A CFD simulation of the top of a coke drum reactor and the outlet pipe of the reactor (vapor line) was developed for the evaluation of the coke deposition on the vapor line. The coke drum is the main part of the delayed coking process. One of the main bottlenecks in the coke drum is the fouling of the vapor line due to coke formation because it could cause plugging and other inefficiencies in the process.
The CFD simulation was implemented in the CFD commercial package Fluent 16.0 using a k – ε turbulent model. ANSYS ICEM CFD pre-processing software was used to discretize the 3D geometry. A mesh was created using mainly tetrahedral elements with approximately 750000 elements. The mesh in the vapor line was reﬁned close to the wall to obtain a value of Y+ tat would best capture the hydrodynamics as coke deposition is a surface phenomenon.
For the evaluation of the coke deposition on the vapor line, a four lump mechanism with three reactions was obtained from experimental data from literature related to the thermal cracking and delayed coking processes. The four lumps are Vacuum Residue Crude (VRC), gases, distillates and coke. From the kinetic mechanism and the hydrodynamic of the reactor gas phase, an initial approximation about the plugging time of the vapor line was made. As two weeks for 30% tube blockage. The coke formation from condensation was not taken into account because it is not possible to obtain condensation under specific operational conditions (temperature and pressure), composition and characteristics of the components in the vapor line. New geometries, configurations and operational conditions are proposed to reduce the amount of coke formed in the vapor line.
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See more of this Group/Topical: Topical 7: 19th Topical Conference on Refinery Processing