Organic emissions during oven drying of wood

When oven drying Douglas fir to determine moisture content, volatile organics evolving from the wood cause error in the moisture measurement. An apparatus was constructed to measure the carbon contained in the evolved organics and to measure the chemical energy content of the organics which evolved at temperatures up to 103°C. Data were collected and used to estimate errors in moisture content measurement. The data were also used to provide insight into differences that exist in fuelwood and how these differences might affect wood heater test results.

For the wood examined, the lower heating value of the evolved organics averaged 283 MJ/kmol carbon. This value indicates that the volatile material had a high oxygen content. Using the average heating value, the mass fraction of oxygen contained in the evolved organics was estimated to be near 0.47. Using the estimated oxygen mass fraction combined with the carbon loss data, errors in moisture content measurement resulting from volatile loss were estimated to range from 0.1% to 2.0% of measured values. The larger of these errors would cause less than a 0.1% error (percent of measured value) in the calculated efficiency of a typical woodstove.

The amount of highly volatile organics was found to vary greatly between different pieces of Douglas fir. For the wood tested, carbon loss ranged from 0.02% to 0.35% of the carbon initially contained in the wood. These differences in fuelwood volatility may affect wood heater performance and possibly cause some of the scatter observed in wood heater test data. Conventional proximate analyses were performed on two wood samples, one exhibiting high volatility at 103°C, the other exhibiting low volatility at 103°C. These proximate analyses did not show significant differences between the two samples.

Bomb calorimetry was used to measure the heating value of the Douglas fir samples both before and after oven drying. The bomb calorimetry, however, proved to not have the sensitivity to accurately measure the small differences in heating value caused by volatile emissions during oven drying.