Stability of agglomerates made from fluid coke at ambient temperature

Fluidized bed agglomeration is used to reduce dust problems and stabilize mixtures of various particulate components. Agglomeration in fluid coking, however, can create heat and mass transfer limitations which increase reactor fouling and decrease process efficiency. The objective of this study was to investigate agglomerate survival in fluidized beds in the absence of reaction using materials that have similar properties to those used in the industrial fluid coking process. Agglomerates consisting of fluid coke and oils were made artificially outside of the fluidized bed, fluidized, and then recovered to determine whether agglomerate breakage, erosion, or growth occurred. This study investigated the effects of agglomerate liquid content, liquid binder viscosity, and fluidizing gas velocity on agglomerate stability. It was found that the onset of complete fragmentation occurred at 0.25 m/s (U/Umf = 26) when the liquid binder viscosity was 6.44 cP and 0.34 m/s (U/Umf = 35) when it was 64.7 cP. During fragmentation, more agglomerate material was recovered from the fluidized bed when the initial agglomerate diameter was 0.007 m compared with larger agglomerates (initial diameters of 0.012 m and 0.0167 m). This was due to the effects of secondary erosion on the fragmentation product.

Graphical abstractThis study investigated the effects of agglomerate liquid content, binder viscosity, initial agglomerate size, and superficial gas velocity using materials with similar properties as those used in the industrial fluid coking process. The objective was to quantify how changing these parameters affect the method and amount of agglomerate destruction caused by fluidization. Increasing the liquid binder viscosity from 6.44 cP to 64.7 cP caused the superficial gas velocity where the onset of complete fragmentation occurred to increase from 0.25 m/s (U/Umf = 26.3) to 0.34 m/s (U/Umf = 35.1).Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights►Wet agglomerates can survive in fluidized beds. ►Agglomerates disappear through 2 mechanisms:oFragmentation (high fluidization velocities)oErosion (low fluidization velocities).►Initial agglomerate size affects fragmentation but not erosion rates.