석탄 연소과정에서 배출된 입자상 물질의 광학 및 물리적 특성에 관한 실험적 연구

Abstract

In this study, we measured the dimensionless light extinction coefficient as an optical characteristic of particulate matter (PM) generated during the combustion reaction of pulverized coal (bituminous coal), a fuel used in thermal power plants. The dimensionless extinction coefficients of bituminous coal PMs measured at combustion reaction temperatures of 550°C, 600°C, and 650°C at 1 bar, were 8.11, 8.42, and 8.69, respectively. Similarly, the measured dimensionless extinction coefficient of PMs generated at the elevated pressures of 3 bar at 550 ℃ also increased to 9.94. We also conducted an analysis of the physical and chemical properties of the particulate matter to identify the optical properties that vary depending on the pre- and post-combustion treatment conditions (reaction temperature, pressure, and relative humidity). To interpret the increase in the dimensionless light extinction coefficient of bituminous coal PM at different reaction temperatures and pressures, EC/OC analysis and Raman spectroscopy were performed on the captured PMs to analyze the carbon structure. In addition, images of the PMs obtained through electron transmission microscopy were analyzed to examine changes in the physical dimension and fractal factors (that are resulted from changes in reaction temperature and pressure). It is believed that the increase in reaction temperature and pressure during the formation of PM increases the scattering effect due to changes in the increase the diameter of each primary particle in the aggregates, the overall physical dimensions and fractal factor of the aggregates and also increases the light absorption effect by increasing the EC content in the particles, thereby increasing the dimensionless light extinction coefficient of bituminous coal PMs. It is found that the OC cotent of the total carbon in PMs captured in high relative humidity conditions combines with sulfate (emitted from the bituminous coal combustion process) can result in the hydrophilicity of the particles, further increasing the aggregation density of PMs. As a result, with high relative humidity, the effect of light scattering (rather than light absorption on incident light) is dominated by aggregate dimension and fractal changes. Since the optical concentration of PM measured by the light extinction method depends on the dimensionless light extinction coefficient of PM (that are affected by not only on the type of fuel but also on the combustion environment (reaction temperature, pressure) and post-combustion environment (relative humidity), it is necessary to use a dimensionless light extinction coefficient appropriate to the fuel used, combustion environment, post-combustion environment, etc. to reduce the difference from the concentration of particulate matter measured by the gravity filter method.