The Regional Municipality of Ottawa-Carleton, Ontario, has invested $4.5 million in the construction of a cogeneration facility at its Robert O. Pickard Environmental Centre (ROPEC). The cogeneration facility will save Ottawa-Carleton taxpayers $650,000 annually. The cost of building and commissioning the plant will be paid off in less than seven years.

Cogeneration is the conversion of energy in one form (burning fuel) into energy in two forms (electricity and heat). Methane is burned to produce both electricity and heat (hence the name cogeneration).

The cogeneration facility burns digester gas in three combustion engine/generators. The digester gas serves as fuel for the engines that drive the generators, producing the electricity. Each unit has a maximum electrical generation capacity of 810 kilowatts; the cogeneration facility can produce up to 2,430 kilowatts, or 2.43 megawatts. Electricity generated is used to power the aeration blowers and centrifuges, substantially reducing the quantity of electricity supplied by Gloucester Hydro. The facility uses as much digester gas as possible, up to 27,000 m³/day, to maximize electricity production.

Heat generated from the engines is utilized and transferred to the plant-wide heating system. Heat is captured from the engines in two ways:

• Each engine is cooled by circulating coolant through cavities in the engine body. Excess heat from the combustion of digester gas raises the coolant temperature to approximately 120°C. The coolant flows to a heat exchanger where the heat is transferred to the plant heating system.
• The exhaust gas which leaves the engine at about 450°C, runs through a heat exchanger (boiler) where it is cooled to about 150°C. The heat is transferred to the plant heating system.

The exhaust gas leaves the building through "mufflers" located on an outside platform and is vented to the atmosphere. The hot water goes into the plant heating system at between 85 and 95°C. The heat generated fulfills all plant needs during the summer; any excess heat is sent to the sewer system as hot water. In the winter months, boilers are used as needed.

About 37% of the available energy in the digester gas is converted to electricity, and 48% to thermal energy. This could provide power for an entire year to over 1,000 homes.

The engine/generator control system is connected to ROPEC's computerized Supervisory Control and Data Acquisition (SCADA) system; this allows plant operators to monitor and control the operations of the cogeneration system from the control centre.

In 1996, ROPEC spent $2.7 million to purchase electricity. The cogeneration plant is expected to save $900,000 per year on electricity purchases.