Thermal decomposition and combustion chemistry of cellulosic biomass

Emissions from open vegetation fires contribute significantly to global atmospheric dynamics. However, the value of improved quantification of areas burned and knowledge of the composition and structure of biomass fuel is compromised in current emissions modelling and measurement by inadequate understanding of the chemistry of biomass combustion. Physical models of the behaviour of open vegetation fires also have relied on over-simplified combustion chemistry. Considerable knowledge of the thermal degradation and combustion of cellulose, the major constituent of the terrestrial biomass, exists but has yet to make an impact in the fields of atmospheric emissions monitoring and open vegetation fire behaviour modelling. This article provides an interpretive summary of the current knowledge of the chemistry and dynamics of the processes of thermal degradation and combustion of cellulosic biomass and discusses the role of these processes in determining the emissions from, and behaviour of, open fires in such fuels. The important role of competitive thermal decomposition is emphasised, as a driver and regulator of emissions and fire spread (short-term, local effects) and global carbon distributions (long-term, global effects).

► The thermoconversion chemistry of cellulosic biomass is reviewed interpretively.
► Competition between char and volatile formation controls biomass combustion reactions.
► Thermal and chemical feedbacks between reactions influence the competition outcomes.
► Outcomes lead to flaming or glowing combustion with different emissions and behaviour.
► Emissions monitoring could be improved by incorporating this basic knowledge.