On-line Cyclic Voltammetry Sensor for the Continuous Measurement of TTA, EA and AA, 2012 PaperCon Conference

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Advanced control of the kraft pulping process is often limited by the absence of fast, reliable and accurate on-line measurements of liquor composition. The conventional manual titration method provides adequate accuracy, but not the rate required for efficient process control. An on-line liquor sensor employing the principles of electrochemistry and cyclic voltammetry has been developed by Honeywell. We present results of trials conducted in the recovery area at two pulp mills. The sensor was used to monitor the white liquor composition in the first causticizing tank after the slaker. The sensor is composed of a three platinum electrode probe, probe excitation electronics, a data acquisition system and a scale inhibitor dispensing system. To achieve a stable measurement, a scale inhibitor is continuously dispensed to the tip of the probe. Sensor data were compared to laboratory data obtained by manual titration. Good measurement stability was obtained over 4 months of continuous operation. Maintenance activity consisted in refilling the scale inhibitor tank once a week. Sensor measurements of active alkali, effective alkali and total titratable alkali were within 3 percent of laboratory-obtained values. This sensor measures liquor composition parameters at the rate required for advanced control of the causticizing process.