Behavior of Boron in Coal During Natural and Industrial Combustion Processes

Abstract

The concentration of boron in coals, heat-affected residues from burning coal seams, and industrial coal-fired power plants was determined using the following techniques: Direct Current Arc (DCAES), Inductively Coupled Plasma (ICP), and Prompt Gamma Neutron Activation Analysis (PGNAA) spectrometry. The objective was to assess the effect of temperature and other related factors on the mobilization of this element in heat-affected coal seams and during combustion. During the combustion of coal, B is partitioned into bottom ash, flyash retained by particle attenuation (usually electrostatic precipitation), and fine flyash, some of which reaches the atmosphere with the stack gases. Hence, coat burning is a source of B in the atmosphere, but it is not considered to be concentrated enough in most cases to have detrimental effects on vegetation, even in the close environs of power stations. The comparison of results on the variation of B in heat-affected coal seams indicates that the behavior of B during the natural heating/burning of coal is dependent on the temperature of the system and the nature of the process. Boron content of chars /coke, as compared to the coal, is lower in the oxidation /combustion zone, possibly due to volatilization of B. Some enrichment of B has been noted in the carbonization zone. The high B content of semicoke containing coal tar pitch suggests that B becomes concentrated in the liquid fractions of the carbonization by-products during the natural heating of coal. The highest concentration of B occur in a carbonaceous shale beneath the semicoke zone, suggesting that the carb, taceous shale acted as a barrier and absorbed boron-enriched tar.