Reduction of emission of nitric oxide from combustion processes and utilization of abundant carbon dioxide

Potential substitutes for natural gas and lignite fly ash during heterogeneous reburning were examined in a bench-scale apparatus equipped with a simulated reburning and burnout furnace. A wide range of waste materials and industrial by-products show overall NO reduction efficiency up to 88%. Mixed fuel containing scrap tire and Fe2O3 is particularly effective. Though its cost is constrained by the energy-intensive operation of grinding tire, the estimated raw-material cost is better than that of natural gas reburning and highly competitive against SCR. A first-level approximation study of selectivities of nitrogen species to form NO in burnout zone reveals the importance of HCN and char nitrogen reaction mechanisms.;Recent studies have demonstrated that activated carbonaceous material containing alkali and alkaline earth metals can serve as effective NO reduction medium in post-combustion zone at temperatures 400 to 800°C. This work demonstrates that biomass fly ash, a by-product of pine-bark fired grate boilers, is a viable and effective NO reducing agent in post-combustion zone, 300 to 600°C. It requires no chemical or physical activation and no additional fuel. CO formed during carbon gasification enhances NO reduction but has to be abated before flue gas release. Empirical rate expressions for carbon gasification and NO reduction are developed for the design of a NO reduction unit in the post-combustion zone.;It is known that polar solvents swell coal, break hydrogen-bonds in the macromolecular structure, and enhance coal liquefaction efficiencies. Both gas sorption technique and scanning electron microscopy reveal that drying, interaction with supercritical CO2 and degassing all alter the physical structure of the coal. Further, the effects of interaction of coal with supercritical CO2 on NO emission and unburned carbon (UBC) in various combustion environments has been studied at the bench-scale level. Emphasis has been on breaking the NO reduction observed during coal reburning and on improving carbon burnout during combustion. The change in physical structure mentioned above significantly altered the fuel nitrogen reaction pathways. Consequently, NO reduction during reburning using bituminous coal has increased and NO emission during oxidation of lignite has reduced. These benefits have been achieved without negative impacts on UBC.