Pollution is one of the greatest concerns with pulverized coal combustion. With tightening standards on pollution emissions, more information is needed to create better design models. Burner modifications are the most efficient changes that can be made to assure sufficient carbon burnout and low NOx emissions. Experiments were performed in the BYU Flat Flame Burner (FFB) lab, operating under fuel rich conditions for pyrolysis experiments and fuel lean conditions for char oxidation experiments. Effects of temperature, coal rank, residence time, and post flame oxygen content on mass release, nitrogen release, and reactivity were examined. Elemental and Inductively coupled plasma (ICP) analyses were used to determine the mass and nitrogen release of coals and chars. FT-IR was used to determine gas phase nitrogen compositions on selected experiments. Results of char oxidation experiments were fit to a first-order model to obtain an Arrhenius pre-exponential factor, while activation energies were approximated using a published correlation. CPD model calculations were used to find experimental residence times and particle diameters that obtained full pyrolysis yields. Oxy-fuel experiments were performed by switching the burner diluent gas from N2 to CO2. Oxy-fuel experiments exhibited a rank effect in nitrogen release. Bituminous coal tests showed no statistically significant difference in mass or nitrogen release between the two conditions. A sub-bituminous coal exhibited a greater mass and nitrogen release for the same residence time under the CO2 environment, which could be due to early gasification of the char. Two samples of a chemically treated coal with different additive concentrations were tested against an untreated sample for combustion enhancement. The treated samples showed an increase on the order of 15% absolute in pyrolysis yield compared to the untreated sample. An increase in reactivity on the order of 35% was observed for the higher concentrated sample, but not for the lower treatment concentration. Gas phase nitrogen measurements showed both HCN and NH3 at the 1300 K gas temperature condition. HCN and NH3 release during pyrolysis was largely rank dependent, with more HCN formed initially than NH3 for 5 of the 6 samples. However, a Polish bituminous coal was found to have more NH3 than HCN. These nitrogen species data can be used to evaluate or refine nitrogen transformation mechanisms.
College and Department
Ira A. Fulton College of Engineering and Technology; Chemical Engineering
BYU ScholarsArchive Citation
Sowa, John M., "Studies of Coal Nitrogen Release Chemistry for Oxyfuel Combustion and Chemical Additives" (2009). Theses and Dissertations. 2014.
coal, pyrolysis, combustion, nitrogen release, additive, Oxy-fuel, Oxycombustion