DD-washer performance optimization using the latest measurement technology

Various types of washing equipment are used for pulp washing in a fiberline. Each has a unique mechanical design
and operating principle. Optimizing the performance of each piece of washing equipment in the fiberline will give
high total efficiency for the pulp washing. In this work, the performance of the Andritz drum displacer washer was
studied using the latest measurement technology.
The performance of a DD-washer was studied under mill conditions. The measurement of total dissolved solids (TDS)
by a process refractometer was used to create an on-line balance across the washing equipment. Real-time equivalent
wash yield (Y10 -value) values were calculated from the balance sheet. The conditions (cake washing consistency and
number of washing stages) were changed step-by-step. The effects of the changes on the DD-washer's performance
were monitored from the on-line results. The research work was carried out at two different Finnish kraft pulp mills,
one of which produces hardwood pulp with a continuous digester and the other producing softwood pulp with batch
digesters. At the hardwood mill, several process refractometers were installed on DD-washers before and after O2
delignification, and at the softwood mill, several refractometers were installed on the four-stage DD-washer after batch
The results showed that the selected variables had an effect on the performance of the washer. Increasing the number
of washing stages increased the Y10 value. Higher cake consistency during the displacement washing had a positive
effect on washing efficiency. However, the consistency should not be so high that the pulp cake drainage properties
start to prevent the flow of wash water through the cake. On-line measurements allow real-time monitoring and the
optimal driving mode of the washer to be chosen. In the future, measurement-based automatic control of the number
of washing stages and cake washing consistency could be built. This could be advantageous, for example, for fiber
lines running different wood species, variable production or when the drainage properties of pulp change. 

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Author: Riku Kopra; Simo Karjalainen; and Pekka Tervola
DD-washer performance optimization using the latest measurem

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