Method for treating maleic anhydride wastewater

Abstract

The invention relates to the technical field of maleic anhydride wastewater treatment processes, and discloses a maleic anhydride wastewater treatment method which comprises the following steps: (1) respectively introducing maleic anhydride wastewater and low-temperature tail gas discharged by an incinerator into a tail gas primary washing tower from the upper part and the lower part of the tail gas primary washing tower to carry out first countercurrent contact, first tail gas and a first liquid phase are obtained respectively; (2) circulating a part of the first liquid phase back to the tail gas primary washing tower to serve as a part of the maleic anhydride wastewater; and leading the residual first liquid phase out of the tail gas primary washing tower. The method provided by the invention does not need to add alkali for neutralization, does not discharge high-salt sewage after biochemical treatment, does not generate sludge hazardous waste, and better meets the requirements of environmental protection and energy conservation.

Description

Technical Field

[0001] The invention relates to the technical field of maleic anhydride wastewater treatment process, and in particular to a method for treating maleic anhydride wastewater. Background Art

[0002] At present, the n-butane oxidation method has gradually replaced the benzene catalytic oxidation method as the main method for preparing maleic anhydride. Most of the maleic anhydride post-treatment of the n-butane oxidation method adopts a solvent absorption-desorption process. The used solvent needs to be regenerated because it contains impurities such as acetic acid, acrylic acid, n-butanol, and maleic anhydride. The regeneration of the solvent basically adopts a water washing method, and then the water phase and the solvent phase are separated by a centrifuge. The separated water phase contains acetic acid, acrylic acid, maleic acid, solvent (DBP or DIBE), etc. Among them, the solvent DBP has a benzene ring, and DIBE has a saturated six-membered ring. The chemical oxygen demand (COD value) of the sewage is about 20000-30000 mg / L, the pH value is 1-2, the B / C (biochemical oxygen demand / chemical oxygen demand) ratio is low, and the biodegradability is poor.

[0003] At present, most industries use biochemical methods, wet oxidation, and multiple-effect evaporation followed by incineration for treatment. However, due to the poor biodegradability of the sewage, pretreatment, anaerobic treatment, aerobic treatment, and post-treatment are required. The process is long, the land area is large, the investment is large, and the operation and maintenance are complicated. There are also industrial plants that use traditional incineration methods to spray wastewater into direct-fired incinerators, but this method consumes a large amount of fuel gas, which is economically unreasonable. Although the wet oxidation method can treat wastewater containing benzene rings and difficult to biodegrade, it also has the defects of high energy consumption and poor economy due to the need for high temperature and high pressure conditions. Multiple-effect evaporation requires additional steam, and at the same time, it has a high corrosion to process pipeline equipment in an acidic and high-level environment.

[0004] CN105953239A discloses a stripping, evaporation, reduction, incineration and rapid cooling device and method for acrylic acid wastewater. The device includes a wastewater neutralization and concentration system, an incineration system, a flue gas rapid cooling system, and a flue gas dust removal system. In this method, wastewater containing acrylic acid is sent to a stripping tower, and after the organic light components are stripped out, it is sent to a steamer for concentration. The concentrated wastewater is sent to an incinerator for harmless treatment, and the generated flue gas is washed by a venturi dust collector and discharged into the atmosphere. This prior art realizes the stripping, concentration and final removal of organic components of wastewater to ensure that the discharge of three wastes can meet the requirements of national environmental protection standards. However, this method has the problems of complex processing flow, and requires the consumption of a large amount of steam and fuel gas, resulting in energy waste. Summary of the invention

[0005] The purpose of the present invention is to provide a more energy-saving and environmentally friendly method for treating maleic anhydride wastewater.

[0006] In order to achieve the above object, the present invention provides a method for treating maleic anhydride wastewater, the method comprising:

[0007] (1) introducing maleic anhydride wastewater and low-temperature tail gas discharged from an incinerator into the tail gas primary washing tower from the upper and lower parts thereof respectively for first countercurrent contact to obtain a first tail gas and a first liquid phase respectively; the feed temperature of the low-temperature tail gas is 70-130° C., and the water content in the low-temperature tail gas is in an unsaturated state; the temperature of the maleic anhydride wastewater is 50-80° C.;

[0008] (2) recycling a portion of the first liquid phase back to the tail gas primary scrubbing tower as a portion of the maleic anhydride wastewater; and leading the remaining first liquid phase out of the tail gas primary scrubbing tower.

[0009] Preferably, in step (1), the feed temperature of the low-temperature tail gas is 100-120° C., and the water vapor partial pressure in the low-temperature tail gas is 5-10 kPa.

[0010] Preferably, in step (1), the conditions of the first countercurrent contact are controlled so that the temperature in the tail gas primary scrubbing tower is 55-75°C.

[0011] Preferably, in step (1), the water vapor partial pressure in the first tail gas is 15.75-38.536 kPa.

[0012] Preferably, in step (1), the introduction mass flow ratio of the maleic anhydride wastewater to the low-temperature tail gas is 1:35-70, preferably 1:40-60.

[0013] Preferably, in step (1), the temperature of the maleic anhydride wastewater is 50-65°C, and the COD value of the maleic anhydride wastewater is 20000-30000 mg / L.

[0014] According to a preferred specific embodiment, the method described in step (2) further comprises: after the remaining first liquid phase is drawn out of the tail gas primary washing tower, it is introduced into the incinerator described in step (1) for incineration treatment.

[0015] Preferably, the mass flow ratio of the maleic anhydride wastewater to the first liquid phase introduced into the incinerator is 1-15:1, preferably 6-13:1.

[0016] Preferably, the mass flow ratio of the first liquid phase circulating back to the exhaust gas primary scrubbing tower to the low-temperature exhaust gas is 1:2-10.

[0017] Preferably, the first tail gas is passed through an electric demister to remove entrained droplets.

[0018] Compared with the prior art, the method provided by the present invention has at least the following advantages:

[0019] 1) In the exhaust gas primary scrubbing tower, the low-temperature waste heat that cannot be recycled in the exhaust gas discharged by the incinerator is fully utilized as a heat source, and by utilizing the unsaturated water content in the exhaust gas, the moisture in the maleic anhydride wastewater is taken away, so that the maleic anhydride wastewater can be quickly evaporated and concentrated without other energy consumption.

[0020] 2) The present invention preferably uses the tail gas discharged from the incinerator of the maleic anhydride device as the low-temperature tail gas described in the present invention, and uses maleic anhydride wastewater to further absorb organic pollutants such as maleic anhydride and dibutyl phthalate in the low-temperature tail gas, thereby reducing the concentration of tail gas pollutants and further improving the calorific value of the maleic anhydride wastewater, which is more in line with environmental protection and energy-saving requirements.

[0021] 3) The present invention preferably uses a direct-fired incinerator to treat the concentrated first liquid phase, utilizes the organic matter therein as fuel, and discharges water and carbon dioxide through incineration, thereby achieving zero discharge of maleic anhydride wastewater; and this part of heat can be recovered through a steam superheater, an incinerator air intake preheater, etc. Compared with other maleic anhydride wastewater treatment methods, there is no need to add alkali for neutralization, no high-salt wastewater is discharged after biochemical treatment, and no sludge hazardous waste is generated, which is more in line with environmental protection and energy-saving requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a process flow diagram of a method for treating waste gas and maleic anhydride wastewater by using an incinerator and low-temperature tail gas waste heat according to a preferred specific embodiment of the present invention.

[0023] Description of Reference Numerals

[0024] Q1 and Q2 are both tail gas from the absorption tower; Q3 is fuel; Q4 is low-temperature tail gas; Q5 is the first tail gas; Y1 is maleic anhydride wastewater; Y2 is a part of the first liquid phase; Y3 is the remaining first liquid phase; L1 is a regenerative incinerator; L2 is a direct-fired incinerator; T1 is a primary tail gas washing tower; T2 is an electric demister; T3 is a chimney; B1 is a circulating pump; B2 is a circulating liquid cooler; CWS is a circulating cooling water supply pipe; CWR is a circulating cooling water return pipe; TC is a temperature controller. DETAILED DESCRIPTION

[0025] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0026] As mentioned above, the present invention provides a method for treating maleic anhydride wastewater, the method comprising:

[0027] (1) introducing maleic anhydride wastewater and low-temperature tail gas discharged from an incinerator into the tail gas primary washing tower from the upper and lower parts thereof respectively for first countercurrent contact to obtain a first tail gas and a first liquid phase respectively; the feed temperature of the low-temperature tail gas is 70-130° C., and the water content in the low-temperature tail gas is in an unsaturated state; the temperature of the maleic anhydride wastewater is 50-80° C.;

[0028] (2) recycling a portion of the first liquid phase back to the tail gas primary scrubbing tower as a portion of the maleic anhydride wastewater; and leading the remaining first liquid phase out of the tail gas primary scrubbing tower.

[0029] In the present invention, "the feed temperature of the low-temperature tail gas is 70-130°C, and the water content in the low-temperature tail gas is in an unsaturated state" means that the water vapor content of the low-temperature tail gas does not reach the maximum limit at this temperature within a specific range of 70-130°C. In the primary tail gas washing tower, the unsaturated low-temperature tail gas can further carry away the moisture in the maleic anhydride wastewater, so that the maleic anhydride wastewater can be quickly evaporated and concentrated.

[0030] Preferably, in step (1), the feed temperature of the low-temperature tail gas is 80-130° C., and the water content in the low-temperature tail gas is unsaturated. The “water content is unsaturated” mentioned in this preferred condition has a similar meaning to the above.

[0031] More preferably, in step (1), the feed temperature of the low-temperature tail gas is 100-120°C, and the water vapor partial pressure in the low-temperature tail gas is 5-10 kPa. The inventors of the present invention have found in their research that under this preferred condition, the method described in the present invention can make the treatment efficiency of maleic anhydride wastewater higher and more in line with the requirements of energy conservation and environmental protection.

[0032] Preferably, in step (1), the conditions of the first countercurrent contact are controlled so that the temperature in the tail gas primary scrubbing tower is 55-75°C.

[0033] Preferably, in step (1), the water vapor partial pressure in the first tail gas is 15.75-38.536 kPa. After the low-temperature tail gas and the maleic anhydride wastewater are in first countercurrent contact, a large amount of water in the maleic anhydride wastewater is taken away, so the water vapor content in the first tail gas is significantly increased.

[0034] In the present invention, the temperature of the first tail gas is consistent with the temperature in the tail gas primary washing tower.

[0035] Preferably, in step (1), the introduction mass flow ratio of the maleic anhydride wastewater to the low-temperature tail gas is 1:35-70, more preferably 1:40-60. By controlling the introduction mass flow ratio of the maleic anhydride wastewater to the low-temperature tail gas within a specific range, the heat exchange efficiency between the low-temperature tail gas and the maleic anhydride wastewater can be maximized, and the heat of the low-temperature tail gas can be fully utilized. The inventors of the present invention have found in their research that under this more preferred condition, the method of the present invention can make the treatment efficiency of maleic anhydride wastewater higher and more in line with the requirements of energy conservation and environmental protection.

[0036] Preferably, in step (1), the temperature of the maleic anhydride wastewater is 50-65°C, and the COD value of the maleic anhydride wastewater is 20000-30000 mg / L.

[0037] According to a preferred specific embodiment, the method described in step (2) further comprises: after the remaining first liquid phase is drawn out of the tail gas primary washing tower, it is introduced into the incinerator described in step (1) for incineration treatment.

[0038] Preferably, the mass flow ratio of the maleic anhydride wastewater to the first liquid phase introduced into the incinerator is 1-15:1, preferably 6-13:1.

[0039] Preferably, the mass flow ratio of the first liquid phase circulating back to the exhaust gas primary washing tower to the low-temperature exhaust gas is 1:2-10. The mass flow ratio of the first liquid phase circulating back to the exhaust gas primary washing tower to the low-temperature exhaust gas will affect the washing efficiency of the exhaust gas primary washing tower. By increasing the first liquid phase circulating back to the exhaust gas primary washing tower, the contact area between the wastewater and the low-temperature exhaust gas in the exhaust gas primary washing tower is increased, thereby improving the mass transfer and heat transfer efficiency of the maleic anhydride waste gas and the wastewater. Secondly, the first liquid phase circulating back to the exhaust gas primary washing tower is cooled by heat exchange with the circulating cooling water, which can prevent the wastewater in the washing tower from being excessively evaporated and concentrated. The inventors of the present invention have found in their research that under this more preferred condition, the method described in the present invention can make the treatment efficiency of maleic anhydride wastewater higher and more in line with the requirements of energy conservation and environmental protection.

[0040] Preferably, the method of the present invention further comprises: before performing step (1), first introducing the maleic anhydride wastewater into the tail gas primary scrubbing tower, and then performing the operation described in step (1) and starting the cycle. The amount of maleic anhydride wastewater introduced is related to the mass flow rate of the low-temperature tail gas.

[0041] Preferably, the first tail gas is passed through an electric demister to remove entrained droplets.

[0042] The present invention has no particular restrictions on the specific type of the low-temperature tail gas and the material composition thereof, as long as the temperature and water content of the low-temperature tail gas are within the range required by the present invention. However, in order to make the treatment method of maleic anhydride wastewater described in the present invention more in line with the requirements of energy conservation and environmental protection, the present invention preferably uses the tail gas generated in the maleic anhydride production process as the low-temperature tail gas described in the present invention.

[0043] Preferably, in step (2), the incineration temperature in the incinerator is 700-950°C, more preferably 830-880°C; the residence time of the first liquid phase introduced into the incinerator in the incinerator is 1-3s, more preferably 1.5-2.5s.

[0044] In step (2) of the present invention, the first liquid phase introduced into the incinerator can be used as the sole fuel for incineration treatment, or other fuels (such as liquefied gas) can be introduced simultaneously for auxiliary combustion. Those skilled in the art can make a choice based on the actual heat required for treatment. The present invention will not be elaborated herein, and those skilled in the art should not interpret this as a limitation of the present invention.

[0045] According to a preferred embodiment, before the first countercurrent contact, the liquid portion is evenly distributed through a distributor and then countercurrently contacted with the gas portion.

[0046] In order to better understand the purpose, process technology and function of the present invention, the following Figure 1 The preferred specific embodiments of the present invention are described in detail, but the present invention is not limited thereto. The method of the present invention comprises:

[0047] The tail gas Q1 of the absorption tower discharged during the production of maleic anhydride is introduced into the regenerative incinerator L1, and the tail gas Q2 of the absorption tower discharged during the production of maleic anhydride and the increased fuel Q3 are introduced into the direct-fired incinerator L2, and are discharged together after incineration treatment to form the low-temperature tail gas Q4, and the low-temperature tail gas Q4 is introduced into the tail gas primary washing tower T1 from the lower part of the tail gas primary washing tower T1, and the maleic anhydride waste water Y1 is introduced into the tail gas primary washing tower T1 from the upper part of the tail gas primary washing tower T1 after being pressurized by a pump and evenly distributed by a distributor, and the low-temperature tail gas Q4 and the maleic anhydride waste water Y1 are subjected to a first countercurrent contact in the tail gas primary washing tower T1 to obtain the first tail gas Q5 and the first liquid phase; the first tail gas Q5 is treated by the electric precipitator T2 and then discharged into the atmosphere through the chimney T3;

[0048] A portion of the first liquid phase Y3 is pressurized by the circulating pump B1 and temperature-controlled by the circulating cooler B2 and then circulated back to the exhaust gas primary washing tower T1 as a portion of the maleic anhydride waste water Y1, and the remaining first liquid phase Y2 is pressurized by the circulating pump B1 and introduced into the direct-fired incinerator for incineration together with the added fuel Q3.

[0049] The method provided by the present invention utilizes the low-temperature tail gas discharged from the incinerator as a heat source to concentrate maleic anhydride wastewater, while increasing the content of organic matter in the maleic anhydride wastewater and greatly increasing its calorific value. Compared with other process treatment methods in the industry, it has the advantages of being more energy-saving and environmentally friendly, running smoothly, and being simple to operate and maintain.

[0050] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, the raw materials used are all commercially available products.

[0051] In the following examples, the composition of the treated maleic anhydride wastewater is shown in Table 1.

[0052] The calculation method of the calorific value of the organic matter in the first liquid phase introduced into the incinerator to provide the fuel gas required for the vaporization and incineration of the maleic anhydride wastewater is as follows:

[0053] Table 1

[0054] Components Content / wt% Normal pressure boiling point / ℃ water 97.5 99.8 Maleic acid 1.4 275 Fumaric Acid 0.4 355.5 Phthalic acid 0.45 230 Dibutyl phthalate 0.25 340

[0055] By querying relevant data, it can be obtained that at room temperature, the heat of combustion of maleic acid is -11987kJ / kg; the heat of combustion of fumaric acid is -15600kJ / kg; the heat of combustion of phthalic acid is -19419kJ / kg; and the heat of combustion of dibutyl phthalate is -30993kJ / kg.

[0056] The incinerator burns under a slight positive pressure, the incineration temperature is 800°C, the heat required to absorb the moisture from the liquid phase at room temperature to the gas phase at 800°C is 4000kJ / kg; the supplementary fuel gas combustion heat is calculated as 52kJ / g; the thermal efficiency of the incinerator is calculated as 90%.

[0057] The wastewater flow is m, unit is t; the contents of water, maleic acid, fumaric acid, phthalic acid, and dibutyl phthalate are a, b, c, d, and e, respectively, unit is %;

[0058] Then: Fuel gas consumption required for wastewater combustion = m×(a×4000-b×11987-c×15600-d×19419-e×30993)÷100÷52÷90%;

[0059] The first liquid phase introduced into the incinerator provides the wastewater with a proportion of heat required for vaporization and incineration treatment = (b×11987+c×15600+d×19419+e×30993)÷(a×4000)×100%;

[0060] According to the composition in Table 1, it can be calculated that the fuel gas required for 1 t / h of untreated maleic anhydride wastewater = (97.5×4000-1.4×11987-0.4×15600-0.45×19419-0.25×30993) ÷ 100 ÷ 52 ÷ 90% = 74.89 kg / t;

[0061] The proportion of heat required for the vaporization and incineration of the untreated 1t / h maleic anhydride wastewater is = (1.4×11987+0.4×15600+0.45×19419+0.25×30993) ÷ (97.5×4000)×100% = 10.13%.

[0062] Example 1

[0063] The low-temperature tail gas discharged from the incinerator enters from the bottom of the tail gas primary scrubber with a flow rate of 520t / h, a temperature of 105°C, a water vapor partial pressure of 5kPa, and a non-methane total hydrocarbon content of 50mg / m 3 , maleic anhydride wastewater is evenly distributed through a distributor in the middle of the tail gas primary scrubber and then contacts with the low-temperature tail gas in the first countercurrent to obtain the first tail gas and the first liquid phase respectively; wherein, the maleic anhydride wastewater feed flow rate is 10t / h, the temperature is 60℃, and the COD is 25000mg / L; the temperature of the first tail gas is 66℃, and the water vapor partial pressure is 26.16kPa; the temperature of the first liquid phase is 66℃, 1.5t / h is continuously extracted and atomized and then incinerated in the incinerator, and the circulating first liquid phase is circulated back to the tail gas primary scrubber at a flow rate of 125t / h; the COD of the first liquid phase introduced into the incinerator is 200000mg / L. The incinerator uses liquefied gas as fuel, and controls the furnace temperature of the direct-fired incinerator to 840℃, with a residence time of 2 seconds.

[0064] The amount of fuel gas used in the incinerator during the treatment process increased by 0.84 kg / h, indicating that the calorific value of the organic matter in the first liquid phase introduced into the incinerator can provide 98.77% of the heat required for the wastewater's own vaporization and incineration treatment.

[0065] Examples 2-8 of the present invention and Comparative Example 1 are carried out using a process similar to that of Example 1, except that the parameters of the conditions used are changed, see Table 2 for details.

[0066] Comparative Example 2

[0067] The maleic anhydride wastewater is directly introduced into a direct-fired incinerator for incineration treatment, and liquefied gas fuel is introduced to assist combustion, and stays in the direct-fired incinerator at a temperature of 840°C for 2s;

[0068] Among them, the flow rate of maleic anhydride wastewater is 10t / h and the temperature is 60℃; the flow rate of liquefied gas fuel is 550kg / h;

[0069] During the treatment process, liquefied gas fuel is used in the direct-fired incinerator. The calorific value of organic matter in maleic anhydride wastewater is low, and the heat released by the combustion of this part of organic matter is not enough to provide the heat required for the vaporization and incineration of the maleic anhydride wastewater itself, resulting in high energy consumption costs.

[0070] The detailed parameters and effect data of each embodiment and comparative example are shown in Table 2.

[0071] Table 2

[0072]

[0073] It can be seen from the data in the above table that the treatment of maleic anhydride wastewater by the technical solution provided by the present invention can achieve zero discharge of maleic anhydride wastewater, and no or only a small amount of fuel gas needs to be introduced. In particular, the technical solution of Example 4 provided by the present invention increases the amount of fuel gas to -71.1 kg / h, which means that in the process of treating maleic anhydride wastewater in Example 4, not only does no additional fuel gas need to be added, but the calorific value of the organic matter introduced into the first liquid phase of the incinerator can also release heat equivalent to 71.1 kg of fuel gas per hour.

[0074] Moreover, compared with other maleic anhydride wastewater treatment methods, the technical solution provided by the present invention does not require the addition of alkali for neutralization, does not discharge high-salt wastewater after biochemical treatment, and does not generate sludge hazardous waste, which is more in line with environmental protection and energy-saving requirements.

[0075] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for treating maleic anhydride wastewater, characterized in that: The method includes: (1) introducing maleic anhydride wastewater and low-temperature tail gas discharged from an incinerator into the tail gas primary washing tower from the upper and lower parts thereof respectively for first countercurrent contact to obtain a first tail gas and a first liquid phase respectively; the feed temperature of the low-temperature tail gas is 70-130° C., and the water content in the low-temperature tail gas is in an unsaturated state; the temperature of the maleic anhydride wastewater is 50-80° C.; (2) recycling a portion of the first liquid phase back to the tail gas primary scrubbing tower as a portion of the maleic anhydride wastewater; and leading the remaining first liquid phase out of the tail gas primary scrubbing tower.

2. The method according to claim 1, wherein: In step (1), the feed temperature of the low-temperature tail gas is 100-120° C., and the water vapor partial pressure in the low-temperature tail gas is 5-10 kPa.

3. The method according to claim 1 or 2, wherein: In step (1), the conditions of the first countercurrent contact are controlled so that the temperature in the tail gas primary scrubbing tower is 55-75°C.

4. The method according to claim 3, wherein: In step (1), the water vapor partial pressure in the first tail gas is 15.75-38.536 kPa.

5. The method according to any one of claims 1 to 4, wherein: In step (1), the introduction mass flow ratio of the maleic anhydride wastewater to the low-temperature tail gas is 1:35-70, preferably 1:40-60.

6. The method according to any one of claims 1 to 5, wherein: In step (1), the temperature of the maleic anhydride wastewater is 50-65°C, and the COD value of the maleic anhydride wastewater is 20000-30000 mg / L.

7. The method according to claims 1-6, wherein: The method described in step (2) further includes: after the remaining first liquid phase is drawn out of the tail gas primary washing tower, it is introduced into the incinerator described in step (1) for incineration treatment.

8. The method according to claim 7, wherein: The mass flow ratio of the maleic anhydride wastewater to the first liquid phase introduced into the incinerator is 1-15:1, preferably 6-13:

1.

9. The method according to claim 7 or 8, wherein: The mass flow ratio of the first liquid phase circulating back to the exhaust gas primary washing tower to the low-temperature exhaust gas is 1:2-10.

10. The method according to any one of claims 1 to 9, wherein: The first tail gas is passed through an electric demister to remove entrained droplets.

Images