Energy- and cost-efficient ventilation for Alaskan mine

Tuesday, 24 June 2014
Energy- and cost-efficient ventilation for Alaskan mine

Canary birds are especially sensitive to methane and carbon monoxide and at one time were regularly used in coal mining as an early warning system: any signs of distress from a bird indicated to the miners that conditions were unsafe. Today’s mines are ventilated. Using VACON® AC drives to control fans and blowers at a mine in Alaska has significantly improved the energy-efficiency of the ventilation system.

Automation Electric and Controls Inc.1 is a value-added distributor and integrator of AC drive systems based in Mt. Vernon, WA, USA. Bob Alexander, partner in Automation Electric and Controls, is well known locally and in Alaska, where he spends much time providing variable frequency drive (VFD) solutions for a variety of applications. Mr Alexander has been travelling to Alaska for decades developing relationships and a solid reputation; he started in the 1990’s by providing VFD solutions to lumber and paper mills throughout Alaska. A recent successful and exciting VFD installation for Automation Electric and Controls was at a large underground mine in Alaska.

The mine currently uses 100 hp (75 kW) motors with soft starters for the ventilation fans and blowers that provide air to the miles of underground tunnels and roads that form the mine. Powering the motors is costly because energy is very expensive when hydropower is not available, and this depends on the annual rainfall. Some years, hydropower is available for seven months but other years only for one month. Hydropower is delivered via dozens of miles of cable and costs the mine USD 0.10 (EUR 0.08) /kWh. When hydropower is not available, the mine has to use local power generated by diesel generators at a cost of USD 0.35 (EUR 0.27) /kWh.

Great energy savers with short payback period and excellent quality

Knowing that variable frequency drives (VFDs) were great energy savers when used with fans because of the affinity laws2, Mr Alexander wanted to bring this technology to the mine. He discussed with a key engineer at the mine about providing 100 hp (75 kW) VFDs in NEMA 12 (IP54) enclosures to replace the soft starts in the mine.

Years earlier, Mr Alexander had read about VACON AC drives in a trade magazine and had requested a catalog. “I remembered Vacon when this project opportunity came up and contacted Vacon Inc. in the USA,” Mr Alexander says. “The proven track record of the VACON® NXS AC drives and their easy-to-use interface made them a contender for this project. The easy startup and successful testing of the first 100 hp (75 kW) VACON NXS AC drive installed in the mine showed the excellent quality and level of support provided by Vacon. However, even more exciting was the short payback period: thanks to the energy savings, the cost of the drive was paid back in a matter of months!” When the first VACON NXS AC drive was installed on a test fan, this resulted in energy savings of 33 kWh an hour! That translates into annual savings of USD 100,000 (EUR 77,369) for generator power or USD 28,000 (EUR 21,663) for hydropower, and that is just for one fan.

With these favorable results from the test fan, approval was obtained to install VACON AC drives on a large number of the ventilation fans and blowers in the mine. Once the project has been completed, the estimated annual energy cost savings to the mine will be considerable – and could be enormous, depending on the power rate they are paying, with the added bonus of an improved power factor.

In detail

1 Established in 2003, Automation Electric and Controls Inc. based in Mt. Vernon, Skagit County, Washington, USA is a licensed ETL 508A panel building shop that has provided products for companies all over the world, for example in Canada, the Caribbean, Cayman Islands, Australia, all over the Continental United States and in Alaska and Hawaii. 

2 The affinity laws for pumps/fans are used in hydraulics and HVAC to express the relationship between variables involved in pump or fan performance (such as head, volumetric flow rate, shaft speed) and power. They apply to pumps, fans, and hydraulic turbines. In these rotary implements, the affinity laws apply both to centrifugal and axial flows.

The affinity laws are useful as they allow prediction of the head discharge characteristic of a pump or fan from a known characteristic measured at a different speed or impeller diameter. The only requirement is that the two pumps or fans are dynamically similar, that is the ratios of the fluid forced are the same. Source: Wikipedia 

Please note that Vacon joined the Danfoss Group in December 2014.