Incorporation of hydrodynamics and ash chemistry into a unified model for prediction of agglomeration in fluidized beds

Study of particle growth or agglomeration involves a detailed understanding of both the thermodynamics of phases that lead to the liquid binder formation or the binder-liquid chemistry, and also the fluid dynamics of particles in the system. As particle growth progresses and the particle size distribution changes, the bed hydrodynamics such as particle collision frequencies also change continuously. This progression makes it challenging to predict the kinetics of particle growth, since the chemistry and physics-based parameters are interlinked. Models that can incorporate interdependencies and variations in both bed hydrodynamics and binder chemistry are required for more accurate predictions. Penn State has developed a unique two-particle collision based model that combines the two effects mentioned above. The model is being applied to polydispersed fluidized bed combustion and gasification systems. In the Penn State model, thermodynamic equilibrium calculations are used to estimate the amounts of slag-liquid in the system, while the evolution of particle collision frequencies is accounted for by tracking the number density of differently sized particles, while using the kinetic theory of granular flow. Computational fluid dynamics modeling is used in conjunction to obtain initial inputs to the model. The model helped to gain an understanding of low-temperature ash agglomeration in these systems and understand parameters that may promote the initiation of agglomerate growth at the particle-level. Using the Penn State ash agglomeration model, attempts have been made to predict the operating conditions (in terms of both ash chemistry and particle physics) under which the occurrence of ash agglomeration is more likely in fluidized bed gasification and combustion systems. This model can further be extended to predict the rate of particle size growth and deposition issues in allied industries.