Canadian Mining Journal

Feature

Will Sudbury super stack be needed by Vale after retrofit project?

At more than 388m high and just over 36m wide at base, Vale’s “Super Stack” in Sudbury is unquestionably the city’s most outstanding feature.



At more than 388m high and just over 36m wide at base, Vale’s “Super Stack” in Sudbury is unquestionably the city’s most outstanding feature.

In fact, it’s also one of Northern Ontario’s more outstanding features because it’s literally the tallest structure in the north and can be seen for miles from every direction as it towers over the city.

Even Sudbury’s world-renown “Big Nickel” pales by comparison when it comes to size and impressive landmarks.

Built from almost 16,500m3 of concrete and strengthened with nearly 956 tonnes of 38mm and 13mm re-bar, the stack is a solid monument that has withstood the harshest of conditions that Mother Nature could throw at it.

Extreme cold and blowing snow, fierce winds and driving rain, heat and lightning, and even ground-shaking tremours, have barely made a mark on the stack. And, the fact that it’s also lined from top to bottom with 6.4mm nickel stainless steel and that its walls are 1.1m thick at the base and 267mm at the top, have all added to make the stack almost indestructible.

It was clearly built to last and since it started rising on the horizon in 1970, and subsequently going into service on August 21, 1972, the stack has performed as planned by safely carrying sulphur dioxide from INCO’s (now Vale’s) Copper Cliff smelter high into the atmosphere and away from the city.

However, long before any SO(2) reaches the atmosphere, a complex steel flue system almost 1.1km long has been designed to handle the 725 deg (F) gases.

Travelling at more than 88 km/h through 88 nickel-stainless steel diaphragm-type expansion joints, the gases are carefully monitored by 13 environmental control stations strategically placed along the flue system to collect and determine the dust burden, temperature, and volume of the gas flow.

Clearly the super stack has been designed with the environment in mind, but Vale is moving forward to make things in Sudbury even cleaner by embarking on a $1-billion AER (Atmosphere Emissions Reduction) Project to dramatically reduce emissions even further.

Eighty-five per cent further is what Vale is projecting as the company plans to capture sulphur-bearing gases from the smelter’s converter aisle at Copper Cliff and significantly reduce dust and metal emissions.

As mentioned earlier, the process of handling the gases is complex and involves a long and heavy system comprised of rectangular and circular sections, some as large as 7m in diameter, and flues, that combine to weigh 3,300 tons.

Trestles, bents and towers on which the flues are supported involve another 2,300 tons of steel, so once again, it’s not only a complex set-up, but a heavy one too.

Vale’s retrofit of its Copper Cliff smelter is a huge undertaking but one that the company is obviously committed to otherwise why would it have invested close to $100 million on research and development of the project even before it was approved by the Ontario Ministry of the Environment and other governing bodies?

Kelly Strong, Vale’s Vice-president of Ontario and U.K. Operations, knows why:

As he recently told the Greater Sudbury Chamber of Commerce, Strong says: “As  Sudbury’s largest private employer and mining company, Vale plays a large part in ensuring the community continues to thrive and prosper and we’re working to implement new and innovative solutions that will create the next generation of sustainable mining.”

Strong admitted that spending $1 billion on a project that “will not result in any new nickel” is a lot of money to spend on a project, “but it’s the right thing to do.”

He said that some may argue the AER Project is being driven solely by government regulations, Vale is actually going beyond compliance at the conclusion of the Project, down to 20 kilotonnes of SO(2) per year versus the regulatory limit of 66 kilotonnes per year.

Proudly, Strong repeats what was mentioned earlier, “that represents and an 85 per cent  reduction from today’s rates and significantly cleaner air for our community.”

To further explain about the work that will be undertaken during the complete retrofit of the converter aisle, Strong says: “Sulphur dioxide that currently goes up the super stack from our existing converters will be sent to our acid plant, converted to sulphuric acid, and sold.”

“A tremendous amount of work has already been completed on this project. With the help of a local company, we’ve successfully installed our first new converter and it’s operating exactly as planned in terms of gas capture and increased efficiencies. Detailed engineering is currently underway on the next converter replacement and fabrication of the new vessel is on track.”

Strong continued by saying: “Engineering is also underway on a new state-of-the-art secondary bag house, which is essentially like a giant vacuum cleaner to capture dust and emissions. It will be about the size of an NHL hockey rink and one of the biggest of its kind in North America.”

“Given the tremendous reduction in emissions and change in the processes, Vale is working to figure out if it should continue to use the 338m super stack, or build something smaller that would operate more efficiently by using less natural gas to heat and maintain than the super stack?”

That’s a question Vale is working on now but should the answer be “go smaller,” then the next question around Sudbury will be: “What’s going to happen to the landmark Super Stack. Will it come down.?”

For the sake of notoriety, you can bet the “Big Nickel” hopes so.