Study On Changing Law Of The Char Surface Structure In The Combustion Process

With the development of energy shortage and environment deterioration, people pay more and more attention to the study of coal utilization. The foundation of coal studies is the surface structure of char and the accurate description of its changing during char combustion. The effective token way in which the surface structure of char changes is that the distribution of surface aperture and the pore area ratio on the char surface, it has remarkable influence on gasification, liquefaction, combusted ratio of the coal. But in view of the complexity of the coal surface structure , and the restriction of the measured competence, mathematics descriptive method and computing capability in the past, people can only carry on apparent describing or qualitative analysis to the change of char surface during char combustion, and the study on it is still limited to setting-up of the hole model. The subject studies the variational law of char surface structure during char combustion, using SPFD to describe the surface structure of char, and establishes the relationship among the quantity of pore N, the scale of pore r and the pore area ratio S on the char surface. Then the experience relational models between SPFD and S was deduced, namely realizing the mechanism explaining in theory that SPFD describe the structure of char surface pore effectively.The main contents of this paper are as following:First, the char surface structure test technology and its current situation were summarized, including the understanding of char surface structure variations during combustion, and the test technology of surface structure. And discussing the description methods of char surface structure, the application of SEM and its current studying.Secondly, a certain study about Fractal theory has been done, and a computer application program in which SPFD value of char SEM image can be calculated automatically has been programmed, combining the characteristics of Fractal theory and MATLAB software. Analyzing to SEM images with this procedure, we can obtain the surface structure information of char, such as the quantity of pore N, the scale of pore r and SPFD value. We also establish the relational model between the pore area ratio S on the char surface and SPFD value, and deduce the experience relational expression by fitting to the curve, thus realized the quantitative description of the char surface structure. Finally, discussing the char surface variational law during char combustion, studying the variational law of SPFD through altering the burning temperature and the burning time. And the influence factors on the surface structure during char combustion, such as the diameter of particle, coal, acid washing, etc., has been studied, and then a series of experiment conclusions were drawn.