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(125d) Going with the (mass) Flow: Retrofitting Screw and Hopper Insert Technology for Improved Feeding of Milled Phosphate in Egypt

McGee, E., Ajax Equipment Limited

Helical screws are a well-established means of feeding a wide range of bulk solids though sometimes the technology is misapplied without proper understanding of the material being handled and the application needs. Enhancements in performance are possible with an approach based on characterisation of the bulk and technological design which counters flow issues and offers improved process capabilities. To illustrate shortcomings and a successful retrofit solution, a case study will be presented on a silo and feed system for a mineral processing plant in Egypt. This suffered from unreliable flow in the form of either too much (flushing) or no flow (arching) even with the addition of various ‘flow aids’. This meant that plant operability was severely limited. A problem statement was produced and a review of the installation and the causes of the operating problems were established. These identified the flow regime in the hopper as one of the major issues for performance issues. Details of the testing performed on the powder and the design approach this helped inform will be presented. This helped develop a retrofit solution which included an improved flow geometry hopper bottom section, a flow insert and a new twin screw feeder. Details of these items will be presented as well as the cooperative working between the supplier of the technological aspects of design and the end user. This approach provided site with an efficient solution with hopper and insert parts manufactured locally, whilst the twin screw feeder was supplied directly from the UK. The installation was carried out and the commissioning outcomes of the retrofit actions for the plant will be reported.


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