Keep this number in mind: 30 megawatts.
That’s roughly the peak electrical demand for a city the size of Marion — population 34,768 by the 2010 Census, with slightly more than 15,000 households and no major energy-consuming industry — according to Jim McCalley, Iowa State University professor of electrical and computer engineering.
Marion has contracted with Plasma Power to provide 300 tons of garbage per day to the firm’s first-of-its-kind plasma arc plant. The plant would produce steam. The city is checking into setting up a municipal utility to use that steam to run turbines to create electricity.
Is it feasible? Consultants are currently studying that question for the city.
Lou Circeo, director of plasma research at the Georgia Institute of Technology and a leading authority on plasma-arc technology, said a waste-to-energy plasma-arc plant is in the preliminary stage of construction in the Tees Valley of northeast England.
It is projected to generate 49 megawatts while consuming 950 tons of garbage per day.
A demonstration plant nearing completion near Bordeaux, France, will generate 12 megawatts from 150 tons of garbage a day, Circeo said.
That’s 1 megawatt for every 19.4 tons of trash fuel from the British plant, and 1 megawatt for every 12.5 tons for the French plant.
Marion’s contract to deliver 300 tons of garbage daily to Plasma Power’s plant would be enough to generate 15.5 megawatts in the English plant, or 24 megawatts in France.
In other words:
By those figures, a Marion plant would either be much more efficient than any currently planned, if it is to provide all the city’s power. Or it would require more trash than the 300 tons a day now planned.
A municipal power plant using garbage as fuel, however, wouldn’t necessarily have to meet Marion’s peak demand of 30 megawatts, McCalley noted.
A 30-megawatt plant “would satisfy peak and therefore some capacity would sit idle for much of the year,” McCalley wrote in an email. “An alternative investment would be to let (Alliant Energy) satisfy peak — for a charge of course — and build less than 30 megawatt.”
There is another possibility for a city-owned power plant: Instead of serving individual home and business customers, just supply power wholesale to Alliant, or any other large utility willing to buy it, at a negotiated rate.
In that case, the Iowa Utilities Board would become involved if a municipal utility needed to build a transmission line to the regional grid, or if the purchasing utility was regulated.
Marion residents generate about 25 tons a trash a day, which is collected by the city. Business and industry generates another 75 tons, which is transported by private haulers.
Trash collected by the city goes to the Cedar Rapids/Linn County Solid Waste Agency’s Site 2 landfill on Marion’s northeast edge, which handles about 600 tons of waste daily from Cedar Rapids, Marion and elsewhere.
The waste agency’s board voted last year to direct up to 100 tons a day to the plasma arc plant. Diverting trash means the landfill would receive less money in tipping fees. The diversion also means the landfill wouldn’t fill up as fast.
Waste agency spokesman Joe Horaney declined to comment on Marion’s feasibility study and its potential impact on the area’s waste stream.