浅析如何做好芳烃抽提装置的清洁生产

A Brief Analysis of Clean Production on Aromatic Extraction Units

大庆石化公司两套芳烃抽提装置均采用UOP生产技术,通过萃取、精馏后得到高纯度的苯、甲苯和二甲苯产品。芳烃抽提装置存在低负荷待料循环时间长,不合格油品每月大约产生100t,原料罐和产品罐在脱水过程中每天大约损失300kg油品,且罐没有氮封,存在三苯挥发损失,采样点物料损失多,泵房送风机运行效果差,三苯放空气体现场排放,装置废水排放量达1.1t/h等问题。通过实施"两头一尾"生产方案,每天可节约蒸汽160t、循环水3500t和大量的电能,年创利润300余万元;对不合格油品进行回炼后,年创效益156万元;在物料罐顶部增设氮封,并在氮封阀前安装限流孔板,减少三苯排放;将普通阀门采样器更换为环保无泄漏采样器;将送风机的加热介质改为热量较高的0.3MPa蒸汽;采用活性炭纤维有机回收装置处理回流罐排放气体;检修设备置换气体排入火炬;气抽子凝水利用,每年减少新鲜水消耗3000t。以上方案实施后,现场空气中三苯含量由原来的平均130mg/L降至25mg/L以下。

PetroChina Daqing Petrochemical Company′s two aromatic extraction units both used UOP production technology,which produced high purity of benzene,methylbenzene and dimethylbenzene by extraction and rectification.These aromatic extraction units had some drawbacks.Their downtime for waiting for feedstock at low load was too long;monthly output of oil products below standard was about 100t;about 300kg of oil products were lost per day in the dehydration process for feedstock tanks and product tanks（in addition,these tanks were not nitrogen sealed）;there was volatilization loss of benzene,methylbenzene and dimethylbenzene;many materials were lost at sampling points;the performance of the air feeders in the pump room was poor;some benzene,methylbenzene and dimethylbenzene were directly vented on site;the wastewater discharge from the units reached 1.1t/h.With the introduction of the＂two extraction units and one rectification unit＂process,the company could save 160t of steam,3500t of circulating water and a large amount of electric power per day.Annual profit from this upgrade could exceed three million yuan.The reprocessing of unqualified oil products could bring the company 1.56 million yuan in revenue per year.Other measures included adding nitrogen sealing at the top of material tanks,installing throttling orifice plates in front of nitrogen sealing valves to reduce the discharge of benzene,methylbenzene and dimethylbenzene,replacing ordinary valve samplers with environmentally friendly leakage-free samplers,changing the heating medium for air feeders to 0.3MPa steam with higher heat value,using active carbon fiber recovering units to treat the gas discharged by reflux accumulators,venting the gases from displaced equipment during overhauls into torches,and recycling air pump condensed water（as a result,fresh water consumption drops by 3000 tons per year）.After the above measures are taken,the concentration of benzene,methylbenzene and dimethylbenzene in the air on the site has dropped to less than 25mg/L from 130mg/L.