Research Of Ambience Effect On Mechanism And Kinetics Of Coal Combustion And SO₂/NO_x Transfer

Environment atmosphere during coal combustion has important effect on fuel combustion process and the characteristics of pollutant migration. Both experimental research and theoretical analysis are applied to explore the combustion mechanism and characteristics of combustion kinetics, reveal the transport mechanism of combustion pollutants, and obtain the environmental atmosphere effects on combustion characteristics and pollutant emission characteristics. The key factors and main parameters of the combustion characteristics are found out. The study has important academic significance and industrial applications.Firstly, combustion characteristics of three kinds of coal are studied by thermal analysis experiment in the environmental atmosphere of O₂/N₂ and O₂/CO₂. Environment atmosphere effect on combustion mechanism and combustion kinetics are explored, and the main parameters of coal combustion are carried out. In O₂/N₂ and O₂/CO₂ environment atmosphere, the oxygen-rich atmosphere can significantly improve the combustion characteristics of coal and coal gangue, and the oxygen concentration effect of on fuel combustion increases when the fixed carbon content of fuel increases. As the oxygen concentration increases, both TG and DTG curves of the fuel combustion shift to the low temperature region, and combustion characteristics of pulverized coal are improved. Oxygen concentration has remarkable influence on coke combustion. At the same oxygen concentration, CO₂ atmosphere has greater adverse effects on combustion properties of coal than N₂ becuase heat of CO₂ is larger and CO₂ affects the diffusion of CO₂ generated in the coal combustion. O₂/CO₂ results in coal ignition and burnout temperature increasing. The presence of CO₂ changes the coke combustion characteristics, and high CO₂ concentration has greater impact on coal combustion. In the experimental range, high oxygen concentration is very beneficial to improve coal combustion. With the increase of oxygen concentration, the average activation energy of the fuel increases, but the increase of frequency factor is more significant, and then the combustion rate increases quickly. The environment atmosphere, particle size and heating rate have considerable influence on coal combustion dynamics. There is kinetic compensation effect between average activation energy and frequency factor, that is lnA=mE+n.Secondly, the environmental atmosphere effects of chlorine additives on the mechanism of SO₂ migration and limestone desulfurization efficiency in the dry desulfurization process are researched by experiments and theoretical analysis. The additives include NaCl, KCl, MgCl₂, CaCl₂ and K₂CO₃. The effects of environmental atmosphere produced by chlorinated additives are explored, and the method of Gibbs free energy are used to analysis the process of limestone desulfurization and reveal the mechanism and kinetics in the presence of chloride additives. Chloride salts can improve the desulfurization efficiency of limestone, and the additives have greater impact on sulfur emission of the coal when chlorinated additives are used as the additives. In the experimental range, the order of chlorine salt effects on limestone desulfurization efficiency is: NaCl, MgCl₂, KCl and CaCl₂. The additives have significant influence on sulfur release and migration for coal and coal gangue, and both SO₂ concentration and total amount decrease. Experimental results show that the additives have greater effect on the sulfur release of coal gangue. Gibbs free energy is used to reveal the reaction mechanism of chlorine additive in the dry desulfurization process by limestone. Gibbs free energy calculation results show that the mechanism of chlorine additives improving the limestone desulfurization efficiency is that additive itself can generate desulfurization reaction, and it also promotes the desulfurization reaction of CaO through chlorination reaction. The experimental results are consistent with the theoretical analysis, and the chlorine additive effect on limestone desulfurization characteristics is obtained.Thirdly, the effects of combustion atmosphere on NO_x migration mechanism and formation characteristics in fluidized bed reactor are studied by numerical simulation, NO_x migration mechanism is revealed, and NO_x emission characteristics is obtained. The effects of the factors, such as fuel type, gas-solid flow and temperature field, are studied in detail. Both NO and N₂O formation increase significantly, when the excess air ratio increases in the fluidized bed reactor. The amount of NO and N₂O is affected by the ratio of primary air to secondary air. The total of NO_x increases with the increase of the ratio. In the fuel combustion process, the production capacity of NO and N₂O not only has relationship to fuel nitrogen content, but also has relationship to the O/N and H/N ratio of the fuel. These two ratios also have direct effect on the formation type of NO_x. The amount of NO_x increases as these two ratios increase. The quantity of inert particles in fluidized bed has remarkable effect on the migration of NO and N₂O. The quantity of inert particles directly affects the temperature distribution in the fluidized bed reactor, and then both the NO and N₂O formation and migration are affected. Reduce inert particle amount can reduce the NO and N₂O emissions.