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CVRD Inco plugs sulphur dioxide holes

By IAN ROSS 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.


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.

Capturing the last bit of fugitive SO 2 emissions from CVRD Inco's converters is the company's latest move to slash airborne pollutants 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 to treat gas coming off the roasters.

As well, there was expansion of an existing acid plant to handle clean SO 2 from the new gas-scrubbers and construction of a weak acid plant to replace a flash furnace slime system and to treat metals scrubbed at the gas cleaning facility.

But the last major source of SO 2 emissions in the whole smelting process is the converters.

About 75 per cent of remaining emissions come from the company's five converters, says Marshall.

Converters are part of the sequenced smelting process, converting furnace matte into bessemer matte, and removing more iron and sulphur to send precious metals downstream to the refinery to begin the first stages of copper-nickel separation.

To tackle the problem, the company has a massive $42 million research and development project underway called its No. 8 Converter.

"This is a plant scale R & D project that's bigger than any operating converter we have," says Frank Javor, the company's health and environment superintendent.

In a conventional converter, its one mouth is regularly opened and closed to pour in metal. Moving the gas collection hoods out of the way to allow cranes to get access means many "fugitive emissions" escape. Normally the gases that are collected go up the Superstack. What's not collected ends up going through roof ventilators.

The experimental No. 8 has two mouths, the first of its kind in the nickel industry. The second mouth is used to ventilate the off-gas.

During the first phase of research, the off-gas will be sent to the Superstack. But the  upcoming second phase will collect as and route it by duct work to a gas cleaning plant built in 2005. That duct work connection is close to completion.

Eventually a new and bigger gas cleaning plant will be constructed to handle all the off-gas from all of Inco's operating converters.

Javor says the company is still learning how to use the new converter, but environmentally, it's design and secondary hooding makes it easier to capture fugitive gases in a strength that it can be effectively treated.

Over the years, Inco has reduced stack emissions so much that the Superstack  is "much too large for the small amounts of gas we are still exhausting," says Javor.

Four natural gas burners and three large fans are needed to push and pull gases up the stack.

Marshall says there will always be some type of stack, but in the long term, the Superstack could be replaced with a small chimney. The emissions will also change to a lower sulphur content.

With new ownership for Inco, the company is just starting to explore what environmental technologies are available.

"There's a number of things we're doing to reduce our footprint," says Javor, including improving dust control and their re-greening efforts to create a larger buffer zone around the operation.

Old slag piles along Big Nickel Mine Road, near Dynamic Earth, have been sloped and clay-capped to hold soil. The company is in the process of hydro-seeding them  

And there will be more stringent regulations in the near future since Ottawa is working on its Clear Air Act which will have limits for airborne particulate as well.

For the mining industry, the federal government enacted a legal instrument last year called Pollution Prevention Planning with targets for particulate for metals emissions with an environmental code of practice. 

"The (kilotonne) limits will continue to go down," says Javor. "Society expects it, they're demanding it and we're up for the challenge."