Spraying slurries in fluidized beds: Impact of slurry properties on spray characteristics and agglomerate formation

Abstract

AbstractFluid coking is a process that upgrades heavy oil. In a fluid coker, heavy oil is sprayed into a fluidized bed of hot coke particles, where it undergoes thermal cracking. The formation of wet agglomerates, caused by poor contacting between the heavy oil and coke particles, slows thermal cracking and leads to operating problems. The product vapours exiting the coker are scrubbed to condense the heavier components, which are recycled to the coker. The recycle stream contains unwanted suspended fines that could affect the interaction between the liquid feed and the bed particles, and the resulting agglomerate formation. In open air, the presence of suspended solids had a negligible impact on spray behaviour. The impacts on agglomerate stability and liquid distribution were studied in a fluidized bed of sand at 130°C by spraying a gum arabic solution that was formulated to simulate oil‐coke agglomerate formation in fluid cokers. Within the fluidized bed, changing the concentration of suspended solids in the liquid feed affected agglomerate stability and liquid distribution. Different mechanisms were considered to explain this change in agglomeration behaviour: increased viscosity, spray characteristics, drying kinetics, and the solids filler effect. A dedicated experimental plan was designed to test each hypothesis. The only significant impact of the suspended solids resulted from a filler effect within the agglomerates: The fines made the agglomerates more resistant to breakage in the fluidized bed. This only occurred, however, when the suspended solids were wettable by the liquid; non‐wettable suspended solids, instead, weakened agglomerates.