Fines deposition during hydrotreating: Effects of catalyst size and bed arrangement

Fines deposition presents a significant problem during the hydrotreating of bitumen-derived gas oils. The accumulation of fines leads to reactor clogging and consequently, pressure drop buildup. At critical levels, the hydrotreating reactor must be prematurely shutdown, resulting in substantial economic losses for refineries. Hence, research into finding measures to address fines deposition is crucial and of interest to stakeholders in the refining industry. This research explored the effects of catalyst size and bed arrangement on fines deposition, with the goal of identifying strategies to obtain longer hydrotreating run times. Cold and hot flow fines deposition tests were conducted in three-zone reactors using NiMo/gamma-Al2O3 catalysts, with sizes ranging from 1.3 to 2.5 mm. Under cold flow conditions, maximum fines deposition was reached in 12, 14, and 25 days for 1.3, 1.6, and 2.5 mm catalyst sizes, respectively. For the hot flow tests, maximum fines deposition occurred in 15, 17, and 28 days for 1.3, 1.6, and 2.5 mm catalyst sizes, respectively. Thus, both flow tests suggested that reducing catalyst size accelerated fines deposition, primarily due to straining. However, when the catalyst bed was arranged with decreasing size from top to bottom of the reactor, the time to reach maximum fines deposition increased to 28 days (cold flow) and 34 days (hot flow). Therefore, configuring the catalyst bed to have a downward gradient of decreasing catalyst size is proposed as a potential strategy to extend hydrotreating run times.