Uptake of fluids by boreal wood chips: Implications for bioenergy

As part of a long term study of pipeline transport of wood chips for bioenergy applications, we have determined the uptake of two fluids by hardwood and softwood chips from the boreal forest. Water or oil would be the likely carrier fluids in pipelining wood chips for ultimate use as bioenergy (e.g. any of combustion, gasification, pyrolysis to form bio-oil, or fermentation to ethanol). Uptake of water and a heavy gas oil by spruce and aspen poplar wood chips has been measured as a function of immersion time. One unit (mass) of spruce wood chips with an initial moisture level of 53% (wet basis, all percentages expressed as mass %) immersed in water for 48 h absorbs an additional 0.52 units of water to reach a moisture level of 69%, initial water uptake is rapid, with a subsequent very slow increase with time; equilibrium does not appear to have been reached. One unit of spruce chips immersed in heavy gas oil for 48 h absorbs 0.41 units of heavy gas oil to reach an oil content of 29%; uptake of oil is slower than water, and has not reached an equilibrium. Similar figures for aspen poplar are an initial moisture level of 45%, an uptake of an additional 0.57 units of water to reach a moisture level of 65%, and an uptake of 0.51 units of oil to reach an oil content of 34%. For both oil and water, draining in excess of one hour does not reduce the measured uptake of water or oil. The moisture level in wood chips after immersion is not affected by the initial moisture level in the chip; lost water due to drying is quickly reabsorbed. Oil uptake is significantly higher in wood chips that have a lower initial moisture content.