| Hardwood lumber drying is achieved through air-drying, pre-drying, conventional steam heated drying, vacuum drying, or dehumidification drying. Part of the environmental burden from drying hardwood lumber is organic compounds contained in the hot, humid kiln air as VOCs (volatile organic compounds). Volatile organic compounds are lower atmospheric level ozone precursors detrimental to human and environmental health. This project was designed to develop an estimate of the amount of VOC emissions released from conventional, steam heated hardwood dry kilns. The estimates were developed for yellow-poplar, red oak, white oak, black cherry, red maple, and sugar maple. VOC emissions were quantified using laboratory equipment including a small laboratory oven for lumber drying, a heated sampling line, and a total hydrocarbon analyzer. Across four temperature treatments, red oak released a statistically higher VOC amount per percentage change in moisture content compared to the other species. Temperature, moisture content, and drying time effects on average VOC release were present for yellow-poplar, red oak, white oak, and black cherry while red maple and sugar maple were unaffected. VOC emission data from nine charges of each species dried using the recommended standard kiln temperature schedule indicated that, over the average total moisture content range of the charges, red oak released the largest average sampled amount of VOCs---1.27 pounds per MBF. White oak was statistically different than all other species with a lower average release than red oak, but larger than the remaining four species. Considering all species together, both total drying time and species had an impact on total VOC release during drying using the standard kiln temperature schedules. |
