Ash Component Analysis

The elements found in the ash are distinguished by their concentrations in the dry coal into three groups  

Of course, irregular contents occur, but in general, the analysis methods are adapted to the level of concentration to be measiu-ed. 

To produce comparable ash compositions, the conditions of ashing or combustion must be rigidly controlled. Hence, the coal sample mass, ashing temperature, time, atmosphere, and equipment specification are well defined. There are several standards with final ashing temperatures varying among 150 °C (plasma ashing), 575 C (for salty coals), 750 C (ISO 1171 [25]), and 815 C. 

XRF is used frequently because of its quick, simple, and accurate character measuring down to the parts-per-million (ppm) level (ASTM D-4326 [78]). The method cannot detect hydrogen, carbon, oxygen, and nitrogen. Also sulfur is determined by another method. The sulfur from the ash, which is present as sulfate, is determined as sulfur trioxide (SO3) according to ASTM D-1757 [79]. 

As soon as the fraction of the sulfur is known, it is justified to recalculate all other detected elements to their oxide state for reporting. Correspondingly, the gained ash analysis comprises the oxides of the major and minor elements as well as the SO3 value. Such ash analyses are reported in Table 3.14. 

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