Abstract
Effect of oxygen enrichment on flow field, temperature, concentration distribution, emission, and fuel economy has been studied inside a pilot-scale Rotary Hearth Furnace (RHF) for two separate conditions with or without varying the fuel amount. In varying fuel condition (when amount of fuel is reduced with oxygen enrichment to maintain the flame temperature constant), the fuel consumption was reduced by 14.9 pct, when oxygen enrichment in increased from 21 to 35 pct. Under this condition, the high-temperature zone showed a shift, more towards the upstream of the flame with an increase in the oxygen enrichment and led to a decrease in heat transfer towards the bottom part of the furnace, not desirable for pellet reduction at the bottom. In case of constant fuel (fuel volume remaining constant irrespective of oxygen enrichment), the high-temperature zone spreads away from the burner and such shift progressively becomes more with an increase in the oxygen enrichment. More importantly, in this case, efficiency heat transfer from the top to the bottom of the furnace increased with oxygen enrichment. Specific CO2emission per ton of DRI produced showed a sharp decrease with an increase in oxygen enrichment, mainly in fuel varying condition. In contrast, the emission remained more or less similar in fuel constant condition.
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Abbreviations
- \( C_{1\varepsilon } \), \( C_{2\varepsilon } \), \( C_{3\varepsilon } \),\( C_{\mu } \) :
-
Constants of standard k-ε model
- \( C_{P} \) :
-
Specific heat at constant pressure, J/kg K
- \( C_{pm} \) :
-
Average specific heat at constant pressure, J/kg K
- \( C_{k} \) :
-
Concentration of gas component k (CO and CO2), moles/m3
- \( D_{k} \) :
-
Diffusion coefficient for gas species k (CO and CO2), m2/s
- \( E \) :
-
Total energy per unit mass, J/kg
- \( E_{a} \) :
-
Activation energy, J/mol
- \( G_{b} \) :
-
Production of turbulent kinetic energy by buoyancy, J/m3s
- \( G_{k} \) :
-
Production of turbulent kinetic energy by velocity gradient, J/m3s
- \( g_{j} \) :
-
Component of gravitational vector in the j th direction, m/s2
- \( I \) :
-
Radiation intensity, W/m2 sr
- \( I_{b} \) :
-
Black body radiation intensity, W/m2
- \( I_{bw} \) :
-
Black body radiation at furnace temperature, W/m2
- \( I_{in} \) :
-
Intensity of incoming ray, W/m2 sr
- \( K \) :
-
Equilibrium constant
- \( K_{eff} \) :
-
Effective thermal conductivity of the pellet, W/m K
- \( k \) :
-
Turbulent kinetic energy, m2/s2
- \( k_{{Fe_{x} O_{y} }} ,k_{C} \) :
-
Rate constant which follows the Arrhenius law. Here x = 1, 2, 3 and y = 1, 3, 4. \( k_{{Fe_{x} O_{y} }} = A_{{Fe_{x} O_{y} }} \exp \left( {\frac{{ - E_{{Fe_{x} O_{y} }} }}{RT}} \right) \), \( k_{C} = A_{C} \exp \left( {\frac{{ - E_{C} }}{RT}} \right) \)
- \( k_{o} \) :
-
Pre-exponential constant, m2/s
- \( M \) :
-
Molecular weight, kg/mol
- \( \overrightarrow {n} \) :
-
Outward normal vector
- \( P \) :
-
Total pressure inside the pellet, atm
- \( P_{{CO,CO_{2} }} \) :
-
Partial pressure of CO and CO2
- \( p \) :
-
Pressure, Pa
- \( Q \) :
-
Total heat of the reaction \( Q = \sum\limits_{i} {R_{i} \left( { - \Delta H_{i} } \right)} \) Ri represents the reaction rate for the species ‘i’ in mol/m3, and ΔH represents the heat of the ith reaction in J/mole
- \( R \) :
-
Universal gas constant, J/mol K
- \( r \) :
-
Distance of a point from the center of the pellet, m
- \( \overrightarrow {r} \) :
-
Position vector, m
- \( S_{chem} \) :
-
Source term of heat of chemical reaction, J/m3 s
- \( S_{k} \) :
-
Source term of gas species k (CO and CO2) in species transport equation, J/m3 s
- \( S_{rad} \) :
-
Source term for heat of radiation, J/m3 s
- \( Sc_{t} \) :
-
Turbulent Schmidt number
- \( \overrightarrow {s} \) :
-
Unit direction vector, m
- \( T \) :
-
Pellet temperature, K
- \( T_{0} \) :
-
Initial temperature of pellet, K
- \( t \) :
-
Time, s
- \( u_{i} \) :
-
Velocity component, m/s
- \( Y_{i} \) :
-
Mass fraction of species i
- \( Y_{P} \) :
-
Mass fraction of any product species
- \( Y_{R} \) :
-
Mass fraction of any reactant species
- \( \beta \) :
-
Coefficient of thermal expansion
- \( \delta_{ij} \) :
-
Kronecker delta
- \( \varepsilon \) :
-
Dissipation rate of turbulent kinetic energy per unit mass, m2/s3
- \( \varepsilon_{w} \) :
-
Wall emissivity
- \( {\rm K} \) :
-
Absorption coefficient, 1/m
- \( \mu \) :
-
Molecular viscosity, kg/m s
- \( \mu_{eff} \) :
-
Effective viscosity, kg/m s
- \( \mu_{t} \) :
-
Turbulent viscosity, kg/m s
- \( v_{i,r} \) :
-
Stoichiometric coefficient for reactant i in reaction r
- \( v^{\prime\prime}_{i,r} \) :
-
Stoichiometric coefficient for product i in reaction r
- \( \rho \) :
-
Density, kg/m3
- \( \sigma \) :
-
Stefan-Boltzmann constant, W/m2 K4
- \( \sigma_{k} \) :
-
Turbulent Prandtl number for k in standard k–ε model
- \( \sigma_{\varepsilon } \) :
-
Turbulent Prandtl number for ε in standard k–ε model
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Manuscript submitted May 31, 2020; accepted September 14, 2020.
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Saleem, S., Roy, G.G. Effect of Oxygen Enrichment on Flow Field, Temperature, and Gas Concentration Profile Inside a Pilot-Scale Rotary Hearth Furnace. Metall Mater Trans B 51, 2735–2755 (2020). https://doi.org/10.1007/s11663-020-01981-y
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DOI: https://doi.org/10.1007/s11663-020-01981-y