In August 2020 ProProcess was awarded the Engineering, Procurement and Construction Contract for the Fines Flotation Mobile Pilot Plant for Anglo American. This world class test facility for platinum concentrate flowsheet optimisation had to be designed with maximum road transportability in mind, as this pilot plant is earmarked to be moved around various concentrator sites owned by Anglo. To this end the entire plant consisting of 40+ flotation cells (including a high intensity flotation cell), a mill,  ~30 tanks (some agitated), ~50 pumps (including centrifugal slurry, peristaltic, vertical spindle), blowers, compressors, etc were fitted onto 16 road transportable ISO frame skids conforming to 40ft marine container dimensions.

We asked the leads in each discipline what design challenges they faced on this project, this is what they had to say:

Stefan Van Dyk (Project Management): The aim of this project was to produce a modular, transportable, cost effective and built for purpose pilot plant. Pilot plants have much less stringent  equipment requirements than production plants and this needs to be kept in consideration to avoid over designing the plant, thus unnecessarily escalating the capital outlay. This required a lot of out of the box thinking and many new ideas and concepts were explored to ensure a built for purpose plant.

Anglo American has very high safety, maintainability and operation requirements and standards for their production plants. As the pilot plant would be placed into a production environment it was crucial to determine which standards to adhere to and where concessions could be obtained.

Tanja Marcus (Process Lead): For the process to operate effectively adequate buffer capacity between the individual unit operations needed to be catered for in the design. A slurry with a high density (S.G. >3) is fed into the plant. To avoid settling of this material in the tanks a very steep angle of 45-60 degrees on the tank cones had to be used. The tanks also had to fit the height of the skid, thus limiting the tank height to ~1.8m. This lead to oddly shaped vessels that consist mainly of cone, with very little tan-to-tan height.

Some of the reagents required on the plant are hazardous. To avoid additional equipment in the form of a scrubber and associated neutralisation reagents, the potential hazard was designed out to cause minimal risk.

Kean Southern (Mechanical Lead): ProProcess applied our specialised modular approach to the design of this plant for simplified site installation and ease of transport. This meant each skid frame was custom designed and built to 40ft shipping container dimensions, eliminating any restrictions on road transport, or the need for special permits.

All equipment is pre-mounted, piped up and tested at our workshop before shipment to site. Once testing is complete, all that is required is for flexible, interconnecting piping between the frames to be disconnected (which is made easy with the use of flanges and claw couplings). Given the numerous pipe sections run between frames, each connection of flexible hose needed to be tagged to ensure the correct hoses were reconnected during assembly. Since the plant arrives on site already partially assembled, site installation is a breeze.

Emile Strydom-Bouwer (Electrical Lead): All skids are prewired to Male Power Sockets on local junction boxes. The MCCs are similarly prewired to Male Power Sockets on the MCC wall. The interlinking cables have a Female Power Socket at either end thus no on site glanding and terminations will take place. A potential problem is that the cable can be energised and cause an electrical shock. We, as a design team, mitigated this risk by specifically manufacturing a late-make/early-break pin set and connected it to the safety circuit. Thus the cable can only be energised once fully inserted at both ends.

Roger Gavin (Drawing Office Lead): The ability to sample and monitor operations is of paramount importance on a pilot plant, therefore operator access was given priority over maintenance access. The design team optimised use of the limited space available, focusing on metallurgical requirements primarily, whilst still providing maintenance access for essential maintenance expected during short piloting campaigns.

Hot dip galvanising was chosen for corrosion protection of the ISO frames. Due to galvanising bath size constraints, the structures were designed as a combination of fully welded frames for the roof and floor, with bolt-on columns to complete the assembly.

To avoid the construction of complex concrete bunded areas at each test site location, ProProcess also designed structural bunds in ISO frame format. These bunds, complete with removable sump pumps, are transported separately, and essentially form the ‘foundation’ for the plant structure when placed on a flat surface. Since they are supported at the four corners of the ISO frames, the bund ‘foundation’ can tolerate a certain amount of unevenness, which is compensated for by shimming the corners to ensure a level final base for the ISO frames making up the balance of the plant.

Sergio Burelli commented on the Civil design:  The plant is made up of ISO frame ‘blocks’, all it needs is a flat surface to stand on. The civils are therefore a simple concrete slab.