Circulating Fluidized Bed (CFB) Gasifier, CFD Simulation ANSYS Fluent Training

Description

Circulating Fluidized Bed Project Description

the Circulating Fluidized Bed gasifier is popular in industrial applications and academic studies because of its intrinsic advantages in high circulating rate, low operating temperature, broad fuel flexibility, and negligible pollutant emissions. In this simulation, a simple CFB cycle has been simulated, and results obtained.

The system consists of two inlets, a vertical inlet for oxidizer and a horizontal inlet for fuel; the air and fuel, after mixed, start flameless combustion in a vertical section and then enter the cyclone to separate unburned ashes as polluted air, unburn fuel circulates to bottom of the downstream section and enters the process again and heavy sands and ashes exit from the bottom outlet. The particle density function (PDF) has been used in this simulation to simulate solid dynamics.

Geometry & Mesh

The 3-D domain of this simulation has been designed in ANSYS Design Modeler.

The meshing of this present model has been generated by ANSYS Meshing software. The mesh grid is unstructured, and the total cell number is 1537941 elements. The figure below shows an overview of the performed mesh.

 

 

 

CFD Simulation

To simulate the present model, several assumptions are considered, which are:

• The solver is pressure-based.
• The effect of gravity on the flow has been considered
• The hot zone wall model is considered a heat flux

The following is a summary of the steps for defining the problem and its solution.

 

Models
k-epsilon	Viscous model
Standard wall function	Near -Wall treatment
Pressure based	Solver
steady	Timestep
Non – premixed combustion	Species model
Chemical equilibrium	State relation
Non-adiabatic	Energy treatment
P1	Radiation model
On	Discrete phase model
Unsteady particle tracking	Particle treatment
Combusting	Injection type
On	Energy
Boundary conditions
Velocity-inlet		Air inlet
18 m/s	Fluid inlet velocity
300 k	Temperature
1	Internal emissivity
0	Soot mass fraction
0	Mean mixture fraction
0	Mixture fraction variance
Escape	Discrete phase BC type
Velocity inlet		Bio inlet
15 m/s	Particle inlet velocity
330 k	Temperature
1	Internal emissivity
0	Soot mass fraction
1	Mean mixture fraction
0	Mixture fraction variance
Escape	Discrete phase BC type
Pressure outlet		Cyclone outlet
0	Supersonic gage pressure
Pressure outlet		Qr outlet
-120w	heat flux
wall		Q2 wall
stationary wall	wall motion
heat flux	Thermal condition
250 w	heat flux
wall		wall
stationary wall	wall motion
Non	Thermal condition

Circulating Fluidized Bed Results

The simulation results show that the ignition of the fuel-air mixture in the vertical chamber and the hot gases resulting from the ignition is cooled in the cyclone and the second chamber, and the polluting gases of the maximum face are also examined. Unburned materials are separated inside the cyclone and re-entered the combustion process.

The counter below shows pressure, temperature, and gas volume fraction.