Unsteady-state coupled firebox-reactor modeling of a naphtha pyrolysis furnace considering CO2 emission and coke formation

Reducing CO 2 emissions from high-carbon-emitting processes is essential for achieving carbon neutrality . Naphtha pyrolysis processes emit substantial CO 2 due to LNG combustion for heat supply. However, existing modeling studies primarily focus on predicting olefin yields without considering firebox CO 2 emissions and often assume steady-state conditions, failing to capture the dynamic behavior caused by coke formation in the reactor. This study addresses these limitations by developing an unsteady-state coupled firebox-reactor model that comprehensively incorporates key furnace phases: furnace wall, flue gas, tube wall, and process gas. The model accounts for heat transfer across these phases and includes coke formation mechanisms. The calibrated model using plant data demonstrated high prediction accuracy for ethylene yield (RMSE = 0.236, R 2 = 0.9810), propylene yield (RMSE = 0.867, R 2 = 0.9120), and coke thickness (RMSE = 1.06, R 2 = 0.9826). Case studies were conducted to evaluate the effects of combustion gas flow rate on CO 2 emissions, olefin yield, and pressure drop. Results showed that increased heat supply enhanced olefin production but also intensified pressure drop and CO 2 emissions. The proposed model provides a robust theoretical foundation for optimizing furnace operation, including decoking schedules, and serves as a practical tool for enhancing process safety and reducing environmental impact.