A Computational Model to Simulate Decoking in Steam-Cracking Furnace Coils

Steam cracking produces ethylene via non-catalytic high temperature pyrolysis of hydrocarbons inside coils in the furnace's radiant zone.  During cracking, coke buildup on the coil's internal surfaces inhibits heat transfer.  Ultimately, either a metal temperature limit or pressure drop increase necessitates periodic decoking of coils with steam/air mixture. To further understand the effect of process parameters on decoking, a 2D axisymmetric CFD (computational fluid dynamics) model has been developed to simulate decoking in steam-cracking furnace coils. The model accounts for both oxidation and steam gasification reaction kinetics and incorporates key process parameters and heat flux from a furnace. A multi-stage pseudo-transient numerical framework has been developed to simulate the decoke cycle of industrial furnaces in a computationally affordable manner. Furthermore, the numerical technique ensures mass conservation during various stages of decoking.