Device, system and method for utilizing waste heat after desulfurization and denitrification of coke oven flue gas

Abstract

The invention relates to the technical field of coking flue gas desulfurization and denitrification treatment, in particular to a device, a system and a method for utilizing waste heat generated after desulfurization and denitrification of coke oven flue gas. The invention provides a coke oven flue gas waste heat utilization device after desulfurization and denitrification, which comprises a first heat exchanger and a second heat exchanger, a first access port is connected with an outlet of a desulfurization and denitrification device through a first connecting pipeline, and a flue gas discharge port is connected with an induced draft fan through a second connecting pipeline; the heat exchange medium discharge port is connected with the first heat exchange medium input port through a third connecting pipeline, and the second access port is connected with the first heat exchange medium output port through a fourth connecting pipeline; and the second heat exchange medium input port and the second heat exchange medium output port are respectively connected with the input end and the output end of the equipment to be subjected to heat exchange. According to the flue gas working condition and desulfurization and denitrification configuration, waste heat can be recycled on the premise that the flue gas emission requirement is met.

Description

Technical Field

[0001] The present invention relates to the technical field of desulfurization and denitrification of coking flue gas, and in particular to a device and method for utilizing waste heat after desulfurization and denitrification of coke oven flue gas. Background Art

[0002] The desulfurization and denitrification process is mostly used for the end treatment of coke oven flue gas. According to the flue gas temperature, a waste heat boiler is added in front of the desulfurization and denitrification device to extract part of the heat. However, the current desulfurization and denitrification system mostly adopts a dry process, and the temperature drop before and after the system is small. The exhaust temperature of the chimney outlet is generally 180-190℃, and there is still room for waste heat to be used. There is an urgent need for a device that can recycle waste heat according to the flue gas working conditions and desulfurization and denitrification configuration, while meeting the flue gas emission requirements. Summary of the invention

[0003] The present disclosure aims to solve at least one of the technical problems existing in the prior art or related art.

[0004] To this end, in a first aspect of the present disclosure, there is provided a waste heat utilization device after desulfurization and denitrification of coke oven flue gas, comprising a first heat exchanger and a second heat exchanger, wherein the first heat exchanger has a first access port, a second access port, a flue gas discharge port and a heat exchange medium discharge port, and the second heat exchanger has a first heat exchange medium input port, a second heat exchange medium input port, a first heat exchange medium output port and a second heat exchange medium output port, wherein the first access port is connected to the outlet flue gas of the desulfurization and denitrification device through a first connecting pipeline, and the flue gas discharge port is connected to the induced draft fan through a second connecting pipeline;

[0005] The heat exchange medium discharge port is connected to the first heat exchange medium input port through a third connecting pipeline, and the second access port is connected to the first heat exchange medium output port through a fourth connecting pipeline;

[0006] The second heat exchange medium input port and the second heat exchange medium output port are respectively connected to the input end and the output end of the equipment to be heat exchanged.

[0007] In a feasible embodiment, a bypass pipeline is further included, wherein the bypass pipeline has an inlet end and an outlet end, the inlet end is communicated with the first connecting pipeline, and the outlet end is communicated with the second connecting pipeline.

[0008] In a feasible implementation manner, the bypass pipeline is further provided with a plurality of stop valves.

[0009] In a feasible implementation manner, the plurality of stop valves include a first stop valve and a second stop valve, wherein the first stop valve is disposed on a side close to the first access port, and the second stop valve is disposed on a side close to the smoke exhaust port.

[0010] In a feasible implementation manner, the first heat exchanger is configured as a flue gas-water heat exchange type heat exchanger.

[0011] In a feasible implementation manner, the second heat exchanger is configured as a water-to-water heat exchange type heat exchanger.

[0012] In a feasible implementation manner, the heat exchange medium of the second heat exchanger is set to desalted water or heating circulating water or refrigeration circulating water.

[0013] In a feasible implementation manner, a third stop valve is provided on a side of the first connecting pipeline close to the first access port, and a fourth stop valve is provided on a side of the second connecting pipeline close to the smoke exhaust port.

[0014] In a third aspect of the present disclosure, a desulfurization and denitrification system is provided, comprising the above-mentioned device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas.

[0015] In a third aspect of the present disclosure, a method for utilizing waste heat from coke oven flue gas after desulfurization and denitrification is provided, comprising:

[0016] Connecting the first heat exchanger between the flue gas duct at the outlet of the desulfurization and denitration system and the induced draft fan, so that the flue gas exchanges heat in the first heat exchanger;

[0017] The heat exchange medium generated by the first heat exchanger enters the second heat exchanger, and the generated cooled flue gas enters the chimney through the induced draft fan for discharge;

[0018] The heat exchange medium after heat exchange in the first heat exchanger passes through the second heat exchanger and then enters the heat exchange device.

[0019] Compared with the prior art, the present invention at least includes the following beneficial effects: the present invention arranges a first heat exchanger between the flue gas duct at the outlet of the desulfurization and denitrification system and the induced draft fan, and arranges a second heat exchanger between the heat exchange equipment waiting for the heat / cold user point and the first heat exchanger, and can recycle the waste heat according to the flue gas working conditions and the desulfurization and denitrification configuration, on the premise of meeting the flue gas emission requirements. Among them, the first heat exchanger has a first access port, a second access port, a flue gas discharge port and a heat exchange medium discharge port, the second heat exchanger has a first heat exchange medium input port, a second heat exchange medium input port, a first heat exchange medium output port and a second heat exchange medium output port, the heat exchange medium discharge port is connected to the first heat exchange medium input port through a third connecting pipeline, and the second access port is connected to the first heat exchange medium output port through a fourth connecting pipeline, so as to avoid the heat exchange medium directly entering the first heat exchanger in an extremely cold condition to cause equipment damage, and at the same time avoid the flue gas temperature being locally lower than the dew point temperature to cause corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0022] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the exemplary embodiments below. The accompanying drawings are only for the purpose of illustrating exemplary embodiments and are not to be considered as limiting the present application. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0023] Figure 1 It is a front view structural schematic diagram of the present disclosure;

[0024] Figure 2 It is a structural schematic diagram of the upper seat disclosed in the present invention.

[0025] in, Figure 1 to Figure 2 The corresponding relationship between the reference numerals and the component names is as follows:

[0026] 100-desulfurization and denitrification device; 200-induced draft fan; 300-chimney; 400-heat exchange equipment; 500-deaerator; 600-feedwater pump; 700-waste heat boiler; 800-desalting water tank; 900-deaerator feedwater pump.

[0027] 1-first heat exchanger; 11-first access port; 12-second access port; 13-smoke exhaust port; 14-heat exchange medium exhaust port; 2-second heat exchanger; 21-first heat exchange medium input port; 22-second heat exchange medium input port; 23-first heat exchange medium output port; 24-second heat exchange medium output port; 3-first connecting pipeline; 31-third stop valve; 32-fourth stop valve; 4-second connecting pipeline; 5-third connecting pipeline; 6-fourth connecting pipeline; 7-bypass pipeline; 71-inlet end; 72-outlet end; 73-first stop valve; 74-second stop valve. DETAILED DESCRIPTION

[0028] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0029] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0030] At present, the end-of-pipe treatment of coke oven flue gas mostly adopts desulfurization and denitrification technology, and according to the flue gas temperature, a waste heat boiler is added in front of the desulfurization and denitrification device to extract part of the heat. However, the current desulfurization and denitrification systems mostly adopt dry process, and the temperature drop before and after the system is small. The exhaust temperature of the chimney outlet is generally 180-190℃, and there is still room for waste heat to be utilized. The existing coke oven flue gas desulfurization and denitrification system does not have a waste heat utilization device.

[0031] Based on this, the embodiment of the present disclosure provides a device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas, which includes a first heat exchanger and a second heat exchanger, wherein the first access port is connected to the outlet flue gas of the desulfurization and denitrification device through a first connecting pipeline, and the flue gas discharge port is connected to the induced draft fan through a second connecting pipeline; the heat exchange medium discharge port is connected to the first heat exchange medium input port through a third connecting pipeline, and the second access port is connected to the first heat exchange medium output port through a fourth connecting pipeline; the second heat exchange medium input port and the second heat exchange medium output port are respectively connected to the input end and the output end of the equipment to be heat exchanged. The present disclosure can recycle waste heat according to the flue gas working conditions and the desulfurization and denitrification configuration, on the premise of meeting the flue gas emission requirements.

[0032] The following is a detailed description of the device for utilizing waste heat after desulfurization and denitration of coke oven flue gas through a specific embodiment:

[0033] Reference Figures 1 to 2 As shown, in a first aspect of the present disclosure, a waste heat utilization device after desulfurization and denitrification of coke oven flue gas is provided, comprising a first heat exchanger 1 and a second heat exchanger 2, the first heat exchanger 1 having a first access port 11, a second access port 12, a flue gas exhaust port 13 and a heat exchange medium exhaust port 14, the second heat exchanger 2 having a first heat exchange medium input port 21, a second heat exchange medium input port 22, a first heat exchange medium output port 23 and a second heat exchange medium output port 24, the first access port 11 is connected to the outlet flue gas of the desulfurization and denitrification device 100 through a first connecting pipeline 3, and the flue gas exhaust port 13 is connected to the induced draft fan 200 through a second connecting pipeline 4; the heat exchange medium exhaust port 14 is connected to the first heat exchange medium input port 21 through a third connecting pipeline 5, and the second access port 12 is connected to the first heat exchange medium output port 23 through a fourth connecting pipeline 6; the second heat exchange medium input port 22 and the second heat exchange medium output port 24 are respectively connected to the input end and the output end of the equipment to be heat exchanged.

[0034] The present invention arranges a first heat exchanger 1 between the outlet flue gas duct of the desulfurization and denitrification device 100 and the induced draft fan 200 to exchange heat between the heat exchange medium and the flue gas to reduce the exhaust temperature. A second heat exchanger 2 is arranged between the heat exchange device 400 waiting for the heat / cold user point and the first heat exchanger 1. The waste heat can be recycled based on the flue gas working conditions and the desulfurization and denitrification configurations while meeting the flue gas emission requirements. The second heat exchanger 2 can prevent the heat exchange medium from directly entering the first heat exchanger 1 under extremely cold conditions to cause equipment damage, and at the same time prevent the flue gas temperature from being locally lower than the dew point temperature to cause corrosion. Furthermore, the first heat exchanger 1 and the second heat exchanger 2 of the present disclosure may include a mounting shell and a heat exchanger body, and the first access port 11, the second access port 12, the smoke exhaust port 13, the heat exchange medium exhaust port 14, the first heat exchange medium input port 21, the second heat exchange medium input port 22, the first heat exchange medium output port 23, and the second heat exchange medium output port 24 may be interfaces provided on the heat exchanger body, or may be interfaces provided on the mounting shell and connected to the heat exchanger body, and the above interfaces are intended to form a heat exchange passage that is different from the prior art in the present disclosure, and the interface selection may be selected from interfaces such as threaded connection and quick connector. The selection of each pipeline in the present disclosure is a conventional selection in this field and will not be repeated here, and the pipeline is not limited to a physical pipeline, and may also be a passage formed by directly connecting two connected devices, structures, and equipment.

[0035] In some embodiments, a bypass pipeline 7 is further included. The bypass pipeline 7 has an inlet end 71 and an outlet end 72 . The inlet end 71 is connected to the first connecting pipeline 3 , and the outlet end 72 is connected to the second connecting pipeline 4 .

[0036] In this embodiment, the bypass pipeline 7 and the valve can realize the offline maintenance of the first heat exchanger 1, and the maintenance does not affect the original process operation. Furthermore, the bypass pipeline 7 is also provided with a plurality of stop valves, which can seal the bypass pipeline 7 in sections to improve the maintenance efficiency.

[0037] In some embodiments, the plurality of stop valves include a first stop valve 73 and a second stop valve 74 . The first stop valve 73 is disposed on a side close to the first access port 11 , and the second stop valve 74 is disposed on a side close to the smoke exhaust port 13 .

[0038] In this embodiment, the stop valves include a first stop valve 73 and a second stop valve 74. The first stop valve 73 and the second stop valve 74 are respectively arranged on both sides of the first heat exchanger 1 to prevent the pressure of the bypass pipe 7 from causing a large pressure difference between the first heat exchanger 1 and the auxiliary pipelines.

[0039] In some embodiments, the first heat exchanger 1 adopts a flue gas-water heat exchange type to reduce the flue gas temperature from 180-190°C to 150-160°C.

[0040] In this embodiment, the flue gas-water heat exchanger is a type of heat exchange equipment, which transfers the waste heat in the flue gas to water by contact heat exchange, thereby realizing energy recovery and utilization. The working principle of the flue gas-water heat exchanger is based on the principle of heat exchange, that is, when two substances at different temperatures contact each other, heat will be transferred from the high-temperature substance to the low-temperature substance until the temperatures of the two are equal. In the flue gas-water heat exchanger, the high-temperature flue gas and the low-temperature water flow through different parts of the equipment respectively, and heat exchange is carried out through the heat transfer pipe. In this process, heat is transferred from the flue gas to the water, so that the temperature of the water increases and the temperature of the flue gas decreases. Specifically, the first heat exchanger 1 disclosed in the present invention is mainly composed of a shell, a heat transfer pipe and a sealing material. The shell is the main structure of the equipment, which is used to support and protect the internal components. The heat transfer pipe is a component for realizing heat exchange, and the flue gas and water flow on both sides of the heat transfer pipe respectively to transfer heat. The sealing material is used to seal the flue gas and water flow channels to ensure that the two fluids will not mix, so as to facilitate heat transfer.

[0041] In some embodiments, the second heat exchanger 2 is configured as a water-to-water heat exchange type heat exchanger.

[0042] In this embodiment, the second heat exchanger 2 disclosed in the present invention is also called a cooling tower or a cooler, which is mainly used to dissipate the heat generated in the production process into the atmosphere by heat exchange with the outside air to achieve the purpose of cooling. The principle of the water-to-water exchanger is based on the basic principles of heat conduction and heat convection, and heat transfer is achieved by exchanging water with air. In a feasible selection of the second heat exchanger 2, it includes a water tank, a water pump, a water pipe, a cooling tower and a fan. Its working principle is that first, the water pump draws in the high-temperature water generated by the first heat exchanger 1 and transports it to the cooling tower through the water pipe. The heat in these high-temperature waters needs to be transferred and dissipated by contact with the outside air. In the cooling tower, water is evenly sprayed in the tower through a spray system to form a thin film. The cooling tower usually uses multiple layers of fillers, and the function of the fillers is to increase the contact surface area, make the water evenly distributed, and also increase the effect of heat exchange. When the water film contacts the outside air, heat transfer occurs between the water and the air. Because the heat is transferred from the high-temperature water to the thin film water layer on the contact surface by heat conduction. The air sweeps and impacts the thin film water layer, causing the thin water film on the water layer to evaporate rapidly. During the evaporation process, the heat in the water will be consumed, thereby reducing the temperature of the water. At the same time, the fan will also introduce air through the cooling tower to form a state of air flow in the cycle. The cooling effect in the air increases the contact area with the thin film water layer, accelerates the transfer of heat, and takes away the evaporated water vapor. It should be noted that the above working principle is the basic working principle of the second heat exchanger 2. In the technical solution disclosed in the present invention, whether the second heat exchanger 2 performs heat exchange or adjusts the temperature of the high-temperature water generated by the first heat exchanger 1 needs to be debugged according to the downstream heat exchange equipment. For example, if the downstream heat exchange equipment is set as a heating equipment, then the second heat exchanger 2 may not perform heat exchange or produce a low cooling effect. If the downstream equipment is a refrigeration equipment, the second heat exchanger 2 increases the heat exchange and cooling power to cool the high-temperature water. Furthermore, the heat exchange medium of the second heat exchanger 2 is set to desalted water or heating circulating water or refrigeration circulating water.

[0043] In some embodiments, a third stop valve 31 is provided on one side of the first connecting pipeline 3 close to the first access port 11, and a fourth stop valve 32 is provided on one side of the second connecting pipeline 4 close to the smoke exhaust port 13 to meet the needs of daily inspection and maintenance. Each stop valve of the present disclosure can be a manual stop valve or an electric stop valve or an electric butterfly valve, and the present disclosure specifically uses an electric stop valve.

[0044] In a second aspect of the present disclosure, a desulfurization and denitrification system is provided, comprising the above-mentioned device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas.

[0045] In a third aspect of the present disclosure, there is provided a method for utilizing waste heat from coke oven flue gas after desulfurization and denitrification, characterized in that it comprises:

[0046] The first heat exchanger 1 is connected between the flue gas duct at the outlet of the desulfurization and denitration system and the induced draft fan 200 to exchange heat between the heat exchange medium and the flue gas;

[0047] The heat exchange medium is heat exchanged in the second heat exchanger 2 before entering the first heat exchanger 1;

[0048] The heat exchange medium after heat exchange in the first heat exchanger 1 passes through the second heat exchanger 2 and then enters the heat exchange equipment.

[0049] Connecting the first heat exchanger between the flue gas duct at the outlet of the desulfurization and denitration system and the induced draft fan, so that the flue gas exchanges heat in the first heat exchanger;

[0050] The heat exchange medium generated by the first heat exchanger enters the second heat exchanger, and the generated cooled flue gas enters the chimney through the induced draft fan for discharge;

[0051] The heat exchange medium after heat exchange in the first heat exchanger passes through the second heat exchanger and then enters the heat exchange device.

[0052] The present disclosure arranges the first heat exchanger 1 between the flue gas duct at the outlet of the desulfurization and denitration system and the induced draft fan to exchange heat between the heat exchange medium and the flue gas to reduce the exhaust gas temperature;

[0053] Step 2: Before the heat exchange medium enters the primary heat exchanger, it first passes through the second heat exchanger 2 for heat exchange, so as to avoid the heat exchange medium directly entering the first heat exchanger 1 under extremely cold conditions to cause equipment damage, and to avoid the flue gas temperature being locally lower than the dew point temperature to cause corrosion;

[0054] Step 3: After the heat exchange medium passes through the second heat exchanger 2, the waste heat can be utilized according to different working conditions:

[0055] Working condition 1: Desulfurization and denitration are equipped with a waste heat boiler. The heat exchange medium can be desalted water. The desalted water is sent to the deaerator after heat exchange and temperature rise, and then enters the waste heat boiler through the boiler feed water pump to improve the efficiency of the waste heat boiler.

[0056] Working condition 2: The waste heat boiler 700 is not configured for desulfurization and denitrification. The heat exchange medium is cooling / heating circulating water, which is sent to warm water type refrigerators or heating users for cooling in summer and heating in winter, making full use of the waste heat.

[0057] Working condition three: Desulfurization and denitrification are equipped with a waste heat boiler 700, but the waste heat of the flue gas is relatively large, and there is still surplus after meeting the needs of the deaerator 500. Working condition one can be combined with working condition two, and the first heat exchanger 1 can be divided into areas and the heat exchange area can be reasonably configured. On the premise of meeting the needs of the deaerator, the waste heat can be recovered for cooling or heating.

[0058] In the present disclosure, the terms "first", "second", and "third" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance; the term "plurality" refers to two or more, unless otherwise expressly defined. The terms "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; "connected" can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present disclosure can be understood according to the specific circumstances.

[0059] In the description of the present disclosure, it is necessary to understand that the directions or positional relationships indicated by the terms "up", "down", "left", "right", "front", "back", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or unit referred to must have a specific direction, be constructed and operated in a specific orientation, and therefore, should not be understood as a limitation on the present disclosure.

[0060] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0061] The above are only preferred embodiments of the present disclosure and are not intended to limit the present disclosure. For those skilled in the art, the present disclosure may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas, characterized in that: The invention comprises a first heat exchanger and a second heat exchanger, wherein the first heat exchanger has a first access port, a second access port, a smoke exhaust port and a heat exchange medium exhaust port, and the second heat exchanger has a first heat exchange medium input port, a second heat exchange medium input port, a first heat exchange medium output port and a second heat exchange medium output port, wherein: The first access port is connected to the outlet flue gas of the desulfurization and denitration device through a first connecting pipeline, and the flue gas discharge port is connected to the induced draft fan through a second connecting pipeline; The heat exchange medium discharge port is connected to the first heat exchange medium input port through a third connecting pipeline, and the second access port is connected to the first heat exchange medium output port through a fourth connecting pipeline; The second heat exchange medium input port and the second heat exchange medium output port are respectively connected to the input end and the output end of the equipment to be heat exchanged.

2. The device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas according to claim 1, characterized in that: A bypass pipeline is also included, wherein the bypass pipeline has an inlet end and an outlet end, wherein the inlet end is communicated with the first connecting pipeline, and the outlet end is communicated with the second connecting pipeline.

3. The device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas according to claim 2, characterized in that: The bypass pipeline is also provided with a plurality of stop valves.

4. The device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas according to claim 3, characterized in that: The plurality of stop valves include a first stop valve and a second stop valve, wherein the first stop valve is arranged at a side close to the first access port, and the second stop valve is arranged at a side close to the smoke exhaust port.

5. The device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas according to claim 1, characterized in that: The first heat exchanger is configured as a flue gas-water heat exchange type heat exchanger.

6. The device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas according to claim 1, characterized in that: The second heat exchanger is configured as a water-to-water heat exchange type heat exchanger.

7. The device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas according to claim 6, characterized in that: The heat exchange medium of the second heat exchanger is set to desalted water or heating circulating water or refrigeration circulating water.

8. The device for utilizing waste heat after desulfurization and denitrification of coke oven flue gas according to claim 1, characterized in that: A third stop valve is provided on a side of the first connecting pipeline close to the first access port, and a fourth stop valve is provided on a side of the second connecting pipeline close to the smoke exhaust port.

9. A desulfurization and denitrification system, characterized in that: It comprises the waste heat utilization device after desulfurization and denitrification of coke oven flue gas as described in any one of claims 1 to 8 above.

10. A method for utilizing waste heat from coke oven flue gas after desulfurization and denitrification, characterized in that: include: Connecting the first heat exchanger between the flue gas duct at the outlet of the desulfurization and denitration system and the induced draft fan, so that the flue gas exchanges heat in the first heat exchanger; The heat exchange medium generated by the first heat exchanger enters the second heat exchanger, and the generated cooled flue gas enters the chimney through the induced draft fan for discharge; The heat exchange medium after heat exchange in the first heat exchanger passes through the second heat exchanger and then enters the heat exchange device.

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