Modeling 'hot flow' and 'cold flow' solids deposition from waxy mixtures
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AbstractThis study presents a mathematical model, based on moving boundary formulation, for solids deposition from 'waxy' mixtures. An experimental study was undertaken to measure the wax precipitation temperature (WPT) of several compositions of a multi-component 'waxy' mixture, at controlled cooling rates. The results of this study indicated the WPT of a 'waxy' mixture is not a constant property, as it varied with the cooling rate. The mathematical model was used to describe the static cooling of 'waxy' mixtures in a cylindrical vessel. The predictions for the liquid region, deposit region temperature profile, the deposit layer growth and the location of the liquid-deposit interface were validated with recent experimental results. The model was extended for studying wax deposition from 'waxy' mixtures under turbulent flow, in radial direction in a circular pipe. The effects of various operating parameters on the wax deposit thickness during "hot flow" and "cold flow" scenarios were investigated. The model predictions indicated a higher value of mixture temperature, pipe wall temperature, and heat transfer coefficient yield a thinner deposit at steady state. The mathematical model was further extended for solids deposition from 'waxy' mixtures under turbulent flow in a pipeline. Predictions were obtained for the deposit growth with time, both radially and axially in the pipeline, under 'hot flow' and 'cold flow' conditions. The results of this study suggest that solids deposition, in pipelines carrying 'waxy' mixtures under turbulent flow, could be decreased by maintaining the flow under 'cold flow' conditions. This study provides further confirmation that solids deposition from 'waxy' mixtures or crude oils can be modeled satisfactorily as a thermally-driven process.
Bibliography: p. 144-151