June 01, 2002
Facilities Designed to Divert Wastes from Landfill Benefit from Corrosion Resistance
The largest stainless steel building in North America came close to never being built, at least from stainless steel.
When the city of Edmonton, Alberta, decided it needed a facility to transform 200,000 tonnes of municipal solid waste and biosolids into compost each year, planners envisioned a conventional carbon steel-frame building to house the sprawling aeration bays. The interior and structural elements would be epoxy-coated, to ward off corrosion from gases produced during composting.
But Behlen Industries, Canada's largest manufacturer and supplier of pre-engineered metal buildings systems, had a better idea. "To address the corrosion issue, we proposed another metal building system, which is roll-formed out of stainless steel and is frameless," says Scott Timms, Behlen's director of sales and marketing. The system was also close to $1 million less expensive than epoxy-coated steel.
The $100-million Edmonton Composting Facility, which opened in March 2000, boasts three aeration halls covering 23,000 square metres (almost 2.5 hectares) enclosed by walls and ceiling made of corrugated S30400 stainless steel. It was the first time Behlen incorporated stainless in its frameless design, which is strong enough to span the aeration bays using only two sets of columns as additional roof support.
"If you took a piece of paper and folded it like an accordion, you could stand it on end," notes Timms. "That's basically what we do." For the Edmonton project, coils of stainless were roll-formed into four-foot-wide grooved panels, then joined together, like a big Meccano set, with stainless steel bolts. Behlen subsequently used stainless to build a second composting plant, in Prince Edward Island, and has been hired to erect a third, in New York state.
The decision to go with stainless steel is paying off, says the plant's process manager, Scott Gamble. "I've never seen any corrosion or any indication of disrepair. A lot of people in the industry are very envious of us because we have that inner skin." Gamble adds that he recently learned of another composting plant, built of coated steel; it faces a million-dollar bill to repair corrosion.
The temperature inside the aeration hall is a humid 25o to 30oC, and the interior is constantly exposed to steam and minute amounts of ammonia and organic compounds given off during composting. "There are a lot of cumulative effects on a piece of steel that sits in a fog day-in, day-out," says Gamble. "A lot of finishes just were not designed for such conditions."
The Edmonton plant enabled the city of 650,000 to meet the Canadian target of diverting at least half of all waste from landfills by the year 2000. TransAlta Corp., the electrical utility that built and managed it on the city's behalf for its first year of operation, uses about half the 100,000 tonnes of compost produced annually to reclaim land from a strip mine. The remainder is used to improve agricultural land, to control erosion during highway construction, and protect sports fields. Sold to the city in mid-2001, the facility is now managed by Earth Tech (Canada) Ltd.