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Char crystalline transformations during coal combustion and their implications for carbon burnout
Author(s) -
Robert H. Hurt
Publication year - 1999
Language(s) - English
Resource type - Reports
DOI - 10.2172/775207
Subject(s) - char , high resolution transmission electron microscopy , coal , combustion , crystallinity , fly ash , coal combustion products , thermal power station , boiler (water heating) , materials science , chemical engineering , carbon fibers , mineralogy , environmental science , transmission electron microscopy , nanotechnology , waste management , chemistry , composite material , organic chemistry , engineering , composite number
Residual, or unburned carbon in fly ash affects many aspects of power plant performance and economy including boiler efficiency, electrostatic precipitator operation, and ash as a salable byproduct. There is a large concern in industry on the unburned carbon problem due to a variety of factors, including low-NOx combustion system and internationalization of the coal market. In recent work, it has been found that residual carbon extracted from fly ash is much less reactive than the laboratory chars on which the current kinetics are based. It has been suggested that thermal deactivation at the peak temperature in combustion is a likely phenomenon and that the structural ordering is one key mechanism. The general phenomenon of carbon thermal annealing is well known, but there is a critical need for more data on the temperature and time scale of interest to combustion. In addition, high resolution transmission electron microscopy (HRTEM) fringe imaging, which provides a wealth of information on the nature and degree of crystallinity in carbon materials such as coal chars, has become available. Motivated by these new developments, this University Coal Research project has been initiated with the following goals: (1) To determine transient, high-temperature, thermal deactivation kinetics as a function of parent coal and temperature history. (2) To characterize the effect of the thermal treatment on carbon crystalline structure through high-resolution transmission electron microscopy and specialized, quantitative image analysis

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