Biomass combustion improves Trollhättan air quality, case study

District heating is the most common method for heating buildings in Sweden. Approximately half of the buildings in Sweden have district heating, including the city of Trollhättan. The motto of the community is "Trollhättan – the supporter of good environment". In the past, Trollhättan has won two national awards for its clean environment, and has also received the King Carl XVI Gustaf Environmental Prize, which is given annually to the most environmentally friendly municipalities in Sweden.

The history of Trollhättan Energi, the municipal energy company, dates back over a century. Over the years, the company has expanded into several new business areas and has developed into "the city's new environmental company". Today, it is responsible for the municipal power grid, district heating network, water and sewage, as well as for the fiber optic network for TV, telephone and broadband. It also sells district heat, water and biogas.

"Our goal is to produce heat as environmentally friendly as possible with current technology and to work towards a sustainable society," says Magnus Blomster, Operations Manager, District Heat, at Trollhättan Energi. "Environmental awareness is a theme that runs throughout the company. In addition to our low prices, it is the biggest argument that makes customers choose district heating as their primary heating. This also applies to industrial customers who increasingly see us as the most stable producer of heating as oil prices keep rising."

Much cleaner air

Thanks to replacing fossil fuels with biomass in district heating, Trollhättan Energi has contributed to improving air quality in the community. The emissions have been reduced by tens of thousands of metric tons of carbon dioxide a year.

In 2011, the Lextorp CHP plant produced a total of 147 GWh of heat and electricity. It is in operation 11 months per year with a two week scheduled shutdown in May and September. According to the company, replacing half of such production with fossil fuel would correspond to about 26,000 tons of CO₂.

Sustainable energy production

Trollhättan Energi has three heating plants. Lextorp CHP is the most recent one, and started to generate heat for the district heating network in the end of 2005 and electricity in early 2006. Valmet supplied Lextorp with Biopower 5 DH modularized biomass power plant providing the plant with solutions for sustainable energy production.

The plant has a power output of 3.6 MWe and a thermal output of 17 MWth, the latter comprising 12.5 MWth generated by back-pressure steam from the turbine and 4.5 MWth by a flue gas condenser.

The biomass-fired Lextorp plant has minimal environmental impact. It incorporates the patented BioGrate combustion technology to burn biofuels with high combustion efficiency and low NO_x and CO₂ emissions. The grate – the heart of a biomass-fired power plant – squeezes out all the biomass fuel's energy, even from very wet fuels.

The fuel at Lextorp is a mixture of bark, sawdust and forest residues, all representing a renewable energy source. It is acquired locally, within a radius of about 100 kilometers around the plant. Fuel consumption is about 22 m³ per hour or about 530 m³ per day.

Replacing about 35,000 m³ of heavy fuel oil

The biomass-fueled plant has strengthened the company's goal of delivering environmental benefits. Approximately 95% of the district heating in Trollhättan is derived from biomass fuel. According to the company's calculations, it would need about 35,000 m³ of oil per year to produce the same amount of district heat that the company now produces with wood-based biomass. Oil is now only used in special cases as a reserve fuel during the coldest seasons.

"The investment in the biomass-fired CHP plant has made us less dependent on oil. Using local biomass fuel instead of burning fossil fuels has also led to savings," Blomster comments. "Looking only at the costs of fuel, they have been reduced by 70%. We are aware of the fact that a cogeneration plant of this size requires more maintenance than an equivalent oil-fired boiler. But even so, the plant has paid itself back in 3-4 years through lower fuel costs and an increased production of electricity." But even so, after the fourth year of operation we will already make the return on investment through lower fuel costs and increased electricity production.

"Our future challenges include maintaining the low rates we have on district heat and continuing our efforts to keep fuel prices at current levels. Due to the TPA (Third Party Access) right, we will need to continue to work hard to deliver a competitive, environmentally friendly product at a low price. Customer satisfaction and delivery reliability are a must," Magnus concludes.

For more information about reducing or replacing fossil fuels with biomass, contact your Valmet Power representative.