Petrography of coal combustion char: A review

This paper presents a history of coal combustion char nomenclature, classification, and petrography. A synopsis of the combustion of coal is developed to contextualise the subject and introduce the importance of devolatilisation, the formation of char, and its combustion, as well as the relationships between the properties of coal and the conditions of devolatilisation and between the physical properties of char and the conditions of combustion. A synopsis of the influence of coal petrographic properties on coal combustion is also provided considering the influence of coal rank and macerals on combustion efficiency and char morphology. The issue of inertinite is explained to emphasise its relevance to the development of char nomenclature, classification, and petrography, and to explain how the unfavourable image of inertinite has changed over the years because of the effort made by several research teams. This study attempts to present the most complete list of works related to the earlier studies on char, development of a nomenclature, and classification attempts since the late 1980 s till the 'Kentucky classification' in early-90's and the international collaborative work undertaken by the working groups of the International Committee for Coal and Organic Petrology.