Process for treating wastewater and waste gas from acrylonitrile production device

Abstract

The application discloses a wastewater and waste gas treatment process for an acrylonitrile production device, and belongs to the technical field of wastewater and waste gas treatment. The process comprises the following steps: (1) a nitrile removal process: adding an alkaline substance into condensate of a four-effect evaporator to adjust the pH value, and reacting to obtain water discharged from the nitrile removal process; introducing first part of atmospheric discharge of an AOGI waste gas incineration system into the water discharged from the nitrile removal process to adjust the pH value; (2) a cyanide breaking process: the water discharged from the step (1) is introduced into a UV / H2O2 advanced oxidation process to react, and water discharged from the cyanide breaking process is obtained; introducing all atmospheric discharge of a WWI waste water incineration system and second part of atmospheric discharge of the AOGI waste gas incineration system into the water discharged from the cyanide breaking process to adjust the pH value; (3) the water discharged from the step (2) is sequentially treated by an A / A / O process and a biological filter EBF, and can be discharged up to the standard. The treatment process realizes waste treatment by waste, so that the wastewater and waste gas generated in the acrylonitrile production device can be stably discharged up to the standard, and carbon and nitrogen emission reduction of the acrylonitrile production device is realized.

Description

Technical Field

[0001] This invention belongs to the field of wastewater and waste gas treatment technology, specifically relating to a wastewater and waste gas treatment process for an acrylonitrile production unit. Background Technology

[0002] Acrylonitrile, a common chemical raw material, is an important monomer for synthetic fibers, synthetic rubber, and synthetic resins, widely used in industries such as acrylic fiber, nitrile rubber or latex, and ABS engineering resins. Because existing acrylonitrile production facilities employ the propylene / ammonia oxidation process, which includes reaction, recovery, refining, and four-effect evaporation units, the characteristic compounds in the process wastewater are primarily organic nitriles and inorganic cyanides containing nitrogen groups. This is a significant characteristic of the process wastewater from acrylonitrile production facilities. Nitrogen exists in various forms, including -C≡N, five- or six-membered nitrogen-containing heterocycles, NH3, -NH2, or nitrogen on -NH-. Whether it's wastewater entering the biological treatment unit of the wastewater treatment plant, or emissions from waste gas incineration or wastewater incineration, all contain C and N elements. Furthermore, wastewater incineration emissions also contain sulfur-containing compounds such as SO2 and SO3.

[0003] Wastewater generated during the refining of acrylonitrile is called refined water. In existing technologies, acrylonitrile process wastewater, which is refined water, is concentrated and condensed in a quadruple-effect evaporator to form high-concentration wastewater and low-concentration wastewater. The low-concentration wastewater enters a wastewater treatment plant, while the high-concentration wastewater enters a WWI (Waster Water Incinerator) system for incineration, producing CO2, water vapor, NOx, and SO2. The exhaust gas generated by the system, containing CO2, CO, N2, unreacted O2, and hydrocarbons, enters an AOGI (Absorber Off Gas Incinerator) system for incineration, also producing CO2, water vapor, NOx, and SO2. Both processes use natural gas as an energy source and are vented into the atmosphere after high-temperature incineration. The SO2 content in the exhaust gas must be 0-50 mg / m³. 3 NOx is 0-100 mg / m³ 3 CO content 0-100 mg / m³ 3 Other characteristic organic pollutants, such as acrylonitrile, are <0.5 mg / m³. 3 Acetonitrile < 50 mg / m³ 3 Hydrogen cyanide < 1.9 mg / m³ 3 wait.

[0004] Patent CN103304096A discloses a method for treating acrylonitrile wastewater using ozone catalytic coupling with biological nitrification. The incoming water first enters an equalization tank for water quality adjustment, then flows through a pre-oxidation tower and a catalytic oxidation tower, followed by an ozone removal tank to remove residual ozone, and then a nitrification tank to remove ammonia nitrogen before being discharged from a clear water tank. This invention involves pre-oxidation and catalytic oxidation of the equalization tank effluent, increasing the operating cycle of the wastewater treatment plant. It does not fundamentally solve the problem of wastewater biodegradability, nor does it reduce atmospheric emissions from the acrylonitrile production plant's incinerator exhaust.

[0005] Patent CN202529945U relates to a wastewater treatment system for acrylonitrile and acrylic fiber production plants. An alkaline hydrolysis treatment device is connected to the acrylonitrile production wastewater discharge pipeline and to a homogenizer / conditioner. A coagulation sedimentation or coagulation flotation device A is connected to the polymerization process wastewater discharge pipeline and to the homogenizer / conditioner. The homogenizer / conditioner is connected to an aerobic biological treatment device, which is then connected to an advanced oxidation treatment device. The advanced oxidation treatment device is connected to a hydrolysis acidification-aerobic device or an A / O device. A coagulation sedimentation or coagulation flotation device B is connected to the spinning process wastewater discharge pipeline and to the hydrolysis acidification-aerobic device or an A / O device. This system mixes pretreated wastewater from each plant with wastewater from other plants that do not require pretreatment for centralized treatment, achieving compliant discharge. However, the system incorporates alkaline hydrolysis, which fails to achieve the goal of energy conservation and carbon reduction, and also cannot reduce atmospheric emissions from the incinerator exhaust gas of the acrylonitrile production unit. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a wastewater and waste gas treatment process for acrylonitrile production facilities. This process achieves waste-to-waste treatment, ensuring that the wastewater and waste gas generated in the acrylonitrile production facilities can be stably discharged in compliance with standards, thereby reducing carbon and nitrogen emissions from the acrylonitrile production facilities.

[0007] To achieve the above objectives, according to one aspect of the present invention, a process for treating wastewater and exhaust gas from an acrylonitrile production plant is provided, comprising the following steps:

[0008] (1) Nitrile removal process: Alkaline substances are added to the condensate of the four-effect evaporator to adjust the pH value to 11-13, and the reaction is carried out for a certain time to obtain nitrile removal process effluent; the first part of the atmospheric emissions of the AOGI waste gas incineration system is introduced into the nitrile removal process effluent to adjust the pH value of the nitrile removal process effluent to 9-11.

[0009] (2) Cyanide removal process: The effluent from step (1) enters the UV / H2O2 advanced oxidation process and reacts for a certain time to obtain effluent from the cyanide removal process; all atmospheric emissions from the WWI wastewater incineration system and the second part of atmospheric emissions from the AOGI waste gas incineration system are introduced into the effluent from the cyanide removal process to adjust the pH value of the effluent from the cyanide removal process to 7.5-9.0.

[0010] (3) The effluent from step (2) is treated sequentially by the A / A / O process and the biological filter EBF to meet the discharge standards.

[0011] In some embodiments, in step (1), the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

[0012] In some embodiments, in step (1), the reaction temperature is room temperature and the reaction time is 3-6 hours.

[0013] In some embodiments, in step (1), the first part of the atmospheric emissions introduced into the AOGI waste gas incineration system adjusts the pH of the effluent from the acrylonitrile removal process to 9.5-10.5.

[0014] In some embodiments, in step (2), the amount of hydrogen peroxide added in the UV / H2O2 advanced oxidation process is 300-700 mg / L.

[0015] In some embodiments, in step (2), the reaction temperature is room temperature and the reaction time is 2-5 hours.

[0016] In some embodiments, in step (2), all atmospheric emissions from the WWI wastewater incineration system and a second portion of atmospheric emissions from the AOGI waste gas incineration system are introduced to adjust the pH of the cyanide-breaking process effluent to 8.0-8.5.

[0017] In some embodiments, the volume ratio of the first part of the atmospheric emissions and the second part of the atmospheric emissions from the AOGI waste gas incineration system is (1.5-2.5):1.

[0018] In some embodiments, in step (3), the A / A / O process conditions are: the hydraulic retention time in the anaerobic tank is 15-30h, the hydraulic retention time in the anoxic tank is 20-40h, and the hydraulic retention time in the aerobic tank is 15-30h.

[0019] In some embodiments, in step (3), the hydraulic retention time of the biological filter EBF is 2-4 hours.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) This invention provides a low-cost, low-energy-consumption wastewater and waste gas treatment process for acrylonitrile production equipment. At the same time, the atmospheric emission materials of the AOGI waste gas incineration system and the WWI wastewater incineration system are introduced into the process, which greatly improves the biodegradability of wastewater and achieves the goals of treating waste with waste, reducing atmospheric emissions from acrylonitrile production equipment and ensuring stable compliance of wastewater biochemical units with discharge standards.

[0022] (2) The treatment process of the present invention is simple to operate, low in cost, and the effluent quality can meet the direct discharge quality requirements of GB31571-2015. Attached Figure Description

[0023] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0024] Figure 1 This is a flowchart of the wastewater and waste gas treatment process of an acrylonitrile production unit according to an embodiment of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0026] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0027] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0028] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0029] The wastewater of this invention refers to the wastewater generated during the refining of acrylonitrile in an acrylonitrile production unit, specifically the condensate from the four-effect evaporator in the acrylonitrile production unit, hereinafter referred to as the four-effect evaporator condensate. Nitrogen-containing organic compounds are a significant characteristic pollutant of the four-effect evaporator condensate. Nitrogen is present in nitrogen-containing heterocyclic compounds, organic nitrile compounds, and inorganic cyanide compounds, resulting in high CODcr (dichromate oxygen demand) and total nitrogen levels in the wastewater. Organic nitrile compounds and inorganic cyanides are highly toxic or extremely toxic compounds, and are the main factors leading to the extremely poor biodegradability of the four-effect evaporator condensate, with a BOD5 / COD ratio of only about 0.004.

[0030] This invention provides a process for treating wastewater and exhaust gas from an acrylonitrile production plant, comprising the following steps:

[0031] (1) Nitrile removal process: Alkaline substances are added to the condensate of the four-effect evaporator to adjust the pH value to 11-13, and the reaction is carried out for a certain time to obtain nitrile removal process effluent; the first part of the atmospheric emissions of the AOGI waste gas incineration system is introduced into the nitrile removal process effluent to adjust the pH value of the nitrile removal process effluent to 9-11.

[0032] (2) Cyanide removal process: The effluent from step (1) enters the UV / H2O2 advanced oxidation process and reacts for a certain time to obtain effluent from the cyanide removal process; all atmospheric emissions from the WWI wastewater incineration system and the second part of atmospheric emissions from the AOGI waste gas incineration system are introduced into the effluent from the cyanide removal process to adjust the pH value of the effluent from the cyanide removal process to 7.5-9.0.

[0033] (3) The effluent from step (2) is treated sequentially by the A / A / O process and the biological filter EBF to meet the discharge standards.

[0034] According to the treatment process of the present invention, in some embodiments, in step (1), the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate. The alkaline substance in the present invention is used to adjust the pH value of the acrylonitrile-containing wastewater, thereby providing the necessary conditions for subsequent reactions.

[0035] According to the processing technology of the present invention, in some specific embodiments, in step (1), the alkaline substance can be used in the form of an aqueous solution, and the mass concentration of the aqueous solution of the alkaline substance can be 30%-50%.

[0036] Furthermore, in some specific embodiments, in step (1), an alkaline substance is added to the condensate of the four-effect evaporator to adjust the pH value to preferably 11.5-12.5.

[0037] According to the processing technology of the present invention, in some embodiments, in step (1), the reaction temperature is room temperature and the reaction time is 3-6 hours. It is understood that the reaction time can be any specific value among 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, and 6 hours, or any value within the range of 3-6 hours.

[0038] Furthermore, in some specific embodiments, the reaction time in step (1) is preferably 4-5.5 h.

[0039] In this invention, during the nitrile removal process, by adding an alkaline substance to the condensate of the four-effect evaporator to adjust the pH value and reacting for a certain period of time, the organic nitrile in the condensate of the four-effect evaporator can be converted into amides or ammonium carboxylate substances, thereby achieving the goal of converting highly toxic organic nitrile into non-toxic substances.

[0040] Furthermore, according to the treatment process of the present invention, in some specific embodiments, in step (1), the first part of the atmospheric emissions introduced into the AOGI waste gas incineration system adjusts the pH value of the effluent from the acrylonitrile removal process to 9.5-10.5.

[0041] In this invention, the first portion of atmospheric emissions introduced into the AOGI waste gas incineration system during the nitrile removal process refers to the first portion of atmospheric emissions from the AOGI waste gas incineration system being introduced to the outlet of the nitrile removal process. The acidic gases in these emissions are used to adjust the pH value of the effluent from the nitrile removal process to a specific range. On one hand, the waste gas, primarily composed of NOx compounds, effectively adjusts the pH value required by the process, while simultaneously solving the problem of NOx compound emissions polluting the atmosphere. On the other hand, the nitrate or nitrite compounds formed after entering the wastewater can generate nitrogen gas in the subsequent denitrification reaction in the biological system, achieving the goal of treating waste with waste.

[0042] This invention does not impose specific limitations on the reaction apparatus for the UV / H2O2 advanced oxidation process; conventional UV / H2O2 advanced oxidation reaction apparatus in the art can be used. For example, the reaction apparatus may include a reactor body, which includes, but is not limited to, a stainless steel tank. A UV lamp is located in the center of the reactor body, and the UV lamp is covered by a quartz glass sleeve. The upper and lower ends of the tank are connected by pipes, and an electromagnetic metering pump drives the liquid flow inside the tank.

[0043] According to the processing technology of the present invention, in some embodiments, in step (2), the amount of hydrogen peroxide added in the UV / H2O2 advanced oxidation process is 300-700 mg / L.

[0044] According to the processing technology of the present invention, in some embodiments, in step (2), the ultraviolet light wavelength in the UV / H2O2 advanced oxidation process is 250-260 nm, and the ultraviolet lamp irradiation power is 0.3-0.6 kW·h / m 3 .

[0045] According to the processing technology of the present invention, in some embodiments, in step (2), the reaction temperature is room temperature and the reaction time is 2-5 hours.

[0046] In some specific embodiments, the specific steps of the UV / H2O2 advanced oxidation process may be to add a certain amount of H2O2 to the wastewater, mix it evenly, and then pump it into the reaction tank, turn on the ultraviolet lamp, and start the reaction.

[0047] Furthermore, according to the treatment process of the present invention, in some specific embodiments, in step (2), all atmospheric emissions from the WWI wastewater incineration system and the second part of atmospheric emissions from the AOGI waste gas incineration system are introduced to adjust the pH value of the effluent from the cyanide-breaking process to 8.0-8.5.

[0048] In this invention, the second portion of atmospheric emissions introduced into the cyanide removal process from the WWI wastewater incineration system and the AOGI waste gas incineration system refers to all atmospheric emissions from the WWI wastewater incineration system and the remaining portion from the AOGI waste gas incineration system after deducting the first portion of atmospheric emissions consumed in the cyanide removal process. This is introduced to the outlet of the cyanide removal process. On one hand, the NOx and SO3 compounds in the two waste gases can effectively adjust the pH value required by the process. Simultaneously, the residual hydrogen peroxide in the UV / H2O2 advanced oxidation process can undergo a redox reaction with SO2, reducing the problem of residual hydrogen peroxide and preventing excessive hydrogen peroxide from affecting the subsequent biological treatment system. This also solves the problem of NOx, SO3, and SO2 compounds polluting the atmosphere. Furthermore, the nitrate, nitrite, and sulfate compounds formed after entering the wastewater can generate nitrogen gas in the denitrification reaction of the subsequent biological treatment system or be discharged with the wastewater, preventing NOx, SO3, and SO2 compounds from being released into the atmosphere, thus achieving the goal of treating waste with waste.

[0049] According to the processing technology of the present invention, in some embodiments, the volume ratio of the first part of atmospheric emissions and the second part of atmospheric emissions of the AOGI waste gas incineration system is (1.5-2.5):1.

[0050] According to the treatment process of the present invention, in some embodiments, the BOD5 / COD value of the wastewater after the nitrile removal process and the cyanide removal process is greater than 0.5, indicating that the treatment process of the present invention can completely remove recalcitrant, nitrification-inhibiting and toxic substances from the wastewater and improve the biodegradability of the wastewater.

[0051] In this invention, the wastewater treated by the nitrile removal and cyanide removal processes further enters the A / A / O process and the EBF biological filter for treatment. Optionally, the wastewater treated by the nitrile removal and cyanide removal processes can be entered into the A / A / O process and EBF biological filter together with other wastewater in the plant area, for example, it can be entered into the A / A / O process and EBF biological filter together with the circulating water discharge and desalination station wastewater in the plant area. This invention does not have any special limitations in this regard and can be adjusted according to the actual situation.

[0052] According to the processing technology of the present invention, in some embodiments, in step (3), the A / A / O process conditions are: the hydraulic retention time of the anaerobic tank is 15-30h, the hydraulic retention time of the anoxic tank is 20-40h, and the hydraulic retention time of the aerobic tank is 15-30h.

[0053] In this invention, wastewater treated in an anoxic tank enters an aerobic tank for nitrification. Part of the nitrified effluent is returned to the anoxic tank, while the remaining effluent enters a sedimentation tank for sedimentation and separation. Part of the sludge is returned to the anoxic tank, and the supernatant is discharged as treated effluent to subsequent processes. This invention can use conventional A / A / O process parameters; for example, the nitrification effluent return ratio can be 200%-600%, and the sedimentation tank sludge return ratio can be 30%-90%.

[0054] In this invention, the A / A / O process is an abbreviation for Anaerobic-Anoxic-Oxic (biological nitrogen and phosphorus removal), also known as the anaerobic-anoxic-aerobic process. In some specific embodiments, wastewater and returned sludge first enter the anaerobic tank and are completely mixed. After a certain period of anaerobic decomposition, some nitrogen-containing compounds are converted into N2 (denitrification) and released. The polyphosphate-accumulating microorganisms (PABs, etc.) in the returned sludge release phosphorus, satisfying the bacteria's phosphorus requirements. Then, the wastewater flows into the anoxic tank, where denitrifying bacteria use undecomposed carbonaceous organic matter in the wastewater as a carbon source to reduce nitrate ions that have been returned from the aerobic tank via internal circulation to N2 and release them. Next, the wastewater flows into the aerobic tank, where ammonia nitrogen in the water undergoes nitrification to produce nitrate ions. Simultaneously, the organic matter in the water is oxidized and decomposed to provide energy for the phosphorus-absorbing microorganisms. The microorganisms absorb phosphorus from the water, which enters their cell tissues and accumulates within them. After sedimentation and separation, the phosphorus is discharged from the system as phosphorus-rich sludge.

[0055] According to the processing technology of the present invention, in some embodiments, in step (3), the hydraulic retention time of the biological filter EBF is 2-4h.

[0056] EBF, or engineered bacteria biofilter, is a fixed-bed biofilter formed by loading bio-enhanced engineered bacteria onto porous materials such as activated carbon and ceramsite. Its purpose is to remove recalcitrant COD from wastewater. In actual operation, aeration occurs from the bottom of the filter, maintaining dissolved oxygen at 1-6 mg / L. Water flows upward through the fixed bed, effectively removing most of the recalcitrant COD from the water.

[0057] This invention does not impose any special restrictions on A / A / O ponds and biological filter EBFs; conventional A / A / O ponds and biological filter EBFs in the art can be used.

[0058] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to further explain and illustrate the content of the present invention by way of example, and are not intended to limit the present invention.

[0059] In this invention, the testing methods for each performance parameter in the embodiments and comparative examples are as follows:

[0060] Chemical oxygen demand (CODcr): Dichromate method, tested according to HJ828-2017 standard;

[0061] Five-day biochemical oxygen demand (BOD5): tested according to HJ505-2009 standard;

[0062] Total organic carbon (TOC): tested according to HJ 501-2009 standard;

[0063] Total nitrogen (TN): Tested according to BSEN12260-2003 standard;

[0064] Ammonia nitrogen (NH3-N) content: tested according to HJ / T 195-2005 standard;

[0065] NO3-N content: tested according to HJ / T 198-2005 standard;

[0066] Total cyanide content: tested according to HJ 484-2009 standard;

[0067] Total phosphorus content: tested according to DIN EN ISO 6878-2004 standard;

[0068] Suspended solids content: tested according to GB / T 11901-1989 standard;

[0069] The contents of acrylonitrile, acrolein, cyanopyridine, succinic acid, and propionitrile were determined according to the General Rules for Gas Chromatography (JY / T 0574-2020) using headspace gas chromatography-mass spectrometry (GC-MS). Internal standard curves were prepared using acrylonitrile solutions at mass ratios of 5 mg / L, 10 mg / L, and 50 mg / L.

[0070] In this invention, the wastewater to be treated used in the examples and comparative examples is the condensate from the four-effect evaporator of a certain acrylonitrile production unit, and the conventional water quality is shown in Table 1.

[0071] Table 1. Typical water quality of condensate from a quadruple-effect evaporator

[0072] .

[0073] The content of characteristic pollutants in the condensate of the four-effect evaporator was determined by gas chromatography-mass spectrometry, as shown in Table 2.

[0074] Table 2. Content of characteristic pollutants in condensate from a quadruple-effect evaporator

[0075] .

[0076] This wastewater has low biodegradability, with a BOD5 / COD ratio that is too low to be detected.

[0077] Example 1

[0078] The wastewater and exhaust gas treatment process for the acrylonitrile production unit described in this embodiment is illustrated in the process flow diagram below. Figure 1 As shown. Specifically, it includes the following steps:

[0079] Nitrile removal process: Add a 48% sodium hydroxide solution to the condensate of the quadruple-effect evaporator to adjust its pH value to 11.5, react at room temperature for 5.5 hours. After the nitrile removal reaction, the pH value drops to 11.1. Then, introduce the first part of the atmospheric emissions from the AOGI waste gas incineration system into the effluent of the nitrile removal process to adjust the pH value of the effluent of the nitrile removal process to 10.5.

[0080] Cyanide removal process: The effluent from the cyanide removal process enters a three-stage UV / H2O2 advanced oxidation process, with an ultraviolet light wavelength of 254nm and an ultraviolet lamp irradiation power of 0.4kw·h / m 3 Hydrogen peroxide at a concentration of 300 mg / L was added, and the reaction was carried out at room temperature for 3.5 hours. After the reaction, the pH value dropped to 9.4, and approximately 50 mg / L of hydrogen peroxide remained, yielding the effluent from the cyanide removal process. All atmospheric emissions from the WWI wastewater incineration system and the second part of atmospheric emissions from the AOGI waste gas incineration system were then introduced into the effluent to adjust its pH value to 8.3. The volume ratio of the first part of atmospheric emissions from the AOGI waste gas incineration system to the second part of atmospheric emissions was 2:1. Testing showed that the total cyanide content in the effluent from the cyanide removal process decreased to below 1 mg / L, and the BOD5 / COD ratio was 0.58.

[0081] The effluent from the cyanide removal process sequentially enters the anaerobic, anoxic, and aerobic tanks of the A / A / O biological system. The hydraulic retention time (HRT) in the anaerobic tank is 30 hours, in the anoxic tank it is 30 hours, and in the aerobic tank it is 40 hours. After treatment in the aerobic tank, the wastewater enters the secondary sedimentation tank for sedimentation and separation. The nitrified liquid and sludge from the secondary sedimentation tank are returned to the anoxic tank, with a nitrified liquid return ratio of 300% and a sludge return ratio of 50%. Then, the effluent enters the biological filter (EBF) with an empty tower hydraulic retention time of 3 hours. The treated effluent is then directly discharged.

[0082] The effluent quality of EBF meets the requirements of GB31571-2015 for direct discharge water quality. Specific data are shown in Table 3.

[0083] Example 2

[0084] The wastewater and exhaust gas treatment process for the acrylonitrile production unit described in this embodiment is illustrated in the process flow diagram below. Figure 1 As shown. Specifically, it includes the following steps:

[0085] Nitrile removal process: Add a 50% sodium carbonate solution to the condensate of the quadruple-effect evaporator to adjust its pH to 12.5. React at room temperature for 4 hours. After the nitrile removal reaction, the pH drops to 12.3. Introduce the first part of the atmospheric emissions from the AOGI waste gas incineration system into the effluent of the nitrile removal process to adjust the pH of the effluent of the nitrile removal process to 9.5.

[0086] Cyanide removal process: The effluent from the cyanide removal process enters a three-stage UV / H2O2 advanced oxidation process, with an ultraviolet light wavelength of 260nm and an ultraviolet lamp irradiation power of 0.5kw·h / m 3 700 mg / L of hydrogen peroxide was added, and the reaction was carried out at room temperature for 5 hours. After the reaction, the pH value dropped to 9.4, and approximately 50 mg / L of hydrogen peroxide remained, yielding the effluent from the cyanide removal process. All atmospheric emissions from the WWI wastewater incineration system and the second part of atmospheric emissions from the AOGI waste gas incineration system were then introduced into the effluent to adjust its pH value to 8.5. The volume ratio of the first part of atmospheric emissions from the AOGI waste gas incineration system to the second part of atmospheric emissions was 2:1. Testing showed that the total cyanide content in the effluent from the cyanide removal process decreased to below 1 mg / L, and the BOD5 / COD ratio was 0.59.

[0087] The effluent from the cyanide removal process, along with an equal amount of circulating water discharge and wastewater from the desalination station, enters the anaerobic, anoxic, and aerobic tanks of the A / A / O biological system. The hydraulic retention time (HRT) in the anaerobic tank is 25 hours, in the anoxic tank it is 25 hours, and in the aerobic tank it is 20 hours. After treatment in the aerobic tank, the wastewater enters the secondary sedimentation tank for sedimentation and separation. The nitrified liquid and sludge from the secondary sedimentation tank are returned to the anoxic tank, with a nitrified liquid return ratio of 400% and a sludge return ratio of 70%. The effluent then enters the biological filter (EBF) with an empty tower hydraulic retention time of 4 hours. The treated effluent is then directly discharged.

[0088] The effluent quality of EBF meets the requirements of GB31571-2015 for direct discharge water quality. Specific data are shown in Table 3.

[0089] Table 3. Effluent water quality of EBF and direct discharge water quality according to GB31571-2015 in the examples.

[0090] .

[0091] Comparative Example 1

[0092] The nitrile removal and cyanide destruction processes in this comparative example are the same as in Example 1, except that neither the nitrile removal nor cyanide destruction processes introduce atmospheric emissions from the plant's AOGI waste gas incineration system and WWI wastewater incineration system. Testing showed that the total cyanide content in the effluent from the cyanide destruction process reached 8.9 mg / L, the pH value was 10.1, and the BOD5 / COD ratio was 0.13. Due to the extremely low biodegradability of the wastewater, it could not be fed into a biological treatment system for further treatment.

[0093] Comparative Example 2

[0094] The nitrile removal and cyanide destruction processes in this comparative example are the same as those in Example 1. The difference is that the nitrile removal process introduces the tail gas from the WWI wastewater incineration system, while the cyanide destruction process does not introduce any atmospheric emissions from the WWI wastewater incineration system or the atmospheric emissions from the AOGI waste gas incineration system. The specific steps are as follows:

[0095] Nitrile removal process: Add a 48% sodium hydroxide solution to the condensate of the quadruple-effect evaporator to adjust its pH to 11.5. React at room temperature for 5.5 hours. After the nitrile removal reaction, the pH drops to 11.1. Then, introduce the tail gas from the WWI wastewater incineration system into the effluent of the nitrile removal process to adjust the pH of the effluent to 10.3.

[0096] Cyanide removal process: The effluent from the cyanide removal process enters a three-stage UV / H2O2 advanced oxidation process, with an ultraviolet light wavelength of 254nm and an ultraviolet lamp irradiation power of 0.6kw·h / m 3Hydrogen peroxide at a concentration of 300 mg / L was added, and the reaction was carried out at room temperature for 3.5 hours. After the reaction, the pH value dropped to 9.4, and approximately 50 mg / L of hydrogen peroxide remained, yielding the effluent from the cyanide removal process. Testing revealed that the total cyanide content in the effluent was 15.0 mg / L, and the BOD5 / COD ratio did not increase. This water quality did not meet the standards for entering the biological treatment unit of the wastewater treatment plant, and therefore it could not be used for further treatment in the biological treatment system.

[0097] Comparative Example 3

[0098] This comparative example uses a conventional stripping tower process to treat wastewater from an acrylonitrile production unit, without any nitrile removal or cyanide reduction processes. Atmospheric emissions from the AOGI waste gas incineration system and the WWI wastewater incineration system are treated using the conventional stripping tower process. Testing showed that the pH value of the stripping tower effluent decreased to 4.9, while NOx was detected in the wastewater treatment plant's tail gas collection system, indicating that this tail gas could not be completely absorbed by the stripping tower effluent.

[0099] As can be seen from Example 1 and Comparative Example 3, the traditional four-effect evaporation + stripping tower process used in Comparative Example 3 to treat wastewater and exhaust gas from an acrylonitrile production unit was ineffective. This is because the pH value of the stripping tower effluent is essentially neutral, which does not effectively absorb acidic gases. Consequently, it fails to achieve the goals proposed in this invention: treating waste with waste, reducing atmospheric emissions from acrylonitrile production units, and ensuring stable and compliant discharge from the wastewater treatment plant's biochemical unit.

[0100] As can be seen from Example 1 and Comparative Example 1, in Comparative Example 1, neither the AOGI waste gas incineration system nor the WWI wastewater incineration system's atmospheric emissions were introduced into the nitrile removal and cyanide destruction processes. The total cyanide content in the effluent from the cyanide destruction process reached 8.9 mg / L, while the BOD5 / COD ratio was 0.13. Due to the excessively low biodegradability of the wastewater, it could not be fed into the biological treatment system for further treatment. As can be seen from Example 1 and Comparative Example 2, in Comparative Example 2, the tail gas from the WWI wastewater incineration system was introduced into the nitrile removal process, while all atmospheric emissions from the WWI wastewater incineration system and the AOGI waste gas incineration system were not introduced into the cyanide destruction process. The total cyanide content in the effluent from the cyanide destruction process was 15.0 mg / L, and the BOD5 / COD ratio was not increased. The water quality did not meet the requirements for entering the biological treatment unit of the wastewater treatment plant, therefore it could not be fed into the biological treatment system for further treatment. Therefore, through the acrylonitrile removal and cyanide destruction processes of this invention, and by introducing atmospheric emissions from the plant's AOGI waste gas incineration system and WWI wastewater incineration system, recalcitrant, nitrification-inhibiting, and toxic substances in the condensate of the four-effect evaporator are removed, significantly increasing the BOD5 / COD ratio. This results in a significant improvement in the biodegradability of the treated wastewater, achieving the goals of treating waste with waste, reducing atmospheric emissions from acrylonitrile production units, and ensuring stable compliance with discharge standards from the wastewater treatment plant's biochemical unit.

[0101] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A process for treating wastewater and exhaust gas from an acrylonitrile production plant, characterized in that, Includes the following steps: (1) Nitrile removal process: Alkaline substances are added to the condensate of the four-effect evaporator to adjust the pH value to 11-13, and the reaction is carried out for a certain time to obtain nitrile removal process effluent; the first part of the atmospheric emissions of the AOGI waste gas incineration system is introduced into the nitrile removal process effluent to adjust the pH value of the nitrile removal process effluent to 9-11. (2) Cyanide removal process: The effluent from step (1) enters the UV / H2O2 advanced oxidation process and reacts for a certain time to obtain effluent from the cyanide removal process; all atmospheric emissions from the WWI wastewater incineration system and the second part of atmospheric emissions from the AOGI waste gas incineration system are introduced into the effluent from the cyanide removal process to adjust the pH value of the effluent from the cyanide removal process to 7.5-9.

0. (3) The effluent from step (2) is treated sequentially by the A / A / O process and the biological filter EBF to meet the discharge standards.

2. The wastewater and waste gas treatment process for acrylonitrile production unit according to claim 1, characterized in that, In step (1), the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

3. The wastewater and waste gas treatment process for acrylonitrile production equipment according to claim 1, characterized in that, In step (1), the reaction temperature is room temperature and the reaction time is 3-6 hours.

4. The wastewater and waste gas treatment process for acrylonitrile production equipment according to claim 1, characterized in that, In step (1), the first part of the atmospheric emissions introduced into the AOGI waste gas incineration system is used to adjust the pH value of the effluent from the acrylonitrile removal process to 9.5-10.

5.

5. The wastewater and waste gas treatment process for acrylonitrile production unit according to claim 1, characterized in that, In step (2), the amount of hydrogen peroxide added in the UV / H2O2 advanced oxidation process is 300-700 mg / L.

6. The wastewater and waste gas treatment process for acrylonitrile production unit according to claim 1, characterized in that, In step (2), the reaction temperature is room temperature and the reaction time is 2-5 hours.

7. The wastewater and waste gas treatment process for acrylonitrile production unit according to claim 1, characterized in that, In step (2), all atmospheric emissions from the WWI wastewater incineration system and the second part of atmospheric emissions from the AOGI waste gas incineration system are introduced to adjust the pH of the effluent from the cyanide-breaking process to 8.0-8.

5.

8. The wastewater and waste gas treatment process for acrylonitrile production unit according to claim 1, characterized in that, The volume ratio of the first part of atmospheric emissions and the second part of atmospheric emissions in the AOGI waste gas incineration system is (1.5-2.5):

1.

9. The wastewater and waste gas treatment process for acrylonitrile production unit according to claim 1, characterized in that, In step (3), the A / A / O process conditions are as follows: the hydraulic retention time in the anaerobic tank is 15-30h, the hydraulic retention time in the anoxic tank is 20-40h, and the hydraulic retention time in the aerobic tank is 15-30h.

10. The wastewater and waste gas treatment process for acrylonitrile production unit according to claim 1, characterized in that, In step (3), the hydraulic retention time of the biological filter EBF is 2-4 hours.

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