Simulation of the coking phenomenon in the superheater of a steam cracker Amit V. Mahulkar, Geraldine J. Heynderickx n , Guy B. Marin Laboratory for Chemical Technology, Ghent University, Technologiepark 914, B-9052 Gent, Belgium HIGHLIGHTS  Coke formation in convection section of steam cracker is simulated using CFD.  Coking occur due to thermal degradation of liquid feed deposited on tube wall.  Thickest coke layer is observed in inlet-bend due to impingement of droplets.  Complete evaporation of the heavy feed would eliminate the coke formation.  Feed spray with finer droplet size would reduce the coking rates. article info Article history: Received 3 May 2013 Received in revised form 8 July 2013 Accepted 8 August 2013 Available online 22 August 2013 Keywords: Coke formation Steam cracking CFD Convection section Spray flow abstract Coke formation in the convection section of a steam cracker occurs when heavy feeds are cracked. This work presents CFD simulations of coke formation in the mixture superheater tubes in the convection section of a steam cracker. The hydrocarbon feed used for the simulations is a gas condensate. Eleven representative chemical species are selected, based on their boiling points, to mimic the entire range of feed components. The liquid–vapor spray flow in the mixture superheater tube is simulated based on an Eulerian–Lagrangian approach using ANSYS FLUENT 13.0. Evaporation of multicomponent droplets suspended in the vapor phase or deposited on a tube wall is considered. The mixture superheater tubes make three horizontal passes (11.3 m long and 0.077 m diameter) through the convection section. The droplet–wall interaction model considers ‘Splash’, ‘Rebound induced breakup’, ‘Rebound’ and ‘Stick’. The amount of liquid deposited on the mixture superheater tube wall is obtained by simulating the spray flow. The amount of coke formed from the liquid deposited on a wall is based on the phase separation model of (Wiehe, 1993). Industrial & Engineering Chemistry Research 32, 2447–2454. Spatial variations of the coke layer formed in the mixture superheater tubes as a function of outer tube wall temperatures and initial droplet diameter are presented. For outer tube wall temperatures lower than the boiling point of the highest-boiling species in the feed a 1 mm thick coke layer is formed over a period of 1 month. For outer tube wall temperatures higher than the boiling point of the highest boiling component in the feed no coke is formed in the mixture superheater tubes. This work provides guidelines to minimize the extent of coke formation in the steam cracker convection section when a heavy feed is cracked. It also provides possible remedies to completely eliminate the coking problem when cracking heavy feeds. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Due to an ever increasing demand to produce lighter and more valuable hydrocarbons like ethylene and propylene on the one hand, and an increasing supply of cheaper but heavier crude oil on the other hand, the industrial steam crackers are forced to operate with heavy feeds. It is very likely that the operating protocol and/ or the design of the existing industrial steam crackers will need to be adapted. It can be expected that these changes will essentially involve increasing the heat input in the steam cracker in order to retain complete evaporation and sufficient over-heating of the heavier crude oil feeds within the convection section of the steam cracker. In this work, with the help of CFD simulations, the magnitude of possible fouling problem due to the use of heavy feeds is estimated and the remedies to avoid the same are suggested. The constructional features of the convection section of steam cracker are taken from the earlier work of De Schepper et al. (2010). In the convection section three types of heat exchangers are placed one below the other (Fig. 1(a)). In the top, where flue gas temperatures are low, a liquid feed evaporator is Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science 0009-2509/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ces.2013.08.021 n Corresponding author. Tel.: þ32 9 264 45 32; fax: þ32 9 264 45 99. E-mail address: Geraldine.Heynderickx@UGent.be (G.J. Heynderickx). Chemical Engineering Science 110 (2014) 31–43