Numerical Simulation Of Adiabatic Trickle Bed Reactor For Catalytic Diesel Hydrocracking

With the deeper extraction of petroleum resources,the quality of processed crude oil in China has become increasingly heavier and poorer,further resulting in enhanced density,low cetane number,high heavy aromatics content of catalytic diesel.Furthermore,in order to reduce the effects of severe weather,e.g.,fog haze,more restrictive environmental regulations and emission standards for the content of heavy aromatic,sulfur nitrogen and other compounds in oil are published.Nowadays,hydrocracking technology of catalytic diesel is one of the most direct,effective and widely used method in the petroleum industry to convert low-quality catalytic diesel with high molecular weight into high-octane gasoline and improve the quality of product.Trickle bed reactor(TBR)is a three-phase fixed bed reactor,which is widely applied to hydrocracking process.In this work,a mathematic model of hydrocracking of catalytic diesel was established in TBR,which combined computational fluid dynamics(CFD)with a kinetic model of hydrocracking.The model can be used to guide the TBRs design and optimization and industrialization amplification.The numerical simulation of fluid flow and hydrocracking reaction of catalytic diesel from one petrochemical research institute in laboratorial small-scale TBR was studied by CFD with FLUENT 16.2.First of all,a cold model was established to simulate the gas-liquid two-phase flow process in TBR,using Euler-Euler multiphase flow model.Fluid-flow characteristics(i.e.,bed pressure drop,the liquid volume fraction)without reaction were mainly investigated in this work.The fluid-fluid interfacial force model under high pressure was added to fluid region and catalyst bed layer to optimize the flow field in TBR.In order to verify the rationality of the flow field in TBR,the effects of space velocity of catalytic diesel and mass flow rate of hydrogen on the hydrodynamics of TBR were investigated.Secondly,when the flow field in TBR is stable,the reaction characteristics(e.g.,conversion of crude oil,yield of products,hydrogen consumption rate,temperature distribution)of the hydrocracking were investigated by adding hydrocracking kinetics model into the CFD mathematic model.The modified kinetics model of hydrocracking based on Stangeland model and parameters related to this modified model were selected in terms of the characteristics of raw oil and products.The fourth order Runge-Kutta method,which is added into species transport equations by User Defined Functions(UDF)written with C language,was applied to making the solution for the kinetic equations to simulate the conversion of lumps.The hydrogen consumption rate in hydrocracking process based on conservation of carbon mass in reaction system was calculated through associating with molecular weight and hydrocarbon ratio of lumps.The energy source terms were calculated through associating with hydrogen consumption rate,indicating the changes of temperature in TBR.Finally,the effects of space velocity of crude oil,mass flow rate of hydrogen and reaction temperature on the hydrocracking process in TBR were investigated.With space velocity of crude oil increasing from 0.28 h-1 to 2.22 h-1,the conversion of reactor outlet decrease from 99.58%to 52.79%,and the temperature difference of reactor bed layer decrease from 12.77 K to 5.83 K.To some degree,the distillations of product can be chosen by changing space velocity of crude oil.With the increase of space velocity of crude oil,the yield of jet fuel increase,and the yields of L-naphtha and H-naphtha decrease.The mathematic model of hydrocracking of catalytic diesel and simulated results can provide theoretical basis for design and industrialization amplification of TBRs.