Research On Improving The Yield Of Propylene Of FCC Gas Fractionation Process

The gas fractionation of FCC (Fluid Catalytic Cracking) unit often used three columns, depropanizer, dethanizer and propylene column, to separate propylene in the gas product of FCC unit. High product purity of propylene was specified so that the columns should operate at the conditions of high reflux ratios and large power consumptions. It is a common knowledge that the yield of propylene of the process could only reach at95%, which is hard to be improved.Aspen Plus was used to simulate the gas fractionation processes. Result shows that the loss of propylene in the process has two main reasons. One reason is that the gas product at the top of the deethanizer has some propylene. The other is that some propylene exits in the bottom of the propylene tower. After that, the operation of the deethanizer was optimized to find wheather there some ways to increase the yield of propylene. Simultation shows that the yield of propylene can’t be increased even that tower was operated at total reflux ratio. Based on the above analysis, this work proposed a new metheod for gas fractionation unit. The process only uses two columns to separate propylene. Result shows that the propylene yield can be increased to more than99%, but the feed concentration has a significant impact on the operation of propylene tower. Sensitivity analysis showed that C2compounds in feed should be controlled at the level of less than0.18%. This result was also proved by dynamic simulation.Finally, the new process was implemented on the2#gas fractionation unit of Wuhan Petrochemical Co. Sinopec. The indusrial results showed that the process can operate well with a propylene yield of99%, while C2in feed was controlled lower than0.1%. This new method could also lower the operation cost, and the economic benift could rearch about12.12million RMB per year.