[Ocean Chemical News] Jiujiang Petrochemical’s first set of VOCs exhaust gas treatment facilities was completed by CCCC

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Several typical technologies and application examples for the treatment of volatile organic compounds (VOCs) waste gas in the refining and chemical industry are introduced. Examples: ① The waste gas from the oil trap and flotation tank in the petrochemical sewage treatment plant is treated with the technology of "desulfurization and total hydrocarbon concentration homogenization-catalytic oxidation", and the waste gas from the aeration tank The "washing-adsorption" device is used for treatment; ② The gasoline loaded oil and gas are treated with "low-temperature diesel absorption" technology, and the oil and gas recovery rate is greater than 95%; the gasoline low-temperature diesel absorption device purifies the exhaust gas and the jet fuel loaded oil and gas uses "total hydrocarbon concentration homogenization-catalytic oxidation" "Technical treatment; ③ VOCs exhaust gases from intermediate oil tanks and sewage pools should be treated with "low-temperature diesel absorption - alkali desulfurization + total hydrocarbon concentration homogenization - catalytic oxidation" technology; ④ rubber exhaust gas should be treated with "pretreatment (condensation, filtration) - catalytic oxidation" technology; ⑤ The VOCs waste gas emitted from chlorobenzene and nitrochlorobenzene units and raw material and product storage tanks is centrally processed using the "regenerative combustion-sodium hydroxide alkali liquid absorption-activated carbon adsorption" technology. The indicators such as total methane hydrocarbons, benzene, toluene and xylene in the treated purified gas all meet the* * Emission standards. Volatile organic compounds (VOCs) pollution prevention and control work is * * “One of the important tasks of environmental protection in the 13th Five-Year Plan is the refining and chemical industry. * * Focus on the VOCs management industry. Regarding VOCs governance, * * A series of standards were promulgated, e.g.: GB 31570--2015 "Petroleum Refining Industry Pollutant Emission Standards", GB 31571--2015 (Petrochemical Industry Pollutant Emission Standards), etc. Currently, Tianjin refining and chemical companies implement the most stringent standards and decrees. The main indicators and requirements include: ①The incineration method stipulates that the mass concentration of purified gas VOCs (measured as non-methane total hydrocarbons NMHC) shall not be greater than 20 mg/m3, and the non-incineration method shall not exceed 80 ms/m3; the mass concentration of benzene shall not be greater than 4 ms/m3; the odor concentration shall not be greater than 1 000; ② Volatile organic liquid storage tanks with actual vapor pressure not less than 2.8 kPa shall adopt floating roof tanks, and the volume fraction of VOCs (measured as methane) detected on the top of the tank shall not exceed 2 000uL/L; ③ Storage tanks for volatile hazardous chemicals such as benzene should be equipped with oil and gas recovery devices and other treatment facilities on the basis of internal floating roof tanks. Based on technologically advanced, mature and reliable engineering examples, several typical technologies and application examples of VOCs waste gas treatment in the refining and chemical industry are introduced. 1 Typical technologies and engineering examples of VOCs waste gas treatment 1.1 VOCs waste gas treatment in sewage treatment plants VOCs waste gases such as grease traps, air flotation tanks, and homogeneous conditioning tanks in refining sewage treatment plants should be treated with "desulfurization and total hydrocarbon concentration homogenization-catalytic oxidation" ∞o technology. Waste gases such as aeration tanks and oxidation ditches should be treated with "washing-adsorption" technology. PetroChina has built a set of 5dam3/h oil trap, air flotation tank, homogeneous conditioning tank, sludge tank and other exhaust gas "desulfurization and total hydrocarbon concentration homogenization-catalytic oxidation" set at the sewage treatment plant of a refining and chemical company in Hebei Province, and a set of 23dam3/h aeration tank exhaust gas "washing-adsorption" combined device. The exhaust gas from the aeration tank removes sludge droplets and some odorous substances through "washing", and removes VOCs and other pollutants through "adsorption"; the saturated adsorbent is regenerated by the hot gas discharged from the catalytic oxidation reactor, about once every three months, and the regenerated gas is returned to the catalytic oxidation treatment. After treatment, the waste gas from the enterprise's sewage treatment plant complies with the requirements of Hebei Province DB13/2322-2016 "Volatile Organic Compound Emission Control Standard for Industrial Enterprises". In November 2016, the sampling and analysis results of the gas at the inlet and outlet of the catalytic oxidation reactor of the combined unit are shown in Table 1. 1.jpg The concentration of human odor in the aeration tank exhaust gas scrubber is generally greater than 4000. After "washing and adsorption" treatment, the odor concentration is less than 20. The mass concentration of NMHC at the inlet of the adsorption tank is 50 to 200 mg/m3. In the early stage of adsorption, the mass concentration of NMHC at the outlet of the adsorption tank is less than 10mg/m3. After 2 months, it increases to 20-40mg/m3. Regeneration is arranged when it reaches 50ms/m3. 1.2 To control VOCs exhaust gas from volatile organic liquid loading operations, gasoline, naphtha, jet fuel, and aromatic hydrocarbon loading operations should be treated with different combinations of processes such as low-temperature diesel absorption, activated carbon adsorption, condensation, and membrane separation. If the standards cannot be met after treatment, catalytic oxidation, thermal storage oxidation, incineration and other devices can be used for treatment. Sinopec originally had a set of oil and gas low-temperature diesel absorption device loaded on a gasoline train with a processing capacity of 300m3/h in a refining and chemical company in Shandong Province. The NMHC mass concentration of the purified gas was less than 18g/m3, and the oil and gas recovery rate was greater than 95%. The company has built a new 4dam3/h "total hydrocarbon concentration homogenization-catalytic oxidation" device to process the jet fuel train and car loading oil and gas together with the tail gas of the original gasoline train loading oil and gas low-temperature diesel absorption device. The gas composition of the inlet and outlet of the catalytic oxidation reactor is shown in Table 2. The mass concentration of NMHC in the purified gas is less than 20 mg/m3, and the concentrations of benzene, toluene, and xylene are all below the detection limit. 2.jpg 1.3 Volatile organic liquid storage tanks VOCs exhaust gas treatment Volatile organic liquid storage tanks should give priority to floating roof tanks or pressure storage tanks to control VOCs emissions. However, the exhaust gases emitted from acidic water tanks, dirty oil tanks, etc. contain relatively high concentrations of oil vapors (VOCs), hydrogen sulfide, organic sulfides, etc., and the odor is severe, so low-temperature diesel absorption + alkali washing + catalytic oxidation or thermal storage oxidation technology should be used for treatment; benzene, toluene, and xylene floating roof tank emissions need to be treated, and activated carbon adsorption or pretreatment-catalytic oxidation technology should be used. 1.3.1 Low-temperature diesel absorption + catalytic oxidation device for combined sulfur oil and gas in tank area. There are dozens of "low-temperature diesel absorption and alkali liquid desulfurization" devices (hereinafter referred to as low-temperature diesel absorption) in the country, which are used for sulfur-containing oil and gas such as acid water tanks and dirty oil tanks. Among them, diesel absorbs oil and gas, organic sulfides and most hydrogen sulfide, and sodium hydroxide solution absorbs residual hydrogen sulfide. After the exhaust gas is processed, the mass concentration of NMHC is less than 25,000 mg/m3, the organic sulfide removal rate is close to 100%, and the hydrogen sulfide removal rate is more than 99%. It complies with GB 14554--1993 "Emission Standard of Odor Pollutants" and GB20950--2007 (Emission Standard of Air Pollutants for Oil Storage Depots), but does not meet the "Petroleum Refining Industry Pollutant Emission Standard" and the standards of Tianjin and Beijing. To this end, Sinopec Fushun Petrochemical Research Institute has developed the following process: ①The low-temperature diesel absorption and activated carbon adsorption process of the tank area exhaust gas has a VOCs removal rate of more than 98%; ② The low-temperature diesel absorption and catalytic oxidation (or thermal storage oxidation) process of the tank area exhaust gas, according to the local requirements, the mass concentration of NMHC is less than 80 or 20 mg/In3; ③ The low-temperature diesel absorption-incineration process of the tank area exhaust gas, the mass concentration of NMHC is less than 20 mg/m3. In 2015, a company in Qingdao completed an industrial test for the incineration treatment of VOCs waste gas low-temperature diesel absorption device tail gas into the hydrogenation unit heating furnace, Claus tail gas incinerator, CO waste heat boiler, and ammonia incinerator. The mass concentration of NMHC in the purified gas was less than 20 mg/m3. Sinopec uses a "low-temperature diesel absorption, alkaline liquid desulfurization + total hydrocarbon concentration homogenization - catalytic oxidation" device (referred to as low-temperature diesel absorption + catalytic oxidation device) to treat VOCs waste gas from a total of 24 intermediate oil storage tanks and 4 sewage pools in the storage and transportation tank area of a refining and chemical enterprise in Shanghai, asphalt, heavy dirty oil, light dirty oil, etc. The exhaust gas treatment capacity of the catalytic oxidation unit is 5 dam3/h, the inlet temperature of the catalytic oxidation reactor is about 350°C. The gas compositions at the device inlet, low-temperature diesel absorption tower outlet, and catalytic oxidation reactor outlet are shown in Table 3. The concentrations of benzene, toluene, and xylene in the purified gas are less than the detection limit, and the mass concentration of NMHC is less than 30 mg/m3, which is far better than Shanghai DB 3 1-933--2015 (Comprehensive Emission Standard of Air Pollutants). 3.jpg 1.3.2 Aromatic hydrocarbon tank area exhaust gas buffering homogenization and catalytic oxidation device Sinopec’s internal floating roof tank storage materials in the aromatic hydrocarbons tank area of ​​a petrochemical enterprise in Shanghai include benzene, toluene, xylene, sulfolane and other components. The exhaust gas from the oily sewage tank area and sewage pool is processed by a 7dam3/h buffering homogenization and catalytic oxidation device. The mass concentrations of NMHC and benzene in the purified gas are less than 20.1 mg/m3 respectively. 1.4 VOCs exhaust gas treatment from the oxidative demercaptan unit. Gasoline and liquid hydrocarbon oxidative demercaptan exhaust gases should be processed in a Claus exhaust incinerator or a low-temperature diesel absorption device. If the low-temperature diesel oil cannot meet the emission standards after absorption, it can be further processed in a catalytic oxidation device, a thermal storage oxidation device, an incinerator, etc. There are many sets of low-temperature diesel absorption devices for oxidative demercaptan tail gas in China. Gasoline oxidative demercaptan tail gas contains high concentrations of gasoline oil vapor and organic sulfides. The economic benefits of low-temperature diesel absorption are very good. Sinopec applied a "low temperature diesel absorption" device in a refining and chemical company in Shandong Province to treat gasoline oxidative demercaptan tail gas. The amount of oil and gas recovered was 502.7t/a. The absorbed tail gas was sent to the Claus tail gas incinerator for treatment to meet emission standards."] Liquid hydrocarbon oxidation demercaptan tail gas mainly contains organic sulfides, and the concentration of dimethyl disulfide can reach several thousand mg/m3. If it is directly fed into the Claus tail gas incinerator, attention must be paid to safety issues and whether the incineration flue gas SO2 emissions exceed the standard. Sinopec's refining and chemical company in Shanghai originally sent the liquid hydrocarbon oxidation demercaptan tail gas to the Claus tail gas incinerator for treatment, but the flue gas SO2 did not meet the new standard GB31570--2015 emission requirements (100mg/m3). In 2015, the company built a low-temperature diesel absorption device to absorb the exhaust gas and then send it to the Claus exhaust incinerator for treatment, solving the problem of excessive flue gas. 1.5 Rubber plant VOCs waste gas treatment VOCs waste gas from production plants such as styrene-butadiene rubber (SBS) and butadiene rubber should be pre-treated (condensation, defogging, filtration, washing). Catalytic oxidation technology should be used to recover heat through steam generation and other methods. 1.5.1 SBS rubber waste gas "condensation-defogging-catalytic oxidation" device Sinopec's waste gas emissions from the SBS rubber production process in a rubber factory in Beijing mainly include flash steam at the outlet of the screw extruder and rubber pellet drying gas. The flash gas is mainly composed of water vapor and high-concentration cyclohexane, which has great recovery value; the exhaust volume of the rubber pellet drying wind is large, and the mass concentration of NMHC is 5000-8000 mg/m3. In September 2007, the rubber factory built a set of 30 Dam3/h processing capacity SBS rubber exhaust gas "condensation-demist.catalytic oxidation" device, the flash gas first undergoes two-stage condensation pretreatment, most of the water and cyclohexane in the exhaust gas are recovered, and the generated non-condensable gas is mixed with the dry gas of the rubber particles, in sequence After passing through the demister, heat exchanger, heater, etc., the exhaust gas is heated to above 260°C and enters the catalytic oxidation reactor. Under the action of the catalyst, VOCs are oxidized into CO2 and H2O. The mass concentration of NMHC in the purified gas is less than 100 mg/m3. The reaction heat generated by oxidation is recovered through the heat exchanger, and part of the reaction heat is used for drying SBS colloidal particles. It can reduce the emission of organic matter by 900 tons per year. All the condensed water and cyclohexane recovered by the device are reused in the SBS synthesis system, which can save 808,000 yuan/a; the discharged high-temperature purified gas is reused in the colloidal drying system to replace part of the water vapor, saving 910,000 yuan. At the end of 2012, according to the requirements of the new standards, by replacing the new WSH catalyst and adjusting the operating parameters, the NMHC of the purified gas of the device dropped below 20 mg/m3, and cyclohexane fell below the detection limit, in line with * * emission standards. 1.5.2 Butadiene rubber exhaust gas "filtration, demisting and catalytic oxidation" device. The VOCs exhaust gas of the butadiene rubber post-treatment unit of the above-mentioned rubber factory of Sinopec in Beijing is about 70dam3/h, and the main pollutant is hexane. In 2014, the "filtration, demisting and catalytic oxidation" device was completed and put into use. It uses WSH-2F honeycomb precious metal catalyst. The inlet temperature of the catalytic oxidation reactor is 220-260oC and the outlet temperature is 370-470oC. The NMHC quality of the exhaust gas before treatment is The concentration is 5000~10000mg/m3. The mass concentration of NMHC in the purified gas after treatment is less than 5mg/m3, and the hexane is lower than the detection limit; the hexane oxidation reaction heat is used to produce 8kg/cm2 steam 1~3t/h, and the steam is incorporated into the steam pipe network in the factory. After the device is put into use, it can reduce VOCs emissions by nearly 2,000 tons per year. 1.6 VOCs waste gas treatment of propylene oxide/styrene (PO/SM) unit. The tail gas produced by propylene oxide/styrene (PO/SM) should be treated by catalytic oxidation technology, using precious metal catalysts. In a Sino-foreign joint venture of Sinopec in Zhejiang Province, the exhaust gas emitted from the epoxy propylene styrene (PO/SM) production unit contains benzene, toluene, acetaldehyde, ethylbenzene, propylene oxide, styrene and other volatile organic compounds. The organic matter mass concentration is 2800-20000mg/m3, and the exhaust gas flow rate is 86dam3/h. Using a dual-series catalytic oxidation device, the WSH-2 precious metal catalyst has been used continuously for more than 5 years. The mass concentrations of NMHC, acetaldehyde and styrene in the purified gas are less than 80, 5, and 2 mg/m3 respectively, and the NMHC removal rate is greater than 97%. 1.7 Waste gas treatment from aniline production The waste gas from aniline production should be treated by pretreatment and catalytic oxidation. Precious metal catalysts are recommended. Pretreatment includes vacuum pump tail gas circulating water cooling and mist removal. Sinopec’s Technical Guidelines for Comprehensive VOCs Control recommend that VOCs exhaust gases from large petrochemical companies should be collected and processed in a centralized manner by region and type. Therefore, the company built a set of 20dam3/h aniline equipment and VOCs waste gas centralized catalytic oxidation treatment equipment such as raw material tank areas, using WSH-2N Pt.Pd-ce catalyst, which has high hydrocarbon-based oxidation activity and high selectivity (more than 95% of organic nitrogen is converted into nitrogen). After the 72-h performance assessment of the device, the main pollutant emissions in the purified gas are as follows:: The mass concentrations of NMHC and NOx are 4.36 and 6.6 mg/m3 respectively, and the mass concentrations of benzene, aniline, * * * , cyclohexane concentration are all lower than the detection limit, and all indicators are far better than the requirements of GB31571--2015 (Petrochemical Industry Pollutant Emission Standard). Project examples: Sinopec produces benzene as raw material at a chemical company in Jiangsu Province * * * ,aniline, * * , rubber antioxidants and other benzene chemical products. These benzene chemical plants and (raw materials, intermediate products, finished products) tank areas emit VOCs exhaust gases during the production process. There are a total of 12 process exhaust outlets and 85 volatile organic liquid storage tanks. The main pollutants in the exhaust gases are benzene, * * * , aniline, cyclohexane, * * , C and the same, among which, * * * , Aniline belongs to nitrogen-containing volatile organic compounds (NVOCs). The mass concentration of total hydrocarbons (methane + non-methane total hydrocarbons) at the process exhaust outlet is roughly 1000-28000mg/m3, and the mass concentration of benzene is 600-16000mg/m3. * * * The mass concentration of aniline is 400-800mg/m3, the mass concentration of aniline is 1000-2000mg/m3, the mass concentration of cyclohexane is 4000-28000mg/m3, and the mass concentration of propylene glycol is 1000-18000mg/m3. Most exhaust gases contain two or more organic pollutants. The total hydrocarbon mass concentration in the exhaust of 85 storage tanks is basically less than 30,000mg/m3. 1.8 Waste gas treatment from chlorobenzene production Chlorbenzene production waste gas should be treated by regenerative combustion-sodium hydroxide alkali liquid absorption and activated carbon adsorption process; alkali liquid absorbs hydrogen chloride (HCl), and activated carbon absorbs dioxin. Table 4 shows the gas composition analysis at the inlet and outlet of the regenerative oxidation (RTO) unit. 4.jpg Project examples: Sinopec has a chlorobenzene device, a nitrochlorobenzene device, a surfactant device and 14 raw material and product storage tanks in the chlorobenzene device area of ​​a chemical company in Jiangsu Province to emit VOCs waste gas. The waste gas contains chlorobenzene, benzene and other pollutants, of which chlorobenzene is a chlorine-containing volatile organic compound (CVOCs). For the above-mentioned waste gas, the company built a set of 15dam3/h "thermal oxidation (RTO)-absorption-adsorption" centralized treatment device, with an NMHC removal rate of more than 99%. The mass concentration of NMHC in the purified gas is 10 mg/m3, and chlorobenzene, The concentration of pollutants such as benzene and HCl is below the detection limit. The mass concentration of dioxin is 0.016~0.043ng/m3 (toxic equivalent TEQ). The purified gas complies with GB31571--2015 "Petrochemical Industry Pollutant Emission Standard". 2 Conclusion Based on technologically advanced, mature and reliable engineering examples, typical technologies for VOCs waste gas treatment are recommended from petrochemical sewage treatment plants, volatile organic liquid loading operations, volatile organic liquid storage tanks, oxidative demercaptan units, rubber units, epoxy propylene styrene (PO/SM) units, aniline units, chlorinated benzene units, etc. By adopting reasonable and efficient treatment technologies, the indicators such as NMHC, benzene, toluene and xylene in the purified gas all meet the * * Emission standards, VOCs exhaust gas has achieved good treatment results.