Experimental and numerical study on multiphase fluid dynamics of coal and blends with biomass (sugarcane bagasse) in a lab-scale full-loop circulating fluidized bed gasifier

ABSTRACT

The current research presents a 3-D hydrodynamic simulation of the fluidized bed riser with a validated CFD model at different superficial gas velocities and inventory composition (coal of 2 kg is blended with sugarcane bagasse weights 0.2 kg and 0.8 kg). The experiments are performed by varying superficial gas velocity (0.5 U_mf to 3 U_mf), coal particle size (460 μm and 460 μm), and coal bed inventory size (1.5 kg and 2 kg) in a pilot-scale circulating fluidized bed riser of 100 mm diameter and 3000 mm height. The CFD model results are in good agreement with experimental pressure drop and solid volume fraction. The effect of drag and lift force in fluidization hydrodynamics has been studied. The validated CFD model is then extended to predict the hydrodynamics of the three-fluid, coal-sugarcane bagasse-air system. A mixing factor is defined to quantify the mixing behavior of coal and sugarcane bagasse. It is concluded that a 200 gm sugarcane bagasse blend has good mixing than the 800 gm blends. For efficient mixing, coal and sugarcane bagasse fluidized beds should operate in the 2 U_mf to 4 U_mf superficial gas velocity range. The results of axial and radial distribution of coal, sugarcane bagasse and air volume fraction, pressure drop, slip velocity, and fluidized bed heights are presented.

KEYWORDS:

• Fluidization
• circulating fluidized bed
• Eulerian-Eulerian
• coal
• sugarcane bagasse
• computational fluid dynamics

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notations

${\alpha }_g$= Bed Voidage	=
${\rho }_{\mathit{sus}}$= Suspension Density	=
$L_m$= Distance between Pressure Measuring points	=
$\mathrm{\Delta h}$= Hight Difference in Manometer	=
${\rho }_s$= Solid Density	=
${\rho }_g$= Gas Density	=
${\alpha }_s$= Solid Volume Fraction	=
${\alpha }_g$= Gas Volume Fraction	=
${\alpha }_c$= Coal Volume Fraction	=
$v_s$= Solid Velocity	=
$v_g$= Gas Velocity	=
$\mathrm{\Delta }\mathit{P}$= Pressure Drop	=
${\epsilon }_s$= Bulk Viscosity	=
$K_{\mathit{sg}}$= Momentum Exchange Coefficient	=
$C_d$= Drag Coefficient	=
$R_{\mathit{es}}$= Particles Reynolds Number	=
$\mathit{f}$= Drag Factor	=
$v_{\mathit{rs}}$= Relative Settling Velocity	=
${\gamma }_{{\theta }_s}$= Collisional Energy Dissipation	=
$\mathit{\epsilon }$= Dissipation Rate	=
$C_l$= Coefficient of lift	=
${\vec{v}}_{\mathit{m}}$= Mixture Velocity	=
$h_f$= Fluidized bed Height	=
${\bar{\alpha }}_{\mathit{sb}}$ =Average Sugarcane bagasse Volume fraction	=
$U_{\mathit{mf}}$= Minimum fluidization velocity	=
$\vec{g}=$Acceleration due to Gravity	=
$F_{\mathit{ext}}$= External Force	=
${\tau }_s$= Stress Tensor for Solid Phase	=
${\tau }_g$= Stress Tensor for Gas Phase	=
${\theta }_s$= Granular Temperature	=
$e_{\mathit{ss}}$= Restitution Coefficient	=
$g_o$= Radial Particles Distribution Function	=
${\alpha }_{{\mathit{s}}_{max}}$= Solid Packing Limits	=
${\alpha }_{\mathit{sb}}$= Sugarcane bagasse Volume Fraction	=
${\mu }_{\mathit{col}}$= Collisional Viscosity	=
$d_s$= Particle Diameter	=
${\mu }_{\mathit{kin}}$= Viscosity due to fluctuation in kinetic Energy	=
${\mu }_f$= Frictional Viscosity	=
$\mathit{\varphi }$= Internal Frictional Angel	=
$I_{2\mathit{D}}$= Second Invariant of Devitorial Stress Tensor	=
${\mu }_g$= Gas Viscosity	=
${\mu }_s$= Solid Viscosity	=
$P_s$= Solid Pressure	=
$\mathit{k}$= Turbulent kinetic Energy	=
${Re}_{\omega }$= Vorticity Reynolds Number	=
${\rho }_m$= Mixture Density	=
$G_{\mathit{k},\mathit{m}}$= Turbulent kinetic Energy	=
$m_f$ = Mixing Factor	=
${\bar{\alpha }}_{\mathit{s}{b}_i}=$ Sugarcane bagasse volume fraction in the sampling layer	=
$U_{\mathit{sup}}$= Superficial gas velocity	=