Measurement of Circulation, Retention Times and Flow Patterns in an Electrolytic Refinery by Using Radioactive Tracers

This paper describes full-scale plant studies in a nickel electrolytic refinery by use of radioactive tracers. The method is particularly suitable since the flow of materials has to be kept to that pertaining under normal conditions. After considering the properties of the electrolyte, the sensitivity of detection, the possible contamination of the factory and other factors, 24Na and 82Br (with activities of 5 or 6 mCi each) were chosen as the tracers. The tracer was measured in situ by a dip-counting method using a water-cooled scintillation probe, a survey meter placed on the outer surface of a pipe junction and a well-type scintillation counter in the laboratory. The first experiment was to measure the circulation time through the electrolytic process by means of the peak-to-peak method. The resulting time, seven hours, was unexpectedly short in comparison with calculations. The second experiment was concerned with electrolyte flowing through two purifying vessels, each with a different construction. The same mixer was used for both vessels, each with outlets at the top. The inlets were on the opposite side, in one case at the top and in the other at the bottom. The experiment showed that the difference in the residence times was remarkably large. The third experiment was carried out in a series of electrolytic cells. Labelled electrolyte was continuously injected into a cathode chamber and 20- to 30-ml samples were periodically taken at nine different points by means of a special sampler. As a result, the flow patterns of the electrolyte were determined and the rapid mixing within the chamber was observed. Further, the flow rate of the electrolyte into the chamber was calculated by the continuous dilution method. (author)