Voidage and Pressure Profile Characteristics of Sand−Iron Ore−Coal−FCC Single-Particle Systems in the Riser of a Pilot Plant Circulating Fluidized Bed

Abstract

Hydrodynamic behaviors of single system of particles were investigated in a circulating fluidized bed (CFB) unit. Particles belonging to Geldart groups A and B like sand of various sizes (80, 300, 417, 522, 599, and 622 µm), FCC catalyst (120 µm), iron ore (166 and 140 µm), and coal (335 and 168 µm) were used to study the hydrodynamic characteristics. Superficial air velocity used in the present study ranged between 2.01 and 4.681 m/s and corresponding mass fluxes were 12.5-50 kg/(m 2 s). A CFB needs the creation of some special hydrodynamic conditions, namely a certain combination of superficial gas velocity, solids circulation rate, particle diameter, density of particle, etc. which can give rise to a state wherein the solid particles are subjected to an upward velocity greater than the terminal or free fall velocity of the majority of the individual particles. The hydrodynamics of the bed was investigated in depth and theoretical analysis is presented to support the findings. Based on gas-solid momentum balance in the riser, a distinction between apparent and real voidage has been made. The effects of acceleration and friction on the real voidage have been estimated. Results indicated a 0.995 voidage for higher superficial gas velocity of 4.681 m/s.

Study of Hydrodynamics and Dry Beneficiation Characteristics of Coal in the Riser of a Circulating Fluidized Bed Reactor

“…This drastic reduction in static pressure may be due to the reasons as explained earlier. The values of static pressure at higher velocity were low compared to a lower velocity [7]. Figure 4 shows the typical effect of the solids circulation rate on the static pressure profile for air-coal at a constant velocity of 2.01 m=s.…”

“…It was observed that the effect of gas velocity in the dilute zone was almost negligible but in the dense zone there was a considerable change in voidage. The general tendency for the dense region was to expand with decreasing gas flow at a constant solid circulation rate [7].…”

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

“…Slightly simplified engineering models [30] consider dependence of the dependent variables (ε, ρ f , U p and ΔP PT ) on the axial (vertical) coordinate. If an average (constant) gas density can be considered, the three balance equations for U p , ε and ΔP PT have to be solved [31,32].…”

Computational characterisation of intermittent hydrodynamic behaviours in a riser with Geldart A particles

“…As the flow intermittency is closely related to the heterogeneous distribution of hydrodynamic parameters and the non-equilibrium flow state, which can further result in fluidisation faults such as stagnant zones, hot spots, particle adhesion to the wall, slugs, and even defludisation, it is necessary to understand the hydrodynamic characteristics of the intermittent flow behaviours in a CFB with Geldart A particles. Despite extensive studies conducted on the experimentation and simulation of CFBs with Geldart A particles [3][4][5][6][7][8][9], the knowledge about flow intermittency is still limited. Brereton and Grace [10] derived an intermittency index from the measured suspension density fluctuating signals to quantify the nonuniformity of the flow field in a riser.…”