(362c) Liquid Spreading Rates On Gas Fluidized Particles

Fluidization is used extensively in industry for heat and mass transfer applications, including fluidized bed reactors, dryers, fluid catalytic converters and fluid cokers. Fluid coking involves the injection of a heavy hydrocarbon liquid into the fluidized bed through feed nozzles. The liquid hydrocarbon chains are cracked at the particle surface, forming lighter hydrocarbon gases and rejected carbon solid (coke). This makes the efficiency of the coker dependent on the spreading of liquid. Spreading of liquid far from the nozzles occurs through collisions of wet and dry particles and their motion due to fluidization.

Simulations of fluidized beds are challenging due to the multiple scales of importance, ranging from the overall unit dimensions down to the gas dynamics and particle-liquid interactions. To get a full understanding of the system, a multi-scale approach is necessary. We present particle-resolved simulations of ~1000 particles. A sample flow field for a small simulation is shown in the figure. While these simulations allow for the direct modeling of gas-solid interactions, they are computationally expensive, making the addition of a liquid phase impractical. Instead of resolving the liquid films, we track the volume of liquid on each particle.

In this work we examine the spreading of liquid through a fluidized bed through particle-particle collisions, without (at this stage) considering the inter-particle forces due to liquid bridges and their agglomerating effects. We study multiple solids volume fractions, and consider the effect of liquid surface tension and viscosity. From these simulations, we determine effective liquid diffusion rates both horizontally and vertically. The goal of this work is to enhance our knowledge of liquid spreading through a fluidized bed, and to assess the dependence of the spreading rates on liquid properties and solids volume fraction.

Figure 1: Cross-section of simulation domain with solids volume fraction 0.3. Coloring indicates normalized non-dimensional velocity.