Emissions of NOx and SO₂ from Coals of Various Ranks, Bagasse, and Coal-Bagasse Blends Burning in O₂/N₂ and O₂/CO₂ Environments.

Oxy-coal combustion is a viable technology, for new and existing coal-fired power plants, as it facilitates carbon capture and, thereby, can mitigate climate change. Pulverized coals of various ranks, biomass, and their blends were burned to assess the evolution of combustion effluent gases, such as NO x, SO 2, and CO, under a variety of background gas compositions. The fuels were burned in an electrically heated laboratory drop-tube furnace in O 2 /N 2 and O 2 /CO 2 environments with oxygen mole fractions of 20%, 40%, 60%, 80%, and 100%, at a furnace temperature of 1400 K. The fuel mass flow rate was kept constant in most cases, and combustion was fuel-lean. Results showed that in the case of four coals studied, NO x emissions in O 2 /CO 2 environments were lower than those in O 2 /N 2 environments by amounts that ranged from 19 to 43% at the same oxygen concentration. In the case of bagasse and coal/bagasse blends, the corresponding NO x reductions ranged from 22 to 39%. NO x emissions were found to increase with increasing oxygen mole fraction until ∼50% O 2 was reached; thereafter, they monotonically decreased with increasing oxygen concentration. NO x emissions from the various fuels burned did not clearly reflect their nitrogen content (0.2–1.4%), except when large content differences were present. SO 2 emissions from all fuels remained largely unaffected by the replacement of the N 2 diluent gas with CO 2, whereas they typically increased with increasing sulfur content of the fuels (0.07–1.4%) and decreased with increasing calcium content of the fuels (0.28–2.7%). Under the conditions of this work, 20–50% of the fuel-nitrogen was converted to NO x . The amount of fuel-sulfur converted to SO 2 varied widely, depending on the fuel and, in the case of the bituminous coal, also depending on the O 2 mole fraction. Blending the sub-bituminous coal with bagasse reduced its SO 2 yields, whereas blending the bituminous coal with bagasse reduced both its SO 2 and NO x yields. CO emissions were generally very low in all cases. The emission trends were interpreted on the basis of separate combustion observations.