NEW RESULTS ABOUT THE MECHANISM OF TLE FOULING IN STEAM CRACKERS

The deposition of coke-like products was studied in the postcracking z one (< 500-degrees-C) of a laboratory pyrolysis reactor coupled with a thermobalance. By means of C-14-labelled hydrocarbons, data on the co ntribution of individual feedstock components to the coke formation we re obtained. Reactive, volatile hydrocarbons, like toluene and hexyne, do not contribute significantly to the deposits if they pass the post cracking zone undecomposed. The results favour as a dominant mechanism in transfer line heat exchanger fouling the condensation of heavy com ponents of the fuel oil fraction and precipitation of tar droplets. At a catalytically active steel surface the coke formation from a cracke r effluent at 500-degrees-C is strongly influenced by steam dilution.