Optimization of the impregnation circulation alkalinity at Metsä Board Kaskinen
Previously, a customized Valmet Cooking Liquor Measurement was installed to the impregnation stage of the chemi-mechanical pulping process at Metsä Board's Kaskinen mill in Finland. Now the customer targets to improve the process control and stabilize the alkalinity, resulting in more stable pulp quality, while optimizing the impregnation chemical charge.
After the introduction of the new controls there has been far less quality variation and especially control of the tensile strength has eased with our Metsä High Yield Tensile grade
Kimmo Lähdes, Operations Manager, Metsä Board Kaskinen
Summary
Location
Kaskinen, Finland
Customer challenge
Alkalinity levels in the wood chips impregnation circulation stage are monitored with Valmet Cooking Liquor Measurement. The customer now targeted to utilize the measurement data to improve the process control by reducing chemical consumption, costs, pulp quality variation, and environmental load.
The impregnation circulation alkalinity control was implemented as an extension to the existing Valmet BCTMP Optimizer for more degrees of freedom to the quality control.
Results
Up to 49% decrease in the alkalinity level variation when compared to the initial situation without the use of Valmet BCTMP Optimizer (Figure 1)
On average, the use of make-up chemicals like NaOH was reduced by about 25% by controlling the chemical consumption in the impregnation stage
After stabilization of the alkalinity level, there was no need to remove the concentrate from the impregnation circulation for post-treatment, which will also contribute to evaporation plant stability
In long-term use, the off-grade pulp has been reported to reduce when production has switched from one pulp grade to another. By having the continuous Valmet Cooking Liquor Measurement, operators are now able to adjust the impregnation liquor composition without delays
Keywords
Chemi-Mechanical Pulping, Automation, Europe
Figure 1. Impregnation stage alkalinity trends a) before and b) after Valmet BCTMP Optimizer (Axes: X=time (d), Y=range of variation)
