Tail gas treatment system

Abstract

The utility model provides a tail gas treatment system which comprises a carbon monoxide removal reactor, a first heat exchanger, a nitrous oxide decomposition reactor, an SCR (Selective Catalytic Reduction) reactor, a booster fan and a return pipeline, a material outlet of the carbon monoxide removal reactor is connected with a material inlet of the nitrous oxide decomposition reactor through a second pipeline and a low-temperature medium channel of the first heat exchanger, and a material outlet of the nitrous oxide decomposition reactor supplies materials to the booster fan through a third pipeline, a high-temperature medium channel of the first heat exchanger and a fourth pipeline. And the air outlet end of the booster fan is connected with the second pipeline through a return pipeline, and supplies materials to the SCR reactor through a fifth pipeline. The device is simple in structure and low in maintenance cost, can be used for efficiently treating nitrous oxide-containing tail gas for a long period, and meets the environmental protection requirement.

Description

Technical Field

[0001] This utility model relates to the chemical industry, and in particular to an exhaust gas treatment system. Background Technology

[0002] The exhaust gas produced during the adipic acid production process contains N2O, NOx, N2, organic matter, CO, and water. N2O has a global warming potential (GWP) 310 times that of CO2 and is a major ozone-depleting substance, capable of remaining stable in the atmosphere for over 100 years. Therefore, reducing N2O emissions from the adipic acid production process has always been a significant challenge for the industry.

[0003] Currently, N2O treatment generally employs methods such as thermal decomposition, selective catalytic reduction, direct catalytic decomposition, and separation and purification. Among these, direct catalytic decomposition is considered the most economical and environmentally friendly way to reduce N2O emissions due to its advantages, including simple process, low cost, no need for additional raw materials, and avoidance of secondary pollution.

[0004] CN113304607A discloses a process for the decomposition of nitrous oxide. A feed gas is mixed with compressed air to obtain a mixed gas with a nitrous oxide concentration of 8-10%. The mixed gas is sequentially heated to 420-460°C through a first heat exchanger and a second heat exchanger. It then enters the upper shell of the reactor shell through the feed gas inlet and is evenly distributed in the middle shell by an upper gas distribution mechanism. There, it comes into contact with a particulate catalyst (metal oxide) and undergoes a decomposition reaction to obtain decomposed gas. This decomposed gas is discharged from the decomposed gas outlet of the reactor shell through a lower gas collection mechanism. The discharged decomposed gas has a temperature of 650-750°C and, as a heat medium, passes through a second heat exchanger to cool to 300-350°C before entering the SCR reactor. There, residual nitric oxide and nitrogen dioxide in the feed gas react with ammonia to generate nitrogen gas. A drawback of this process is the need to dilute the feed gas with compressed air. Using air for dilution increases the space velocity in the SCR reactor, necessitating an increase in the catalyst dosage and reactor size. More importantly, the CO contained in the exhaust gas has reducing properties, which can reduce the catalyst to its elemental form at high temperatures, and also seriously affect the catalyst's lifespan, thereby affecting the decomposition and treatment efficiency of N2O.

[0005] Therefore, how to design a treatment system for nitrous oxide-containing exhaust gas with low energy consumption, high efficiency in nitrous oxide decomposition, and long operating cycle, and how to develop related decomposition methods, are problems that urgently need to be solved by those skilled in the art. Utility Model Content

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing an exhaust gas treatment system that has a simple structure, low maintenance costs, and can treat nitrous oxide-containing exhaust gas over long periods with high efficiency, thus meeting environmental protection requirements.

[0007] The technical solution for achieving this utility model is: a tail gas treatment system, comprising a carbon monoxide removal reactor, a first heat exchanger, a nitrous oxide decomposition reactor, an SCR reactor, a booster fan, and a return pipeline. The material inlet of the carbon monoxide removal reactor is connected to the tail gas source via the first pipeline, and the material outlet of the carbon monoxide removal reactor is connected to the material inlet of the nitrous oxide decomposition reactor via a second pipeline and the low-temperature medium channel of the first heat exchanger. The material outlet of the nitrous oxide decomposition reactor supplies material to the booster fan via a third pipeline, the high-temperature medium channel of the first heat exchanger, and a fourth pipeline. The outlet of the booster fan is connected to the second pipeline via the return pipeline and supplies material to the SCR reactor via a fifth pipeline.

[0008] It also includes a steam-water separator, which is connected in series on the first pipeline. The first pipeline is equipped with an emergency venting pipeline, and its opening and closing are controlled by a first valve.

[0009] It also includes a second heat exchanger, the low-temperature medium channel of which is connected in series with the first pipeline, and the high-temperature medium channel of which is connected to the material outlet of the SCR reactor.

[0010] It also includes a start-up heater, and the low-temperature medium channel of the first heat exchanger is connected to the material inlet of the nitrous oxide decomposer through the start-up heater.

[0011] It also includes a third heat exchanger, which is connected in series on the fourth pipeline and divides the fourth pipeline into an upper section and a lower section.

[0012] A compressed air inlet is provided on the fourth pipeline, and its opening and closing are controlled by a second valve. Specifically, a compressed air inlet is provided on the lower section of the fourth pipeline.

[0013] The fifth pipeline includes a circulation section and a feeding section. The upstream end of the circulation section is connected to the outlet end of the booster fan, and the downstream end is connected to the fourth pipeline, located upstream of the third heat exchanger (i.e., the downstream end is connected to the upper section of the fourth pipeline). The upstream end of the feeding section is connected to the fourth pipeline, located downstream of the third heat exchanger (the upstream end of the feeding section is connected to the lower section of the fourth pipeline), and the downstream end feeds the SCR reactor. Preferably, the flow ratio of the reflux pipeline to the circulation section is 1:0 to 0.1.

[0014] It also includes a first bypass pipeline, which is connected in parallel with the low-temperature medium channel of the first heat exchanger. A third valve is installed on the first bypass pipeline, and the flow ratio between the first bypass pipeline and the low-temperature medium channel of the first heat exchanger is 1:1.6 to 10.

[0015] It also includes a second bypass pipeline, the upstream end of which is connected to the fourth pipeline and is located upstream of the third heat exchanger (i.e., the upstream end of the second bypass pipeline is connected to the upper section of the fourth pipeline), and the downstream end is connected to the feeding section. A fourth valve is installed on the second bypass pipeline, and the flow ratio between the second bypass pipeline and the upper section of the fourth pipeline is 1:25 to 35.

[0016] The above technical solution has the following beneficial effects:

[0017] 1. This utility model's exhaust gas treatment system introduces a carbon monoxide removal reactor to remove reducing gases (carbon monoxide) from the exhaust gas, protecting the catalyst in the nitrous oxide decomposition reactor, extending the catalyst's lifespan, and thus extending the operating cycle of the exhaust gas treatment system. In this system, the exhaust gas from the nitrous oxide decomposition reactor is cooled by heat exchange, then pressurized by a booster fan, and partially recirculated to mix with the exhaust gas from the carbon monoxide removal reactor, diluting the nitrous oxide concentration in the exhaust gas and meeting the inlet requirements of the downstream nitrous oxide decomposition reactor. Furthermore, the exhaust gas from the nitrous oxide decomposition reactor undergoes cyclic decomposition treatment to improve the decomposition rate of nitrous oxide in the exhaust gas. The remaining gas is sent to the SCR reactor, which also has a high pressure, meeting the inlet requirements of the SCR reactor. While ensuring denitrification, this allows for a reduction in the amount of catalyst used in the SCR reactor and / or a reduction in the size of the SCR reactor.

[0018] 2. The exhaust gas treatment system of this utility model controls the heat exchange of carbon monoxide-removed exhaust gas in the first heat exchanger by connecting a first bypass pipe in parallel to the low-temperature medium channel of the first heat exchanger and setting a third valve to control the opening degree to control the flow ratio between the first bypass pipe and the low-temperature medium channel of the first heat exchanger. This controls the heat exchange of carbon monoxide-removed exhaust gas in the first heat exchanger, thereby controlling the inlet temperature of the gas entering the nitrous oxide decomposition reactor, meeting the operating requirements of the nitrous oxide decomposition reactor, and is simple in structure and easy to maintain.

[0019] 3. The exhaust gas treatment system of this utility model uses the exhaust gas from the nitrous oxide decomposition reactor as a high-temperature medium to heat the inlet gas of the nitrous oxide decomposition reactor. The gas is then diverted to the third heat exchanger for heat exchange with water to generate steam for external energy supply. In conjunction with the downstream booster fan, the gas flow is pressurized and heated, effectively utilizing the heat of nitrous oxide decomposition. In addition, this utility model, by setting a second bypass pipeline and a fourth valve to control the opening, can control the pressure increase and heat exchange of the exhaust gas after heat exchange and cooling in the first heat exchanger in the third heat exchanger and the booster fan. This meets the pressure and temperature requirements of the diluted carbon monoxide removal exhaust gas and the inlet gas of the SCR reactor. The system is simple in structure and easy to maintain.

[0020] 4. The exhaust gas treatment system of this utility model designs the fifth pipeline as a circulation section and a feeding section, and sets the downstream end of the circulation section upstream of the third heat exchanger (i.e., the upper part of the fourth pipeline) and the upstream end of the feeding section downstream of the third heat exchanger (i.e., the lower part of the fourth pipeline), so that the exhaust gas section that has been pressurized and heated by the booster fan exchanges heat with water through the third heat exchanger to generate steam for external energy supply, thereby improving the heat utilization rate.

[0021] According to the applicant's tests and verifications, the system operating cycle of this utility model reaches 7500-8200 hours, the nitrous oxide in the exhaust gas is maintained at 0.06-0.15 vol%, and the water vapor produced per unit volume of exhaust gas is 4096-5125 kg / h.

[0022] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details. Attached Figure Description

[0023] Figure 1 This is a connection diagram of the present invention.

[0024] In the attached diagram, 1 is the carbon monoxide removal reactor, 2 is the first heat exchanger, 3 is the nitrous oxide decomposition reactor, 4 is the SCR reactor, 5 is the booster fan, 6 is the first bypass pipeline, 7 is the reflux pipeline, 8 is the steam-water separator, 9 is the emergency vent pipeline, 10 is the second heat exchanger, 11 is the start-up heater, 12 is the third heat exchanger, 13 is the compressed air inlet, 14 is the second bypass pipeline, 101 is the first pipeline, 102 is the second pipeline, 103 is the third pipeline, 104 is the fourth pipeline, 105 is the fifth pipeline, 105a is the circulation section, 105b is the feeding section, a is the first valve, b is the second valve, c is the third valve, and d is the fourth valve. Detailed Implementation

[0025] In this invention, the catalyst packed in the carbon monoxide removal reactor can be at least one of catalyst A, catalyst B, or catalyst C, and the catalyst used in the N2O decomposer can be catalyst D. Specifically:

[0026] Catalyst A is a palladium-based catalyst, Pd / Al2O3, with a Pd loading of 1 wt% and an activity temperature of 160–250 °C.

[0027] Catalyst B is Pt / ZrO2-Al2O3, with Pt loading of 1 wt%, ZrO2 (0.4 moles)-Al2O3 (0.6 moles), and an activity temperature of 150-230℃;

[0028] The catalyst C is Pt / Fe2O3, with Pt loading of 1 wt% and an activity temperature of 140–180 °C.

[0029] Catalyst D has the following molar ratio: nickel:copper:barium:neodymium:aluminum = 0.4:0.2:0.6:0.03:2, and its N2O decomposition rate is 72.3% to 98.4% at 375℃ to 400℃.

[0030] The sources of catalysts A, B, C, and D are not limited, as long as the activity temperature is within the required range. They can be purchased or prepared in-house, and the preparation method is not limited, as long as the above components are maintained. Optionally, they can be obtained by ordinary impregnation, drying, and calcination.

[0031] Example 1

[0032] See Figure 1The exhaust gas treatment system includes a carbon monoxide removal reactor 1, a first heat exchanger 2, a nitrous oxide decomposition reactor 3, an SCR reactor 4, and a booster fan 5. The carbon monoxide removal reactor 1 can be filled with one or more of catalysts A, B, or C for catalytic CO removal, while the nitrous oxide decomposition reactor is filled with catalyst D for catalytic nitrous oxide decomposition. The material inlet of the carbon monoxide removal reactor 1 is connected to the exhaust gas source via a first pipeline 101. In this embodiment, a steam-water separator 8 is also included, connected in series on the first pipeline 101. An emergency vent pipeline 9 is installed on the first pipeline 101, located upstream of the steam-water separator, and its opening and closing are controlled by a first valve a. Typically, a valve is also installed between the emergency vent pipeline 9 and the steam-water separator 8. In this embodiment, a second heat exchanger 10 is also included. The low-temperature medium channel of the second heat exchanger 10 is connected in series with the first pipeline 101 and is located downstream of the steam-water separator 8. The high-temperature medium channel of the second heat exchanger 10 is connected to the material outlet of the SCR reactor 4. N2O and nitrogen oxide detection points are set at the downstream end of the high-temperature medium channel of the second heat exchanger 10. The material outlet of the carbon monoxide removal reactor 1 is connected to the material inlet of the nitrous oxide decomposition reactor 3 via the second pipeline 102 and the low-temperature medium channel of the first heat exchanger 2. In this embodiment, a start-up heater 11 is also included. The low-temperature medium channel of the first heat exchanger 2 is connected to the material inlet of the nitrous oxide decomposition reactor 3 through the start-up heater 11. It is used to raise the temperature of the incoming gas into the nitrous oxide decomposition reactor 3 when the system starts up to meet the operating requirements (the operating requirements are considered to be met when the system pressure reaches 100 kPa). After the system stabilizes, the start-up heater 11 stops working. The material outlet of the nitrous oxide decomposition reactor 3 supplies material to the booster fan 5 via the third pipeline 103, the high-temperature medium channel of the first heat exchanger 2, and the fourth pipeline 104. In this embodiment, a third heat exchanger 12 is also included. The high-temperature medium channel of the third heat exchanger 12 is connected in series with the fourth pipeline 104, dividing the fourth pipeline 104 into an upper section and a lower section. The low-temperature medium in the low-temperature medium channel of the third heat exchanger 12 is warm water. A compressed air inlet 13 is provided on the lower section of the fourth pipeline, located between the third heat exchanger 12 and the booster fan 5, and its opening and closing are controlled by a second valve b. The outlet of the booster fan 5 is connected to the second pipeline 102 via a return pipeline 7, and the connection point between the return pipeline 7 and the second pipeline 102 is located upstream of the first heat exchanger 2. Typically, a detection point is set on the second pipeline 102 to detect the concentration of nitrous oxide, and it is located downstream of the connection point between the return pipeline 7 and the second pipeline 102 and upstream of the first heat exchanger 2.

[0033] The outlet of the booster fan 5 also supplies feed to the SCR reactor 4 via the fifth pipeline 105. Specifically, the fifth pipeline 105 includes a circulation section 105a and a feeding section 105b. The upstream end of the circulation section 105a is connected to the outlet of the booster fan 5, and the downstream end is connected to the upper section of the fourth pipeline, located upstream of the third heat exchanger 12. The upstream end of the feeding section 105b is connected to the lower section of the fourth pipeline 104, located downstream of the third heat exchanger 12, and the downstream end of the feeding section 105b supplies feed to the SCR reactor 4. Generally, valves are installed on the return pipeline 7, the circulation section 105a, and the feeding section 105b. The concentration requirements of nitrous oxide (7-12v%) at the detection point are met by controlling the operating load of the booster fan 5 and the return flow rate of the return pipeline 7. Furthermore, it also includes a first bypass pipe 6, which is connected in parallel with the low-temperature medium channel of the first heat exchanger 2, and a third valve c is installed on the first bypass pipe 6.

[0034] Furthermore, it also includes a second bypass pipe 14. The upstream end of the second bypass pipe 14 is connected to the fourth pipe 104 (specifically, downstream of the first heat exchanger 2 and upstream of the third heat exchanger 12, i.e., the upper section of the fourth pipe), and the downstream end is connected to the fifth pipe 105 and located downstream of the third heat exchanger 12. Specifically, the downstream end of the second bypass pipe 14 is connected to the feeding section 105b, and a fourth valve d is installed on the second bypass pipe 14. The second bypass pipe 14 is the heating gas flow for the SCR reactor 4, and the inlet gas temperature of the SCR reactor 4 can be adjusted by controlling the flow rate of the second bypass pipe 14.

[0035] It is worth noting that control valves can be installed on each pipeline according to actual needs. The flow rate can be adjusted by using the system settings in this example and coordinating valve control, ultimately achieving energy self-sufficiency within the system and increasing system capacity. Furthermore, catalysts A, B, and C function to catalyze the removal of CO or C organic matter. This invention does not exhaustively list all such catalysts; for example, other catalysts with similar functions and the same catalytic operating temperature as those listed in this application are also applicable. Catalyst D functions to catalyze the decomposition of nitrous oxide. Again, this invention does not exhaustively list all such catalysts; other similar catalysts are also applicable.

[0036] In summary, this invention ensures the lifespan of the nitrous oxide decomposition catalyst by introducing a carbon monoxide removal reactor. Furthermore, the design of the pipelines and valves allows for clear differentiation between primary and secondary control functions, ensuring stable operation and further guaranteeing the lifespan of the catalysts in each reactor.

[0037] Example 2

[0038] The method for treating exhaust gas using the treatment system described in Example 1, wherein the carbon monoxide removal reactor is filled with catalyst A and the nitrous oxide decomposition reactor is filled with catalyst D, and the space velocity in the carbon monoxide removal reactor is approximately 2000 h⁻¹. -1 The space velocity in the nitrous oxide decomposition reactor is approximately 1000 h⁻¹. -1 The steps include:

[0039] System startup: Compressed air is introduced into the system through compressed air inlet 13. After all systems are normal and contain air carrier gas, the booster fan 5 is started. The booster fan 5 forms a closed loop of air, namely, the closed loop of booster fan 5 outlet - first heat exchanger 2 - start-up heater 11 - nitrous oxide decomposition reactor 3 - first heat exchanger 2 - third heat exchanger 12 - booster fan 5 inlet. When the system pressure reaches 100 kPa, that is, the process conditions are stable, the input of compressed air is stopped, and the start-up heater 11 and / or the third heat exchanger 12 are used for initial heating.

[0040] The above completes the system startup process. The following steps will then be performed:

[0041] 1) Take the tail gas generated from the oxidation of alcohol ketones or cyclohexanol with nitric acid to produce adipic acid. First, pass it through three continuously connected packed towers to absorb the nitric oxide and nitrogen dioxide (this is a conventional process). Then, separate the water vapor in the gas-water separator 8 to obtain the tail gas.

[0042] To illustrate the operation of this system, the exhaust gas (v / v) composition used is as follows: 0.7% water, 46.75% nitrogen, 5.3% oxygen, 0.04% nitric oxide, 37.2% nitrous oxide, 7% carbon dioxide, 3% carbon monoxide, and 0.01% organic matter.

[0043] 1-1) Exhaust gas emissions of 9114.5 Nm 3 After passing through the second heat exchanger 10, the temperature rises to 185.5℃. The gas effluent from the SCR reactor 4 serves as the high-temperature medium for the second heat exchanger 10. Finally, after the NOx and N2O concentrations are tested and found to meet the standards, the gas is vented through the vent pipe.

[0044] 1-2) The gas phase after passing through the second heat exchanger 10 enters the carbon monoxide removal reactor 1, and the reactor outlet temperature is 245.7℃;

[0045] 1-3) The tail gas from the decarbonization reactor 1 is mixed with the gas from the first pressurized feed stream output by the booster fan 5 to form a feed stream. The flow rate of the first pressurized feed stream in the return pipe 7 is controlled to keep the concentration of nitrous oxide in the mixed gas in the feed stream at 8.71v%. That is, the circulation section 105a is closed so that the flow rate of the second pressurized feed stream is 0.

[0046] 1-4) The feed flow then branches into a main feed flow and a bypass feed flow. The main feed flow exchanges heat with the discharge flow and is then sent to the nitrous oxide decomposer 3. The bypass feed flow is sent directly to the nitrous oxide decomposition process. The flow ratio of the bypass feed flow to the main feed flow is 1:4, that is, the flow ratio of the first bypass pipe 6 to the low temperature medium channel of the first heat exchanger 2 is 1:4.

[0047] 2-1) The exhaust gas from the nitrous oxide decomposition reactor 3 is split into a first discharge stream (upper section of the fourth pipeline) and a second discharge stream (second bypass pipeline) after heat exchange in the first heat exchanger 2. The flow ratio between the second bypass pipeline 14 and the upper section of the fourth pipeline is controlled at 1:35. The first discharge stream passes through the third heat exchanger 12, where the heat from the exhaust gas is used to convert hot water into steam. At this point, low-pressure steam with a temperature of 165.3℃ and a flow rate of 5125 kg / h is obtained. The stream passing through the third heat exchanger 12 is transported to the booster fan 5 via the lower section of the fourth pipeline. As the inlet gas for the booster fan 5, the stream is compressed by the booster fan to obtain a pressurized stream with a temperature of 211.5℃ and a pressure of 135 kPa.

[0048] 2-2) The material flow after passing through the booster fan 5 is divided into a first pressurized material flow and a second pressurized material flow. The first pressurized material flow completes the cycle in 1-3). The second pressurized material flow merges with the upper part of the fourth pipeline through the circulation section 105a and is sent to the upstream of the third heat exchanger 12 for circulation and feeding into the SCR reactor, thereby ensuring the inlet temperature (maintained at 180-220℃) and pressure (maintained at 95-100Kpa) requirements of the SCR reactor. Among them, after exiting the third heat exchanger 12, the flow ratio of the lower section of the fourth pipeline and the feeding section 105b is 22:8.

[0049] 2-3) The airflow fed into the SCR in the feeding section 105b is 8Nm 3 The mixture of ammonia gas and nitrogen gas is introduced into the SCR reactor 4, where it reacts with the ammonia gas to generate nitrogen gas. The exhaust gas discharged from the SCR reactor 4 is then discharged into the atmosphere after heat exchange in the second heat exchanger 10.

[0050] Tests showed a temperature of 48.1℃, nitrous oxide concentration of 0.06%, and nitrogen oxide (NOx) concentration of 2.5 mg / m³. 3 The system can operate continuously for 8200 hours under constant space velocity and inlet temperature, producing 5125 kg / h of low-pressure steam. The pressure difference of the SCR reactor is 0.5 kPa, ensuring smooth reactor flow and reducing the burden on pipeline diameter.

[0051] Example 3

[0052] The difference from Example 2 is that the decarbonization reactor 1 is filled with catalyst B.

[0053] 1-1) Exhaust gas emissions of 9114.5 Nm 3After passing through the second heat exchanger 10, the temperature rises to 172.8℃. The gas effluent from the SCR reactor 4 serves as the high-temperature medium for the second heat exchanger 10. Finally, after the NOx and N2O concentrations are tested and found to meet the standards, the gas is vented through the vent pipe.

[0054] 1-2) The gas phase after passing through the second heat exchanger 10 enters the carbon monoxide removal reactor 1, and the reactor outlet temperature is 226.2℃;

[0055] 1-3) The tail gas from the carbon monoxide removal reactor 1 is mixed with the gas from the first pressurized feed stream output by the booster blower 5 to form a feed stream. The flow rate of the first pressurized feed stream in the return pipe 7 is controlled to keep the concentration of nitrous oxide in the mixed gas in the feed stream at 9.12v%. That is, the flow rate ratio of the first pressurized feed stream and the second pressurized feed stream is 1:0.02.

[0056] 1-4) The feed flow then branches into a main feed flow and a bypass feed flow. The main feed flow exchanges heat with the discharge flow and is then sent to the nitrous oxide decomposer 3. The bypass feed flow is sent directly to the nitrous oxide decomposition process. The flow ratio of the bypass feed flow to the main feed flow is 1:5, that is, the flow ratio of the first bypass pipe 6 to the low temperature medium channel of the first heat exchanger 2 is 1:5.

[0057] 2-1) The exhaust gas from the nitrous oxide decomposition reactor 3 is split into a first discharge stream and a second discharge stream after heat exchange in the first heat exchanger 2, and the flow ratio between the second bypass pipe 14 and the upper part of the fourth pipe is controlled to be 1:32. The first discharge stream passes through the third heat exchanger 12, where the heat from the exhaust gas is used to convert hot water into steam. At this time, low-pressure steam with a temperature of 167.2℃ and a flow rate of 5015 kg / h is obtained. The flow passing through the third heat exchanger 12 serves as the inlet gas for the booster blower 5. After being compressed by the booster blower, it becomes a pressurized flow with a temperature of 215.3℃ and a pressure of 136 kPa.

[0058] 2-2) The material flow after passing through the booster blower 5 is divided into a first pressurized material flow and a second pressurized material flow. The first pressurized material flow completes the 1-3) cycle. The second pressurized material flow merges with the upper part of the fourth pipeline through the circulation section 105a and is sent to the upstream of the third heat exchanger 12 for circulation and feeding into the SCR reactor, thereby ensuring the inlet temperature (maintained at 180-220℃) and pressure (maintained at 95-100Kpa) requirements of the SCR reactor. After exiting the third heat exchanger 12, the flow ratio of the lower section of the fourth pipeline and the feeding section 105b is 25:8.

[0059] 2-3) The exhaust gas from the SCR is fed into the feeding section 105b and contains 8 Nm of gas. 3Ammonia gas is mixed with nitrogen gas and fed into SCR reactor 4, where it reacts with the ammonia to produce nitrogen gas. The exhaust gas from SCR reactor 4 is then discharged after heat exchange in the second heat exchanger 10. Measurements show a temperature of 48.7℃, nitrous oxide concentration of 0.10%, and nitrogen oxide (NOx) concentration of 2.5 mg / m³. 3 The system can operate continuously for 8300 hours with constant air velocity and inlet temperature, producing 5015 kg / h of low-pressure steam.

[0060] Example 4

[0061] The difference from Example 2 is that the decarbonization reactor 1 is filled with catalyst C.

[0062] 1-1) Exhaust gas emissions of 9114.5 Nm 3 After passing through the second heat exchanger 10, the temperature rises to 159.7℃. The gas effluent from the SCR reactor 4 serves as the high-temperature medium for the second heat exchanger 10. Finally, after the NOx and N2O concentrations are tested and found to meet the standards, the gas is vented through the vent pipe.

[0063] 1-2) The gas phase after passing through the second heat exchanger 10 enters the carbon monoxide removal reactor 1, and the reactor outlet temperature is 181.5℃;

[0064] 1-3) The tail gas from the carbon monoxide removal reactor 1 is mixed with the gas from the first pressurized feed stream output by the booster blower 5 to form a feed stream. The flow rate of the first pressurized feed stream in the return pipe 7 is controlled to keep the concentration of nitrous oxide in the mixed gas in the feed stream at 11.3v%. That is, the flow rate ratio of the first pressurized feed stream and the second pressurized feed stream is 1:0.06.

[0065] 1-4) The feed flow then branches into a main feed flow and a bypass feed flow. The main feed flow exchanges heat with the discharge flow and is then sent to the nitrous oxide decomposer 3. The bypass feed flow is sent directly to the nitrous oxide decomposition process. The flow ratio of the bypass feed flow to the main feed flow is 1:6, meaning the flow ratio between the first bypass pipe 6 and the low-temperature medium channel of the first heat exchanger 2 is 1:6.

[0066] 2-1) The exhaust gas from the nitrous oxide decomposition reactor 3 is split into a first discharge stream and a second discharge stream after heat exchange in the first heat exchanger 2. The flow ratio between the second bypass pipe 14 and the upper part of the fourth pipe is controlled at 1:25. The flow ratio between the second bypass pipe 14 and the combined flow rates of the fifth pipe 105 and the fourth pipe 104 is 1:30. The first discharge stream passes through the third heat exchanger 12, where the heat from the exhaust gas is used to convert hot water into steam. At this point, low-pressure steam with a temperature of 159.1℃ and a flow rate of 4096 kg / h is obtained. Part of the stream passing through the third heat exchanger 12 then becomes the inlet gas for the booster blower 5. After being compressed by the booster blower, it becomes a pressurized stream with a temperature increase to 213.5℃ and a pressure of 135 kPa. The other part enters the SCR.

[0067] 2-2) The material flow after passing through the booster blower 5 is divided into a first pressurized material flow and a second pressurized material flow. The first pressurized material flow completes the 1-3) cycle. The second pressurized material flow merges with the upper part of the fourth pipeline through the circulation section 105a and is sent to the upstream of the third heat exchanger 12 for circulation and feeding into the SCR reactor, thereby ensuring the inlet temperature (maintained at 180-220℃) and pressure (maintained at 95-100Kpa) requirements of the SCR reactor. After exiting the third heat exchanger 12, the flow ratio of the lower section of the fourth pipeline and the feeding section 105b is 30:8.

[0068] 2-3) The exhaust gas from the SCR is fed into the feeding section 105b and contains 8 Nm of gas. 3 Ammonia gas is mixed with nitrogen gas and fed into SCR reactor 4, where it reacts with the ammonia to produce nitrogen gas. The exhaust gas from SCR reactor 4 is then discharged after heat exchange in the second heat exchanger 10. Measurements show a temperature of 49.3℃, nitrous oxide concentration of 0.15 vol%, and nitrogen oxide (NOx) concentration of 2.5 mg / m³. 3 The system can operate continuously for 7500 hours with constant air velocity and inlet temperature, producing 4096 kg / h of low-pressure steam.

[0069] Compare with Example 1

[0070] The system used in this example differs from that in Example 2 in that a carbon monoxide removal reactor is not added, while other circuit connections remain unchanged, ensuring the system's normal operation. The system exhaust gas showed a nitrous oxide content of 0.25%, and the system can operate continuously for approximately 4000 hours under constant space velocity and inlet temperature.

[0071] Compare with Example 2

[0072] The system used in this example differs from that in Example 2 in that, in steps 1-3), the flow ratio of the first pressurized material flow to the second pressurized material flow is 1:0.2, and a detection point is set on the second pipeline 102 to detect that the concentration of nitrous oxide exceeds 12v%, which does not meet the requirements.

[0073] Compare with Example 3

[0074] The system used in this example differs from that in Example 2 in that, in steps 1-4), the flow ratio of the first bypass pipe 6 to the low-temperature medium channel of the first heat exchanger 2 is 1:7, the feed gas temperature entering the nitrous oxide decomposition reactor 3 reaches 400℃, and after continuous operation for 5000 hours, the nitrogen oxide (NOx) concentration is 3.2 mg / m³. 3 The nitrous oxide content in the exhaust gas was 0.31%.

[0075] Compare with Example 4

[0076] The system used in this example differs from that in Example 2 in that, in step 2-1), the flow ratio between the second bypass pipe 14 and the upper section of the fourth pipe is controlled to be 1:20, and the nitrogen oxide (NOx) concentration is 3.5 mg / m³. 3 After 6000 hours of continuous operation, the nitrous oxide content in the exhaust gas was 0.25%.

Claims

1. An exhaust gas treatment system, characterized in that: It includes a carbon monoxide removal reactor (1), a first heat exchanger (2), a nitrous oxide decomposition reactor (3), an SCR reactor (4), and a booster fan (5). The material inlet of the carbon monoxide removal reactor (1) is connected to the tail gas source via the first pipeline (101), and the material outlet of the carbon monoxide removal reactor (1) is connected to the material inlet of the nitrous oxide decomposition reactor (3) via the second pipeline (102) and the low-temperature medium channel of the first heat exchanger (2). The material outlet of the nitrous oxide decomposition reactor (3) is supplied to the booster fan (5) via the third pipeline (103), the high-temperature medium channel of the first heat exchanger (2), and the fourth pipeline (104). The outlet of the booster fan (5) is connected to the second pipeline (102) via the return pipeline (7) and supplies material to the SCR reactor (4) via the fifth pipeline (105).

2. The exhaust gas treatment system according to claim 1, characterized in that: It also includes a steam-water separator (8), which is connected in series on the first pipeline (101), and the first pipeline (101) is provided with an emergency venting pipeline (9), which is controlled to open and close by a first valve (a).

3. The exhaust gas treatment system according to claim 1, characterized in that: It also includes a second heat exchanger (10), the low temperature medium channel of the second heat exchanger (10) is connected in series with the first pipeline (101), and the high temperature medium channel of the second heat exchanger (10) is connected to the material outlet of the SCR reactor (4).

4. The exhaust gas treatment system according to claim 1, characterized in that: The fourth pipeline (104) is provided with a compressed air inlet (13), and its opening and closing are controlled by a second valve (b).

5. The exhaust gas treatment system according to claim 1, characterized in that: It also includes a start-up heater (11), and the low-temperature medium channel of the first heat exchanger (2) is connected to the material inlet of the nitrous oxide decomposer (3) through the start-up heater (11).

6. The exhaust gas treatment system according to claim 1, characterized in that: It also includes a first bypass pipe (6), which is connected in parallel with the low-temperature medium channel of the first heat exchanger (2), and a third valve (c) is installed on the first bypass pipe (6). The flow ratio of the first bypass pipe (6) and the low-temperature medium channel of the first heat exchanger (2) is 1:1.6~10.

7. The exhaust gas treatment system according to claim 1, characterized in that: It also includes a third heat exchanger (12), which is connected in series with the fourth pipeline (104) and divides the fourth pipeline (104) into an upper section and a lower section.

8. The exhaust gas treatment system according to claim 7, characterized in that: The fifth pipeline (105) includes a circulation section (105a) and a feeding section (105b). The upstream end of the circulation section (105a) is connected to the outlet end of the booster fan (5), and the downstream end is connected to the upper section of the fourth pipeline. The upstream end of the feeding section (105b) is connected to the lower section of the fourth pipeline, and the downstream end supplies material to the SCR reactor (4). The flow ratio of the return pipeline (7) to the circulation section (105a) is 1:0~0.

1.

9. The exhaust gas treatment system according to claim 8, characterized in that: It also includes a second bypass pipe (14), the upstream end of which is connected to the upper section of the fourth pipe, and the downstream end of which is connected to the fifth pipe (105) and located downstream of the third heat exchanger (12). A fourth valve (d) is installed on the second bypass pipe (14). The flow ratio of the second bypass pipe (14) to the upper section of the fourth pipe is 1:25~35; the flow ratio of the lower section of the fourth pipe to the feeding section (105b) is 16~30:6~9.

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