Estimation of Kinetic Parameters of Coking Reaction Rate in Pyrolysis of Naphtha

The run length of cracking furnaces is limited by the formation of coke on the internal skin of the reactor tubes. The reaction mechanism of thermal cracking of hydrocarbons is generally accepted as free-radical chain reactions. On the basis of the plant output data and the insight in the mechanisms for coke formation in pyrolysis reactors, a kinetic model describing the coke formation has been developed. It consists of seven reactions for coke formation assuming that the sources of coke formation are ethylene, propylene, butadiene and benzene, toluene, xylene and styrene. The coking model was combined with a rigorous kinetic model for the pyrolysis of naphtha and a reactor model. The parameters for this model were determined using nonlinear Marquardt optimization method.The sum of squares of the deviations between the calculated and plant data was used as the objective function and minimized by the appropriate choice of the portion of each reaction involved in coke formation. Finally the simulated and plant output results agree in a good accuracy.