Carbonaceous Material Deposition from Heavy Hydrocarbon Vapors. 2. Mathematical Modeling

A two-dimensional mathematical model was developed to predict the deposit formation from hydrocarbon vapor products in a straight tube with either constant and uniform wall heat flux or constant and uniform outside wall temperature, assuming physical condensation as the mechanism. A single condensable pseudo-component is modeled to transport, condense, and form the deposit layer on the wall. Two cases corresponding to different physical situations are simulated. In the first case, the model was used to simulate deposition results in a long tube downstream of a bitumen coking reactor. Experimental results of the effects of vapor temperature, addition of secondary steam, and vapor residence time or vapor velocity on deposition compared favorably with model calculations. The second case modeled a single transfer line exchanger tube, which is characterized by highly turbulent flow. The temperature profiles of quenched vapor and tube skin, vapor pressure drop, and the thickness of the deposit layer are predicted.