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石油炼化过程包含一系列分离、纯化操作,消耗大量水资源的同时也产生大量的废水[1-3]。据估计每处理1 t原油产生废水量为0.4~1.6 t,废水中含有大量的石油类、挥发酚、重金属等有毒、难降解物质,因此,炼化废水也被称为典型的工业危险废物[4-5]。未经处理直接排放不仅会污染环境,还会降低产品回收率,错失水资源回收利用的机会[6]。目前,炼化废水经隔油、气浮、生化单元处理后部分回用,外排水经由深度处理达到《石油炼制工业污染物排放标准》(GB 31570—2015)标准规定限值后外排[7-8]。非均相催化臭氧氧化技术由于其绿色、清洁、不产生二次污染等特点被广泛应用于废水的深度处理,但由于废水水质的复杂化程度加剧和外排水水质标准的不断提高,导致经由单一深度处理技术处理后达标较为困难,同时,对于深度处理单元的污染物去除率要求更高[9-11]。
东北某炼化公司深度处理单元主要包括多介质过滤器、臭氧催化氧化池、MBBR(moving-bed biofilm reactor移动床生物膜反应器)、电催化、活性碳滤罐,臭氧催化氧化池作为生化出水的第1个处理单元,对废水中微生物难降解的有机物具有较高的去除作用,同时可提高废水的可生化性[12-13]。该臭氧催化氧化单元采用传统非均相臭氧催化氧化技术,催化剂的优劣对臭氧催化氧化单元污染物去除率起到关键作用[9, 14]。工程化应用的非均相催化剂主要是金属离子负载型,基体普遍采用氧化铝基,但负载的金属离子种类繁多[15-18]。有研究[19-20]表明,负载不同金属离子的催化剂在催化臭氧氧化处理同一种废水时污染物去除率存在较大差异。负载锰氧化物的催化剂可显著提高苯类物质的矿化速率,负载铁氧化物的催化剂对酿酒废水有较高的COD去除率[15, 21]。WU等[22]研究表明,γ-Al2O3负载Mn、Ce催化臭氧氧化处理1-氨基-4-溴蒽醌-2-磺酸时,对污染物的去除率较高。LI等[23]研究表明,Al2O3负载Mn、Fe、Ce 3种金属处理奶牛养殖废水时,废水COD去除率可达48.9%。因此,如何做到将废水水质参数与催化剂负载组分相关联,得到与废水水质适配的负载金属离子成为亟需解决的关键问题。此外,催化剂制备过程中受焙烧温度、焙烧时间等因素的影响。
此次更换催化剂为某研究院根据炼化公司外排水水质参数针对性设计的催化剂制备方案和制备条件,催化剂生产完成后,随机抽样送至具有CMA (China metrology accreditation) 资质的第三方检测公司进行催化剂性能测定并出具测试报告。符合要求后送至炼化公司进行催化剂的更换,对更换后臭氧催化氧化单元污染物去除情况进行分析,以期为臭氧催化氧化单元的实际工程应用提供技术支撑。
臭氧催化氧化池更换铝基催化剂的工程应用
Engineering application of ozone catalytic oxidation tank to replace alumina -based catalyst
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摘要: 为解决某炼化公司外排水装置臭氧催化氧化单元污染物去除率低,能耗高的问题,将臭氧催化氧化池原有催化剂(氧化铝基+活性碳棒)更换为某研究院基于炼化公司外排水水质参数所制备的专性催化剂,对更换前后污染物去除率和臭氧剂量进行分析。结果表明:专性催化剂具有良好的晶型和发达的孔隙结构,常态化运行后,更换催化剂后的氧化池COD去除率达到42.98%~62.63%,远高于未更换的氧化池(8.96%~20.64%)。对多介质过滤器进水、臭氧催化氧化池进水、臭氧催化氧化池出水(更换、未换)分别取样测定COD、TOC、UV254和荧光光谱,发现多介质过滤器只可通过截留作用去除分子质量较大的类腐殖质等物质,去除率较低;更换催化剂后臭氧催化氧化池的COD去除率达50.86%、TOC去除率达46.62%、UV254去除率达82.17%、荧光类物质去除率可达96.23%。臭氧催化氧化池出水(更换)B/C值为0.56(臭氧催化氧化池进水B/C值为0.21),经由臭氧催化氧化处理后,出水可生化性提高。常态化运行期间臭氧剂量为:更换催化剂的氧化池1.31~1.68 g·g−1(以COD计),均值为1.58 g·g−1,未更换催化剂的氧化池为4.15 g·g−1,表明更换催化剂后可显著降低臭氧的消耗。以上结果表明,炼化公司外排水装置更换臭氧催化剂后污染物处理负荷大幅度提高,臭氧消耗量减少,节能减排成效显著。Abstract: In order to solve the problem of low pollutant removal rate and high energy consumption in the ozone catalytic oxidation unit of the external drainage device of a refining and chemical company. The original catalyst (alumina base+activated carbon rod) in the ozone catalytic oxidation tank was replaced with a specific catalyst prepared by a research institute based on the water quality parameters of the refining company's external drainage. And the pollutant removal rate and ozone dose were analyzed before and after the replacement. The results show that the specific catalyst has a good crystal form and a well-developed pore structure. After normal operation, the COD removal rate of the oxidation tank after the catalyst replacement could reach 42.98%~62.63%, which was much higher than that of the unreplaced oxidation tank (8.96%~20.64%). The water samples from the incoming water of the multi-media filter, the incoming water of the ozone catalytic oxidation tank, and the effluent water of the ozone catalytic oxidation tank (replaced and unreplaced) were taken and their COD, TOC, UV254 and fluorescence spectra were tested, respectively. It was found that the multi-media filter could only remove humic substances with higher molecular weight through interception, and the removal rate was low; After replacing the catalyst, the COD,TOC, UV254 and fluorescent substance removal rates of the ozone catalytic oxidation tank reached 50.86%, 46.62%, 82.17% and 96.23%, respectively. The B/C value of the effluent from the ozone catalytic oxidation tank (replaced) was 0.56 (the B/C value of the incoming water to the ozone catalytic oxidation tank was 0.21). After catalytic ozonation treatment, the biodegradability of the effluent increased. The ozone dose during normal operation was following: 1.31~1.68 g·g−1 (calculated by COD), for the oxidation tank with catalyst replacement with an average value of 1.58 g·g−1, 4.15 g·g−1 for the oxidation tank without catalyst replacement, which indicated that the replacement of catalyst could significantly reduce ozone consumption. Above results showed that after replacing the ozone catalyst in the external drainage device of the refining and chemical company, the pollutant treatment load has been greatly increased, the ozone consumption has been reduced, and the energy saving and emission reduction have achieved remarkable results.
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表 1 Al2O3和催化剂的比表面积及孔径分布
Table 1. Specific surface area and pore size distribution of Al2O3 and catalysts
催化剂 比表面积/(m2·g−1) 平均孔径/nm 孔容/(cm3·g−1) 氧化铝 206.13 7.76 0.42 催化剂 228.50 7.99 0.48 -
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