Abstract
The three-dimensional (3-D) comprehensive mathematical model was developed to simulate the coal gasification process in an entrained flow gasifier with a swirl burner. The models employed or developed includes the coal devolatilization model, the char combustion and gasification model, the gas homogeneous reaction model, the random-trajectory model, gas turbulence model, and the P-1 radiation model. The solution of models was executed based on the computational fluid dynamics (CFD). By qualitatively comparing the results at different swirl number, the significant influences of swirl on characteristics of coal gasification such as flow distributions, gas temperature and product composition including hydrogen (H2), carbon monoxide (CO), etc., and on the performance of coal gasification such as averaged exit product composition, carbon conversion rate and cold gas efficiency, were in detail discussed. Especially, a proper swirl number (S ≤ 0.65) in favor of gasification was found for the investigated gasifier in this paper.
Nomenclature
- A, B
Empirical constants in Eddy-Dissipation model
- Ai
Proportional coefficient of devolatilization, char heterogeneous reactions and gas homogeneous reactions (1/s)
- Ap
Projected area of particle (m2)
- ap
Equivalent absorption coefficient of particles in cell (1/m)
- ag
Gas absorption coefficient (1/m)
- a, b
Global reaction exponents for the species X and Y in gases homogeneous reactions
- C1, C2
Turbulent model constants
- CD
Drag coefficient
- Cp, cp
Specific capacity of gas species and particle (J/(kg⋅K))
- D
Averaged diameter of the inlet of gasification agent (m)
- Dji
Mass diffusion coefficient of component j in component i (m2/s)
- Dj,m
Mass diffusion coefficient for species j in the mixture (m2/s)
- di, do
Inner and outer diameters of the inlet of gasification agent (m)
- dp
Diameter of particle (m)
- Ei
Activation energy of devolatilization, char heterogeneous reactions and gas homogeneous reactions (kJ/mol)
- Ep
Equivalent emission of particles in cell (1/m)
- Fdi, Fgi
Drag force and gravity (N)
- fv,0
Mass fraction of volatiles initially present in the particle
- G
Incident radiation in P-1 radiation model (W/m)
- gi
Acceleration of gravity (m/s2)
- H
Total enthalpy (J/kg)
- h
Convective heat transfer coefficient between particle and gas phase (W/(m2⋅K))
- k1
Kinetic rate of devolatilization (1/s)
- kci
Kinetic rate of char heterogeneous reactions (kg/(m2⋅s⋅Pa0.5))
- LHV
Low heating value of coal (J/kg)
- Mj, Mw,j
Molecular weight of species j (g/mol)
- Mc(s)
Molecular weight of carbon (g/mol)
- mp
Mass of coal particle (kg)
- mp,0
Mass of initial particle (kg)
- N
Total number of chemical species in the system
- Nu
Nusselt number
- P
Static pressure (Pa)
- Pr
Prandtl number
- pi
Partial pressure of O2, CO2, and H2O (Pa)
- QC
Convective heat transferred between particle and gas phase (J/s)
- QG
Gasification heat (J/s)
- QR
Radiative heat transferred between particle and gas phase (J/s)
- qri
Radiation flux (W/m2)
- R
Universal gas constant (J/(K⋅mol))
- Red
Reynolds number based on the particle diameter and the relative velocity
- S
Swirl number
- Sh
Sherwood number
- Sp
Surface area of particle, m2
- Sϕ
Generalized source term
- Sϕp
Source term of interaction between coal particle and gas phase
- Sct
Turbulent Schmidt number
- Tg
Temperature of gas (K)
- Tp
Temperature of particle (K)
- ui
Instantaneous gas velocity (m/s)
Time-mean velocity of gas phase (m/s)
Fluctuating velocity of gas phase (m/s)
- upi
Velocity of particle (m/s)
- vR, vj
Stoichiometric coefficients for reactant and any species in the system
- Xi
Mole fraction of species i
- xi
Coordinate (m)
- Yj
Mass fraction of species j
- YR, YP
Mass fraction of any product and reactant species
- yc
Carbon mass fraction on dry basis of coal
- Z
Modulus of the mean rate-of-strain tensor
- Δmpi
Mass change for each particle (kg)
- Δt
Integration time step between particle and gas phase (s)
Standard formation enthalpy of products (J/kg)
Reaction heat of volatile (J/kg)
Carbon complete combustion heat (J/kg)
- ρ
Gas density (kg/m3)
- κ
Turbulent kinetic energy (m2/s2)
- ε
Dissipation rate of turbulent kinetic energy (1/(m2⋅s3))
- εp
Emissivity of particle
- ϕ
Generalized dependent variable
- Γ
Generalized diffusion coefficient
- Γr
Radiation parameter related to the absorption and scattering coefficients
- μ
Molecular viscosity (kg/(m⋅s))
- μt
Turbulent viscosity (kg/(m⋅s))
- λ
Molecular thermal conductivity (W/(m⋅K))
- λt
Turbulent thermal conductivity (W/(m⋅K))
- σ
Stefan-Boltzmann constant, 5.67 × 10−8 W/(m2⋅K4)
- σκ, σε
Turbulent Prandtl number for κ and ε equations in realizable κ-ε model
Acknowledgements
This work was supported by the National Natural Science Foundation of China [No. 51506199] and the Fundamental Research Funds for the Central Universities [2302018FRF-TP-18-095A1].
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