Aspects of liquor flow in a model chip digester measured using electrical resistance tomography

Digesters for chemical pulping are pressurized reactors that create relative flow between process liquors and wood chips to delignify the wood and produce kraft pulp. As digester size has increased to accommodate higher production rates, operating problems related to liquor flow have increased. These have included accelerated corrosion, decreased countercurrent washing efficiency, problems with chip movement, and increased pulp non-uniformity. In this work, we used an 8-plane electrical resistance tomography (ERT) system to examine a number of important liquor flow issues in a 1/30 scale-model section of a chip digester: the effect of the particle to vessel size ratio on liquor flow uniformity, flow adjacent to the digester walls, and flow exiting the central downcomer.