Cross-Cuts COMPRESSED AIR, NATURALLY (November 01, 1988)

Cobalt, Ont., is justly Cfamous for its silver mines and the turn-of-the- century boom that made it the cradle of Canadian mining. It was a time of unbounded optimism and new developments in mineral processing and mining. One invention saved the silver companies lots of money, but it has received rather scant attention. The discovery came about like this: One spring day near the beginning of this century, Charles Taylor was walking along the Ottawa River near Montreal. Water was flowing over a dam and under the river ice. Nothing peculiar in that, except that domes were rising from the surface of the ice. Taylor pierced several of these bubble-shaped formations and found that compressed air escaped.

He theorized that when a mixture of air and water is compressed, the air separates and rises. The air compresses, not the water, because of the difference in molecular structures. Using this principle, Taylor invented a way of harnessing hydraulic air-compression by dropping the air/water mixture through a shaft to an underground chamber. He designed the chamber to allow the water to flow through and, at the same time, compress the air.

Thus was born, in 1910, the world’s first and only water-powered compressed air plant — the Ragged Chutes Compressed Air Plant. It was built on the Montreal River near Cobalt, Ont. The plant replaced expensive, coal-fired steam plants that supplied the silver mines with vital power.

Ragged Chutes was designed to produce air compressed to 862.5 kPa, according to literature from Ontario Hydro, the owner of the station since 1945. The intake shaft is 107 m deep, and the tunnel chamber has a blow-off valve to prevent increased pressure. Control gates limit the amount of water entering the plant works. As well, the two intake heads can be raised or lowered.

From the heads, the water is fed into one pipe which widens just before the bottom. This decreases the pressure in the pipe and allows the air bubbles to collect and merge. At the base of the shaft are two, steel- sheathed concrete cones that break the initial impact of the air/water mixture and direct its flow into the horizontal chamber. The chamber collects the compressed air and channels it to a receiver pipe 61 cm in diameter. The receiver then carries the compressed air to a valve house where it is transmitted to Cobalt for distribution.

The blow-off valve is a pipe 30 cm in diameter situated beside the receiver and leading to a point underwater on the river bed. It reaches into the tunnel chamber to the critical depth, where it rests in water as long as the air is compressed to 862.5 kPa. But when the pressure increases, the water level within the chamber lowers slightly, allowing the excess pressure to escape. When it blows, a stream of water often shoots more than 30 m into the air. The geyser no longer spurts its column of water, because the plant was shut down following a fire in 1981. However, a volunteer group of citiz ens in Cobalt has launched a fund-raising campaign to raise the bucks to house a working model of Ragged Chutes, which was donated by Ontario Hydro, and to develop parkland around the building. IN-SITU MINING A deep, low-grade copper deposit near Casa Grande, Ariz., will be the site of a test in situ mining project over the next several years.

The deposit contains an estimated 800 million tons averaging 0.4% copper oxide with internal higher-grade zones. It sits between 1,400 and 2,600 ft below the surface and is separated from the overlying sources of groundwater by a thick layer of bedrock.

In the first year of the research project, fresh water will be injected and recovered to establish permeability, flow rate and direction of solution movement. Hydrological studies and data- gathering for environmental permits will also be conducted. If this first stage proves out, the joint venture research project between subsidiaries of Asarco Inc. and Freeport-McMoran Gold Co. will advance to the second stage, which will include injecting dilute acid solutions under pressure into pores and fractures of the ore-bearing rock. The solution will dissolve the copper and carry it to a recovery well. This liquid will be pumped to surface and the copper recovered by solvent extraction and electrowinning.

Jon Ahlness, technical project officer for the U.S. Bureau of Mines, another project participant, says that if successful, “in situ mining may open to development approximately a dozen large copper oxide deposits in Arizona.” This method could be used to mine deposits that are too deep for open-pit mining and too low-grade for underground extraction.

Cobalt, Ont., is justly Cfamous for its silver mines and the turn-of-the- century boom that made it the cradle of Canadian mining. It was a time of unbounded optimism and new developments in mineral processing and mining. One invention saved the silver companies lots of money, but it has received rather scant attention. The discovery came about like this: One spring day near the beginning of this century, Charles Taylor was walking along the Ottawa River near Montreal. Water was flowing over a dam and under the river ice. Nothing peculiar in that, except that domes were rising from the surface of the ice. Taylor pierced several of these bubble-shaped formations and found that compressed air escaped.

He theorized that when a mixture of air and water is compressed, the air separates and rises. The air compresses, not the water, because of the difference in molecular structures. Using this principle, Taylor invented a way of harnessing hydraulic air-compression by dropping the air/water mixture through a shaft to an underground chamber. He designed the chamber to allow the water to flow through and, at the same time, compress the air.

Thus was born, in 1910, the world’s first and only water-powered compressed air plant — the Ragged Chutes Compressed Air Plant. It was built on the Montreal River near Cobalt, Ont. The plant replaced expensive, coal-fired steam plants that supplied the silver mines with vital power.

Ragged Chutes was designed to produce air compressed to 862.5 kPa, according to literature from Ontario Hydro, the owner of the station since 1945. The intake shaft is 107 m deep, and the tunnel chamber has a blow-off valve to prevent increased pressure. Control gates limit the amount of water entering the plant works. As well, the two intake heads can be raised or lowered.

From the heads, the water is fed into one pipe which widens just before the bottom. This decreases the pressure in the pipe and allows the air bubbles to collect and merge. At the base of the shaft are two, steel- sheathed concrete cones that break the initial impact of the air/water mixture and direct its flow into the horizontal chamber. The chamber collects the compressed air and channels it to a receiver pipe 61 cm in diameter. The receiver then carries the compressed air to a valve house where it is transmitted to Cobalt for distribution.

The blow-off valve is a pipe 30 cm in diameter situated beside the receiver and leading to a point underwater on the river bed. It reaches into the tunnel chamber to the critical depth, where it rests in water as long as the air is compressed to 862.5 kPa. But when the pressure increases, the water level within the chamber lowers slightly, allowing the excess pressure to escape. When it blows, a stream of water often shoots more than 30 m into the air. The geyser no longer spurts its column of water, because the plant was shut down following a fire in 1981. However, a volunteer group of citiz ens in Cobalt has launched a fund-raising campaign to raise the bucks to house a working model of Ragged Chutes, which was donated by Ontario Hydro, and to develop parkland around the building. IN-SITU MINING A deep, low-grade copper deposit near Casa Grande, Ariz., will be the site of a test in situ mining project over the next several years.

The deposit contains an estimated 800 million tons averaging 0.4% copper oxide with internal higher-grade zones. It sits between 1,400 and 2,600 ft below the surface and is separated from the overlying sources of groundwater by a thick layer of bedrock.

In the first year of the research project, fresh water will be injected and recovered to establish permeability, flow rate and direction of solution movement. Hydrological studies and data- gathering for environmental permits will also be conducted. If this first stage proves out, the joint venture research project between subsidiaries of Asarco Inc. and Freeport-McMoran Gold Co. will advance to the second stage, which will include injecting dilute acid solutions under pressure into pores and fractures of the ore-bearing rock. The solution will dissolve the copper and carry it to a recovery well. This liquid will be pumped to surface and the copper recovered by solvent extraction and electrowinning.

Jon Ahlness, technical project officer for the U.S. Bureau of Mines, another project participant, says that if successful, “in situ mining may open to development approximately a dozen large copper oxide deposits in Arizona.” This method could be used to mine deposits that are too deep for open-pit mining and too low-grade for underground extraction.