Chlorine and ash removal from salt-laden woody biomass by washing and pressing

Abstract

Over 11 million cubic meters of timber were harvested from the coastal forests of British Columbia in 2017. For transport, the logs are usually floated in the water and towed along the coastal waters along Fraser River to sawmills. The submerged timber's chlorine content is up to 100 times higher than the timber harvested from inland. The sawmill residues leftover from cutting the salt-laden timber are unsuitable to be burned in boilers. In this study, ground sawdust, bark, and wood chips of three species: Douglas fir, hemlock, and western red cedar from the Lower Mainland, as well as spruce-pine-fir (SPF) from Vancouver Island, were washed for 5 min using tap water under constant stirring and pressed on a flat metal bed for 30 s using a mechanical hydraulic press. The chlorine content dropped from 2,000–24,000 ppm to below 700 ppm db (dry basis). The low salt biomass meets the ISO 17225-2 quality standard for wood pellets. The chlorine removal efficiency of this treatment method was 88–95%. The reduction in ash content of the washed and pressed samples ranged was 45–85% of the ash in the untreated biomass.