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Title: An Investigation of Solids Deposition from Two-Phase Wax–Solvent–Water Mixtures
Author: Kasumu, Adebola Sadiq
Advisor: Mehrotra, Anil K.
Keywords: Engineering--Chemical;Engineering--Environmental;Engineering--Petroleum
Issue Date: 5-May-2014
Abstract: This study presents an investigation of the thermophysical behaviour and deposition tendency of “waxy” mixtures, with and without the addition of water as a liquid phase. In the first part, the wax precipitation temperature (WPT) of several compositions of a multi-component waxy mixture (comprising a multi-component paraffinic wax dissolved in a multi-component solvent) was measured at controlled cooling rates. Results indicated that the WPT of a waxy mixture is not a constant property, as it varied with the cooling rate. Experimental results were used to express the WPT as a function of the cooling rate and mixture composition. With the WPT being dependent on the cooling rate, it may not correspond to the thermodynamic liquidus temperature for the liquid-to-solid phase transformation process. The deposition of solids from single-phase and two-phase waxy mixtures (second phase being water) was studied using two different experimental apparatuses. A flow-loop apparatus was used to study the effects of water content, wax mixture and coolant temperatures, and flow rate, in two-phase waxy mixtures flowing under turbulent flow conditions. A cold finger apparatus was used to further investigate the effects of time and stirring rate on wax deposition in single-phase waxy mixtures, and the effect of water content in two-phase waxy mixtures. In both sets of experiments, the water content of the deposit was found to be not related to the water content of the waxy mixture. The deposit mass (on a water-free basis) decreased with an increase in Reynolds number, the mixture temperature, and/or the coolant temperature. The deposit mass both increased and decreased with the water content of the waxy mixture, depending on the deposition time. Results showed the solids deposition from waxy mixtures to be a fast process; for example, 56% of the deposition process in the cold-finger experiments was completed in 0.07% of the time to reach steady-state. The deposition data were analyzed with a steady-state heat-transfer model, which also indicated that the liquid–deposit interface temperature was close to the wax appearance temperature (WAT) of the waxy mixture. The predictions from a transient heat-transfer model, based on the moving boundary formulation, matched satisfactorily the effect of time on the deposition process in the cold-finger experiments. Overall, the results of this study confirm that the deposition process from waxy mixtures is a relatively very fast process, and is primarily thermally-driven.
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