Hydrodynamics and Erosion Modeling of Fluidized Bed Combustors

Abstract

Hydrodynamics and erosion of Fluidized Bed Combustors (FBCs) containing tubes have been analyzed through the use of the hydrodynamic model, which has been developed at New York University, utilizing a CRAY Y-MP/832 supercomputer and a CONVEX C210 minisupercomputer. Particle velocity fields and bed dynamics including bubble formation and motion and bed expansion and collapse were analyzed for high pressure cold and hot beds. The cold beds were studied by (a) optimizing tube models for simulating a circular tube, (b) varying the distance from distributor plate to the tubes, (c) changing tube size, and (d) using vertical tubes. Atmospheric and pressurized fluidized bed combustors were also simulated and compared to each other for bubble size, bubble frequencies, particle jets, and tube erosion. In particular, the computation revealed bubble coalescence which causes high particle jets. Threshold velocity has been analyzed utilizing Hertz contact theory and the maximum shear theory (Tresca). Tube erosion was predicted utilizing the Finnie erosion model and the modified Finnie model, which considers the threshold velocity and compared to each other. Computed results show that the distance from distributor to the tubes, tube size, tube orientation and operating pressure have significant effect on bed dynamics and tube erosion. The threshold velocity is found to significantly influence the prediction of erosion.