This paper presents a novel approach toward a fundamental understanding of ash deposit phenomena and describes a laboratory bench-scale technique for assessing the slagging and fouling potential of mineral matter in coal in a boiler firing pulverized fuel. Coal ash deposits collected from boiler tube surfaces have been found to differ from the composition of the coal ash as fired; i.e., selective deposition has occurred. Data are presented to show that analysis of the distribution of mineral matter in the coal matrix can account for this difference. The technique that has been developed consists of a gravity fractionation of pulverized coal so that the ash can be analyzed in groups of particles that are capable of unique behavior in the boiler. The collective behavior of individual ash particles during combustion is not necessarily equivalent to the behavior of a mixture of all ash particles as would be determined by conventional ASTM tests.

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