RU2561770C2 - Operating method of combined-cycle plant - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: invention relates to power industry. An operating method of a combined-cycle plant (CCP) is provided by designing of an after-heating heat exchanger for cooling of a steam-gas mixture at the high pressure turbine outlet in the form of two in-series located heat exchangers with the corresponding redistribution of flows of heated water, from which cooling water vapour is generated. CCP operating method involves an arrangement system of steam closed and open cooling of hot elements of a flow part of the gas turbine. Besides, CCP operating method provides for operation in a heat-extraction mode with simultaneous generation of electrical and heat energy.

EFFECT: invention allows improving operating efficiency of the plant.

4 cl, 4 dwg

Description

The invention relates to a power system, in particular to combined cycle plants (CCGT) operating on a mixture of steam and fuel combustion products.

There is a known method of operation of a gas turbine installation, which consists in compressing air, burning fuel in it, mixing the resulting combustion products with additional compressed air and taking part of the combustion products after their expansion in the turbine and their joint compression with additional compressible air while reducing the flow rate of the latter (see copyright certificate SU No. 1744290, class F02C 3/34, 06/30/1992).

This method, although it implements a rational combustion process, but requires additional energy for additionally compressible cooling air, which reduces the efficiency of the process.

There is a known method of CCGT operation, including the formation of a working steam-gas mixture, expansion of the latter in a turbine with the completion of work, drainage of the steam-gas mixture flow by introducing water with a temperature below the condensation temperature of water in the gas-vapor mixture, removal of dried gases and condensate drain (see copyright certificate SU No. 547121, CL F01K 21/04, 12/07/1982).

However, with this method of operation of the installation, large heat losses occur (latent heat of condensation), since not all water is removed from the gas-vapor mixture and water due to undercooling of the gas-vapor mixture, since it is necessary to supply a large amount of cold water, which, in turn, leads to that the drained water from the condenser will also be cold, which means that the heat returned through the recycling circuit will be reduced, i.e. more heat will be lost to the environment and more energy will need to be spent to produce cold water.

The closest to the invention in technical essence and the achieved result is the CCGT operation method, which consists in compressing the ambient air with intermediate cooling by a compressor, which is fed into the combustion zone of the combustion chamber, into which fuel is simultaneously supplied, and the resulting combustion products are mixed in the mixing zone of the chamber combustion with steam to obtain a gas-vapor mixture at the outlet of the combustion chamber, which, as a working fluid, is sent to a gas-vapor turbine, in which the energy of the gas-vapor flow the new mixture is converted into mechanical energy of rotation of the turbine rotor, then the water vapor is condensed in a vacuum condenser, the vacuum in which is created by a vacuum compressor that removes non-condensed gaseous products of combustion, and the condensed water is heated in heat exchangers (see patent RU No. 2476690, class F01K 21 / April 4, 2011).

This method of CCGT operation ensures that the vapor-gas mixture does not overheat at the inlet to the vacuum condenser. This method of operation of a CCGT unit provides at the same time a high level of profitability of a CCGT unit, since it allows the operation of a CCGT unit with a significantly higher pressure in the combustion chamber at the initial temperature of the working fluid in front of the turbine, in comparison with the currently operated classical binary CCGT units. With an increase in the design pressure in the combustion chamber, the design profitability of the CCGT unit operating according to this method grows.

However, this growth is constrained by the fact that in this method, the parameters of the water at the inlet to the warming heat exchanger for cooling the vapor-gas mixture at the outlet of the high-pressure turbine (HPH) already correspond to the parameters of water in a two-phase state. It is necessary to maintain the temperature of the gas-vapor working mixture at the outlet of this warming heat exchanger above the saturation temperature of the water supplied to it. With an increase in the design pressure in the combustion chamber, it is necessary to increase the pressure of the cooling steam and, accordingly, the water pressure at the inlet to the heating heat exchanger. With an increase in the design pressure in the combustion chamber, the saturation temperature of the feed water rises, and it is necessary to increase the temperature of the vapor-gas mixture at the outlet of the warming heat exchanger and, therefore, at the outlet of the vapor-gas mixture from the fuel assembly. For this reason, an increase in the heat transfer in the HPT due to the increase in the calculated initial pressure at the turbine inlet is accompanied by a partial decrease in the heat transfer in the HPT due to an increase in the calculated temperature and pressure of the working fluid at the exit of the HPT. Ultimately, this circumstance leads to a decrease in the growth rate of the design efficiency of the CCGT unit, due to an increase in the pressure of the working fluid in front of the first stage of the turbine.

In the description of the CCGT operation method according to patent RU No. 2476690, the cooling scheme for the hot parts of a combined cycle gas turbine is not shown, and modern high-temperature CCGTs require such cooling.

The objective of the invention: improving the efficiency of CCGT, ensuring the economical operation of CCGT using only steam cooling, ensuring the operation of CCGT in the mode of combined generation of heat and electric energy.

The technical result is that:

- increase the heat transfer of the theater of operations, reducing the design pressure at the outlet of the theater;

- provide cost-effective operation of CCGT when using closed steam cooling, since the heat taken from the working fluid by closed-circuit cooling steam is used to heat the secondary cooling steam to the calculated value of enthalpy;

- provide a minimum reduction in the efficiency of CCGT operation caused by the use of open steam cooling in combination with closed one, since they reduce the cost of operating a high-pressure air compressor and additionally increase the estimated operating heat transfer of a high-pressure turbine;

- ensure the CCGT operation in the mode of combined generation of heat and electric energy, heating the water supplied to the heating needs by the heat of air from the exit of the fuel heater, while lowering the air temperature in front of the high-pressure air compressor and, therefore, reducing the cost of operating this compressor.

This problem is solved, and the technical result is achieved due to the fact that the CCGT operation method consists in compressing air with intermediate cooling by an air compressor, which is fed into the combustion zone of the combustion chamber, into which fuel is simultaneously supplied, the resulting combustion products are mixed in the mixing zone combustion chambers with cooling secondary water vapor to produce a gas-vapor mixture at the outlet of the combustion chamber, which, as a working fluid, is sent to a gas-vapor turbine in which the flow energy the steam-gas mixture is converted into mechanical energy of rotation of the turbine rotor, then the water vapor is partially condensed in a vacuum condenser, the vacuum in which is created by a vacuum compressor that removes non-condensed gaseous products of combustion, the condensed water is heated in the main and additional heat exchangers for intermediate air cooling, as well as in a heating cooling heat exchanger gas-vapor mixture at the outlet of the high-pressure turbine and the flue gas cooling heat exchanger, while:

- the warming gas-gas mixture cooling heat exchanger at the outlet of the high-pressure turbine is made in the form of two successively installed heat exchangers: a hot gas-gas mixture heat exchanger and a cold gas-vapor mixture heat exchanger; only part of the water from the outlet of the exhaust gas cooling heat exchanger is supplied to the additional air-to-air heat exchanger, the rest of this water is fed to the inlet to the heat exchanger of the cold gas mixture, and to the inlet of the heat exchanger of the hot gas mixture heated water / water vapor from the exits of the main and additional heat exchangers for intermediate air cooling and from the outlet of the heat exchanger of the cold gas mixture;

- the unit is equipped with a heat exchanger for preheating to the calculated enthalpy of the secondary cooling steam with heat from the steam returned from the closed cooling path of the turbine;

- the unit is equipped with a sequentially located heat exchanger for preheating the water-cooler and a heat exchanger for subsequent generation of a steam-cooler from this water-cooler, intended for open steam cooling of the hot elements of the turbine with the subsequent discharge of the steam-cooler into the turbine flow part;

- the unit is equipped with a heat exchanger for heating water for heating needs with air from the exit of the fuel heater.

Separation of the water flows after it leaves the flue gas cooling heat exchanger and the direction of one of these flows into the cold gas-vapor mixture heat exchanger allows decreasing the temperature of the gas-vapor mixture at the outlet of the fuel assembly and, therefore, increasing the working heat transfer in it. At design pressures of the cooling steam injected into the combustion chamber above 32 bar, the water temperature at the outlet of the flue gas cooling heat exchanger, provided that it operates optimally, does not reach the saturation temperature and is constant. Accordingly, if a part of the water leaving the exhaust gas cooling heat exchanger is sent to the cold vapor-gas mixture heat exchanger, then at design pressures in the combustion chamber above 32 bar, the temperature of the gas-vapor mixture at the exit of the cold gas-vapor mixture heat exchanger can be kept below the saturation temperature. Consequently, the calculated temperature behind the theater will be reduced. As a result, the efficiency of CCGT unit is increased.

The calculations show that the efficiency of CCGT is increasing.

When using closed turbine cooling, the cooler draws heat from a working fluid expanding in the turbine. As a result, the temperature at the outlet of the theater is reduced and, consequently, the amount of heat transferred to the secondary cooling pair in the heating heat exchanger for cooling the vapor-gas mixture at the outlet of the theater is reduced. Providing the unit with a heat exchanger for heating to the calculated enthalpy of the secondary cooling water / steam with heat from the steam returned from the closed cooling path of the turbine, this underheating can be compensated by returning the heat taken from the working fluid that occurs during closed cooling.

The use of an open version of cooling with the release of the cooler into the turbine flow path unambiguously leads to a noticeable decrease in the useful electric power of modern CCGT units. Providing the unit with a heat exchanger for pre-heating the water cooler and a heat exchanger for the subsequent generation of the steam cooler reduces the air temperature in front of the high-pressure air compressor without losing heat of the cycle, since the steam cooler is mixed in the turbine with the main working fluid, performs useful work and participates in heating secondary cooling steam behind the theater. The decrease in air temperature is achieved due to the fact that the proportion of air cooled to a minimum temperature in front of the high-pressure air compressor increases, since the cooling of the air in the air heat exchanger for preheating the water-cooler, designed for open cooling, is carried out due to the part of the air cooled in the additional heat exchanger intermediate air cooling. The air at the outlet of the additional heat exchanger of the intermediate air cooling has a higher temperature than at the outlet of the main heat exchanger of the intermediate air cooling and the heat exchanger intended for preheating the water-cooler going for open cooling. As a result, the air temperature in front of the high pressure air compressor after mixing air flows becomes lower. The operating costs of a high-pressure air compressor are reduced, which in turn reduces the drop in CCGT useful electric power arising from the need to use open cooling with the release of a steam cooler in the turbine flow path.

At the same time, the estimated proportion of water entering the additional heat exchanger for intermediate cooling of the air from the outlet of the flue gas cooling heat exchanger decreases, and, consequently, the proportion of water directed to the heat exchanger of the cold vapor-gas mixture increases. This increase in water flow rate makes it possible to reduce the design temperature head at the cold end of the heat exchanger of the cold gas mixture by reducing the design temperature of the gas mixture at the outlet of the cold gas mixture. This circumstance also leads to a calculated decrease in the temperature behind the HPT, which leads to an increase in heat drop in it. As a result, the decrease in CCGT net electric power, which arises from the need for open cooling, is still further reduced.

The use of air as the heat carrier from the exit of the fuel heater for heating water supplied for heating needs allows the CCGT to operate in the mode of combined generation of heat and electric energy. This further reduces the air temperature in front of the high-pressure compressor. Accordingly, the costs of its work are reduced. However, after the transfer of heat from air to water, this heat does not return to the cycle, as in the variant with air pre-heating of the water-cooler intended for open cooling, but leaves the cycle. Accordingly, a decrease in the turbine’s net power will be partially offset only by a partial reduction in the cost of operating a high-pressure air compressor.

Figure 1 presents an embodiment of a schematic thermal circuit of a combined cycle steam turbine with a two-cylinder combined cycle gas turbine. Figure 2 shows a variant of the CCGT scheme taking into account closed steam cooling of the hot elements of a combined cycle gas turbine. Figure 3 shows a variant of the CCGT scheme, taking into account open and closed steam cooling of the hot elements of a combined cycle gas turbine. Figure 4 shows a variant of the CCGT scheme taking into account open and closed steam cooling of the hot elements of a combined cycle gas turbine with combined generation of heat and electric energy. The figures do not show typical equipment present in gas-vapor schemes, for example, a fuel supply system, chemical water treatment units, a deaeration unit, condensate and feed pumps, etc.

The CCGT in figure 1 contains a low-pressure air compressor 1, a high-pressure air compressor 2, a combustion chamber 3, a high-pressure gas turbine 4, a low-pressure gas turbine 5, an electric generator 6, a vacuum condenser 7, a vacuum compressor 8 , flue gas cooling heat exchanger 9, main air intermediate cooling heat exchanger 10, additional air intermediate cooling heat exchanger 11, hot gas-vapor mixture heat exchanger 12, air heater 13, atmospheric condenser 14, storage tank 15, cooling tower 16, air fuel preheater 17, heat exchanger cold vapor-gas mixture 18.

In Fig. 1, the air compressor 1 is connected inlet to the outlet of the air heater 13 and connected to the air inlet to the heat exchanger 10 and the air inlet to the heat exchanger 11. The heat exchanger 10 is connected to the air outlet of the fuel preheater 17 and the air compressor 2 inlet by the air outlet 11 with its air outlet connected to the air inlet to the fuel heater 17. The air compressor 2 with its outlet connected to the air inlet to the combustion chamber 3, the fuel inlet of which is connected to the fuel outlet from the fuel preheater I am 17, and the steam input of the combustion chamber 3 is connected to the outlet of water / water vapor from the heat exchanger 12. The input for water / water vapor to the heat exchanger 12 is connected to the water / water vapor exits from the heat exchangers 10, 11 and 18. The output of the gas-vapor mixture is combustion chamber 3 connected to the entrance to the theater 4, which is connected to the input of the gas-vapor mixture to the heat exchanger 12 by the output of the gas-vapor mixture, and the outlet of the gas-vapor mixture from the heat exchanger 12 is connected to the input of the gas-vapor mixture to the heat exchanger 18, which is connected to the high-pressure pump by the output of the gas-vapor mixture 5. Vacuum condenser 7, the input for the gas-vapor mixture is connected to the outlet of the high pressure pump 5, the output for non-condensed gaseous products of combustion to the inlet of the vacuum compressor 8. The vacuum condenser 7 is connected to the water outlet of the cooling tower 16 by the water inlet, the vacuum condenser 7 is connected to the water inlet to the cooling tower 16 and with the water inlet to the heat exchangers 9 and 10. The water outlet from the heat exchanger 9 is connected to the water inlets to the heat exchangers 11 and 18. The water outlet from the air heater 13 is connected to the water inlet to the cooling tower 16. Air inlet to the air heater 13 soy dinen with atmosphere. The output of non-condensable gaseous products of combustion from the vacuum condenser 7 is connected to the inlet of the vacuum compressor 8. The output of non-condensable gaseous products of combustion from the vacuum compressor 8 is connected to the input of non-condensable gaseous products of combustion of the heat exchanger 9, and the outlet of the cooled non-condensable gaseous products of combustion from the heat exchanger 9 is connected to the inlet to the atmospheric condenser 14. The gas outlet from the atmospheric condenser 14 communicates with the atmosphere, and the water outlet from union of water entering the air heater 13, tank 15 and accumulator-water entering the cooling tower 16.

The differences between FIG. 2 and FIG. 1 are as follows.

In Fig.2, the CCGT unit additionally contains a heat exchanger 19 for reheating the secondary cooling steam to the calculated enthalpy of heat from the water vapor returned from the closed circuit of the theater of cooling 4.

The differences between FIG. 3 and FIG. 2 are as follows.

In Fig. 3, the CCGT unit additionally contains a water-air heat exchanger 20 for preheating the water-cooler and a heat exchanger 21 for the subsequent generation of a steam-cooler designed for open steam cooling of the hot elements of the turbine.

The differences of FIG. 4 from FIG. 3 are as follows.

In Fig. 4, the CCGT unit additionally contains a heat exchanger 22 for heating the network water.

Between figure 1 and figure 2 there are differences in the connections of nodes and assemblies. In Fig.2, the outlet of water / water vapor from the heat exchanger 12 is connected to the inlet for water / water vapor to the heat exchanger 19. The heat exchanger 19 by the inlet for water vapor coming from the outlet of the closed steam cooling circuit of the turbine engine 4 is connected to the outlet of this cooling steam from the circuit closed steam cooling of the theater of operations 4. The exit from the heat exchanger 19 for the heated water / water vapor in it is connected to the entrance to the closed circuit of the steam cooling of the theater 4 and then to the exit of the heat exchanger 19 for the water vapor cooled in it from the closed steam circuit smooth cooling of the fuel assembly 4. The output for the water vapor flows mixed after the heat exchanger 19 is connected to the input of the secondary cooling steam into the combustion chamber 3.

Between figure 1 and figure 3 there are differences in the connections of nodes and assemblies. The dashed line shows the movement of water from which steam is generated for open cooling of the hot elements of the theater 4 with the release of the steam cooler in the flow section of the theater 4. In Fig. 3, the water outlet from the vacuum condenser 7 is also connected to the water inlet to the heat exchanger 20, the water outlet / water vapor from which is connected to the inlet of water / water vapor to the heat exchanger 21, and the output of water vapor from the heat exchanger 21 is connected to the inlet of the separate hot elements of the theater 4, having an outlet for steam to the flow part of the theater 4. Air inlet to the heat exchanger 20 is connected to the outlet of the air compressor 1, and the air outlet is connected to the inlet of the air compressor 2. The heat exchanger 21 is the inlet for water vapor coming from the outlet of the closed steam cooling circuit of the theater 4, is connected to the outlet of the cooling steam from the closed steam cooling circuit of the theater 4 The output of this steam from the heat exchanger 21 is connected to the input for this steam in the heat exchanger 19, the output from which for this steam is connected to the output of the secondary cooling steam from the heat exchanger 19 and to the entrance to the combustion chamber 3. Water / water outlet water vapor from the heat exchanger 12 is connected to the inlet for water / water vapor in the heat exchanger 19, and the output for the cooling secondary steam formed from the water / water vapor entering the heat exchanger 19 is connected to the entrance to the closed cooling circuit of the theater 4 and the output to the heat exchanger 19 for cooling steam from the closed steam cooling circuit of the turbine engine 4. The output for the water vapor flows mixed after the heat exchanger 19 is connected to the input of the secondary cooling steam into the combustion chamber 3.

Between figure 3 and figure 4 there are differences in the connections of nodes and assemblies. In Fig. 4, the air outlet from the fuel preheater 17 is connected to the air inlet to the heat exchanger 22, the air outlet from which is connected to the air inlet to the air compressor 2. The water inlet to the heat exchanger 22 is intended for the inlet of return network water, and the outlet is for the supplying network water to the consumer .

CCGT according to the scheme shown in figure 1, works as follows.

Atmospheric air is preheated in the air heater 13, then compressed with intermediate cooling in heat exchangers 10 and 11 and fed into the combustion zone of the combustion chamber 3, into which fuel is fed, which is preheated in the fuel heater 17, and the resulting combustible mixture is burned. At the same time, water vapor is introduced into the mixing zone of the combustion chamber 3 from the heat exchanger 12. The resulting vapor-gas mixture is sent to the theater 4, expanded and then sent through the heat exchanger 12 to the heat exchanger 18 and then to the high pressure pump 5, where it is expanded and then sent to the vacuum condenser 7. Non-condensing gaseous combustion products are removed from the vacuum condenser 7 by a vacuum compressor 8, cooled in a heat exchanger 9 and fed to an atmospheric condenser 14, where they are cooled by water from the outlet of the vacuum condenser 7 and then released into the atmosphere.

Part of the water from the vacuum condenser 7 is fed to heat exchangers 9 and 10, and another part of the water is sent to the cooling tower 16. One part of the water from the outlet of the atmospheric condenser 14 is sent to the air heater 13 to heat the air, another part of the water is sent to the cooling tower 16 and the storage tank 15 From the air heater 13, the water is then fed to the cooling tower 16, from where it is supplied to the water inlet to the vacuum condenser 7. The excess condensed water, if provided for by the CCGT operating mode, is sent to the storage tank 15.

Differences in the operation of CCGT according to the circuit shown in Fig. 3 from the circuit in Fig. 1 are as follows.

Part of the water from the outlet of the vacuum condenser 7 (shown by a dotted line) is heated in the heat exchanger 20, from the outlet of which water / water vapor is sent to the heat exchanger 21 to generate a steam cooler, which is supplied to the turbine engine 4 for open steam cooling of the hot elements of the turbine, followed by steam discharge -cooler into the flow part of the turbine engine 4. The water in the heat exchanger 20 is heated with part of the air after the air compressor 1, and the air cooled in the heat exchanger 20 is directed to the inlet of the air compressor 2. Water / water vapor p from the outlet of the heat exchanger 12 is sent to the heat exchanger 19, where it is heated with the heat of water vapor returned from the closed circuit of the theater of operations 4, and after the heat exchanger 19, part of the formed water vapor is sent to the closed circuit of the theater of operations 4. The remaining part of the formed water vapor is sent to mix with water vapor returned from the closed circuit cooling of the theater 4 and then subsequently cooled in heat exchangers 21 and 19. Next, the mixed water vapor is sent to the combustion chamber 3.

When operating the CCGT according to the scheme in figure 2, in contrast to figure 3, the water vapor returned from the closed circuit cooling of the theater 4, is fed to the heat exchanger 19.

In contrast to the operation of the CCGT unit according to scheme 3, when the CCGT unit is operated according to the scheme in Fig. 4, air from the output of the fuel preheater 17 is supplied to the input of the heat exchanger 22, in which the return network water is heated for its further supply to the consumer. Air from the outlet of the heat exchanger 22 is fed into the mixture with the air leaving their heat exchangers 10 and 20.

The present invention can be used in energy, shipbuilding, gas pumping stations and in other industries where plants with a combined cycle are used.

Claims (4)

1. The method of operation of a combined-cycle plant (CCGT), which consists in the fact that the air compressor compresses the air with intermediate cooling, which is fed into the combustion zone of the combustion chamber, which simultaneously serves fuel, the resulting combustion products are mixed in the mixing zone of the combustion chamber with cooling secondary water steam to obtain a gas-vapor mixture at the outlet of the combustion chamber, which is sent as a working fluid to a gas-vapor turbine, in which the energy of the gas-vapor mixture flow is converted into mechanical energy The rotation of the turbine rotor, then the water vapor is partially condensed in a vacuum condenser, the vacuum in which is created by a vacuum compressor that discharges non-condensed gaseous products of combustion, the condensed water is heated in the main and additional heat exchangers for intermediate air cooling, as well as in the heating heat exchanger for cooling the gas-vapor mixture at the outlet of high pressure turbines and a flue gas cooling heat exchanger, while the heating gas-fired cooling heat exchanger si at the outlet of the high-pressure turbine are made in the form of two successively installed heat exchangers: a hot gas-vapor mixture heat exchanger and a cold gas-vapor mixture heat exchanger, only part of the water from the outlet of the flue gas cooling heat exchanger is supplied to the additional air-to-air heat exchanger, the rest of this water is supplied to the inlet a heat exchanger of a cold steam-gas mixture, and heated water / steam from the outputs of the main and additional Tel'nykh intermediate heat exchangers and cooling air output from a heat exchanger cold-vapor mixture. 2. The method of operation of a combined-cycle plant according to claim 1, characterized in that the plant is equipped with a heat exchanger for heating up to the calculated enthalpy of the secondary cooling steam with heat from the steam returned from the closed cooling path of the turbine. 3. The method of operation of a combined-cycle plant according to claim 2, characterized in that the installation is equipped with a sequentially arranged heat exchanger for pre-heating the water-cooler and a heat exchanger for subsequent generation of the steam-cooler from this water-cooler, intended for open steam cooling of hot turbine elements, followed by ejection of a steam cooler into the flow part of the turbine. 4. The method of operation of a combined-cycle plant according to claim 3, characterized in that the plant is equipped with a heat exchanger for heating water for heating needs with air from the exit of the fuel heater.

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