Computer-Controlled Scanning Electron Microscopy of Minerals in Coal
AUTHOR: Nina Skorupska, Anne Carpenter
DATE: December 1993
The latest in the series of Perspectives from IEA Coal Research reviews and assesses computer-controlled scanning electron microscopy (CCSEM).
A number of boiler operating problems (slagging, fouling, corrosion and erosion) are caused by the mineral matter and inorganic constituents in coal. A knowledge of the mineral forms present and the distribution of inorganic species is important in predicting a coal's ash deposition behaviour. The nature of the inorganic constituents can be the determining factor in their behaviour during the ash deposition process, along with boiler design and operating conditions.
CCSEM provides data on the size, association, composition and abundance of mineral components in coal. It can also be used to study the inorganic constituents in chars, fly ash and ash deposits. Thus CCSEM can follow the changes in the size, chemistry and shape of the mineral grains through the various stages of combustion to fly ash formation. One advantage of the CCSEM technique over the more conventional methods of coal mineral analysis, such as those described by ASTM and other standards organisations, is that it avoids the need for separation of the mineral matter from the coal by low temperature ashing. Therefore the inherent problems of transformation and reaction of mineral matter are eliminated. Complete CCSEM systems are commercially available, incorporating all the necessary computer hardware and software. But they are expensive, with prices currently ranging from about 250,000 (British pounds) upwards, depending on the sophistication of the system. However, once the investment is made, the cost of a CCSEM analysis and a conventional chemical analysis are similar, depending on the amount of information required in the CCSEM analysis. Although some reservations have been expressed about the CCSEM technique, some utilities are now requesting CCSEM analyses in coal specifications.