Solids Deposition from Multicomponent Wax−Solvent Mixtures in a Benchscale Flow-Loop Apparatus with Heat Transfer

Abstract

The deposition of solids from mixtures of a paraffinic wax (C20−C40) dissolved in a multicomponent solvent (C9−C16) was studied under laminar flow conditions. A novel benchscale flow loop was developed, which consisted of a jacketed heat-exchange section for solids deposition on the inner surface of an aluminum tube. Experiments were performed to investigate the effects of the wax−solvent mixture composition, hot and cold stream temperatures, flow or shear rate, deposition residence time, and hydrodynamic entry length on the deposition process. The data were analyzed with a pseudo-steady-state heat-transfer model, which validated the solids deposition process to be controlled primarily by heat transfer. The mass of deposited solids was related to the ratio of temperature difference across the deposit layer and the overall temperature difference. Gas chromatography (GC) analyses of the deposited layer showed significant shifts in the carbon number distribution. The C20+ content of the deposit layer was observed to be higher, by ∼70%−200%, than that of the corresponding wax−solvent mixture.

Investigation of wax deposit ‘sloughing’ from paraffinic mixtures in pipe flow

“…In the heat‐transfer approach, the liquid‐deposit interface temperature is taken to be equal to the WAT of the wax solution throughout the deposition process. Batch cooling studies under static and sheared conditions and bench‐scale flow‐loop studies have confirmed the interface temperature ( T d ) to remain constant, and close to the WAT, during the gelling and deposit‐growth periods. It is also pointed out that the heat‐transfer approach has been validated with experimental measurements under both the ‘hot flow’ (i.e.…”

“…One important observation about the deposition process, at steady state, is that the liquid‐deposit interface temperature, T d , has been shown to be constant and equal to the WAT . That is, the temperature, T d , between R h and R d is constant (and equal to the WAT of the ‘waxy’ mixture).…”

“…The heat‐transfer modelling approach considers the deposit formation and growth to be a partial solidification or freezing process along with crystallization . According to the heat‐ transfer approach, the deposition occurs because of a temperature difference between the hot ‘waxy’ mixture temperature and the colder surroundings.…”

“…The key observations from experimental and modelling studies, based on the heat‐transfer approach, are: (1) the deposition process starts soon after the pipe‐wall is exposed to a temperature below the WAT and continues at a relatively fast pace until a steady‐state is achieved, (2) the steady‐state liquid‐deposit interface temperature, T d , is always equal to the WAT of the liquid phase of the ‘waxy’ mixture, (3) the concentration of heavier paraffins in the deposit increases with time (referred to as ‘deposit aging’), (4) an increase in the coolant temperature yields a smaller deposit‐layer thickness, (5) an increase in the ‘waxy’ mixture temperature yields a smaller deposit‐layer thickness, (6) an increase in the ‘waxy’ mixture flow rate, or Reynolds number (in both laminar and turbulent flow regimes), yields a smaller deposit‐layer thickness, (7) even though the rate of heat transfer depends on the temperature difference between the ‘waxy’ mixture and the coolant, ( T h – T c ), the deposit‐layer thickness does not depend on it, and (8) the deposit‐layer thickness depends on the temperature difference between the ‘waxy’ mixture and the WAT, ( T h – WAT), and between the WAT and the coolant temperature, (WAT– T c ), such that it increases with a decrease in ( T h – WAT) and/or an increase in (WAT – T c ).…”

Deposition apparatus to study the effects of polymers and asphaltenes upon wax deposition

“…While flow loop deposition studies date back several decades (Jessen and Howell, 1958;Cole and Jessen, 1960;Hunt, 1962;Jessen and Mendell, 1970;Mendell and Jessen, 1972;Weingarten and Euchner, 1988) more recent work has focused on the fundamental understanding to the deposition process, as well as the ability to accurately model deposition behavior (Burger et al, 1981;Brown et al, 1993;Creek et al, 1999;Singh et al, 2000;Apte et al, 2001;Singh et al, 2001a,b;Matzain et al, 2002;Paso and Fogler, 2003;Venkatesan and Fogler, 2004;Parthasarathi and Mehrotra, 2005;Merino-Garcia et al, 2007). A survey of such studies shows that four key factors determine the rate and nature of the deposit formed: the flow rate (Weingarten and Euchner, 1988;Creek et al, 1999;Singh et al, 2000), the temperature field, (Cole and Jessen, 1960;Burger et al, 1981;Creek et al, 1999;Singh et al, 2000) the composition of the oil Singh et al, 2001b), and the nature of the surface (Cole and Jessen, 1960;Parks, 1960;Jorda, 1966;Kok and Saracoglu, 2000;Zhang et al, 2002).…”