Numerical simulation of bituminous coal combustion in a fullscale tiny-oil ignition burner: Influence of excess air ratio

The progression of ignition was numerically simulated with the aim of realizing a full-scale tiny-oil ignition burner that is identical to the burner used in an 800MWe utility boiler. The numerical simulations were conducted for four excess air ratios, 0. 56, 0. 75, 0. 98 and 1. 14 (corresponding to primary air velocities of 17, 23, 30 and 35 m/s, respectively), which were chosen because they had been used previously in practical experiments. The numerical simulations agreed well with the experimental results, which demonstrate the suitability of the model used in the calculations. The gas temperatures were high along the center line of the burner for the four excess air ratios. The flame spread to the burner wall and the high-temperature region was enlarged in the radial direction along the primary air flow direction. The O ₂ concentrations for the four excess air ratios were 0. 5%, 1. 1%, 0. 9% and 3. 0% at the exit of the second combustion chamber. The CO peak concentration was very high with values of 7. 9%, 9. 9%, 11. 3% and 10. 6% for the four excess air ratios at the exit of the second combustion chamber.