Unfortunately, ADG has low heat content and is difficult to use as an energy source. Furthermore, much of the gas is not used in this process and must be flared before being released into the atmosphere. Flaring is a relatively clean form of combustion, but Portland realized that it also wasted a potential energy source. In 1993, the City of Portland began looking for an alternative to traditional flaring one which would be cleaner and more environmentally responsible. In 1995, a feasibility study was completed and it was determined that city s best option for utilizing surplus ADG was a fuel cell.
Fuel cells use hydrogen in a chemical reaction that produces electricity, water and waste heat.
In this case, the source of fuel was biogas a renewable and naturally produced fuel that would be available free of charge. In July 1999, Portland began successfully using its ADG fuel cell. The electrical output of the fuel cell is estimated at 1.3 million kilowatt-hours enough electricity to fuel more than 100 homes for an entire year. Carbon dioxide emissions will be reduced by 695 tons annually because traditional fossil fuel-based energy will no longer be required. Over the life of the fuel cell 14,000 tons of CO 2 will be offset.