Harmony Gold Mine recently embarked on a project to rework old slimes dams around its goldfields area after realising that improved refining methods would yield good profits. These dams are located in a 5 to 10 km radius around the Phoenix plant between Welkom and Virgina. Once reworked, the excess slurry had to be pumped to a new tailings dam 20 km away near the old St Helena shafts. Harmony also required a system to monitor the energy usage at the remote sites and determine the kWh per ton of product consumed.
Welkom Industrial Controls (WIC) was given the job of monitoring the remote process sites and gathering the data at a central point, with reports being generated for assessment by management. However, there were a number of obstacles. The number one concern was to ensure the data arrived at the desired location. With the use of standard radio or wireless telemetry, a clean line of sight over the distance was required; but with a number of obstacles such as old slimes dams, mine headgear and trees, WIC needed to find a communication method that would overcome this. The answer was an Access Point Name (APN) network – a gateway between a GPRS or 3G mobile network provider and another computer network. Thanks to Vodacom and Westermo’s MRD-350 wireless GSM router, all seven remote sites were accessible.
The next hurdle was to manage the information and ensure that the data arrived in the correct order, correctly date and time stamped. At each point a Schneider M340 PLC was used as a remote terminal to gather the data and transmit it via distributed network protocol (DNP3). The Remote Terminal Unit (RTU) monitored data points and generated events when it determined that the data should be reported, for example when it changed value. It was interrogated initially with what DNP3 terms an Integrity Poll. This caused the RTU to send all buffered events and also all static point data to the master station. At the master station an Invensys Wonderware Intouch SCADA with a Historian server was implemented. All reporting was viewed on the Wonderware information server via the web.
With the concept and backbone now taken care of, the next task was to monitor the actual process. Firstly, the power on all the pump motors needed to be accurately measured. This was achieved by installing Schneider PM750 panel meters on every motor. This gave the ability to monitor voltage, current, power, power factor and kilowatt hours amongst others. All slurry and water flows were monitored with Flowmetrix SAFsonic or Doppler flowmeters. The sensors were extremely easy to fit externally to the pipe and simple to set up, with no additional equipment needed. Water and slurry pressures were monitored by Endress+Hauser PMC131 static pressure transmitters. Melco Instruments fitted all slurry transmitters with chemical seals to ensure a longer life for the instruments.
After six months of development and installation, with no downtime to the plant or the pump stations, the installation was successfully completed. Welkom Industrial Controls had met the customer’s requirements with the standard and passion that the company’s clients have come to expect.
For more information contact Llewellyn Coveney-Winter, Welkom Industrial Controls, +27 (0)57 357 5724, [email protected], www.wic.co.za
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