NO Emissions Under Pulverized Char Mild Combustion in O2/CO2 Preheated By a Circulating Fluidized Bed: Effect of H2o Addition

MILD (moderate or intense low-oxygen dilution) combustion of pulverized char in O₂/CO₂ was achieved by preheating fuel in a circulating fluidized bed (CFB). The purpose of this research was to study effects of H₂O addition on NO emissions under MILD combustion of pulverized char. First, the preheating characteristics were evaluated, including the conversion ratios of each fuel component and the composition of the coal gas. To calculate the nitrogen balance in the preheating process, the gas in the loop seal was changed to O₂/N₂. The results indicate that the concentrations of H₂ and CH₄ increased with the increasing H₂O concentration in the primary gas, and the conversion ratio of nitrogen was above 0.40. The heating value of high-temperature coal gas also increased. Next, the effects of H₂O addition on NO emissions were investigated. Increasing H₂O concentrations in the primary gas could reduce NO emissions. And the combustion efficiency was above 97.0%. These results demonstrate that the oxy-fuel preheating combustion technology with H₂O addition could achieve clean, efficient combustion of pulverized char.