Performance testing of a new drying kiln at a sawmill for air flow and moisture content

The performance of a new drying kiln at a sawmill in Kumasi was determined by carrying out tests on the airflow in the kiln which had been loaded with lumber, and monitoring the distribution of the final moisture content of the lumber after the termination of the kiln-drying. The contents of the kiln were 16 packages, made up of 13 packages of 25mm thick Wawa ( Triplochiton scleroxylon), one package of mainly 83 and 25 mm thick Celtis (Celtis milbraedii), and two packages of 25mm thick Ceiba ( Ceiba pentandra) and Chenchen ( Antiaris toxicaria) boards. The air speed was measured at various locations in the loaded kiln using an anemometer. The moisture content was monitored mainly on the Triplochiton boards using an electrical resistance- type moisture meter. The air speed varied from 0.1 to 1.7 m/sec, and averaged 1.01m/sec for the whole charge. The active airflow through the lumber packages was 39,138m3/h, and the air leakage from the fans was 23,097m3/h. The air leakage was moderate, and the active airflow was not enough. The fan capacity was insufficient to enable uniform final moisture content to be achieved for the drying of the Triplochiton, a species with high initial moisture content. The final moisture content for the Celtis varied from 12.6 to 25.5 %. There were many drying defects in the dried Celtis boards, clearly indicating that it is inadvisable to mix different species and the thickness in the same kiln load. The average final moisture content of 12.3% for the Triplochiton was above the average of 10% usually found in Triplochiton contracts. The standard deviation of 1.01 % was too high. The kiln needs to be set slightly below the desired final moisture content for export order.