Application of Process Tomography as a Tool for Better Understanding of Fluidization Quality in a Conventional Fluidized Bed

Y. T. Makkawi and P. C. Wright

Department of Mechanical and Chemical Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK

ABSTRACT

The hydrodynamics and solid flow structure quality in a cold conventional fluidized bed has been studied using electrical capacitance tomography (ECT). The system compromises a twin-plane ECT in a 150-mm diameter acrylic column. The experiments were carried out at ambient conditions and under different fluidization velocities ranging from 0.1 to 1-m/s using air as the fluidizing medium. A mixture of spherical ballotini ranging between 300-700 Om diameter and average density of 2600 kg/m3 were used as the fluidizing particles. Measurement of solid volume ratio was recorded over a 20-s interval at a 100 Hz sampling rate. A new method for measuring the minimum fluidization velocity has been described, based on the time series ECT measurements. Three different fluidization regimes with distinct transitions have been identified: single bubble regime, multi-bubble regime and exploding bubble regime. As a first step in providing a “quantitative” definition of fluidization quality (FQ), a simple non-dimensional group is proposed. Unlike the pressure drop method, the ECT measurement technique with its non-intrusive nature proves its reliability in fluidization studies. This study is the first in series in an attempt to describe the solid-gas distribution, bed hydrodynamics and fluidization quality in a conventional fluidized bed using the ECT system.

Keywords Fluidized Bed; Electrical Capacitance Tomography; Fluidization Quality; Hydrodynamics