Cutting the rope

Source: www.miningmagazine.com

‘Roping’ is a serious operating condition that adversely impacts productivity in terms of OPEX and mineral recovery rates. MM looks at the latest advances in wireless cyclone monitoring technology that offers to address this challenge.

The Teghut mine is a major copper and molybdenum open-pit mining operation in Armenia’s northern province of Lori. Its copper concentrator is designed to handle up to 7.5Mt/y of ore-feed to the plant.

Like many similar miners, its owners Vallex faced a persistent operational challenge leading to diminished recovery rates and downtime associated with its eight cyclones, which were offering sub-optimal performance and consistently presenting coarse material to flotation tanks – from which valuable copper would be sent on to the tailings facility.

‘Roping’ is a condition where the apex or spigot at the bottom of the cyclone becomes overloaded. The cyclone then throws coarse material into the overflow stream which reports to flotation, where large particles sink to the bottom before ending up as tailings. In serious cases of coarse particles presenting over an extended period, all grinding operations must cease whilst float cells are cleaned.

Vallex was determined to find a better way of doing things and approached integrated solutions provider, FLSmidth Krebs. “We knew we could solve their challenge by upgrading cyclones with our new wireless roping detection sensors to allow real-time condition monitoring of cyclones in the control room in a user-friendly graphical interface,” states Barry Buttler, cyclone product manager at FLSmidth Krebs. “We provide operators with the information required to take immediate corrective action when a ‘roping’ underflow discharge has occurred.”

It meant that Vallex could produce a finer overflow product and do away with the problem of ‘plugging.’

Installation and results

In July 2017, FLSmidth Krebs’ SmartCyclone suite was installed and commissioned at Teghut. Critically, it is the first wireless roping detection solution of its type – an integrated monitoring and control solution for reducing cyclone-related process disturbances, improving cyclone overflow particle size distribution, and predicting and controlling cyclone maintenance schedules. Its aim is to optimise closed-circuit grinding processes.

Bob Dickey, COO at Vallex, is delighted to talk about the results three months later. “Since the date of installation we have had zero downtime associated with ‘plugging’ or problems caused by coarse material in the float deck. During the previous 18-month period, the same issues with our float decks were causing downtime of about 12 hours a month on average,” he states.

“Installing this package has allowed us to run our gMAX33 cyclones more effectively and efficiently through its ability to measure cyclone underflow, flare and flow and to have a better distribution of ground material. In the past, a failed liner on a cyclone would collapse and send coarse material to the float deck. This system has allowed us to immediately shut down the cyclone when flow is lost.”

Ore variability at Vallex makes it difficult to calculate the improvement in recovery rates, but Dickey cites savings equating to US$250,000 per month due to eliminating downtime and the expense of deploying maintenance teams.

“Wired systems that monitor ‘roping’ have been available for a number of years, but our wireless SmartCyclone is something very different in terms of how it is operated,” explains Buttler, who has overseen the commissioning process. “Previously, every sensor placed on a cyclone needed its own node box. These had to daisy-chained together before feeding into a controller that would then transmit the data. Pulling out a cyclone to replace the liner was a serious maintenance problem. This wireless aspect of our technology makes cyclone maintenance so much easier because there is no longer a need for cables to be disconnected when a cyclone needs to be taken off the manifold.”

The wireless SmartCyclone system relies on a locally mounted central controller that can handle up to 16 sensors per unit; it provides real-time detection and communication of roping and/or wear data from the wireless sensors to the manifold controller for forwarding to the control room via a single Ethernet cable.

Wired sensors require a laborious and time-consuming calibration process each time they are installed to provide reliable information on roping status. A wireless design offers the advantage of sensors that do not require calibration and can be installed and operated on a ‘plug and play’ basis.

For consistent, high quality feed to flotation, cyclone feed density and pressure must be optimised, a process requiring operator vigilance and knowledge to make adjustments. As a next step, the partnership is working towards full integration of SmartCyclone with its other automated processes. “We are looking at how we can integrate the basic system into the existing automation circuit to take automated actions when roping cases appear,” says Buttler.

“So far we have only deployed the basic package but now we want to see what other benefits we can realise. At present, it is up to the operators to act and take corrective action, but we know we can take it way beyond this in the future. We have already designed an Expert Package that can operate and optimise cyclones automatically and manage pump speed and water addition, as well as calculate how many cyclones need to be running at any given time.”

In terms of the potential to improve mineral recovery rates, he believes use of this technology is in its infancy. “As user experiences become known, we are anticipating a massive wave of interest. The cost/benefit ratio already makes its own case,” he states.

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