SIMULATION AND OPTIMIZATION OF COIL DECOKING IN ETHANE PYROLYSIS FURNACE

A detailed model of coupled heat transfer in the firebox and coke oxidation in the coils of a commercial ethane pyrolysis furnace was developed to simulate the decoking process. The model was created by combining a plug flow reactor model, the shrinking core model, and the zonal approach method to approximately describe the fluid flow in the coils, the gas-solid heterogeneous reactions of coke gasification, and the heat transfer in the furnace. The simulation accurately modeled the decoking time and CO₂ mole fraction at the coil outlets. The model may be used to evaluate existing decoking processes, and new decoking procedures can be investigated by iterative approximation. The model can be used to validate the following steady-state operating conditions: coil outlet temperature, coil inlet temperature, decoking time, coil outlet CO₂ mole fraction, and the maximum external tube wall temperature, resulting in lower consumption of steam and air and a reduction in residual coke. This work has provided essential information for the development of advanced on-line coke-burning procedures for ethylene production.