Numerical Simulation On Submicron Particle Formation During Coal Combustion

Most of fuel consumed in power station in China, now and in the future, is coal. Coal combustion supplies us the necessary heat and electricity, but at the same time, it would bring serious particulate matter pollution. Research shows that coal combustion is one main source of inhalable particles in the atmosphere, and a great deal of organic pollutants and various toxic metals deposit on the surfaces of fine particles, which are greatly harmful for human health and ecological environment. Therefore, it has great significances to study the formation mechanism, evolution and emission characteristics and other aspects of submicron particulate matter from coal combustion.Firstly, this thesis discusses the serious harm of sub-micron particle emission on human and inhabitation environment, which means it important and necessary to study sub-micron particle formation and controlling method, then according to the research work on the formation fundamental theories and control ways of sub-micron particles enriched with trace elements up to date in detail, their advantage and its disadvantages are systematically analyzed about the latest developments in numerical simulation and experiment study on formation theories and control ways of sub-micron particles. Thus this could clarify their research ideas. Based on this idea, the relevant research word follows.This paper analysises the existing domestic and international three more perfect vaporization model: the vaporization model of Quann,Zeng Taofang and Zhou. After they were explored, which would be found out the following problems and shortcoming: the vaporization model of Quann ignores the impact of the control of proliferation in molten and vaporization on the surface of molten, and it has not considered that other sources of CO2 in char has an effect on balance reaction at the surface of mineral particles; the vaporization model of Zeng Taofang thinks the vapor pressure at the surface of molten is 0, this can cause the calculated gasification mass transfer coefficients excessive; the vaporization model of Zhou considers the porous particle is not flammable. These studies can lay the foundation for establishing a more reasonable vaporization model in future.Subsequently, on the basis of early vaporization model, three vaporization models of mineral were established contraposing the problems and shortcoming: the vaporization model of included mineral, organically-associated mineral elements and excluded mineral. After the vaporization models of mineral were numerical simulation, it can be seen that apart from the temperature,pressure, the saturation vapor pressure of element is the most fundamental reasons. The vaporization rate of organically-associated mineral elements is exponential growth with the temperature. As for the vaporization of excluded mineral, the more the modulus,aperture, the higher the temperature and the lower the CO2 pressure which can increase the vaporization.Finally, based on aerosol theory, the dynamic characteristics of submicron particulate matter in coal combustion were theoretically analyzed, and the characteristic time of various stages was defined. Through the contrast of model calculation and particle formation experimental, The results showed that nucleation is the main causes of sub-micron particles formation; otherwise, the rapid growth of submicron particle depends on the condensation. This study could provide a theoretical basis for controlling the formation of submicron particulate matter.