Flow characteristic studies on the gas-liquid-solid circulating fluidized bed based on system stability. (April 2019) - Razzak, Shaikh A.
Highlights: Overall pressure balance evaluated in the entire flow loop of GLSCFB system. Flow characterization of the three-phase GLSCFB under a wide range of operating conditions have been studied. Effect of particle, size and shape effect on flow characteristic discussed. Two flow regimes found in circulating fluidized bed conditions. Abstract: Gas-liquid-solid circulating fluidized bed (GLSCFB) is considered as superior technology over conventional Gas-liquid-solid fluidized beds. The GLSCFB consist of two interconnected riser and downer columns facilitating solid circulation between the columns by pressure balance. The overall pressure balance is an important parameter for stable operation of the system. The present communication reports an experimental investigation to correlate the pressure balance and hydrodynamics behavior and the stability of the GLSCFB. In this regard, two spherical shape glass bead particles (500 and 1200 μm in size), two irregular shape lava rock particles (500 and 920 μm in size) are used as solid phase, air as gas phase and saline-water as liquid phase. For flow characterization, superficial solids velocity ( Us ), normalized superficial solids velocity ( U s U l ), solids holdup (ɛ s ) and gas holdups (ɛ g ) are considered as measureable parameters. The experimental observations indicates that the solids holdup have significant impact of size, density and shape of the particles on hydrodynamics behavior. The drag effect on the particles and their terminal settling velocity are the main factors on solids holdup distribution. The average solids holdups decrease with the increase on net superficial liquid velocity ( U l − U t ) and normalized superficial liquid velocity ( U l U t ). Effects of different parameters ( Ua, Ul, Ug, U l U t, U l − U t ) are considered to study the hydrodynamics behavior on superficial solids velocity, solids and gas holdups. Two operating regimes are found under different operating conditions. In Region-I, superficial solids velocity increases with the increases of superficial, net superficial and normalized superficial liquid velocity whereas in Region-II solids velocities remain constant. For the case of cross-sectional phase holdups, both gas and solids holdups decrease with the increases of superficial liquid velocity.