Study On Removal Of Propene From FCC Dry Gas By Membrane-Absorption Hybrid Process

In order to make use of the residual ethylene in dry gas of fluid catalytic cracking (FCC), some domestic oil refineries together with scientific research academies developed the technology of preparing ethylbenzene with ethylene in dry gas. However, the consumptions of ethylbenzene, energy and catalyst were increased due to the high concentration of propene in dry gas. In practical production, the adjustments of technical parameters for the absorption-stabilization system, such as increasing absorbent flux and lowering absorbent temperature, were used to reduce the concentration of propene in dry gas. Yet this method demanded high consumption of energy. To solve this problem, a new technology of combination of membrane technology and absorption-stabilization system was proposed in this work. Through simulation by HYSYS, it is shown that the new technology not only reduces the energy consumption, but also accords with the requirement of propene concentration in dry gas. This paper mainly includes:The model for absorption-stabilization system is established by HYSYS. And the simulating results tally with practical data, which indicates that calculation methods and property data are accurate and credible, i.e. the model accords well with practical production.Through the analysis of the flux and temperature of absorbent, reflux ratio in stabilization column, the temperature of feed gas in desorption column are investigated, and their effects on energy consumption and the weight of dry gas, stable gasoline and liquefied petroleum gas(LPG) are ascertained.By changing the technology parameters, the concentration of propene in dry gas reduced from 1.1%(v) in Operating Condition 1 to 0.3%(v) in Operating Condition 2. However, the cold and hot energy consumptions of Operating Condition 1 decrease by 108% and 122% respectively compared with those of Operating Condition 2.Considering the high energy consumption of Operating Condition 2, coupling technology of membrane separation and absorption-stabilization system is proposed in this paper. The new technology can be alternative processes, i.e. membrane separator before absorber, membrane separator after absorber, and membrane separator before the second absorber. Compared with the practical process, the cold and heat load of the new ones decrease by 42.4%, 28.2%, 29.2% and 44.5%, 31.3%, 31.6% respectively. In comprehensive consideration of the cold and heat load in column and economic analysis, coupling membrane separator before absorber column is the optimum process. Through system heat analysis, it is known the new technology, i.e. coupling membrane separator before absorber column can match well with the energy supplied by fractionation system, and can apply in production practice integrating with the fractionation system.