Study on atomic sodium release from pulverised coal particles in a pre-mixed natural gas flame
Atomic sodium release during coal combustion has been shown to be a significant factor in fouling and corrosion of heat transfer surfaces within industrial coal-fired boilers. Although there has been significant research into the final forms of sodium from combustion, information about the release of sodium is limited. An initial study of the release of atomic sodium from pulverised coal particles in a pre-mixed natural gas flame was conducted using planar laser induced fluorescence, PLIF. Measurements were made of the intensity of sodium fluorescence, coal particle velocities and gas phase temperature within the flame in a purpose-designed laminar flame facility that provides similar time-temperatures history to coal particles in their early stages of combustion in an industrial coal-fired boiler. The velocity of the coal particles was measured to be about 6.1 m/s using particle streak velocimetry obtained from the natural luminescence of the hot particles and a 2.25 ms gate of the CCD camera. Temperatures were measured using thermocouples, and the maximum measured temperature was ~1500 °C. Calibration of the sodium fluorescence was not undertaken, but useful information was obtained of the release rate of sodium atoms from combusting pulverised coal particles.
Mineral matter and trace-element vaporization in a laboratory-pulverized coal combustion system.
The composition and size distribution of fly ash produced by burning a Montana lignite at two temperatures, 2050 and 2450, were determined. The ash showed a bimodal size distribution with a submicron fraction that was significantly enriched in the volatile trace species. The amount of submicron aerosol increased markedly with combustion temperature, from 4% of the ASTM ash value of the coal at 2050 K to 20% at 2450 K, supporting the hypothesis that the enrichment in more volatile species of the smaller ash particles is due to a process of vaporisation and recondensation of mineral constituents.
Morphology of aggregates
Abstract This paper gives a new geometrical method for analyzing the shape of colloidal aggregates from electron micrographs. The silhouette of an aggregate is treated as a plane figure, for which are calculated the radii of gyration about the two central principal axes in the plane. The ratio of these radii is taken as the anisometry of the figure, and other parameters are also calculated including the area and bulkiness, as well as a “structure factor” which expresses the excess area swept out by the figure as it rotates. These parameters characterize the two-dimensional projection of the aggregate; in order to relate this to the three-dimensional aggregate, we have generated floes by computer simulation (based on the method of M. Vold) and determined their two-dimensional parameters. Qualitative similarity is shown between the appearance of the simulated floes and of actual electron micrographs of carbon black.