Apparatus and method for treating ammonia oxidation reaction tail gas

Abstract

The application provides a kind of ammonia oxidation reaction tail gas processing device and processing method, the processing device includes the absorption unit, CO2-HCN removal unit and ammonia stripping unit connected in sequence;The ammonia stripping unit is also independently connected with the absorption unit and CO2-HCN removal unit respectively;The processing method comprises: ammonia oxidation reaction tail gas is imported into absorption tower, and tower kettle obtains absorption liquid containing NH3, HCN and CO2;The absorption liquid is removed gas phase CO2 at the top of CO2-HCN removal tower, and HCN is hydrolyzed in tower kettle, to obtain tower kettle liquid;The obtained tower kettle liquid enters ammonia stripping tower, and the purity of ammonia gas obtained at the top is ≥99wt%, and the wastewater obtained in tower kettle is recycled;The processing method has simple process flow, can recover NH3 in ammonia oxidation reaction tail gas with high purity, improve ammonia oxidation reaction raw material utilization rate, reduce the emission of tail gas and wastewater, and has good economic benefits.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tail gas treatment, and particularly relates to a device and method for treating tail gas of an ammonia oxidation reaction. BACKGROUND

[0002] The ammonia oxidation reaction is an important route for synthesizing nitrile chemicals such as acrylonitrile and isophthalonitrile, but the reaction tail gas contains excessive NH3 in the reaction raw materials and HCN and CO2 generated by the side reaction, which is difficult to treat. If it is directly discharged into the plant-wide waste gas treatment system, a large amount of NH3 will be lost, resulting in low raw material utilization and increased production cost. In the existing NH3 recovery process, CO2 cannot be removed to recover high-purity NH3, which limits the recycling and reuse of the recovered NH3 to some extent. At the same time, due to the high toxicity of HCN, the emission standard is strict. If electrolysis or hydrogen peroxide oxidation is used to break HCN, on the one hand, the fixed investment of equipment is high, and on the other hand, the decomposition reaction will occur during the hydrogen peroxide oxidation process to generate O2, increasing the risk of system combustion and explosion.

[0003] CN101491747A discloses a method for treating isophthalonitrile production waste gas, comprising the following steps:

[0004] (1) The waste gas from the isophthalonitrile production line first enters a pretreater to remove impurities therein: (2) enters a heat exchanger: (3) enters a catalytic combustion furnace for low-temperature catalytic combustion, and hydrogen cyanide is selectively oxidized by the catalyst into non-toxic nitrogen, carbon dioxide and water, and ammonia is retained: (4) the waste gas after decyanation enters a heat exchanger to preheat the waste gas to be treated, and itself is cooled: (5) enters a water cooler to be cooled to normal temperature, and the cooled decyanation ammonia-containing waste gas is introduced into an ammonia absorption tower, ammonia is absorbed by the sprayed sulfuric acid solution at the top, and ammonium sulfate is generated and recovered, thereby completing the treatment of the isophthalonitrile production waste gas. This method uses combustion method to remove hydrogen cyanide, which has high energy consumption and high investment, and cannot effectively remove CO2 to recover high-purity ammonia.

[0005] CN112439302A discloses a tail gas treatment method in a propylene nitrile production system, comprising the following steps: a. The tail gas generated in the propylene nitrile production system is sent to an absorption tower for absorption treatment after being washed or cooled and separated; b. The tail gas after absorption by the absorption tower is discharged to a tail gas treatment device for tail gas treatment, and the tower kettle liquid in the absorption tower is pumped to a recovery tower as rich water to further desorb propylene nitrile, hydrocyanic acid and acetonitrile; c. The tower kettle liquid in the recovery tower is pumped to the absorption tower as poor water to further absorb propylene nitrile and other organic substances. This method washes and absorbs the ammonia in the tail gas, but does not deeply treat the CO2 and HCN contained therein, resulting in a large amount of impurities in the recovered ammonia-containing solution, which cannot be effectively utilized.

[0006] In summary, how to provide a safe and effective removal of ammonia oxidation reaction tail gas of CO2 and HCN, and recovery of high purity NH3 processing method become the current urgent technical problems. SUMMARY

[0007] In view of the problems existing in the prior art, the purpose of the present application is to provide a kind of ammonia oxidation reaction tail gas processing device and processing method, the processing device is designed to the problem that NH3 and HCN are difficult to handle in process tail gas CO2-HCN removal unit of HCN decomposition and CO2 removal is integrated, and it is optimized with absorption unit and ammonia stripping unit Process, thereby safely and efficiently recovering high-purity ammonia, and the cost is relatively low, and has good economic benefits.

[0008] To achieve this purpose, the present application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a kind of ammonia oxidation reaction tail gas processing device, the processing device includes absorption unit, CO2-HCN removal unit and ammonia stripping unit connected in sequence;

[0010] The ammonia stripping unit is also independently connected with the absorption unit and CO2-HCN removal unit.

[0011] The following is a preferred technical solution of the present application, but not as a limitation of the technical solutions provided by the present application, through the following technical solutions, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0012] As a preferred technical solution of the present application, the absorption unit includes absorption tower, first external circulation pump and external circulation cooler connected in sequence.

[0013] Preferably, the bottom of the absorption tower is connected with the first external circulation pump.

[0014] As a preferred technical solution of the present application, the CO2-HCN removal unit includes CO2-HCN removal tower, second external circulation pump, first reboiler and filter.

[0015] Preferably, the bottom of the CO2-HCN removal tower is connected with the first reboiler through the second external circulation pump, and the second external circulation pump is connected with the ammonia stripping unit through the filter.

[0016] Preferably, the first external circulation pump is connected with the CO2-HCN removal tower.

[0017] Preferably, the CO2-HCN removal tower includes a plate tower.

[0018] Preferably, the tray type of the plate column includes any one of baffle tray, bubble cap tray or float valve tray.

[0019] Preferably, the filter precision is ≤0.1 μm, such as 0.02 μm, 0.04 μm, 0.06 μm, 0.08 μm or 0.1 μm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0020] As a preferred technical solution of the present application, the ammonia evaporation unit comprises an ammonia evaporation column, a third external circulation pump, a condenser, a second reboiler and a phase separator.

[0021] Preferably, the liquid phase outlet of the filter is connected to the ammonia evaporation column, the bottom of the ammonia evaporation column is connected to the second reboiler through the third external circulation pump, and the top of the ammonia evaporation column is connected to the phase separator through the condenser.

[0022] Preferably, an ammonia gas collecting pipeline is arranged between the condenser and the phase separator.

[0023] Preferably, the phase separator is further connected to an organic phase liquid pump.

[0024] Preferably, the ammonia evaporation column comprises a plate column.

[0025] Preferably, the tray type of the plate column includes bubble cap tray or float valve tray.

[0026] As a preferred technical solution of the present application, the third external circulation pump is further connected to the top of the CO2-HCN removal column and the top of the absorption column, respectively and independently.

[0027] In the second aspect, the present application provides a treatment method of ammonia oxidation reaction tail gas, which is performed by using the treatment device of the first aspect, and comprises the following steps:

[0028] (1) passing the ammonia oxidation reaction tail gas into the absorption unit to obtain absorption liquid and gas containing NH3, HCN and CO2;

[0029] (2) delivering the absorption liquid containing NH3, HCN and CO2 obtained in step (1) to the CO2-HCN removal unit to remove gaseous CO2 and hydrolyze HCN, thereby obtaining column still liquid;

[0030] (3) delivering the column still liquid obtained in step (2) to the ammonia evaporation unit after filtration to obtain ammonia gas and waste water;

[0031] Part of the waste water is returned to the absorption unit, and part of the waste water is returned to the CO2-HCN removal unit.

[0032] In the present application, the treatment method first absorbs NH3, HCN and CO2 gas, and then the obtained absorption liquid enters the CO2-HCN removal unit, and the removal of gaseous CO2 and the hydrolysis of HCN are realized in the same unit, thereby avoiding the safety problem caused by the emission of highly toxic HCN into the environment, and compared with the existing electrolysis or hydrogen peroxide oxidation treatment technology, the cost is low, the risk of combustion and explosion is eliminated, the undecomposed HCN oligomers are filtered out through the filter, then high-purity NH3 is recovered through the ammonia evaporation unit and utilized, and the economic benefit of the whole system operation is improved; and the wastewater produced by the ammonia evaporation unit is recycled for resource utilization, which can further improve the ammonia recovery rate and economy. In addition, the treatment method also reduces energy consumption through reasonable planning and utilization of heat, and has good application prospect.

[0033] As a preferred technical solution of the present application, the treatment method more specifically comprises:

[0034] (1) passing the ammonia oxidation reaction tail gas into an absorption tower to obtain a gas containing HCN and NH3 at the top of the tower and an absorption liquid containing NH3, HCN and CO2 at the bottom of the tower;

[0035] Part of the obtained absorption liquid is returned to the absorption tower after cooling; another part is preheated and then sent to the CO2-HCN removal tower;

[0036] (2) removing gaseous CO2 at the top of the CO2-HCN removal tower and hydrolyzing HCN at the bottom of the tower to obtain tower bottom liquid from the absorption liquid obtained in step (1);

[0037] Part of the obtained tower bottom liquid is returned to the CO2-HCN removal tower after heat exchange; another part is filtered and then sent to the ammonia evaporation tower;

[0038] (3) performing ammonia evaporation operation in the ammonia evaporation tower with the tower bottom liquid obtained in step (2), and obtaining ammonia gas and liquid phase after condensation from the gas phase at the top of the tower; the obtained liquid phase is subjected to phase separation operation, and the water phase is returned to the ammonia evaporation tower, and the organic phase is discharged;

[0039] Wastewater is obtained at the bottom of the tower, and the obtained wastewater is divided into three parts, the first part is returned to the ammonia evaporation tower after heating, the second part enters the top of the CO2-HCN removal tower, and the third part enters the top of the absorption tower.

[0040] As a preferred technical solution of the present application, the composition of the ammonia oxidation reaction tail gas in step (1) includes: NH3 0.3-10wt%, such as 0.3wt%, 1wt%, 2wt%, 4wt%, 6wt%, 8wt% or 10wt% and the like; HCN 0.05-2.0wt%, such as 0.05wt%, 0.1wt%, 0.5wt%, 1.0wt%, 1.5wt% or 2.0wt% and the like; CO2 0.01-3.0wt%, such as 0.01wt%, 0.1wt%, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% or 3.0wt% and the like; other substances 85-99.64wt%, such as 85wt%, 87wt%, 89wt%, 91wt%, 93wt%, 95wt%, 97wt% or 99.64wt% and the like. The selection of the above values is not limited to the listed values, and other values not listed within the respective value range are also applicable.

[0041] Preferably, the other substances include any one or a combination of at least two of CO, H2O, N2, O2, mononitrile organic compounds or dinitrile organic compounds.

[0042] In the present application, the mononitrile organic compounds include acrylonitrile, benzonitrile or m-tolunitrile, etc.; and the dinitrile organic compounds include m-phthalonitrile, etc.

[0043] Preferably, the content of the organic compounds in the ammonia oxidation reaction tail gas is not more than 2wt%, such as 0.2wt%, 0.5wt%, 1wt%, 1.5wt% or 2wt% and the like, but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0044] Preferably, the absorbent used in the absorption tower in step (1) includes water.

[0045] In the present application, the main body of the absorbent is water, and the content of water is not less than 98wt%. However, since a part of the wastewater in the ammonia evaporation unit will return to the absorption unit for use as an absorbent, the absorbent will also include, but is not limited to, at least one of CO2, NH3, mononitrile organic compounds or dinitrile organic compounds.

[0046] Preferably, under standard conditions, the volume ratio of the ammonia oxidation reaction tail gas to the absorbent is (20-2500):1, 20:1, 50:1, 100:1, 200:1, 300:1, 4001, 500:1, 600:1, 800:1, 1000:1, 1500:1, 2000:1 or 2500:1 and the like, but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0047] Preferably, the operating pressure of the absorption tower in step (1) is 0.05-1.5 MPaG, for example 0.50 MPaG, 0.1 MPaG, 0.5 MPaG, 0.8 MPaG, 1.0 MPaG, 1.2 MPaG, 1.5 MPaG, etc., but not limited to the listed values, and other values not listed within the range are also applicable.

[0048] Preferably, the content of HCN and NH3 in the gas containing HCN and NH3 in step (1) is not more than 1 ppm, for example 0.1 ppm, 0.2 ppm, 0.5 ppm, 0.8 ppm, or 1 ppm, etc., and the selection of the above values is not limited to the listed values, and other values not listed within the range are also applicable.

[0049] As a preferred technical solution of the present application, the temperature of the absorption liquid in step (1) reaches 60-100℃ after preheating, for example 60℃, 70℃, 80℃, 90℃, or 100℃, etc., but not limited to the listed values, and other values not listed within the range are also applicable.

[0050] Preferably, the operating pressure of the CO2-HCN removal tower in step (2) is 0.05-2.0 MPaG, for example 0.05 MPaG, 0.1 MPaG, 0.3 MPaG, 0.5 MPaG, 1.0 MPaG, 1.1 MPaG, 1.5 MPaG, or 2.0 MPaG, etc., but not limited to the listed values, and other values not listed within the range are also applicable.

[0051] In the present application, the operating pressure of the CO2-HCN removal tower is particularly important for the removal effect of CO2 and HCN. If the pressure is too low, HCN cannot be fully hydrolyzed and removed; if the pressure is too high, the CO2-HCN removal effect will be poor, and the operating temperature needs to be correspondingly increased to achieve the ideal removal effect, but this will also significantly increase energy consumption and unnecessarily increase equipment investment.

[0052] The reaction equation of HCN hydrolysis is as follows:

[0053] HCN + 2H2O → HCOOH + NH3

[0054] Preferably, the operating temperature of the tower kettle of the CO2-HCN removal tower in step (2) is ≥110℃, for example 110℃, 120℃, 150℃, 170℃, 190℃, 200℃, 210℃, or 220℃, etc., but not limited to the listed values, and other values not listed within the range are also applicable.

[0055] Preferably, the gaseous phase in the overhead of the CO2-HCN removal column in step (2) comprises: CO2≥85wt%, such as 85wt%, 87wt%, 89wt%, 91wt%, 92wt%, 95wt% or 98wt%, etc.; H2O≤10wt%, such as 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, etc.; NH3≤5wt%, such as 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, etc. The selection of the above values is not limited to the listed values, and other values not listed within the respective value range are also applicable.

[0056] Preferably, after the column bottom liquid in step (2) is filtered, the content of HCN is ≤1ppm, such as 0.1ppm, 0.2ppm, 0.5ppm, 0.8ppm or 1ppm, etc. The selection of the above values is not limited to the listed values, and other values not listed within the respective value range are also applicable.

[0057] As a preferred technical solution of the present application, the operating pressure of the ammonia stripping column in step (3) is 0.2-3.0MPaG, such as 0.2MPaG, 0.5MPaG, 0.8MPaG, 1.1MPaG, 1.5MPaG, 2.0MPaG, 2.5MPaG or 3.0MPaG, etc., but not limited to the listed values, and other values not listed within the value range are also applicable.

[0058] In the present application, the operating pressure of the ammonia stripping column has an important influence on the purity of the recovered ammonia gas. If the operating pressure is too low, it will result in a decrease in the purity of the ammonia gas recovered at the top of the column; if the operating pressure is too high, it will result in unnecessary increases in energy consumption and equipment investment costs.

[0059] Preferably, the temperature of the condensation in step (3) is 30-50℃, such as 30℃, 35℃, 40℃, 45℃ or 50℃, etc., but not limited to the listed values, and other values not listed within the value range are also applicable.

[0060] In the present application, the condensation temperature needs to be controlled. If the temperature is too high, it will result in a decrease in the purity of ammonia in the gas phase; if the temperature is too low, it will result in unnecessary increases in energy consumption and equipment investment costs.

[0061] Preferably, the reflux ratio of the aqueous phase reflux in step (3) is 1-10, such as 1, 3, 5, 7, 9 or 10, etc., but not limited to the listed values, and other values not listed within the value range are also applicable.

[0062] In the present application, in order to ensure the purity of the recovered ammonia gas, the reflux ratio of the ammonia stripping tower also needs to be controlled. If the reflux ratio is too low, the purity of the ammonia gas collected at the top of the tower will be reduced; if the reflux ratio is too high, the energy consumption and the unnecessary increase in equipment investment cost will be caused.

[0063] Preferably, the ammonia gas obtained in step (3) is reused in the ammonia oxidation reaction unit, and the purity is ≥ 99wt%, such as 99wt%, 99.1wt%, 99.2wt%, 99.3wt%, 99.4wt%, 99.5wt% or 99.6wt%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0064] Preferably, the ammonia content in the wastewater obtained from the tower bottom of step (3) is ≤ 100ppm, such as 10ppm, 20ppm, 30ppm, 40ppm, 50ppm, 60ppm, 70ppm, 80ppm, 90ppm or 00ppm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0065] Preferably, the second part of the wastewater in the wastewater obtained from the tower bottom of step (3) accounts for 10-30wt% of the total, such as 10wt%, 15wt%, 20wt%, 25wt% or 30wt%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0066] In the present application, a part of the wastewater obtained from the tower bottom of the ammonia stripping tower is returned to the CO2-HCN removal tower, which can effectively reduce the content of ammonia in the gas phase at the top of the CO2-HCN removal tower, but the amount of return needs to be controlled. If the amount of return is too small, the content of ammonia in the gas phase at the top will increase, thereby causing the loss of ammonia to increase; if the amount of return is too large, in order to ensure the removal effect of CO2 and HCN, the energy consumption of the tower will increase significantly.

[0067] In addition, in the wastewater obtained from the tower bottom of step (3), the first part of the wastewater accounts for 8-20wt% of the total, and the third part accounts for 10-80wt% of the total wastewater.

[0068] Compared with the prior art, the present application has the following beneficial effects:

[0069] (1) The treatment device of the present application is designed to solve the problem of difficult treatment of NH3 and HCN in process tail gas, and combines an absorption unit and an ammonia stripping unit to design a removal unit integrating HCN decomposition and CO2 removal, and the energy is integrated through the cross heat exchange of cold and hot streams. On the basis of safely and efficiently treating the tail gas, the energy consumption of the device is greatly reduced, and the investment cost is low.

[0070] (2) The processing method described in this invention has a simple process flow and can recover NH3 in the tail gas of ammonia oxidation reaction with high purity, improve the utilization rate of raw materials for ammonia oxidation reaction, reduce tail gas emissions, and has good economic benefits. Attached Figure Description

[0071] Figure 1 This is a schematic diagram of the operation process of an ammonia oxidation reaction tail gas treatment device provided in Embodiment 1 of the present invention.

[0072] Among them, 1-absorption unit, 11-absorption tower, 12-first external circulation pump, 13-external circulation cooler, 2-CO2-HCN removal unit, 21-CO2-HCN removal tower, 22-second external circulation pump, 23-first reboiler, 24-filter, 3-ammonia stripping unit, 31-ammonia stripping tower, 32-third external circulation pump, 33-condenser, 34-second reboiler, 35-phase separator, 36-organic phase discharge pump.

[0073] Arrows indicate the direction of material flow. Detailed Implementation

[0074] To better illustrate the present invention and facilitate understanding of its technical solutions, the present invention is further described in detail below. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0075] In one specific embodiment, the present invention provides a treatment device for tail gas from an ammonia oxidation reaction, the treatment device comprising an absorption unit 1, a CO2-HCN removal unit 2, and an ammonia stripping unit 3 connected in sequence.

[0076] The ammonia stripping unit 3 is also independently connected in a loop with the absorption unit 1 and the CO2-HCN removal unit 2.

[0077] Furthermore, the absorption unit 1 includes an absorption tower 11, a first external circulation pump 12, and an external circulation cooler 13 that are sequentially and circulated together; the bottom of the absorption tower 11 is connected to the first external circulation pump 12.

[0078] Furthermore, the CO2-HCN removal unit 2 includes a CO2-HCN removal tower 21, a second external circulation pump 22, a first reboiler 23, and a filter 24.

[0079] Furthermore, the bottom of the CO2-HCN removal tower 21 is connected to the first reboiler 23 via the second external circulation pump 22, and the second external circulation pump 22 is also connected to the ammonia stripping unit 3 via the filter 24.

[0080] Further, the first external circulation pump 12 is connected with the CO2-HCN removal tower 21.

[0081] Further, the CO2-HCN removal tower 21 comprises a plate tower; the plate type of the plate tower comprises any one of a baffle plate, a bubble cap plate or a float valve plate.

[0082] Further, the filter 24 has a filtering precision of ≤0.1 μm.

[0083] Further, the ammonia evaporation unit 3 comprises an ammonia evaporation tower 31, a third external circulation pump 32, a condenser 33, a second reboiler 34 and a phase separator 35.

[0084] Further, the liquid phase outlet of the filter 24 is connected with the ammonia evaporation tower 31, the bottom of the ammonia evaporation tower 31 is connected with the second reboiler 34 through the third external circulation pump 32, and the top of the ammonia evaporation tower 31 is connected with the phase separator 35 through the condenser 33.

[0085] Further, an ammonia gas collecting pipeline is arranged between the condenser 33 and the phase separator 35.

[0086] Further, the phase separator 35 is further connected with an organic phase liquid pump 36.

[0087] Further, the ammonia evaporation tower 31 comprises a plate tower; the plate type of the plate tower comprises a bubble cap plate or a float valve plate.

[0088] Further, the third external circulation pump 32 is further connected with the top of the CO2-HCN removal tower 21 and the top of the absorption tower 11 respectively and independently.

[0089] In the following specific embodiments, the components of the tail gas and the overhead gas phase are analyzed and detected by using a gas chromatography method, the ammonia content in the waste water is detected by using a titration method, and the HCN content is detected by using a spectrophotometry method.

[0090] The following are typical but non-limiting embodiments of the present application:

[0091] Embodiment 1:

[0092] The present embodiment provides a treatment device for ammonia oxidation reaction tail gas, which is based on the treatment device in the specific embodiments, wherein:

[0093] The plate type of the CO2-HCN removal tower 21 is a baffle plate;

[0094] The filtering precision of the filter 24 is 0.1 μm;

[0095] The tray type of the ammonia stripping column 31 is a bubble cap tray.

[0096] The present embodiment also provides a treatment method for the tail gas of the ammoxidation reaction, which is performed by using the treatment device described above, and a schematic diagram of the operation process is shown in Figure 1 The treatment method comprises the following steps:

[0097] (1) The tail gas from the reaction unit in the production process of isophthalonitrile is introduced into the absorption tower 11, wherein the specific composition of the tail gas is shown in Table 1; the operating pressure of the absorption tower 11 is controlled to be 0.15 MPaG, the water content in the absorbent is 99 wt%, the volume ratio of the tail gas (standard condition) to the absorbent is 500:1, and the contents of HCN and NH3 in the gas phase obtained at the top of the tower are both less than 0.5 ppm;

[0098] Part of the absorption liquid obtained at the tower bottom is returned to the absorption tower 11 after being cooled, so that the external circulation amount is 10 times the amount of the absorbent, and the temperature at the tower bottom is controlled to be 15℃; another part is preheated to 100℃ and then delivered to the CO2-HCN removal tower 21;

[0099] (2) The operating pressure of the CO2-HCN removal tower 21 is controlled to be 0.8 MPaG, the operating temperature at the tower bottom is controlled to be 170℃, the composition of the gas phase obtained at the top of the tower is CO291 wt%, H2O 7 wt% and NH3 2 wt%;

[0100] Part of the liquid obtained at the tower bottom is returned to the CO2-HCN removal tower 21 after heat exchange, and the temperature at the tower bottom is controlled; another part is filtered and then used to preheat the absorption liquid delivered to the CO2-HCN removal tower 21, and then delivered to the ammonia stripping column 31;

[0101] (3) The operating pressure of the ammonia stripping column 31 is controlled to be 1.1 MPaG, the condensing temperature is controlled to be 50℃, the reflux ratio is controlled to be 5, and the purity of NH3 collected at the top of the tower is controlled to be 99.5 wt%, which is reused to the ammoxidation reaction unit; the wastewater collected at the tower bottom contains 100 ppm of ammonia and 0.9 ppm of HCN, and the wastewater is divided into three parts, the first part (20 wt%) is returned to the ammonia stripping column 31 after being heated, and the temperature at the tower bottom is controlled; the second part (10 wt%) is introduced into the top of the CO2-HCN removal tower 21, and the third part (70 wt%) is introduced into the top of the absorption tower 11.

[0102] Table 1

[0103] Mass fraction / wt% [NH3] 2.5 HCN 1.0 O2 2.1 CO2 1.4 CO 0.7 H2O 1.3 [N2] 90.2 Organics 0.8

[0104] Embodiment 2:

[0105] The present embodiment provides a treatment device for the tail gas of the ammoxidation reaction, which is based on the treatment device in the specific embodiment, and wherein:

[0106] The tray type of the CO2-HCN removal tower 21 is a bubble cap tray;

[0107] The filtering precision of the filter 24 is 0.08 μm;

[0108] The tray type of the ammonia stripping tower 31 is a float valve tray.

[0109] The embodiment also provides a treatment method of the ammonia oxidation reaction tail gas, which is performed by using the treatment device.

[0110] (1) The tail gas from the reaction unit in the acrylonitrile production process is introduced into the absorption tower 11, wherein the specific composition of the tail gas is shown in Table 2; the operating pressure of the absorption tower 11 is controlled to be 0.05 MPaG, the water content in the absorbent is 98 wt%, the volume ratio of the tail gas (standard condition) to the absorbent is 2000:1, and the HCN and NH3 contents in the gas phase obtained at the top of the tower are both less than 1 ppm;

[0111] Part of the absorption liquid obtained at the tower kettle is returned to the absorption tower 11 after being cooled, so that the external circulation amount is 50 times the amount of the absorbent, and the temperature at the tower kettle is controlled to be 20℃; another part of the absorption liquid is preheated to 60℃ and then transported to the CO2-HCN removal tower 21;

[0112] (2) The operating pressure of the CO2-HCN removal tower 21 is controlled to be 0.3 MPaG, the operating temperature at the tower kettle is controlled to be 120℃, the gas phase composition obtained at the top of the tower is 88 wt% of CO2, 8 wt% of H2O and 4 wt% of NH3;

[0113] Part of the liquid obtained at the tower kettle is returned to the CO2-HCN removal tower 21 after heat exchange, and the temperature at the tower kettle is controlled; another part of the liquid is filtered and then preheats the absorption liquid transported to the CO2-HCN removal tower 21, and then is transported to the ammonia stripping tower 31;

[0114] (3) The operating pressure of the ammonia stripping tower 31 is controlled to be 0.8 MPaG, the condensing temperature is controlled to be 40℃, the reflux ratio is 6, the purity of the NH3 collected at the top of the tower is 99.5 wt%, and the NH3 is reused to the ammonia oxidation reaction unit; the wastewater collected at the tower kettle is obtained, wherein the ammonia content is 50 ppm, and the HCN content is 0.5 ppm; the obtained wastewater is divided into three parts, the first part (8 wt%) is returned to the ammonia stripping tower 31 after being heated, and the temperature at the tower kettle is controlled; the second part (30 wt%) is introduced into the top of the CO2-HCN removal tower 21, and the third part (62 wt%) is introduced into the top of the absorption tower 11.

[0115] Table 2

[0116]

[0117]

[0118] Example 3:

[0119] The present example provides a treatment method for the tail gas of the ammonia oxidation reaction, which refers to the treatment method in Example 2, the only difference being that the operating pressure of the CO2-HCN removal tower 21 in step (2) is 0.05 MPaG.

[0120] Example 4:

[0121] The present example provides a treatment method for the tail gas of the ammonia oxidation reaction, which refers to the treatment method in Example 1, the only difference being that the operating pressure of the CO2-HCN removal tower 21 in step (2) is 2.0 MPaG.

[0122] Example 5:

[0123] The present example provides a treatment method for the tail gas of the ammonia oxidation reaction, which refers to the treatment method in Example 3, the only difference being that the operating pressure of the CO2-HCN removal tower 21 in step (2) is 0 MPaG.

[0124] Example 6:

[0125] The present example provides a treatment method for the tail gas of the ammonia oxidation reaction, which refers to the treatment method in Example 4, the only difference being that the operating pressure of the CO2-HCN removal tower 21 in step (2) is 2.5 MPaG.

[0126] Example 7:

[0127] The present example provides a treatment method for the tail gas of the ammonia oxidation reaction, which refers to the treatment method in Example 1, the only difference being that in step (3), the second part (5wt%) of the wastewater obtained from the ammonia stripping tower 31 enters the top of the CO2-HCN removal tower 21.

[0128] Example 8:

[0129] The present example provides a treatment method for the tail gas of the ammonia oxidation reaction, which refers to the treatment method in Example 1, the only difference being that in step (3), the operating pressure of the ammonia stripping tower 31 is 0 MPaG.

[0130] The purity of the ammonia gas recovered by the treatment methods described in Examples 3-8 was determined, and the results are shown in Table 3.

[0131] Table 3

[0132] Ammonia purity / wt% Example 3 99.5 Example 4 99.8 Example 5 93.2 Example 6 96.3 Example 7 92 Example 8 95.7

[0133] From the above examples, it can be seen that examples 1-4 use the ammonia oxidation reaction tail gas treatment device and the corresponding treatment method described in the present application, and by further controlling the conditions in the treatment process, the purity of the recovered ammonia gas can reach more than 99wt%; in example 5, the operating pressure of the CO2-HCN removal tower is too small, which causes the HCN and CO2 and other acidic gases to fail to meet the removal index, the ammonia gas purity of the overhead product of the ammonia stripping tower is 93.2wt%, which does not meet the purity requirement; in example 6, the operating pressure of the CO2-HCN removal tower is too large, under the same operating temperature, which causes the HCN and CO2 and other acidic gases to fail to meet the removal index, the ammonia gas purity of the overhead product of the ammonia stripping tower is 96.3wt%, which does not meet the purity requirement; in example 7, the reflux ratio of the CO2-HCN removal tower is too small, which causes the HCN and CO2 and other acidic gases to fail to meet the removal index, the NH3 purity of the overhead product of the ammonia stripping tower is 92wt%, which does not meet the purity requirement; in example 8, the operating pressure of the ammonia stripping tower is too small, which causes the ammonia gas purity of the overhead product of the ammonia stripping tower to be 95.7wt%, which does not meet the purity requirement.

[0134] The above examples are used to illustrate the device and detailed method of the present application, but the present application is not limited to the above device and detailed method, i.e. it does not mean that the present application must rely on the above device and detailed method to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the operation of the present application, addition of auxiliary operation, selection of specific mode, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. An apparatus for treating an ammonia oxidation reaction tail gas, characterized by comprising: The processing device comprises an absorption unit, a CO2-HCN removal unit and an ammonia stripping unit connected in sequence; The ammonia stripping unit is further connected with the absorption unit and the CO2-HCN removal unit respectively to form a circulation connection; The absorption unit comprises an absorption tower, a first external circulation pump and an external circulation cooler connected in sequence to form a circulation connection; The absorption tower is connected with the first external circulation pump; The CO2-HCN removal unit comprises a CO2-HCN removal tower, a second external circulation pump, a first reboiler and a filter; The CO2-HCN removal tower is connected with the first reboiler through the second external circulation pump to form a circulation connection, and the second external circulation pump is connected with the ammonia stripping unit through the filter; The first external circulation pump is connected with the CO2-HCN removal tower; The CO2-HCN removal tower comprises a plate tower; The ammonia stripping unit comprises an ammonia stripping tower, a third external circulation pump, a condenser, a second reboiler and a phase separator; The liquid phase outlet of the filter is connected with the ammonia stripping tower, the bottom of the ammonia stripping tower is connected with the second reboiler through the third external circulation pump to form a circulation connection, and the top of the ammonia stripping tower is connected with the phase separator through the condenser to form a circulation connection; An ammonia gas collecting pipeline is arranged between the condenser and the phase separator; The phase separator is further connected with an organic phase liquid pump; The ammonia stripping tower comprises a plate tower.

2. The processing device of claim 1, wherein, The plate type of the plate tower comprises any one of a baffle plate, a bubble cap plate or a float valve plate.

3. The processing device of claim 1, wherein, The filter has a filtering precision of ≤0.1 μm.

4. The processing device of claim 1, wherein, The plate type of the plate tower comprises a bubble cap plate or a float valve plate.

5. The processing device of claim 1, wherein, The third external circulation pump is further connected with the top of the CO2-HCN removal tower and the top of the absorption tower respectively.

6. A method for treating an ammonia oxidation reaction tail gas, characterized by, The processing method is performed by using the processing device according to any one of claims 1-5, and the processing method comprises the following steps: (1) passing an ammonia oxidation reaction tail gas into the absorption tower to obtain a gas containing HCN and NH3 at the top of the tower and an absorption liquid containing NH3, HCN and CO2 at the bottom of the tower; part of the obtained absorption liquid is returned to the absorption tower after being cooled, and another part is transported to the CO2-HCN removal tower; (2) removing gaseous CO2 at the top of the CO2-HCN removal tower from the absorption liquid obtained in step (1), hydrolyzing HCN at the bottom of the tower to obtain a tower bottom liquid; part of the obtained tower bottom liquid is returned to the CO2-HCN removal tower after being heat exchanged, and another part is transported to the ammonia stripping tower after being filtered; (3) performing ammonia stripping operation on the tower bottom liquid obtained in step (2) in the ammonia stripping tower, obtaining ammonia gas and liquid phase after condensation from the gas phase at the top of the tower, and performing phase separation operation on the obtained liquid phase to return the water phase to the ammonia stripping tower and discharge the organic phase; waste water is obtained at the bottom of the tower, and the obtained waste water is divided into three parts, the first part is returned to the ammonia stripping tower after being heated, the second part is introduced into the top of the CO2-HCN removal tower, and the third part is introduced into the top of the absorption tower.

7. The treatment method according to claim 6, characterized in that, The composition of the ammonia oxidation reaction tail gas in step (1) comprises: NH3 0.3-10 wt%, HCN 0.05-2.0 wt%, CO2 0.01-3.0 wt%, and other substances 85-99.64 wt%.

8. The treatment method according to claim 7, characterized in that, The other substances include any one or a combination of at least two of CO, H2O, N2, O2, mononitrile organic compounds or dinitrile organic compounds.

9. The processing method according to claim 6, wherein The content of the organic compounds in the tail gas of the ammoxidation reaction is not more than 2wt%.

10. The processing method of claim 6, wherein, The absorbent used in the absorption tower in step (1) includes water.

11. The treatment method according to claim 10, characterized in that, The volume ratio of the tail gas of the ammoxidation reaction to the absorbent is (20-2500):

1.

12. The treatment method of claim 6, wherein, The operating pressure of the absorption tower in step (1) is 0.05-1.5MPaG.

13. The treatment method of claim 6, wherein, The content of HCN and NH3 in the gas containing HCN and NH3 in step (1) is not more than 1ppm.

14. The treatment method of claim 6, wherein, The temperature of the absorption liquid after preheating in step (1) reaches 60-100℃.

15. The treatment method of claim 6, wherein, The operating pressure of the CO2-HCN removal tower in step (2) is 0.05-2.0MPaG.

16. The treatment method of claim 6, wherein, The operating temperature of the tower kettle of the CO2-HCN removal tower in step (2) is ≥110℃.

17. The treatment method of claim 6, wherein, The gas phase obtained from the top of the CO2-HCN removal tower in step (2) contains: CO2≥85wt%, H2O≤10wt%, NH3≤5wt%.

18. The treatment method of claim 6, wherein, The content of HCN in the filtered tower kettle liquid in step (2) is ≤1ppm.

19. The treatment method of claim 6, wherein, The operating pressure of the ammonia stripping tower in step (3) is 0.2-3.0MPaG.

20. The treatment method of claim 6, wherein, The temperature of the condensation in step (3) is 30-50℃.

21. The treatment method of claim 6, wherein, The reflux ratio of the water phase reflux in step (3) is 1-10.

22. The treatment method of claim 6, wherein, The obtained ammonia gas in step (3) is reused to the ammoxidation reaction unit, and the purity is ≥99wt%.

23. The treatment method of claim 6, wherein, The content of ammonia in the wastewater obtained from the tower kettle in step (3) is ≤100ppm.

24. The treatment method of claim 6, wherein, The second part of the wastewater in the wastewater obtained from the tower kettle in step (3) accounts for 10-30wt% of the total amount.

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