Forgotten technology to produce compressed air at a fraction of the cost of conventional compressor plants
A $3.5 million demonstration project aimed at reintroducing a technology used to produce compressed air in Northern Ontario’s Cobalt mining camp more than 100 years ago is scheduled to commence operation by mid-June.A closed circuit hydraulic air compressor will be constructed in an abandoned 17-metre ventilation shaft at the former Big Nickel Mine, a tourist attraction that is now part of Dynamic Earth, a geoscience centre in Sudbury operated by Science North.
The demonstration project will be modeled on the Ragged Chutes hydraulic air compressor plant designed by Canadian engineer Charles Havelock Taylor in 1910. The Ragged Chutes plant included a dam on the Montreal River and a 9.5-foot diameter shaft blasted to a depth of 107 metres. Intake pipes at the top of the shaft introduced air into the water as it plunged down the shaft. The force of the water compressed the air, which was then piped to a dozen mines to provide pneumatic power.
Ragged Chutes required no fuel, cost almost nothing to operate and ran continuously for 70 years with two brief interludes for maintenance.
Funding for the demonstration project is being provided by the Ontario government’s Northern Ontario Heritage Fund, the Ontario Electricity Independent System Operator and the Ultra Deep Mining Network (UDMN), a federal government supported Business-Led Networks Centers of Excellence program managed by the Centre of Excellence in Mining Innovation.
Unlike the Ragged Chutes plant, the demonstrator at Dynamic Earth will use a pump to recirculate the water in the shaft, but it will still be much more efficient than compressor plants currently used in most mines.
“To provide 5,000 cubic feet per meter of compressed air at 125 psi, an electrically powered, state-of-the-art screw compressor would require 1.2 megawatts of power,” said Dean Millar, MIRARCO Mining Innovation research chair for energy in mining.
“With a hydraulic air compressor, we’d only require .7 megawatts (to power the pumps), so that’s half a megawatt less to deliver the same amount of pneumatic power. The difference shows how much more efficient the hydraulic air compressor is relative to a state-of-the-art mechanical compressor.”
The hydraulic air compressor in this example would require two one-metre diameter raisebored shafts – one to a depth of 100 meters and one to a depth of 120 metres.
Over and above the energy efficiency, the advantage of the hydraulic air compressor is that aside from the pump it has no moving parts, significantly increasing its reliability and longevity.
Electro-hydraulic power packs are increasingly used to drive jumbo drills in today’s modern mines, concedes Millar, but compressed air power is still used to sink shafts and in orebodies around the world that are not conducive to extensive mechanization, pneumatically powered jackleg drills are still widely used.
Millar has no doubts about the ability of the demonstrator to efficiently produce compressed air, but he also hopes to prove the value of the technology for deep mine cooling and possibly even carbon capture.
“This particular technology has been demonstrated at large scale in the mining sector 18 times over, so that means we move forward with this project with a very high level of technical confidence,” said Millar.
“The research value in this is that the 18 prior hydraulic air compressors were limited to using about 100 metres of depth because if they went deeper, the pressure of the compressed air would be sufficiently high that there would be significant solubility loss. The gases would dissolve in the water at high pressure and they would bypass a separator. That would reduce the productivity of the hydraulic air compressor.”
However, Millar and the MIRARCO research team think they can overcome the problem by using an additive to change the solubility properties of the water so the gas doesn’t dissolve in it.
Producing compressed air at higher pressure opens up a range of additional applications for hydraulic air compression technology, including cooling.
“The higher the pressure of the compressed air, the more cooling power we can deliver,” said Millar. “We anticipate that with the pressure we will produce from the demonstrator we will be able to deliver an air stream that will be approximately -60° Centigrade. We could take that stream of cold air and mix it with the mine ventilation air to bring down the aggregate temperature of the mine.”
An even more intriguing application would be the use of hydraulic air compression technology for carbon capture. Introducing off gases containing carbon dioxide and nitrogen from a gas or coal plant into a hydraulic air compressor could be an effective means of carbon mitigation, claims Millar, because carbon dioxide solubility is significantly higher than any of the other atmospheric gases.
“Clearly, while we see our prime mission as one where we are meeting the needs of industry to produce lower-cost compressed air and, thereafter, a less expensive means of cooling mines, we have this other application as well waiting in the wings which is where mining technology could be spun back out to mainstream industry – the electric generating sector, for example – as a means of carbon capture. We are very excited about that because it would be a way for the mining industry to earn its spurs as the vehicle for delivering large-scale carbon mitigation. This, I admit, is a personal vision, but the technology shows every promise of being able to deliver on that.”
Commercialization is an integral part of the hydraulic air compressor demonstration project. In fact, one of the criteria for receiving funding from the UDMN is the expectation of commercialization outcomes, as well as academic papers and development of highly qualified personnel.
To assist in the commercialization of the technology, Millar has partnered with several companies with the required expertise to design and construct a hydraulic air compressor, including Black Rock Engineering, Cementation Canada, Riventa Canada, and Admira Distributed Hybrid Energy Systems.
Once the project is successfully demonstrated, Millar’s company, Electrale Innovation Limited, will be in a position to sell the technology to mines considering new compressors or refurbishing existing compressor stations.
