Role of Pressure in Coking of Thin Films of Bitumen

Abstract An important step in the formation of product from feed in a fluidized‐bed coker is the evolution of product and coke from layers of vacuum residue on the surfaces of heated particles and from liquid inside agglomerates of liquid and solid. In the present study, the yield of coke from Athabasca vacuum residue was measured using a reactor based on rapid induction heating of thin films of liquid feed on the surface of pieces of Curie‐point alloy. This approach allowed measurement of the yield of coke at pressures from 101–652 kPa, temperatures of 503 and 530°C, and reaction times from 10 to 240 s. When the liquid was reacted in thin films of ca. 20 µm, the effects of temperature and pressure on coke yield were insignificant. As the film thickness was increased to 120 µm, the yield of coke increased at all conditions. The yield of coke from thicker films was only sensitive to total pressure at 503°C reaction temperature, when the pressure was increased from 377 kPa to 652 kPa. Observable bubbling due to cracking reactions during coking was suppressed by increasing pressure, and the transition from quiescent liquid to bubbling liquid increased from circa 26 µm at 101.3 kPa to 78 µm at 652 kPa at 503°C. The bubbling transition was much less sensitive to pressure at 530°C, falling in the range from 22 µm to 43 µm as pressure increased from 101.3 to 652 kPa. These results suggest that the most important effect of pressure will be on the physical behaviour of liquid feed, due to its impact on bubble evolution from liquid inside agglomerates of liquid and solid particles. Depending on the liquid/solid ratio in an agglomerate, the formation of bubbles inside such a structure would make it weaker and easier to disperse on the fluidized bed reactor.