Cogeneration Supports Sustainability Goals

This article is an excerpt from the May/June 2011 InTech magazine, “Cogeneration supports sustainability goals” by Ingemar Lidhamn and Marianne Lindeborg.

In the town of Örebro, 124 miles (200 km) to the west of Stockholm, Sweden, the tall chimney of E.ON’s heating and power station is visible from a distance. White grey water vapor often billows out of the chimney from the biggest boiler,wood chip which is fired by bio fuels and heats the water for the district heating network and provides steam for the electrical production.

District heating is a common method of heating for property in Scandinavia. Large boilers in the power station heat hot water, which is pumped around in a submerged pipe network to properties where heat exchangers transfer the heat to the buildings’ own waterborne heating systems. The properties are residential apartment buildings, office buildings, and detached houses, and in Örebro, there is also a historic castle, parts of which date back to the 1300s.

The heating and power station in Örebro has approximately 99% of all the buildings in Örebro connected to its district heating network; the network also extends to some smaller towns and in the Örebro county. Approximately half of the 280,000 inhabitants use district heating from E.ON for heating and hot water.

In a normal year, the heating and power station with three boilers produces approximately 1 TWh (terawatt-hour) of heating. The boilers also provide steam to the turbines, which in turn are connected to generators that produce electricity, typically about 300 GWh (gigawatt-hour) per annum. The largest and most efficient boiler, P5, is fired with bio fuels, such as sawdust, woodchips, bark, and turf, and has an output of 165–170 MW. It has a turbine and generator in common with the oil-fired boiler P4, and together the two have an output of approximately 300 MW heating and 100 MW electricity. In addition, the heating and power station has a hot water boiler of 140 MW, which is only used for peak loads during the coldest days of winter when the temperature can fall to below -22°F (-30°C). In addition to that, the district heating network gets a boost of 35 MW hot water from excess heat at a refuse facility 12 miles (20 km) from Örebro.

Environmental issues are always at the top of the agenda for E.ON’s heating and power station in Örebro. Three old boilers from the 1960s have recently been dismantled, and a new bio fuel fired boiler, P6, is being built in their place, which will reduce the heating and power station’s environmental impact still further. The new 70 MW boiler is fired with bio fuel, even twigs and stumps, and with that in operation, in a couple of years, the heating and power station’s environmental impact will be significantly reduced.

In terms of environmental objectives, among other things E.ON is working with a concept called “Sustainable City,” where focus is on energy, waste, and transport. Together with Örebro, E.ON is planning the city’s sustainable development from a social, economic, and environmental perspective. The city has set high environmental targets, with a reduction of carbon dioxide by 40% per inhabitant for 2020.

The fuel mix of the boilers consists to 20–30% of peat, and the rest is wood chips of various kinds. Samples are taken from the incoming fuels for analysis. Since the fuel is stored outdoor and analysis takes a day to process, the mixing of the various fractions of the fuels are done “by experience” of the driver in a front loader. He determines the quality and moisture content of the fuel and makes a good mix for the boiler that way.

“The new boiler makes a major contribution by replacing the old oil fired boiler. It reduces the CO2 emissions by 84,000 tons per annum, the equivalent of the emissions of 28,000 petrol powered cars. In addition, the transport of the bio fuel will be by rail instead of trucks to a much greater degree. It is part of our collaboration in Örebro city’s environmental objective of being a sustainable city,” said E.ON’s Jonas Vilhelmsson.

E.ON Örebro has approximately 120 employees. It is owned by E.ON Värme Sverige AB, which delivers district heating in 45 networks and operates around 600 boilers in Sweden. E.ON Värme Sverige AB is part of E.ON Nordic, which produces and supplies energy in the form of electricity, gas, heating, cooling, and refuse treatment and energy-related services to the Nordic market. E.ON Nordic is part of the German E.ON group with over 90,000 employees and establishments in Europe, the U.S., and Russia.

Read the full article at InTech magazine.

About the Authors

Ingemar Lidhamn works for ABB (Ingemar.Lidhamn@se.abb.com), and Marianne Lindeborg is a Swedish journalist specializing in the energy industry and heavy industry.

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