Jacqueline B. A. Card

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.

A light scattering method to discriminate between coal and fly ash particles dispersed in air

Abstract A light scattering technique has been developed that can discriminate between cold coal and fly ash particles dispersed in air. The method is able to measure particle size, and so could also yield the separate size distributions within a mixture. The experimental system was tested using particles that were approximately spherical. Discrimination was demonstrated for four coal samples and their corresponding ash.

An exploration of the potential use of a CCD camera for absorption spectroscopy in scattered light at the rainbow

The advent of the CCD camera has made it possible to record light intensity as a function of two dimensions. In this paper, we have explored the cameras potential to measure spectra in scattered light at the rainbow by recording the intensity as a function of angle and wavelength. To this end, white light from a xenon arc lamp was scattered from water sprays containing various concentrations of water-soluble food dyes. Comparisons were made with theoretical spectra calculated using Mie theory Qualitatively agreement was excellent. Quantitatively agreement was reasonable, but there were some discrepancies as yet to be explained. Although the main rainbow is insensitive to the particle size distribution, if concentration of the absorbing species is to be recovered accurately an independent means of determining the particle sizes will be necessary.

A new method for the recovery of the size distribution of bi-modal particle systems

An instrument is proposed for the visualization and measurement of mixtures of small and large particles. It is based on the concept that light scattering by small particles is dependent upon wavelength but is insensitive to scattering angle. The opposite is true for large particles. The instrument generates a scatter diagram which is a combination of scattered intensity as a function of both angle and wavelength. The influence of quite small volume fractions of particles as small as mixed with particles is easily seen. Calibration measurements were performed on latex particles suspended in water and the method was then extended to measure sizes of silica, glass and coal particles dispersed in air and a flame. The size distributions were recovered using the Phillips - Twomey inversion scheme.