Pellet-Fueled District Heating Systems
Boras Energi
Boras Energi's small, district heating plant in Sandared used three oil-fired boilers in the early 1990s, two of 1300-kW capacity and one of 800-kW. Design load was approximately 3000 kW at -20oC. After investigating biomass fuels, the company selected pellets because of their high-energy density and ease of handling on a small site. One of the 1300-kW boilers was replaced with a 1750-kW, pellet-fueled boiler that meets about 80% of the annual energy requirements, or about 7,700 MWh. The older oil units were also upgraded. As of 2001, three large institutional customers and 41 houses of varying size purchased heat from the plant, with more users anticipated.
Pellet fuel is delivered to the plant by truck every 4-6 days in the winter and every14 days in the summer. Transportation energy is saved because small, frequent oil deliveries have been displaced. Sulfur emissions have been reduced by approximately 600 kgs per year and nitrogen oxide by two-thirds to 1,250 kg per year; and 1400 tons of fossil fuel-derived carbon dioxide emissions have been avoided.
Boras Energi district heating plant pellet storage bins and stack.
Boras Energi district heating plant pellet storage bins and stack.
The oil boiler retrofitted to burn pellets.
The pellet delivery auger and pellet burner at the front of the boiler.
Boras Energi pellet-fueled boiler.
Combustion air delivery.
Overhead auger bringing pellets from storage bin to burner.
Header connecting twin storage bins to auger.
Automated ash removal system.
Circulating pumps.
Boras Energi district heating system plan.
Nearby school buildings heated by the Boras Energi plant.
Cogenerating Pellet-Fueled District Heating Systems
Combined Heat and Power: The Hasselby Power Plant
The Hasselby Power Plant, owned by Fortum Power and Heat AB, is located on the shore of Lake Malaren and provides heat and power for northwestern suburbs of the Stockholm area. This was the first of Stockholm Energi's district heat-production plants to be inaugurated in 1959. During the first decades, the plant was fuelled with oil, but between 1983 and 1993 coal was used.
The plant now operates three, 100-MW boilers, fueled almost entirely with pellets delivered by ship from mills in Sweden's northern forest products industry. It was the first biomass-fired, co-generation power plant in the Stockholm area.
The Hasselby Power Plant.
The Hasselby Power Plant.
The quay where pellets arrive by ship from northern Sweden.
Pellets are stored in large indoor bunkers.
Pellet storage bunker.
A large screw moves pellets from the bunker to a conveyor (shown above in empty bunker).
The screw dumps the pellets onto a conveyor belt.
The conveyor moves the pellets to the grinding mills.
Pellets are pulverized in these grinders, much like coal.
Hasselby coal boilers, retrofitted to burn pulverized wood pellets.
Dual-fuel burner.
Turbine deck of the power house.
Turbine deck of the power house.