Fast pyrolysis of forestry residue: 2. Physicochemical composition of product liquid

In this second article on fuel oil, use of forestry residue pyrolysis liquids, their physicochemical properties, and the behavior of these liquids are described. Understanding of the chemical composition of forestry residue liquids enables the selection of correct handling and storage conditions. Forestry residue is one of the most viable biomass feedstocks for liquid production in Northern softwood forest zone. A 10-25 wt% top phase with a high heating value is produced from forestry residue due to the high content of extractives and low water content. However, it has high solid and ash contents. The main product, bottom phase, is similar to bark-free wood pyrolysis liquid: volatile acids 8-10 wt%; aldehydes and ketones 10-15 wt%; water 25-30 wt%; "sugar constituents" 30-35 wt%; water-insoluble, mainly lignin-based constituents 15-20 wt%; and extractives (2-6 wt%). Its physical properties (water 28 wt%, pH 3.0, viscosity at 40°C 15 cSt, LHV 14 MJ/kg, solids < 0.05 wt%), making it suitable for fuel oil use. The solids content is typically lower than in pine liquids. Needles and bark in forestry residue, especially in fresh green feedstock, yields high alkali metal (400-1000 mg/kg), ash (0.1-0.2 wt%), and nitrogen (0.1-0.4 wt%) contents of the liquid compared to pine (50 mg/kg, 0.02-0.03 wt%, < 0.1 wt%, respectively) liquids. This results in higher NO_x and particulates emissions in combustion. In pyrolysis of forestry residue attention should be paid on solids/alkali removal and decrease in nitrogen content.