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UBC Theses and Dissertations

Characterization of screw feeder compression and its effect on wood-chip cellulose accessibility Villalba Chehab, Miguel Esteban


Wood-chip compression and enzyme impregnation are used as pre-treatment prior to refining to reduce energy consumption and improve pulp quality. This work aims at characterizing the effect of compression ratios on cellulose accessibility to the enzyme impregnation. This objective was achieved by quantifying the amount of glucose produced in the enzyme treatment of compressed wood-chips with a high-performance liquid chromatograph. A laboratory compressor and a controlled uniaxial load set-up were implemented to test different compression ratios and compression rates. The stress and strain data from the wood-chips compression was applied to torque equations to predict the power consumption of a screw feeder. The trial results showed that cellulose accessibility increased with compression ratio. High compression ratios were required to improve the hydrolysis rate significantly. Compression rate had no apparent effect on the cellulose accessibility. The improved accessibility is due to changes in morphology of the wood-chips as well as removal of the extractives. Microscopy imaging of wood-chip cross-sections showed buckling and fractures of the cell walls. Fractures lead to improved enzyme penetration and the reduction of chips size lead to higher available surface area. Using the compression data from the trials, screw feeder performance could be determined for different compression ratios. The calculations predicted that compressing at around 5:1 compression ratio achieved a good balance between power consumption, screw feeder capacity and improvement in cellulose accessibility.

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