Liquid Flow through Packed Columns of Cooked Wood Chips

A key parameter affecting liquor flow in a pulp digester is the flow resistance through the chip column as a function of operating conditions. A laboratory apparatus was built to measure the pressure drop through a packed bed of wood chips as a function of chip size distribution, chip lignin content (Kappa number), compacting pressure and liquid velocity. Tests confirmed that the flow resistance depended primarily on the void fraction of the chip bed and the liquor velocity through it. The bed void fraction was affected by the chip size and size distribution, the Kappa number of the chips (which affected their flexibility), the compaction force applied to the chip column and the liquor flow velocity.