Coke deposition by physical condensation of poly-cyclic hydrocarbons in the transfer line exchanger (TLX) of olefin plant

The formation and deposition of coke in industrial pyrolysis quenching system is a serious problem. There are two mechanisms for the deposition of coke inside the exchanger tubes of naphtha crackers. In the first, called chemical deposition, the coke formed by chemical reactions at the higher temperature region is deposited in the first half of the tubes. In the second half of the tubes, however because of the lower temperature (T<500 °C), the coke deposition increases due to the physical condensation of heavy polycyclic hydrocarbons. An accurate prediction of the exchanger parameters such as outlet temperature, pressure and coke thickness inside the tubes is required for the ethylene plant operators. A comprehensive mathematical model for a Transfer Line Exchanger (TLX) system in the industrial plant has been developed. The model incorporates a semi-empirical coke formation equation to predict a coke deposition rate both chemically and physically and the effect of this coke on the TLX steady state and operational time performance. This paper presents some of the results of the computer simulation for the naphtha pyrolysis quench cooler.