Investigation of unburned carbon particles in fly ash by means of laser light scattering

A new optical method to determine the percentage of unburned carbon particles in fly ash from combustion of pulverized coal has been developed. The technique exploits the different properties of particles of ash and coal in the elastic scattering of polarized light. The polarization measurements were performed using a linearly polarized laser source and a receiving system able to simultaneously detect the scattered radiation polarized in parallel and orthogonal planes, under the scattering angle of 60°. The parallel and perpendicular components of the scattered light intensities are measured in order to determine the polarization ratio. The operation of the system was tested under various conditions using monodisperse glass spheres. The performance of the novel device was assessed in several sets of measurements with samples of fly ash produced from coal fired power plants. A correlation between the relative content of coal and ashes and the polarization ratio of scattered light was demonstrated. The resulting polarization ratio showed values ranging from 1.25 to 0.94 for a carbon content of 1.17 wt% and 16.3 wt%, respectively. The uncertainty on the measured percentage of unburned carbon was about 1%. The proposed device represents an attractive tool for monitoring real-time burnout and combustion efficiency.