Effect Of Microstructure Of Coal Char On NO_x Reduction By Reburning

With the social development, attention has been increasingly focused on environmental protection. NO_x has be found to be a great threat to both environment and human health. The reduction of NO_x emission resulted from coal-fired power station is the key to control the atmospheric pollution. Reburning is referred to as an extremely potential and promising low-NO_x combustion technology. Coal is found to be an excellent reburning fuel because of wide sources and low cost. Further investigations on reburning mechanism and kinetics and reburning conditions are considerably significant on devolopment of reburning technology.In this paper, Longping anthracite?LP?, Inner Mongolia bituminous coal 1#?NM1?, Inner Mongolia bituminous coal 2#?NM2? and Xilinguole lignite?XM? were selected as the tested coal for the research. The organic functional groups and mineral component which in the coal were characterized by using the Fourier transform infrared spectroscopy?FTIR?, the evolution of char microstructure with pyrolysis temperature were performed by using the Raman spectroscopy. The denitration reaction were performed on the thermal gravimetric analyzer with the method of temperature programmed in the atmosphere of NO and N₂. The NO_x reduction characteristics under different oxygen densities, reaction temperature, pyrolysis temperature and inorganic mineral have been analyzed in horizontal tube furnace experimental system and drop tube furnace experimental system with coal char and demineralized coal chars in the atmosphere of NO, N₂, O₂ and CO₂.The microstructure was quantitatively characterized by Raman spectroscopy. It was found that with increasing the pyrolysis temperature, macromolecular network structure was pyrolysed and polycondensation at temperatures ranging from 600 to 900?,a lot of edge structures and defective structures were generated, characteristic parameters I_D1/I_G and I_D3/I_G were gradually increased, characteristic parameters I_G/I_All was gradually reduced; when the temperature over 900?, the edge structures and defective structures were began to change to the graphite structures, characteristic parameters I_D1/I_G and I_D3/I_G were gradually reduced, characteristic parameters I_G/I_All was gradually increased. meanwhile we were linked the evolution of char microstructure to the denitration reaction, it was found that with increasing the pyrolysis temperature, the edge structures and defective structures were gradually eliminated, the carbonaceous structure became more ordered, which resulted in the increase of the activation energy and the decrease of the NO removal efficiency.The influencing of char reburning were analyzed. It was found that with increasing the oxygen densities, the reducing atmosphere of the reaction was destructed, the NO removal efficiency was gradually decreased; The increasing of the reburning temperature was good for reduce NO by coal char in a certain range of reburning temperature, but the excessive reburning temperature would caused the thermal NO and transformed a large number of fuel nitrogen, witch were reduced the NO removal efficiency; With increasing the pyrolysis temperature the microstructure of coal char was changed, the surface was inerting, the reaction was decreased,which resulted in the decrease in NO removal efficiency; Inorganic mineral in coal ash had some catalytic on reburning, when compared with demineralized coal char, raw coal char showed higher NO removal efficiency.