A flue gas waste heat recovery system and method

Abstract

The present application relates to the technical field of waste heat recovery, and discloses a flue gas waste heat recovery system and method. The flue gas waste heat recovery system comprises a first heat storage system, a second heat storage system and a first preheating system. The first heat storage system comprises a heat storage tank and a first heat exchanger connected in sequence with a boiler flue gas outlet. The second heat storage system comprises a spray tank and a first liquid storage tank connected in sequence with a nozzle. The first preheating system comprises the spray tank and the heat releasing side of a second heat exchanger connected in sequence, the heat storage tank and the heat releasing side of a third heat exchanger connected in sequence, a first compressor, the heat absorbing side of the second heat exchanger, the heat absorbing side of the third heat exchanger and the gas inlet of the boiler connected in sequence. The heat releasing side of the second heat exchanger is connected with the first liquid storage tank, and the heat releasing side of the third heat exchanger is connected with the heat storage tank. Through twice heat exchange of flue gas, the flue gas heat recovery rate is improved, and energy waste caused by direct flue gas emission is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste heat recovery, in particular to a flue gas waste heat recovery system and method. BACKGROUND

[0002] Coal-fired, gas-fired boilers and incinerators will produce a large amount of high-temperature flue gas when processing working medium. The high-temperature flue gas carries a large amount of heat. If the high-temperature flue gas is directly discharged into the atmosphere, not only will it cause thermal pollution, but also will cause energy waste.

[0003] In related technologies, an air preheater is arranged on the flue, and the air preheater is used to heat the air to be introduced into the boiler or incinerator with the flue gas to increase the temperature of the air, thereby increasing the utilization rate of the flue gas heat.

[0004] However, the above-mentioned flue gas recovery system still contains a large amount of heat after heat exchange with air, resulting in low heat utilization rate of flue gas, thereby causing energy waste. SUMMARY

[0005] Therefore, the present application provides a flue gas waste heat recovery system and method to solve the problem that the flue gas still contains a large amount of heat after heat exchange with air, resulting in low heat utilization rate of flue gas, thereby causing energy waste.

[0006] In a first aspect, the present application provides a flue gas waste heat recovery system, comprising:

[0007] A first heat storage system comprising a heat storage tank and a boiler flue gas outlet, a first heat exchanger connected in sequence, the heat storage tank has a first medium, and the first heat exchanger is located in the first medium;

[0008] A second heat storage system comprising a spray tank and a first liquid storage tank, a nozzle connected in sequence, the first liquid storage tank has a second medium, the nozzle is located in the spray tank, and the spray tank is in communication with the first heat exchanger;

[0009] A first preheating system comprising the spray tank and the heat releasing side of the second heat exchanger connected in sequence, the heat storage tank and the heat releasing side of the third heat exchanger connected in sequence, the first compressor, the heat absorbing side of the second heat exchanger, the heat absorbing side of the third heat exchanger and the air inlet of the boiler connected in sequence;

[0010] The heat releasing side of the second heat exchanger is in communication with the first liquid storage tank, and the heat releasing side of the third heat exchanger is in communication with the heat storage tank.

[0011] Beneficial effects: The flue gas generated by the boiler enters the first heat exchanger after the boiler flue gas outlet, and the flue gas in the first heat exchanger exchanges heat with the first medium in the heat storage tank to transfer the heat in the flue gas to the first medium, thereby reducing the temperature of the flue gas and increasing the temperature of the first medium. The cooled flue gas enters the spray tank, and the second medium in the first storage tank is sprayed out through the nozzle to atomize the second medium (the atomized second medium is countless small droplets), which can increase the contact area of the atomized second medium with the flue gas. The atomized second medium exchanges heat with the flue gas to transfer the heat in the flue gas to the atomized second medium. Part of the atomized second medium (small droplets with a temperature higher than the first set value and a volume smaller than the second set value) absorbs heat and changes to gaseous second medium. Part of the atomized second medium (small droplets with a temperature lower than the first set value and / or a volume greater than the second set value) absorbs heat and converges to form droplets, which fall to the bottom of the spray tank under the action of gravity. After heat exchange is completed, the temperature of the flue gas is further reduced. By performing two heat exchanges on the flue gas, the flue gas heat recovery rate is improved, and energy waste caused by direct flue gas discharge is reduced. The first compressor generates compressed air and delivers the compressed air to the heat absorption side of the second heat exchanger. At the same time, the gaseous-liquid mixed second medium in the spray tank is delivered to the heat release side of the second heat exchanger. The gaseous-liquid mixed second medium exchanges heat with the compressed air to preheat the compressed air, thereby increasing the temperature of the compressed air and condensing the gaseous second medium into liquid. The liquid second medium is returned to the first storage tank. The compressed air on the heat absorption side of the second heat exchanger is delivered to the heat absorption side of the third heat exchanger. At the same time, the first medium in the heat storage tank after heat absorption is delivered to the heat release side of the third heat exchanger. The first medium exchanges heat with the compressed air to further preheat the compressed air, thereby further increasing the temperature of the compressed air and reducing the temperature of the first medium. After heat exchange is completed, the first medium with reduced temperature is returned to the heat storage tank. The compressed air on the heat absorption side of the third heat exchanger is delivered to the boiler through the boiler air inlet for boiler combustion. By preheating the compressed air, the combustion efficiency of the boiler is improved, thereby reducing the fuel consumption of the boiler.

[0012] In an alternative embodiment, the first heat exchanger comprises:

[0013] a first heat-conducting box body and a second heat-conducting box body;

[0014] a first partition plate located in the first heat-conducting box body and separating the first heat-conducting box body into a first sealed cavity and a second sealed cavity, the first sealed cavity being in communication with the boiler flue gas outlet;

[0015] a second partition plate located in the second heat-conducting box body and separating the second heat-conducting box body into a third sealed cavity and a fourth sealed cavity, the fourth sealed cavity being in communication with the spray tank;

[0016] a first flue gas flow channel, two ends of which are communicated with the first sealed cavity and the third sealed cavity respectively;

[0017] a second flue gas flow channel, two ends of which are communicated with the third sealed cavity and the second sealed cavity respectively;

[0018] a third flue gas flow channel, two ends of which are communicated with the third sealed cavity and the fourth sealed cavity respectively.

[0019] Beneficial effects: The flue gas generated by the boiler is transported into the first sealed cavity through the boiler flue gas outlet. With the continuous transportation of flue gas into the first sealed cavity, the flue gas in the first sealed cavity is transported into the third sealed cavity through the first flue gas flow channel, the flue gas in the third sealed cavity is transported into the second sealed cavity through the second flue gas flow channel, the flue gas in the second sealed cavity is transported into the fourth sealed cavity through the third flue gas flow channel, and the flue gas in the fourth sealed cavity is transported into the spray tank. The first heat-conducting box is divided into the first sealed cavity and the second sealed cavity by the first partition plate, the second heat-conducting box is divided into the third sealed cavity and the fourth sealed cavity by the second partition plate, and the two ends of the first flue gas flow channel are communicated with the first sealed cavity and the third sealed cavity respectively, the two ends of the second flue gas flow channel are communicated with the third sealed cavity and the second sealed cavity respectively, and the two ends of the third flue gas flow channel are communicated with the third sealed cavity and the fourth sealed cavity respectively, so as to prolong the transportation path of the flue gas in the first heat exchanger, thereby increasing the transportation time of the flue gas in the first heat exchanger, improving the heat exchange efficiency of the first medium and the high-temperature flue gas, and further improving the efficiency of flue gas waste heat recovery and the energy utilization rate of the whole flue gas waste heat recovery system.

[0020] In an alternative embodiment, further comprising:

[0021] a flue gas pipeline, which comprises a first smooth pipe section, a rotating acceleration pipe section and a second smooth pipe section connected in sequence, the first smooth pipe section is communicated with the boiler flue gas outlet, at least part of the second smooth pipe section extends into the heat storage tank, and the second smooth pipe section is communicated with the first sealed cavity, and a plurality of spiral protrusions are arranged in the rotating acceleration pipe section;

[0022] a rotating shaft, one end of which extends into the second smooth pipe section, and the other end of which extends out of the second smooth pipe section and into the heat storage tank;

[0023] a support rod, which is fixedly connected with the inner wall of the second smooth pipe section and rotationally connected with the rotating shaft;

[0024] a first fan blade, which is located in the second smooth pipe section and fixedly connected with the rotating shaft;

[0025] a second fan blade, which is located in the heat storage tank and fixedly connected with the rotating shaft.

[0026] Beneficial effects: The flue gas generated by the boiler is sequentially conveyed to the first sealing cavity through the boiler flue gas outlet, the first smooth pipe section, the rotating acceleration pipe section and the second smooth pipe section. When the flue gas enters the rotating acceleration pipe, the spiral protrusions guide the flue gas to rotate. Since the rotating acceleration pipe section is provided with a plurality of spiral protrusions, the flue gas flow channel of the rotating acceleration pipe section is narrowed, so that the flow cross section of the flue gas in the rotating acceleration pipe is reduced, so that the flow rate of the flue gas after entering the rotating acceleration pipe is accelerated (part of the pressure energy of the flue gas is converted into kinetic energy). After the flue gas passes through the rotating acceleration pipe, the rotating high-flow-rate flue gas enters the second smooth pipe section to impact the first fan blade in the second smooth pipe section, thereby driving the first fan blade to rotate, and the rotation of the first fan blade drives the second fan blade to rotate, so that the second fan blade stirs the first medium in the heat storage tank, so that the first medium in the heat storage tank is uniformly heated, avoiding the case that the temperature of the first medium in the area near the first heater is too high, resulting in a decrease in the heat exchange efficiency of the first medium and the flue gas. Through the rotating acceleration pipe section, the flue gas passing therethrough is rotated and the flow rate is increased, so as to increase the impact force on the first fan blade, thereby increasing the efficiency of converting the mechanical energy of the first fan blade, and further improving the stirring efficiency of the second fan blade for the first medium.

[0027] In an alternative embodiment, further comprising:

[0028] A first valve body and a first flow meter, the flue gas in the fourth sealing cavity is sequentially conveyed to the spray tank through the first flow meter and the first valve body, and the first valve body is a one-way valve;

[0029] A temperature detection member for obtaining the temperature of the flue gas after passing through the first flow meter;

[0030] A second valve body, the second medium in the first liquid storage tank is conveyed to the nozzle through the second valve body.

[0031] Beneficial effects: The first valve body is used to prevent the gas in the spray tank from flowing back to the first heat exchanger. The flue gas flow rate conveyed to the spray tank can be obtained through the first flow meter, and the temperature of the flue gas after passing through the first flow meter can be obtained through the temperature detection member. According to the flue gas flow rate and the temperature, the opening degree of the second valve body is adjusted to adjust the flow rate of the second medium conveyed to the spray tank.

[0032] In an alternative embodiment, further comprising a second preheating system, which comprises a second liquid storage tank, a Rankine cycle system and a liquid inlet of the boiler connected in sequence, and the Rankine cycle system is connected in series with the flue gas outlet of the spray tank.

[0033] Beneficial effects: the flue gas in the spray tank is transported to the Rankine cycle system through the flue gas outlet, at the same time, the third medium in the second liquid storage tank is transported to the Rankine cycle system, the Rankine cycle system extracts the heat of the flue gas and heats the third medium transported thereto to preheat the third medium. The preheated third medium is transported to the boiler through the liquid inlet of the boiler. By preheating the third medium, the energy consumption of the boiler for heating the third medium is reduced, thereby reducing the waste of energy.

[0034] In an alternative embodiment, the Rankine cycle system comprises:

[0035] an evaporator, the inlet of the heat-releasing side of which is in communication with the flue gas outlet of the spray tank, and the outlet of the heat-releasing side of which is in communication with the outside world;

[0036] a condenser, the outlet of the heat-releasing side of which is in communication with the inlet of the heat-absorbing side of the evaporator through an expansion valve, and the inlet of the heat-releasing side of which is in communication with the outlet of the heat-absorbing side of the evaporator through a second compressor;

[0037] the second liquid storage tank is in communication with the inlet of the heat-absorbing side of the condenser, and the outlet of the heat-absorbing side of the condenser is in communication with the liquid inlet of the boiler. Beneficial effects: the flue gas is transported to the heat-releasing side of the evaporator, at the same time, the liquid fourth medium in the condenser is transported to the heat-absorbing side of the evaporator after passing through the expansion valve, the fourth medium exchanges heat with the flue gas, the fourth medium changes from liquid to gas after absorbing heat, and the temperature of the flue gas is further reduced. The flue gas with reduced temperature is transported to the outside world. The gaseous fourth medium is further compressed by the compressor and transported to the heat-releasing side of the condenser, at the same time, the third medium in the liquid storage tank is transported to the heat-absorbing side of the condenser, the third medium exchanges heat with the gaseous fourth medium, the third medium absorbs heat to increase the temperature of the third medium, and the gaseous fourth medium condenses to become liquid. The Rankine cycle system further absorbs the waste heat of the flue gas and preheats the third medium by using the waste heat of the flue gas.

[0038] In an alternative embodiment, the second preheating system further comprises a fourth heat exchanger, the inlet of the heat-releasing side of the fourth heat exchanger is in communication with the outlet of the heat storage tank, the outlet of the heat-releasing side of the fourth heat exchanger is in communication with the inlet of the heat storage tank, the inlet of the heat-absorbing side of the fourth heat exchanger is in communication with the outlet of the heat-absorbing side of the condenser, and the outlet of the heat-absorbing side of the fourth heat exchanger is in communication with the liquid inlet of the boiler.

[0039] Beneficial effects: The first medium in the heat storage tank is transported to the heat releasing side of the fourth heat exchanger, at the same time, the third medium in the heat absorbing side of the condenser is transported to the heat absorbing side of the fourth heat exchanger, the third medium exchanges heat with the first medium, the third medium absorbs heat to further increase the temperature of the third medium, the temperature of the first medium is reduced, and the third medium in the heat absorbing side of the fourth heat exchanger is transported to the liquid inlet of the boiler after being heated, and the first medium in the heat releasing side of the fourth heat exchanger is transported to the heat storage tank after being cooled. The third medium is preheated to reduce the energy consumption of the boiler for heating the third medium, thereby further reducing the fuel consumption.

[0040] In an alternative embodiment, a heat network system is further included, which comprises a boiler liquid outlet, a heat network pipeline and a second liquid storage tank connected in sequence.

[0041] Beneficial effects: The third medium heated by the boiler is transported to the heat network system through the boiler liquid outlet to provide heat energy for users, and the cooled third medium is transported back to the second liquid storage tank.

[0042] In a second aspect, the application further provides a flue gas waste heat recovery method, comprising:

[0043] The first medium is in the heat storage tank, and the first heat exchanger is located in the first medium, and the flue gas generated by the boiler passes through the first heat exchanger, and the flue gas in the first heat exchanger exchanges heat with the first medium in the heat storage tank;

[0044] The nozzle is located in the spray tank, the second medium in the first liquid storage tank is transported to the nozzle and sprayed out of the nozzle, at the same time, the flue gas passing through the first heat exchanger is transported to the spray tank, and the second medium sprayed out of the nozzle exchanges heat with the flue gas;

[0045] The first compressor extracts compressed air, and the compressed air is transported to the heat absorbing side of the second heat exchanger, at the same time, the second medium in the spray tank is transported to the heat releasing side of the second heat exchanger, the second medium in the heat absorbing side of the second heat exchanger exchanges heat with the compressed air, after the heat exchange is completed, the compressed air in the heat absorbing side of the second heat exchanger is transported to the heat absorbing side of the third heat exchanger, and the second medium in the heat releasing side of the second heat exchanger is transported to the first liquid storage tank; at the same time, the first medium in the heat storage tank is transported to the heat releasing side of the third heat exchanger, the first medium exchanges heat with the compressed air in the heat absorbing side of the third heat exchanger, after the heat exchange is completed, the compressed air in the heat absorbing side of the third heat exchanger is transported to the air inlet of the boiler, and the first medium in the heat releasing side of the third heat exchanger is transported to the heat storage tank.

[0046] Beneficial effects: Through twice heat exchange of the flue gas, the flue gas heat recovery rate is improved, and the energy waste caused by direct flue gas emission is reduced. The compressed air is preheated to improve the combustion efficiency of the boiler, thereby reducing the fuel consumption of the boiler. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 It is the principle schematic view of the flue gas waste heat recovery system in the application;

[0048] Figure 2 It is the principle schematic view of the heat storage tank, flue gas pipeline, first fan blade, second fan blade, first heat exchanger and first medium in the application;

[0049] Figure 3 It is the sectional view of the first heat exchanger in the application.

[0050] Mark explanation:

[0051] 100, boiler;

[0052] 201, first heat exchanger; 2011, first heat conduction box; 20111, first sealing cavity; 20112, second sealing cavity; 2012, second heat conduction box; 20121, third sealing cavity; 20122, fourth sealing cavity; 2013, first partition plate; 2014, second partition plate; 2015, first flue gas flow channel; 2016, second flue gas flow channel; 2017, third flue gas flow channel; 202, heat storage tank;

[0053] 301, spraying tank; 302, first liquid storage tank; 303, nozzle;

[0054] 401, second heat exchanger; 402, third heat exchanger; 403, first compressor;

[0055] 500, flue gas pipeline; 501, first smooth pipe section; 502, rotating acceleration pipe section; 503, second smooth pipe section;

[0056] 601, rotating shaft; 602, support rod; 603, first fan blade; 604, second fan blade;

[0057] 701, second liquid storage tank; 702, evaporator; 703, condenser; 704, second compressor; 705, expansion valve; 706, fourth heat exchanger;

[0058] 800, heat network pipeline;

[0059] P1, first valve body; P2, second valve body; P3, third valve body; P4, fourth valve body; P5, fifth valve body; P6, sixth valve body; P7, seventh valve body; P8, eighth valve body;

[0060] S1, first flow meter; S2, second flow meter; S3, temperature detection piece; S4, motor; S5, first pump body; S6, second pump body; S7, third pump body; S8, fourth pump body; S9, fifth pump body. DETAILED DESCRIPTION

[0061] The technical solutions of the present application will be described clearly and completely in combination with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0062] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0063] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0064] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0065] The technical solutions of the present application will be described clearly and completely in combination with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. Figures 1 to 3 , the embodiments of the flue gas waste heat recovery system and method of the present application are described.

[0066] According to the embodiments of the present application, a flue gas waste heat recovery system is provided, such as Figure 1As shown, it comprises a first heat storage system, a second heat storage system and a first preheating system, the first heat storage system comprises a heat storage tank 202 and a boiler 100 flue gas outlet, a first heat exchanger 201 in sequence, the heat storage tank 202 has a first medium, and the first heat exchanger 201 is located in the first medium; the second heat storage system comprises a spray tank 301 and a first liquid storage tank 302, a nozzle 303 in sequence, the first liquid storage tank 302 has a second medium, the nozzle 303 is located in the spray tank 301, and the spray tank 301 is communicated with the first heat exchanger 201; the first preheating system comprises the spray tank 301 and the heat releasing side of the second heat exchanger 401 in sequence, the heat storage tank 202 and the heat releasing side of the third heat exchanger 402 in sequence, the first compressor 403, the heat absorbing side of the second heat exchanger 401, the heat absorbing side of the third heat exchanger 402 and the gas inlet of the boiler 100 in sequence; the heat releasing side of the second heat exchanger 401 is communicated with the first liquid storage tank 302, and the heat releasing side of the third heat exchanger 402 is communicated with the heat storage tank 202.

[0067] In the embodiment, as shown in Figure 1 and Figure 2 The heat storage tank 202 is made of heat insulation material to reduce the loss of heat in it. The shape of the heat storage tank 202 can be cylindrical, square or other common tank shape. The heat storage tank 202 is also provided with a temperature sensing rod and a liquid level gauge. The temperature of the first medium in the heat storage tank 202 is obtained by the temperature sensing rod, and the liquid level of the first medium is obtained by the liquid level gauge. The heat storage tank 202 stores the first medium, which can be a liquid with high specific heat capacity and high thermal stability. Preferably, the first medium is heat conducting oil. The first heat exchanger 201 is immersed in the first medium in the heat storage tank 202. The material of the first heat exchanger 201 can be iron, copper, aluminum alloy, copper alloy or other common heat conducting materials. The first heat exchanger 201 is communicated with the boiler 100 flue gas outlet through a pipeline. The flue gas generated by the boiler 100 is transported into the first heat exchanger 201 after passing through the boiler 100 flue gas outlet. Since the material of the first heat exchanger 201 is heat conducting material, the heat of the flue gas in the first heat exchanger 201 is transferred to the first medium, so that the temperature of the flue gas is reduced and the temperature of the first medium is increased, thereby realizing the preliminary recovery of the waste heat of the flue gas.

[0068] In the embodiment, as shown in Figure 1As shown, the material of the spray tank 301 can be alloy steel, aluminum alloy or other common high-pressure tank body materials, and the shape of the spray tank 301 can be adjusted as required. Specifically, the spray tank 301 is cylindrical. The flue gas often carries part of the acid gas, such as sulfur dioxide and hydrogen chloride. The material of the inner wall of the spray tank 301 can be acid-resistant stainless steel or other acid-resistant materials, or the inner wall of the spray tank 301 can be treated (acid-resistant coating is added) to improve the corrosion resistance of the spray tank 301 and prolong the service life of the spray tank 301. The flue gas inlet of the spray tank 301 is communicated with the first heat exchanger 201 through a pipeline. The nozzle 303 is located at the top of the spray tank 301 and above the flue gas inlet of the spray tank 301, and the nozzle 303 covers the flue gas inlet of the spray tank 301. The nozzle 303 is made of silicon carbide ceramic material or other acid-resistant materials, so that the nozzle 303 can resist the long-term corrosion of the corrosive components in the flue gas, thereby reducing the maintenance frequency and replacement cost of the nozzle 303 and improving the reliability of the flue gas waste heat recovery system. The nozzle 303 is communicated with the first liquid storage tank 302 through a pipeline, and the first liquid storage tank 302 stores a second medium. The second medium can be a liquid with high specific heat capacity and high thermal stability. Specifically, the second medium in the embodiment is water, and the material of the first liquid storage tank 302 can be stainless steel, plastic or other corrosion-resistant materials. The shape of the first liquid storage tank 302 can be adjusted as required, which is not limited herein. The second medium in the first liquid storage tank 302 is delivered to the nozzle 303 and sprayed from the nozzle 303 as atomized second medium. The atomized second medium is countless small droplets. The atomized second medium can increase its contact area with the flue gas. The atomized second medium exchanges heat with the flue gas to transfer heat from the flue gas to the atomized second medium. Part of the atomized second medium (small droplets with a temperature higher than a first set value and a volume smaller than a second set value) is converted into gaseous second medium after absorbing heat. Part of the atomized second medium (small droplets with a temperature lower than the first set value and / or a volume larger than the second set value) converges to form droplets after absorbing heat. Under the action of gravity, the droplets fall to the bottom of the spray tank 301, and the small droplets sprayed on the inner wall of the spray tank 301 also converge to the bottom of the spray tank 301. After heat exchange, the temperature of the flue gas is further reduced, and the temperature of the second medium collected at the bottom of the spray tank 301 is increased, thereby achieving further recovery of the waste heat of the flue gas.

[0069] In the embodiment, the alkaline substance can be added to the first liquid tank 302 periodically, and the alkaline substance can be one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide and potassium hydroxide. The alkaline substance is dissolved in the second medium and sprayed out by the nozzle 303 to neutralize the acidic gas in the flue gas, so that the acidity of the second medium collected at the bottom of the spray tank 301 is reduced, the corrosiveness of the second medium collected at the bottom of the spray tank 301 to the inner wall of the spray tank 301 and the subsequent equipment is reduced, and the service life of the flue gas waste heat recovery system is prolonged.

[0070] In the embodiment, the flue gas heat recovery rate is improved by twice heat exchange of the flue gas, and the energy waste caused by direct flue gas emission is reduced.

[0071] In the embodiment, as Figure 1As shown, the bottom of the spray tank 301 is communicated with the inlet of the heat releasing side of the second heat exchanger 401 through a pipeline, and the pipeline is provided with a fifth pump body S9 and a third valve body P3. The fifth pump body S9 is a hydraulic pump, and the third valve body P3 is an electromagnetic valve. The fifth pump body S9 is used for pumping the second medium in the spray tank 301 into the heat releasing side of the second heat exchanger 401, and the third valve body P3 is used for controlling the flow of the second medium delivered from the spray tank 301 into the heat releasing side of the second heat exchanger 401. The outlet of the heat storage tank 202 is communicated with the inlet of the heat releasing side of the third heat exchanger 402 through a pipeline, and the pipeline is further provided with a fourth valve body P4. The fourth valve body P4 is used for controlling the flow of the first medium delivered from the heat storage tank 202 into the heat releasing side of the third heat exchanger 402. The outlet of the heat releasing side of the second heat exchanger 401 is communicated with the first liquid storage tank 302 through a pipeline, and the outlet of the heat releasing side of the third heat exchanger 402 is communicated with the inlet of the heat storage tank 202 through a pipeline. The pipeline is provided with a fifth valve body P5 and a second pump body S6. The second pump body S6 is a hydraulic pump, and the fifth valve body P5 is an electromagnetic valve. The second pump body S6 is used for pumping the first medium in the heat releasing side of the third heat exchanger 402 into the heat storage tank 202, and the fifth valve body P5 is used for controlling the flow of the first medium delivered from the heat releasing side of the third heat exchanger 402 into the heat storage tank 202. The motor S4 drives the first compressor 403 to rotate. The first compressor 403 is communicated with the inlet of the heat absorbing side of the second heat exchanger 401 through a pipeline, the outlet of the heat absorbing side of the second heat exchanger 401 is communicated with the inlet of the heat absorbing side of the third heat exchanger 402 through a pipeline, and the outlet of the heat absorbing side of the third heat exchanger 402 is communicated with the air inlet of the boiler 100 through a pipeline. The first heat exchanger 201 and the second heat exchanger 401 are both plate heat exchangers, the first compressor 403 is an air compressor, and the first compressor 403 is used for extracting air to generate compressed air.The first compressor 403 generates compressed air and delivers the compressed air to the heat absorption side of the second heat exchanger 401, and the gaseous-liquid mixed second medium in the spray tank 301 is delivered to the heat release side of the second heat exchanger 401, the gaseous-liquid mixed second medium exchanges heat with the compressed air to preheat the compressed air, so that the temperature of the compressed air is increased, the gaseous second medium is condensed into liquid state, and the temperature of the liquid second medium is decreased, the cooled liquid second medium returns to the first liquid storage tank 302, the compressed air on the heat absorption side of the second heat exchanger 401 is delivered to the heat absorption side of the third heat exchanger, and the heat-absorbed first medium in the heat storage tank 202 is delivered to the heat release side of the third heat exchanger 402, the first medium exchanges heat with the compressed air to further preheat the compressed air, so that the temperature of the compressed air is further increased, and the temperature of the first medium is decreased, after the heat exchange is completed, the first medium with decreased temperature returns to the heat storage tank 202, and the compressed air on the heat absorption side of the third heat exchanger 402 is delivered to the boiler 100 through the boiler 100 air inlet to be used for the combustion of the boiler 100, by preheating the compressed air, the combustion efficiency of the boiler 100 is improved, thereby reducing the fuel consumption of the boiler 100.

[0072] In the embodiment, as Figure 2 and Figure 3As shown, the first heat exchanger 201 includes a first heat-conducting box 2011, a second heat-conducting box 2012, a first partition plate 2013, a second partition plate 2014, a first flue gas flow channel 2015, a second flue gas flow channel 2016 and a third flue gas flow channel 2017. The first partition plate 2013, the second partition plate 2014, the first heat-conducting box 2011 and the second heat-conducting box 2012 are all made of heat-conducting materials, such as metal alloys. The first partition plate 2013 is located in the first heat-conducting box 2011, and divides the first heat-conducting box 2011 into a first sealed cavity 20111 and a second sealed cavity 20112, and the first sealed cavity 20111 is in communication with the flue gas outlet of the boiler 100. The second partition plate 2014 is located in the second heat-conducting box 2012, and divides the second heat-conducting box 2012 into a third sealed cavity 20121 and a fourth sealed cavity 20122, and the fourth sealed cavity 20122 is in communication with the spray tank 301. The two ends of the first flue gas flow channel 2015 are in communication with the first sealed cavity 20111 and the third sealed cavity 20121 respectively, the two ends of the second flue gas flow channel 2016 are in communication with the third sealed cavity 20121 and the second sealed cavity 20112 respectively, and the two ends of the third flue gas flow channel 2017 are in communication with the third sealed cavity 20121 and the fourth sealed cavity 20122 respectively. The flue gas generated by the boiler 100 is transported into the first sealed cavity 20111 through the flue gas outlet of the boiler 100. With the continuous transportation of the flue gas, the flue gas in the first sealed cavity 20111 is transported into the third sealed cavity 20121 through the first flue gas flow channel 2015, the flue gas in the third sealed cavity 20121 is transported into the second sealed cavity 20112 through the second flue gas flow channel 2016, the flue gas in the second sealed cavity 20112 is transported into the fourth sealed cavity 20122 through the third flue gas flow channel 2017, and finally the flue gas in the fourth sealed cavity 20122 is transported into the spray tank 301. Through such a structural design, the transportation path of the flue gas in the first heat exchanger 201 is prolonged, the transportation time of the flue gas in the first heat exchanger 201 is increased, the first medium has a longer heat exchange time with the high-temperature flue gas, thereby improving the heat exchange efficiency of the first medium and the high-temperature flue gas, and further improving the efficiency of flue gas waste heat recovery and the energy utilization rate of the entire flue gas waste heat recovery system.

[0073] In the present embodiment, as Figure 2The device also includes flue gas pipeline 500, rotating shaft 601, support rod 602, first fan blade 603 and second fan blade 604. Flue gas pipeline 500 includes first smooth tube segment 501, rotating acceleration tube segment 502 and second smooth tube segment 503 connected in sequence, first smooth tube segment 501 is connected with flue gas outlet of boiler 100 through pipeline, part of second smooth tube segment 503 extends into heat storage tank 202 and is connected with heat storage tank 202 in a sealed manner, and second smooth tube segment 503 is connected with first sealing cavity 20111 through pipeline, rotating acceleration tube segment 502 is provided with multiple spiral protrusions. One end of rotating shaft 601 extends into second smooth tube segment 503, and the other end extends out of second smooth tube segment 503 and into heat storage tank 202. Support rod 602 is fixedly connected with the inner wall of second smooth tube segment 503 and is rotatably connected with rotating shaft 601, support rod 602 is a rod, and the two ends of support rod 602 are fixedly connected with the opposite inner side walls of second smooth tube segment 503, rotating shaft 601 penetrates the middle part of support rod 602 and is rotatably connected with support rod 602 through a bearing, the bearing can limit the movement of rotating shaft 601 along the axial direction of rotating shaft 601, and rotating shaft 601 is also rotatably connected with second smooth tube segment 503 through a bearing. Support rod 602 supports and fixes rotating shaft 601. First fan blade 603 is located in second smooth tube segment 503 and is fixedly connected with rotating shaft 601, and second fan blade 604 is located in heat storage tank 202 and is fixedly connected with rotating shaft 601. The flue gas generated by boiler 100 is sequentially conveyed into first sealing cavity 20111 through flue gas outlet of boiler 100, first smooth tube segment 501, rotating acceleration tube segment 502 and second smooth tube segment 503. When the flue gas enters the rotating acceleration tube, the spiral protrusions guide the flue gas to rotate, and because rotating acceleration tube segment 502 is provided with multiple spiral protrusions, the flue gas flow passage of rotating acceleration tube segment 502 is narrowed, so that the flow cross section of the flue gas in the rotating acceleration tube is reduced, the flow speed of the flue gas after entering the rotating acceleration tube is accelerated, part of the pressure energy of the flue gas is converted into kinetic energy, and the flue gas with high rotating flow speed is formed. The flue gas with high rotating flow speed enters second smooth tube segment 503 and impacts first fan blade 603 in second smooth tube segment 503, pushes first fan blade 603 to rotate, first fan blade 603 drives second fan blade 604 to rotate, and second fan blade 604 stirs the first medium in heat storage tank 202, so that the first medium in heat storage tank 202 is uniformly heated, and the situation that the temperature of the first medium near the first heater is too high and the heat exchange efficiency of the first medium and the flue gas is reduced is avoided. The pressure energy of the flue gas is converted into kinetic energy through rotating acceleration tube segment 502, the impact force on first fan blade 603 is improved, first fan blade 603 can rotate, and second fan blade 604 stirs the first medium.The design effectively improves the heating uniformity of the first medium, avoids local overheating, improves the heat exchange efficiency of the first medium and flue gas, and further improves the performance of the entire flue gas waste heat recovery system, so that the flue gas waste heat recovery system can operate more stably and efficiently.

[0074] In the embodiment, as shown in Figure 1 The first valve body P1 and the second valve body P2 are both solenoid valves, the first flow meter S1 is a flue gas flow meter, the first valve body P1, the temperature detection member S3 and the first flow meter S1 are installed on the pipeline between the fourth sealing cavity 20122 and the spray tank 301, the flue gas in the fourth sealing cavity 20122 is sequentially conveyed to the spray tank 301 after passing through the first flow meter S1 and the first valve body P1, the first valve body P1 is a one-way valve, which is used to avoid the backflow of the gas in the spray tank 301 to the first heat exchanger 201. The temperature detection member S3 is installed on the pipeline downstream of the first flow meter S1, which is used to obtain the temperature of the flue gas after passing through the first flow meter S1. The second valve body P2 is installed on the pipeline between the first liquid storage tank 302 and the nozzle 303, and a first pump body S5 is also arranged on the pipeline, which is used to pump the second medium in the first liquid storage tank 302 to the nozzle 303. The second medium in the first liquid storage tank 302 is conveyed to the nozzle 303 after passing through the second valve body P2, and the second valve body P2 is used to control the flow of the second medium conveyed from the first liquid storage tank 302 to the spray tank 301. The flue gas flow conveyed to the spray tank 301 can be obtained by the first flow meter S1, and the temperature of the flue gas after passing through the first flow meter S1 can be obtained by the temperature detection member S3. According to the flue gas flow and temperature, the opening of the second valve body P2 is adjusted to adjust the flow of the second medium conveyed to the spray tank 301. When the flue gas temperature is high and the flow is large, the opening of the second valve body P2 is appropriately increased to increase the flow of the second medium, so as to better exchange heat with the flue gas; when the flue gas temperature is low and the flow is small, the opening of the second valve body P2 is reduced to reduce the flow of the second medium, so as to avoid unnecessary waste. By arranging the first valve body P1, the first flow meter S1, the temperature detection member S3 and the second valve body P2, the monitoring and adjustment of the flue gas flow, temperature and second medium flow are realized. The self-adaptive adjustment function enables the system to dynamically adjust the flow of the second medium according to the actual flue gas working condition, and ensures the efficiency and stability of heat exchange.

[0075] In the embodiment, as shown in Figure 1As shown, the second preheating system comprises a second liquid storage tank 701, a Rankine cycle system, and a liquid inlet of the boiler 100 connected in sequence, and the Rankine cycle system is connected in series with the flue gas outlet of the spray tank 301. The Rankine cycle system comprises an evaporator 702, a condenser 703, an expansion valve 705, and a second compressor 704. The second liquid storage tank 701 is a cooling tower, and a third medium in the second liquid storage tank 701 is cooling water. The flue gas outlet of the spray tank 301 is connected to the inlet of the heat-releasing side of the evaporator 702 through a pipeline, and the outlet of the heat-releasing side of the evaporator 702 is connected to the outside. The outlet of the heat-releasing side of the condenser 703 is connected to the inlet of the heat-absorbing side of the evaporator 702 through a pipeline, and the expansion valve 705 is arranged on the pipeline. The inlet of the heat-releasing side of the condenser 703 is connected to the outlet of the heat-absorbing side of the evaporator 702 through a pipeline, and the second compressor 704 is arranged on the pipeline. The second liquid storage tank 701 is connected to the inlet of the heat-absorbing side of the condenser 703 through a pipeline, and a second flow meter S2 is arranged on the pipeline to obtain the flow of the third medium transported from the second liquid storage tank 701 to the heat-absorbing side of the condenser 703. The outlet of the heat-absorbing side of the condenser 703 is connected to the liquid inlet of the boiler 100 through a pipeline. The flue gas is transported to the heat-releasing side of the evaporator 702, and at the same time, the liquid fourth medium in the condenser 703 is transported to the heat-absorbing side of the evaporator 702 after passing through the expansion valve 705. The fourth medium exchanges heat with the flue gas, and the fourth medium changes from a liquid state to a gaseous state after absorbing heat, and the temperature of the flue gas is further reduced. The flue gas with reduced temperature is transported to the outside. The gaseous fourth medium is further compressed by the compressor and transported to the heat-releasing side of the condenser 703, and at the same time, the third medium in the liquid storage tank is transported to the heat-absorbing side of the condenser 703. The third medium exchanges heat with the gaseous fourth medium, the temperature of the third medium is increased after absorbing heat, and the gaseous fourth medium changes from a gaseous state to a liquid state. The Rankine cycle system further absorbs the waste heat of the flue gas, and the waste heat of the flue gas is used to preheat the third medium. By preheating the third medium, the energy consumed by the boiler 100 to heat the third medium is reduced, thereby reducing energy waste.

[0076] In the embodiment, as Figure 1As shown, the second preheating system further comprises a fourth heat exchanger 706, and the heat releasing side inlet of the fourth heat exchanger 706 is communicated with the outlet of the heat storage tank 202 through a pipeline, and a sixth valve P6 is arranged on the pipeline, the sixth valve P6 is an electromagnetic valve, and the sixth valve P6 is used for controlling the flow of the first medium delivered from the heat storage tank 202 to the heat releasing side of the fourth heat exchanger 706. The heat releasing side outlet of the fourth heat exchanger 706 is communicated with the inlet of the heat storage tank 202 through a pipeline, and a second pump S6 is arranged on the pipeline. The heat absorbing side inlet of the fourth heat exchanger 706 is communicated with the heat absorbing side outlet of the condenser 703, and the heat absorbing side outlet of the fourth heat exchanger 706 is communicated with the liquid inlet of the boiler 100 through a pipeline, and a seventh valve P7 and a third pump S7 are arranged on the pipeline. The seventh valve P7 is an electromagnetic valve, and is used for adjusting the flow of the cooling water delivered into the boiler 100. The third pump S7 is used for pumping the cooling water in the second storage tank 701 into the boiler 100. According to the flow of the cooling water obtained by the second flow meter S2, the opening degree of the sixth valve P6 can be adjusted, so as to adjust the flow of the first medium delivered into the heat releasing side of the fourth heat exchanger 706. The first medium in the heat storage tank 202 is delivered into the heat releasing side of the fourth heat exchanger 706, and the third medium in the heat absorbing side of the condenser 703 is delivered into the heat absorbing side of the fourth heat exchanger 706. The third medium exchanges heat with the first medium, the third medium absorbs heat, so that the temperature of the third medium is further increased, the temperature of the first medium is decreased, the third medium in the heat absorbing side of the fourth heat exchanger 706 is delivered into the liquid inlet of the boiler 100 after being heated, and the first medium in the heat releasing side of the fourth heat exchanger 706 is delivered into the heat storage tank 202 after being cooled. The third medium is preheated, so that the energy consumed by the boiler 100 for heating the third medium is reduced, and the consumption of fuel is further reduced.

[0077] In an alternative embodiment, a heat network system is further included, which comprises the liquid outlet of the boiler 100, a heat network pipeline 800, and the second storage tank 701 communicated in sequence. The third medium heated by the boiler 100 is delivered into the heat network system through the liquid outlet of the boiler 100, so as to provide heat energy for users, and the cooled third medium is delivered into the second storage tank 701. The fourth pump S8 and the eighth valve P8 are arranged between the heat network pipeline 800 and the second storage tank 701. The fourth pump S8 is used for pumping the cooling water in the heat network pipeline 800 into the second storage tank 701. The eighth valve P8 is an electromagnetic valve, and is used for adjusting the flow of the cooling water delivered between the heat network pipeline 800 and the second storage tank 701.

[0078] The embodiment provides a flue gas waste heat recovery method, comprising the following steps:

[0079] S1, the first medium is in the heat storage tank 202, the first heat exchanger 201 is located in the first medium, the flue gas generated by the boiler 100 passes through the first heat exchanger 201, and the flue gas in the first heat exchanger 201 exchanges heat with the first medium in the heat storage tank 202. In this step, the high-temperature flue gas discharged by the boiler 100 enters the first heat exchanger 201 and fully contacts the first medium in the heat storage tank 202 to perform heat transfer. The first medium absorbs the heat in the flue gas, the temperature rises, and the temperature of the flue gas decreases, realizing the preliminary recovery of the waste heat of the flue gas. The first medium here is usually selected to be a substance with high specific heat capacity and thermal stability, such as molten salt, which can effectively store heat.

[0080] S2, the nozzle 303 is located in the spraying tank 301, the second medium in the first liquid storage tank 302 is transported to the nozzle 303 and sprayed out by the nozzle 303, and at the same time, the flue gas passing through the first heat exchanger 201 is transported to the spraying tank 301, and the second medium sprayed out by the nozzle 303 exchanges heat with the flue gas. The flue gas cooled by the first heat exchanger 201 enters the spraying tank 301, and the second medium in the first liquid storage tank 302 is atomized into small droplets by the nozzle 303 and sprayed out, and fully contacts the flue gas. The second medium absorbs the heat in the flue gas, part of which is converted into gas, and part of which is gathered into droplets and falls into the bottom of the spraying tank 301, further reducing the temperature of the flue gas and improving the waste heat recovery efficiency. The second medium can be selected according to actual conditions to be a liquid with good heat absorption performance, such as water or a specific solution.

[0081] S3, the first compressor 403 extracts compressed air, and the compressed air is delivered to the heat absorption side of the second heat exchanger 401, at the same time, the second medium in the spray tank 301 is delivered to the heat release side of the second heat exchanger 401, the second medium in the heat absorption side of the second heat exchanger 401 exchanges heat with the compressed air, after the heat exchange is completed, the compressed air in the heat absorption side of the second heat exchanger 401 is delivered to the heat absorption side of the third heat exchanger 402, the second medium in the heat release side of the second heat exchanger 401 is delivered to the first liquid storage tank 302; at the same time, the first medium in the heat storage tank 202 is delivered to the heat release side of the third heat exchanger 402, the first medium exchanges heat with the compressed air in the heat absorption side of the third heat exchanger 402, after the heat exchange is completed, the compressed air in the heat absorption side of the third heat exchanger 402 is delivered to the gas inlet of the boiler 100, and the first medium in the heat release side of the third heat exchanger 402 is delivered to the heat storage tank 202. In this step, the compressed air extracted by the first compressor 403 is first heat exchanged with the second medium delivered from the spray tank 301 in the second heat exchanger 401, and is preliminarily preheated. Then, the compressed air is further heat exchanged with the first medium delivered from the heat storage tank 202 in the third heat exchanger 402, and the temperature is further increased. Finally, the preheated compressed air is delivered to the gas inlet of the boiler 100, and is used for combustion of the boiler 100, thereby improving the combustion efficiency of the boiler 100. The second medium and the first medium are respectively returned to the first liquid storage tank 302 and the heat storage tank 202 after heat exchange, so as to participate in the heat exchange process again.

[0082] The implementation principle of the embodiment is that: the flue gas waste heat recovery method fully recovers the waste heat in the flue gas through twice heat exchange of the flue gas, and reduces the waste of energy. At the same time, the recovered waste heat is used to preheat the compressed air, thereby improving the combustion efficiency of the boiler 100 and reducing the fuel consumption of the boiler 100. The step-by-step and cyclic waste heat recovery and utilization mode significantly improves the energy utilization rate of the whole system, meets the requirements of energy saving and emission reduction, and provides an effective solution for energy saving and environmental protection in industrial production.

[0083] The above are preferred embodiments of the present application, and do not limit the protection scope of the present application, therefore: any equivalent changes made on the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A flue gas heat recovery system, characterized by, include: The first thermal storage system includes a thermal storage tank (202) and a boiler (100) flue gas outlet and a first heat exchanger (201) connected in sequence. The thermal storage tank (202) contains a first medium, and the first heat exchanger (201) is located in the first medium. The second heat storage system includes a spray tank (301) and a first liquid storage tank (302) and a nozzle (303) connected in sequence. The first liquid storage tank (302) contains a second medium. The nozzle (303) is located in the spray tank (301). The spray tank (301) is connected to the first heat exchanger (201). The first preheating system includes the heat release side of the spray tank (301) and the second heat exchanger (401) connected in sequence, the heat release side of the heat storage tank (202) and the third heat exchanger (402) connected in sequence, and the heat absorption side of the first compressor (403), the heat absorption side of the second heat exchanger (401), the heat absorption side of the third heat exchanger (402) and the air inlet of the boiler (100) connected in sequence. The heat-dissipating side of the second heat exchanger (401) is connected to the first liquid storage tank (302), and the heat-dissipating side of the third heat exchanger (402) is connected to the heat storage tank (202). The first heat exchanger (201) includes: First heat-conducting box (2011) and second heat-conducting box (2012); The first partition plate (2013) is located inside the first heat-conducting box (2011) and divides the first heat-conducting box (2011) into a first sealing cavity (20111) and a second sealing cavity (20112). The first sealing cavity (20111) is connected to the flue gas outlet of the boiler (100). The second partition plate (2014) is located inside the second heat-conducting box (2012) and divides the second heat-conducting box (2012) into a third sealing cavity (20121) and a fourth sealing cavity (20122). The fourth sealing cavity (20122) is connected to the spray tank (301). The first flue gas flow channel (2015) is connected at both ends to the first sealing cavity (20111) and the third sealing cavity (20121), respectively; The second flue gas flow channel (2016) is connected at both ends to the third sealing cavity (20121) and the second sealing cavity (20112), respectively; The third flue gas flow channel (2017) is connected at both ends to the third sealing cavity (20121) and the fourth sealing cavity (20122), respectively; The flue gas duct (500) includes a first smooth pipe section (501), a rotation acceleration pipe section (502), and a second smooth pipe section (503) connected in sequence. The first smooth pipe section (501) is connected to the flue gas outlet of the boiler (100). At least a portion of the second smooth pipe section (503) extends into the heat storage tank (202) and is connected to the first sealing cavity (20111). The rotation acceleration pipe section (502) is provided with a plurality of spiral protrusions. a rotating shaft (601) with one end extending into the second smooth tube section (503) and the other end extending out of the second smooth tube section (503) and into the heat storage tank (202); a support rod (602) with one end fixedly connected to the inner wall of the second smooth tube section (503) and the other end rotatably connected to the rotating shaft (601); a first fan blade (603) located in the second smooth tube section (503) and fixedly connected to the rotating shaft (601); a second fan blade (604) located in the heat storage tank (202) and fixedly connected to the rotating shaft (601); a first valve body (P1) and a first flow meter (S1), the flue gas in the fourth sealed cavity (20122) is sequentially conveyed into the spray tank (301) through the first flow meter (S1) and the first valve body (P1), and the first valve body (P1) is a one-way valve; a temperature detection member (S3) for obtaining the temperature of the flue gas after passing through the first flow meter (S1); a second valve body (P2), the second medium in the first liquid storage tank (302) is conveyed to the nozzle (303) through the second valve body (P2).

2. The flue gas heat recovery system of claim 1, wherein, It also includes a second preheating system, which includes a second liquid storage tank (701), a Rankine cycle system and a liquid inlet of the boiler (100) connected in sequence, and the Rankine cycle system is connected in series with the flue gas outlet of the spray tank (301).

3. The flue gas heat recovery system of claim 2, wherein, The Rankine cycle system comprises: an evaporator (702) with its heat releasing side inlet connected to the flue gas outlet of the spray tank (301) and its heat releasing side outlet connected to the outside; a condenser (703) with its heat releasing side outlet connected to the heat absorbing side inlet of the evaporator (702) through an expansion valve (705) and its heat releasing side inlet connected to the heat absorbing side outlet of the evaporator (702) through a second compressor (704); the second liquid storage tank (701) is connected to the heat absorbing side inlet of the condenser (703), and the heat absorbing side outlet of the condenser (703) is connected to the liquid inlet of the boiler (100).

4. The flue gas heat recovery system of claim 3, wherein, The second preheating system further comprises a fourth heat exchanger (706) with its heat releasing side inlet connected to the outlet of the heat storage tank (202), its heat releasing side outlet connected to the inlet of the heat storage tank (202), its heat absorbing side inlet connected to the heat absorbing side outlet of the condenser (703), and its heat absorbing side outlet connected to the liquid inlet of the boiler (100).

5. The flue gas heat recovery system of claim 4, wherein, It also includes a heat network system comprising a boiler (100) liquid outlet, a heat network pipeline (800) and a second liquid storage tank (701) connected in sequence.

6. A flue gas heat recovery method, characterized by, The flue gas waste heat recovery system of any one of claims 1-5 further comprises: the heat storage tank (202) contains a first medium, and the first heat exchanger (201) is located in the first medium, the flue gas generated by the boiler (100) passes through the first heat exchanger (201), and the flue gas in the first heat exchanger (201) exchanges heat with the first medium in the heat storage tank (202); The nozzle (303) is located in the spray tank (301), the second medium in the first liquid storage tank (302) is delivered to the nozzle (303) and sprayed out by the nozzle (303), at the same time, the flue gas in the first heat exchanger (201) is delivered to the spray tank (301), and the second medium sprayed out by the nozzle (303) exchanges heat with the flue gas; The first compressor (403) extracts compressed air, and the compressed air is delivered to the heat absorption side of the second heat exchanger (401), at the same time, the second medium in the spray tank (301) is delivered to the heat release side of the second heat exchanger (401), the second medium in the heat absorption side of the second heat exchanger (401) exchanges heat with the compressed air, after the heat exchange is completed, the compressed air in the heat absorption side of the second heat exchanger (401) is delivered to the heat absorption side of the third heat exchanger (402), and the second medium in the heat release side of the second heat exchanger (401) is delivered to the first liquid storage tank (302); at the same time, the first medium in the heat storage tank (202) is delivered to the heat release side of the third heat exchanger (402), the first medium exchanges heat with the compressed air in the heat absorption side of the third heat exchanger (402), after the heat exchange is completed, the compressed air in the heat absorption side of the third heat exchanger (402) is delivered to the gas inlet of the boiler (100), and the first medium in the heat release side of the third heat exchanger (402) is delivered to the heat storage tank (202).

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