Economic Benefits Derived from Recovering Chemicals and Reducing Viscosity of Liquor with Electrolytic Process at Kraft Pulp Mills, 2000 Pulping / Process & Product Quality Conference Proceedings

R. F. Caro, K. G. Fuller--This paper describes the major benefits that can be derived from using electrolysis in the recovery cycle at kraft pulp mills. An electrolytic (EL) membrane process was pilot tested for recovery of chemicals from weak black liquor first at a kraft pulp mill and later at a recycling paper mill. The EL process proved to be effective in removing caustic and lignin from black liquor at both of those sites.

Further tests were performed to determine the feasibility of using electrolysis to enhance the fluid properties of black liquor. Viscosity tests were performed on EL-treated and untreated liquor samples containing between 15-65% solids. The kinematic viscosity measurements for EL-treated liquor containing 65% solids and at 70 degrees C were about 0.45 cm 2 /sec. The raw liquor had a viscosity of 4.5 cm 2 /sec under the same conditions.

The projected cost of unbleached pulp can be reduced from about $440 per ton to less than $350 per ton by using electrolysis to treat the weak black liquor stream. The net profit margin for a 300 tons-per-day pulp mill can be increased by over $7 million per year.

The EL treated liquor can improve the thermal efficiency of the evaporator and increase the combustion efficiency of conventional recovery boilers. The projected energy recovered with electrolytic treatment can be over 50% higher than the conventional recovery process.