Drying Rates of Wood Chips During Compression Drying

Authors

  • Zhihua Liu
  • John G. Haygreen

Keywords:

Compression drying, wood chips, wood density, particle size, pressure

Abstract

Compression drying is basically a process of forcing the free water in wood to move under high hydrostatic pressure through a solid structure. Fundamental information regarding the time-dependent characteristic of compression drying is necessary to develop efficient commercial processes. The purpose of this study is to provide an initial evaluation of the effect of some factors—pressure, wood density, and particle (chip) size—on free water extraction.

Five species—aspen, balsam fir, jack pine, red maple, and red oak—were tested in this study. For each species both typical pulp size chips and particles from hammermilled chips were used. Drying rates were determined under constant ram face pressures at 500 psi, 1,000 psi, 1,500 psi, and 2,000 psi, respectively. The concept of drying rate is one of the important factors in dealing with compression drying, especially in designing dewatering pressure cycles.

The most efficient compression drying is achieved during the first two minutes. Drying rates are negligible after 3 to 4 minutes of constant pressure in the 500 to 2,000 psi range. The analysis of variance for species shows highly significant differences in final moisture contents. Size of chips had a significant effect on final moisture contents Compressed density of hammermilled chips is slightly higher than that of unrefined chips. High density chips require higher pressure to initiate effective drying rates.

References

Blankenhorn, Paul R., and Richard E. Weyers. 1980. Moisture effects on an energy balance developed for using forest biomass as a fuel. For. Prod. J.11(30):41.nHaygreen, J. G. 1981. Potential for compression drying of green wood chip fuel. For. Prod. J.8(31): 46-51.nHaygreen, J. G. 1982. The mechanics of compression drying. For. Prod. J.10(32):30.nMcCabe, W. L., and J. C. Smith. 1976. Unit operations of chemical engineering. 3rd ed. McGraw-Hill, NY. P. 784.nSchwartzberg, H. G., J. R. Rosenau, and G. Richardson. 1973. The removal of water by expression. AIChE Symposium Series.163(73)177.nSteel, R. G. D., and J. H. Torrie. 1980. Principles and procedures of statistics—A biometrical approach. 2nd ed. McGraw-Hill, Inc., New York, NY.nWeisberg, S., and K. J. Koehler. 1981. IVAN Users Manual. Version 2.1. University of Minnesota. School of Statistics. Technical Report Number 266.nWilliams, R. M. 1976. Simultaneous cringing, drying, sizing, and conveying wet bark for fuel preparation. Energy and the Wood Product Industry. FPRS.n

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Published

2007-06-27

Issue

Number 2 / April 1985

Section

Research Contributions

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