Flow Uniformity in a Model Digester Measured with Electrical Resistance Tomography

Dimiter S Vlaev1,2 and Chad P J Bennington1

1 Dept. of Chem. and Bio. Engineering, UBC, Vancouver, BC V6T 1Z4, cpjb@chml.ubc.ca

2 Pulp and Paper Research Institute of Canada, 3800 Wesbrook Mall, Vancouver, BC V6S 2L9

ABSTRACT

The ability to create uniform liquor flow in the counter-current zones of a continuous digester was studied in the laboratory using a 40L model digester equipped with an eight-plane electrical resistance tomography (ERT) sensor array. Conductively tagged fluid flows were visualised moving through a stationary bed of uncooked wood chips for a range of process flow conditions. Simulations using scaled axial (upflow) and downcomer-screen (radial) flows were used to model the counter-current zones in two industrial digesters. These were compared with flow patterns obtained by varying the ratio of upflow to downcomer-screen flow over a wider range. The optimal flow ratios and fluxes are discussed with regard to radial and vertical zone uniformity.

Keywords Electrical Resistance Tomography, Kraft Pulping, Chip Digester, Liquor Flows