Analysis On Key Factors Of Process Optimization And Long-term Operation Of Catalytic Cracking Unit

With the heavy and poor quality of crude oils becoming more and more serious,the coking of catalytic cracking units is getting more and more serious,which limits the long-cycle operation of the units.Through effectively solving the coked problem to ensure the long-cycle operation of the plant and achieve smooth and safe operation is the imperative technical requirements of the catalytic cracking production process.In this paper,the operation of an 800,000 t/a catalytic cracking unit of a refining company of China National Petroleum Corporation was studied,and it been found that the serious coking problems of the reaction system and fractionation system in the last operating cycle of the unit were mainly coking inside the settler,blockage of coke blocks in the slurry heat exchanger,and poor heat exchange effect of the crude oils.The results show that the main factors of coking include:(1)poor crude oils and slurry properties;(2)low feedstock preheating temperature;(3)low agent-oil ratio;(4)low slurry circulation volume and slurry flow rate in the tube bundle;(5)improper operating conditions of the fractionator.In response to the above factors,operational optimization and technical modification measures were proposed,including:(1)increase the agent-oil ratio to6.85 to suppress coking in the reaction system by changing the regenerator operating conditions through feedstock optimization;(2)change the original feedstock and slurry system flow so as to increase the feedstock preheating temperature to above230°C,slurry circulation volume to 223t/h and slurry flow rate in the tube bundle to1.89m/s(3)Optimize the operating conditions of the fractionation column to improve the coking problem of the fractionation system by controlling the slurry residence time in the column to less than 5 min.The control and optimization of key factors solved the coking problem of the unit,and the cost per ton of oil in the auxiliary materials and catalyst of the unit was accordingly reduced by 6.45 RMB and 6.95 RMB,with significant economic benefits and far-reaching impact on extending the operation cycle of the unit.