Denitration system

Abstract

The utility model relates to a denitration system which comprises a pyrolyzing furnace, a first steam channel, a heating assembly and a second steam channel. The pyrolyzing furnace is used for decomposing a urea solution and generating ammonia steam; one end of the first steam channel is communicated with the pyrolyzing furnace, and the other end is communicated with a flue; the heating assemblies are arranged on the first steam channel and used for heating ammonia steam in the first steam channel, and the multiple heating assemblies are arranged at intervals in the flowing direction of the ammonia steam; the two ends of the second steam channel communicate with the first steam channel and are connected with the heating assembly in parallel, and ammonia steam selectively flows through the heating assembly or the second steam channel. By means of the technical scheme, it is guaranteed that the temperature of the ammonia steam is in a high state all the time, the ammonia steam is prevented from generating crystals in the first steam channel, the situation that the ammonia content of the ammonia steam is reduced due to the fact that ammonia crystals are separated out is avoided, blocking of the first steam pipeline is also avoided, and the denitration effect on flue gas is guaranteed.

Description

Technical Field

[0001] The present disclosure relates to the field of denitrification, and specifically, to a denitrification system. Background Art

[0002] The flue gas generated by the boiler combustion in a thermal power plant contains a large amount of NOx. In order to avoid air pollution, in related technologies, the selective catalytic reduction (SCR) process is usually used to denitrify the flue gas. It is necessary to hydrolyze the urea solution to produce ammonia vapor, transport the ammonia vapor to the flue through a pipeline, spray the ammonia vapor into the reaction layer at the tail of the flue through a nozzle, and the ammonia on the reaction layer reacts with the NOx in the flue gas to achieve the denitrification treatment of the flue gas. However, during the process of transporting the ammonia vapor to the flue through the pipeline, the heat of the ammonia vapor will gradually dissipate through the pipeline, and the temperature of the ammonia vapor will gradually decrease, resulting in the formation of ammonia crystals in the pipeline, the reduction of the ammonia content in the vapor, the reduction of the denitrification effect on the flue gas, and at the same time, the crystals are also likely to cause pipeline blockage, further affecting the denitrification effect on the flue gas. Summary of the Utility Model

[0003] The purpose of the present disclosure is to provide a denitrification system to at least partially solve the problems existing in the related technologies.

[0004] The purpose of the present disclosure is to provide a denitrification system, including:

[0005] A pyrolysis furnace for decomposing the urea solution and generating ammonia vapor;

[0006] A first steam channel, one end of which is connected to the pyrolysis furnace, and the other end is used to be connected to the flue;

[0007] A heating component is arranged on the first steam channel for heating the ammonia vapor in the first steam channel. In the flow direction of the ammonia vapor, a plurality of the heating components are arranged at intervals; and

[0008] A second steam channel, both ends of which are respectively connected to the first steam channel and are arranged in parallel with the heating component, wherein the ammonia vapor selectively flows through the heating component or through the second steam channel.

[0009] Optionally, the heating component includes a first control valve arranged on the first steam channel. One end of the second steam channel close to the pyrolysis furnace is connected to the first steam channel through the first control valve, and the first control valve is used to control the ammonia vapor to flow through the heating component or through the second steam channel.

[0010] Optionally, a first temperature sensor and a second temperature sensor for detecting the temperature of the ammonia vapor are provided on the first steam channel. The first temperature sensor is electrically connected to the first control valve, and the second temperature sensor is disposed on a side of the heating assembly away from the pyrolysis furnace.

[0011] Optionally, the heating assembly includes a heat source and a first heating box body communicated with the heat source. The first steam channel passes through the first heating box body for heat exchange between the ammonia vapor and the heat source.

[0012] Optionally, the denitration system further includes a mixing assembly for mixing the ammonia vapor and air to dilute the ammonia vapor. The mixing assembly includes:

[0013] An air inlet channel, one end of which is communicated with the external environment and an air pump is provided on the air inlet channel. The air inlet channel is at least partially disposed in the flue to heat the air by using the waste heat of the flue gas; and

[0014] A mixing box body, which is communicated with the other end of the air inlet channel and is communicated with the flue through the first steam channel. The ammonia vapor and the air are mixed in the mixing box body to dilute the ammonia vapor.

[0015] Optionally, a third temperature sensor for detecting the temperature of the ammonia vapor is provided on the first steam channel, and a fourth temperature sensor for detecting the temperature of the air is provided on the air inlet channel. The third temperature sensor is disposed on a side of the mixing box body close to the pyrolysis furnace, and the fourth temperature sensor is disposed on a side of the mixing box body close to the air inlet channel.

[0016] Optionally, the first steam channel is at least partially disposed in the flue to heat the ammonia vapor by using the waste heat of the flue gas.

[0017] The denitration system further includes a third steam channel. Two ends of the third steam channel are respectively communicated with the first steam channel and are respectively located on two sides of the flue. Wherein, the ammonia vapor selectively flows through the flue or through the third steam channel.

[0018] Optionally, the denitration system further includes a second control valve provided on the first steam channel. One end of the third steam channel close to the pyrolysis furnace is communicated with the first steam channel through the second control valve. The second control valve is used to control the ammonia vapor to flow through the flue or through the third steam channel.

[0019] Optionally, the denitration system further includes:

[0020] A first solution channel, one end of which is in communication with the urea solution and the other end of which is in communication with the pyrolysis furnace;

[0021] A second heating box body, which is in communication with a heat source. The first solution channel passes through the second heating box body and is used for enabling the urea solution to exchange heat with the heat source so as to heat the urea in the first solution channel; and

[0022] A second solution channel, both ends of which are respectively in communication with the first solution channel and are respectively located on both sides of the second heating box body. Wherein, the urea solution selectively flows through the heating box body or flows through the second solution channel.

[0023] Optionally, the denitration system further includes a third control valve arranged on the first solution channel. One end of the second solution channel far from the pyrolysis furnace is in communication with the first solution channel through the third control valve, and the third control valve is used for controlling the urea solution to flow through the second heating box body or flow through the second solution channel.

[0024] Through the above technical solution, every time the ammonia vapor flows a certain distance, it can be heated by the heating component, ensuring that the temperature of the ammonia vapor always remains at a relatively high level, avoiding the formation of crystals in the first vapor channel, preventing the reduction of ammonia content caused by the precipitation of ammonia crystals, and also avoiding the blockage of the first vapor pipeline, ensuring the denitration effect on the flue gas. The ammonia vapor selectively flows through the heating component or flows through the second vapor channel. When the temperature of the ammonia vapor is high enough and does not require heating, the ammonia vapor can not flow through the heating component, and the heating component does not need to be started, improving the flexibility of the use of the denitration system and making the denitration system more energy-saving. At the same time, the setting of multiple heating components enables operators to repair a single heating component under the condition that the denitration system is operating normally. The operator can only stop the heating component that needs to be repaired, and the heating components that do not need to be repaired still remain in operation, ensuring the operation efficiency of the denitration system.

[0025] Other features and advantages of the present disclosure will be described in detail in the subsequent specific implementation part. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings are used to provide a further understanding of the present disclosure, and constitute a part of the specification. Together with the following specific implementation, they are used to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the drawings:

[0027] Figure 1 is a schematic structural diagram of a denitration system provided by an exemplary embodiment of the present disclosure.

[0028] DESCRIPTION OF THE REFERENCE NUMERALS

[0029] 100 - Pyrolysis furnace, 200 - First steam channel, 201 - Flue, 202 - First temperature sensor, 203 - Second temperature sensor, 204 - Third temperature sensor, 205 - Second control valve, 300 - Heating component, 301 - First control valve, 302 - First heating box, 400 - Second steam channel, 500 - Heat source, 600 - Mixing component, 601 - Intake channel, 602 - Mixing box, 603 - Air pump, 604 - Fourth temperature sensor, 700 - Third steam channel, 800 - First solution channel, 801 - Second heating box, 802 - Second solution channel, 803 - Third control valve. Detailed implementation manners

[0030] The following will describe in detail the detailed implementation manners of the present disclosure with reference to the accompanying drawings. It should be understood that the detailed implementation manners described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0031] In the present disclosure, unless otherwise stated, the orientation terms used generally refer to the orientation of the relevant components in the actual use state. "Inside and outside" can refer to the inside and outside of the contour of the corresponding component or its inside and outside in the environment where it is located according to the specific context. In addition, when the following description involves the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The terms "first", "second", etc. used in the present disclosure are used to distinguish one element from another element, and do not have an order and importance.

[0032] As Figure 1 shown, the present disclosure provides a denitration system, including a pyrolysis furnace 100, a first steam channel 200, a heating component 300 and a second steam channel 400. The pyrolysis furnace 100 is used to decompose the urea solution and generate ammonia steam; one end of the first steam channel 200 is connected to the pyrolysis furnace 100, and the other end is used to be connected to the flue 201; the heating component 300 is arranged on the first steam channel 200 and is used to heat the ammonia steam in the first steam channel 200. In the flowing direction of the ammonia steam, a plurality of heating components 300 are arranged at intervals; both ends of the second steam channel 400 are respectively connected to the first steam channel 200 and are arranged in parallel with the heating component 300. Among them, the ammonia steam selectively flows through the heating component 300 or through the second steam channel 400.

[0033] Through the above technical solution, every time the ammonia vapor flows a certain distance, it can be heated by the heating component 300, ensuring that the temperature of the ammonia vapor remains at a relatively high level, avoiding the formation of crystals in the first steam channel 200, preventing the reduction of ammonia content caused by the precipitation of ammonia crystals in the ammonia vapor, and also avoiding the blockage of the first steam pipeline, thus ensuring the denitrification effect on the flue gas. The ammonia vapor can selectively flow through the heating component 300 or through the second steam channel 400. When the temperature of the ammonia vapor is high enough and does not require heating, the ammonia vapor can bypass the heating component 300, and the heating component 300 does not need to be started, improving the flexibility of the denitrification system and making the denitrification system more energy-efficient. At the same time, the setting of multiple heating components 300 enables operators to repair a single heating component 300 while the denitrification system is operating normally. The operator can only stop the heating component 300 that needs to be repaired, and the heating components 300 that do not need to be repaired remain in operation, ensuring the operating efficiency of the denitrification system.

[0034] A first control valve 301 can be provided on the heating component 300 in the first steam channel 200. One end of the second steam channel 400 close to the pyrolysis furnace 100 is connected to the first steam channel 200 through the first control valve 301. The first control valve 301 is used to control the ammonia vapor to flow through the heating component 300 or through the second steam channel 400. Through the first control valve 301, the selective flow of the ammonia vapor between the heating component 300 and the second steam channel 400 can be realized, and the temperature of the ammonia vapor can be adjusted as needed to avoid insufficient temperature of the ammonia vapor. The first control valve 301 can control the ammonia vapor to flow through the heating component 300 when the temperature of the ammonia vapor is less than the first preset value; when the temperature of the ammonia vapor is greater than or equal to the first preset value, it controls the ammonia vapor to flow through the second steam channel 400. The first preset value and the second preset value here can be determined according to the desulfurization effect of the ammonia vapor. When the temperature of the ammonia vapor is between the first preset value and the second preset value, while avoiding the formation of crystals in the first steam channel 200, it can also ensure that the reaction efficiency of the ammonia vapor after being sprayed onto the reaction layer remains at a relatively high level to ensure the desulfurization effect of the flue gas.

[0035] A first temperature sensor 202 and a second temperature sensor 203 for detecting the temperature of ammonia vapor respectively may be provided on the first steam channel 200. The first temperature sensor 202 is electrically connected to the first control valve 301, and the second temperature sensor 203 is arranged on the side of the heating assembly 300 away from the pyrolysis furnace 100. The first temperature sensor 202 can be linked with the first control valve 301. When the temperature of the ammonia vapor is less than the first preset value, it controls the ammonia vapor to flow through the heating assembly 300 to ensure that when the temperature of the ammonia vapor is too low, it can be heated by the heating assembly 300 in time, ensuring that the temperature of the ammonia vapor is within the ideal range. When the temperature of the ammonia vapor is greater than or equal to the first preset value, it controls the ammonia vapor to flow through the second steam channel 400. At this time, the heating assembly 300 is not used, making the denitration system more energy-efficient. The second temperature sensor 203 can detect the temperature of the ammonia vapor heated by the heating assembly 300, playing a monitoring role for the heating assembly 300 to ensure the use effect of the heating assembly 300. When the temperature of the heated ammonia vapor is still less than the first preset value, it indicates that the heating effect of the heating assembly 300 is insufficient and the heating efficiency of the heating assembly 300 needs to be improved. When the temperature of the ammonia vapor is much greater than the second preset value, it indicates that the heating effect of the heating assembly 300 is too high, and the heating assembly 300 needs to reduce the heating efficiency to avoid waste of energy.

[0036] The heating assembly 300 may include a heat source 500 and a first heating box body 302 communicated with the heat source 500. The first steam channel 200 penetrates through the first heating box body 302 for enabling the ammonia vapor to exchange heat with the heat source 500. The heat source 500 here can be high-temperature steam or other high-temperature materials or substances such as high-temperature liquid. When the ammonia vapor flows through the first heating box body 302, the ammonia vapor can exchange heat with the heat source 500 to increase the temperature of the ammonia vapor. The part of the first steam channel 200 penetrating through the first heating box body 302 can be set as a curve to increase the flow path of the ammonia vapor in the first heating box body 302, ensuring sufficient heat exchange between the ammonia vapor and the heat source 500 and improving the heating efficiency.

[0037] The denitration system may further include a mixing component 600 for mixing ammonia vapor with air to dilute the ammonia vapor. The mixing component 600 includes an air inlet channel 601 and a mixing box 602. One end of the air inlet channel 601 is communicated with the external environment, and an air pump 603 is arranged on the air inlet channel 601. The air inlet channel 601 is at least partially accommodated in the flue 201 to heat the air by using the waste heat of the flue gas. The mixing box 602 is communicated with the other end of the air inlet channel 601 and is communicated with the flue 201 through the first steam channel 200. The ammonia vapor and air are mixed in the mixing box 602 to dilute the ammonia vapor. By mixing the ammonia vapor with air through the mixing component 600, the ammonia vapor is diluted, the concentration of the ammonia vapor is controlled, and the denitration efficiency is ensured. If the concentration of the ammonia vapor is too high, it will cause the remaining ammonia after the reaction of ammonia and flue gas, resulting in waste of ammonia. Since a large amount of heat is also carried in the flue gas, using the waste heat of the flue gas to heat the air can prevent the temperature of the air from being too low, avoid a significant decrease in the temperature of the ammonia vapor after mixing with the air, and avoid crystallization of the ammonia vapor in the mixing box 602 due to temperature reduction. At the same time, heating the air with the waste heat of the flue gas also reasonably utilizes the heat of the flue gas, improves the energy utilization rate, and reduces energy consumption.

[0038] A third temperature sensor 204 for detecting the temperature of the ammonia vapor may be arranged on the first steam channel 200, and a fourth temperature sensor 604 for detecting the temperature of the air may be arranged on the air inlet channel 601. The third temperature sensor 204 is arranged on one side of the mixing box 602 close to the pyrolysis furnace 100, and the fourth temperature sensor 604 is arranged on one side of the mixing box 602 close to the air inlet channel 601. The third temperature sensor 204 can detect the temperature of the ammonia vapor entering the mixing box 602, and the fourth temperature sensor 604 can detect the temperature of the air entering the mixing box 602 to ensure that the concentration and temperature of the mixed ammonia vapor are appropriate. For example, when the third temperature sensor 204 detects that the temperature of the ammonia vapor entering the mixing box 602 is less than the first preset value mentioned above, or when the fourth temperature sensor 604 detects that the temperature of the air entering the mixing box 602 is less than the first preset value mentioned above, the temperature of the ammonia vapor can be increased through the heating component 300 to ensure that the temperature of the diluted ammonia vapor remains between the first preset value and the second preset value.

[0039] As described above, the waste heat of the flue gas can be used to heat the air. In addition, the waste heat of the flue gas can also be used to heat the ammonia vapor. The first steam channel 200 can be at least partially disposed in the flue 201 to utilize the waste heat of the flue gas to heat the ammonia vapor. The denitration system can further include a third steam channel 700. The two ends of the third steam channel 700 are respectively communicated with the first steam channel 200 and are respectively located on both sides of the flue 201. Among them, the ammonia vapor selectively flows through the flue 201 or through the third steam channel 700. When the temperature of the ammonia vapor is high enough and does not require heating, the ammonia vapor can flow through the third steam channel 700 instead of flowing through the flue 201, which improves the flexibility of the denitration system. When the temperature of the ammonia vapor is low and the ammonia vapor needs to be heated, the ammonia vapor can flow through the flue 201 to utilize the waste heat of the flue gas to heat the ammonia vapor, improving the energy utilization rate and reducing energy consumption.

[0040] The denitration system can further include a second control valve 205 provided on the first steam channel 200. One end of the third steam channel 700 close to the pyrolysis furnace 100 is communicated with the first steam channel 200 through the second control valve 205. The second control valve 205 is used to control the ammonia vapor to flow through the flue 201 or through the third steam channel 700. The above-mentioned third temperature sensor 204 can be linked with the second control valve 205. When the temperature of the ammonia vapor is less than the third preset value, it controls the ammonia vapor to flow through the flue 201 to ensure that the temperature of the ammonia vapor is within the ideal range. When the temperature of the ammonia vapor is greater than or equal to the third preset value, it controls the ammonia vapor to flow through the third steam channel 700. At this time, the ammonia vapor can bypass the flue 201. The third preset value here can be adaptively adjusted according to the temperature of the air detected by the fourth temperature sensor 604. The higher the temperature of the air, the closer the third preset value is to the above-mentioned first preset value. The lower the temperature of the air, the greater the difference between the third preset value and the above-mentioned first preset value, ensuring that the temperature of the ammonia vapor is high enough and has enough heat to compensate for the air, avoiding the temperature of the diluted ammonia vapor being too low and causing the ammonia vapor to crystallize in the mixing box 602.

[0041] Generally speaking, in order to ensure the decomposition efficiency of the urea solution and make it easier for the urea solution to decompose into ammonia vapor, it is necessary to preheat the urea solution. During the process of transporting the urea solution to the pyrolysis furnace 100, the heat of the urea solution will gradually dissipate through the pipeline, and the temperature of the urea solution will gradually decrease, which affects the efficiency of the urea solution decomposing into ammonia vapor. At this time, the denitration system can also include a first solution channel 800, a second heating box 801, and a second solution channel 802. One end of the first solution channel 800 is connected to the urea solution, and the other end is connected to the pyrolysis furnace 100; the second heating box 801 is connected to the heat source 500, and the first solution channel 800 passes through the second heating box 801 to enable the urea solution to exchange heat with the heat source 500 to heat the urea in the first solution channel 800; both ends of the second solution channel 802 are respectively connected to the first solution channel 800 and are located on both sides of the second heating box 801. Among them, the urea solution selectively flows through the heating box or through the second solution channel 802. While transporting the urea solution into the pyrolysis furnace 100 through the first solution channel 800, when the temperature of the urea solution is insufficient, the urea solution can be heated by the second heating box 801 to ensure the temperature of the urea solution. When the urea solution does not need to be heated, the urea solution can flow through the second solution channel 802 instead of flowing through the second heating box 801. At this time, the second heating box 801 does not need to be used, improving the flexibility of the denitration system and making the denitration system more energy-efficient.

[0042] The denitration system can also include a third control valve 803 provided on the first solution channel 800. One end of the second solution channel 802 away from the pyrolysis furnace 100 is connected to the first solution channel 800 through the third control valve 803. The third control valve 803 is used to control the urea solution to flow through the second heating box 801 or through the second solution channel 802. A fifth temperature sensor and a sixth temperature sensor can be provided on the first solution channel 800. The fifth temperature sensor can be provided on the side of the second heating box 801 away from the pyrolysis furnace 100 and is linked with the third control valve 803. The sixth temperature sensor can be provided on the side of the second heating box 801 close to the pyrolysis furnace 100. When the temperature of the urea solution is less than the fourth preset value, control the urea solution to flow through the second heating box 801 to ensure that the temperature of the urea solution is within the ideal range. When the temperature of the urea solution is greater than or equal to the fourth preset value, control the urea solution to flow through the second solution channel 802. At this time, the urea solution can bypass the second heating box 801. The fourth preset value here can be determined according to the decomposition efficiency of the urea solution.

[0043] The preferred embodiments of the present disclosure have been described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure. In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without conflict. To avoid unnecessary repetition, the present disclosure will not separately describe various possible combination manners.

[0044] In addition, any combination can be made between various different embodiments of the present disclosure, as long as it does not violate the idea of the present disclosure, and it should also be regarded as the content disclosed by the present disclosure.

Claims

1. A denitration system, characterized in that: include: a pyrolysis furnace to decompose the urea solution and produce ammonia vapor; a first steam channel, one end of which is connected to the pyrolysis furnace and the other end of which is connected to the flue; a heating component, disposed on the first steam channel, and used for heating the ammonia steam in the first steam channel, wherein a plurality of the heating components are disposed at intervals in the flow direction of the ammonia steam; and The second steam channel has two ends respectively communicated with the first steam channel and is arranged in parallel with the heating component, wherein the ammonia vapor selectively flows through the heating component or through the second steam channel.

2. The denitration system according to claim 1, characterized in that: The heating component includes a first control valve arranged on the first steam channel, and one end of the second steam channel close to the pyrolysis furnace is connected to the first steam channel through the first control valve. The first control valve is used to control the ammonia steam to flow through the heating component or through the second steam channel.

3. The denitration system according to claim 2, characterized in that: The first steam channel is provided with a first temperature sensor and a second temperature sensor for respectively detecting the temperature of the ammonia steam. The first temperature sensor is electrically connected to the first control valve, and the second temperature sensor is arranged on a side of the heating assembly away from the pyrolysis furnace.

4. The denitration system according to claim 1, characterized in that: The heating assembly includes a heat source and a first heating box connected to the heat source. The first steam channel passes through the first heating box to enable heat exchange between the ammonia steam and the heat source.

5. The denitration system according to claim 1, characterized in that: The denitration system further includes a mixing component for mixing the ammonia vapor with air to dilute the ammonia vapor, the mixing component comprising: an air inlet passage, one end of which is in communication with the external environment and is provided with an air pump, wherein the air inlet passage is at least partially accommodated in the flue to heat the air using the residual heat of the flue gas; and A mixing box is communicated with the other end of the air inlet passage and is communicated with the flue through the first steam passage. The ammonia steam and the air are mixed in the mixing box to dilute the ammonia steam.

6. The denitration system according to claim 5, characterized in that: A third temperature sensor for detecting the temperature of the ammonia vapor is provided on the first steam channel, and a fourth temperature sensor for detecting the temperature of the air is provided on the air intake channel. The third temperature sensor is provided on a side of the mixing box body close to the pyrolysis furnace, and the fourth temperature sensor is provided on a side of the mixing box body close to the air intake channel.

7. The denitration system according to claim 1, characterized in that: The first steam channel is at least partially contained in the flue gas to heat the ammonia steam using waste heat of the flue gas. The denitration system further includes a third steam channel, both ends of which are respectively connected to the first steam channel and are located on both sides of the flue, wherein the ammonia vapor selectively flows through the flue or the third steam channel.

8. The denitration system according to claim 7, characterized in that: The denitrification system also includes a second control valve arranged on the first steam channel, and one end of the third steam channel close to the pyrolysis furnace is connected to the first steam channel through the second control valve, and the second control valve is used to control the ammonia steam to flow through the flue or through the third steam channel.

9. The denitration system according to claim 1, characterized in that: The denitration system further comprises: a first solution channel, one end of which is in communication with the urea solution and the other end of which is in communication with the pyrolysis furnace; a second heating box, which is in communication with a heat source, and through which the first solution channel passes, for enabling the urea solution to exchange heat with the heat source, so as to heat the urea in the first solution channel; and The second solution channel has two ends respectively communicated with the first solution channel and two ends respectively located on two sides of the second heating box, wherein the urea solution selectively flows through the heating box or flows through the second solution channel.

10. The denitration system according to claim 9, characterized in that: The denitrification system also includes a third control valve arranged on the first solution channel, and the end of the second solution channel away from the pyrolysis furnace is connected to the first solution channel through the third control valve, and the third control valve is used to control the urea solution to flow through the second heating box or through the second solution channel.

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