Effects of compressibility factor on fluid catalytic cracking unit riser hydrodynamics

A detailed steady state FCC riser process model is simulated for the first time with different compressibility (Z) factor correlations using gPROMS software. A 4-lump kinetic model is used where gas oil cracks to form gasoline, coke and gases. The usual practice has been the assumption that the FCC riser gas phase is an ideal gas at every point under any condition (varying C/O ratio, riser diameter, operating temperature and pressure, etc.). This work found that the Z factor varies at every point across the riser height depending on riser operating pressure and temperature, diameter and C/O ratio. It also shows that the magnitude of deviation of a gas phase from ideal gas behaviour can be measured over the riser height. The Z factor correlation of Heidaryan et al. (2010a) is found to be suitable for predicting the Z factor distribution in the riser.