Influence of lignocellulose and plant cell walls on biomass char morphology and combustion reactivity

The firing of biomass or co-firing of biomass with coal has become a common practice in power generation industry worldwide as a cost-effective means to move towards lower carbon footprint. However, the relationship between the properties of biomass and combustion behaviour is not well understood, yet. In this study, we investigated the links between biomass lignocellulosic composition and plant cell wall types, and how they would collectively influence char morphology and reactivity. Five different biomass, i.e. pinewood, distiller dried grains with solubles (DDGS), miscanthus, wheat straw and wheat shorts, in two size fractions were thermochemically pre-treated to alter their lignocellulosic compositions resulting in 50 different samples with varying compositions. Plant cell type and morphology of raw biomass particles were examined using SEM. Biomass char samples were prepared using a fast heating drop tube furnace (DTF) and a slow heating muffle furnace. The morphology of char particles was examined using an oil-immersion microscope whilst the intrinsic reactivity of chars was studied using a thermogravimetric analyser (TGA). Pre-treatments affected most biomass tested in similar trends but to varying degrees, particularly in terms of lignocellulosic composition, cell wall structure and char morphology. Results show that lignocellulosic composition (and plant cell wall types) of biomass correlated well with char morphology and char reactivity. Therefore, it is possible to predict aspects of combustion behaviour from biomass lignocellulosic composition for this selection of samples tested. This work provides a base study for establishing lignocellulosic composition as a key indicator in fuel selection.