Effects of pressure on particle velocity profile in CFBS
The pressure has a positive effect on the mixing conditions since increasing pressure value causes stronger turbulence in the riser which results in better mixing of particulate solids and gases. In this study the effects of pressure on particle velocity profile in CFBs is investigated based on previously developed 2D CFB hydrodynamic model which uses the particle-based approach. In the modeling, the CFB riser was analyzed in two regions: The bottom zone in turbulent fluidization regime was modeled in detail as two-phase flow which was subdivided into a solid-free bubble phase and a solid-laden emulsion phase. In the upper zone core-annulus solids flow structure was established. The pressure drop through the bottom zone was assumed to be equal to the weight of the solids and considered only in axial direction. In the upper zone, pressure drop due to the hydrodynamic head of solids was considered in axial direction while pressure drop due to solids acceleration was also considered in axial and radial directions. The model results compared fairly well with experimental data of axial pressure drop profiles and radial particle velocity profiles from the literature. The hydrodynamic behavior of CFB is greatly affected by the inlet bed pressure values. Increasing operating pressure led to a decrease in the difference between the particle velocity in the riser core region and the wall region probably due to increased turbulence.