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UBC Theses and Dissertations

Heat exchanger fouling of some Canadian crude oils Srinivasan, Murugan


Fouling refers to deposition of any kind of extraneous material that appears on the surface of process equipment, such as heat exchangers and reactors. This is a major economic penalty to oil refineries and heavy residuum upgrading units, thus creating incentives for a better understanding of fouling mechanisms which underlie methods to mitigate or control fouling. This research was focussed on a comparative study of the fouling tendencies of three sour crude oils supplied by Shell Canada Limited: Light Sour Blend (LSB), Midale (MDL), and Cold Lake (CLK). The experiments were carried out using a re-circulation fouling loop equipped with an HTRI-type annular electrical probe. Fluids were re-circulated for a 48 hour period from a feed tank, through the annular fouling probe, and back to the tank. The unit was operated at a constant heat flux with time, so that fouling could be tracked by the increase in surface temperature of the probe. Velocity was held constant at 0.75 m/s in most experiments. The unit was pressurized to 860-1240 kPa, depending on the oil used. Bulk temperatures were varied over the range 200-280°C, and surface temperatures covered the range 330-380°C. The decrease in overall heat transfer coefficient varied from 3% to 60%, with most results being in the range 10-32%, depending on conditions. Fouling resistances up to 0.3 m²K/kW were recorded. The effects of various parameters, namely surface temperature, bulk temperature, film temperatures, and annular velocities, on fouling rates were studied for Light Sour blend in detail. When correlating temperature effects on fouling rates, some authors use the surface temperature, while others use the average film temperature, Tf = 0.5 (Ts + T b). In this study both were examined. A slightly modified film temperature, which gave more weight to the surface temperature, was found to be the best. Deposits carefully recovered from the HTRJ probe, after each experiment, were analyzed using energy dispersive x-ray, giving point analyses on the deposit surface, and by micro elemental analysis for bulk content of C, H, S and N. Thermogravimetry was used to determine bulk ash content.

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