CN109737440B - Boiler flue gas deep waste heat recovery system and method - Google Patents

Boiler flue gas deep waste heat recovery system and method Download PDF

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CN109737440B
CN109737440B CN201910151570.3A CN201910151570A CN109737440B CN 109737440 B CN109737440 B CN 109737440B CN 201910151570 A CN201910151570 A CN 201910151570A CN 109737440 B CN109737440 B CN 109737440B
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flue gas
temperature
heat
boiler
heat exchanger
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CN109737440A (en
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刘�文
杨敏华
曹东辉
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Jinan Municipal Engineering Design and Research Institute Group Co Ltd
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Jinan Municipal Engineering Design and Research Institute Group Co Ltd
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    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02ATECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A30/00Adapting or protecting infrastructure or their operation
    • Y02A30/27Relating to heating, ventilation or air conditioning [HVAC] technologies
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02BCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00Energy efficient heating, ventilation or air conditioning [HVAC]
    • Y02B30/62Absorption based systems
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00Combustion technologies with mitigation potential
    • Y02E20/34Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery

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Abstract

The invention discloses a flue gas deep waste heat recovery system and a method, wherein primary net backwater sequentially passes through an air preheater to exchange heat with cold air, enters a high-temperature end of an absorption heat pump to be heated, enters a second wall type heat exchanger to exchange heat with high-temperature flue gas, and finally enters a boiler to be reheated; the heated cold air is introduced into the boiler to provide oxygen; the low-temperature flue gas after the high-temperature flue gas is cooled enters a spray tower to be sprayed and cooled, and the cooled flue gas is discharged; and the spray liquid is neutralized and then pumped into the first dividing wall type heat exchanger to heat the secondary net backwater, the condensed spray liquid enters the absorption heat pump to be subjected to heat recovery again, the heat is transferred to the primary net backwater, and the spray liquid after being cooled again is conveyed to a spray layer of the spray tower to spray and cool the flue gas. The temperature of the flue gas can be reduced to below 30 ℃, and the efficiency of the gas boiler is greatly improved.

Description

Boiler flue gas deep waste heat recovery system and method
Technical Field
The invention belongs to the technical field of industrial boilers and energy conservation, relates to a boiler flue gas deep waste heat recovery method, and particularly relates to a boiler flue gas deep waste heat recovery technology based on a direct-combustion absorption heat pump, a direct-contact heat exchanger, an air preheater and a dividing wall type heat exchanger.
Background
The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.
With the implementation of clean heating in northern areas, gas boiler heating becomes an important heating mode. According to the clean heating plan, the newly added natural gas heating area is 18 hundred million square meters in 2017-2021 of the city of '2 + 26', the newly added gas is 230 hundred million cubic meters, wherein 5 million steam tons are newly built/reconstructed for the gas-fired boiler, and 56 hundred million cubic meters are newly added. The gas resources in China are not abundant, and the improvement of the gas heat supply efficiency is very important. Meanwhile, in the boiler loss, the flue gas waste heat loss is the largest one.
At present, the commonly used flue gas waste heat recovery technology of a gas boiler is mainly divided into two technologies, namely an absorption heat pump technology and a direct and indirect heat exchanger technology. The absorption heat pump is a large water/water heat pump unit which takes heat energy as power and utilizes the absorption characteristic of solution to pump the heat energy from a low-temperature heat source to a high-temperature heat source. The absorption heat pump technology can reduce the temperature of the flue gas to below 30 ℃, but the investment is large, and about 120 ten thousand investment is made for recovering 1MW heat; in the heat exchanger technology, the temperature of the flue gas is limited by the temperature of a cold source and is generally difficult to be reduced to below 50 ℃, the flue gas is condensed to a certain temperature and can be condensed to generate acid condensate water, and the acid condensate water can cause severe corrosion to the heat exchanger, so that an anti-corrosion heat exchanger is required to be adopted, no matter 316L or modified materials are adopted, the manufacturing cost is very high, and no corrosion is guaranteed.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention aims to provide a deep flue gas waste heat recovery system and a deep flue gas waste heat recovery method. The system and the method can reduce the temperature of the flue gas to be below 30 ℃, not only can greatly improve the efficiency of the gas-fired boiler, but also can condense a large amount of water vapor in the flue gas and harmful substances in the flue gas, realize the recycling of water and further reduce the influence of the flue gas on the surrounding environment.
In order to solve the problems, the technical scheme of the invention is as follows:
a boiler flue gas deep waste heat recovery system comprises a first dividing wall type heat exchanger, a second dividing wall type heat exchanger, an absorption heat pump, an air preheater and a spray tower, wherein a primary network water return pipeline is sequentially connected with a heat medium channel of the air preheater, a low-temperature cold source end of the absorption heat pump, a cold medium channel of the second dividing wall type heat exchanger and a boiler;
a cold medium channel of the air preheater is connected with an air source, and a hot medium channel of the second wall type heat exchanger is connected with a flue gas outlet of the boiler;
the outlet of the heat medium channel of the second divided wall type heat exchanger is connected with the gas inlet of the spray tower;
the tower kettle of the spray tower is connected with an intermediate water supply pipeline through a pump, the intermediate water supply pipeline is connected with an inlet of a heat medium channel of the first dividing wall type heat exchanger, one end of an intermediate water return pipeline is connected with an outlet of the heat medium channel of the first dividing wall type heat exchanger, and the other end of the intermediate water return pipeline is connected with a spray layer of the spray tower through a high-temperature heat source end of the absorption heat pump;
and the inlet and the outlet of the cold medium pipeline of the first dividing wall type heat exchanger are respectively connected with the secondary network water return pipeline and the secondary network water supply pipeline.
In heat pipe engineering, a heat main line is commonly and commonly called a primary network, and the primary network refers to a total pipe network through which hot water from a heat supply station flows, generally only to a heat exchange station, and does not directly heat users.
The secondary network is a hot water pipeline which is directly connected with a hot user after the local heat exchange station exchanges heat with the primary network. That is, heat is transferred from the primary network to the secondary network through the heat exchanger, and the secondary network conducts users.
The net return water temperature is higher once, preheats the air through air heater at first, heats the air to the uniform temperature, and the air that is heated is carried the oxygen suppliment to the boiler in, can avoid low temperature air to get into the boiler and produce the detonation phenomenon, and to the situation that adopts flue gas backward flow low-nitrogen combustion technique, can avoid low temperature air and flue gas to mix the back and produce the condensation simultaneously.
The air is preheated by the air preheater, so that more heat in the return water of the primary net can be recovered, and the temperature of the return water of the primary net is reduced. The cooled primary net return water enters the absorption heat pump, the absorption heat pump absorbs heat in the medium water, then the heat is transferred to the primary net return water, and the primary net return water is heated, so that the medium water can be cooled. Because the temperature of the intermediate water has little difference with the temperature of the primary network backwater, and the intermediate water is only required to be cooled to about 20 ℃ from about 45 ℃, the investment of the heat pump can be obviously reduced. Meanwhile, the primary net return water with higher temperature is used for exchanging heat and cooling the high-temperature flue gas by using the dividing wall type heat exchanger, the temperature of the cooled flue gas is higher, and at about 80 ℃, water vapor in the flue gas can not be condensed at the temperature, so that the corrosion of the acidic condensate water to the heat exchanger can be effectively avoided.
The low-temperature flue gas after primary cooling enters a spray tower and is subjected to secondary waste heat recovery by adopting a spray cooling method, so that the temperature of the flue gas can be reduced to below 30 ℃. Because the heat in the flue gas is fully utilized, the efficiency of the gas boiler is greatly improved. And with the flue gas cooling below 30 ℃, can condense a large amount of vapor in the flue gas to get into the condensate water with the more harmful substance condensation in the flue gas, this part condensate water gets into and sprays the aquatic, and after neutralization treatment, the shower water of higher temperature can carry out the heat transfer through dividing wall heat exchanger and secondary net return water, heats the secondary net return water, with further improvement thermal utilization ratio.
Preferably, the boiler flue gas depth waste heat recovery system further comprises a dosing device, and the dosing device is connected with the spray tower. The chemical adding device adds alkaline substances into the spray tower to neutralize spray water and prevent the dividing wall type heat exchanger from being corroded.
Preferably, the first dividing wall type heat exchanger and the second dividing wall type heat exchanger are plate type heat exchangers.
Preferably, a first valve is connected between a water supply pipeline and a water return pipeline of the primary net water return air preheater.
The flow of primary net return water to the air preheater can be adjusted by adjusting the opening degree of the first valve, and then the temperature of heated air and the temperature of cooled primary net return water are adjusted, so that the normal operation of the boiler is ensured, the proper temperature of the primary net return water is adjusted, and the condensation effect on high-temperature flue gas is ensured.
Preferably, a second valve is connected between the water supply pipeline and the water return pipeline of the primary-network backwater absorption heat pump. The opening and closing degree and the opening degree of the second valve are adjusted to adjust the proportion of the primary network backwater to the absorption heat pump, so that the adjustment of the temperature of the primary network backwater and the adjustment of the temperature of the medium water are realized, the better cooling effect on high-temperature smoke is ensured, and the better cooling effect on low-temperature smoke is ensured.
A deep waste heat recovery method for flue gas comprises the following steps:
the primary net backwater sequentially passes through the air preheater to exchange heat with cold air, enters the low-temperature end of the absorption heat pump to be heated, enters the second wall type heat exchanger to exchange heat with high-temperature flue gas, and finally enters the boiler to be reheated;
the heated cold air is introduced into the boiler to provide oxygen; the low-temperature flue gas after the high-temperature flue gas is cooled enters a spray tower to be sprayed and cooled, and the cooled flue gas is discharged;
and the spray liquid is neutralized and then pumped into the first dividing wall type heat exchanger to heat the secondary net backwater, the condensed spray liquid enters the absorption heat pump to be subjected to heat recovery again, the heat is transferred to the primary net backwater, and the spray liquid after being cooled again is conveyed to a spray layer of the spray tower to spray and cool the flue gas.
Preferably, the temperature of the heated cold air is 20-30 ℃.
The temperature of the return water of the primary net is about 55 ℃, so that the cold air can be better heated.
Preferably, the temperature of the low-temperature flue gas after the high-temperature flue gas is cooled is 80-85 ℃.
Preferably, the temperature of the spray liquid delivered to the spray layer is 18-22 ℃.
Preferably, the temperature of the high-temperature flue gas is 145-155 ℃.
The invention has the beneficial effects that:
the flue gas temperature is reduced to be below 30 ℃, the efficiency of the gas-fired boiler is greatly improved, if the flue gas temperature at the outlet of the boiler is calculated to be 150 ℃, the efficiency of the boiler is improved by more than 15 percent, the gas is saved, and the operating cost is reduced. Meanwhile, a large amount of water vapor in the flue gas is condensed, so that a part of harmful substances can be condensed, and the flue gas can be used as water supplement of a heat supply network to enter a large network after neutralization treatment.
The waste heat of the high-temperature flue gas section (more than or equal to 85 ℃) is recovered by using a dividing wall type heat exchanger, and the flue gas of the section is not condensed, so that the heat exchanger is prevented from being corroded by condensed water; the low-temperature flue gas section (85-30 ℃) adopts a spray tower to recover waste heat, the heat exchange effect is good, the dosing device is used for neutralizing condensed water, the corrosion of intermediate water to the heat exchanger is avoided, and an expensive 316L or other modified material heat exchanger is not needed.
And recovering the heat of the low-temperature section of the flue gas by adopting secondary network backwater and a heat pump in a segmented manner. In the section of the medium water with the temperature of 55-45 ℃, a plate heat exchanger is used for heating secondary net backwater; in the 45-20 ℃ section, the absorption heat pump technology is adopted to heat the primary net backwater, and the heat pump investment is reduced compared with the method of only using the heat pump to recover the intermediate water with the temperature of 55-20 ℃.
The waste heat of the flue gas is recovered by an air-primary net backwater-flue gas mode, the air is heated to be above 20 ℃, the deflagration phenomenon caused by the fact that low-temperature air enters a boiler can be avoided, and meanwhile, the condensation generated after the low-temperature air and the flue gas are mixed can be avoided for the situation that a flue gas backflow low-nitrogen combustion technology is adopted. Compared with the traditional flue gas-air type air preheater, the air-primary net backwater air preheater has large heat exchange coefficient, reduces the heat exchange area and saves the investment.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a process flow diagram of the present invention.
The system comprises a chemical feeding device 1, a spray tower 2, a first dividing wall type heat exchanger 3, an air preheater 4, an absorption heat pump 5, and a second dividing wall type heat exchanger 6.
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
As shown in fig. 1, a boiler flue gas deep waste heat recovery system comprises a first dividing wall type heat exchanger 3, a second dividing wall type heat exchanger 6, an absorption heat pump 5, an air preheater 4, a spray tower 2 and a dosing device 1, wherein a primary network water return pipeline is sequentially connected with a heat medium channel of the air preheater 4, a low-temperature cold source end of the absorption heat pump 5, a cold medium channel of the second dividing wall type heat exchanger 6 and a boiler;
the cold medium channel of the air preheater 4 is connected with an air source, the air source at the position can be an air compressor or a fan, and the hot medium channel of the second wall type heat exchanger 6 is connected with a boiler flue gas outlet;
the outlet of the heat medium channel of the second divided wall type heat exchanger 6 is connected with the gas inlet of the spray tower 2;
the tower kettle of the spray tower 2 is connected with an intermediate water supply pipeline through a pump, the intermediate water supply pipeline is connected with an inlet of a heat medium channel of the first dividing wall type heat exchanger 3, one end of an intermediate water return pipeline is connected with an outlet of the heat medium channel of the first dividing wall type heat exchanger 3, and the other end of the intermediate water return pipeline is connected with a spray layer of the spray tower 2 through a high-temperature heat source end of the absorption heat pump 5;
an inlet and an outlet of a cold medium pipeline of the first dividing wall type heat exchanger 3 are respectively connected with a secondary network water return pipeline and a secondary network water supply pipeline;
the dosing device 1 is connected with the spray tower 2 through a pump. The chemical adding device 1 adds alkaline substances into the spray tower through a pump so as to neutralize spray water and prevent the dividing wall type heat exchanger from being corroded.
The spray tower is also called spray tower, and the tower is provided with no filler or tower plate and an absorption tower with a nozzle. The liquid enters from the top of the tower and is sprayed into a mist shape or a raindrop shape through the nozzle, and the gas enters from the lower part of the tower and is closely contacted with the mist shape or the raindrop shape liquid for mass transfer and heat transfer.
The dividing wall type heat exchanger is characterized in that cold fluid and hot fluid are separated by a layer of solid wall surface (pipe or plate), are not mixed, and exchange heat through a dividing wall. The first and second divided wall heat exchangers 3, 6 may be plate heat exchangers.
Specifically, a first valve is connected between a water supply pipeline and a water return pipeline of the primary-network water return air preheater. The flow of primary net return water to the air preheater can be adjusted by adjusting the opening degree of the first valve, and then the temperature of heated air and the temperature of cooled primary net return water are adjusted, so that the normal operation of the boiler is ensured, the proper temperature of the primary net return water is adjusted, and the condensation effect on high-temperature flue gas is ensured. Meanwhile, valves are arranged on a water supply pipeline and a water return pipeline of the primary-network backwater to the air preheater respectively so as to control the flow speed and the flow of the primary-network backwater to the air preheater.
The intermediate water supply pipeline and the intermediate water return pipeline are both provided with valves. And valves are arranged on the water supply pipeline and the water return pipeline of the intermediate water leading to the absorption heat exchanger.
And a second valve is connected between the water supply pipeline and the water return pipeline of the primary network backwater absorption heat pump. The opening and closing degree and the opening degree of the second valve are adjusted to adjust the proportion of the primary network backwater to the absorption heat pump, so that the adjustment of the temperature of the primary network backwater and the adjustment of the temperature of the medium water are realized, the better cooling effect on high-temperature smoke is ensured, and the better cooling effect on low-temperature smoke is ensured. Meanwhile, valves are arranged on the water supply pipeline and the water return pipeline.
And valves are arranged on the water supply pipeline and the water return pipeline of the primary network backwater to the second divided wall type heat exchanger.
In heat pipe engineering, a heat main line is commonly and commonly called a primary network, and the primary network refers to a total pipe network through which hot water from a heat supply station flows, generally only to a heat exchange station, and does not directly heat users.
The secondary network is a hot water pipeline which is directly connected with a hot user after the local heat exchange station exchanges heat with the primary network. That is, heat is transferred from the primary network to the secondary network through the heat exchanger, and the secondary network conducts users.
The net return water temperature is higher once, preheats the air through air heater at first, heats the air to the uniform temperature, and the air that is heated is carried the oxygen suppliment to the boiler in, can avoid low temperature air to get into the boiler and produce the detonation phenomenon, and to the situation that adopts flue gas backward flow low-nitrogen combustion technique, can avoid low temperature air and flue gas to mix the back and produce the condensation simultaneously.
The air is preheated by the air preheater, so that more heat in the return water of the primary net can be recovered, and the temperature of the return water of the primary net is reduced. The cooled primary net return water enters the absorption heat pump, the absorption heat pump absorbs heat in the medium water, then the heat is transferred to the primary net return water, and the primary net return water is heated, so that the medium water can be cooled. Because the temperature of the intermediate water has little difference with the temperature of the primary network backwater, and the intermediate water is only required to be cooled to about 20 ℃ from about 45 ℃, the investment of the heat pump can be obviously reduced. Meanwhile, the primary net return water with higher temperature is used for exchanging heat and cooling the high-temperature flue gas by using the dividing wall type heat exchanger, the temperature of the cooled flue gas is higher, and at about 80 ℃, water vapor in the flue gas can not be condensed at the temperature, so that the corrosion of the acidic condensate water to the heat exchanger can be effectively avoided.
The low-temperature flue gas after primary cooling enters a spray tower and is subjected to secondary waste heat recovery by adopting a spray cooling method, so that the temperature of the flue gas can be reduced to below 30 ℃. Because the heat in the flue gas is fully utilized, the efficiency of the gas boiler is greatly improved. And with the flue gas cooling below 30 ℃, can condense a large amount of vapor in the flue gas to get into the condensate water with the more harmful substance condensation in the flue gas, this part condensate water gets into and sprays the aquatic, and after neutralization treatment, the shower water of higher temperature can carry out the heat transfer through dividing wall heat exchanger and secondary net return water, heats the secondary net return water, with further improvement thermal utilization ratio.
A deep waste heat recovery method for flue gas comprises the following steps:
the primary net backwater sequentially passes through the air preheater to exchange heat with cold air, enters the low-temperature end of the absorption heat pump to be heated, enters the second wall type heat exchanger to exchange heat with high-temperature flue gas, and finally enters the boiler to be reheated;
the heated cold air is introduced into the boiler to provide oxygen; the low-temperature flue gas after the high-temperature flue gas is cooled enters a spray tower to be sprayed and cooled, and the cooled flue gas is discharged;
and the spray liquid is neutralized and then pumped into the first dividing wall type heat exchanger to heat the secondary net backwater, the condensed spray liquid enters the absorption heat pump to be subjected to heat recovery again, the heat is transferred to the primary net backwater, and the spray liquid after being cooled again is conveyed to a spray layer of the spray tower to spray and cool the flue gas.
The flow of various working media is respectively as follows:
smoke side: the high-temperature flue gas enters a dividing wall type heat exchanger positioned at the tail part of the boiler, the water is returned to be reduced to 80 ℃ through a primary net, and the steam in the flue gas is in an overheated state at the moment; the flue gas with the temperature of 80 ℃ enters a spray tower, is cooled to 30 ℃ by intermediate water in the spray tower and is discharged into the atmosphere. At this point 80% of the water vapour in the flue gas was cooled and neutralised by the dosing device.
Air side: in the air preheater, the air is heated to 20-30 ℃ by the primary net backwater and then sent to the boiler by the fan. If a flue gas backflow low-nitrogen combustion technology is adopted, heated air and flue gas can be guaranteed not to be condensed after being mixed according to different backflow proportions.
The primary net water return side: the return water temperature of the primary net is about 55 ℃, the return water enters an air preheater to reduce the temperature, then enters a heat pump and a partition wall type heat exchanger at the tail part of the boiler to be heated, and finally enters the boiler to be heated.
Cooling medium water by flue gas: the return water temperature of the medium water in the flue gas cooling is about 20 ℃, the medium water enters the spray tower and is heated to 55 ℃ by the flue gas, then the medium water enters the secondary side plate heat exchanger, the return water is reduced to 45 ℃ through the secondary network, then the medium water enters the absorption heat pump, the temperature is reduced to 20 ℃, and finally the medium water enters the spray tower to complete the circulation.
The secondary net backwater side: the secondary net backwater is about 40 ℃, enters a dividing wall type heat exchanger, is heated to 50 ℃ by intermediate water, and is conveyed to a user for heating.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. The utility model provides a boiler flue gas degree of depth waste heat recovery system which characterized in that: the primary net water return pipeline is sequentially connected with a heat medium channel of the air preheater, a low-temperature cold source end of the absorption heat pump, a cold medium channel of the second dividing wall type heat exchanger and a boiler;
a cold medium channel of the air preheater is connected with an air source, and a hot medium channel of the second wall type heat exchanger is connected with a flue gas outlet of the boiler;
the outlet of the heat medium channel of the second divided wall type heat exchanger is connected with the gas inlet of the spray tower;
the tower kettle of the spray tower is connected with an intermediate water supply pipeline through a pump, the intermediate water supply pipeline is connected with an inlet of a heat medium channel of the first dividing wall type heat exchanger, one end of an intermediate water return pipeline is connected with an outlet of the heat medium channel of the first dividing wall type heat exchanger, and the other end of the intermediate water return pipeline is connected with a spray layer of the spray tower through a low-temperature heat source end of the absorption heat pump;
and the inlet and the outlet of the cold medium pipeline of the first dividing wall type heat exchanger are respectively connected with the secondary network water return pipeline and the secondary network water supply pipeline.
2. The boiler flue gas deep waste heat recovery system of claim 1, characterized in that: the boiler flue gas depth waste heat recovery system further comprises a dosing device, and the dosing device is connected with the spray tower.
3. The boiler flue gas deep waste heat recovery system of claim 1, characterized in that: the first dividing wall type heat exchanger and the second dividing wall type heat exchanger are plate type heat exchangers.
4. The boiler flue gas deep waste heat recovery system of claim 1, characterized in that: a first valve is connected between a water supply pipeline and a water return pipeline of the primary net water return air preheater.
5. The boiler flue gas deep waste heat recovery system of claim 1, characterized in that: and a second valve is connected between the water supply pipeline and the water return pipeline of the primary network backwater absorption heat pump.
6. A deep waste heat recovery method for flue gas is characterized in that: the method comprises the following steps:
the primary net backwater sequentially passes through the air preheater to exchange heat with cold air, enters a low-temperature cold source end of the absorption heat pump to be heated, enters a second wall type heat exchanger to exchange heat with high-temperature flue gas, and finally enters the boiler to be reheated;
the heated cold air is introduced into the boiler to provide oxygen; the low-temperature flue gas after the high-temperature flue gas is cooled enters a spray tower to be sprayed and cooled, and the cooled flue gas is discharged;
and the spray liquid is neutralized and then pumped into the first dividing wall type heat exchanger to heat the secondary net backwater, the condensed spray liquid enters the absorption heat pump to be subjected to heat recovery again, the heat is transferred to the primary net backwater, and the spray liquid after being cooled again is conveyed to a spray layer of the spray tower to spray and cool the flue gas.
7. The deep flue gas waste heat recovery method according to claim 6, characterized in that: the temperature of the heated cold air is 20-30 ℃.
8. The deep flue gas waste heat recovery method according to claim 6, characterized in that: the temperature of the low-temperature flue gas after the high-temperature flue gas is cooled is 80-85 ℃.
9. The deep flue gas waste heat recovery method according to claim 6, characterized in that: the temperature of the spray liquid conveyed to the spray layer is 18-22 ℃.
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