Effect of multiphase radiation on coal combustion in a pulverized coal jet flame

Abstract

The accurate modeling of coal combustion requires detailed radiative heat transfer models for both gaseous combustion products and solid coal particles. A multiphase Monte Carlo ray tracing (MCRT) radiation solver is developed in this work to simulate a laboratory-scale pulverized coal flame. The MCRT solver considers radiative interactions between coal particles and three major combustion products (CO 2 , H 2 O, and CO). A line-by-line spectral database for the gas phase and a size-dependent nongray correlation for the solid phase are employed to account for the nongray effects. The flame structure is significantly altered by considering nongray radiation and the lift-off height of the flame increases by approximately 35%, compared to the simulation without radiation. Radiation is also found to affect the evolution of coal particles considerably as it takes over as the dominant mode of heat transfer for medium-to-large coal particles downstream of the flame. To investigate the respective effects of spectral models for the gas and solid phases, a Planck-mean-based gray gas model and a size-independent gray particle model are applied in a frozen-field analysis of a steady-state snapshot of the flame. The gray gas approximation considerably underestimates the radiative source terms for both the gas phase and the solid phase. The gray coal approximation also leads to under-prediction of the particle emission and absorption. However, the level of under-prediction is not as significant as that resulting from the employment of the gray gas model. Finally, the effect of the spectral property of ash on radiation is also investigated and found to be insignificant for the present target flame.

Development of a multiphase photon Monte Carlo method for spray combustion and its application in high-pressure conditions

“…Impact of multiphase radiation is expected to be much stronger in coal combustion, where the hot coal particles are expected to lose significant amounts of energy by radiative cooling [56,57]. The PMC solver presented here has already been extended for such applications [57,58]. Additionally, the multiphase PMC solver can be used in coupled simulations of combustion in the presence of a nonemitting liquid spray (instead of liquid fuel), such as simulations of fire extinction through water sprays.…”

The impact of radiative heat transfer in combustion processes and its modeling – with a focus on turbulent flames

“…In such conditions, the concentration of CO2 is elevated and the heat transfer can be dominated by RHT, which becomes in turn a critical component for the boiler design. The importance of considering non-grey gas radiation model was established [240], [241] as well as the impact of the particle distribution on the prediction of radiative heat transfer [242]. Wu et al [240] carried out RANS simulations of a lab-scale pulverized coal flame using an Eulerian-Lagrangian description of the multiphase flow and a detailed chemistry coupled to a PaSR model.…”

Full-spectrum correlated-k-distribution look-up table for radiative transfer in nonhomogeneous participating media with gas-particle mixtures

“…The target configuration is a laboratory-scale pulverizedcoal flame with the central air jet entraining bituminous coal particles into the hot flue gas [29]. This flame has been studied in a wide range of coal combustion focusing on ignition and pyrolysis characteristics [30], turbulence models [31], chemistry [32] and radiation effects [2]. To model this coal flame, a Eulerian-Lagrangian method implemented in OpenFOAM-2.3.x is used with the carrier gas modeled by Eulerian equations and the particles tracked in a Lagrangian framework.…”

“…For gas phase combustion, a systematically reduced methane mechanism [32] is used to model the kinetics. Other physical models and numerical algorithms used here are the same as those used in [2]. It should be noted that the purpose of this modelling is not to resolve the flame details quantitatively with sophisticated turbulence and combustion models, but to demonstrate the validity of both the FSK-Gray and the FSK-FSK schemes in a realistic flame.…”

“…Due to its dependence on the fourth power in temperature, radiative heat transfer is the dominant heat transfer mode during combustion of solid fuels, e.g., pulverized or fluidized bed coal combustion [1][2][3][4][5][6][7]. Therefore, a high-fidelity radiation model accounting for radiative contributions from both gas phase and particulate phase is of great importance for in-depth insight of solid combustion simulations.…”