A new brown stock washing method

A NEW BROWN STOCK WASHING OPTIMIZATION METHOD FOR ECONOMICAL PULP PRODUCTION Jari Kapanen and Lasse Kuusisto Metso Paper Automation Inc., Tampere, Finland brown stock washing, process control, washing models, automation, optimization controls A new method of achieving stable control of brown stock washing lines has been implemented in four kraft pulp mills in Finland. This method is based upon the development of a new model of the washing process called Washing Potential in Diffusion. This model has been adapted for the control of several commercial brown stock washers. Once the stability of the individual washers has been achieved, higher level optimization controls then produce stability in the entire washing line during normal production and during production rate changes and during wood species changes. The optimization control programs achieve more stable and increased washing efficiency resulting in lower washing losses, reduced loading on evaporation plants and higher pulp outlet consistencies. This technical paper describes the development and implementation of a brown stock washing optimization system. Results from kraft mill production lines are presented. Until recently, the brown stock washing area has not been highly automated and its performance not been optimized in any significant way. In most pulp mills the brown stock washers are equipped with basic instrumentation and the individual control loops are supervised by a DCS system. The coordination of these individual loops is done manually by the operators. In any manual operation the results vary with the individual so the stability of the operation is not optimized in many cases. But many mills are now realizing that poor performance of the brown stock washers can have a significant impact on the stability of operation and the production costs in other related processes. For instance, poor washing of the pulp can result in higher bleaching chemical consumption. Organic materials that