Post DO brightness has long been the subject of spirited debate on whether or not you should even measure it for bleach plant control or stage performance evaluation. Many mills have measured in the past and used it to adjust the CI02 dosage according to its results, while many mills do not see any value in using this measurement. The DO and Eop stages perform together in that the DO stage oxidizes the lignin using CI02, but then the Eop stage dissolves the oxidized lignin by adding caustic. For this reason, many mills do not measure brightness or kappa until after the Eop stage. This paper will study data from this measurement and show how it correlates to the pre DO measurements and the post Eop measurements. It is well established that DO brightness is not very useful in a conventional bleach plant. We will instead study data from two 02 delignified bleach lines to evaluate whether or not this measurement is useful for control. From these data correlations we will evaluate whether this measurement should be used for feedback control of CI02 on the DO stage. We will also evaluate whether this measurement should be used for feed forward controls to the oxygen and peroxide used in the Eop stage. It appears from this initial data study that there is reasonable potential to use the Post DO brightness when it is in the above 60 range to improve the controls on the DO and Eop stages.
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