Abstract
Predicting thermal radiation for oxy-coal combustion highlights the importance of the radiation models for the spectral properties of gases and particles. This study numerically investigates radiation behaviours in small and large scale furnaces through refined radiative property models, using the full-spectrum correlated k (FSCK) model and Mie theory based data, compared with the conventional use of the weighted sum of grey gases (WSGG) model and the constant values of the particle radiation properties. Both oxy-coal combustion and air-fired combustion have been investigated numerically and compared with combustion plant experimental data. Reasonable agreements are obtained between the predicted results and the measured data. Employing the refined radiative property models achieves closer predicted heat transfer properties to the measured data from both furnaces. The gas-phase component of the radiation energy source term obtained from the FSCK property model is higher within the flame region than the values obtained by using the conventional methods. The impact of using non-grey radiation behaviour of gases through the FSCK is enhanced in the large scale furnace as the predicted gas radiation source term is approximately 2–3 times that obtained when using the WSGG, while the same term is in much closer agreement between the FSCK and the WSGG for the pilot-scale furnace. The predicted total radiation source term (from both gases and particles) is lower in the flame region after using the refined models, which results in a hotter flame (approximately 50–150 K higher in this study) compared with results obtained from conventional methods. In addition, the predicted surface incident radiation reduces by using the refined radiative property models for both furnaces, in which the difference is relevant with the difference in the predicted radiation properties between the two modelling techniques. Numerical uncertainties resulting from the influences of combustion model, turbulent particle dispersion and turbulence modelling on the radiation behaviours are discussed.
Highlights
Oxyfuel combustion has been regarded as one of the most promising technologies for both new and existing power stations in order to achieve a near-zero CO2 emission [1,2]
This study numerically investigates radiation behaviours in small and large scale furnaces through refined radiative property models, using the full-spectrum correlated k (FSCK) model and Mie theory based data, compared with the conventional use of the weighted sum of grey gases (WSGG) model and the constant values of the particle radiation properties
The impact of using non-grey radiation behaviour of gases through the FSCK is enhanced in the large scale furnace as the predicted gas radiation source term is approximately 2–3 times that obtained when using the WSGG, while the same term is in much closer agreement between the FSCK and the WSGG for the pilot-scale furnace
Summary
Oxyfuel combustion has been regarded as one of the most promising technologies for both new and existing power stations in order to achieve a near-zero CO2 emission [1,2]. Developments of the Monte Carlo method have been able to provide LBL accuracy within coupled combustion applications [22], it is still an active challenge to apply this approach to large-scale multi-phase applications Narrow band models, such as the statistical narrow band (SNB) and correlated k models, are capable of reducing this burden to a few hundred intervals, this is still too expensive for CFD approaches, which require the resolution of the radiation intensity field across a fine spatial and angular resolution [21,23]. Due to model availability and computational cost, the research on CFD simulation of real solid fuel combustors with the relatively more rigorous radiation models for the spectral properties of gases and particles (such as, FSCK and Mie data based methods) is limited Development of these refined radiation models could provide a better understanding of the gas and particle radiation behaviours for oxyfuel combustion, making it very important to investigate the radiative heat transfer for these conditions in real small and large scale combustors.
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