In this study, trees of Michelia compressa thinned from an area of a Plain Afforestation Program
in Pingtung were cut into segments 1 m in length for charcoal making. The specific gravity
and moisture content were measured. The carbonization and chimney temperatures were separately
measured with K-type thermocouples during wood charcoal production and wood vinegar collection
in an earthen kiln. After discharging the charcoal, yields were calculated by weighing. In
order to investigate the properties of the wood charcoal affected by differences in the carbonization
temperature in the earthen kiln, the refined degree, pH value, carbon content, and true density
tests were performed for specimens sampled at different carbonization temperatures. Quantities of
the collected wood vinegar were periodically measured. The specific gravity, pH value, acidity, tar
content, and component analysis of the wood vinegar were determined for samples collected at different chimney temperatures.
The volume specific gravity and moisture content of M. compressa were 0.49 and 46.3%,
respectively. From the measured carbonization temperature at each measuring point in the kiln, a
curve of different temperatures was obtained. Carbonization temperatures in the upper part of the
kiln rose faster and earlier than did those in the lower part. The highest temperature in the upper
part of the kiln exceeded 740℃ at the end of carbonization, whereas the temperature in the lower
part was only 570℃. The yield of wood charcoal was 27.10%. Carbon retention was 47.84%. The
refined degree of the wood charcoal ranged 1.9~6.2, and decreased significantly with an increasing
carbonization temperature. The pH value of wood charcoal was 8.57~9.42 and increased a
little with an increase of carbonization temperature. The true density of wood charcoal increased
with an increase in the carbonization temperature. The yield of wood vinegar was 10.49% in the
charcoaling process. The quantity of wood vinegar collected at chimney temperatures of < 100℃
made up 85.03% of the total, while the amount notably decreased at temperatures of > 101℃. The
specific gravity and pH value of the wood vinegar increased with an increasing chimney temperature.
The acidity and tar content of the wood vinegar were not appreciably affected by the chimney
temperature. Concentrations of acids, phenols, alcohols, and neutral compounds ranged 51.2~59.2,
19.8~22.6, 15.7~20.6, 5.3~6.4%, respectively, for wood vinegar collected at different chimney
temperatures.