Recirculation system for wet operation of boiler

Abstract

The utility model discloses a boiler wet-state operation recirculation system. A large amount of working medium is discharged into the drain flash tank through temperature and pressure reduction, the process brings a large amount of heat loss, and meanwhile, a large amount of steam discharged from the drain flash tank brings a large amount of working medium loss. The device is characterized in that drain water of a steam-water separator is communicated with a water storage tank (15), an outlet of the water storage tank is communicated with a circulating pipeline (21), and the circulating pipeline is communicated to an inlet of a coal economizer after passing through a circulating pump (10); the circulating pipeline is connected with a cooling water pipeline in parallel, the cooling water pipeline comprises a heat exchanger (6), a hot water inlet of the heat exchanger is communicated with the circulating pipeline through an inlet pipe (26), and a hot water outlet of the heat exchanger is communicated with the circulating pipeline through an outlet pipe (22). The device is used for wet-state operation recirculation of the boiler.

Description

Technical Field

[0001] The utility model relates to a boiler wet operation recirculation system. Background Art

[0002] When the boiler is in 20%THA condition, the boiler is in wet operation, and the working medium at the outlet of the water-cooled wall is a steam-water mixture. At this time, the high and low heaters of some units cannot be put into operation normally, or the feed water is not heated enough after being put into operation, and the feed water temperature is very low. The low feed water temperature causes the boiler to produce less steam, the amount of steam flowing through the heating surface of the superheater is small, and a large amount of working medium is discharged into the drain expansion tank after being cooled and reduced in pressure. This process itself brings a large amount of heat loss, and at the same time, a large amount of steam discharged from the drain expansion tank brings a large amount of working medium loss. Utility Model Content

[0003] The purpose of the utility model is to solve the above-mentioned problems and provide a boiler wet operation recirculation system.

[0004] The above purpose is achieved through the following technical solutions:

[0005] A boiler wet operation recirculation system, comprising an economizer, a steam-water separator and a high-pressure heater, wherein the water discharge of the steam-water separator is connected to a water storage tank, the outlet of the water storage tank is connected to a circulation pipeline, and the circulation pipeline is connected to the inlet of the economizer after passing through a circulation pump;

[0006] A minimum flow return pipeline is connected between the circulation pump outlet and the water tank outlet;

[0007] A circulating pump heating pipeline is connected between the economizer outlet and the circulating pump outlet;

[0008] A circulating pump supercooling pipeline is connected between the outlet of the high-pressure heater and the outlet of the water storage tank;

[0009] The circulating pipeline is connected in parallel with the cooling water pipeline, the cooling water pipeline includes a heat exchanger, the hot water inlet of the heat exchanger is connected to the circulating pipeline through an inlet pipe, and the hot water outlet of the heat exchanger is connected to the circulating pipeline through an outlet pipe.

[0010] In the boiler wet operation recirculation system, a flow orifice plate and a second flow regulating valve are installed on the minimum flow return pipeline.

[0011] In the boiler wet operation recirculation system, a first regulating valve and a second stop valve are installed on the heating pipeline of the circulation pump.

[0012] In the boiler wet operation recirculation system, a second regulating valve and a third stop valve are installed on the subcooling pipeline of the circulation pump. Beneficial Effects

[0013] 1. The working fluid returned from the water storage tank to the economizer inlet of the utility model directly heats the working fluid at the economizer inlet, which is beneficial to increase the inlet feed water temperature of the economizer and also increases the inlet feed water temperature of the water-cooled wall. Under the same amount of fuel, the steam production at the furnace outlet is increased, which is beneficial to the safe operation of the superheater.

[0014] 2. The utility model is provided with a cooling water pipeline, which can prevent high-temperature boiler water from entering the motor of the circulating pump and causing damage to the circulating pump.

[0015] 3. The utility model is provided with a circulating pump supercooling pipeline, which can prevent the circulating water at the inlet of the recirculating pump from flashing and causing cavitation of the circulating pump when the load is rapidly reduced.

[0016] 4. The utility model sets a minimum flow return pipeline, which can improve the regulating characteristics of the circulating pump and maintain the minimum safe flow of the circulating pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the principle diagram of the utility model;

[0018] In the figure: 1. steam-water separator; 2. economizer; 3. high-pressure heater; 4. first shut-off valve; 5. second shut-off valve; 6. heat exchanger; 7. cooling water outlet pipe; 8. cooling water inlet pipe; 9. third shut-off valve; 10. circulating pump; 11. first flow regulating valve; 12. thermometer; 13. first stop valve; 14. flow meter; 15. water storage tank; 16. circulating pump heating pipeline; 17. circulating pump subcooling pipeline; 18. atmospheric expansion tank; 19. first regulating valve; 20. second stop valve; 21. circulating pipeline; 22. outlet pipe; 23. second flow regulating valve; 24. flow orifice plate; 25. minimum flow return pipeline; 26. inlet pipe; 27. second regulating valve; 28. third stop valve. DETAILED DESCRIPTION

[0019] Reference Figure 1 A boiler wet operation recirculation system, which comprises an economizer 2, a steam-water separator 1 and a high-pressure heater 3, wherein the drain of the steam-water separator is connected to a water storage tank 15, the outlet of the water storage tank is connected to a circulation pipeline 21, and the circulation pipeline is connected to the inlet of the economizer after passing through a circulation pump 10;

[0020] A minimum flow return pipeline 25 is connected between the outlet of the circulation pump and the outlet of the water storage tank. Part of the water pumped out of the outlet of the circulation pump is led to the outlet of the water storage tank after passing through the flow orifice plate and the second flow regulating valve, thereby improving the regulating characteristics of the circulation pump and maintaining the minimum safe flow of the circulation pump.

[0021] A circulating pump heating pipeline 16 is connected between the economizer outlet and the circulating pump outlet to prevent the recirculating pump from being subjected to thermal shock;

[0022] A circulating pump subcooling pipeline 17 is connected between the outlet of the high-pressure heater and the outlet of the water storage tank. When the load is rapidly reduced, the water at the outlet of the high-pressure heater is led to the outlet of the water storage tank through the circulating pump subcooling pipeline to prevent the circulating water at the inlet of the recirculating pump from flashing and causing cavitation of the circulating pump when the load is rapidly reduced.

[0023] The circulation pipeline is connected in parallel with the cooling water pipeline, and the cooling water pipeline is used to prevent high-temperature boiler water from entering the motor of the recirculation pump. The cooling water pipeline includes a heat exchanger 6, and the hot water inlet of the heat exchanger is connected to the circulation pipeline through an inlet pipe 26, and the hot water outlet of the heat exchanger is connected to the circulation pipeline through an outlet pipe 22.

[0024] In the boiler wet operation recirculation system, a flow orifice plate 24 and a second flow regulating valve 23 are installed on the minimum flow return pipeline.

[0025] In the boiler wet operation recirculation system, a first regulating valve 19 and a second stop valve 20 are installed on the circulation pump heating pipeline.

[0026] In the boiler wet operation recirculation system, a second regulating valve 27 and a third stop valve 28 are installed on the subcooling pipeline of the circulation pump.

[0027] Working principle: Water enters from the economizer inlet header, passes through the economizer, furnace to the steam-water separator, and after steam-water separation, the separated water enters the water storage tank and is sent to the economizer again by the circulating pump;

[0028] When the water level in the water tank is too high, the water in the water tank is led out to the atmospheric expansion tank through the water level control valve of the water tank;

[0029] A cooling water pipeline is provided, and a thermometer 12 is installed on the circulating water pipeline to monitor its temperature. When the temperature is too high, the second shut-off valve 5 on the inlet pipe and the third shut-off valve 9 on the outlet pipe are opened, and the first shut-off valve 4 on the circulating pipeline is closed. At this time, the circulating water is heat-exchanged by the heat exchanger to lower the water temperature, and then circulated by the circulating pump to prevent the high-temperature boiler water from entering the circulating pump motor and causing damage. The heat exchanger is a plate heat exchanger with a cooling water inlet pipe 8 and a cooling water outlet pipe 7. The cooling water is supplied by external water.

[0030] The recirculation system is designed to maintain the working medium flow rate in the boiler water-cooled wall tube at 30% BMCR (or above) during the startup process and when the boiler is running in a recirculation mode at low load. At this time, the working medium flow is: water enters from the economizer inlet header, passes through the economizer, furnace to the steam-water separator, and after steam-water separation, the separated water enters the water storage tank and is sent to the economizer again by the circulating pump. The separated steam enters the ceiling wall system, and then flows through the first-stage superheater, the second-stage partition screen superheater and the final-stage superheater in turn, and finally is led out by the main steam pipeline. When the unit load reaches the minimum DC load (30% BMCR load), the recirculation system exits operation and enters the hot standby state. At this time, the amount of feed water entering the boiler is equal to the amount of steam entering the steam turbine.

[0031] When the boiler is started, water is first added to the boiler and the corresponding exhaust (steam) is performed. The recirculation pump is started and the recirculation pipeline is put into operation. At this time, the feed water flowing through the boiler water wall is composed of two parts: feed water + recirculation flow. After starting the circulation pump, the heat of this recirculation volume is recovered.

[0032] It is beneficial to the safe operation of the superheater. The working fluid returned from the water storage tank to the economizer inlet directly heats the working fluid at the economizer inlet, which is beneficial to increase the inlet feed water temperature of the economizer, and also increases the inlet feed water temperature of the water-cooled wall. Under the same amount of fuel, the steam production at the furnace outlet increases, and the problem of superheater overheating can be effectively alleviated.

[0033] It is conducive to the safe operation of the boiler at low load. Under ultra-low load, the start-up circulation pump is used for wet operation, and the working medium flow in the water-cooled wall tube is maintained at a level higher than the minimum flow.

Claims

1. A boiler wet operation recirculation system, comprising an economizer, a steam-water separator and a high-pressure heater, characterized in that: The water drain of the steam-water separator is connected to the water storage tank, the outlet of the water storage tank is connected to the circulation pipeline, and the circulation pipeline is connected to the inlet of the economizer after passing through the circulation pump; A minimum flow return pipeline is connected between the circulation pump outlet and the water tank outlet; A circulating pump heating pipeline is connected between the economizer outlet and the circulating pump outlet; A circulating pump supercooling pipeline is connected between the outlet of the high-pressure heater and the outlet of the water storage tank; The circulating pipeline is connected in parallel with the cooling water pipeline, the cooling water pipeline includes a heat exchanger, the hot water inlet of the heat exchanger is connected to the circulating pipeline through an inlet pipe, and the hot water outlet of the heat exchanger is connected to the circulating pipeline through an outlet pipe.

2. The boiler wet operation recirculation system according to claim 1 is characterized in that: A flow orifice plate and a second flow regulating valve are installed on the minimum flow return pipeline.

3. The boiler wet operation recirculation system according to claim 2 is characterized in that: The heating pipeline of the circulation pump is provided with a first regulating valve and a second stop valve.

4. The boiler wet operation recirculation system according to claim 3 is characterized in that: The second regulating valve and the third stop valve are installed on the subcooling pipeline of the circulating pump.

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