Air emissions can be a limiting factor in obtaining the required permits to operate a plant when biomass is dried prior to further processing. Aged ponderosa pine, fresh ponderosa pine, Douglas-fir, and juniper were rotary dried to final moisture contents of 10 to 25 percent. The drum of the dryer was heated to temperatures of 200°C to 425°C. Total hydrocarbon emissions and the emission of various compounds were measured. While wood type strongly influenced emission levels, they were not strongly correlated with temperature or final moisture content. Total hydrocarbon emissions ranged from 0.10 to 0.25 g·kg−1 of ovendry biomass for aged material to 6.9 g·kg−1 for fresh material. Ethanol emissions averaged 7,621 and 2,591 mg·kg−1 for the fresh pine and the Douglas-fir, respectively, compared with less than 30 mg·kg−1 for the aged material. Acetic acid emissions were also greatest for the fresh pine.

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