Process Modeling, Simulation, And Optimization Of Fluidized Catalytic Cracking Unit With High Efficiency Combustor

The fluidized catalytic cracking unit (FCCU) with high efficiency combustor wasdeveloped to process various types of feedstocks. Coke on spent catalyst could betotally converted to CO2with few or no CO promoter in regenerator, while the cokecontent of regenerated catalyst was still kept to be a very low level. Considering thecoupling effects of riser reactor, disengagement vessel,1ststage high efficiencycombustor, and2ndstage dense bed regenerator and the complexity of flow pattern in1ststage combustor, this work developed the rigorous fundamental steady state modeland the corresponding process simulation platform for this type of FCCU.The riser model was based on the one dimensional steady state model proposedby Gupta et al, applying the oil cracking kinetice method of true and pseudocomponents, which was coupled with mass balance equations, energy balanceequations, and gas/solid flow pattern description model. The solid cluster model wasbased on to develop the gas/solid flow pattern model. Considering the huge number ofcracking reactions existing within the oil cracking reaction network, the volumeelement method was used to develop the key model equations. The disengagementvessel model included the free board model and the stripper model. The free boardmodel assumed no chemical reactions occurred there, which could account for thepressure drop effects of multistage cyclones within the equipment. The stripping cokeon spent catalyst was featured by the published multistage stripping model, which wasthen coupled with the mass balance equations and the energy balance equations. Thegas/solid flow pattern within the combustor was calculated via the solid cluster model,which was then coupled with coke combustion kinetics model, mass balanceequations, and energy balance equations, forming the steady state model for thecombustor. And the model could account for the effects of pressure drop of thecyclones located at the outlet of combustor. The2ndstage dense bed regeneratormodel included the dense region model and the free board model. The gas/solidcontinuous stirred tank model was based on to feagure the flow pattern within thedense bed region. The bed voidage was calculated via the published industrialcorrelations. These was then followed by coupling with the coke combustion kineticsmodel, mass balance equations, and energy balance equations. The free board modelassumed no solid particle existing within the reactor, so PFR based reactor model wasused to simulate the free board region. The developed model could account for the different pressure loss including the static pressure lose, pressure loss due to frictionbetween gas phase and wall, and pressure loss within the outlet multistage cyclones.The process simulation platform for the combustor-style FCCU was developedusing the Aspen Custom ModelerTMsoftware. In order to overcome the shortcomingsof this software which could not handle models with huge number of variables or withcomplex ODEs, this work applied the method of Fortran programming based on thesoftware platform to solve the models of riser reactor, combustor, and the free boardregion of2ndstage dense bed regenerator.This work observed the effects of seven key process operating variables such asfeed flow rate and feed temperature on the run state of the whole FCCU, hoping togive instructive guidelines for the field operation, engineering design, and processoptimization of this type of FCCU. The technologies of quench injection in riserreactor, catalyst heat remover, and combustion air oxygen enrichment were analysedfor their application potential on the FCCU. Applicatioin of quench injection on theriser could control the residence time of hot oil gas and catalyst within the reactor, sothe products distribution could be tuned up. The addition of catalyst heat removerimproved the operator’s ability to adjust the unit heat balance, so that the gas/solidtemperature at the feed inlet of riser reactor and the ratio of regenerated catalyst flowrate to mixed feed flow rate could be controlled. The technology of oxygenenrichment in combustion air intensified the ability of catalyst regeneration ofcombustor-style regenerator, improved the initial activity and selectivity of unitbalance catalyst. The three technologies could complement with each other, formingthe combined process intensification technology. The simulation results showed thatthe application of this technology elevated the field operation level, considering itsablity to comtrol the ratio of regenerated catalyst flow rate to feed flow rate, theenvironmental temperature of oil cracking reactions, the residence time of hot oil gasand catalyst in riser reactor, and the coke content of regenerated catalyst.