CHEMICAL ENGINEERING TRANSACTIONS VOL. 29, 2012 A publication of The Italian Association of Chemical Engineering Online at: www.aidic.it/cet Guest Editors: Petar Sabev Varbanov, Hon Loong Lam, Jiří Jaromír Klemeš Copyright © 2012, AIDIC Servizi S.r.l., ISBN 978-88-95608-20-4; ISSN 1974-9791DOI: 10.3303/CET1229230 Please cite this article as: Mahulkar A. V., Heynderickx G. J. and Marin G. B., (2012), Simulation of coking in convection section of steam cracker, Chemical Engineering Transactions, 29, 1375-1380 1375 Simulation of Coking in Convection Section of Steam Cracker Amit V. Mahulkar, Geraldine J. Heynderickx *, Guy B. Marin Laboratory of Chemical Technology, Ghent University, Krijgslaan 281 (S5) 9000 Gent, Belgium Geraldine.Heynderickx@UGent.be This work presents CFD simulations of coke formation in the tubes of the mixture over-heater in the convection section of a steam cracker. An actual industrial feed (Gas condensate) composition is used in the simulations. The spray flow (liquid droplets in the feed) entering the tubes is simulated based on Eulerian-Lagrangian approach including a species model and a multicomponent evaporation of the droplets, using ANSYS FLUENT 13.0. The tubes of the mixture over-heater makes 3 horizontal passes (11.3 m long and 0.077 m in diameter) with U-bends connecting the passes. Droplet-wall interaction like splashing, limited splashing, rebound and stick are considered. Due to these interactions some liquid is deposited on the tube wall. The liquid deposited on the tube wall undergo partial evaporation and thermal degradation to form coke based on phase separation model of Wiehe (1993). Finally, the spatial variation in coke formation in the over-heater tube is presented as a function of various outer tube wall temperatures. For outer tube wall temperatures below the boiling point of the highest boiling compound in the feed, coke formation (~ 1 mm thick in 1 month) is observed mainly at the bends. For outer tube wall temperatures above this boiling point no coke is formed in the tubes except at the bends. 1. Introduction Due to the ever increasing heavy nature of crude oil, it is expected that several changes will be required in the operating protocol of a steam cracking unit, initially designed to crack lighter feeds. An already observed change is the thermal degradation of partially evaporated feed entering the mixture over-heater tubes and the subsequent coke formation in these tubes. There is at least one industrial incident known to the authors where a tube of the over-heater choked and subsequently cracked due to internal coke formation. The importance of the coking issue is also stressed by several patents for reducing coke formation in the over-heater tubes (Chandrasekharan et al., 2005; Grondman, 1983). In the presented work, the spatial variation in coke formation in the tubes of the over-heater is studied with respect to the most important operating parameter i.e. flue gas temperature. 2. Problem definition De Schepper et al. (2010) calculated that about 30 % of the liquid feed remains un-evaporated in the pre-heater/ evaporator, another heat exchanger in the convection section of a steam cracker. The partially evaporated feed (30 % liquid and 70 % vapor) is mixed with the over-heated steam, coming from yet another heat exchanger in the convection section of a steam cracker, in a feed-steam mixing nozzle. The high velocity steam atomizes the liquid feed that remains non-evaporated in the nozzle, thus creating a spray flow at the entrance of the over-heater tubes. The liquid droplets flow through the