Research Of Heavy Oil Coking Process And Optimization Of Coking Tower Feeding Mod

This paper focuses on the optimization of heavy oil delayed coking process and coke tower feeding mode and is intended for use in summary on the basis of previous experience put forward by further optimization of the recycle ratio and the coke tower feeding mode in order to reduce the recycling ratio when processing Tahe heavy oil to ensure a long term, high efficiency and safe operation in commercial delayed coking unit.Heavy oil coking process research is for the purpose of determining the proper recycle ratio in Tahe atmospheric residue delayed coking process by assessing the coking factors of radiation feedstock under different recycle ratio.Coking factor is an important indicator to predict the coking tendency of delayed coking feedstock in radiation preheating pipes. A small coking factor indicates a slower coking rate and a longer operation period of heating furnace,on the other hand, a large coking factor means that the preheater has a high coking rate, which results in a short operating term of the delayed coking unit.The coking factor assessment results show the coking tendency and coke formation rate become higher as the recycle ratio decreases. In comparison with other refiner’ radiation section feedstock coking factors, recycle ratio should be at least 0.5 in Tahe atomspheric residue delayed coking unit in order to keep a safe and long term operation.With Tahe atmospheric residue as delayed coking feedstock, the effects of different feeding modes between balance(upper tower) and conventional(bottom tower) on product distributions have also been tested. The results show that, in comparison with conventional bottom tower feeding mode,balance(upper tower) feeding has such advantages as lower yields of dry gas and coke formation, so the total liquid yield increase by 0.87 percentage, with a slight decrease of naphtha and diesel and a significant increase of coker gas oil under the same operation conditions in delayed coking process. However,the gas composition and the properties of naphtha and diesel almost remainthe same, and the properties of coker gas oil become slightly poor, which will not has remarkable negative effects on downstream processes.The properties of petroleum coke also remain the same for both feeding modes with a sulfur content of more 4w%, which can only be sold as high sulfur coke or as the fuel for CFB boiler to generate steam and electricity.In comparison with convention feeding mode, the properties of radiation section feed are slightly poorer but will have no remarkable and negative effects on the safe and long term operation of delayed coking unit.