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Study aims to optimize natural cooling system

December 1, 2009
by Norm Tollinsky
In: Research with 0 Comments

A natural cooling system at Vale Inco’s Creighton Mine is the envy of every deep underground mine in the world. A large mass of broken rock in an open pit acts as a natural heat exchanger, warming the mine’s air in the winter and cooling it in summer. Fresh air is drawn through the rock mass into 128 slusher trenches and tramways around the footwall of the pit. The air then flows into a main collector drift on the 800-foot level and is circulated throughout the mine through three individual fresh air systems.

The system has been in use since 1965, saving tens of millions of dollars, but a planned deepening of the mine to 10,000 feet could exhaust its cooling capacity and force the company to install a costly mechanical refrigeration solution. Hoping to avoid the huge capital expenditure and operating costs of mechanical refrigeration, Vale Inco commissioned Sudbury-based MIRARCO Mining Innovation to evaluate the possibility of optimizing the cooling capacity of the current system.Using a thermodynamic model of the rock mass and computer simulation, MIRARCO concluded that the cooling capacity of the natural ventilation system could be optimized by automating the opening and closing of doors in the slusher trenches and tramways, said Dale McKinnon, MIRARCO’s lead researcher on the project.

Automation

Currently, the doors are opened and closed manually once a month. Automating them would allow the company to regulate the airflow daily to extend the cooling capacity of the rock mass through the summer.
“Automation could reduce the temperature by at least one degree Celsius,” said McKinnon. “It doesn’t sound like a lot, but it’s significant.”

When the temperature exceeds 31.5 degrees Celsius, miners may be required to incorporate periodic rest periods into their schedule. That impacts productivity. “As you go deeper,” explained McKinnon, “the geothermal gradient causes the work environment to be warmer.”
A final decision on using automation to optimize the system is still under consideration.

The Creighton pit operated from the 1920s to 1987, said Doug O’Connor, senior ventilation specialist at Vale Inco. The slusher trenches were excavated to access and extract ore around the pit.
“They drove a drift out, drilled raises into the ore, then blasted them and slushed out the ore.”

Today, the slusher trenches serve as airways.

“Our main fresh air fans are located underground,” said O’Connor. “They draw the air down through the pit, so the air passes over the rock mass, through the tramways and slusher trenches into the ore pass systems and then, from there, it’s collected and distributed through our fresh air systems.”

The trenches are at different elevations and are exposed to varying volumes of rock mass.

“The trenches closer to surface have very little rock on them, so they get cold very quickly and they get hot very quickly, so we use the doors on the trenches and tramways as controls.”

One-of-a-kind

The natural cooling system may be the only one of its kind in the world, said O’Connor.

“It’s very unique. It’s the only one in the world that I’m aware of.

There are some variations of it. The Kidd Mine in Timmins created ice stopes by blasting through a part of their operation into an open pit and they’re pulling some air through there, but it’s not on a scale that we have.”

The audit conducted by MIRARCO “will make sure that we’re maximizing its use and look at options to either increase its capacity or make it more efficient so we’re getting cooler air than we’re getting now.”

www.mirarco.org
www.inco.com

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