With mines looking to reduce their energy costs and carbon footprint, RMI Pressure Systems has shown exactly how much can be saved by applying variable frequency drives (VFD) control technology to its pumping systems.
Specialists in high pressure reciprocated pumps, RMI Pressure Systems conducted a comparison between three of its emulsion pump sets at work in two mines in the north of Shaanxi province in China – a country where the company has provided pumping solutions for three decades. While one mine was operating a full fixed speed system (with no VFD) and a full VFD system, the second mine was operating a single VFD system. The energy consumption of these three different systems – full fixed speed, single VFD, and full VFD – could therefore be compared directly.The study showed that an upgrade from full fixed speed to either single VFD or full VFD systems would lead to considerable savings in energy costs – ranging from 10% to 20%. Using data from each mines’ SCADA system, the study considered the on-load time and off-load time of each of four RMI emulsion pumps at each underground mine site, as well as the times during which the pumps were non-operational. During on-load time, flow is sent to the roof supports, while in off-load time, the flow is diverted back to the tank – as demand at the roof supports has been satisfied. An average power consumption value was calculated over 15 days for each pump system, which delivers hydraulic fluid power to critical mine roof support infrastructure.Based on an operating condition of 24 hours a day and 365 days a year, the total kilowatts consumed per year was calculated, as well as the cost of that power – using the current cost per kilowatt of electricity. When comparing the energy consumed by the full fixed speed pumps with that consumed by the full VFD pumps, an energy cost saving of over 20% was revealed.The study was able to reflect the annual saving, as well as savings over 15 years – the typical life span of an RMI pump – by applying a full VFD to the four emulsion pump system. Over a single year, a saving of almost ¥1.5 million (over US$205 000) would result from upgrading from a full fixed speed to a full VFD system; over 15 years, this would amount to over ¥22 million (over US$3 million).The study also pointed to energy cost savings of over 10% when comparing the full fixed speed to the single VFD system. Similarly, if a mine upgraded from a single VFD to a full VFD system, the energy saving could be almost 12%.Apart from the direct energy savings, the RMI VFD control technology facilitates a more sympathetic operation of the pumps by increasing the electrical current gradually as the pump starts up and overcomes inertia. By avoiding pressure spikes that jolt the equipment, VFD control technology can also reduce the maintenance required and extend the life equipment.
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