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Lignin measurement in fiber and filtrate

Advances in kappa measurement and control

Developments in optical inline sensors have enabled a differentiated and accurate measurement of lignin concentrations in pulp suspensions in various forms such as filtrate kappa and fiber kappa or total kappa, summarizing both. These contemporary sensors are more specific, smaller and smarter and allow for significantly improved process control in bleaching and pulping operations.

The single point kappa analyzer SPK-5500 uses the same optical measuring principle as a multi-point kappa analyzer but is mounted directly to the pulp processing pipeline and measures continuously the kappa number of pulp suspensions. As a result of this simplification, complicated and costly auxiliaries such as remote pulp samplers, associated water valves and transport lines become redundant.

The inline dissolved lignin transmitter DLT-5500 can directly and continuously measure dissolved lignin concentrations, also known as filtrate kappa. Filtrate kappa can contribute between 10-50% to the total kappa number but has a much higher variability compared with fiber kappa. The DLT is successfully applied to optimize brown stock washing and oxygen stage control.

In feed lines to bleach plants the combined fiber and filtrate kappa, referred to as bleach load, can be measured by using a bleach load transmitter BLT-5500.

As a result of these new technological advancements, pulp makers have now choices of measuring lignin concentrations in various forms. These measurements can be successfully utilized to optimize cooking, brown stock washing, O2 delignification and bleaching with minimum operator bias. The pay back for these capital investments comes from increased yield, reduced chemical costs, stable pulp quality through enhanced process control.