An investigation of fluidized-bed scaling—capacitance probe measurements in a pressurized fluidized-bed combustor and a cold model bed

Abstract

In order to investigate the validity of the scaling relationships for fluidized beds suggested by Fitzgerald and Crane, and Glicksman, comparative measurements of the bubble activity have been carried out in a pressurized fluidized bed burning coal, and in a smaller pressurized model bed operated at slightly above room temperature and scaled to match the hot bed. The hot bed, located at New York University, we operated at a pressure of p = 0.79 MPa and a temperature of T = 870°C, while the model bed, at Chalmers University of Technology, was operated at p = 0.24 MPa and T = 27°C. The bubble activity was measured at two corresponding positions in each bed with the aid of capacitance probes. The parameters compared were the mean bubble volume fraction, and the nondimensional forms of the mean bubble frequency, the mean pierced length of bubbles, the mean bubble rise velocity, and the local mean visible bubble flow rate per unit area. The measurements in the model bed were made with three different bed materials: the hot-bed material and an Olivine sand, both sieved down to a size distribution in accordance with the scaling laws, and the full-sized hot-bed material. The results show that in order to get a similar behaviour between the beds, it is important to operate the model bed at the conditions predicted by the scaling laws. Deviations in fluidizing velocity, pressure or particle size distribution from the scaling law values significantly affect the results. When operating at the properly scaled conditions, the local bubble parameters, expressed in dimensionless form, are in good agreement between the two beds.