Fouling of a Heated Rod in a Stirred Tank System

Abstract

A batch stirred tank device has been developed for measuring fouling from oil samples. The unit consists of a baffled tank equipped with a centrally mounted long blade stirrer, and an electrically heated rod located at 40% of the radius of the tank. Heat transfer from the rod was first characterized. The velocity field was measured, from which the approach velocity to the probe was determined, which allowed the wall shear on the heating probe to be calculated from a literature equation. Fouling of a heavy oil fraction was studied in 1- to 2-day experiments with bulk oil temperatures typically at 320°C, initial probe surface temperatures to 536°C, and stirrer speeds of 100–900 rpm. Micrometer-sized iron oxide particles were added to the oil, such that fouling was due to a combination of particle deposition and coke formation. Deposition rates were measured thermally from the change in heat transfer coefficient when fouling was relatively heavy, and by thickness and mass accumulation when fouling was light. Effects of oil type, film temperature, stirrer rotation speed (or probe wall shear stress), and concentration of suspended particles on deposition rate and deposit composition are presented.

Acknowledgments

This work was sponsored by Phillips 66. The authors appreciate the contributions of Keith Lawson, Bruce Newman, and David Henning to the development of the system, and to the experimental program. Yonghua Li built the original apparatus and carried out the early experimentation at the University of British Columbia.