McCain Foods Ltd., the multinational food processing company based in Florenceville, N.B., tapped into a new energy source this spring, when it began construction of a new biogas digester for its Whittlesey french fry factory in Britain.
"There's a significant market for biogas, but it must be cleaned,"says Dr. James Smith, a former professor and chair of the department of chemical engineering and applied chemistry at the University of Toronto. "The big drawback is hydrogen sulphide. It's always in biogas, even landfill gas, though it's lower."
Dr. Smith co-invented a system to remove the toxic substance from biogas when he was a professor. Today he works part-time as a senior technical adviser with Eco-Tec Inc., a company based in Pickering, Ont., which markets Dr. Smith's invention. One of these systems operates at the McCain facility in Whittlesey, Cambridgeshire, in Britain.
Wastewater from the potato chip plant is pumped into a lagoon, where bacteria feed on the starch in the water and put out about 300 cubic feet of biogas a minute. The company burns this to run a turbine that produces 1.2 megawatts of electricity - about one-tenth of the energy the plant uses. The gas produced contains about 3000 parts per million hydrogen sulphide but the scrubbing system reduces it to 5-10 ppm before it gets burned.
Dr. Smith's invention is a big step forward for biogas production. Traditional systems for cleaning biogas have had a high operating cost per pound of sulphur removed. The new system is best suited to large, highly contaminated gas sources and removes sulphur at a cost of about 25 cents a pound, Dr. Smith said.
