RU2179248C1 - Process and combined-cycle plant for heat recovery in combined cycle - Google Patents

Abstract

FIELD: power engineering; contact-type combined-cycle plants. SUBSTANCE: spent steam-gas mixture is conveyed from turbine to exhaust-heat boiler/steam generator and to heat exchanger/water heater communicating with external heat consumer; mixture temperature at inlet of this heat exchanger is maintained at value higher by 10-20 C than that of water supplied to heat consumer and mixture pressure is maintained at value higher by 0.03-0.05 MPa than saturation pressure at given temperature; condensate obtained in the process is discharged, degassed, and conveyed to boiler. For implementing proposed process combined-cycle plant is provided, in addition, with condensate take-off, collection, treatment, and circulation system incorporating external water-droplet separators, steam trap on heat exchanger/water heater, condensate deaerator, direct-contact air cooler, and condensate pumps. EFFECT: reduced power loss in process, improved performance characteristics and environmental friendliness. 3 cl, 1 dwg

Description

 The invention relates to the field of energy and can be used to create new and improve existing combined cycle plants / CCGT / contact type (CCGT-K), designed to generate electricity and heat, as well as a power drive, for example, compressors of gas pumping stations of gas pipelines.

 PGU-K is known with mixing steam with products of combustion: steam is injected into the gas path under pressure into the combustion chamber, into the flow part of the turbine. The working fluid in PSU-K is a gas-vapor mixture (ASG). Such plants are most efficient compared to conventional steam or gas turbine plants and combined CCGT, but without mixing: they surpass the best modern steam turbine plants in specific power by 20-100% or more, in efficiency by 5-10% or more at lower capital and operating costs.

The advantages of the CCGT-K cycle over CCGT without mixing (combined circuits with a high-pressure steam generator) are associated with the effect of steam injection: cooling turbine blades, increasing the mass of the working fluid, improving technical and economic indicators (TEC), etc. Work on a gas-vapor mixture dramatically improves environmental indicators: the content of nitrogen oxides NO _x in the exhaust gases decreases as a result of their suppression in the presence of water vapor and a decrease in temperature.

 All this provides high rates of contact CCGT, makes them a promising direction in the development of station energy.

 A known method of heat recovery with the installation, which consists in the fact that the heat of the exhaust gases from the turbine is disposed of in a steam boiler, and the resulting steam is sent for injection into the turbine gas path (V. A. Zysin. Combined combined cycle plants and cycles. M., SEI , 1962, p. 18).

 The fundamental disadvantage of this method is the irretrievable loss of source water, the need for a water source, costly special water treatment (according to the requirements for boiler feed water).

 Closest to the proposed is a technical solution for as. USSR N 1048265 (F 25 В 29/00, F 25 В 11/00, F 01 К 25/10 from 05/06/1982), which was adopted as a prototype.

 In the proposed contact-type gas-vapor installation, a method is implemented that includes compressing air in a compressor, burning fuel in a combustion chamber in compressed air with steam injection, supplying it to an ASG turbine and cooling it after the turbine in series in a recovery boiler-steam generator and in a heat exchanger-water heater connected to external heat consumer, further supply of gases to the expander, separation and removal of droplet moisture, injection of the resulting steam into the gas path of the turbine.

 The installation comprises a gas turbine with a combustion chamber, a compressor, an expander, an electric generator, a gas path with a recovery boiler-steam generator, a heat exchanger-water heater connected to an external heat consumer in series, and is equipped with a system for supplying steam from the boiler and injecting steam into the gas path of the turbine.

 In the heat exchanger, running water from a source from outside is heated. Heated water is sent to an external consumer and partially to the recovery boiler. In the separator behind the heat exchanger, the cooled gases are freed from drip moisture, which is removed from the circuit; warm gases from the last stage of the tail surfaces are released into the atmosphere.

 The task of heat and water recovery in the known solution is not posed and is not solved, but the aim is to increase efficiency in variable operating modes, while generating heat and cold.

 The technical problem solved in the present invention is to reduce energy technology losses and improve technical, economic and environmental performance of the process, providing a closed loop of cyclic water by deep utilization of heat of exhaust gases, including the heat of condensation of water vapor.

The technical problem is solved due to the fact that in a method comprising compressing air in a compressor, burning fuel in a combustion chamber with steam injection, supplying the obtained gas-vapor mixture to a gas turbine, cooling the mixture spent in the turbine in series in a recovery boiler-steam generator and in a heat exchanger-water heater connected to an external heat consumer, further supply of ASG to the expander, separation and removal of moisture from the vapor-gas mixture. The temperature of the ASG at the inlet to the heat exchanger-water heater is maintained at 10-20 ^o C higher than the temperature of the water supplied to the heat consumer, while the ASG pressure is maintained above the saturation pressure at the specified temperature by 0.03-0.05 MPa, and the condensate is removed, subjected degassing and served in a recovery boiler-steam generator.

 In order to increase the efficiency of the process by reducing the compression work in the compressor, the compressed air between the first and second stages of the compressor is cooled and moistened in a mixing (contact) type air cooler by contact heat and mass transfer with condensate in a dropping state, after which the cooled and humidified air is sent to the second stage of the compressor , and the heated condensate - to the recovery boiler-steam generator.

 The method is implemented in a combined-cycle plant containing a gas circuit in which a compressor, a combustion chamber, a gas turbine, a recovery boiler-steam generator, a heat exchanger-water heater connected to an external heat consumer, drip moisture separators and an expander are installed, wherein the compressor and the expander are multi-stage, and the installation is additionally equipped with a condensate drainage, collection, processing and circulation system, including successively located remote static drip moisture separators, lennye between the expander stages and disposed at its outlet, the trap mounted on the heat exchanger-heater, air-mixing type, degasser for degassing the condensate and the condensate pumps.

 The essence of the invention lies in the fact that a closed steam-water path is created from the inlet to the outlet of the boiler, in which the steam is completely condensed, and the working fluid circulates in a closed circuit.

Using the proposed method reduces the content of nitrogen oxides NO _x in the exhaust gases under the influence of water vapor and reduce the temperature of the exhaust gases.

 The main distinguishing feature of the method and installation is the ongoing process of condensing water vapor from ASG in a closed circuit without contact heat exchange with flowing cooling water by transferring this process to a region of higher pressures than in a conventional condenser, which entails an increase in the temperature level of secretion of latent heat of vaporization and allows you to use it, for example, for heating purposes.

 The CCGT-K scheme with condensation is especially effective in the utilization of natural gas combustion products due to the increased content of water vapor in them and the high quality of the condensate released from the combustion products - demineralized water. It does not contain dissolved salts and is chemically pure synthetic water. After degassing, such condensate can be used as boiler feed water; other mechanical or chemical cleaning is not required.

 Modern gasification technologies for low-grade fuels, including sulfur and ash coals, with the production of a pure product, open up the possibilities for the proposed CCGT-K to operate on these fuels, i.e. make their fuel base virtually unlimited.

 This method claims the temperature difference of the coolants in the heat exchanger-water heater - ASG and network outlet water, i.e. hot water supplied to an external heat consumer. This difference is within the range of 10 - 20 degrees, it is chosen empirically and is optimal. In this case, the most economical characteristics of this unit are achieved: weight and size parameters, cost, reliability, etc. At a temperature difference of less than 10 degrees, these characteristics deteriorate: dimensions, metal consumption, construction cost increase, the task of placing it in a gas duct, and more becomes complicated. At a temperature interval of more than 20 mass and dimensions parameters are improved, but the pressure of the mixture required by condensation conditions is significantly increased, and with it the requirements for the design of the heat exchanger and the entire unit, for its operation.

 The claimed pressure difference between ASG and water on the saturation line - 0.03-0.05 MPa - was also experimentally selected as optimal, since it is minimally sufficient for the regeneration (removal) of the bulk of water vapor from ASG, of the order of 90% or more.

 If the pressure drop is less than 0.03 MPa, the condensation conditions worsen, its intensity, and if the pressure drop is more than 0.05 MPa, then this will increase the cost of the installation, worsen operating conditions, etc.

 The drawing shows a diagram of a combined cycle plant.

 A multi-stage compressor 1, a gas turbine 2 with a combustion chamber 3, a recovery boiler-steam generator 4, a heat exchanger-water heater 5, a multi-stage expander 6 equipped with drip separators 7 are sequentially installed in the gas circuit of the installation.

 The boiler-steam generator 4 and the heat exchanger-water heater 5 are enclosed in a sealed heat-insulated chamber 8. An electric generator 9 is installed on the shaft of the gas turbine 2. The installation is equipped with a condensate removal, collection, processing and circulation system, including drip moisture separators 7, condensate drain 10 from the chamber 8, deaerator 11 and condensate pumps 12, 13, 14 and 15 connected by a condensate line 16.

 Between the stages of the compressor 1 is installed air cooler 17 mixing type. The steam trap 10 is equipped with a nozzle with a valve 18 for removing excess condensate from the condensate line. Line 19 serves to supply fuel to the combustion chamber 3. The boiler-steam generator 4 is connected by a steam line 20 to a gas turbine 2 and a combustion chamber 3.

 The method is implemented as follows.

Outside air is sucked in and compressed in a multi-stage compressor 1, compressed air and fuel are fed through line 19 to the combustion chamber 3, where steam is also injected from the recovery boiler-steam generator 4 through the steam line 20. The resulting vapor-gas mixture is sent to the turbine 2. The exhaust gas mixture in the turbine is cooled sequentially in the recovery boiler-steam generator 4 and the heat exchanger-water heater 5 connected to an external heat consumer (heat load). At the inlet to the heat exchanger-water heater 5, the temperature of the ASG is maintained at 10-20 ^° C higher than the temperature of the water supplied to the consumer, and the pressure of the ASG is maintained above the saturation pressure at the indicated temperature by 0.03-0.05 MPa. Under these conditions, the main part of the water vapor contained in the ASG is condensed, and the resulting condensate is removed, subjected to degassing, and fed to the steam boiler 4. The cooled ASG from the heat exchanger 5 is fed to a multi-stage expander 6 for operating excess pressure and separators 7 for trapping and removal condensate in the form of a drop of moisture.

 The condensate from the separators 7 is pumped out by the condensate pump 12 to the condensate line 16. The condensate from the heat exchanger 5 is removed using the condensate drain 10, and the excess water is removed through the pipe 18. Next, the condensate is pumped under pressure into the upper part of the air cooler 17 with a pump 13, where it is sprayed using nozzles ; compressed air from the first stage of compressor 1 is supplied to its lower part. In the air cooler 17 during countercurrent contact heat exchange of compressed air and condensate in the dropping state, the air is humidified and cooled, and the condensate is heated. After that, the air is sent to the second stage of the compressor 1, and the condensate is pumped to the deaerator 11 using the pump 14, where it is degassed. From the deaerator 11 by pump 15, the purified condensate is fed to a recovery boiler-steam generator 4.

 An example of a specific implementation of the method.

Outside atmospheric air with a temperature of 15 ^o C is sucked in an amount of 100 kg / s (model mode) to the first stage of compressor 1, where it is compressed to a pressure of 0.655 MPa, while it is heated to 248 ^o C. From the first stage, air with these parameters is supplied for intermediate cooling in the air cooler 17; 58.4 kg / s condensate from the condensate line is supplied here under pressure and sprayed using nozzles-sprayers. As a result of contact heat and mass transfer in countercurrent condensate in a dropping state and compressor air, the latter is cooled to 88 ^o C and fed to the second stage of compressor 1. In it, air is compressed to 6.45 MPa, its temperature rises to 451 ^o C.

In the combustion chamber 3, fuel (natural gas, consisting mainly of methane) is supplied via line 19 in an amount of 5.263 kg / s with an air flow coefficient of 1.1 and steam is injected from the steam boiler 4 with injection parameters: flow rate 46.8 kg / s, temperature 287 ^o C, pressure 6.69 MPa. Steam is also injected into the turbine 2 for cooling the blades (environmental injection).

At the entrance to the turbine 2, the resulting ASG in the amount of 158.4 kg / s has a pressure of 6.26 MPa and a temperature of 1310 ^o C. The spent ASG 2 in the turbine with a flow rate of 163.6 kg / s, a temperature of 632 ^o C and a pressure of 0.315 MPa are directed in a sealed chamber 8, where it gives off heat to the recovery boiler-steam generator 4 and heat exchanger 5. In this case, the pressure and temperature of the ASG are maintained at the level of 0.3101 MPa and 123 ^o C at the inlet and 0.3054 MPa and 80 ^o C at the outlet (compare with the pressure on the saturation line at temperatures of 123 and 80 ^o C, respectively 0.22 and 0.1013 MPa).

Next, the ASG with a large overpressure (0.3054 MPa) is sent to the multi-stage expander 6 to trigger this pressure. The mode of operation of the latter is maintained such that at its outlet the spent ASG has a temperature of 49.5 ^o C and a pressure of 0.1013 MPa, i.e. minimum sufficient for exhaust into the atmosphere. Such parameters provide the highest possible thermal efficiency of the process.

At the claimed temperature difference of heat carriers 10-20 ^o C in the heat exchanger, water can be heated to 103-113 ^o C, which, by way of example, corresponds to the average heat loads for Russia in the heating season, i.e. The characteristic practical situation is considered.

 Since the pressures 0.3101 and 0.3054 MPa supported in the chamber 8 at the heat exchanger section 5 are significantly higher than the saturation pressure at the given temperature of the CBC, respectively 0.22 and 0.1013 MPa, almost complete condensation of the water contained in the CBC occurs in this section of the chamber 8 vapors (about 93% in this example), including vapors generated from the combustion of hydrogen fuel, with the release of the corresponding amount of heat of vaporization. The rest is released and condensed in expander 6, so that practically dry and cold gases - combustion products - are emitted into the atmosphere.

 In the proposed method, the pressure of the ASG at the inlet to the heat exchanger 5 is of primary importance, since the pressure drop in the area is small, in our example 0.0047 MPa.

Work on the proposed method is characterized by the following indicators:
- power of the compressor, the first and second stages 23.9 and 43.1 MW;
- the degree of expansion and power of the turbine 19.9 and 182.8 MW;
- water consumption in the boiler-steam generator 52 kg / s;
- pressure and water temperature at the inlet of 8.7 MPa and 88 ^o C;
- injection parameters: flow rate 46.8 kg / s, temperature 287 ^o C, pressure 6.7 MPa;
- flow rate and condensate temperature 60.4 kg / s, 80 ^o C;
- expander power 9.59 MW;
- net power of the installation is 124 MW;
- heat supply to the consumer 148.8 MW, including through condensation 98.6%;
- excess condensate in a cycle of 4.7 kg / s;
- gross efficiency of 47.1%;
- fuel utilization factor (taking into account the generation of heat and electricity) 93%.

 Thus, the proposed method and device solve the problem: provide a highly economical combined generation of electricity and heat for heating purposes and other needs in the combined cycle gas contact type with complete water recovery, i.e. closed loop water cycle. At the same time, almost all the heat released to an external consumer is generated due to the condensation of ASG vapor. These are the effect, advantages and distinctive features of the claimed technical solution.

Claims (3)

1. A method of heat recovery in a steam-gas cycle, comprising compressing air in a compressor, burning fuel in a combustion chamber with steam injection, supplying the obtained gas-vapor mixture to a gas turbine, cooling the mixture spent in the turbine in series in a recovery boiler-steam generator and in a heat exchanger-water heater connected with an external heat consumer, further supplying the vapor-gas mixture to the expander, separating and removing droplet moisture from the vapor-gas mixture, characterized in that the air is compressed in multiple stages compressor, the temperature of the gas-vapor mixture at the inlet to the heat exchanger-water heater is maintained at 10-20 ^o C higher than the temperature of the water supplied to the heat consumer, while the pressure of the gas-vapor mixture is maintained above the saturation pressure at the specified temperature by 0.03-0.05 MPa, and the condensate obtained is drained, degassed and fed to a recovery boiler-steam generator.  2. The method according to p. 1, characterized in that the compressed air between the first and second stages of the compressor is cooled and moistened in a mixing type air cooler by contact heat and mass transfer with condensate in a droplet state, after which the cooled and moistened air is sent to the second stage of the compressor, and heated condensate - to the recovery boiler-steam generator.  3. Combined-cycle plant containing a gas circuit in which a compressor, a combustion chamber, a gas turbine, a recovery boiler-steam generator, a heat exchanger-water heater connected to an external heat consumer, and an expander are installed, wherein the compressor and expander are multistage and the installation is additional equipped with a condensate drainage, collection, processing and circulation system, including consecutively located remote static drip moisture separators installed between several stages a step expander and an outlet located on it, a steam trap mounted on a heat exchanger-water heater, a mixing type air cooler, a deaerator for condensate degassing and condensate pumps.