Multotec completes successful repurposing of extensive cyclone installation

This is the perfect demonstration that showcases how mineral processing companies must evolve their approach to deliver on changing client needs. A Mining Review Africa exclusive.

The plant was originally commissioned several years ago and was recently reconfigured.

“We supplied the original cyclones, so we knew they were of high quality, but they needed to be adapted for what is essentially a different flowsheet,” says Bheka Majola, MD of Multotec Processing Equipment. “The challenge was to provide the client with the best technical solution using as much of the old equipment as possible, supplemented where necessary with new units. We worked very closely with the design house responsible for the process plant to achieve this goal.”

He notes that the project was of considerable scale, with the reconfigured plant incorporating 13 different cyclone applications which make use of more than 135 cyclones ranging in size from 100 mm to 750 mm. “We were required to provide equipment with various different materials of construction suitable for the different applications,” he says. “The fact that we manufacture all our cyclones in South Africa in our factory in Spartan meant that this posed no problems for us. We are always able to customise our equipment to meet the demands of a specific site.” Majola adds that the project was particularly interesting for Multotec, given that phosphate projects are not common.

“Phosphate is not entirely new to us but certainly we’ve never done anything in phosphate on this scale before, so our involvement has been very rewarding for us as a company,” he says. In the event, Multotec was able to successfully repurpose most of the cyclones. It was then involved with the commissioning, ramp-up and training of operators on site.

As is usual with any plant start-up, a couple of problems arose post-commissioning related to the cyclones. These were efficiently and successfully addressed by Multotec.

One of the issues was that a specific cyclone installation was cutting too coarse: in other words, too much solid material was going to the cyclone’s overflow. This was causing a bottleneck in one of the plant’s thickeners. The result was that the plant was not able to run for more than about four hours because of high torque levels on the thickener’s rakes.

“After investigating, we were able to identify the problem and devise an appropriate solution,” says Frikkie Enslin, Multotec Processing Equipment’s applications manager.

“It was evident that the particle size distribution (PSD) of the feed to the cyclones differed significantly from what had been given to us during the tender phase. Considering the current infrastructure and the easiest possible conversion, we were able to provide the required parts to convert the current cyclone installation to the cyclone configuration suggested by our in-house cyclone sizing simulations.”

The converted cyclones fitted perfectly into the existing infrastructure and the benefits were immediate. “The cyclone overflow was much cleaner, and one could easily see the difference in the colour of the overflow discharge,” states Enslin. “Furthermore, the load on the tailings thickener was reduced to the point where it was possible to run the thickener without the unplanned stoppages.”

Looking at another challenge that arose after start-up, Enslin says that one of the cyclone applications was designed to remove the maximum number of slimes – typically -25 μm particles – to reduce reagent consumption downstream. This was not being achieved due to the inefficient operation of the cyclones in the original cluster. Not only was the plant producing too little product, but it was also slightly off-spec and reagent costs were very high.

“We inspected all the cyclones individually to make sure they were all of the exact same configuration and in good working condition, and that changes were made where required,” says Enslin.

“Time was also spent on site varying the feed parameters to find the optimal operating conditions. The generated data is now being used to assist the client in keeping the cyclones in an ideal operating condition, even if there are variances in the feed. As part of this solution, changes were made to the current control philosophy to ensure the cyclones are operated at an optimal level, and appropriate training has been given to operators on site.”

The results of the intervention have been positive with the cyclone cluster delivering – to use Enslin’s words – “beautiful desliming”. Minimum slimes are reporting to the underflow and there is also a minimal misplacement of coarser particles to the overflow.

Reviewing Multotec’s work on the phosphate plant, Majola says it underlines the fact the company is not simply an equipment supplier.

“We apply our process expertise to support our clients and we are able to make a real contribution to plant efficiencies, as we’ve demonstrated with this project,” he says. “Our ongoing involvement with the project over a period of years is also illustrative of the long-term partnerships that we generally enjoy with our clients.