Local holdups and phase propagation velocity measurement in GLSCFB riser using electrical resistance tomography and optical fibre probe

The application of Gas-Liquid-solid circulating fluidized beds (GLSCBE) has increased recently in chemical, petrochemical and biochemical industries. Electrical Resistance Tomography (ERT) and optical fibre probe were applied to investigate local phase holdups distribution. Since ERT is applicable only to conductive phase(s), e.g. liquid phase in this study, optical fibre probe was employed simultaneously to quantify all three phases. Water was used as continuous and conductive phase, air as the gas phase and glass beads as solid non-conductive phases. The local conductivity measured by a number of electrodes located at the periphery of the plane, was then further converted into a local phase concentration distribution based on Maxwell's relation. Fibre optic probe was also employed to measure gas holdup independently. A new model was developed to exploit the fibre optic data in differentiating gas bubbles from solid particles in the riser. Gas holdup was higher in the central region and decreased radially, while opposite trend was observed with solid holdup due to the drag forces imposed on solid particles by the gas and liquid upward flow in the riser. By applying cross correlation between the data obtained at two different levels in the riser, the propagation velocity of the nonconductive phase was obtained. Propagation velocity was higher in the central region compared to the wall region and increased with increasing liquid superficial velocity.