Organic working medium-based combined air heater for realizing flue gas waste heat deep recovery anti-freezing system

Abstract

The application discloses a flue gas waste heat deep recovery anti-freezing system based on an organic working medium combined air heater, which comprises a flue gas waste heat utilization device, wherein the flue gas waste heat utilization device comprises an air preheater, a first inlet end of the air preheater is connected with an outlet end of a waste heat recovery auxiliary device, and a second inlet end of the air preheater is connected with a low-temperature flue gas end of a tail flue of a coal-fired boiler; a second outlet end of the air preheater is connected with a third inlet end of a low-temperature economizer through a flue gas flow valve, a third outlet end of the low-temperature economizer is connected with a first outlet end of the air preheater; a spraying device is connected between a spraying inlet and a spraying outlet of the low-temperature economizer through a spraying pipeline, and an organic working medium circulating device is connected between a circulating inlet and a circulating outlet of the low-temperature economizer through a circulating pipeline; the organic working medium circulating device and the spraying device are additionally arranged between the air preheater and an electric dust collector; while high-efficiency waste heat is recovered, the cold end temperature of the air preheater is improved, the air preheater is prevented from being blocked, and the effects of energy saving and consumption reduction and environmental protection of a power plant are achieved.

Description

A deep waste heat recovery and antifreeze system based on an organic working refrigerant combined with a warm air heater. Technical Field

[0001] This invention relates to the field of energy conservation and emission reduction technology in coal-fired power plants, and in particular to a system for deep recovery and antifreeze of flue gas waste heat based on an organic working fluid combined with a warm air heater. Background Technology

[0002] The flue gas temperature of coal-fired boilers is generally around 130℃. The low-temperature, wet, saturated flue gas they carry contains abundant latent heat of vaporization, and direct discharge into the atmosphere would result in significant heat loss. If this waste heat from the flue gas can be recovered and utilized to condense the low-temperature, wet, saturated flue gas, considerable economic benefits can be achieved, while also reducing white plumes, lowering emissions of flue gas pollutants, and saving water.

[0003] In northern my country, winter temperatures are relatively low, sometimes below 0°C and even below -30°C. Air preheaters are prone to low-temperature corrosion and ash accumulation, leading to reduced overall unit economics and, in severe cases, unplanned unit shutdowns. This is a common problem faced by power plants in northern China. Existing coal-fired power plants use low-pressure exhaust steam from the turbine to heat the cold air inlet of the air preheater; these are typically either steam-powered or water-powered air heaters. Traditional air heaters suffer from high auxiliary steam consumption, high energy consumption, and inability to be put into operation during initial boiler startup.

[0004] Chinese patent CN212841498U discloses a waste heat recovery steam boiler, relating to the field of heat recovery. The waste heat recovery structure includes a flue pipe and a water supply pipe. The water supply pipe is spirally wound around the outer wall of the flue pipe, and the heat emitted from the flue pipe heats the water supply pipe. The heated water in the water supply pipe is then sent to the furnace chamber, thereby collecting the waste heat generated by combustion, achieving waste heat collection, preventing heat loss, and avoiding waste. It also includes a treatment tank with a hot water exchange pipe inside for secondary recovery of the waste heat from the flue gas. A spray device is installed above the hot water exchange pipe to spray water and filter dust attached to the flue gas. The filter plate cleans the collected impurities, preventing environmental pollution from impurities in the flue gas. A demister is installed at the flue gas outlet pipe to remove excess water vapor before it is discharged from the outlet pipe. However, this patent application, which relies on the hot water exchange pipe inside the treatment tank for secondary recovery of the waste heat from the flue gas, suffers from insufficient heat exchange efficiency and incomplete utilization of the waste heat. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a deep waste heat recovery and antifreeze system for flue gas based on an organic working fluid combined with a warm air heater. This system adds an organic working fluid circulation device between the air preheater and the dust collector. After the organic working fluid undergoes its first heat exchange with the low-temperature flue gas in the low-temperature economizer, the organic working fluid vapor enters the compressor through the circulation pipeline via the organic working fluid circulation device and is continuously pressurized, becoming high-pressure, high-heat steam. This high-pressure, high-heat steam then enters the secondary air heater, where the secondary air and the high-pressure, high-heat organic working fluid steam complete a second heat exchange. This system efficiently recovers waste heat while simultaneously increasing the cold-end temperature of the air preheater, preventing blockage and providing energy savings, reduced consumption, and environmental benefits.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A flue gas waste heat recovery and antifreeze system based on an organic working fluid combined with a warm air heater includes a flue gas waste heat utilization device. The flue gas waste heat utilization device includes an air preheater 1. The first inlet end A of the air preheater 1 is connected to the outlet end of a waste heat recovery auxiliary device. The second inlet end C of the air preheater 1 is connected to the low-temperature flue gas end of the tail flue of a coal-fired boiler. The second outlet end E of the air preheater 1 is connected to the third inlet end F of a low-temperature economizer 2 through a flue gas flow valve 13. The third outlet end G of the low-temperature economizer 2 is connected to the first outlet end D of the air preheater 1. A spray device is connected between the spray inlet and the spray outlet of the low-temperature economizer 2 through a spray pipeline. An organic working fluid circulation device is connected between the circulation inlet and the circulation outlet of the low-temperature economizer 2 through a circulation pipeline.

[0008] The flue gas waste heat utilization device also includes an electrostatic precipitator 3, an induced draft fan 4, a desulfurization tower 5, and a chimney 6, which are sequentially connected to the first outlet end D of the air preheater 1.

[0009] The waste heat recovery auxiliary device includes an indirect cooling tower 14. The fourth outlet end H of the indirect cooling tower 14 is connected to the fourth inlet end I of the secondary air blower 10. The fifth outlet end J of the secondary air blower 10 is connected to the fifth inlet end K of the secondary air heater 8. The sixth outlet end B of the secondary air heater 8 is connected to the first inlet end A of the air preheater 1 in the phase change heat transfer flue gas waste heat utilization device.

[0010] The spraying device includes a first liquid storage tank 15, the sixth inlet end M of the first liquid storage tank 15 is connected to the spray outlet of the low-temperature economizer 2, the seventh outlet end N of the first liquid storage tank 15 is connected to the seventh inlet end O of the first circulating pump 16, and the eighth outlet end P of the first circulating pump 16 is connected to the spray inlet of the low-temperature economizer 2.

[0011] The cryogenic economizer 2 is equipped with a sprayer at the top.

[0012] Thermocouples are also installed at the spray inlet.

[0013] The organic working fluid circulation device includes a compressor 7. The eighth inlet end Q of the compressor 7 is connected to the circulation outlet of the low-temperature economizer 2. The ninth outlet end R of the compressor 7 is connected to the ninth inlet end S of the secondary air heater 8. The tenth outlet end T of the secondary air heater 8 is connected to the tenth inlet end U of the expansion valve 9. The eleventh outlet end V of the expansion valve 9 is connected to the eleventh inlet end W of the second liquid storage tank 11. The twelfth outlet end X of the second liquid storage tank 11 is connected to the twelfth inlet end Y of the second circulation pump 12. The thirteenth outlet end Z of the second circulation pump 12 is connected to the circulation inlet of the low-temperature economizer 2.

[0014] The organic working fluid circulation system contains an organic working fluid with a boiling point below 100℃ and a freezing point below 0℃. The saturation pressure of the organic working fluid at low temperature is greater than 0.1 MPa, and the condensation pressure of the organic working fluid at room temperature is ≤2.5 MPa.

[0015] The secondary air heater 8 uses a plate heat exchanger.

[0016] The beneficial effects of this invention are as follows:

[0017] 1. The air preheater 1 in the flue gas waste heat utilization device draws low-temperature flue gas from the tail flue of the coal-fired boiler. The flue gas is regulated by the flue gas flow valve 13 and enters the low-temperature economizer 2. The low-temperature flue gas undergoes indirect heat exchange with the heat exchange medium (i.e., organic working fluid) of the low-temperature economizer 2, heating the liquid organic working fluid into a gaseous organic working fluid. After heat exchange, part of the low-temperature flue gas condenses into water, achieving the effect of eliminating white spots in the flue gas. The other part of the flue gas is directly desulfurized by the electrostatic precipitator 3, the induced draft fan 4, and the desulfurization tower 5, and then discharged into the atmosphere from the chimney 6, which has the effect of energy saving and environmental protection.

[0018] 2. After the organic working fluid undergoes indirect heat exchange with the low-temperature flue gas in the low-temperature economizer 2 (i.e., the first heat exchange), a large amount of hot organic working fluid vapor enters the compressor 7 through the organic working fluid circulation device and is continuously pressurized to become high-pressure, high-heat steam. Then, the high-pressure, high-heat steam enters the secondary air heater 8, transferring a large amount of heat energy from the organic working fluid to the secondary air. Finally, the cold organic working fluid returns to its initial state through the expansion valve 9, and then returns to the low-temperature economizer 2 through the second liquid storage tank 11 and the second circulation pump 12, achieving the goal of energy saving and consumption reduction in the power plant.

[0019] 3. After the low-temperature flue gas passes through the low-temperature economizer 2 for heat exchange, a portion of the low-temperature flue gas condenses into water. The flue gas condensate is deposited at the bottom of the low-temperature economizer 2 and passes through the first liquid storage tank 15 and the first circulation pump 16 in sequence through the spray outlet. Then it enters the top spray inlet of the low-temperature economizer 2 to rinse the low-temperature economizer 2 to prevent ash accumulation and to prevent corrosion.

[0020] 4. Secondary air enters the secondary air heater 8 from the intercooling tower 14 of the waste heat recovery auxiliary device through the secondary air blower 10. The secondary air in the secondary air heater 8 completes the second heat exchange with the high-pressure, high-heat organic working fluid steam. The hot secondary air that has completed the heat exchange enters the air preheater 1 to increase the cold end temperature of the air preheater 1 and prevent the air preheater 1 from being blocked. Attached Figure Description

[0021] Figure 1 is a schematic diagram of the structure of the present invention.

[0022] In the diagram: 1. Air preheater; 2. Low-temperature economizer; 3. Electrostatic precipitator; 4. Exhaust fan; 5. Desulfurization tower; 6. Chimney; 7. Compressor; 8. Secondary air heater; 9. Expansion valve; 10. Secondary air blower; 11. Second liquid storage tank; 12. Third air inlet; 13. Flue gas flow valve; 14. Indirect cooling tower; 15. First liquid storage tank; 16. First circulating pump; A. First inlet end; B. Sixth outlet end; C. Second inlet end; D. First outlet end; E. Second outlet end F, Third inlet; G, Third outlet; H, Fourth outlet; I, Fourth inlet; J, Fifth outlet; K, Fifth inlet; M, Sixth inlet; N, Seventh outlet; O, Seventh inlet; P, Eighth outlet; Q, Eighth inlet; R, Ninth outlet; S, Ninth inlet; T, Tenth outlet; U, Tenth inlet; V, Eleventh outlet; W, Eleventh inlet; X, Twelfth outlet; Y, Twelfth inlet; Z, Thirteenth outlet. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] Example

[0025] Referring to Figure 1, a flue gas waste heat deep recovery and antifreeze system based on an organic working fluid combined with a warm air heater includes a flue gas waste heat utilization device. The flue gas waste heat utilization device includes an air preheater 1. The first inlet end A of the air preheater 1 is connected to the outlet end of the waste heat recovery auxiliary device. The second inlet end C of the air preheater 1 is connected to the low-temperature flue gas end of the tail flue of the coal-fired boiler. The second outlet end E of the air preheater 1 is connected to the third inlet end F of the low-temperature economizer 2 through a flue gas flow valve 13. The third outlet end G of the low-temperature economizer 2 is connected to the first outlet end D of the air preheater 1. A spray device is connected between the spray inlet and the spray outlet of the low-temperature economizer 2 through a spray pipeline. An organic working fluid circulation device is connected between the circulation inlet and the circulation outlet of the low-temperature economizer 2 through a circulation pipeline, thereby achieving the purpose of energy saving and consumption reduction in power plants.

[0026] The flow regulating valve 13 can be an electric butterfly valve for easy flow regulation, or a gate valve can be added so that when the electric gate valve loses control, it can be fully opened or fully closed.

[0027] The flue gas waste heat utilization device also includes an electrostatic precipitator 3, an induced draft fan 4, and a desulfurization tower 5 connected in sequence to the first outlet end of the air preheater 1. After desulfurization, the flue gas is discharged into the atmosphere from the chimney 6.

[0028] The waste heat recovery auxiliary device includes an indirect cooling tower 14. The fourth outlet end H of the indirect cooling tower 14 is connected to the fourth inlet end I of the secondary air blower 10. The fifth outlet end J of the secondary air blower 10 is connected to the fifth inlet end K of the secondary air heater 8. The sixth outlet end B of the secondary air heater 8 is connected to the first inlet end A of the air preheater 1 in the phase change heat transfer flue gas waste heat utilization device, thereby increasing the cold end temperature of the air preheater 1 and preventing the air preheater 1 from becoming blocked.

[0029] The spraying device includes a first liquid storage tank 15. The sixth inlet end M of the first liquid storage tank 15 is connected to the spray outlet of the low-temperature economizer 2. The seventh outlet end N of the first liquid storage tank 15 is connected to the seventh inlet end O of the first circulating pump 16. The eighth outlet end P of the first circulating pump 16 is connected to the spray inlet of the low-temperature economizer 2, which prevents ash accumulation in the low-temperature economizer 2 and plays a role in corrosion prevention.

[0030] The cryogenic economizer 2 is equipped with a sprayer at the top.

[0031] A thermocouple is also installed at the spray inlet to measure the flue gas temperature at that location.

[0032] The organic working fluid circulation device includes a compressor 7. The eighth inlet end Q of the compressor 7 is connected to the circulation outlet of the low-temperature economizer 2. The ninth outlet end R of the compressor 7 is connected to the ninth inlet end S of the secondary air heater 8. The tenth outlet end T of the secondary air heater 8 is connected to the tenth inlet end U of the expansion valve 9. The eleventh outlet end V of the expansion valve 9 is connected to the eleventh inlet end W of the second liquid storage tank 11. The twelfth outlet end X of the second liquid storage tank 11 is connected to the twelfth inlet end Y of the second circulation pump 12. The thirteenth outlet end Z of the second circulation pump 12 is connected to the circulation inlet of the low-temperature economizer 2, thereby achieving the purpose of energy saving and consumption reduction in the power plant.

[0033] The organic working fluid circulation system is equipped with an organic working fluid with a boiling point below 100℃ and a freezing point below 0℃. The saturation pressure of the organic working fluid at low temperature is greater than 0.1 MPa to prevent air from entering the working fluid. The condensation pressure of the organic working fluid at room temperature is ≤2.5 MPa to reduce the pressure on the device.

[0034] The secondary air heater 8 uses a plate heat exchanger.

[0035] The working principle of this invention is as follows:

[0036] During operation, the air preheater 1 in the flue gas waste heat utilization device draws flue gas from the low-temperature flue gas at the tail flue of the coal-fired boiler. After being regulated by the flue gas flow valve 13, the flue gas enters the low-temperature economizer 2. The low-temperature flue gas undergoes indirect heat exchange with the heat exchange medium (i.e., organic working fluid) of the low-temperature economizer 2, heating the liquid organic working fluid into a gaseous organic working fluid. After heat exchange, a portion of the low-temperature flue gas condenses into water, achieving the effect of eliminating whitening of the flue gas. The other portion of the flue gas is directly discharged into the atmosphere through the electrostatic precipitator 3, induced draft fan 4, desulfurization tower 5, and chimney 6, which has the effect of energy saving and environmental protection.

[0037] After the organic working fluid undergoes indirect heat exchange with the low-temperature flue gas in the low-temperature economizer 2 (i.e., the first heat exchange), a large amount of hot organic working fluid vapor enters the compressor 7 through the organic working fluid circulation device and is continuously pressurized to become high-pressure, high-heat steam. Then, the high-pressure, high-heat steam enters the secondary air heater 8, transferring a large amount of heat energy from the organic working fluid to the secondary air. Finally, the cold organic working fluid returns to its initial state through the expansion valve 9, and then returns to the low-temperature economizer 2 through the second liquid storage tank 11 and the second circulation pump 12, achieving the goal of energy saving and consumption reduction in the power plant.

[0038] After the low-temperature flue gas passes through the low-temperature economizer 2 for heat exchange, a portion of the low-temperature flue gas condenses into water. The flue gas condensate is deposited at the bottom of the low-temperature economizer 2 and passes through the first liquid storage tank 15 and the first circulation pump 16 in sequence through the spray outlet. Then it enters the top spray inlet of the low-temperature economizer 2 to rinse the low-temperature economizer 2 to prevent ash accumulation and to prevent corrosion.

[0039] Secondary air enters the secondary air heater 8 from the intercooler tower 14 of the waste heat recovery auxiliary device through the secondary air blower 10. The secondary air in the secondary air heater 8 completes a second heat exchange with the high-pressure, high-heat organic working fluid steam. The hot secondary air that has completed the heat exchange enters the air preheater 1 to increase the cold end temperature of the air preheater 1 and prevent the air preheater 1 from becoming blocked.

Claims

1. A flue gas waste heat recovery and antifreeze system based on an organic working fluid combined with a warm air heater, comprising a flue gas waste heat utilization device, characterized in that: The waste heat recovery device includes an air preheater (1), the first inlet A of which is connected to the outlet of the waste heat recovery auxiliary device, and the second inlet C of which is connected to the low-temperature flue gas end of the tail flue of the coal-fired boiler; the second outlet E of which is connected to the third inlet F of the low-temperature economizer (2) through a flue gas flow valve (13), and the third outlet G of the low-temperature economizer (2) is connected to the first outlet D of the air preheater (1); a spraying device is connected between the spraying inlet and the spraying outlet of the low-temperature economizer (2) through a spraying pipeline, and an organic working fluid circulation device is connected between the circulation inlet and the circulation outlet of the low-temperature economizer (2) through a circulation pipeline; the spraying device includes a first liquid storage tank (15), the sixth inlet M of which is connected to the spraying outlet of the low-temperature economizer (2), and the seventh outlet of which is connected to the spraying outlet of the low-temperature economizer (2). End N is connected to the seventh inlet end O of the first circulation pump (16), and the eighth outlet end P of the first circulation pump (16) is connected to the spray inlet of the low-temperature economizer (2); a sprayer is provided at the top inside the low-temperature economizer (2); the organic working fluid circulation device includes a compressor (7), the eighth inlet end Q of the compressor (7) is connected to the circulation outlet of the low-temperature economizer (2), the ninth outlet end R of the compressor (7) is connected to the ninth inlet end S of the secondary air heater (8), the tenth outlet end T of the secondary air heater (8) is connected to the tenth inlet end U of the expansion valve (9), the eleventh outlet end V of the expansion valve (9) is connected to the eleventh inlet end W of the second liquid storage tank (11), the twelfth outlet end X of the second liquid storage tank (11) is connected to the twelfth inlet end Y of the second circulation pump (12), and the thirteenth outlet end Z of the second circulation pump (12) is connected to the circulation inlet of the low-temperature economizer (2).

2. The antifreeze system for deep recovery of waste heat from flue gas based on an organic working fluid combined with a warm air heater according to claim 1, characterized in that: The flue gas waste heat utilization device also includes an electrostatic precipitator (3), an induced draft fan (4), a desulfurization tower (5), and a chimney (6) connected in sequence to the first outlet end D of the air preheater (1).

3. The antifreeze system for deep recovery of waste heat from flue gas based on an organic working fluid combined with a warm air heater according to claim 1, characterized in that: The waste heat recovery auxiliary device includes an intercooling tower (14), the fourth outlet end H of the intercooling tower (14) is connected to the fourth inlet end I of the secondary air blower (10), the fifth outlet end J of the secondary air blower (10) is connected to the fifth inlet end K of the secondary air heater (8), and the sixth outlet end B of the secondary air heater (8) is connected to the first inlet end A of the air preheater (1) in the phase change heat transfer flue gas waste heat utilization device.

4. The antifreeze system for deep recovery of waste heat from flue gas based on an organic working fluid combined with a warm air heater according to claim 1, characterized in that: Thermocouples are also installed at the spray inlet.

5. The antifreeze system for deep recovery of waste heat from flue gas based on an organic working fluid combined with a warm air heater according to claim 1, characterized in that: The organic working fluid circulation system contains an organic working fluid with a boiling point below 100℃ and a freezing point below 0℃. The saturation pressure of the organic working fluid at low temperature is greater than 0.1 MPa, and the condensation pressure of the organic working fluid at room temperature is ≤2.5 MPa.

6. A flue gas waste heat deep recovery and antifreeze system based on an organic working fluid combined with a warm air heater, as described in claim 1 or 3, characterized in that: The secondary air heater (8) uses a plate heat exchanger.

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