Effect of local hydrodynamics on the distribution of liquid sprayed into a Fluidized Bed

Conference Dates

May 22-27, 2016


In industrial thermal cracking processes such as Fluid CokingTM, liquid feedstock is injected into a fluidized bed of hot particles. The quality of liquid-solid contact is crucial for optimizing the product yields and the process operability. The formation of undesired agglomerates, which are generated by poor liquid distribution on solids, needs to be minimized for better mass and heat transfer. Liquid distribution can be improved by either modifying the spray nozzle or adjusting the bed hydrodynamics. The present study focuses on modifying the local bed hydrodynamics by changing the local fluidization velocities.

The Fluid CokingTM process is simulated by injecting an aqueous Gum Arabic solution in a warm bed of sand particles. The effects of velocity in the spray region and in the drying region in fluidized bed on liquid distribution are investigated using different velocity combinations. The fluidization velocity during injection characterizes the velocity in the spray region while the fluidization velocity after injection characterizes the velocity in the drying region. The mass of agglomerates in different size cuts, initial liquid/solid ratio in the agglomerates are measured and used to assess the effect of changing the local hydrodynamics.

The fluidization velocity has a great impact on liquid distribution. A higher fluidization velocity in the spray region improves the liquid distribution by creating drier agglomerates, which break up more quickly. A higher velocity during drying accelerates agglomerate breakup by shear forces, resulting in a smaller mass of wetter agglomerates. Overall, increasing the fluidization velocity in the spray region is more effective than increasing the velocity during drying. The beneficial impact of the fluidization velocity on liquid distribution was observed with sprays of different quality.

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