Dynamic Modeling And Operation Analysis Of FCCU(Fluid Catalytic Cracking Unit) With High Efficient Regenerator

The FCCU (Fluid Catalytic Cracking Unit) with a high efficient regenerator is used for the processing of VGO. Thus, the heat exchanger to remove the excess heat in not included. The carbon on catalyst is completely converted to carbon dioxide by CO promoter. The carbon content on regenerated catalyst is much low. The regenerator is composed of two stages, fast fluidized bed and bubble fluidized bed. The dynamic mechanic model, operation analysis and control structure of the unit had never before been reported.In the paper, simulation, operation analysis such as dynamic behavior, stead state characteristics and stability analysis, and control constructure would be provided, after developing the windows software platform on the basis of the dynamic mechanic model whick has been built for the reactor/regenerator section of the FCCU (Fluid Catalytic Cracking Unit) with a high efficient regenerator.First, a dynamic mechanic model was developed for the unit which is used for processing of VGO. The five lumped kinetic model was adopted in which feed stock, diesel, gasoline, gas and coke lumps are comprised and three first-order reactions are included. Reaction heat for each reaction was estimated separately with combustion heat of lumps. The effect of feed properties on the cracking characteristics was considered by the heavy aromatic content of fresh feed and recycle ratio. The first stage of the regenerator, fast fluidized bed, was constructed with an axial dispersion model in which dynamic distributed parameter equations for carbon and hydrogen content on catalyst and regeneration temperature, pseudo-steady distributed parameter equation for oxygen content in gas and dynamic lumped parameter equation for catalyst inventory are included. The gas velocity in the second stage of the regenerator, bubble fluidized bed, is so slow that the stage was formulated with CSTR model for both gas and catalyst that is composed of dynamic lumped parameter equations for carbon on regenerated catalyst and catalyst holdup, and algebraic equation for oxygen content in gas, and the effect of gas dispersion through the film on the surface of catalyst was considered. According to the balance of pressure, the formula were obtained to calculate the spent, regenerated catalyst transport rate and the catalyst transport rate from the second stage of the regenerator to the bottom of the first which must be determined before the dynamic modeling of the FCCU. The pressure transient response equations for separator at the top of the riser reactor, main fractionator, separator for gas and gasoline and regenerator were proposed on the basis of the equation of state for ideal gas and the change of molecular rates through the vessels. The dead time was considered.