Mechanics of Compression Drying Solid Wood Cubes and Chip Mats

Wood cubes and chip mats were compressed in a cell under ram face pressures to 13,000 psi. The amount of water removed was determined for a range of species of various specific gravities and at several green moisture contents (MCs). The time dependence of the process was also studied. The purpose of this work was to describe the mechanics of compression drying which must be considered in designing commercial equipment. Green MC of wood chip mats was reduced to 45 to 50 percent MC (31 to 33 percent MC, wet basis) at pressures of 13,000 psi. At low pressures of 1,000 to 2,000 psi, moisture was reduced to 60 to 75 percent MC (38 to 43 percent MC, wet basis). There was a significantly greater moisture reduction at these low pressures if the pressure is maintained for up to 2 minutes rather than releasing it immediately once the target pressure is obtained. Water can be removed from high density species but pressures required are higher by a factor of 2 to 3. The chip mat is reduced to about one-sixth of its original volume at 2,000 psi and one-seventh at 6,000 psi. When pressing cubes of high green MC, about 7,000 foot-pounds of work (equivalent to 9 Btu) applied to the wood will remove up to 1 pound of water.

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