Raw (neither desalted nor flashed) crude oils were tested at similar conditions in the HTRI High Temperature Fouling Unit to obtain fouling rates and resistances. Although absolute fouling resistance can be difficult to apply, relative fouling rates were compared to known operating experience, allowing improved designs of heat exchangers and fired heaters in the crude preheat unit, thereby optimizing unit run length.

Fouling resistance as a function of time was measured for Eocene, Ratawi, Lower FARS, and Kuwait Export (KEC) crude oils at surface temperatures ranging between 360°C and 445°C, a nominal bulk temperature of 315°C, and a wall shear stress of 13 Pa. Coking was the dominant fouling mechanism for all tests, which were designed to model conditions in the fired heater. The fouling rates of all four crude oils were found to be exponentially dependent upon temperature with significantly different activation energies; as a result, the fouling propensity was divided into three regimes. At low solid-liquid interface temperatures (~370°C), the relative fouling rates were: Eocene ~ Lower FARS > KEC > Ratawi. At intermediate interface temperatures (~410°C), the fouling rates of all four crude oils were similar. At high surface temperatures (~455°C), the relative fouling rates were: Ratawi > KEC ~ Eocene > Lower FARS.

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