Experiments were conducted in a drop-tube furnace (DTF) to investigate NO emission characteristics of low-rank bituminous coal burning in the primary combustion zone. The combustion tests were performed under high-stoichiometric- ratio (SR) combustion conditions (SR ≥ 1) and low-SR combustion conditions (SR < 1). Along the length of the furnace, concentrations of flue gas species, such as NO, HCN, NH3, CH4, CO, CO2, and O2, were carefully measured during pyrolysis and different SR combustion conditions. The results for high-SR combustion conditions show that high concentrations of O2 favor the conversion of volatile N and char N into NO, with extensive NO formation taking place in the initial stages of combustion. Reducing species, such as CH4, C2H 6, and NH3, in volatile matter were mostly oxidized and generated little effect on NO elimination. Results from low-SR combustion conditions show that there is insufficient O2 for oxidization of combustibles, allowing more hydrocarbons to react with NO. For the coal tested in these experiments, the conversion ratio of fuel N to NO, Rfuel N, yielded the lowest minimum values around SR = 0.9 among all such ratios because of a larger fraction of fuel N being decomposed from coal particles through pyrolysis, as well as char oxidization being reduced to N2. For lower SR conditions, the total fixed nitrogen (TFN), which includes NO, NH 3, and HCN, can be reduced to N2 by homogeneous reactions, so that the remaining N in char becomes the major contributor of NO emissions in the burnout zone.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology