THE USE OF SCANNING ELECTRON-MICROSCOPY FOR CLASSIFICATION OF COAL CHARS DURING COMBUSTION

Scanning electron microscopy is demonstrated to be a useful tool for m onitoring the performance of industrial boilers. For industrial applic ations the main advantage of scanning electron microscopy over optical microscopy is the short feedback time between sampling and reporting to the combustion engineer. The final stages of coal combustion are re lated to size, morphology and structure of the chars formed by pyrolys is of coal particles. Current classifications, based on optical micros copy, identify char particles as seen in cross-section and the paramet ers include pore width and size of inter-pore walls. Scanning electron microscopy, which has found less application, observes the outer shap e of whole char particles. Internal features such as pore width and su rface structure are relevant to combustion regimes I-II, but for the h igh-temperature II-III regimes, information on the outermost layer of the particles is needed. The analysis of chars sampled from a near-bur ner zone in a 400 MW power plant showed that the proportion of massive + 50 mum material in half-burned coal could be taken as an index of b urner performance.