Coke formation in furnace tubes in ethane cracking processes

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Ethylene producers suffer from huge production, efficiency and economic losses due to fouling of the reactor tubes by coke formation in their hydrocarbon-steam cracking units. The accumulation of coke in the furnace tubes increases the pressure drop across the tubes and reduces the heat transfer to the gases flowing in the tubes. When either the pressure drop or the furnace heat load reaches a critical value, the ethane-steam cracking process has to be stopped and the coke in the furnace tubes has to be removed. Decoking is typically performed every 30-90 days and each ethane cracker is in the decking or non-production mode for up to 15% of the time. Hence, understanding and reducing the coke formation in the furnace tubes is very important to ethylene manufacturers; operationally and economically. Our work centers on three key areas: understanding how plant operating conditions influences the gas-phase kinetics that control conversion of reaction by-products to coke, correlating these results to lab-scale simulated coking studies, and employing detailed coke characterization studies to understand how plant operating conditions, and particularly components in the ethane-steam feed, impact the properties of the coke. Important variables to be studied in this work include temperature, ethane-steam residence time in the hot zone, steam and sulfur content, and nature of the substrate surface. Existing state-of-the-art research tools combined with extensive knowledge developed over three years of previous collaborative work will be used to reach these goals. Over the course of this work, two research associates and two graduate students will be trained under this project and will be ready to join the Canadian industrial and academic workforce. The knowledge and expertise gained from this work will be transferred to our industrial partner, NOVA Chemicals, so that it can be used as a predictive model of how different plant operating conditions will impact coking rates. This new understanding of hydrocarbon-steam cracking process will also have a broader benefit for other steam-based petrochemical processes within Alberta and Canada where coking is a problem.