Comprehensive treatment method of sulfur-containing waste alkali

Abstract

The invention relates to the technical field of chemical wastewater treatment, and particularly discloses a comprehensive treatment method of sulfur-containing waste alkali, which comprises the following steps: S1, a pretreatment step: storing sulfur-containing waste alkali liquor in an adjusting and homogenizing tank for homogenizing treatment, and then pumping the sulfur-containing waste alkali liquor to a deoiling and diluting tank for standing separation to remove oil and solid impurities; s2, a wet oxidation (WO) step: pressurizing the pretreated waste alkali liquor to 60 bar through a booster pump, mixing the pretreated waste alkali liquor with compressed air with the flow of 230 Nm < 3 > / h, heating the mixture to 178 DEG C through a preheater, enabling the mixture to enter a reactor, carrying out oxidation reaction under the conditions of 200-240 DEG C and 3-5 barg for 30-60 minutes, cooling a reaction product, and enabling the cooled reaction product to enter a gas-liquid separator for separation; through the effects of wet oxidation, evaporative crystallization and chemical oxidation, organic matters and sulfides in the sulfur-containing waste alkali liquor can be efficiently degraded, the COD removal rate is remarkably increased, meanwhile, the common problems of sludge bulking, water quality fluctuation sensitivity and the like in traditional biological treatment are avoided, and the stability and reliability of the treatment process are ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical wastewater treatment, and particularly relates to a comprehensive treatment method for sulfur-containing waste alkali. Background Art

[0002] In the chemical production process, sulfur-containing waste alkali liquor is a common industrial wastewater, and its treatment has always been an important issue in the field of environmental protection. With the rapid development of the chemical industry, the output of sulfur-containing waste alkali liquor has increased year by year, and its composition has become increasingly complex, mainly containing sulfides, organic matter, high concentrations of salt and a small amount of heavy metals and other harmful substances. If these substances are directly discharged without effective treatment, they will cause serious pollution to the environment and threaten the ecological balance and human health.

[0003] At present, the treatment technologies for sulfur-containing waste alkali liquor mainly include chemical precipitation, biological treatment and advanced oxidation technology. Chemical precipitation converts pollutants into insoluble precipitates by adding chemical agents, but this method has limited treatment efficiency and is prone to produce a large amount of secondary pollutants such as sulfur-containing iron sludge, which increases the difficulty and cost of subsequent treatment. Biological treatment relies on the metabolic action of microorganisms to degrade organic matter. However, the high salinity, high toxicity and large fluctuations in water quality of sulfur-containing waste alkali liquor seriously restrict the stability and efficiency of biological treatment methods, and problems such as sludge swelling and decreased treatment effect often occur. Advanced oxidation technology, such as wet oxidation (WO), has improved treatment efficiency to a certain extent, but when used alone, there are still problems such as incomplete treatment and high energy consumption. In addition, the treatment effect of high-concentration sulfur-containing waste alkali liquor still needs to be improved.

[0004] What is particularly noteworthy is that when treating sulfur-containing waste alkali liquor, existing technologies often find it difficult to simultaneously achieve efficient degradation of organic matter and sulfide, significantly improve COD removal rate, and ensure the stability and reliability of the treatment process. Especially when faced with high-concentration and complex-component sulfur-containing waste alkali liquor, traditional methods often appear to be inadequate and difficult to meet increasingly stringent environmental emission standards, so staff need to improve them. Summary of the Invention

[0005] The object of the present invention is to provide a comprehensive treatment method for sulfur-containing waste alkali to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A comprehensive treatment method for sulfur-containing waste alkali comprises the following steps:

[0008] S1, pretreatment step: the sulfur-containing waste alkali liquor is stored in an adjustment homogenization tank for homogenization treatment, and then pumped to an oil removal dilution tank for static separation to remove oil and solid impurities;

[0009] S2, wet oxidation (WO) step: the pre-treated waste alkali solution is pressurized to 60 bar by a booster pump with a flow rate of 230 Nm 3 / h of compressed air, heated to 178 ° C in a preheater, and then enter the reactor for oxidation reaction at 200-240 ° C and 3-5 barg. The reaction time is 30-60 minutes. The reaction product is cooled and then enters the gas-liquid separator for separation. The gas phase is decompressed and discharged to high altitude. The liquid phase is neutralized to pH 6.5-8.5 and then enters the intermediate storage tank.

[0010] S3, evaporation crystallization step: the wastewater in the intermediate storage tank is pumped into the negative pressure evaporation crystallization device, and evaporated and crystallized under the conditions of vacuum degree of 0.70-0.85 bar and temperature of 55-70°C. The separated salt is dried and then transported as solid waste for disposal. The evaporated condensate and the chemical oxidation product water are mixed in a volume ratio of 1:1 and then enter the treatment water tank;

[0011] S4, chemical oxidation step: the wastewater from the exhaust gas treatment system is stored in a storage tank, pumped into a chemical oxidation reaction tank to react with an oxidant, the produced water after the reaction is mixed with the produced water from evaporation and crystallization and then enters the treatment water tank, and the final discharged water quality meets the first-level standard of GB8978-1996 "Integrated Wastewater Discharge Standard".

[0012] Preferably, in step S2, before the waste alkali liquor enters the reactor, 10 wt% sodium hydroxide solution is added through an alkali addition pump to adjust the pH to 7-10.

[0013] Preferably, in step S2, the reactor is filled with a honeycomb titanium-based distributed filler to increase the gas-liquid mixing uniformity to above 90%.

[0014] Preferably, in step S3, the vacuum degree of the distillation kettle of the negative pressure evaporation crystallization device is maintained by a vacuum pump, and the evaporated water vapor is condensed by the condenser and then enters the recovered water metering tank.

[0015] Preferably, in step S4, the oxidant is 30 wt% hydrogen peroxide or sodium hypochlorite solution, the reaction time is 1 hour, and the COD removal rate is ≥90%.

[0016] Preferably, in step S1, the deoiling and dilution tank is divided into a deoiling area and a storage area, a deoiling tank is provided on the top, an impurity discharge port is provided on the bottom, and nitrogen is used to seal to prevent exhaust gas from escaping.

[0017] Preferably, in step S2, the reactor is started by introducing medium-temperature steam at 250°C and 40 bar.

[0018] Preferably, in step S3, if the wastewater COD is less than 500 mg / L and meets the first-level standard of GB 8978-1996, the evaporation crystallization unit is directly bypassed.

[0019] Preferably, it also includes a wastewater pool for collecting cleaning fluid and drainage generated during equipment repair and maintenance. The volume of the wastewater pool is 30m 3 .

[0020] Preferably, in step S3, the slag discharge condition of the distillation kettle is that the material is basically discharged within 10 minutes, and the slag discharge time is set to 8 to 12 minutes according to the debugging results.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Through the synergistic effect of wet oxidation, evaporative crystallization and chemical oxidation, the organic matter and sulfide in the sulfur-containing waste alkali liquor can be efficiently degraded, and the COD removal rate can be significantly improved. At the same time, the common problems of sludge swelling and water quality fluctuation sensitivity in traditional biological treatment can be avoided, ensuring the stability and reliability of the treatment process.

[0023] (2) By adopting a closed treatment process, the waste gas generated by the wet oxidation and evaporation crystallization units is strictly treated and then discharged in compliance with the standards, and the liquid products are neutralized and mixed before being discharged in compliance with the standards. In addition, no chemical sludge or biological sludge is generated during the entire process, which effectively solves the secondary pollution problems of sludge disposal and waste gas escape in traditional processes.

[0024] (3) Through the evaporation crystallization process, the salt in the wastewater is recovered in solid form, which can be further utilized as a resource and reduce the generation of hazardous waste. At the same time, the heat released by the wet oxidation reaction is used to preheat the feed, and the evaporation crystallization adopts negative pressure and low temperature operation to reduce energy consumption, making the overall process more economical and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a processing flow chart of the present invention. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] Example 1:

[0028] See also Figure 1 As shown, a comprehensive treatment method for sulfur-containing waste alkali, the specific implementation steps are as follows:

[0029] Pretreatment step: The sulfur-containing waste alkali liquor (COD 105708mg / L, TDS 114483mg / L) from the refinery is transported to the adjustment homogenization tank for homogenization treatment with a residence time of 2 hours. The homogenized waste alkali liquor is transported to the homogenization tank by a delivery pump at a speed of 10m 3 / h flow rate pumped to the degreasing dilution tank, and left to stand for separation for 4 hours. During the separation process, the upper oil is collected and discharged through the top degreasing tank, and the solid impurities precipitated at the bottom are regularly discharged to obtain the pre-treated waste alkali liquor (oil content <50mg / L, suspended solids <100mg / L).

[0030] Wet oxidation (WO) step: the pre-treated waste alkali liquid is pressurized to 60 bar by a booster pump and 3 / h of compressed air. The mixed liquid flows through a preheater to exchange heat with the reaction products, reaching a temperature of 178°C before entering the reactor. The reactor is filled with honeycomb titanium-based distributed packing, and the reaction temperature is controlled at 220°C, 4 barg, and 45 minutes. The reaction product is cooled to 55°C before entering a gas-liquid separator. The gas phase is depressurized by a pressure reducing valve and discharged through a 15-meter-high exhaust stack. The liquid phase is adjusted to a pH of 7.5 by adding 10% sulfuric acid solution before entering an intermediate storage tank.

[0031] Evaporation crystallization step: the wastewater in the intermediate storage tank (COD 3234mg / L, TDS126947mg / L) was evaporated to 5m 3 The product is pumped into a negative pressure evaporation crystallization device at a flow rate of 0.80 bar / hour, with an evaporation temperature of 65°C. The secondary steam generated during the evaporation process is condensed in a condenser, and the condensed water is mixed with the water produced by chemical oxidation in a 1:1 volume ratio. The concentrate is crystallized and centrifuged to produce a salt residue (primarily composed of Na2SO4) with a moisture content of less than 5%, which is then transported to a hazardous waste disposal site for landfill.

[0032] Chemical oxidation step: Wastewater from the exhaust gas treatment system (COD 64,686 mg / L) was transferred to a storage tank. A 30 wt% hydrogen peroxide solution (COD:H₂O₂ = 1:1.2 by mass) was added via a metering pump and reacted at room temperature and pressure for one hour. After the reaction, the COD of the wastewater was reduced to 6,000 mg / L (90.7% removal efficiency). After mixing with evaporation and crystallization condensate, the COD was reduced to 1,500 mg / L, meeting the Class I emission standard of GB 8978-1996 (COD ≤ 100 mg / L requires further treatment).

[0033] Abnormal situation handling: When the system detects that the inlet COD is less than 500mg / L, it automatically switches to bypass mode and the wastewater goes directly into the treatment water tank without passing through the evaporation crystallization unit. The cleaning wastewater generated by equipment maintenance is collected to a 30m 3 The wastewater pool is regularly sent back to the pretreatment unit for treatment.

[0034] Treatment effect:

[0035] Total COD removal rate: 98.6%;

[0036] Salt recovery rate: 92%;

[0037] Final effluent quality: COD 138.5mg / L, TDS 55394mg / L;

[0038] Waste gas emissions: SO2<50mg / m 3 , NOx<100mg / m 3 .

[0039] Example 2:

[0040] See also Figure 1 As shown, a comprehensive treatment method for sulfur-containing waste alkali, the specific implementation steps are as follows:

[0041] Pretreatment step: The sulfur-containing waste alkali liquor (COD 119629mg / L, TDS 142105mg / L) from the petrochemical plant is transported to the adjustment homogenization tank for homogenization treatment with a residence time of 3 hours. The homogenized waste alkali liquor is transported to the 8m 3 The wastewater is pumped at a flow rate of 100 / h to a parallel degreasing dilution tank and allowed to stand for separation for 5 hours. During the separation process, a nitrogen sealing system (nitrogen purity ≥ 99.5%) is used to prevent waste gas from escaping. The upper oil is automatically collected and discharged through the top degreasing tank, and the solid impurities precipitated at the bottom are regularly discharged through an electric slag discharge valve, resulting in pretreated waste alkali liquor (oil content <30mg / L, suspended solids <50mg / L).

[0042] Wet oxidation (WO) step: the pre-treated waste alkali solution is pressurized to 60 bar by a parallel booster pump and the 250 Nm 3 / h compressed air. The mixed liquid flows through the preheater to exchange heat with the reaction product, and after the temperature rises to 180℃, it enters the reactor. The reactor is filled with specially designed titanium-based structured packing (specific surface area ≥500m 2 / m 3 ), controlling the reaction temperature at 235°C, the pressure at 4.5 barg, and the reaction time for 50 minutes. 12 wt% sodium hydroxide solution was continuously added via an alkali addition pump to maintain the pH of the reaction system at 8.5. The product after the reaction was cooled in two stages (first by heat exchange with the feed, then by a circulating water cooler) to 60°C before entering a gas-liquid separator. The gas phase was depressurized by a pressure reducing valve and discharged through an 18 m high exhaust stack. The liquid phase was adjusted to pH 7.0 by adding 20% ​​sulfuric acid solution before entering an intermediate storage tank.

[0043] Evaporation crystallization step: the wastewater in the intermediate storage tank (COD 55729mg / L, TDS144516mg / L) was evaporated to 6m 3 / h flow rate is pumped into the negative pressure evaporation crystallization device, the vacuum degree is controlled at 0.75bar, and the evaporation temperature is 60℃. The evaporation system adopts a double-effect evaporation design, with the first effect evaporation temperature at 70℃ and the second effect evaporation temperature at 50℃, reducing steam consumption by 35%. During the evaporation process:

[0044] The secondary steam is condensed through a titanium condenser;

[0045] The COD of the condensate is reduced to 120 mg / L and mixed with the chemical oxidation product water in a static mixer at a volume ratio of 1.2:1;

[0046] The concentrated solution is crystallized in a forced circulation crystallizer and centrifuged to obtain a mixed salt with a water content of less than 3% (Na2SO4 content ≥85%, NaCl content ≤10%);

[0047] The salt residue is packed in ton bags and transported to the resource utilization center.

[0048] Chemical oxidation step: Wastewater from the exhaust gas treatment system (COD 77,441 mg / L) was transferred to a storage tank. A composite oxidant (15 wt% hydrogen peroxide and 10 wt% sodium hypochlorite, mixed in a 3:1 volume ratio) was added via a metering pump system. The reaction was conducted at 35°C for 70 minutes under the control of an automatic pH control system (pH 8.0-9.0). After the reaction, the COD of the wastewater dropped to 8,500 mg / L (removal efficiency 89%). After mixing with evaporation and crystallization condensate, the COD was 1,800 mg / L, meeting the GB 8978-1996 Class III emission standard (COD ≤ 2,000 mg / L).

[0049] Intelligent control system: The DCS system is used to monitor the operating parameters of each unit in real time. When the inlet COD is less than 800mg / L and the TDS is less than 80,000mg / L, the bypass program is automatically started. The evaporation crystallization unit is equipped with an automatic slag discharge system. The slag discharge cycle is automatically adjusted according to the online turbidity monitoring results (usually 8-15 minutes). The equipment cleaning wastewater is automatically diverted into the wastewater pool after online pH monitoring.

[0050] Treatment effect:

[0051] Total COD removal rate: 98.5%;

[0052] Salt recovery rate: 94.5%;

[0053] Final effluent quality: COD 162mg / L, TDS 80680mg / L;

[0054] Waste gas emissions: SO2<30mg / m3 , NOx<80mg / m 3 ;

[0055] Steam energy consumption: 1.2 tons of steam / ton of wastewater.

[0056] This embodiment is suitable for the treatment of complex sulfur-containing waste alkali liquor with high salt content (TDS>100,000 mg / L) and high COD (>100,000 mg / L). All equipment parameters and process conditions are optimized within the allowable range, and key equipment adopts a dual-system redundancy design to ensure continuous and stable operation.

[0057] Comparative Example:

[0058] Description of prior art:

[0059] The traditional "chemical precipitation and biological treatment" combined process is used to treat sulfur-containing waste alkali liquor. The specific process is as follows:

[0060] Chemical precipitation unit: The waste alkali liquor first enters the regulating tank (pH 10-12, COD about 120,000 mg / L), and FeSO4·7H2O (dosage 5 g / L) and PAM (2 mg / L) are added. The precipitation time is 4 hours to generate FeS precipitate, and the COD of the supernatant is reduced to 80,000-90,000 mg / L.

[0061] Biological treatment unit: A two-stage A / O biological treatment system is used with a total hydraulic retention time of 72 hours, supplemented with nitrogen and phosphorus nutrient sources (C:N:P=100:5:1), and the final effluent COD is about 500-800 mg / L.

[0062] Sludge treatment unit: produces chemical sludge (containing FeS) and biological sludge, which is transported for disposal after plate and frame filtration (water content 75-80%).

[0063] Comparative analysis table:

[0064]

[0065]

[0066] Performance comparison:

[0067] Processing efficiency:

[0068] The COD removal rates of Examples 1 and 2 (above 98.5%) are significantly higher than those of the prior art (85-90%).

[0069] The treatment effect of existing technologies on high-concentration wastewater (COD>100,000 mg / L) drops sharply.

[0070] Secondary pollution control:

[0071] This technology achieves zero sludge generation, while existing technologies produce a large amount of sulfur-containing iron sludge (hazardous waste code: HW17);

[0072] The existing technology has the problem of H2S unorganized emission, but this technology can achieve emission standards for waste gas.

[0073] Economical:

[0074] The operating cost of Example 1 was reduced by 48.6%, and that of Example 2 was reduced by 42.9%;

[0075] The sludge disposal cost of the existing technology accounts for 35-40% of the total cost.

[0076] stability:

[0077] This technology has strong adaptability to influent fluctuations (COD ± 30%);

[0078] The existing technology is prone to problems such as sludge swelling when water quality fluctuates.

[0079] Resource recycling:

[0080] Example 2: Realize salt resource utilization (Na2SO4 purity 85%);

[0081] The existing technology has no resource recovery link.

[0082] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A comprehensive treatment method for sulfur-containing waste alkali, characterized in that: The following steps are involved: S1, pretreatment step: the sulfur-containing waste alkali liquor is stored in an adjustment homogenization tank for homogenization treatment, and then pumped to an oil removal dilution tank for static separation to remove oil and solid impurities; S2, wet oxidation (WO) step: the pre-treated waste alkali solution is pressurized to 60 bar by a booster pump with a flow rate of 230 Nm 3 / h of compressed air, heated to 178 ° C in a preheater, and then enter the reactor for oxidation reaction at 200-240 ° C and 3-5 barg. The reaction time is 30-60 minutes. The reaction product is cooled and then enters the gas-liquid separator for separation. The gas phase is decompressed and discharged to high altitude. The liquid phase is neutralized to pH 6.5-8.5 and then enters the intermediate storage tank. S3, evaporation crystallization step: the wastewater in the intermediate storage tank is pumped into the negative pressure evaporation crystallization device, and evaporated and crystallized under the conditions of vacuum degree of 0.70-0.85 bar and temperature of 55-70°C. The separated salt is dried and then transported as solid waste for disposal. The evaporated condensate and the chemical oxidation product water are mixed in a volume ratio of 1:1 and then enter the treatment water tank; S4, chemical oxidation step: the wastewater from the exhaust gas treatment system is stored in a storage tank, pumped into a chemical oxidation reaction tank to react with an oxidant, the produced water after the reaction is mixed with the evaporation and crystallization produced water and then enters the treatment water tank, and the final discharged water quality meets the discharge standards.

2. A comprehensive treatment method for sulfur-containing waste alkali according to claim 1, characterized in that: In step S2, before the waste alkali liquor enters the reactor, 10 wt% sodium hydroxide solution is added through an alkali addition pump to adjust the pH to 7-10.

3. A comprehensive treatment method for sulfur-containing waste alkali according to claim 1, characterized in that: In step S2, the reactor is filled with honeycomb titanium-based distributed fillers to increase the gas-liquid mixing uniformity to more than 90%.

4. A comprehensive treatment method for sulfur-containing waste alkali according to claim 1, characterized in that: In step S3, the vacuum degree of the distillation kettle of the negative pressure evaporation crystallization device is maintained by a vacuum pump, and the evaporated water vapor is condensed by the condenser and enters the recovered water metering tank.

5. A comprehensive treatment method for sulfur-containing waste alkali according to claim 1, characterized in that: In step S4, the oxidant is 30 wt% hydrogen peroxide or sodium hypochlorite solution, the reaction time is 1 hour, and the COD removal rate is ≥90%.

6. A comprehensive treatment method for sulfur-containing waste alkali according to claim 1, characterized in that: In step S1, the deoiling and dilution tank is divided into a deoiling area and a storage area, with a deoiling tank on the top and an impurity discharge port on the bottom, and is sealed with nitrogen to prevent exhaust gas from escaping.

7. A comprehensive treatment method for sulfur-containing waste alkali according to claim 1, characterized in that: In step S2 , the reactor is started by introducing medium-temperature steam at 250° C. and 40 bar.

8. A comprehensive treatment method for sulfur-containing waste alkali according to claim 1, characterized in that: In step S3, if the wastewater COD is less than 500 mg / L and meets the first-level standard of GB 8978-1996, the evaporation crystallization unit is directly bypassed.

9. A comprehensive treatment method for sulfur-containing waste alkali according to claim 1, characterized in that: It also includes a wastewater pool for collecting cleaning fluids and drainage generated during equipment repair and maintenance. The wastewater pool has a capacity of 30m 3 .

10. The comprehensive treatment method for sulfur-containing waste alkali according to claim 1, characterized in that: In step S3, the slag discharge condition of the distillation kettle is that the material is basically discharged within 10 minutes, and the slag discharge time is set to 8 to 12 minutes based on the debugging results.

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