Coke formation in furnace tubes in ethane cracking processes

乙烯生产商由于在其烃-蒸汽裂化单元中焦炭形成而导致反应器管结垢，从而遭受巨大的生产、效率和经济损失。焦炭在炉管中的积聚增加了管两端的压降，并减少了对在管中流动的气体的热传递。当压力降或炉热负荷达到临界值时，必须停止乙烷-蒸汽裂解过程，并必须除去炉管中的焦炭。脱焦通常每30-90天进行一次，每个乙烷裂化器在高达15%的时间内处于甲板或非生产模式。因此，了解和减少炉管中的焦炭形成对于乙烯制造商在操作上和经济上都非常重要。我们的工作集中在三个关键领域：了解工厂操作条件如何影响控制反应副产物转化为焦炭的气相动力学，将这些结果与实验室规模的模拟焦化研究相关联，并采用详细的焦炭表征研究来了解工厂操作条件，特别是乙烷-蒸汽进料中的组分，如何影响焦炭的性质。在这项工作中要研究的重要变量包括温度，乙烷-蒸汽在热区的停留时间，蒸汽和硫含量，以及衬底表面的性质。将利用现有的最先进的研究工具，结合过去三年合作工作中积累的广泛知识，实现这些目标。在这项工作的过程中，两名研究助理和两名研究生将在这个项目下接受培训，并将准备加入加拿大工业和学术界的劳动力。从这项工作中获得的知识和专业知识将转移到我们的工业合作伙伴NOVA Chemicals，以便它可以用作不同工厂操作条件如何影响焦化率的预测模型。这种对烃-蒸汽裂化工艺的新理解也将对阿尔伯塔和加拿大的其他基于蒸汽的石化工艺具有更广泛的益处，其中焦化是一个问题。

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.