Improving brown stock washing by on-line measurement - Mill investigations

The aim of the study was to examine and improve the brown stock washing result and efficiency. It was done by utilizing realtime measurement devices and a monitoring system created for the purpose. Research work was carried out by installing 12 refractometers in the brown stock washing line at a Finnish kraft pulp mill. Refractometers continuously measure the dissolved solid contents of filtrate fractions. The refractometers and created monitoring system enabled the continuous evaluation of a washing result. The results indicated that the amount of washing loss had a clear influence on the performance of oxygen delignification, which was observed from the oxygen delignification's kappa reduction, chemical consumption and reactor's temperature. The results also indicated that by utilizing measurements it could be possible to control washers operation and then reduce washing losses from brown stock washing substantially. Results show that it is possible to evaluate the efficiency and the result of brown stock washing by utilizing continuous refractometer measurements and advanced data-analyzing tools. However, it is not simple and many variables should be noted if the aim is to develop and utilize a continuous monitoring system more efficiently.