This work presents the model for the development of a computer aided tool for heavy oil thermal cracking process simulation. It is proposed a dual plug flow reactor representation for the light pyrolysis of petroleum distillation residues in coil-type reactors. The resulting reactor model consists of two parallel plug flows, one vapor and the other liquid, traveling at different speeds in a coil. Reaction is assumed to be the rate controlling process with equilibrium between the phases. Because of the pyrolysis reactions and pressure drop, vaporization takes place continuously along the coil so there is a decrease in the liquid hold-up. The model derived uses a heuristic lumping approach based on pilot plant data and the resulting pseudokinetic scheme presents a certain feed independence within the range of stocks available for the study. An industrial case study (delayed coking) is explored to provide insight into the problem of reconciling the kinetics of pyrolysis and carbonization for the upgrade of distillation residues. (C) 2001 Elsevier Science: Ltd. All rights reserved.2541794683692