Tail gas treatment system and method

Abstract

The invention provides a tail gas treatment system and method.The tail gas treatment system comprises a carbon monoxide removal reactor, a first heat exchanger, a nitrous oxide decomposition reactor, an SCR reactor, a booster fan and a backflow pipeline, and a material inlet of the carbon monoxide removal reactor is connected with a tail gas source through a first 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 efficiently treat nitrous oxide-containing tail gas for a long period, and meets the environmental protection requirement.

Description

Technical Field

[0001] The present invention relates to the field of chemical industry, and in particular to a tail gas treatment system and method. Background Art

[0002] The tail gas produced by the adipic acid production process contains N2O, NOx, N2, organic matter, CO and water, etc. The global warming potential (GWP) of N2O is 310 times that of CO2, and it is also a substance that seriously depletes the ozone layer. It can exist stably in the atmosphere for more than 100 years. Therefore, the reduction of N2O in the tail gas produced by the adipic acid production process has always been a huge challenge facing the industry.

[0003] At present, N2O is generally treated by thermal decomposition, selective catalytic reduction, direct catalytic decomposition, separation and purification, etc. Among them, direct catalytic decomposition is considered to be the most economical and environmentally friendly way to reduce N2O emissions because of its advantages such as simple process, low cost, no addition of additional raw materials and avoidance of secondary pollution.

[0004] CN113304607A discloses a decomposition process of nitrous oxide, wherein the raw gas is mixed with compressed air to obtain a mixed gas, wherein the concentration of nitrous oxide is 8-10%, and the mixed gas is heated to 420-460°C through the first heat exchanger and the second heat exchanger in turn, enters the upper shell from the raw gas inlet of the reactor shell, is evenly distributed in the middle shell through the upper gas distribution mechanism, contacts with a granular catalyst (metal oxide), decomposes and reacts to obtain a decomposed gas, and is discharged from the decomposed gas outlet of the reactor shell through the lower gas collection mechanism. The discharged decomposed gas has a temperature of 650-750°C, passes through the second heat exchanger as a heat medium, is cooled to 300-350°C, enters the SCR reactor, and the residual nitric oxide and nitrogen dioxide in the raw gas react with ammonia to generate nitrogen. The disadvantage of this process is that the raw gas needs to be diluted with compressed air. If air is used for dilution, the space velocity of the SCR will increase, thereby increasing the amount of catalyst in the SCR reactor and increasing the size of the SCR reactor. More importantly, the CO contained in the exhaust gas is reducing and can reduce the catalyst to a single substance at high temperatures, which can seriously affect the service life of the catalyst and thus the decomposition efficiency of N2O.

[0005] Therefore, how to design a treatment system for nitrous oxide tail gas with low energy consumption, high nitrous oxide decomposition efficiency and long operation cycle and develop related decomposition methods are problems that need to be urgently solved by technical personnel in this field. Summary of the invention

[0006] One of the purposes of the present invention is to provide a tail gas treatment system in view of the deficiencies in the prior art, which has a simple structure and low maintenance cost, can treat tail gas containing nitrous oxide with high efficiency over a long period of time, and meet environmental protection requirements.

[0007] The second object of the present invention is to provide the application of the above tail gas system in the treatment of tail gas in adipic acid production process.

[0008] The third object of the present invention is to provide a method for treating tail gas using the above system, which has low operating cost, long maintenance cycle, and can also provide heat to the outside, thereby improving the utilization value of the tail gas.

[0009] The technical solution for achieving one of the purposes of the present invention is: an exhaust gas treatment system, comprising a decarbon monoxide reactor, a first heat exchanger, a nitrous oxide decomposition reactor, an SCR reactor, a booster fan, and a reflux pipeline, wherein the material inlet of the decarbon monoxide reactor is connected to the exhaust gas source via the first pipeline, the material outlet of the decarbon monoxide reactor is connected to the material inlet of the nitrous oxide decomposition reactor via the second pipeline and the low-temperature medium channel of the first heat exchanger, the material outlet of the nitrous oxide decomposition reactor is supplied to the booster fan via the third pipeline, the high-temperature medium channel of the first heat exchanger, and the fourth pipeline, and the gas outlet end of the booster fan is connected to the second pipeline via the reflux pipeline and supplies the SCR reactor via the fifth pipeline.

[0010] It also includes a steam-water separator, which is connected in series on a first pipeline. An emergency venting pipeline is provided on the first pipeline, and its opening and closing is controlled by a first valve.

[0011] It also includes a second heat exchanger, wherein a low-temperature medium channel of the second heat exchanger is connected in series to the first pipeline, and a high-temperature medium channel of the second heat exchanger is connected to a material outlet of the SCR reactor.

[0012] 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.

[0013] It also includes a third heat exchanger, which is connected in series to the fourth pipeline and divides the fourth pipeline into a fourth pipeline upper section and a fourth pipeline lower section.

[0014] A compressed air inlet is arranged on the fourth pipeline, and the opening and closing is controlled by the second valve. Specifically, a compressed air inlet is arranged on the lower section of the fourth pipeline.

[0015] 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, the downstream end is connected to the fourth pipeline, and is located upstream of the third heat exchanger (that is, 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, and is 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 1:0-0.1.

[0016] 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 arranged 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 1:1.6-10.

[0017] It also includes a second bypass pipeline, the upstream end of which is connected to the fourth pipeline, located upstream of the third heat exchanger (that is, the upstream end of the second bypass pipeline is connected to the upper part of the fourth pipeline), and the downstream end is connected to the feeding section. A fourth valve is arranged on the second bypass pipeline, and the flow ratio between the second bypass pipeline and the upper part of the fourth pipeline is 1:25-35.

[0018] The decarbon monoxide reactor is filled with at least one of a palladium-based catalyst and a platinum-based catalyst.

[0019] The technical solution to achieve the second purpose of the present invention is: the above tail gas treatment system is applied to the tail gas treatment of adipic acid production process. In the tail gas of adipic acid production process, nitrous oxide accounts for 35-45wt%, nitrogen monoxide accounts for 0.01-1wt%, and carbon monoxide accounts for 1-5wt%.

[0020] The technical solution for achieving the third object of the present invention is to provide a method for treating tail gas from a process for producing adipic acid, comprising the following steps:

[0021] 1) After the carbon monoxide in the tail gas is removed by the carbon monoxide removal process, the exhaust gas is sent to the nitrous oxide decomposition process through the feed flow to decompose the nitrous oxide therein;

[0022] In some feasible schemes, the catalyst used in the carbon monoxide removal process is selected from at least one of a palladium catalyst or a platinum catalyst. Specifically, the palladium catalyst or the platinum catalyst can be selected according to the specific process requirements. Preferably, the catalyst is a palladium catalyst or a platinum catalyst with an active temperature of 140 to 260°C. Optionally, the active temperature can be 140 to 160°C, 160 to 180°C, 180 to 200°C, 200 to 220°C, 220 to 240°C or 240 to 260°C.

[0023] In some feasible schemes, before step 1), the process further includes inputting compressed air as a system carrier gas into the nitrous oxide decomposition process, and when the pressure of the nitrous oxide decomposition system reaches 100 kPa, that is, when the process working condition is stable, the input of compressed air is stopped. It is worth noting that in this process, it is only necessary to input compressed air before the working condition is stable, and the gas generated by the method itself can subsequently maintain the range of nitrous oxide that the system can withstand, and can be stably maintained at 7-12 v%.

[0024] In some specific schemes, the tail gas is a tail gas containing nitrous oxide, nitric oxide and carbon monoxide, wherein nitrous oxide accounts for 35-45wt%, nitric oxide accounts for 0.01-1wt%, and carbon monoxide accounts for 1-5wt%. Under the important premise of maintaining long-term operation and low energy consumption (external production capacity), the high-content nitrous oxide tail gas emission can be maintained at 0.6v~0.18v%.

[0025] In a preferred embodiment, the feed stream includes a main feed stream and a bypass feed stream; wherein the main feed stream is sent to the nitrous oxide decomposition process after heat exchange with the discharge stream, and the bypass feed stream is directly sent to the nitrous oxide decomposition process. Preferably, the flow ratio of the main feed stream to the bypass feed stream is 1.6 to 10:1, preferably 4 to 6:1, for example, 1.6:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1. By regulating the main feed stream and the bypass feed stream, the dynamic balance between the feed temperature required for the nitrous oxide decomposition process and the full utilization of energy is ensured. Generally, the feed temperature of the nitrous oxide decomposition process needs to be maintained at 365-400°C.

[0026] In some feasible schemes, the tail gas is heated to 140-200°C before being sent to the decarbonation process. One of the factors for selecting the temperature is related to the active temperature of the catalyst used in the decarbonation process. Generally, the temperature can be raised to 140-160°C, 160-180°C or 180-200°C.

[0027] In some feasible schemes, after the tail gas is subjected to the carbon monoxide removal process, the exhaust gas temperature is 180-250°C, which can be selected as 180-200°C, 200-220°C, 220-240°C or 240-250°C.

[0028] 2) The exhaust gas from the nitrous oxide decomposition process is divided into two exhaust streams after heat exchange with the feed stream: the first exhaust stream is refluxed to the nitrous oxide decomposition process to make the concentration of nitrous oxide in the feed gas of the nitrous oxide decomposition process 7-12v%; the second exhaust stream is sent to the SCR process for SCR reaction and then discharged.

[0029] In a preferred embodiment, the flow ratio of the first discharge flow to the second discharge flow is 25-35:1, for example, 25:1, 28:1, 30:1, 32:1 or 35:1.

[0030] In a preferred embodiment, after the first discharge flow is heat exchanged, a branch discharge flow undergoes a pressurization process to become a pressurized flow, and the pressurized flow is divided into two pressurized flows: the first pressurized flow refluxes and is directly sent to the nitrous oxide decomposition process or is mixed with the feed flow and then sent to the nitrous oxide decomposition process; the second pressurized flow is directly sent to the SCR process or is sent to the SCR process after heat exchange or is merged with the second discharge flow and then sent to the SCR process. The two branch discharge flows are sent to the SCR process.

[0031] In a preferred embodiment, the pressure of the pressurized stream is 130-150 kPa, and 130 kPa, 135 kPa, 140 kPa, 145 kPa or 150 kPa can be selected. The flow ratio of the first pressurized stream to the second pressurized stream is 1:0-0.1, and the flow rate of the second pressurized stream cannot be too large, and is maintained at 1:0-0.1, preferably 1:0-0.05, for example 1:0, 1:0.01, 1:0.05, 1:0.08 or 1:0.1. Under the above ratio, it can meet the system adjustment requirements and ensure the effective power of the booster fan.

[0032] In a preferred embodiment, the flow ratio of the first branch discharge flow to the second branch discharge flow is 16-30:6-9, for example, 16:6, 16:7, 16:8, 16:9, 20:6, 20:7, 20:8, 20:9, 25:6, 25:7, 25:8, 25:9, 30:6, 30:7, 30:8 or 30:9.

[0033] By reasonable diversion and forming a cycle, the temperature, pressure and other working conditions of the nitrous oxide decomposition process and the SCR process can be guaranteed, the treatment effect of nitrous oxide can be guaranteed, and the excess energy can be used to generate power externally.

[0034] The above technical solution has the following beneficial effects:

[0035] 1. The tail gas treatment system of the present invention introduces a carbon monoxide removal reactor to remove reducing gas (carbon monoxide) in the tail gas, protect the catalyst in the nitrous oxide decomposition reactor, extend the service life of the catalyst in the nitrous oxide decomposition reactor, and further extend the operation cycle of the tail gas treatment system; in the tail gas treatment system of the present invention, the exhaust gas of the nitrous oxide decomposition reactor is subjected to heat exchange and cooling, and then pressurized by a booster fan, and then partially refluxed and mixed with the exhaust gas of the carbon monoxide removal reactor to dilute the concentration of nitrous oxide in the exhaust gas to meet the requirements of the downstream nitrous oxide decomposition reactor for intake air. In addition, the exhaust gas of the nitrous oxide decomposition reactor is subjected to a cyclic decomposition treatment to improve the decomposition rate of nitrous oxide in the tail gas; the remainder is sent to the SCR reactor, which also has a relatively high pressure to meet the requirements of the SCR reactor for intake air. On the basis of ensuring denitration, the amount of catalyst in the SCR reactor can be reduced and / or the size of the SCR reactor can be reduced.

[0036] 2. The exhaust gas treatment system of the present invention connects a first bypass pipeline in parallel to the low-temperature medium channel of the first heat exchanger, and sets a third valve to control the opening to control the flow ratio between the first bypass pipeline and the low-temperature medium channel of the first heat exchanger, thereby controlling the heat exchange amount of the carbon monoxide-removed exhaust gas in the first heat exchanger, and then controlling the intake temperature of the nitrous oxide decomposition reactor, thereby meeting the operating conditions of the nitrous oxide decomposition reactor, and has a simple structure and convenient maintenance.

[0037] 3. The exhaust gas treatment system of the present invention utilizes the exhaust gas of the nitrous oxide decomposition reactor as a high-temperature medium to heat the intake air of the nitrous oxide decomposition reactor, and diverts the exhaust gas to the third heat exchanger for heat exchange with water to generate steam for external energy supply, and cooperates with the downstream booster fan to increase the pressure and temperature of the air flow, thereby effectively utilizing the decomposition heat of nitrous oxide. In addition, the present invention can control the pressure increase and heat exchange amount of the exhaust gas after heat exchange and cooling in the first heat exchanger in the third heat exchanger and the booster fan by setting a second bypass pipeline and setting a fourth valve to control the opening, thereby meeting the pressure and temperature requirements of the diluted carbon monoxide removal exhaust gas and the SCR reactor intake air, and has a simple structure and is easy to maintain.

[0038] 4. The exhaust gas treatment system of the present invention designs the fifth pipeline as a circulation section and a feeding section, and arranges the downstream end of the circulation section upstream of the third heat exchanger (i.e., the upper section of the fourth pipeline), and the upstream end of the feeding section downstream of the third heat exchanger (i.e., the lower section of the fourth pipeline), so that the exhaust gas part that is 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 utilization rate of heat.

[0039] 5. The present invention first utilizes the carbon monoxide removal process to remove carbon monoxide in the tail gas and releases heat, and the exhaust gas is sent to the nitrous oxide decomposition process to decompose the nitrous oxide therein, and then the pressurized exhaust gas of the nitrous oxide decomposition process is used as the dilution carrier gas and the intake gas of the SCR reactor. By adopting the treatment method of the present invention, the system operation cycle reaches 7500-8200h, the nitrous oxide in the tail gas is maintained at 0.06-0.15v%, and the unit volume of tail gas produces 4096-5125kg / h of water vapor to the outside.

[0040] Further description is given below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a connection diagram of the present invention.

[0042] In the accompanying drawings, 1 is a decarbon monoxide reactor, 2 is a first heat exchanger, 3 is a nitrous oxide decomposition reactor, 4 is an SCR reactor, 5 is a booster fan, 6 is a first bypass pipeline, 7 is a reflux pipeline, 8 is a steam-water separator, 9 is an emergency venting pipeline, 10 is a second heat exchanger, 11 is a start-up heater, 12 is a third heat exchanger, 13 is a compressed air inlet, 14 is a second bypass pipeline, 101 is a first pipeline, 102 is a second pipeline, 103 is a third pipeline, 104 is a fourth pipeline, 105 is a fifth pipeline, 105a is a circulation section, 105b is a feeding section, a is a first valve, b is a second valve, c is a third valve, and d is a fourth valve. DETAILED DESCRIPTION

[0043] In the present invention, the catalyst loaded in the decarbon monoxide reactor can be selected from at least one of catalyst A, catalyst B or catalyst C, and the catalyst used in the N2O decomposer can be selected from catalyst D, specifically:

[0044] Wherein, catalyst A is: palladium catalyst, Pd / Al2O3, Pd loading is 1wt%, and its active temperature is 160-250°C;

[0045] Catalyst B is Pt / ZrO2-Al2O3, with a Pt loading of 1wt%, ZrO2 (0.4 mole)-Al2O3 (0.6 mole), and an active temperature of 150-230°C;

[0046] Catalyst C is Pt / Fe2O3, with a Pt loading of 1wt% and an active temperature of 140-180°C;

[0047] Catalyst D has a catalyst component molar ratio of nickel: copper: barium: neodymium: aluminum = 0.4:0.2:0.6:0.03:2, and a N2O decomposition rate of 72.3% to 98.4% at 375°C to 400°C.

[0048] The sources of the above catalysts A, B, C and D are not limited, as long as the active temperature is within the required range. They can be purchased or made at home, 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 roasting.

[0049] Example 1

[0050] See also Figure 1The tail gas treatment system includes a decarbon monoxide reactor 1, a first heat exchanger 2, a nitrous oxide decomposition reactor 3, an SCR reactor 4, and a booster fan 5. Among them, the decarbon monoxide reactor 1 can be filled with any one or more of catalyst A, catalyst B or catalyst C for catalytic removal of CO reaction, and the nitrous oxide decomposition reactor is filled with a catalyst D for catalytic decomposition of nitrous oxide. The material inlet of the decarbon monoxide reactor 1 is connected to the tail gas source through the first pipeline 101. In this embodiment, it also includes a steam-water separator 8, and the steam-water separator 8 is connected in series on the first pipeline 101. The first pipeline 101 is provided with an emergency venting pipeline 9, which is located upstream of the steam-water separator and is controlled to be opened and closed by the first valve a. Usually, a valve is also provided between the emergency venting 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 on 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. The downstream end of the high-temperature medium channel of the second heat exchanger 10 is provided with N2O and nitrogen oxide detection points. The material outlet of the decarbon monoxide reactor 1 is connected to the material inlet of the nitrous oxide decomposition reactor 3 through 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, which is used to heat the intake air entering the nitrous oxide decomposition reactor 3 when the system is started to meet the working condition requirements (when the system pressure reaches 100kpa, it is considered to meet the working condition requirements). After the system is stable, the start-up heater 11 stops working. The material outlet of the nitrous oxide decomposition reactor 3 supplies the booster fan 5 through 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, and the high temperature medium channel of the third heat exchanger 12 is connected in series to the fourth pipeline 104, and the fourth pipeline 104 is divided into the fourth pipeline upper section and the fourth pipeline lower section. The low temperature medium of the low temperature medium channel of the third heat exchanger 12 is warm water, and a compressed air inlet 13 is arranged on the fourth pipeline lower section. The compressed air inlet is located between the third heat exchanger 12 and the booster fan 5, and is controlled to open and close by the second valve b. The air outlet of the booster fan 5 is connected to the second pipeline 102 through the return pipeline 7, and the connection between the return pipeline 7 and the second pipeline 102 is located upstream of the first heat exchanger 2. Typically, a detection point is provided on the second pipeline 102 for detecting the concentration of nitrous oxide, and 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 .

[0051] The outlet end of the booster fan 5 also supplies the SCR reactor 4 through 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 end 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 the SCR reactor 4. Generally, valves are provided on the reflux pipeline 7, the circulation section 105a, and the feeding section 105b. Among them, by controlling the operating load of the booster fan 5 and the reflux amount of the reflux pipeline 7, the concentration requirement (7-12v%) of nitrous oxide at the detection point is met. Furthermore, it also includes a first bypass pipeline 6 , which is connected in parallel with the low-temperature medium channel of the first heat exchanger 2 , and a third valve c is provided on the first bypass pipeline 6 .

[0052] Furthermore, it also includes a second bypass pipeline 14, the upstream end of which is connected to the fourth pipeline 104 (specifically, downstream of the first heat exchanger 2 and upstream of the third heat exchanger 12, i.e., the upper part of the fourth pipeline), and the downstream end is connected to the fifth pipeline 105 and is located downstream of the third heat exchanger 12. Specifically, the downstream end of the second bypass pipeline 14 is connected to the feed section 105b, and a fourth valve d is provided on the second bypass pipeline 14. The second bypass pipeline 14 is a heated air flow for the intake of the SCR reactor 4, and the intake temperature of the SCR reactor 4 can be adjusted by controlling the flow rate of the second bypass pipeline 14.

[0053] It is worth noting that control valves can be set on each pipeline according to actual needs, and the flow rate can be adjusted by setting the system of this example and coordinating the control of the valve, so as to finally achieve self-sufficiency in energy consumption in the system and increase the system capacity. In addition, the role of catalysts A, B, and C is to catalyze the removal of CO or C organic matter, which the present invention fails to list in full. For example, other catalysts with similar functions and the same catalytic operating temperature as those listed in this application are also applicable to the present invention. The role of catalyst D is to catalyze the decomposition of nitrous oxide, which the present invention also fails to list in full. Other similar catalysts are also applicable.

[0054] In summary, the present invention introduces a decarbonation reactor to ensure the service life of the nitrous oxide decomposition catalyst. In addition, the arrangement of pipelines and valves makes the control of the entire system clear in priority and stable in operation, thereby more effectively ensuring the service life of the catalyst in each reactor.

[0055] Example 2

[0056] The method for treating tail gas by using the treatment system of Example 1, wherein the carbon monoxide removal reactor is filled with catalyst A, the nitrous oxide decomposition reactor is filled with catalyst D, and the space velocity in the carbon monoxide removal reactor is about 2000h -1 , the space velocity in the nitrous oxide decomposition reactor is about 1000h -1 . The steps include:

[0057] System start-up: Compressed air is introduced into the system through the compressed air inlet 13. After all systems are normal and contain air carrier gas, the booster fan 5 is started, and the air is circulated in a closed loop through the booster fan 5, i.e., a 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-boost fan 5 inlet. When the system pressure reaches 100 kPa, that is, the process condition is stable, the input of compressed air is stopped, and the startup heater 11 and / or the third heat exchanger 12 are used for initial heating.

[0058] The above completes the system startup, and then proceed to the following steps:

[0059] 1) The tail gas generated by the oxidation process of alcohol ketone or cyclohexanol with nitric acid to produce adipic acid is first passed through three packed towers connected in series to absorb nitrogen monoxide and nitrogen dioxide (a conventional process), and then the water vapor is separated from the tail gas by a steam-water separator 8 to obtain the tail gas.

[0060] In order to specifically illustrate the operation of this system, the tail gas (v / v) used has the following composition: 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);

[0061] 1-1) Exhaust gas at 9114.5Nm 3 / h After passing through the second heat exchanger 10, the temperature rises to 185.5°C, and the outlet gas of the SCR reactor 4 is used as the high-temperature medium of the second heat exchanger 10. Finally, after the NOx and N2O concentrations are tested to meet the standards, they are discharged through the vent pipe;

[0062] 1-2) The gas phase passes through the second heat exchanger 10 and enters the decarbon monoxide reactor 1, and the reactor outlet temperature is 245.7°C;

[0063] 1-3) The tail gas from the decarbon monoxide reactor 1 is mixed with the gas of the first pressurized stream output by the booster fan 5 to form a feed stream, and the flow rate of the first pressurized stream in the reflux line 7 is controlled so that the concentration of nitrous oxide in the mixed gas in the feed stream is controlled at 8.71v%. That is, the circulation section 105a is closed so that the flow rate of the second pressurized stream is 0;

[0064] 1-4) the feed stream is then branched into a main feed stream and a bypass feed stream, wherein the main feed stream is sent to the nitrous oxide decomposer 3 after heat exchange with the discharge stream, and the bypass feed stream is directly sent to the nitrous oxide decomposition process, and the flow ratio of the bypass feed stream to the main feed stream is 1:4, that is, the flow ratio of the first bypass pipeline 6 and the low-temperature medium channel of the first heat exchanger 2 is 1:4;

[0065] 2-1) The exhaust gas from the nitrous oxide decomposition reactor 3 is divided into a first discharge flow (upper section of the fourth pipeline) and a second discharge flow (second bypass pipeline) after heat exchange in the first heat exchanger 2, and the flow ratio between the second bypass pipeline 14 and the upper section of the fourth pipeline is controlled to be 1:35. The first discharge flow passes through the third heat exchanger 12, and the heat of the exhaust gas is used to convert hot water into steam. At this time, the low-pressure steam temperature is 165.3°C and the flow rate is 5125kg / h. The flow passing through the third heat exchanger 12 is transported to the booster fan through the lower section of the fourth pipeline as the inlet gas of the booster fan 5. After being compressed by the booster fan, a pressurized flow is obtained, and the temperature rises to 211.5°C and the pressure is 135KPa;

[0066] 2-2) The material flow after the booster fan 5 is divided into the first pressurized material flow and the second pressurized material flow. The first pressurized material flow completes the cycle of 1-3); the second pressurized material flow passes through the circulation section 105a and merges with the upper section of the fourth pipeline, 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°C) and pressure (maintained at 95-100Kpa) requirements of the SCR reactor. Among them, after leaving the third heat exchanger 12, the flow ratio of the lower section of the fourth pipeline and the feed section 105b is 22:8;

[0067] 2-3) The airflow fed into the SCR in the feed section 105b is 8Nm 3 / h ammonia and enters the SCR reactor 4 to react with ammonia to generate nitrogen. The tail gas discharged from the SCR reactor 4 is discharged after heat exchange in the second heat exchanger 10.

[0068] After testing, the temperature was 48.1℃, nitrous oxide was 0.06%, and nitrogen oxides (NOx) were 2.5mg / m 3 , the system can run continuously for 8200h when the air velocity and inlet temperature remain unchanged, and the low-pressure steam produced to the outside is 5125kg / h. The pressure difference of the SCR reactor is 0.5kpa, and the reactor flows smoothly, which reduces the burden on the pipeline diameter.

[0069] Example 3

[0070] The difference from Example 2 is that the decarbon monoxide reactor 1 is filled with catalyst B.

[0071] 1-1) Exhaust gas at 9114.5Nm 3 / h After passing through the second heat exchanger 10, the temperature rises to 172.8°C, and the outlet gas of the SCR reactor 4 is used as the high-temperature medium of the second heat exchanger 10. Finally, after the NOx and N2O concentrations are tested to meet the standards, they are discharged through the vent pipe;

[0072] 1-2) The gas phase passes through the second heat exchanger 10 and enters the decarbon monoxide reactor 1, and the reactor outlet temperature is 226.2°C;

[0073] 1-3) the tail gas from the decarbon monoxide reactor 1 is mixed with the gas of the first pressurized stream output by the booster fan 5 to form a feed stream, and the flow rate of the first pressurized stream in the reflux line 7 is controlled so that the concentration of nitrous oxide in the mixed gas in the feed stream is controlled at 9.12% by volume. That is, the flow rate ratio of the first pressurized stream to the second pressurized stream is 1:0.02;

[0074] 1-4) the feed stream is then branched into a main feed stream and a bypass feed stream, wherein the main feed stream is sent to the nitrous oxide decomposer 3 after heat exchange with the discharge stream, and the bypass feed stream is directly sent to the nitrous oxide decomposition process, and the flow ratio of the bypass feed stream to the main feed stream is 1:5, that is, the flow ratio of the first bypass pipeline 6 and the low-temperature medium channel of the first heat exchanger 2 is 1:5;

[0075] 2-1) The exhaust gas of the nitrous oxide decomposition reactor 3 is divided into a first discharge flow and a second discharge flow after heat exchange in the first heat exchanger 2, and the flow ratio between the second bypass pipeline 14 and the upper portion of the fourth pipeline is controlled to be 1:32. The first discharge flow passes through the third heat exchanger 12, and the heat of the exhaust gas is used to convert hot water into steam. At this time, the low-pressure steam temperature is 167.2°C and the flow rate is 5015kg / h. The flow passing through the third heat exchanger 12 is used as the inlet gas of the booster fan 5. After being compressed by the booster fan, a pressurized flow is obtained, and the temperature rises to 215.3°C and the pressure is 136KPa.

[0076] 2-2) The material flow passing through the booster fan 5 is divided into a first pressurized material flow and a second pressurized material flow, and the first pressurized material flow is used to complete the 1-3) cycle; the second pressurized material flow passes through the circulation section 105a and merges with the upper section of the fourth pipeline, and is sent to the upstream of the third heat exchanger 12 to circulate and be sent to the SCR reactor, thereby ensuring the inlet temperature (maintained at 180-220°C) and pressure (maintained at 95-100Kpa) requirements of the SCR reactor. Among them, after leaving the third heat exchanger 12, the flow ratio of the lower section of the fourth pipeline and the feed section 105b is 25:8.

[0077] 2-3) The tail gas fed into the SCR in the feeding section 105b and 8Nm 3 / h ammonia and enters the SCR reactor 4 to react with ammonia to generate nitrogen. The tail gas discharged from the SCR reactor 4 is discharged after heat exchange in the second heat exchanger 10. After detection, the temperature is 48.7°C, nitrous oxide is 0.10%, and nitrogen oxides (NOx) are 2.5mg / m 3 , the system can run continuously for 8300h when the air velocity and inlet temperature remain unchanged, and produce 5015kg / h of low-pressure steam to the outside.

[0078] Example 4

[0079] The difference from Example 2 is that the decarbon monoxide reactor 1 is filled with catalyst C.

[0080] 1-1) Exhaust gas at 9114.5Nm 3 / h After passing through the second heat exchanger 10, the temperature rises to 159.7°C, and the outlet gas of the SCR reactor 4 is used as the high-temperature medium of the second heat exchanger 10. Finally, after the NOx and N2O concentrations are tested to meet the standards, they are discharged through the vent pipe;

[0081] 1-2) The gas phase passes through the second heat exchanger 10 and enters the decarbon monoxide reactor 1, and the reactor outlet temperature is 181.5°C;

[0082] 1-3) the tail gas from the decarbon monoxide reactor 1 is mixed with the gas of the first pressurized stream output by the booster fan 5 to form a feed stream, and the flow rate of the first pressurized stream in the reflux line 7 is controlled so that the concentration of nitrous oxide in the mixed gas in the feed stream is controlled at 11.3% by volume. That is, the flow rate ratio of the first pressurized stream to the second pressurized stream is 1:0.06;

[0083] 1-4) The feed stream is then branched into a main feed stream and a bypass feed stream, wherein the main feed stream is sent to the nitrous oxide decomposer 3 after heat exchange with the discharge stream, and the bypass feed stream is directly sent to the nitrous oxide decomposition process, and the flow ratio of the bypass feed stream to the main feed stream is 1:6, that is, the flow ratio of the first bypass pipeline 6 and the low-temperature medium channel of the first heat exchanger 2 is 1:6. ;

[0084] 2-1) The exhaust gas of the nitrous oxide decomposition reactor 3 is divided into the first discharge flow and the second discharge flow after heat exchange in the first heat exchanger 2, and the flow ratio of the second bypass pipeline 14 to the upper part of the fourth pipeline is controlled to be 1:25. The ratio of the flow of the second bypass pipeline 14 to the sum of the flow of the fifth pipeline 105 and the fourth pipeline 104 is 1:30. The first discharge flow passes through the third heat exchanger 12, and the heat of the exhaust gas is used to convert hot water into steam. At this time, the low-pressure steam temperature is 159.1℃ and the flow rate is 4096kg / h. A part of the material flow passing through the third heat exchanger 12 is then used as the inlet gas of the booster fan 5. After being compressed by the booster fan, a pressurized material flow is obtained, and the temperature rises to 213.5℃ and the pressure is 135KPa. The other part enters the SCR.

[0085] 2-2) The material flow passing through the booster fan 5 is divided into a first pressurized material flow and a second pressurized material flow, and the first pressurized material flow completes the 1-3) cycle; the second pressurized material flow passes through the circulation section 105a and merges with the upper section of the fourth pipeline, and is sent to the upstream of the third heat exchanger 12 to circulate and be sent to the SCR reactor, thereby ensuring the inlet temperature (maintained at 180-220°C) and pressure (maintained at 95-100Kpa) requirements of the SCR reactor. Among them, after leaving the third heat exchanger 12, the flow ratio of the lower section of the fourth pipeline and the feed section 105b is 30:8.

[0086] 2-3) The tail gas fed into the SCR in the feeding section 105b and 8Nm 3 / h ammonia and enters the SCR reactor 4 to react with ammonia to generate nitrogen. The tail gas discharged from the SCR reactor 4 is discharged after heat exchange in the second heat exchanger 10. After detection, the temperature is 49.3°C, nitrous oxide is 0.15v%, and nitrogen oxides (NOx) are 2.5mg / m 3 , the system can run continuously for 7500h when the air velocity and inlet temperature remain unchanged, and produce 4096kg / h of low-pressure steam to the outside.

[0087] Comparative Example 1

[0088] The difference between the system used in this example and Example 2 is that no carbon monoxide removal reactor is added to the system, the other line connections remain unchanged, and the system can be maintained to operate normally. The nitrous oxide in the tail gas of the system is detected to be 0.25%, and the system can operate continuously for about 4000 hours when the air velocity and inlet temperature remain unchanged.

[0089] Comparative Example 2

[0090] The system used in this example is different from that in Example 2 in that in step 1-3), the flow ratio of the first pressurized stream to the second pressurized stream 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 requirement.

[0091] Comparative Example 3

[0092] The difference between the system used in this example and Example 2 is that in step 1-4), the flow ratio between the first bypass pipeline 6 and 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°C, and the continuous operation is 5000h, and the nitrogen oxide (NOx) is 3.2mg / m 3 The nitrous oxide content in the tail gas is 0.31v%.

[0093] Comparative Example 4

[0094] The difference between the system used in this example and Example 2 is that in step 2-1), the flow ratio of the second bypass pipeline 14 to the upper section of the fourth pipeline is controlled to be 1:20, and the nitrogen oxide (NOx) is 3.5 mg / m 3 , running continuously for 6000h, the nitrous oxide content in the exhaust gas is 0.25v%.

Claims

1. A tail gas treatment system, characterized in that: It comprises 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 decarbon monoxide reactor (1) is connected to the tail gas source via a first pipeline (101), and the material outlet of the decarbon monoxide reactor (1) is connected to the material inlet of the nitrous oxide decomposition reactor (3) via a 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) 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). The gas outlet end of the booster fan (5) is connected to the second pipeline (102) via the return pipeline (7) and supplies 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), the steam-water separator (8) is connected in series to the first pipeline (101), the first pipeline (101) is provided with an emergency venting pipeline (9), and the opening and closing of the pipeline is controlled by a first valve (a); And / or, further comprising a second heat exchanger (10), wherein a low-temperature medium channel of the second heat exchanger (10) is connected in series to the first pipeline (101), and a high-temperature medium channel of the second heat exchanger (10) is connected to a material outlet of the SCR reactor (4); And / or, a compressed air inlet (13) is provided on the fourth pipeline (104), and its opening and closing is controlled by the second valve (b); And / or, it further comprises a start-up heater (11), wherein the low-temperature medium channel of the first heat exchanger (2) is connected to the material inlet of the nitrous oxide decomposer (3) via the start-up heater (11).

3. The exhaust gas treatment system according to claim 1, characterized in that: The invention also comprises a first bypass pipeline (6), wherein the first bypass pipeline (6) is connected in parallel with the low-temperature medium channel of the first heat exchanger (2), a third valve (c) is arranged on the first bypass pipeline (6), and the flow ratio between the first bypass pipeline (6) and the low-temperature medium channel of the first heat exchanger (2) is 1:1.6-10.

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

5. The tail gas treatment system according to claim 4, characterized in that: The fifth pipeline (105) comprises a circulation section (105a) and a supply section (105b); the upstream end of the circulation section (105a) is connected to the air 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 supply section (105b) is connected to the lower section of the fourth pipeline, and the downstream end supplies the SCR reactor (4); the flow ratio of the return pipeline (7) to the circulation section (105a) is 1:0-0.

1.

6. The tail gas treatment system according to claim 5, characterized in that: The invention also comprises a second bypass pipeline (14), wherein the upstream end of the second bypass pipeline (14) is connected to the upper section of the fourth pipeline, and the downstream end is connected to the fifth pipeline (105) and is located downstream of the third heat exchanger (12); a fourth valve (d) is arranged on the second bypass pipeline (14); the flow ratio between the second bypass pipeline (14) and the upper section of the fourth pipeline is 1:25-35; and the flow ratio between the lower section of the fourth pipeline and the feed section (105b) is 16-30:6-9.

7. Use of the tail gas treatment system according to any one of claims 1 to 6 in the treatment of tail gas in adipic acid production process.

8. A method for treating tail gas in a process for producing adipic acid, characterized in that: The following steps are involved: 1) After the carbon monoxide in the tail gas is removed by the carbon monoxide removal process, the exhaust gas is sent to the nitrous oxide decomposition process through the feed flow to decompose the nitrous oxide in the tail gas; 2) The exhaust gas from the nitrous oxide decomposition process is divided into two exhaust streams after heat exchange with the feed stream: the first exhaust stream is refluxed to the nitrous oxide decomposition process to make the concentration of nitrous oxide in the feed gas of the nitrous oxide decomposition process 7-12v%; the second exhaust stream is sent to the SCR process for SCR reaction and then discharged.

9. The tail gas treatment method according to claim 8, characterized in that: It also includes at least one of the following technical features: 1a) The catalyst used in the carbon monoxide removal step is selected from at least one of a palladium-based catalyst and a platinum-based catalyst; 1b) Before step 1), the method further includes inputting compressed air into the nitrous oxide decomposition process as a system carrier gas, and stopping the input of compressed air after the working condition of the nitrous oxide decomposition process is stable; 1c) tail gas includes nitrous oxide, nitric oxide and carbon monoxide, wherein nitrous oxide accounts for 35-45wt%, nitric oxide accounts for 0.01-1wt%, and carbon monoxide accounts for 1-5wt%; 1d) Step 1) The tail gas is heated to 140-200°C and then sent to the carbon monoxide removal process; 1e) After the exhaust gas is subjected to the carbon monoxide removal process, the exhaust gas temperature is 180-250°C; 2a) the feed stream comprises a main feed stream and a bypass feed stream, wherein the main feed stream is sent to the nitrous oxide decomposition process after heat exchange with the discharge stream, and the bypass feed stream is directly sent to the nitrous oxide decomposition process; 2b) The first discharge flow is divided into a branch discharge flow and a second branch discharge flow after heat exchange, the branch discharge flow becomes a pressurized flow after a pressurization process, and the pressurized flow is divided into two pressurized flows: the first pressurized flow reflux is directly sent to the nitrous oxide decomposition process or is mixed with the feed flow and then sent to the nitrous oxide decomposition process; the second pressurized flow is directly sent to the SCR process or sent to the SCR process after heat exchange or merged with the second discharge flow and sent to the SCR process; the second branch discharge flow is sent to the SCR process; 2c) The flow ratio of the first discharge flow to the second discharge flow is 25-35:1; 2d) The feed temperature of the nitrous oxide decomposition step is 365-400°C.

10. The tail gas treatment method according to claim 9, characterized in that: In technical feature 1a), the active temperature of the catalyst is 140 to 260°C; And / or, in technical feature 2a), the flow ratio of the main feed flow to the bypass feed flow is 1.6 to 10:

1. And / or, in technical feature 2b), the pressure of the pressurized stream is 130-150 kPa; and / or, in technical feature 2b), the flow ratio of the first pressurized stream to the second pressurized stream is 1:0-0.1; And / or, in technical feature 2b), the flow ratio of the first branch discharge flow to the second branch discharge flow is 16-30:6-9.

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