Improvement of Pulp Washing by Addition of Carbon Dioxide, 1995 Pulping Conference Proceedings

Monica Bokström, AGA AB

Pia Kontola, Oy AGA Ab

Addition of carbon dioxide (CO,) to the washing system of an alkaline pulp significantly improves the washing performance. This improvement can be seen as - improved washing efficiency - improved runnability of the wash plant, including reduced maintenance and higher production capacity. The application of carbon dioxide in washing is now in permanent operation in several European mills. In those mills the CO2 is applied with different objectives: to reduce maintenance costs, increase production, reduce carry-over, reduce effluent load or to decrease wash water consumption. The charge of CO2 has to be optimized for each system, as a too high charge will result in lignin and extractives precipitation. The gas is easily dissolved in the alkaline liquors, which means that a simple dissolving equipment can be used. It is however important to have a good regulation of the CO2 charge to avoid negative effects. In the paper the achievements for some mills will be given.