Modelling, simulation, thermodynamic and economic performance analysis of steam and CO₂ as diluents in thermal cracking furnace for ethylene manufacturing

Energy consumption, economic and environmental benefits of thermal cracking furnace have been important topics in ethylene manufacturing. Use of captured CO₂ as alternative diluent in thermal cracking furnace can significantly contribute to CO₂ reduction while the studies on CO₂ as diluent are limited and inaccurate. To carry out comparative analysis of using steam and CO₂ as diluents in propane cracking for ethylene manufacturing, a 1-dimensional (1-D) pseudo-dynamic model of plug flow reactor (PFR) was developed and implemented in gPROMS ModelBuilder®. The model was validated and showed good agreement with industrial data from literature and then was used to analyse the economic and thermodynamic performance of PFR using different diluents. The process analysis includes: (1) impact of diluent-to-propane ratio using steam as diluent; (2) impact of diluent-to-propane ratio using CO₂ and compared with using steam; (3) comparison of pure/mixed diluents in 4 different scenarios. The results indicated that the PFR could reach highest annual production at the steam-to-propane ratio 0.2 and reach highest annual profit at the ratio 0.3 when using steam as diluent. Compared with steam, using CO₂ as diluent hardly changes the annual production, but can significantly increase the run length and the annual profit. The highest annual profit using CO₂ is 10.10 % higher than that using steam and when operating at the diluent-to-propane ratio achieving highest annual profit, using CO₂ as diluent can save 17.44 % energy and reduce the exergy destruction by 20.53 %. Pure CO₂ was recommended as diluent from comparison of pure/mixed diluents in 4 different scenarios. The key findings of this paper provide significant operational guidance for existing thermal cracking furnace using steam as diluent and also provide insights for future new generation diluents design to reduce the energy consumption in quantity and quality and increase the economic benefits of thermal cracking furnace for ethylene manufacturing.