Coke Formation in the Transfer Line Exchanger during Steam Cracking of Hydrocarbons

Abstract

Coke formation under transfer line exchanger conditions, that is, at temperatures from 623 to 873 K and atmospheric pressure, is studied in an electrobalance setup. The coking rate is initially very high (catalytic coking) and drops after a few hours to a constant value. At the studied conditions the observed coking behavior on 15Mo3 alloy pigs can be explained via a catalytic mechanism only, and contributions of the free-radical mechanism and the condensation mechanism are insignificant. Experiments with ethane and naphtha steam cracking effluents and with well-defined reaction mixtures show that the coking rate is independent of the partial pressure of ethene (0-2.7 × 10 4 Pa), ortho-xylene (0-1.0 × 10 4 Pa), heavy aromatic hydrocarbons (0-3.0 × 10 2 Pa), and also 1,3-butadiene (0-2.7 × 10 4 Pa). The rate of coke deposition depends only on the temperature and the ratio of the partial pressures of water to dihydrogen. The activation energy for initial coke formation was estimated to be ∼90 kJ/mol, a value close to the experimentally determined diffusion energy of carbon in iron.

A new dynamic model of crude oil fouling deposits and its application to the simulation of fouling‐cleaning cycles

“…The approach presented is general, not specific to crude oil fouling and can be easily adapted to different geometries and fouling mechanisms, thus it may be applied to other fouling systems. Examples in other petrochemical processes include coke deposition in in transfer line exchangers and furnaces in steam crackers, wax deposition in pipelines, and so forth. Examples in other industries include food (e.g., milk fouling) and water transportation (formation of salt scales).…”

Crude to Olefins: Effect of Feedstock Composition on Coke Formation in a Bench-Scale Steam Cracking Furnace

“…Moreover, it is possible to distinguish between time-dependent fouling regimes. 29 Typically, the initial fouling rate is higher compared to the one observed after long service times for most refining and petrochemical processes, thereby making the abovementioned advantage substantial.…”

Steam Cracking Coke Properties and Their Influence on Furnace Run Length Predictions: Experimental and Modeling Study

“…SEM is the most widely used technique to examine coke morphology. ,,,− ,− A JEOL JSM-7600F scanning electron microscope has been used in this work to examine the surface morphology of the coke by EDX. A Schottky field emission gun is used as an electron source.…”