A Comparative Study of Gray and Non-Gray Methods of Computing Gas Absorption Coefficients and Its Effect On the Numerical Predictions of Oxy-Fuel Combustion

Coal and methane combustion were simulated under air-firing and oxy-firing conditions. For test cases, a 2D axisymmetric model of a lab-scale furnace and a couple of 3D full scale utility boiler models were created. The present study confirms that certain dry and wet recycle ratios imitate the temperature and heat transfer characteristics found in air combustion. A recently developed total emissivity correlation and a non-gray weighted-sum-of-grey-gases (WSGG) model were employed to estimate the gas radiation properties under these firing conditions. In natural gas combustion, differences were clearly seen between the gray and non-gray model predictions. The predicted data was also compared with available measured data for all cases, wherever possible. The errors associated with the use of gray models in oxy-coal combustion can be particularly significant when there are large pockets within the furnace where the gas radiation dominates the particle radiation.