A closed water cooling system for power plants and natural gas heating system for pressure regulating stations

Abstract

The invention discloses a closed water cooling and pressure regulating station natural gas heating system for a power plant, comprising an expansion water tank (1), a water-to-water heat exchanger (8), a closed water return pipe (12) and a plurality of natural gas heaters (14), wherein the expansion water tank (1) is respectively connected to the closed water return pipe (12), the water-to-water heat exchanger (8) and the plurality of natural gas heaters (14) through an expansion water tank outlet pipe (2), and the water outlets of the plurality of natural gas heaters (14) are all connected to the top of the expansion water tank (1) through a closed water outlet pipe (17) of the natural gas heater. The invention makes full use of the waste heat of closed water and the coldness of natural gas, and also considers the risk of natural gas leakage, reasonably arranges gas detectors, timely detects and determines natural gas leakage, and links isolation measures to eliminate the risk of leakage. The system has a simple structure, low investment cost, a safe and reliable system, and low operating cost, and is conducive to energy conservation and emission reduction.

Description

Technical Field

[0001] The invention relates to the technical field of closed water cooling of power plants, and in particular to a closed water cooling system of power plants and a natural gas heating system of a pressure regulating station. Background Art

[0002] The closed cooling water system is an important auxiliary system of the power plant. Its main function is to provide cooling water to the auxiliary equipment of each unit (oil cooler, hydrogen cooler, etc.). The system working fluid is desalted water, which operates in a closed manner throughout the system. The closed water is generally cooled by heat exchange with open circulating water, which is supplied by the circulating water system.

[0003] The temperature of natural gas will decrease after decompression. According to experience, when the natural gas pressure drops by 1.0MPa, its temperature will drop by 6℃. For natural gas pressure regulating stations with large pressure reduction or low incoming natural gas temperature, it is necessary to design a natural gas heating system to ensure the temperature requirements of downstream users.

[0004] For gas power plants, especially gas-steam combined cycle power plants, closed water cooling water systems and natural gas heating systems in pressure regulating stations are indispensable auxiliary systems. In the first batch of gas-steam combined cycle power plants in China, natural gas is generally heated by water bath furnaces or electric heating. The water bath furnace is a device that integrates hot water boilers and heat exchangers. It consists of a furnace body and a burner. It uses desalted water as an intermediate medium for heat transfer, absorbs the heat of natural gas burning in the fire tube, and transfers it to the natural gas in the coil to achieve the purpose of heating natural gas. The water bath furnace combustion also requires an additional set of pressure regulating devices and electric heating devices. This method has high operating costs and a complex system, and the investment cost is also high. Another method is to directly use electric heaters for heating. Since explosion-proof design is required, the investment cost and operating cost of this method are also high, so this method is rarely used.

[0005] In recent years, new gas-steam combined cycle power plants have been built and put into operation. The natural gas pressure regulating station generally uses the circulating water return of the condenser for heating. The advantage is that the cold energy of the natural gas is recycled and utilized, which is equivalent to replacing part of the cooling tower to cool the open water. At the same time, since the open water returns to the natural ventilation tower or the mechanical tower, even if the natural gas leaks into the open water, it can be safely released. However, this method requires two booster pumps, and the circulating water return temperature is not high, so the required heat exchanger area is large. At the same time, it is necessary to consider that before the unit is started and the circulation temperature is low, the open water cannot be used to heat the natural gas, so an additional high-power heater is required. Therefore, the cost of this solution is very high.

[0006] Another natural gas heating solution is to use hot water at 145°C at the outlet of the waste heat boiler condensate heater. The hot water is connected to a main pipe from the outlet of each unit's waste heat boiler condensate heater, and then led to the natural gas pressure regulating station to heat the natural gas. The hot water is cooled to 45°C and then returned to the condenser. The advantages of this system are large heat exchange temperature difference, small heat exchanger area, stainless steel pipe exchange, and low cost; the disadvantages are that high-quality energy is used for heating, the cold energy of natural gas is not recovered, the operating cost is high, and there is a risk of natural gas leakage to condensate. Summary of the invention

[0007] To solve the above problems, the present invention provides a closed water cooling and pressure regulating station natural gas heating system for a power plant, comprising an expansion water tank, a water-to-water heat exchanger, a closed water return pipe and a plurality of natural gas heaters, wherein the expansion water tank is connected to the closed water return pipe, the water-to-water heat exchanger and the plurality of natural gas heaters respectively through an expansion water tank outlet pipe, the closed water return pipe is provided with a closed water pump inlet electric valve, a closed water pump, a closed water pump outlet check valve and a closed water pump outlet electric valve in sequence starting from a side close to the expansion water tank, the water outlets of the plurality of natural gas heaters are all connected to the expansion water tank through a closed water outlet pipe of the natural gas heater, and a natural gas heater closed water outlet pipe gas detector and a natural gas heater closed water outlet electric valve are provided on the closed water outlet pipe of the natural gas heater.

[0008] Preferably, the water inlet of the water-to-water heat exchanger is provided with a closed water inlet electric valve of the water-to-water heat exchanger, the water outlet of the water-to-water heat exchanger is provided with a closed water supply pipe, the closed water supply pipe is provided with a closed water outlet electric valve of the water-to-water heat exchanger and a closed water outlet water temperature sensor of the water-to-water heat exchanger, the water-to-water heat exchanger is also provided with a circulating water supply pipe of the water-to-water heat exchanger, and the circulating water supply pipe of the water-to-water heat exchanger is sequentially connected with the circulating water inlet regulating valve of the water-to-water heat exchanger, the circulating water outlet electric valve of the water-to-water heat exchanger and the circulating water return pipe of the water-to-water heat exchanger.

[0009] Preferably, the water inlet of the natural gas heater is provided with a closed water inlet electric valve of the natural gas heater, the natural gas heater is provided with a natural gas supply pipe of the natural gas heater, the natural gas supply pipe of the natural gas heater is provided with a natural gas inlet isolation valve of the natural gas heater, the natural gas heater is provided with a natural gas return pipe of the natural gas heater, and the natural gas return pipe of the natural gas heater is provided with a natural gas outlet isolation valve of the natural gas heater.

[0010] Preferably, an expansion water tank drain pipe is also provided at the top of the expansion water tank, and an expansion water tank drain pipe gas detector is provided inside the expansion water tank drain pipe.

[0011] Preferably, the water-to-water heat exchanger is a shell and tube heat exchanger, with closed water flowing through the shell side and circulating water flowing through the tube side in a countercurrent arrangement, the cold source of the water-to-water heat exchanger being circulating water, the object to be cooled being closed water, and the pressure on the closed water side being higher than that on the circulating water side.

[0012] Preferably, the natural gas heater is a shell and tube heater, with closed water running through the shell side and natural gas running through the tube side in a countercurrent arrangement. The heat source of the natural gas heater is closed water, the heated object is natural gas, and the pressure on the natural gas side is higher than the pressure on the closed water side.

[0013] Preferably, the closed water pump inlet electric valve, closed water pump outlet electric valve, water-to-water heat exchanger closed water inlet electric valve, water-to-water heat exchanger closed water outlet electric valve, natural gas heater closed water inlet electric valve, natural gas heater closed water outlet electric valve, water-to-water heat exchanger circulating water inlet regulating valve and water-to-water heat exchanger circulating water outlet electric valve are all connected to the power plant control system, and can be remotely controlled.

[0014] Preferably, the water temperature sensor at the closed water outlet of the water-to-water heat exchanger, the gas detector at the closed water outlet pipe of the natural gas heater and the gas detector at the exhaust pipe of the expansion water tank are all connected to the power plant control system to enable remote control.

[0015] The beneficial effects of the present invention are: providing a closed water cooling system for a power plant and a natural gas heating system for a pressure regulating station, combining the closed water cooling system in the power plant with the natural gas heating system in the pressure regulating station, heating the natural gas while satisfying the closed water cooling, making full use of the waste heat of the closed water and the coldness of the natural gas, and also considering the risk of natural gas leakage, reasonably arranging gas detectors, timely detecting and judging natural gas leakage, linking isolation measures, and eliminating the risk of leakage. The system has a simple structure, low investment cost, a safe and reliable system, and a low operating cost, which is conducive to energy conservation and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the present invention;

[0017] In the figure: 1-expansion water tank, 2-expansion water tank outlet pipe, 3-closed water pump inlet electric valve, 4-closed water pump, 5-closed water pump outlet check valve, 6-closed water pump outlet electric valve, 7-water-to-water heat exchanger closed water inlet electric valve, 8-water-to-water heat exchanger, 9-water-to-water heat exchanger closed water outlet electric valve, 10-water-to-water heat exchanger closed water outlet water temperature sensor, 11-closed water supply pipe, 12-closed water return pipe, 13-natural gas heater closed water inlet electric valve, 14-natural gas heater, 15-natural gas heater closed water outlet pipe gas detector, 1 6- natural gas heater closed water outlet electric valve, 17- natural gas heater closed water outlet pipe, 18- expansion water tank drain pipe, 19- expansion water tank drain pipe gas detector, 20- water-to-water heat exchanger circulating water supply pipe, 21- water-to-water heat exchanger circulating water inlet regulating valve, 22- water-to-water heat exchanger circulating water outlet electric valve, 23- water-to-water heat exchanger circulating water return pipe, 24- natural gas heater natural gas supply pipe, 25- natural gas heater natural gas inlet isolation valve, 26- natural gas heater natural gas outlet isolation valve, 27- natural gas heater natural gas return pipe. DETAILED DESCRIPTION

[0018] See also Figure 1 The present invention proposes an embodiment: a closed water cooling and natural gas heating system for a power plant, comprising an expansion water tank 1, a water-to-water heat exchanger 8, a closed water return pipe 12 and two parallel natural gas heaters 14, wherein the expansion water tank 1 is connected to the closed water return pipe 12, the water-to-water heat exchanger 8 and the two parallel natural gas heaters 14 through an expansion water tank outlet pipe 2, and the closed water return pipe 12 is provided with a closed water pump inlet electric valve 3, a closed water pump 4, a closed water pump outlet check valve 5 and a closed water pump outlet electric valve 6 in sequence from the side close to the expansion water tank 1. Valve 6, the water outlet of the natural gas heater 14 is connected to the top of the expansion water tank 1 through the natural gas heater closed water outlet pipe 17, and the closed water return water of the natural gas heater 14 flows into the expansion water tank 1 from top to bottom. The natural gas heater closed water outlet pipe gas detector 15 and the natural gas heater closed water outlet electric valve 16 are provided on the natural gas heater closed water outlet pipe 17. The natural gas heater closed water outlet pipe gas detector 15 is installed in the pipeline between the outlet of the natural gas heater 14 and the natural gas heater closed water outlet electric valve 16.

[0019] Specifically, the expansion water tank outlet pipe 2 is connected to the lower part of the expansion water tank 1 and is used for draining water from the expansion water tank 1 .

[0020] Specifically, the water inlet of the water-to-water heat exchanger 8 is provided with a water-to-water heat exchanger closed water inlet electric valve 7, and the water outlet of the water-to-water heat exchanger 8 is provided with a closed water supply pipe 11, and the closed water supply pipe 11 is provided with a water-to-water heat exchanger closed water outlet electric valve 9 and a water-to-water heat exchanger closed water outlet water temperature sensor 10, and the water-to-water heat exchanger closed water outlet water temperature sensor 10 is installed in the pipeline behind the water-to-water heat exchanger closed water outlet electric valve 9; the water-to-water heat exchanger 8 is also provided with a water-to-water heat exchanger circulating water supply pipe 20, and the water-to-water heat exchanger circulating water supply pipe 20 is sequentially connected to the water-to-water heat exchanger circulating water inlet regulating valve 21, the water-to-water heat exchanger circulating water outlet electric valve 22 and the water-to-water heat exchanger circulating water return pipe 23.

[0021] Specifically, the water inlet of the natural gas heater 14 is provided with a natural gas heater closed water inlet electric valve 13, the natural gas heater 14 is provided with a natural gas heater natural gas supply pipe 24, the natural gas heater natural gas supply pipe 24 is provided with a natural gas heater natural gas inlet isolation valve 25, the natural gas heater 14 is provided with a natural gas heater natural gas return pipe 27, and the natural gas heater natural gas return pipe 27 is provided with a natural gas heater natural gas outlet isolation valve 26.

[0022] Specifically, an expansion water tank drain pipe 18 is further provided on the top of the expansion water tank 1 for draining air from the expansion water tank 1 , and an expansion water tank drain pipe gas detector 19 is provided inside the expansion water tank drain pipe 18 .

[0023] Specifically, the water-to-water heat exchanger 8 is a shell and tube heat exchanger, in which closed water flows through the shell side and circulating water flows through the tube side in a countercurrent arrangement. The cold source of the water-to-water heat exchanger is circulating water, and the object to be cooled is closed water. The pressure on the closed water side is higher than that on the circulating water side.

[0024] Specifically, the natural gas heater 14 is a shell and tube heater, with closed water flowing through the shell and natural gas flowing through the tube in a countercurrent arrangement. The heat source of the natural gas heater 14 is closed water, the heated object is natural gas, and the pressure on the natural gas side is higher than the pressure on the closed water side.

[0025] Specifically, the closed water pump inlet electric valve 3, the closed water pump outlet electric valve 6, the water-to-water heat exchanger closed water inlet electric valve 7, the water-to-water heat exchanger closed water outlet electric valve 9, the natural gas heater closed water inlet electric valve 13, the natural gas heater closed water outlet electric valve 16, the water-to-water heat exchanger circulating water inlet regulating valve 21 and the water-to-water heat exchanger circulating water outlet electric valve 22 are all connected to the power plant control system and can be remotely controlled.

[0026] Specifically, the water temperature sensor 10 at the closed water outlet of the water-to-water heat exchanger, the gas detector 15 at the closed water outlet pipe of the natural gas heater and the gas detector 19 at the emptying pipe of the expansion water tank are all connected to the power plant control system to realize remote control.

[0027] Specifically, the water temperature sensor 10 at the closed water outlet of the water-to-water heat exchanger is used to measure the water temperature at the closed water outlet of the water-to-water heat exchanger 8; the gas detector 15 at the closed water outlet pipe of the natural gas heater is used to measure the gas content in the closed water outlet pipe 17 of the natural gas heater; and the gas detector 19 at the expansion water tank drain pipe is used to measure the gas content in the expansion water tank drain pipe 18.

[0028] Specifically, the closed water supply pipe 11 is supplied to various users of the power plant for cooling. After the closed water absorbs heat, its temperature rises and the water returns to the closed water return pipe 12. After being pressurized by the closed water pump 4, part of the water enters the water-to-water heat exchanger 8 for cooling. The cooled closed water enters the closed water supply pipe 11 and is supplied to users. The other part of the water enters the natural gas heater 14 to heat the natural gas, and the return water enters the top of the expansion water tank 1.

[0029] Specifically, the water-to-water heat exchanger circulating water inlet regulating valve 21 adjusts the flow rate of the water-to-water heat exchanger circulating water 8 according to the reading of the water-to-water heat exchanger closed water outlet water temperature sensor 10, and maintains the closed water supply temperature within a suitable range (generally 46 0 C); For the closed cooling water system, the natural gas heater 14 plays a role in cooling the closed water of a part of the water-to-water heat exchanger 8; when the closed water return temperature of the natural gas heater 14 is low, under the premise that the heat absorption of the circulating water in the water-to-water heat exchanger 8 remains unchanged, the closed water outlet water temperature of the water-to-water heat exchanger 8 will drop, and then the circulating water inlet regulating valve 21 of the water-to-water heat exchanger will be closed, reducing the circulating water flow of the water-to-water heat exchanger 8 and reducing the power of the circulating water pump of the power plant.

[0030] Specifically, when a large amount of natural gas leaks into the closed water side of the natural gas heater 14, the gas detector 15 of the closed water outlet pipe of the natural gas heater can detect it in time. At this time, the closed water inlet electric valve 13 and the closed water outlet electric valve 16 of the natural gas heater will be interlocked and closed to isolate the natural gas leakage.

[0031] It should be noted that the above is only a preferred embodiment of the present invention, and the scope of rights of the present invention cannot be limited thereto. Modifications and changes made by those skilled in the art that do not depart from the spirit and scope of the present invention should all be within the scope of protection of the claims attached to the present invention.

Claims

1. A closed water cooling and natural gas heating system for a power plant and a pressure regulating station, characterized in that: The invention comprises an expansion water tank (1), a water-to-water heat exchanger (8), a closed water return pipe (12) and a plurality of natural gas heaters (14); the expansion water tank (1) is connected to the closed water return pipe (12), the water-to-water heat exchanger (8) and the plurality of natural gas heaters (14) respectively through an expansion water tank outlet pipe (2); the closed water return pipe (12) is provided with a closed water pump inlet electric valve (3), a closed water pump (4), a closed water pump outlet check valve (5) and a closed water pump outlet electric valve (6) in sequence from the side close to the expansion water tank (1); the water outlets of the plurality of natural gas heaters (14) are connected to the expansion water tank (1) through a natural gas heater closed water outlet pipe (17); the natural gas heater closed water outlet pipe (17) is provided with a natural gas heater closed water outlet pipe gas detector (15) and a natural gas heater closed water outlet electric valve (16); An expansion water tank drain pipe (18) is also provided at the top of the expansion water tank (1), and an expansion water tank drain pipe gas detector (19) is provided inside the expansion water tank drain pipe (18); The water-to-water heat exchanger (8) is a shell and tube heat exchanger, in which closed water flows through the shell side and circulating water flows through the tube side, and is arranged in countercurrent. The cold source of the water-to-water heat exchanger is circulating water, and the object to be cooled is closed water. The pressure on the closed water side is higher than the pressure on the circulating water side.

2. A closed water cooling and natural gas heating system for a power plant and a pressure regulating station as claimed in claim 1, characterized in that: The water inlet of the water-to-water heat exchanger (8) is provided with a water-to-water heat exchanger closed water inlet electric valve (7), the water outlet of the water-to-water heat exchanger (8) is provided with a closed water supply pipe (11), the closed water supply pipe (11) is provided with a water-to-water heat exchanger closed water outlet electric valve (9) and a water-to-water heat exchanger closed water outlet water temperature sensor (10), the water-to-water heat exchanger (8) is also provided with a water-to-water heat exchanger circulating water supply pipe (20), the water-to-water heat exchanger circulating water supply pipe (20) is sequentially connected to the water-to-water heat exchanger circulating water inlet regulating valve (21), the water-to-water heat exchanger circulating water outlet electric valve (22) and the water-to-water heat exchanger circulating water return pipe (23).

3. A closed water cooling and natural gas heating system for a power plant and a pressure regulating station as claimed in claim 1, characterized in that: The water inlet of the natural gas heater (14) is provided with a natural gas heater closed water inlet electric valve (13); the natural gas heater (14) is provided with a natural gas heater natural gas supply pipe (24); the natural gas heater natural gas supply pipe (24) is provided with a natural gas heater natural gas inlet isolation valve (25); the natural gas heater (14) is provided with a natural gas heater natural gas return pipe (27); the natural gas heater natural gas return pipe (27) is provided with a natural gas heater natural gas outlet isolation valve (26).

4. A closed water cooling and natural gas heating system for a power plant as claimed in claim 1, characterized in that: The natural gas heater (14) is a shell and tube type heater, with closed water flowing through the shell side and natural gas flowing through the tube side, in a countercurrent arrangement. The heat source of the natural gas heater (14) is closed water, the object to be heated is natural gas, and the pressure on the natural gas side is higher than the pressure on the closed water side.

5. A closed water cooling and natural gas heating system for a power plant and a pressure regulating station according to any one of claims 1 to 3, characterized in that: The closed water pump inlet electric valve (3), the closed water pump outlet electric valve (6), the water-to-water heat exchanger closed water inlet electric valve (7), the water-to-water heat exchanger closed water outlet electric valve (9), the natural gas heater closed water inlet electric valve (13), the natural gas heater closed water outlet electric valve (16), the water-to-water heat exchanger circulating water inlet regulating valve (21) and the water-to-water heat exchanger circulating water outlet electric valve (22) are all connected to the power plant control system to realize remote control.

6. A closed water cooling and natural gas heating system for a power plant as claimed in claim 2, characterized in that: The water temperature sensor (10) at the closed water outlet of the water-to-water heat exchanger, the gas detector (15) at the closed water outlet pipe of the natural gas heater, and the gas detector (19) at the exhaust pipe of the expansion water tank are all connected to the power plant control system, so that remote control can be achieved.

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