CN112283694A - Low-temperature flue gas water recovery and waste heat utilization coupling system of coal-fired power plant and operation method - Google Patents

Low-temperature flue gas water recovery and waste heat utilization coupling system of coal-fired power plant and operation method Download PDF

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Publication number
CN112283694A
CN112283694A CN202011155072.5A CN202011155072A CN112283694A CN 112283694 A CN112283694 A CN 112283694A CN 202011155072 A CN202011155072 A CN 202011155072A CN 112283694 A CN112283694 A CN 112283694A
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control valve
flue gas
temperature
low
communicated
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CN112283694B (en
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刘明
杨凯旋
严俊杰
邢秦安
种道彤
刘继平
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Xian Jiaotong University
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Xian Jiaotong University
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22D—PREHEATING, OR ACCUMULATING PREHEATED, FEED-WATER FOR STEAM GENERATION; FEED-WATER SUPPLY FOR STEAM GENERATION; CONTROLLING WATER LEVEL FOR STEAM GENERATION; AUXILIARY DEVICES FOR PROMOTING WATER CIRCULATION WITHIN STEAM BOILERS
    • F22D1/00—Feed-water heaters, i.e. economisers or like preheaters
    • F22D1/36—Water and air preheating systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J11/00—Devices for conducting smoke or fumes, e.g. flues 
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J15/00—Arrangements of devices for treating smoke or fumes
    • F23J15/02—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J15/00—Arrangements of devices for treating smoke or fumes
    • F23J15/02—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material
    • F23J15/022—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material for removing solid particulate material from the gasflow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J15/00—Arrangements of devices for treating smoke or fumes
    • F23J15/06—Arrangements of devices for treating smoke or fumes of coolers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J15/00—Arrangements of devices for treating smoke or fumes
    • F23J15/08—Arrangements of devices for treating smoke or fumes of heaters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N5/00—Systems for controlling combustion
    • F23N5/26—Details
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00—Combustion technologies with mitigation potential
    • Y02E20/30—Technologies for a more efficient combustion or heat usage
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00—Combustion technologies with mitigation potential
    • Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery

Abstract

The invention discloses a low-temperature flue gas water recovery and waste heat utilization coupling system and an operation method for a coal-fired power plant, wherein the system comprises a rotary air preheater, a low-temperature economizer, a first part adjustable flue gas heat exchanger, a second part adjustable flue gas heat exchanger, a low-temperature flue gas cooler, an electric dust remover, a desulfurizing tower, a flue gas condenser, a flue gas reheater, a chimney, a first stage air heater, a second stage air heater, a plurality of circulating water pumps and a plurality of control valves; the low-temperature flue gas waste heat is recycled to a turbine regenerative system or used for preheating air through a plurality of flue gas heat exchangers, so that the coal consumption of the unit is reduced; water recovery is carried out through a flue gas condenser; the flue gas is reheated by a flue gas reheater, so that low-temperature corrosion to a chimney is reduced; the operation of the adjustable flue gas heat exchanger is controlled by the control valve, and the adjustable flue gas heat exchanger is connected with other flue gas heat exchangers in series to work together under different working conditions, so that the temperature of flue gas entering the electric dust remover is maintained above 90 ℃, and the temperature of circulating water entering the low-temperature flue gas cooler is ensured above 70 ℃, so that the system can safely operate under different environmental temperatures.

Description

Low-temperature flue gas water recovery and waste heat utilization coupling system of coal-fired power plant and operation method
Technical Field
The invention relates to the technical field of coal-fired power generation, in particular to a low-temperature flue gas water recovery and waste heat utilization coupling system of a coal-fired power station and an operation method.
Background
The high-speed development of economy in China is continuously increased, and the stable and powerful support of the energy industry cannot be provided. The coal-fired power generation in a short time is still the main power generation mode in China due to the fact that fossil energy reserves in China. In recent years, China makes great progress in the thermal power generation industry, the efficiency and the operation flexibility of the coal-fired power station are improved, and the reduction of pollutant emission and resource consumption are long-term concerns of the coal-fired power station, so that the deep utilization of waste heat of the coal-fired power station and the continuous reduction of emission of nitrogen oxides, sulfides and standard particulate matters of a thermal power unit have important significance for the energy conservation and emission reduction work of China.
The waste heat recovery of the exhaust smoke of the coal-fired power plant can reduce the heat loss of the exhaust smoke of the boiler, and the conventional means utilizes the heat of the low-temperature exhaust smoke of the boiler through a low-temperature coal economizer or a fan heater, thereby improving the power generation efficiency of the coal-fired power plant. The boiler flue gas water recovery is to treat the boiler flue gas and recover the moisture in the flue gas. Because the conventional coal-fired power plant desulfurization means is wet desulfurization, the wet-desulfurized flue gas vapor reaches a saturated state, the water content of the flue gas reaches 12% -16%, and the water consumption of the 600MW coal-fired power plant wet desulfurization is 80-100 t/h. Through flue gas water recovery, the water content of flue gas can be reduced to 8% -9%, the recovered water can exceed 20kg/s, and even the zero water consumption operation of a unit is achieved. However, the conventional flue gas water recovery and waste heat utilization system is an independent system, which causes the following problems:
1. in the water recovery process, partial latent heat is still available to improve the efficiency of the unit even though the taste is low.
2. The low-temperature flue gas preheating and water recovery system is difficult to match with the variable working condition operation of a unit, and particularly when the environmental temperature is low, the temperature of flue gas entering an electric dust collector is easy to be too low, so that low-temperature corrosion is caused.
Therefore, the low-temperature flue gas water recovery and waste heat utilization system of the coal-fired power plant needs to be further optimized, the variable working condition operation of the unit is urgently needed to be met by reasonably distributing the area of the heat exchanger and recovering the flue gas waste heat, the low-temperature corrosion is reduced, and the circulation efficiency is improved.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide a coupling system for recovering low-temperature flue gas water and utilizing waste heat of a coal-fired power plant and an operation method thereof, wherein the system recovers the low-temperature flue gas waste heat to a turbine regenerative system through a low-temperature economizer so as to reduce the coal consumption of a unit; the air is preheated by the air heater, so that the temperature of the air entering the air preheater is increased, the irreversible loss of the air preheater is reduced, and the coal consumption of a unit is reduced; the flue gas is reheated by a flue gas reheater, so that the flue gas entering a chimney has a superheat degree of 15 ℃, and low-temperature corrosion to the chimney is reduced; the operation of the adjustable flue gas heat exchanger is controlled by the control valve, and the adjustable flue gas heat exchanger is connected with other flue gas heat exchangers in series to work together under different working conditions, so that the temperature of flue gas entering the electric dust remover is maintained above 90 ℃, and the temperature of circulating water entering the low-temperature flue gas cooler is ensured above 70 ℃, so that the system can safely operate under different environmental temperatures.
In order to achieve the purpose, the invention adopts the following technical scheme:
the coupling system for recycling the low-temperature flue gas water and utilizing the waste heat of the coal-fired power plant comprises a rotary air preheater 1, a low-temperature economizer 2, a first part adjustable flue gas heat exchanger 3, a second part adjustable flue gas heat exchanger 4, a low-temperature flue gas cooler 5, an electric dust remover 6, a desulfurizing tower 7, a flue gas condenser 8, a flue gas reheater 9 and a chimney 10, wherein the low-temperature economizer 2 is sequentially communicated with a flue gas outlet of the rotary air preheater 1; a second-stage air heater 11 and a first-stage air heater 12 which are communicated with the air side inlet of the rotary air preheater 1; the system also comprises a flue gas reheating system circulating water pump 13, a second-stage air heater circulating water pump 14, a first-stage air heater circulating water pump 15, a steam turbine reheating system 16, a heat pump heating system 17 and a control valve; a water side inlet of the low-temperature economizer 2 is communicated with a water side outlet of the first part adjustable flue gas heat exchanger 3 through a sixth control valve f, is communicated with a steam turbine heat regenerative system 16 through a fifth control valve e, is communicated with a water side inlet of the first part adjustable flue gas heat exchanger 3 through a fifth control valve e and a third control valve c in sequence, is communicated with a water side outlet of a flue gas reheater 9 through a fifth control valve e, a third control valve c and a fourth control valve d in sequence, is communicated with a water side inlet of the second part adjustable flue gas heat exchanger 4 through a fifth control valve e, a third control valve c, a fourth control valve d and a seventh control valve g in sequence, and is communicated with an inlet of a circulating water pump 13 of the flue gas reheating system through the sixth control valve f and the first control valve a in sequence; the water side outlet of the first part adjustable flue gas heat exchanger 3 is communicated with the inlet of a circulating water pump 13 of a flue gas reheating system through a first control valve a, is communicated with a turbine heat regenerative system 16 through a sixth control valve f and a fifth control valve e in sequence, is communicated with the water side inlet of the first part adjustable flue gas heat exchanger 3 through the sixth control valve f, the fifth control valve e and a third control valve c in sequence, and is communicated with the water side inlet of the first part adjustable flue gas heat exchanger through the sixth control valve f, the fifth control valve e and the third control valve c in sequence, a fourth control valve d and a seventh control valve g are communicated with a water side inlet of the second part of adjustable flue gas heat exchanger 4, communicated with a water side outlet of the second part of adjustable flue gas heat exchanger 4 through a first control valve a and a second control valve b in sequence, and communicated with a water side outlet of the flue gas reheater 9 through a sixth control valve f, a fifth control valve e, a third control valve c and a fourth control valve d in sequence; the water side inlet of the first part of adjustable flue gas heat exchanger 3 is communicated with the water side outlet of the flue gas reheater 9 through a fourth control valve d, is communicated with a turbine heat recovery system 16 through a third control valve c, is communicated with the water side inlet of the second part of adjustable flue gas heat exchanger 4 through a fourth control valve d and a seventh control valve g in sequence, is communicated with the inlet of the flue gas reheating system circulating water pump 13 through a third control valve c, a fifth control valve e, a sixth control valve f and a first control valve a in sequence, and is communicated with the water side outlet of the second part of adjustable flue gas heat exchanger 4 through the third control valve c, the fifth control valve e, the sixth control valve f, the first control valve a and a second control valve b in sequence; the water side outlet of the second part adjustable flue gas heat exchanger 4 is communicated with the inlet of a second stage air heater circulating water pump 14 through a ninth control valve i, is communicated with the inlet of a flue gas reheating system circulating water pump 13 through a second control valve b, is communicated with the water side outlet of a low-temperature flue gas cooler 5 through a ninth control valve i and a tenth control valve j in sequence, is communicated with the water side inlet of the second part adjustable flue gas heat exchanger 4 through a ninth control valve i, a tenth control valve j and an eighth control valve h in sequence, is communicated with a steam turbine reheating system 16 through a second control valve b, a first control valve a, a sixth control valve f, a fifth control valve e, a third control valve c and a fourth control valve d in sequence, is communicated with the water side outlet of a flue gas reheater 9 through a second control valve b, a first control valve a, a sixth control valve f, a fifth control valve e, a third control valve c and a fourth control valve d in sequence, and is communicated with the water side outlet of a flue, The first control valve a, the sixth control valve f, the fifth control valve e, the third control valve c, the fourth control valve d and the seventh control valve g are communicated with a water side inlet of the second part adjustable flue gas heat exchanger 4; the water side inlet of the adjustable flue gas heat exchanger 4 of the second part is communicated with the water side outlet of the flue gas reheater 9 through a seventh control valve g, is communicated with the water side outlet of the low-temperature flue gas cooler 5 through an eighth control valve h, is communicated with the inlet of the second-stage air heater circulating water pump 14 through an eighth control valve h and a tenth control valve j in sequence, is communicated with the turbine heat regenerative system 16 through a seventh control valve g, a fourth control valve d and a third control valve c in sequence, and is communicated with the inlet of the flue gas reheating system circulating water pump 13 through a seventh control valve g, a fourth control valve d, a third control valve c, a fifth control valve e, a sixth control valve f and a first control valve a in sequence; the outlet of the water side of the low-temperature flue gas cooler 5 is communicated with the inlet of a circulating water pump 14 of a second-stage air heater through a tenth control valve j; a water side inlet of the low-temperature flue gas cooler 5 is communicated with a water side outlet of a second-stage air heater 11 through an eleventh control valve k, is communicated with a water side outlet of a first-stage air heater 12 through a fourteenth control valve n, is communicated with a water side inlet of the first-stage air heater 12 through an eleventh control valve k and a twelfth control valve l in sequence, is communicated with an outlet of a circulating water pump 15 of the first-stage air heater through the eleventh control valve k, the twelfth control valve l and a thirteenth control valve m in sequence, and is communicated with a water side inlet of a flue gas condenser 8 and a low-temperature side outlet of a heat pump heat supply system 17 through the fourteenth control valve n and a fifteenth control valve o in sequence; the water side inlet of the second-stage air heater 11 is communicated with the outlet of the second-stage air heater circulating water pump 14; the water side outlet of the second-stage air heater 11 is communicated with the water side inlet of the first-stage air heater 12 through a twelfth control valve l, is communicated with the outlet of the circulating water pump 15 of the first-stage air heater through a twelfth control valve l and a thirteenth control valve m in sequence, is communicated with the water side outlet of the first-stage air heater 12 through an eleventh control valve k and a fourteenth control valve n in sequence, and is communicated with the water side inlet of the flue gas condenser 8 and the low-temperature side outlet of the heat pump heat supply system 17 through an eleventh control valve k, a fourteenth control valve n and a fifteenth control valve o in sequence; the water side inlet of the first-stage air heater 12 is communicated with the outlet of the first-stage air heater circulating water pump 15 through a thirteenth control valve m; the water side outlet of the first-stage air heater 12 is communicated with the water side inlet of the flue gas condenser 8 and the low-temperature side outlet of the heat pump heating system 17 through a fifteenth control valve o; the water side outlet of the flue gas condenser 8 is communicated with the inlet of a circulating water pump 15 of the first-stage air heater and the inlet of the low-temperature side of a heat pump heating system 17; the water side inlet of the flue gas condenser 8 is communicated with the low-temperature side outlet of the heat pump heating system 17; the water side inlet of the flue gas reheater 9 is communicated with the outlet of a circulating water pump 13 of the flue gas reheating system; flue gas from a boiler sequentially passes through a rotary air preheater 1, a low-temperature economizer 2, a first part adjustable flue gas heat exchanger 3, a second part adjustable flue gas heat exchanger 4 and a low-temperature flue gas cooler 5 to be cooled, then enters an electric dust remover 6 and a desulfurizing tower 7 to remove dust and sulfur dioxide in the flue gas, then passes through a flue gas condenser 8 to recover partial moisture and latent heat in the flue gas, passes through a flue gas reheater 9 to raise the temperature to reach the emission standard, and finally enters a chimney 10 to be discharged to the atmosphere; the cold air absorbs heat in the first stage air heater 12 and the second stage air heater 11, and then is sent to the rotary air preheater 1 for further temperature rise, and then sent to the boiler.
When the first control valve a, the fourth control valve d and the fifth control valve e are closed, and the third control valve c and the sixth control valve f are opened, the low-temperature economizer 2 and the first part adjustable flue gas heat exchanger 3 are connected in series to jointly absorb the waste heat of low-temperature flue gas so as to heat the condensed water from the turbine regenerative system; when the third control valve c and the sixth control valve f are closed and the fifth control valve e is opened, the low-temperature economizer 2 absorbs the waste heat of the low-temperature flue gas to heat the condensed water from the turbine regenerative system.
The second control valve b, the third control valve c, the sixth control valve f and the seventh control valve g are closed, when the first control valve a and the fourth control valve d are opened, the first part can adjust the flue gas heat exchanger 3, the flue gas reheating system circulating water pump 13 and the flue gas reheater 9 to form a closed loop, and the first part can adjust the flue gas heat exchanger 3 to absorb the waste heat of the low-temperature flue gas so as to meet the heat load requirement of the flue gas reheater 9 for reheating the flue gas; the first control valve a, the fourth control valve d, the eighth control valve h and the ninth control valve i are closed, when the second control valve b and the seventh control valve g are opened, the second part can adjust the flue gas heat exchanger 4, the flue gas reheating system circulating water pump 13 and the flue gas reheater 9 to form a closed loop, and the second part can adjust the flue gas heat exchanger 4 to absorb the waste heat of the low-temperature flue gas so as to meet the heat load requirement of the flue gas reheater 9 for reheating the flue gas.
When the seventh control valve g, the second control valve b and the tenth control valve j are closed, and the eighth control valve h and the ninth control valve i are opened, the low-temperature flue gas cooler 5 and the second part adjustable flue gas heat exchanger 4 are connected in series to reduce the flue gas temperature to about 95 ℃, circulating water is conveyed to an air preheating device through a second stage air heater circulating water pump 14, and the heat of the part of flue gas is used for preheating air; when the eighth control valve h, the ninth control valve i and the tenth control valve j are opened, the low-temperature flue gas cooler 5 reduces the temperature of the flue gas to about 95 ℃, circulating water is conveyed to an air preheating device through the second-stage air heater circulating water pump 14, and the heat of the flue gas is used for preheating the air.
The twelfth control valve l and the fourteenth control valve n are closed, when the eleventh control valve k, the thirteenth control valve m and the fifteenth control valve o are opened, the second-stage air heater 11 preheats air by using circulating water conveyed by the second-stage air heater circulating water pump 14, the first-stage air heater 12 conveys part of condensed water of the flue gas condenser 8 by using the first-stage air heater circulating water pump 15, part of latent heat recovered by the flue gas condenser 8 is used for preheating air, and the other part of recovered latent heat is conveyed to a heat pump system to be used for heating after the heat quality is improved; and when the eleventh control valve k, the thirteenth control valve m and the fifteenth control valve o are closed, and the twelfth control valve l and the fourteenth control valve n are opened, the second-stage air heater 11 and the first-stage air heater 12 are connected in series, the circulating water delivered by the circulating water pump 14 of the second-stage air heater is jointly used for preheating air, and the latent heat recovered by the flue gas condenser 8 is delivered to the heat pump system to be used for heat supply after the heat quality is improved.
And the working media conveyed by the flue gas reheating system circulating water pump 13, the second-stage air heater circulating water pump 14 and the first-stage air heater circulating water pump 15 are all water.
The flue gas temperature of the flue gas condenser 8 is reduced to 45 ℃ in winter, the flue gas temperature is reduced to 43 ℃ in summer, and 6-8 kg/s of condensed water can be recycled.
The flue gas reheater 9 raises the temperature of the flue gas by 15 ℃, ensures that the flue gas entering the chimney 10 has a superheat degree of 15 ℃, reduces the corrosion to the chimney 10, and meets the flue gas emission standard.
In the operation method of the coal-fired power plant low-temperature flue gas water recovery and waste heat utilization coupling system, when the ambient temperature is higher than 0 ℃, the first control valve a, the fourth control valve d, the fifth control valve e, the eighth control valve h, the ninth control valve i, the eleventh control valve k, the thirteenth control valve m and the fifteenth control valve o are closed, the second control valve b, the third control valve c, the sixth control valve f, the seventh control valve g, the tenth control valve j, the twelfth control valve l and the fourteenth control valve n are opened, the low-temperature economizer 2 and the first part adjustable flue gas heat exchanger 3 are connected in series to jointly absorb the waste heat of low-temperature flue gas so as to heat condensed water from a turbine reheating system, the second part flue gas adjustable heat exchanger 4, the flue gas reheater 9 and the flue gas reheating system circulating water pump 13 form a closed loop, the second part adjustable flue gas heat exchanger 4 absorbs the waste heat of the low-temperature flue gas so as to meet the heat load requirement of the flue gas reheater 9, the first-stage air heater 12, the low-temperature flue gas cooler 5, the second-stage air heater circulating water pump 14 and the second-stage air heater 11 form a closed cycle, and the flue gas heat absorbed by the low-temperature flue gas cooler 5 is used for preheating air; when the ambient temperature is-10 to 0 ℃, the second control valve b, the third control valve c, the sixth control valve f, the seventh control valve g, the tenth control valve j, the eleventh control valve k, the thirteenth control valve m and the fifteenth control valve o are closed, the first control valve a, the fourth control valve d, the fifth control valve e, the eighth control valve h, the ninth control valve i, the twelfth control valve l and the fourteenth control valve n are opened, the low-temperature economizer 2 absorbs the waste heat of the low-temperature flue gas to heat the condensate water from the turbine regenerative system, the first adjustable flue gas heat exchanger 3, the flue gas reheater 9 and the flue gas reheating system circulating water pump 13 form a closed loop, the first adjustable flue gas heat exchanger 3 absorbs the waste heat of the low-temperature flue gas to meet the heat load requirement of the reheated flue gas of the flue gas cooler 9, the first-stage air heater 12, the low-temperature flue gas cooler 5, the second-stage air heater 12, the second-gas cooler 5, the second-temperature, The second part of adjustable flue gas heat exchanger 4, the second stage air heater circulating water pump 14 and the second stage air heater 11 form a closed cycle, and the flue gas heat absorbed by the low-temperature flue gas cooler 5 and the second part of adjustable flue gas heat exchanger 4 is used for preheating air; when the ambient temperature is-20 to-10 ℃, the second control valve b, the third control valve c, the sixth control valve f, the seventh control valve g, the tenth control valve j, the twelfth control valve 1 and the fourteenth control valve n are closed, the first control valve a, the fourth control valve d, the fifth control valve e, the eighth control valve h, the ninth control valve i, the eleventh control valve k, the thirteenth control valve m and the fifteenth control valve o are opened, the low-temperature economizer 2 absorbs the low-temperature flue gas waste heat to heat the condensed water from the turbine regenerative system, the first part of adjustable flue gas heat exchanger 3, the flue gas reheater 9 and the flue gas reheating system circulating pump 13 form a closed-loop cycle, the first part of adjustable flue gas heat exchanger 3 absorbs the low-temperature flue gas waste heat to meet the heat load requirement of the reheated flue gas of the flue gas reheater 9, and the second-stage air heater 11 absorbs the low-temperature flue gas waste heat pump 3 to meet the heat load requirement of the reheated, The low-temperature flue gas cooler 5, the second part adjustable flue gas heat exchanger 4 and the second stage air heater circulating water pump 14 form closed cycle, the flue gas heat absorbed by the low-temperature flue gas cooler 5 and the second part adjustable flue gas heat exchanger 4 is used for preheating air, and the first stage air heater 12 preheats air by using the latent heat recovered by part of the flue gas condenser 8; in addition, the system ensures that the temperature of the flue gas at the outlet of the low-temperature flue gas cooler 5 is maintained above 90 ℃ and the temperature of the circulating water entering the low-temperature flue gas cooler 5 is above 70 ℃ by adjusting the mass flow of the condensed water at the inlet A, adjusting the mass flow of the circulating water entering the low-temperature flue gas cooler 5 through the second-stage air heater circulating water pump 14 and adjusting the mass flow of the circulating water entering the flue gas reheater 9 through the flue gas reheating system circulating water pump 13.
Compared with the prior art, the invention has the following advantages:
1. by distributing the area of the air heater, the latent heat of the water recovery process can be recovered by utilizing part of the flue gas condenser when the ambient temperature is lower.
2. The low-temperature flue gas waste heat is recovered through the low-temperature economizer, the air is preheated through the low-temperature flue gas waste heat and the latent heat generated in the water recovery process of the flue gas condenser through the air heater, the irreversible loss of the air preheater is reduced, and the unit coal consumption is reduced.
3. The area of the heat exchanger and the mass flow of the condensed water are adjusted through the control valve, the temperature of the flue gas entering the electric dust remover is maintained above 90 ℃ at different environmental temperatures, the temperature of the circulating water entering the low-temperature flue gas cooler is ensured above 70 ℃, and the low-temperature corrosion of the electric dust remover and the flue gas heat exchanger is reduced.
4. The temperature of the flue gas entering the electric dust remover is reduced through the flue gas heat exchanger, the dust removal efficiency of the electric dust remover is convenient to improve, the station service power of a unit is reduced, and the pollutant emission of the unit is reduced.
Drawings
FIG. 1 is a schematic diagram of a low-temperature flue gas water recovery and waste heat utilization coupling system of a coal-fired power plant.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
As shown in fig. 1, the coupling system for low-temperature flue gas water recovery and waste heat utilization of a coal-fired power plant comprises a rotary air preheater 1, a low-temperature economizer 2 sequentially communicated with a flue gas outlet of the rotary air preheater 1, a first part adjustable flue gas heat exchanger 3, a second part adjustable flue gas heat exchanger 4, a low-temperature flue gas cooler 5, an electric dust remover 6, a desulfurizing tower 7, a flue gas condenser 8, a flue gas reheater 9 and a chimney 10; the second-stage air heater 11 and the first-stage air heater 12 are communicated with an air side inlet of the rotary air preheater 1; the system also comprises a flue gas reheating system circulating water pump 13, a second-stage air heater circulating water pump 14, a first-stage air heater circulating water pump 15, a steam turbine reheating system 16, a heat pump heating system 17 and control valves a-o; a water side inlet of the low-temperature economizer 2 is communicated with a water side outlet of the first part adjustable flue gas heat exchanger 3 through a sixth control valve f, is communicated with a steam turbine heat regenerative system 16 through a fifth control valve e, is communicated with a water side inlet of the first part adjustable flue gas heat exchanger 3 through a fifth control valve e and a third control valve c in sequence, is communicated with a water side outlet of a flue gas reheater 9 through a fifth control valve e, a third control valve c and a fourth control valve d in sequence, is communicated with a water side inlet of the second part adjustable flue gas heat exchanger 4 through a fifth control valve e, a third control valve c, a fourth control valve d and a seventh control valve g in sequence, and is communicated with an inlet of a circulating water pump 13 of the flue gas reheating system through the sixth control valve f and the first control valve a in sequence; the water side outlet of the first part adjustable flue gas heat exchanger 3 is communicated with the inlet of a circulating water pump 13 of a flue gas reheating system through a first control valve a, is communicated with a turbine heat regenerative system 16 through a sixth control valve f and a fifth control valve e in sequence, is communicated with the water side inlet of the first part adjustable flue gas heat exchanger 3 through the sixth control valve f, the fifth control valve e and a third control valve c in sequence, and is communicated with the water side inlet of the first part adjustable flue gas heat exchanger through the sixth control valve f, the fifth control valve e and the third control valve c in sequence, a fourth control valve d and a seventh control valve g are communicated with a water side inlet of the second part of adjustable flue gas heat exchanger 4, communicated with a water side outlet of the second part of adjustable flue gas heat exchanger 4 through a first control valve a and a second control valve b in sequence, and communicated with a water side outlet of the flue gas reheater 9 through a sixth control valve f, a fifth control valve e, a third control valve c and a fourth control valve d in sequence; the water side inlet of the first part of adjustable flue gas heat exchanger 3 is communicated with the water side outlet of the flue gas reheater 9 through a fourth control valve d, is communicated with a turbine heat recovery system 16 through a third control valve c, is communicated with the water side inlet of the second part of adjustable flue gas heat exchanger 4 through a fourth control valve d and a seventh control valve g in sequence, is communicated with the inlet of the flue gas reheating system circulating water pump 13 through a third control valve c, a fifth control valve e, a sixth control valve f and a first control valve a in sequence, and is communicated with the water side outlet of the second part of adjustable flue gas heat exchanger 4 through the third control valve c, the fifth control valve e, the sixth control valve f, the first control valve a and a second control valve b in sequence; the water side outlet of the second part adjustable flue gas heat exchanger 4 is communicated with the inlet of a second stage air heater circulating water pump 14 through a ninth control valve i, is communicated with the inlet of a flue gas reheating system circulating water pump 13 through a second control valve b, is communicated with the water side outlet of a low-temperature flue gas cooler 5 through a ninth control valve i and a tenth control valve j in sequence, is communicated with the water side inlet of the second part adjustable flue gas heat exchanger 4 through a ninth control valve i, a tenth control valve j and an eighth control valve h in sequence, is communicated with a steam turbine reheating system 16 through a second control valve b, a first control valve a, a sixth control valve f, a fifth control valve e, a third control valve c and a fourth control valve d in sequence, is communicated with the water side outlet of a flue gas reheater 9 through a second control valve b, a first control valve a, a sixth control valve f, a fifth control valve e, a third control valve c and a fourth control valve d in sequence, and is communicated with the water side outlet of a flue, The first control valve a, the sixth control valve f, the fifth control valve e, the third control valve c, the fourth control valve d and the seventh control valve g are communicated with a water side inlet of the second part adjustable flue gas heat exchanger 4; the water side inlet of the adjustable flue gas heat exchanger 4 of the second part is communicated with the water side outlet of the flue gas reheater 9 through a seventh control valve g, is communicated with the water side outlet of the low-temperature flue gas cooler 5 through an eighth control valve h, is communicated with the inlet of the second-stage air heater circulating water pump 14 through an eighth control valve h and a tenth control valve j in sequence, is communicated with the turbine heat regenerative system 16 through a seventh control valve g, a fourth control valve d and a third control valve c in sequence, and is communicated with the inlet of the flue gas reheating system circulating water pump 13 through a seventh control valve g, a fourth control valve d, a third control valve c, a fifth control valve e, a sixth control valve f and a first control valve a in sequence; the outlet of the water side of the low-temperature flue gas cooler 5 is communicated with the inlet of a circulating water pump 14 of a second-stage air heater through a tenth control valve j; a water side inlet of the low-temperature flue gas cooler 5 is communicated with a water side outlet of a second-stage air heater 11 through an eleventh control valve k, is communicated with a water side outlet of a first-stage air heater 12 through a fourteenth control valve n, is communicated with a water side inlet of the first-stage air heater 12 through an eleventh control valve k and a twelfth control valve l in sequence, is communicated with an outlet of a circulating water pump 15 of the first-stage air heater through the eleventh control valve k, the twelfth control valve l and a thirteenth control valve m in sequence, and is communicated with a water side inlet of a flue gas condenser 8 and a low-temperature side outlet of a heat pump heat supply system 17 through the fourteenth control valve n and a fifteenth control valve o in sequence; the water side inlet of the second-stage air heater 11 is communicated with the outlet of the second-stage air heater circulating water pump 14; the water side outlet of the second-stage air heater 11 is communicated with the water side inlet of the first-stage air heater 12 through a twelfth control valve l, is communicated with the outlet of the circulating water pump 15 of the first-stage air heater through a twelfth control valve l and a thirteenth control valve m in sequence, is communicated with the water side outlet of the first-stage air heater 12 through an eleventh control valve k and a fourteenth control valve n in sequence, and is communicated with the water side inlet of the flue gas condenser 8 and the low-temperature side outlet of the heat pump heat supply system 17 through an eleventh control valve k, a fourteenth control valve n and a fifteenth control valve o in sequence; the water side inlet of the first-stage air heater 12 is communicated with the outlet of the first-stage air heater circulating water pump 15 through a thirteenth control valve m; the water side outlet of the first-stage air heater 12 is communicated with the water side inlet of the flue gas condenser 8 and the low-temperature side outlet of the heat pump heating system 17 through a fifteenth control valve o; the water side outlet of the flue gas condenser 8 is communicated with the inlet of a circulating water pump 15 of the first-stage air heater and the inlet of the low-temperature side of a heat pump heating system 17; the water side inlet of the flue gas condenser 8 is communicated with the low-temperature side outlet of the heat pump heating system 17; the water side inlet of the flue gas reheater 9 is communicated with the outlet of a circulating water pump 13 of the flue gas reheating system; flue gas from a boiler sequentially passes through a rotary air preheater 1, a low-temperature economizer 2, a first part adjustable flue gas heat exchanger 3, a second part adjustable flue gas heat exchanger 4 and a low-temperature flue gas cooler 5 to be cooled, then enters an electric dust remover 6 and a desulfurizing tower 7 to remove dust and sulfur dioxide in the flue gas, then passes through a flue gas condenser 8 to recover partial moisture and latent heat in the flue gas, passes through a flue gas reheater 9 to raise the temperature to reach the emission standard, and finally enters a chimney 10 to be discharged to the atmosphere; the cold air absorbs heat in the first stage air heater 12 and the second stage air heater 11, and then is sent to the rotary air preheater 1 for further temperature rise, and then sent to the boiler.
As a preferred embodiment of the present invention, when the first control valve a, the fourth control valve d and the fifth control valve e are closed, and the third control valve c and the sixth control valve f are opened, the low-temperature economizer 2 and the first part adjustable flue gas heat exchanger 3 are connected in series to jointly absorb the waste heat of low-temperature flue gas so as to heat the condensed water from the turbine regenerative system; when the third control valve c and the sixth control valve f are closed and the fifth control valve e is opened, the low-temperature economizer 2 absorbs the waste heat of the low-temperature flue gas to heat the condensed water from the turbine regenerative system.
As a preferred embodiment of the present invention, the second control valve b, the third control valve c, the sixth control valve f and the seventh control valve g are closed, when the first control valve a and the fourth control valve d are opened, the first part of the adjustable flue gas heat exchanger 3, the flue gas reheating system circulating water pump 13 and the flue gas reheater 9 form a closed loop, and the first part of the adjustable flue gas heat exchanger 3 absorbs the low-temperature flue gas waste heat to meet the heat load requirement of the reheated flue gas of the flue gas reheater 9; the first control valve a, the fourth control valve d, the eighth control valve h and the ninth control valve i are closed, when the second control valve b and the seventh control valve g are opened, the second part can adjust the flue gas heat exchanger 4, the flue gas reheating system circulating water pump 13 and the flue gas reheater 9 to form a closed loop, and the second part can adjust the flue gas heat exchanger 4 to absorb the waste heat of the low-temperature flue gas so as to meet the heat load requirement of the flue gas reheater 9 for reheating the flue gas. As a preferred embodiment of the present invention, when the seventh control valve g, the second control valve b and the tenth control valve j are closed, and the eighth control valve h and the ninth control valve i are opened, the low-temperature flue gas cooler 5 and the second part adjustable flue gas heat exchanger 4 are connected in series to reduce the flue gas temperature to about 95 ℃, and the circulating water is delivered to the air preheating device by the second stage air heater circulating water pump 14, and the heat of the flue gas is used for preheating the air; when the eighth control valve h, the ninth control valve i and the tenth control valve j are opened, the low-temperature flue gas cooler 5 reduces the temperature of the flue gas to about 95 ℃, circulating water is conveyed to an air preheating device through the second-stage air heater circulating water pump 14, and the heat of the flue gas is used for preheating the air.
As a preferred embodiment of the present invention, when the twelfth control valve l and the fourteenth control valve n are closed, and the eleventh control valve k, the thirteenth control valve m, and the fifteenth control valve o are opened, the second stage air heater 11 preheats air using the circulating water delivered by the second stage air heater circulating water pump 14, the first stage air heater 12 delivers part of the condensed water of the flue gas condenser 8 through the first stage air heater circulating water pump 15, utilizes the preheated air using part of the latent heat recovered by the flue gas condenser 8, and delivers another part of the recovered latent heat to the heat pump system, and the heat pump system is used for supplying heat after improving the heat quality; and when the eleventh control valve k, the thirteenth control valve m and the fifteenth control valve o are closed, and the twelfth control valve l and the fourteenth control valve n are opened, the second-stage air heater 11 and the first-stage air heater 12 are connected in series, the circulating water delivered by the circulating water pump 14 of the second-stage air heater is jointly used for preheating air, and the latent heat recovered by the flue gas condenser 8 is delivered to the heat pump system to be used for heat supply after the heat quality is improved.
In a preferred embodiment of the present invention, the working mediums delivered by the flue gas reheating system circulating water pump 13, the second stage air heater circulating water pump 14 and the first stage air heater circulating water pump 15 are all water.
As a preferred embodiment of the invention, the flue gas condenser 8 reduces the temperature of the flue gas to 45 ℃ in winter and 43 ℃ in summer, and can recover 6-8 kg/s of condensed water.
As a preferred embodiment of the invention, the flue gas reheater 9 raises the temperature of the flue gas by 15 ℃, ensures that the flue gas entering the chimney 10 has a superheat degree of 15 ℃, reduces the corrosion to the chimney 10, and meets the flue gas emission standard.
The invention relates to an operation method of a low-temperature flue gas water recovery and waste heat utilization coupled system of a coal-fired power plant, when the ambient temperature is higher than 0 ℃, a first control valve a, a fourth control valve d, a fifth control valve e, an eighth control valve h, a ninth control valve i, an eleventh control valve k, a thirteenth control valve m and a fifteenth control valve o are closed, a second control valve b, a third control valve c, a sixth control valve f, a seventh control valve g, a tenth control valve j, a twelfth control valve l and a fourteenth control valve n are opened, a low-temperature economizer 2 and a first part adjustable flue gas heat exchanger 3 are connected in series to jointly absorb the waste heat of low-temperature flue gas so as to heat condensate water from a turbine reheating system, a second part adjustable flue gas heat exchanger 4, a flue gas reheating system circulating water pump 13 form a closed loop cycle, the second part adjustable flue gas heat exchanger 4 absorbs the waste heat of the low-temperature flue gas so as to meet the heat load requirement of the flue gas reheating system 9, the first-stage air heater 12, the low-temperature flue gas cooler 5, the second-stage air heater circulating water pump 14 and the second-stage air heater 11 form a closed cycle, and the flue gas heat absorbed by the low-temperature flue gas cooler 5 is used for preheating air; when the ambient temperature is-10 to 0 ℃, the second control valve b, the third control valve c, the sixth control valve f, the seventh control valve g, the tenth control valve j, the eleventh control valve k, the thirteenth control valve m and the fifteenth control valve o are closed, the first control valve a, the fourth control valve d, the fifth control valve e, the eighth control valve h, the ninth control valve i, the twelfth control valve l and the fourteenth control valve n are opened, the low-temperature economizer 2 absorbs the waste heat of the low-temperature flue gas to heat the condensate water from the turbine regenerative system, the first adjustable flue gas heat exchanger 3, the flue gas reheater 9 and the flue gas reheating system circulating water pump 13 form a closed loop, the first adjustable flue gas heat exchanger 3 absorbs the waste heat of the low-temperature flue gas to meet the heat load requirement of the reheated flue gas of the flue gas cooler 9, the first-stage air heater 12, the low-temperature flue gas cooler 5, the second-stage air heater 12, the second-gas cooler 5, the second-temperature, The second part of adjustable flue gas heat exchanger 4, the second stage air heater circulating water pump 14 and the second stage air heater 11 form a closed cycle, and the flue gas heat absorbed by the low-temperature flue gas cooler 5 and the second part of adjustable flue gas heat exchanger 4 is used for preheating air; when the ambient temperature is-20 to-10 ℃, the second control valve b, the third control valve c, the sixth control valve f, the seventh control valve g, the tenth control valve j, the twelfth control valve l and the fourteenth control valve n are closed, the first control valve a, the fourth control valve d, the fifth control valve e, the eighth control valve h, the ninth control valve i, the eleventh control valve k, the thirteenth control valve m and the fifteenth control valve o are opened, the low-temperature economizer 2 absorbs the low-temperature flue gas waste heat to heat the condensed water from the turbine regenerative system, the first part of adjustable flue gas heat exchanger 3, the flue gas reheater 9 and the flue gas reheating system circulating pump 13 form a closed-loop cycle, the first part of adjustable flue gas heat exchanger 3 absorbs the low-temperature flue gas waste heat to meet the heat load requirement of the reheated flue gas of the flue gas reheater 9, and the second-stage air heater 11 absorbs the low-temperature flue gas waste heat pump 3 to meet the heat load requirement of the reheated, The low-temperature flue gas cooler 5, the second part adjustable flue gas heat exchanger 4 and the second stage air heater circulating water pump 14 form closed cycle, the flue gas heat absorbed by the low-temperature flue gas cooler 5 and the second part adjustable flue gas heat exchanger 4 is used for preheating air, and the first stage air heater 12 preheats air by using the latent heat recovered by part of the flue gas condenser 8; in addition, the system ensures that the temperature of the flue gas at the outlet of the low-temperature flue gas cooler 5 is maintained above 90 ℃ and the temperature of the circulating water entering the low-temperature flue gas cooler 5 is above 70 ℃ by adjusting the mass flow of the condensed water at the inlet A, adjusting the mass flow of the circulating water entering the low-temperature flue gas cooler 5 through the second-stage air heater circulating water pump 14 and adjusting the mass flow of the circulating water entering the flue gas reheater 9 through the flue gas reheating system circulating water pump 13.
The invention provides a coupling system for recycling low-temperature flue gas water and utilizing waste heat of a coal-fired power plant and an operation method, wherein a low-temperature economizer is used for recycling low-temperature flue gas waste heat to a turbine regenerative system so as to reduce the coal consumption of a unit; the air is preheated by the air heater, so that the temperature of the air entering the air preheater is increased, the irreversible loss of the air preheater is reduced, and the coal consumption of a unit is reduced; the flue gas is reheated by a flue gas reheater, so that the flue gas entering a chimney has a superheat degree of 15 ℃, and low-temperature corrosion to the chimney is reduced; the operation of the adjustable flue gas heat exchanger is controlled by the control valve, and the adjustable flue gas heat exchanger is connected with other flue gas heat exchangers in series to work together under different working conditions, so that the temperature of flue gas entering the electric dust remover is maintained above 90 ℃, and the temperature of circulating water entering the low-temperature flue gas cooler is ensured above 70 ℃, so that the system can safely operate under different environmental temperatures.

Claims (9)

1. Coal fired power plant low temperature flue gas water recovery and waste heat utilization coupled system, its characterized in that: the system comprises a rotary air preheater (1), a low-temperature economizer (2) communicated with a flue gas outlet of the rotary air preheater (1) in sequence, a first part adjustable flue gas heat exchanger (3), a second part adjustable flue gas heat exchanger (4), a low-temperature flue gas cooler (5), an electric dust remover (6), a desulfurizing tower (7), a flue gas condenser (8), a flue gas reheater (9) and a chimney (10); a second-stage air heater (11) and a first-stage air heater (12) which are communicated with an air side inlet of the rotary air preheater (1); the system also comprises a flue gas reheating system circulating water pump (13), a second-stage air heater circulating water pump (14), a first-stage air heater circulating water pump (15), a steam turbine reheating system (16), a heat pump heating system (17) and a control valve; the water side inlet of the low-temperature economizer (2) is communicated with the water side outlet of the first part of adjustable flue gas heat exchanger (3) through a sixth control valve (f), is communicated with a turbine regenerative system (16) through a fifth control valve (e), is communicated with the water side inlet of the first part of adjustable flue gas heat exchanger (3) through a fifth control valve (e) and a third control valve (c) in sequence, is communicated with the water side outlet of the flue gas reheater (9) through the fifth control valve (e), the third control valve (c) and a fourth control valve (d) in sequence, and passes through the fifth control valve (e) in sequence, a third control valve (c), a fourth control valve (d) and a seventh control valve (g) are communicated with a water side inlet of the second part adjustable flue gas heat exchanger (4) and are communicated with an inlet of a circulating water pump (13) of the flue gas reheating system through a sixth control valve (f) and a first control valve (a) in sequence; the water side outlet of the first part of adjustable flue gas heat exchanger (3) is communicated with the inlet of a circulating water pump (13) of a flue gas reheating system through a first control valve (a), is communicated with a steam turbine heat regeneration system (16) through a sixth control valve (f) and a fifth control valve (e) in sequence, is communicated with the water side inlet of the first part of adjustable flue gas heat exchanger (3) through the sixth control valve (f), the fifth control valve (e) and a third control valve (c) in sequence, is communicated with the water side inlet of the second part of adjustable flue gas heat exchanger (4) through the sixth control valve (f), the fifth control valve (e), the third control valve (c), the fourth control valve (d) and a seventh control valve (g) in sequence, is communicated with the water side outlet of the second part of adjustable flue gas heat exchanger (4) through the first control valve (a) and the second control valve (b) in sequence, and is communicated with the water side outlet of the second part of adjustable flue gas heat exchanger (4) through the sixth control, The fifth control valve (e), the third control valve (c) and the fourth control valve (d) are communicated with a water side outlet of the flue gas reheater (9); a water side inlet of the first part of adjustable flue gas heat exchanger (3) is communicated with a water side outlet of the flue gas reheater (9) through a fourth control valve (d), is communicated with a steam turbine heat recovery system (16) through a third control valve (c), is communicated with a water side inlet of the second part of adjustable flue gas heat exchanger (4) through a fourth control valve (d) and a seventh control valve (g) in sequence, is communicated with an inlet of a circulating water pump (13) of the flue gas reheating system through a third control valve (c), a fifth control valve (e), a sixth control valve (f) and a first control valve (a), and is communicated with a water side outlet of the second part of adjustable flue gas heat exchanger (4) through a third control valve (c), a fifth control valve (e), a sixth control valve (f), a first control valve (a) and a second control valve (b) in sequence; the outlet of the water side of the second part adjustable flue gas heat exchanger (4) is communicated with the inlet of a second-stage air heater circulating water pump (14) through a ninth control valve (i), is communicated with the inlet of a flue gas reheating system circulating water pump (13) through a second control valve (b), is communicated with the outlet of the water side of a low-temperature flue gas cooler (5) through a ninth control valve (i) and a tenth control valve (j), is communicated with the inlet of the water side of the second part adjustable flue gas heat exchanger (4) through a ninth control valve (i), a tenth control valve (j) and an eighth control valve (h), is communicated with a steam turbine reheating system (16) through a second control valve (b), a first control valve (a), a sixth control valve (f) and a fifth control valve (e), and is communicated with the steam turbine reheating system (16) through a second control valve (b), a first control valve (a), a sixth control valve (f) and a fifth control valve (e), The third control valve (c) and the fourth control valve (d) are communicated with a water side outlet of the flue gas reheater (9), and are communicated with a water side inlet of the second part adjustable flue gas heat exchanger (4) through a second control valve (b), a first control valve (a), a sixth control valve (f), a fifth control valve (e), a third control valve (c), a fourth control valve (d) and a seventh control valve (g) in sequence; the water side inlet of the second part of the adjustable flue gas heat exchanger (4) is communicated with the water side outlet of the flue gas reheater (9) through a seventh control valve (g), is communicated with the water side outlet of the low-temperature flue gas cooler (5) through an eighth control valve (h), is communicated with the inlet of a second-stage heater circulating water pump (14) through an eighth control valve (h) and a tenth control valve (j), is communicated with a turbine regenerative system (16) through the seventh control valve (g), a fourth control valve (d) and a third control valve (c), and is communicated with the inlet of a flue gas reheating system circulating water pump (13) through the seventh control valve (g), the fourth control valve (d), the third control valve (c), the fifth control valve (e), the sixth control valve (f) and the first control valve (a); the outlet of the water side of the low-temperature flue gas cooler (5) is communicated with the inlet of a circulating water pump (14) of a second-stage air heater through a tenth control valve (j); a water side inlet of the low-temperature flue gas cooler (5) is communicated with a water side outlet of a second-stage air heater (11) through an eleventh control valve (k), is communicated with a water side outlet of a first-stage air heater (12) through a fourteenth control valve (n), is communicated with the water side inlet of the first-stage air heater (12) through an eleventh control valve (k) and a twelfth control valve (l) in sequence, is communicated with an outlet of a circulating water pump (15) of the first-stage air heater through the eleventh control valve (k), the twelfth control valve (l) and a thirteenth control valve (m) in sequence, and is communicated with a water side inlet of a flue gas condenser (8) and a low-temperature side outlet of a heat pump heat supply system (17) through the fourteenth control valve (n) and a fifteenth control valve (o) in sequence; the water side inlet of the second-stage air heater (11) is communicated with the outlet of a circulating water pump (14) of the second-stage air heater; a water side outlet of the second-stage air heater (11) is communicated with a water side inlet of the first-stage air heater (12) through a twelfth control valve (l), is communicated with an outlet of a circulating water pump (15) of the first-stage air heater through a twelfth control valve (l) and a thirteenth control valve (m) in sequence, is communicated with a water side outlet of the first-stage air heater (12) through an eleventh control valve (k) and a fourteenth control valve (n) in sequence, and is communicated with a water side inlet of the flue gas condenser (8) and a low-temperature side outlet of the heat pump heat supply system (17) through an eleventh control valve (k), a fourteenth control valve (n) and a fifteenth control valve (o) in sequence; the water side inlet of the first-stage air heater (12) is communicated with the outlet of the first-stage air heater circulating water pump (15) through a thirteenth control valve (m); the water side outlet of the first-stage air heater (12) is communicated with the water side inlet of the flue gas condenser (8) and the low-temperature side outlet of the heat pump heating system (17) through a fifteenth control valve (o); the water side outlet of the flue gas condenser (8) is communicated with the inlet of a first-stage air heater circulating water pump (15) and the low-temperature side inlet of a heat pump heat supply system (17); the water side inlet of the flue gas condenser (8) is communicated with the low-temperature side outlet of the heat pump heating system (17); the water side inlet of the flue gas reheater (9) is communicated with the outlet of a circulating water pump (13) of the flue gas reheating system; flue gas from a boiler sequentially passes through a rotary air preheater (1), a low-temperature economizer (2), a first part adjustable flue gas heat exchanger (3), a second part adjustable flue gas heat exchanger (4) and a low-temperature flue gas cooler (5) to be cooled, then enters an electric dust remover (6) and a desulfurizing tower (7) to remove dust and sulfur dioxide in the flue gas, then partial moisture and latent heat in the flue gas are recovered through a flue gas condenser (8), the temperature is raised through a flue gas reheater (9) to reach the emission standard, and finally the flue gas enters a chimney (10) to be discharged to the atmosphere; the cold air absorbs heat in the first-stage air heater (12) and the second-stage air heater (11), then is sent into the rotary air preheater (1) for further temperature rise, and then is sent into the boiler.
2. The coal-fired power plant low temperature flue gas water recovery and waste heat utilization coupled system of claim 1, characterized in that: when the first control valve (a), the fourth control valve (d) and the fifth control valve (e) are closed, and the third control valve (c) and the sixth control valve (f) are opened, the low-temperature economizer (2) and the first part adjustable flue gas heat exchanger (3) are connected in series to jointly absorb the low-temperature flue gas waste heat so as to heat the condensed water from the turbine heat recovery system; when the third control valve (c) and the sixth control valve (f) are closed and the fifth control valve (e) is opened, the low-temperature economizer (2) absorbs the waste heat of low-temperature flue gas to heat the condensed water from the turbine regenerative system.
3. The coal-fired power plant low temperature flue gas water recovery and waste heat utilization coupled system of claim 1, characterized in that: the second control valve (b), the third control valve (c), the sixth control valve (f) and the seventh control valve (g) are closed, when the first control valve (a) and the fourth control valve (d) are opened, the first part of the adjustable flue gas heat exchanger (3), the flue gas reheating system circulating water pump (13) and the flue gas reheater (9) form a closed loop, and the first part of the adjustable flue gas heat exchanger (3) absorbs the waste heat of low-temperature flue gas to meet the heat load requirement of the reheated flue gas of the flue gas reheater (9); the first control valve (a), the fourth control valve (d), the eighth control valve (h) and the ninth control valve (i) are closed, when the second control valve (b) and the seventh control valve (g) are opened, the second part of the adjustable flue gas heat exchanger (4), the flue gas reheating system circulating water pump (13) and the flue gas reheater (9) form a closed loop, and the second part of the adjustable flue gas heat exchanger (4) absorbs the waste heat of the low-temperature flue gas to meet the heat load requirement of the reheated flue gas of the flue gas reheater (9).
4. The coal-fired power plant low temperature flue gas water recovery and waste heat utilization coupled system of claim 1, characterized in that: when the seventh control valve (g), the second control valve (b) and the tenth control valve (j) are closed, and the eighth control valve (h) and the ninth control valve (i) are opened, the low-temperature flue gas cooler (5) and the second part of adjustable flue gas heat exchanger (4) are connected in series to reduce the temperature of flue gas to about 95 ℃, circulating water is conveyed to an air preheating device through a second-stage air heater circulating water pump (14), and the heat of the flue gas is used for preheating air; and when the tenth control valve (j) is opened, the low-temperature flue gas cooler (5) reduces the temperature of the flue gas to about 95 ℃, circulating water is conveyed to an air preheating device through a second-stage air heater circulating water pump (14), and the heat of the flue gas is used for preheating the air.
5. The coal-fired power plant low temperature flue gas water recovery and waste heat utilization coupled system of claim 1, characterized in that: the twelfth control valve (l) and the fourteenth control valve (n) are closed, when the eleventh control valve (k), the thirteenth control valve (m) and the fifteenth control valve (o) are opened, the second-stage air heater (11) preheats air by using circulating water conveyed by the second-stage air heater circulating water pump (14), the first-stage air heater (12) conveys part of condensed water of the flue gas condenser (8) by using the first-stage air heater circulating water pump (15), part of latent heat recovered by the flue gas condenser (8) is utilized for preheating air, and the other part of recovered latent heat is conveyed to a heat pump system and used for supplying heat after the heat quality is improved; the eleventh control valve (k), the thirteenth control valve (m) and the fifteenth control valve (o) are closed, when the twelfth control valve (l) and the fourteenth control valve (n) are opened, the second-stage air heater (11) and the first-stage air heater (12) are connected in series, circulating water conveyed by a circulating water pump (14) of the second-stage air heater is used for preheating air, latent heat recovered by a flue gas condenser (8) is conveyed to a heat pump system, and the heat pump system is used for supplying heat after the heat quality is improved.
6. The coal-fired power plant low temperature flue gas water recovery and waste heat utilization coupled system of claim 1, characterized in that: and the working media conveyed by the flue gas reheating system circulating water pump (13), the second-stage air heater circulating water pump (14) and the first-stage air heater circulating water pump (15) are all water.
7. The coal-fired power plant low temperature flue gas water recovery and waste heat utilization coupled system of claim 1, characterized in that: the flue gas temperature of the flue gas condenser (8) is reduced to 45 ℃ in winter and 43 ℃ in summer, and condensed water is recovered by 6-8 kg/s respectively.
8. The coal-fired power plant low temperature flue gas water recovery and waste heat utilization coupled system of claim 1, characterized in that: the flue gas reheater (9) raises the temperature of the flue gas by 15 ℃, ensures that the flue gas entering the chimney (10) has the superheat degree of 15 ℃, reduces the corrosion to the chimney (10), and meets the flue gas emission standard.
9. The operation method of the low-temperature flue gas water recovery and waste heat utilization coupled system of the coal-fired power plant as recited in any one of claims 1 to 8, characterized in that: when the ambient temperature is higher than 0 ℃, the first control valve (a), the fourth control valve (d), the fifth control valve (e), the eighth control valve (h), the ninth control valve (i), the eleventh control valve (k), the thirteenth control valve (m) and the fifteenth control valve (o) are closed, the second control valve (b), the third control valve (c), the sixth control valve (f), the seventh control valve (g), the tenth control valve (j), the twelfth control valve (l) and the fourteenth control valve (n) are opened, the low-temperature economizer (2) and the first part of adjustable flue gas heat exchangers (3) are connected in series to jointly absorb low-temperature flue gas waste heat so as to heat condensate water from a turbine heat recovery system, and the second part of adjustable flue gas heat exchangers (4), a flue gas reheater (9) and a flue gas reheating system circulating water pump (13) form a closed cycle, the second part can adjust the flue gas heat exchanger (4) to absorb the waste heat of low-temperature flue gas so as to meet the heat load requirement of reheating flue gas of the flue gas reheater (9), the first-stage air heater (12), the low-temperature flue gas cooler (5), the second-stage air heater circulating water pump (14) and the second-stage air heater (11) form a closed cycle, and the heat of the flue gas absorbed by the low-temperature flue gas cooler (5) is used for preheating air; when the ambient temperature is-10 to 0 ℃, the second control valve (b), the third control valve (c), the sixth control valve (f), the seventh control valve (g), the tenth control valve (j), the eleventh control valve (k), the thirteenth control valve (m) and the fifteenth control valve (o) are closed, the first control valve (a), the fourth control valve (d), the fifth control valve (e), the eighth control valve (h), the ninth control valve (i), the twelfth control valve (l) and the fourteenth control valve (n) are opened, the low-temperature economizer (2) absorbs the low-temperature flue gas waste heat to heat the condensed water from the turbine heat recovery system, the first part can adjust the flue gas heat exchanger (3), the flue gas reheater (9) and the flue gas reheating system circulating water pump (13) to form a closed loop, the first part can adjust the flue gas heat exchanger (3) to absorb the low-temperature flue gas waste heat to meet the heat load requirement of the reheater (9) for reheating the flue gas, the first-stage air heater (12), the low-temperature flue gas cooler (5), the second part adjustable flue gas heat exchanger (4), the second-stage air heater circulating water pump (14) and the second-stage air heater (11) form closed circulation, and flue gas heat absorbed by the low-temperature flue gas cooler (5) and the second part adjustable flue gas heat exchanger (4) is used for preheating air; when the ambient temperature is-20 to-10 ℃, the second control valve (b), the third control valve (c), the sixth control valve (f), the seventh control valve (g), the tenth control valve (j), the twelfth control valve (l) and the fourteenth control valve (n) are closed, the first control valve (a), the fourth control valve (d), the fifth control valve (e), the eighth control valve (h), the ninth control valve (i), the eleventh control valve (k), the thirteenth control valve (m) and the fifteenth control valve (o) are opened, the low-temperature economizer (2) absorbs the low-temperature flue gas waste heat to heat the condensed water from the turbine heat recovery system, the first part can adjust the flue gas heat exchanger (3), the flue gas reheater (9) and the flue gas reheating system circulating water pump (13) to form a closed loop, the first part can adjust the flue gas heat exchanger (3) to absorb the low-temperature flue gas waste heat to meet the heat load requirement of the reheater (9) for reheating the flue gas, the second-stage air heater (11), the low-temperature flue gas cooler (5), the second part of adjustable flue gas heat exchanger (4) and the second-stage air heater circulating water pump (14) form closed circulation, flue gas heat absorbed by the low-temperature flue gas cooler (5) and the second part of adjustable flue gas heat exchanger (4) is used for preheating air, and the first-stage air heater (12) preheats the air by utilizing latent heat recovered by part of the flue gas condenser (8); in addition, the mass flow of condensed water at the inlet A of the system is adjusted, the mass flow of circulating water entering the low-temperature flue gas cooler (5) is adjusted through the second-stage air heater circulating water pump (14), and the mass flow of circulating water entering the flue gas reheater (9) is adjusted through the flue gas reheating system circulating water pump (13), so that the temperature of flue gas at the outlet of the low-temperature flue gas cooler (5) is maintained above 90 ℃, and the temperature of circulating water entering the low-temperature flue gas cooler (5) is ensured above 70 ℃.
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