The distribution of charcoal in coal: geological, palaeoecological and industrial significance.

Lead Research Organisation: Royal Holloway, University of London
Department Name: Earth Sciences

Abstract

Globally coal is, and will continue to be, used in electrical generation and the current imperative is to improve the performance of coal-fired power stations and to reduce emissions. An important element of this drive is to gain a greater understanding of the coal used. Charcoal, formed as a result of wildfires, is common in coal and is often what soils the hands on touch. The aim of this project is to develop methods of reporting charcoal occurrence in coals that will (i) allow cross coal comparison, (ii) be applicable in developing coal specifications for use in industry, forensic science and Geology, (iii) provide a standard and reliable framework for deriving palaeoenvironmental signals from ancient charcoal occurrences and (iv) serve as a predictor of coal behaviour during combustion. Fire is a major Earth System process. Wildfires are influenced by climate and atmospheric oxygen concentrations. Charcoal occurs abundantly in coals and may consist of large pieces or small particles and it may be disseminated within a coal or may occur as discrete bands. Charcoal washed in from a fire outside the peat-forming environment is likely to occur in bands accompanied by sediment. The distribution of charcoal within coals is a powerful tool for understanding peat (precursor to coal) accumulation processes, for interpreting past fire regimes and for recognising climate change, whilst the inert nature and lack of volatiles in charcoal (compared to other coal constituents) influences the combustion and burn out properties and utilisation of coals in an industrial context. However, there is no common scheme for documenting charcoal occurrence in coals and there is minimal data on spatial variation in charcoal distribution or particle size or on the effect this may have on industrial coal utilisation. Selected coals from the Permian (300-250 Million Years ago) of Australia and Russia will be used in this project for the following reasons: (i) they represent peat accumulation in two distinctive vegetation types from different areas thereby testing the wider applicability of results (ii) the peats accumulated at a time of the highest oxygen levels over the past 600 Million Years thereby maximising likely charcoal occurrences, (iii) as expected from ii charcoal is abundant and may make up 40% or more of Permian coal seams and (iv) Permian coals are currently the most important internationally traded coals for electrical generation. The nature of the charcoal deposits will be investigated at Royal Holloway using a variety of microscopic techniques including reflectance microscopy on polished blocks of coal, scanning electron microscopy and maceration of the charcoal from the coal. The in situ distribution and abundance of charcoal will be determined through continuous coal profiles. The abundance data will be compared with those obtained from pulverized sub-samples of the whole coal (as used in industry) and with coal splits. Coal splits that have a variety of charcoal distribution patterns, charcoal clast sources (e.g. wood, fern) and charcoal particle sizes will be investigated for their combustion and burn-out behaviour using a series of experimental rigs based at Npower laboratories. The project will establish the aspects of charcoal distribution, abundance, source and size that prove to be significant in influencing industrial, palaeoecological or geological applications. The relative merits of various investigative techniques will be evaluated. These data will be combined to produce a recommended framework for categorisation of charcoals in coals. New knowledge of charcoals in Permian coals will be applied in palaeoenvironmental reconstruction and used to inform the coal purchasing strategies at Npower.

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