Mathematical Simulation Of The Reaction Process Of F-T Wax Hydrocracking

With the shortage of petroleum resources, the coal begins to play the more and more important role. Fischer-Tropsch (F-T) synthesis is one of the important process to produce oil with coal-gasification. The product of Low-temperature F-T synthesis is mainly composed of C1-C70+ paraffin hydrocarbons and it has higher cetane number, little sulfur and little nitrogen. It can be regarded as clean fuel. But, nearly half percent of the F-T oil is long chain hydrocarbons (C22+), so it cannot be used as liquid fuel directly. Therefor, it is necessary to upgrade the paraffin hydrocarbons with hydrocracking process which purpose is producing the Middle Distillate, gasoline and diesel oil.The wax produced from F-T synthesis is made of the hydrocarbons of C1-C70+, so according to the molecular structure and product distribution of these hydrocarbons, the ADA/PCS method in AspenPlus is used to separate the feed oil into nine lumps and to calculate each lump to obtain its basic physical property, then the lump kinetics model is used to describe the reaction process of hydrocracking. The nine lumps are C1-C4, C5-C9, C10-C14, C15-C22, C22+, iso-C5-C9, iso-C10-C14, iso-C15-C22,iso-C22+, in which C22+is wax oil, C15-22 are heavy diesel oil, C10-14 are light diesel oil, C5-9 are gasoline and C1-4 are gaseous hydrocarbon.Because the default kinetic model in AspenPlus software cannot describe the nine lumps kinetic model of F-T synthesis wax hydrocracking, so in this paper, the Fortran language is used to programming the customized lump kinetic model. On this basis, firstly the Rplug model is used to simulate the isothermal reactor of F-T synthesis wax hydrocracking, the adiabatic reactor with one catalyst bed and the adiabatic reactor with two catalyst beds, then the RadFrac module is used to exploratively calculate the process of hydrocracking reactive distillation. By means of simulating the isothermal reactor, the feasibility of Fortran model is proved, and the optimal operating conditions are got via sensitivity analysis of operating parameters:T=375℃, P=47.5bar, H/O=0.105wt/wt, WHSV=2 Kgwax/h/Kgcat; by means of simulating the adiabatic reactor with one and two catalyst beds we know that when the two reactors have the same feed temperature (294℃) and feed capacity (250g/h), the temperature flying point of the adiabatic reactor with two catalyst beds goes back 0.2m compare to the adiabatic reactor with only one catalyst bed, and in this case, the inactivation of catalyst at high temperature can be effectively avoided; on the basis of reactor simulation result, we calculate the reactive distillation tower, and prove the feasibility of applying the reactive distillation tower in the field of F-T synthesis wax hydrocracking, also we get the discharge location of every lump component:C22 is at the tower bottom, C15-22 is at the 26th tower plate, C10-14 is at the 9th tower plate, C5-9is the liquid phase discharge and C1-4 is the gaseous phase discharge. Thus we believe that the purpose of process intensification and cost saving can be achieved very well by using the reactive distillation tower in the F-T synthesis wax hydrocracking process.