Numerical and Experimental Investigation of Bubbling Gas-Solid Fluidized Beds with Dense Immersed Tube Bundles

Numerical simulations of gas solid bubbling fluidized beds with and without dense immersed horizontal tubes were performed using the Eulerian-Eulerian Two Fluid Model (TFM) and applying the Kinetic Theory of Granular Flow (KTGF). The results were compared with experimental data obtained from a pseudo-2D fluidized bed test rig using a developed digital image analysis technique (DIAT). The influences of dense immersed horizontal tubes on bed properties (bed pressure drop and expansion ratio) and bubble hydrodynamics (bubble size, rise velocity, aspect ratio, and shape factor) were investigated numerically as well as experimentally. In the first part grid sensitivity with different mesh sizes was checked and effects using 2D and 3D domains were examined. Simulations with 3D domains gave better agreement with experimental data but were seen to be computationally expensive. For conducting intensive parametric studies of fluidized bed behavior the use of 2D domains remains indispensable. In the second part it could be shown that dense tube arrangements in the fluidized bed lead to repeated bubble break-up and coalescence in the tube bank region and therefore to fluctuating values of bubble size, rise velocity, aspect ratio, and shape factor. For different superficial velocities similar results were found which shows the high influence of dense immersed tubes on fluidized bed behavior. In addition no significant differences between staggered and in-line tube arrangement were observed. In general the simulations based on the Two Fluid Model showed good agreement with the experimental results.