Numerical Predictions on the Influences of Inlet Temperature and Pressure of Feed Gas on Flow and Combustion Characteristics of Oxy-pulverized Coal Combustion

ABSTRACT

Carbon capture and storage employing oxy-fuel combustion is one of the most promising options to reduce greenhouse gas emission. For the transition from conventional air-fired combustion to oxy-fuel combustion, there is a necessity of detailed investigation of various phenomena that occur during oxy-fuel combustion. Numerical modeling of oxy-fuel combustion process can serve the purpose effectively and efficiently. The current paper presents a thorough numerical investigation of the combustion process of pulverized coal under oxy-fuel conditions. The influence of inlet temperature and pressure of feed gas is investigated in the present study. Computational fluid dynamics simulation is performed for the test facility located at the Institute of Heat and Mass Transfer at Aachen University. The numerical results obtained employing various Reynolds Averaged Navier Stokes (RANS) models have been compared with measured data. The results showed that the strength and axial dispersion of the internal recirculation zone (IRZ) are enhanced at higher inlet temperature. The combustion of volatile matter present in coal shifts near the burner which results in shorter flames at higher inlet temperature. The flame temperature increased by ~9% with increase in inlet feed gas temperature from 313 to 800 K. Inlet feed gas pressure of 10.0 bar has ~38% increment and ~32% reduction in IRZ length and flame length, respectively, than the base case.

KEYWORDS:

• Oxy-fuel combustion
• temperature
• pressure
• CFD
• flame length
• pulverized coal

Nomenclature

A	=	Pre-exponential factor (s−1) Greek symbols
${\bar{U}}_i$	=	Mean velocity in tensorial notation (m.s−1)
${\alpha }_t$	=	Turbulent thermal diffusivity (m2.s−1)
${\bar{U}}_{\theta }$	=	Mean tangential velocity (m.s−1)
${\mu }_t$	=	Eddy viscosity (kg.s.m−1)
${\bar{U}}_z$	=	Mean axial velocity (m.s−1)
${\theta }_R$	=	Radiation temperature (K)
$V_i$	=	Velocity of particle (m.s−1)
$\rho$	=	Density (kg.m−3)
$Y_i$	=	Mass fraction of species i
$\sigma$	=	Stefan–Boltzmann constant (W.m−2.K−4)
E	=	Activation energy (kJ.kg−1)
$k$	=	Absorption coefficient (m−1)
qri	=	Radiative heat flux (W.m−2)
$\mathrm{\forall }$	=	Volume of computational cell (m3)
$d_i$	=	Particle dia. of ith class of particle (m) Subscripts
$d_{max,i}$	=	Maximum dia. of ith class of particle (m)
i	=	Initial state
$d_{min,i}$	=	Minimum dia. of ith class of particle (m)
j	=	Tensor notation’s index
$\dot{s}$	=	Source term in gas phase due to particles (kg.m−3s−1)
g	=	Gas phase
${\dot{s}}_{M_i}$	=	Momentum source term in gas phase due to particles (kg.m−2s−2)
p	=	Particle phase
${\dot{s}}_E$	=	Energy source term in gas phase due to particles (W.m−3)
Pr	=	Prandtl number
Nu	=	Nusselt number
Re	=	Reynolds number