CVRD Inco plugs sulphur dioxide holes.

• Author: Ross, Ian
• Position: SPECIAL REPORT: MINING

It would be a stretch to say CVRD Inco's 380-metre Superstack in Sudbury will ever come tumbling down anytime soon as some sooty industrial relic of the past.

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Where once the nickel mining giant had a well-deserved reputation as a global polluter--belching almost 2,000 kilotonnes yearly of sulphur dioxide (SO 2) into the atmosphere in the early 1970s--the company has spent more than $1 billion in emissions cleaning technology to cut gases by 90 per cent.

The company has reached a 175 kilotonne (kt) limit this year and is well on its way to achieving federal and provincial emission targets of 66 kt by 2015.

The miner proudly boasts it has eliminated 1,700 kilotonnes since 1970. But capturing that last 100 kilotonnes to reach the magic 66 kt number by 2015, as imposed by the federal and provincial governments, will be no easy feat.

"It becomes increasingly more difficulty to capture the gases," says Dave Marshall, project manager of CVRD Inco's Atmospheric Emission Reduction Project. "It used to be you could tackle one or two (SO 2 sources) and get a big bang for the buck.

"Now it becomes more spread out and more difficult to capture and harder to get into a strength to treat and deal with."

The Superstack was an engineering marvel when it was commissioned in 1972. The prevailing theory then was that emissions could be diluted to a harmless concentration. However the result downwind was acid rain.

But erecting one of the world's tallest chimneys at the Copper Cliff smelter gave Sudbury a breather to allow its blackened 'moonscape' landscape to recover and for the city to start its later re-greening efforts.

Now the Superstack is too big for its own good because of the huge technological strides made in reducing emissions.

A major rebuild of the smelter in the early 1990s in switching to flashing furnaces represented a dramatic cutback in reducing emissions from 625,000 kt to 225,000 kt.

Later in 2005-2006, Inco launched its $115 million abatement project with new off gas-scrubbing technology coming off their fluid bed roaster (FBR).

It took out another 55,000 to 60,000 kt of SO 2 as well fine metal particles of nickel, copper and arsenic that usually went up the stack.

The fluid bed roaster plant is part of the smelting process where nickel sulphide is roasted to make nickel oxide feed for refining.

The FBR project involved building or making upgrades to three plants including construction of a wet gas cleaning facility...