Solid circulation and gas bypassing in an internally circulating fluidized bed with an orifice-type draft Tube

Simplified modeling of circulating flow of solids between a fluidized bed and a vertical pneumatic transport tube reactor connected by orifices

“…We have used the value U T = 1.5 m/s for the sand particles as done by Kim et al [10] which corresponds to sharp sand (for ϕ = 0.5-0.65) [48,49]. The model with slip factor and C D = 0.31 provides a fair fitting of the dependence of G FB on superficial velocity in the draft tube (riser) particularly when we take into account that bypassing of the gas from the annulus to the draft tube will increase with increasing gas velocity U f [9,10].…”

“…We have found in the literature [9,10] experimental data only on solids circulation between a fluidized bed and a short draft tube with orifices at the bottom. Ahn et al [9] have measured the circulation flux of solids in the annular fluidized bed (G FB ).…”

“…Ahn et al [9] have measured the circulation flux of solids in the annular fluidized bed (G FB ). The relation between the flux in the annular FB and the solids flux in the draft tube under steady state conditions is given by the equation:…”

“…Three simplified models for the description of vertical transport of solids within the riser have been used in a more general model [19] for the circulating flow of particles between a FB near incipient fluidization and a tube (column) with PT of solids communicating via orifices. Because of lack of relevant experimental data for validation of the models we have used both our measured experimental data and partly data from the literature with dense fluidization flow in the riser [9,10]. The models have been used further for estimating the effects of gas velocity, particle size and height of the fluidized bed on particle velocity, mass flux of particles and pressure drop in a PT column.…”

“…The rate of circulation of solids for systems with two FB chambers connected by an orifice and differing in fluidization regime was described by Korbee et al [2]. The experimental description and modeling of the circulation of solids in a system with one FB reactor and a pneumatic transport (PT) reactor communicating via orifices is scarce in the literature: only six partly relevant experimental studies [9][10][11][12][13][14] describing internally circulating fluidized/moving bed either with a relatively short draft tube [9][10][11], with powder fluidization inside the draft tube and a circulation system with a conical distributor, an annular downwards moving bed and with a draft (riser) tube with regime of fast fluidization and pneumatic transport [12]. Another solid circulation system experimentally studied and modeled [13] used a downward moving annular bed and the measured pressure gradients in the PT-column.…”