Comparison of White Liquor Measurement Gauge Studies: Titration versus benchtop near-infrared analyzer

Abstract
White liquor chemistry, particularly the EA (effective alkali), AA (active alkali), TTA (total
titratable alkali) and sulfide (sulfidity) is extremely important for the recaust plant as well as the
digester operations. Measurements of EA/AA and sulfidity allow the operators in the recaust
plant to target the desired CE (causticizing efficiency) and white liquor strength. For digester
operations, knowledge of white liquor EA and AA allows for proper liquor charging.
This paper describes the results of gauge studies performed on two instruments used to
characterize white liquor: an automatic titrator and a near-infrared benchtop liquor analyzer. The
crossed gauge R&R design was selected because sample batches were large enough for operators
to perform multiple tests. Both gauge studies used 10 sample parts and had 3 operators measure
each part 3 times in blind, random order. The results were analyzed using Minitab® statistical
software.
The results showed that the benchtop liquor analyzer was able to distinguish 6 categories of the
10 parts and had a total variation of 4.2%. The automatic titrator was able to distinguish 3
categories of the 10 parts and had a total variation of 15.8% The conclusion is reached that the
benchtop liquor analyzer is the preferred instrument for the white liquor measurement system.
The final recommendation is to use the benchtop liquor analyzer for periodic verification of the
in-line liquor analyzers in the pulp mill, or as the primary measurement tool if an in-line analyzer
is out of service. 

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