Hydrodynamics of a Liquid–Solid Circulating Fluidized Bed: Effect of Solid Feed Pipe Diameter

Abstract

An experiment was conducted to acquire a set of systematic data on the solids circulation rate and solids holdup in the riser of liquid–solid circulating fluidized bed (lsCFB) to study the effect of solids feed pipe diameter. In the experiment, five kinds of solids feed pipes with inner diameter 9, 12, 22, 25 and 30 mm were provided. The result indicates that onset transitional liquid velocity, onset solids holdup, average solids holdup and solids circulation increase with increase in solids feed pipe diameter. The results substantiate that the solids feed pipe diameter plays an important role on the hydrodynamics of lsCFB in addition to operating liquid velocities (primary and auxiliary), size and density of solids, solids inventory and liquid viscosity. Based on the experimental data, correlations were proposed for predicting the maximum solids circulation rate, solids circulation rate and solids holdup, which could reproduce almost all experimental data with an accuracy of ±8%, ±13% and ±8%, respectively.

Keywords:

• Circulating fluidized bed
• Liquid–solid fluidization
• Hydrodynamics
• Solids feed pipe diameter
• Solids holdup
• Solids circulation rate

Acknowledgement

Guidance received from Prof. Y.B.G. Varma, Professor of Chemical Engineering (Retd.), Indian Institute of Technology, Madras, India is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notations

A = area of the riser, m²

D = diameter of the riser, m

d_p = mean particle size, mm, m

d_o = solids feed pipe diameter, mm

d_or = orifice diameter, mm

F_S = mass discharge rate of solids, kg/s

g = acceleration due to gravity, m/s²

Ga = Galileo number (d_p³gρ_l²/μ_l²)

j_a = superficial auxiliary liquid velocity, (Q_a/A), m/s

j_f = superficial primary liquid velocity, (Q_f/A), m/s

j_l = superficial total liquid velocity, (Q_l/A) = (= j_f + j_a), m/s

j_lm = maximum superficial total liquid velocity, m/s

j_s = solids circulation rate expressed as superficial solids velocity,(w_s/Aρ_s), m/s

j_sm = maximum solids circulation rate, m/s

Q_a = volumetric flow of auxiliary liquid, m³/s

Q_f = volumetric flow of primary liquid, m³/s

Q_l = volumetric flow of liquid phase, (Q_f+ Q_a), m³/s

Q_s = volumetric flow of solid phase, (w_s/ρ_s), m³/s

RMS = root mean square value

u_t = particle terminal velocity, m/s

w_s = solids circulation rate, kg/s

ΔP/Δz = pressure drop at the test section

Greek letters

ε_s = solids holdup (−)

ε_smin = minimum solids holdup (−)

ρ = bulk density of the gas-solid mixture, kg/m³

ρ_l = liquid density, kg/m³

ρ_s = particle density, kg/m³

Δρ = (ρ_s – ρ_l)