Deposition under Turbulent Flow of Wax-Solvent Mixtures in a Bench-Scale Flow-Loop Apparatus with Heat Transfer

摘要

A flow-loop apparatus, incorporating a co-current double-pipe heat exchanger, was developed for investigating the deposition of solids from solutions of a multicomponent wax in a paraffinic solvent under turbulent flow. The deposition experiments were performed at Reynolds numbers of 10 000-31 000 with 7, 10, and 15 mass % wax-solvent mixtures at different hot and cold stream temperatures. In all experiments, the deposit was formed rapidly such that a thermal steady state was attained within 20-30 min. The deposit mass decreased with an increase in the Reynolds number, the wax-solvent mixture temperature, and the coolant temperature. The data were analyzed with a steady-state heat-transfer model, which confirmed the deposit mass to depend upon the relative magnitudes of the thermal resistances in series as well as the fractional temperature drop across the deposit layer. The estimated liquid-deposit interface temperature was shown to be close to the wax appearance temperature of each wax-solvent mixture. The average thermal conductivity of the deposit was estimated to be 0.35 W m~(-1) K~(-1). The gas chromatograph analysis of deposit samples showed their wax content and carbon-number distribution to vary with the deposition time and Reynolds number. Overall, the results of this study confirm that the deposition process from "waxy" mixtures is primarily thermally driven under both laminar and turbulent flow.