Pan stage productivity and efficiency gain at South Johnstone

For many years at South Johnstone Mill, two small copper coil vacuum pans were the primary vessels used for magma preparation. The pans were old and had a number of problems: the pan structures and components were in need of major repair; the pans required considerable manual intervention in operation and would be difficult to automate; product quality from these pans for high-grade footing was not of an acceptable standard, i.e., the grain size was mixed and there was poor consistency from one pan to the next; the cost of repairs to bring the pans to an acceptable working condition far exceeded the benefits that the existing pans could deliver. Following consultation between mill staff, the Sugar Research Institute (SRI) and contractors, it was decided to upgrade one pan by converting it from a 40 tonne coil pan to an 80 tonne conventional centrewell calandria design. This was to be accomplished by using the top and bottom of the existing pan, fitting a new centrewell calandria and inserting a new extended mid-section with an expanded body to give the required additional capacity. The pan was commissioned in June 1997. There was an immediate improvement, with a reduction in fine grain and improved cycle times. To assist with other process problems, the other coil pan was converted into a magma holding vessel. The increased holding capacity allowed for a controlled flow of remelt back to the cffets, which considerably reduced the time lost on the effets.