DISCUSSIONS WITH COMPANIES WHICH BURN COAL IN STEAM GENERATOR UNITS INDICATE THE INADEQUACY OF COAL SPECIFICATIONS. THE COMBUSTION BEHAVIOUR OF COALS CANNOT BE PREDICTED.
IT IS EXPECTED THAT THE MORE DETAILED ANALYSIS OF STRUCTURES AND/BEHAVIOUR OF COAL MATERIAL AND ASSOCIATED MINERAL MATTER WILL INDICATE THE RELATIVE IMPORTANCE OF THE ADDITIONAL SPECIFICATIONS TOWARDS PREDICTIONS OF COAL COMBUSTION CHARACTERISTICS. MORE SO AS COAL SUPPLIES CHANGE MORE RAPIDLY THAN BEFORE ON MARKETS.
The possibility of using laboratory petrographic studies and thermogravimetric analysis (TGA) reactivities in predicting industrial combustion behaviour expressed by entrained flow reactor (EFR) experiments was examined. These come close to the conditions of power generation combustion and provide burn off measurements giving kinetic evaluation of the reaction rate.
The results suggest that in assessing a coal for pulverised fuel combustion, 3 factors should be considered:
rank for similar petrographic composition;
petrographic composition at the same rank;
If petrographic composition is similar, rank is important because reactivity decreases as rank increases, particularly for values of %RO below unity; through the bituminous range the decrease is inversely proportional to %RO. On the other hand, at the same rank coals composed principally of vitrinite macreals can have a reactivity 50% greater than those which are mainly inertinite. This variation amounts to half of the change attributable to rank throughout the bituminous range.
Also, weathering can increase the reactivity of bituminous coals by up to 25% over periods of a year. The use of an oxidation quotient may aid in assessing the extent of weathering.
THE PURPOSE OF THE PROJECT IS TO IDENTIFY COAL PROPERTIES WHICH RELATE TO THE COMBUSTION CHARACTERISTICS OF COAL FEEDSTOCKS IN STEAM GENERATOR UNITS.
BECAUSE PROXIMATE AND ULTIMATE ANALYSES OF COALS, INCLUDING CALORIFIC VALUES, CANNOT PREDICT COMBUSTION BEHAVIOUR, IT IS NECESSARY TO EXTEND RESEARCH TO INCLUDE THE IMPORTANCE OF MICRO-LITHOTYPES AND MACERALS IN COALS AND COAL BLENDS. IN ADDITION, THE MANNER IN WHICH THE PARTICLE SIZE DISTRIBUTIONS AND CHEMICAL COMPOSITION OF MINERAL MATTER INFLUENCE THE STRUCTURE AND HENCE REACTIVITY OF CHAR/COKE SURFACES DURING COMBUSTION WILL BE ASSESSED.