Influence and modelling of wood washing on mineral and organic compositions of three woods (beech, fir and oak)

Abstract

Nowadays, biomass increasingly replaces fossil fuels for domestic heating production. But this leads to gaseous and particulate pollutant emissions. Wood washing is a process which can be applied to reduce such emissions. In the present study, the impact of this process on the extraction of mineral and organic compounds from wood sawdust from three different species (beech, fir and oak) was analyzed, as well as the influence on the wood thermal reactivity. Wood washing leads to a decrease in several ionic elements such as potassium and sodium, which can be largely removed from biomass. Globally, mineral extracts range between 17 and 40% of the initial mass depending of the particle size (ships or sawdust) and of the specie (beech, fir and oak). Moreover, 2% of wood extractives can also be removed from wood. The impacts of wood granulometry, wood drying and washing temperature have been studied to understand the different extraction processes. Wood demineralization has been modelled through pseudo first- and second-order models to derive kinetic parameters of ionic exchanges between water and wood. The pseudo first-order model gives poor results. The second-order model show rapid exchanges with half time reactions approximately equal to 23, 24 and 40 min for beech, fir and oak samples, respectively, washed during a week.