Brown Stock Washing Optimization Using Sensor Based Control - Part 1 Overview, 1998 Process Control, Electrical & Info. Conference Proceedings

All research studies have indicated that the primary control variable in pulp washing is control of the shower flow to a chosen dilution factor. However this is extremely difficult when the other variables involved in the calculation of this dilution factor are not precisely known. Under the best conditions it is nearly impossible to accurately calculate the dilution factor even when inferential methods or soft sensors are involved. This type of control relies upon information that is already known by the operator and the algorithm simply tries to emulate the best approach. Often, the data required to calculate the dilution factor is not reliable and the instruments measuring these variables are inaccurate. These inaccuracies are then magnified by the calculations used to determine the dilution factor.

With a mass measuring gamma gauge on the last washer drum, combined with the drum speed, the total mass of pulp and water leaving the washer per minute can be accurately determined. Even a large error in the tonnage rate or consistency off the last washer produces an insignificant error in the dilution factor calculation by this new control method. With environmental pressures increasing, optimization of the brown stock washing system is crucial.