Effect of Crude Oil Vanadyl Porphyrin Content and Blending on Heat Exchanger Fouling

Abstract

Fouling in the pre-heat train of crude oil distillation unit is a normal occurrence in oil refineries. With the increasing trend of heavy crude oil processing, blending of oils becomes a norm practice in a refinery. Fouling could be enhanced if incompatible oils were blended together. Also, heavy oils typically contain high trace metals composition and their effect towards fouling is yet to be explored. This study has been looking into the effect of changes in the original composition and inter-molecular stability of crude oils towards fouling. A batch system was designed and developed to produce a deposit sample from 3 crude oils of industrial interest. The reactor was successfully commissioned and an operating procedure was established. In the first part of the work, various concentrations of Vanadium were added to crude oils and subjected to high temperature in the test section. The resultant deposits and liquid products were analysed for their molecular structure and weight distribution. Analysis by Inductively Coupled Plasma Mass Spectrometer (ICP-MS) shows the added Vanadium are largely concentrated in the deposits. The amount of deposits produced increases with the concentration of Vanadium in the original samples. Analyses by Size Exclusion Chromatogram (SEC), Gas Chromatography (GC) and UV-Fluorescence Spectroscopy (UVF) show larger and more complex molecules in deposits from oils with high concentration of Vanadium. In the second part, the compatibility regions of crude oil blends were established prior to analysis in the reactor. More deposits were produced from incompatible oil blends though these were lighter and less complex than that of compatible blends. Also, oils that were blended from the incompatible region produced deposits of bigger molecular weight distributions and more complex structures. Results of Thermo-Gravimetric Analysis (TGA) confirmed those of SEC’s and UVF’s of which more volatile components were recorded in active blended deposit samples.