催化裂化装置烟气脱硫脱硝外排废水水质超标原因分析及解决对策

CAUSE ANALYSIS AND COUNTERMEASURES OF WASTEWATER QUALITY EXCEEDING STANDARD IN FCCU FLUE GAS DESULFURIZATION AND DENITRIFICATION

针对某炼化企业催化裂化装置烟气脱硫脱硝外排废水总磷(TP)含量和化学需氧量(COD)超标问题,采用数理统计方法对异常情况进行了分析,通过一系列试验考察了不同絮凝剂对TP的去除效果,确定最优配比用以调整絮凝剂的配方;另外,根据装置运行工艺探讨了滤清模块、外排液流量、絮凝剂的投加量及其浓度、搅拌电机转速、胀鼓过滤器、氧化罐通风量以及原料油性质等对外排废水COD的影响。结果发现,聚合硫酸铁(PFS)对催化裂化装置现用的新鲜催化剂、再生催化剂和废剂罐催化剂中的TP均具有较好的去除效果,TP去除率在65.2%~100%之间。此外,通过加大外排液流量、重置相应的工艺参数、调整絮凝剂投加量及其浓度、保证氧化罐通风量充足以及采用调整反应深度以降低硫含量等手段使外排废水COD达到了环保要求。

Aiming at the problem of excessive total phosphorus(TP)and chemical oxygen demand(COD)in the flue gas desulfurization and denitrification effluent from a refining and catalytic cracking unit(FCCU),the abnormal situation was analyzed by mathematical statistics,a series of experiments were carried out to investigate the effect of different flocculants on TP removal,and the optimal ratio was determined to adjust the formulation of flocculants.According to the operation process of the unit,the influences of the filter module,the flow rate of the effluent,the dosage and concentration of the flocculant,the rotating speed of the stirring motor,the bulging filter,the ventilation rate of the oxidation tank and the properties of raw oil on the COD of the effluent were investigated.The results showed that polymeric ferric sulfate(PFS)had a good removal effect on fresh agent,regenerant and waste agent in catalytic unit,with TP removal rates ranging from 65.2%to 100%.In addition,the COD in the effluent could meet the requirements of environmental protection by increasing the flow rate of effluent,resetting the corresponding process parameters,adjusting the dosage and concentration of flocculant,ensuring sufficient ventilation in the oxidation tank and adjusting the reaction depth to reduce the sulfur content.