Pfaudler Reactor Systems, a specialist in providing glass-lined process components and part of the Process Solutions Group of Robbins & Myers, was recently retained by a South Africa-based precious-metals refiner to upgrade mixers in an effort to significantly increase the capacity of the customer’s process reactors.
Working in conjunction with sister company Chemineer, Pfaudler developed what it describes as a process solution designed to ensure optimum mixing of platinum group metal concentrates, which can severely damage vessels when not configured correctly. Pfaudler Process Engineer Chris Drysdale said: “As platinum group metals are very heavy, the tendency is to run mixers at excessive speeds in order to achieve sufficient solids suspension. This not only increases energy bills, but it causes the heavy metal concentrates to damage the glass interior of the tank, which can make the surface increasingly rougher and ultimately lead to chemical attack and failure of the vessel.”
Using Chemineer’s Maestro process-development software, Pfaudler said it was able to show the customer how efficient top-to-bottom mixing in the tanks would be achieved. The company noted that optimum mixing that keeps solids in suspension also improves productivity by reducing downtime required for cleaning.
Because the dimensions of the customer’s vessels were not standard, Pfaudler said it had to design new dual-flight agitator shafts, but used the same size hub; the new design allowed for a single-diameter shaft with two honed areas for the two flights. The installation also incorporated Pfaudler’s Cryo-Lock system, which uses the cryogenic fit between the glass shaft and the glass impeller hub for precise interference fit. The major benefit gained is that impeller changeover can be carried out inside a reactor, rather than having to remove the drive, shaft or access cover.