Effect of particle size, liquid content and location on the stability of agglomerates in a fluidized bed

Agglomeration is used to generate particles of specific sizes, reduce dust emissions and stabilize particulate mixtures. In Fluid Cokers, which upgrade heavy oil through contact with hot coke particles, agglomeration increases reactor fouling. The objective of this study is to understand how the stability of a wet agglomerate in a fluidized bed is affected by its liquid content, its location and the size of its particles. Agglomerates were made of fluid coke and biodiesel, the shear force required to break them was measured with a new device and agglomerates were introduced in a fluidized bed. The stability of a wet agglomerate in a fluidized bed depends on its liquid content, its bulk density and the Sauter mean diameter of its constituent particles. Increasing liquid content or bulk density increases agglomerate stability while increasing the Sauter mean diameter of its particles reduces its stability. Artificial agglomerates were made from polyurethane foam, magnets and an RFID tag. Agglomerate breakage and location could be detected with an RFID reader. It was found that bigger and denser agglomerates spend less time on the upper surface of the bed. The average survival time of an agglomerate in a fluidized bed is proportional to the critical shear force required to break the agglomerate.

Graphical abstractEffect of variables on the critical shear force required to break up an agglomerate. A multi-linear regression indicated that the stability of an agglomerate depends more strongly on its bulk density or the Sauter mean diameter of its constituent particles than on its fines concentration in its constituent particles.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Wet agglomerate stability in fluidized beds depends on parameters. ► Higher agglomerate liquid content reduces agglomerate breakage. ► Lower agglomerate densities promote agglomerate breakage. ► Agglomerates of larger particles break up more easily. ► Agglomerate lifetime depends on the critical shear force that can break it.