Pulp & paper brownstock washing
Washing away inefficiency
Commercially-proven and environmentally-effective, brownstock washing technology can increase production rates of bleached and non-bleached kraft pulp by as much as 15% through more efficient washing and recovery systems. At the same time, it can reduce effluent loadings and lower bleach plant chemical requirements. Brownstock washing technology can provide operational cost savings with minimal capital expenditures, using traditional or newly designed equipment, with or without oxygen delignification.
Brownstock washing involves the injection of carbon dioxide (CO2) into the wash water for the final stage of the washing cycle. The CO2 dissolves in water to form carbonic acid, which works to reduce the pH levels in the brownstock. Lower brownstock pH reduces fiber swelling, which promotes better pulp drainage and results in improved washing efficiency. Lower pH levels in the pulp will also reduce sodium loss in the washing stage.
Other benefits of adding CO2 include reduced bleach plant chemical requirements through lower chemical oxygen demand carry over, lower dilution factors, improved sheet consistency and higher sodium recovery levels.