A drop tube furnace study of coal combustion and unburned carbon content using optical techniques

The combustion of pulverized coal in a drop tube furnace has been studied optically. The coal passes through an excess air flame to ensure ignition and then burns as it passes down a segmented ceramic tube electrically heated to 1100 °C. The method permits the optical measurement of particle size distribution as a function of residence time. The results of this demonstrate the relative reactivity of the coals used and also indicate that fragmentation may occur. Samples of the particles are taken at each furnace stage for Carbon-Hydrogen-Nitrogen (CHN) analysis. Comparison of the carbon content by mass with the cross-polarization in the backscattered light shows that a linear correlation can be established for particles up to at least 100 μm diameter. This implies the possibility of a simple optical tool for the measurement of unburned carbon content and, thus, for monitoring burnout and combustion efficiency.