Process Development And Economic Evaluation Of Recovering Polymerization Grade C2 Components From FCC Off Gas

Refinery dry gases are mainly from FCC process and delayed coking process and FCC process contributes more than others. Those gases including hydrogen, oxygen, nitrogen, methane, ethane, ethylene and etc. are often lined into the flare system to be burned directly which results in a waste of resources.In this paper, an introduction of the current processes for recovering C2 components from these gases was made and the process simulation boundaries and economic analysis methods were established.Then, a cryogenic process of recovering C2 from FCC off gas was established and an appropriate pressure was found. Then a comparison between recovering C2 from FCC off gas and cracking gas using cryogenic method was made.Third, a novel oil absorption method was developed to recover polymerization grade ethylene using C4, C5 and C6 as absorbents. C2 recovery ratio and process energy cost were analyzed under different process parameters including pressure, temperature, flowrate, theoretical number of stages of each columns. The result shows that C5 consumes less total annualized cost than C4 and C6. So an orthogonal analysis based on C5 absorption of temperature, pressure and absorbent flowrate was conducted to compare the contribution of these factors to C2 recovery ratio and energy consumption. Then the total annualized cost of cryogenic method and absorption method was compared which showed the later costs 3% more than the former.As last, and a thermodynamic model of hydrate reactor was established,validated using Aspen Custom Modeler and two conceptual processes of using oil-absorption and hydrate hybrid method were introduced.