The widespread use of charcoal over a long period has led to the development of a diversity of charcoal production techniques. These have evolved to a point where charcoal with the characteristics needed for specific applications can readily be produced. To improve productivity requires an improved understanding of the fundamentals of carbonisation. Any study of the carbonisation fundamentals needs to consider processes at both the macro- and the microscale. Macroscale processes would appear susceptible to characterisation using existing heat and mass transfer models. Much less is known about microscale processes, i.e. those kinetic, heat transfer and mass transfer processes occurring adjacent to and within individual wood pieces.
The carbonisation of wood is brought about by heating it, in the absence of air, to temperatures sufficiently high for it to undergo substantial thermal decomposition. Temperatures employed are usually in the range 400500°C and a mixture of gases, vapours and a solid residue (charcoal) results. As would be expected, the temperature reached in the production process has a marked influence on the composition and yield of the charcoal produced. However, strong evidence exists to suggest that much of the carbon laid down in the charcoal is formed during secondary reactions undergone by volatile decomposition products formed during thermal breakdown of the wood.
Many factors have the potential to influence the nature of the primary decomposition products and the secondary reactions they undergo. They include: the chemical and physical properties of the wood; its size and shape properties; its moisture content; the heating rate; and the external pressure. What is known about the above factors is reviewed and areas where it is believed further research would be productive are identified.
Key words: charcoal, decomposition, fundamental, processes, wood.
Correspondence: M.A. Connor, Department of Chemical Engineering, The University of Melbourne, Parkville, Victoria 3052, Australia.
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