fed to the input of the controller 30 of 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 of 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 at the outlet of the evaporator 21, the dryness of the refrigerant vapor, 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 vaporous 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 factor :

[0031] = 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. Supplying circulating water to the condenser 8 at a reduced temperature makes it possible to reduce the pressure in the condenser 8, increase the heat drop of water vapor and the useful work performed by 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, the flow controller 26 generates command signals based on the signal from the pressure sensor 27 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 method of operating a combined-cycle plant, according to which organic fuel and atmospheric air compressed in a turbocompressor are fed into the combustion chamber of a gas turbine plant, where the process of combustion of the organic fuel takes place with the formation of combustion products heated to a high temperature, the combustion products are mixed with secondary air, the gases formed during the mixing process are sent to a gas turbine, in the gas turbine the process of expansion of gases takes place and the work of the gas turbine cycle is performed, spent on driving the turbocompressor and electric generator, the exhaust gases in the gas turbine are discharged into the heating path of the waste heat boiler, in which the superheating and evaporative heat exchange surfaces and the heat exchange surface of the gas condensate heater are located sequentially along the flow of gases, turbine condensate and feed water are fed into the heated path of the waste heat boiler,a portion of the turbine condensate heated in the waste heat boiler is recirculated by means of a recirculation pump; in the waste heat boiler, during the process of heat exchange between gases and feed water, water vapor is generated, which is superheated and sent to the steam turbine, and the exhaust gases are discharged into the atmosphere; in the steam turbine, the process of expansion of water vapor takes place and useful work of the steam power cycle is performed, spent on driving the electric generator; the water vapor exhausted in the steam turbine is discharged into a condenser, where, during the process of heat exchange with circulating water, condensation of water vapor and heating of circulating water are carried out, which is discharged through a drain pressure pipeline into the exhaust tower of the cooling tower, where, during the process of heat exchange with atmospheric air, the circulating water is cooled and drained into a collection basin, and the heated atmospheric air is discharged into the atmosphere,continuously monitor and maintain at a given level in accordance with the pressure in the steam turbine condenser the flow rate of circulating water at the condenser inlet by means of a circulating water flow controller connected to a pressure sensor in the condenser and a regulating element installed on the pressure pipeline to the steam turbine condenser, a portion of the circulating water is passed through a recirculation pipeline with a regulating valve, characterized in that the combined cycle plant is implemented with a heat pump including an evaporator, a compressor, a heat pump condenser and a regulating valve, and is supplied with a bypass pipeline of circulating water, and continuously monitor and maintain at a given level the flow rate of water into the evaporator in accordance with the given dryness of the refrigerant vapor at the outlet of the evaporator by means of a flow controller of water directed to the evaporator and passed through the bypass pipeline of circulating water,connected to a refrigerant vapor dryness sensor at the outlet of the evaporator, a regulating valve installed on the water supply pipeline to the evaporator, and a regulating electric valve installed on the bypass pipeline of the circulating water, while in order to maintain the pressure in the condenser of the steam turbine at a given level, the circulating water flow regulator is additionally connected to a regulating valve installed on the recirculation pipeline, in addition, in the condenser of the heat pump, the turbine condensate is heated before being fed to the heat exchange surface of the gas condensate heater.

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