Eco-efficient practice(8)-Waste can be turned into heat energy

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In Gothenburg, second biggest city in Sweden, 30 percent of district heating and 5 percent of electricity come from waste incineration in Renova’s waste co-generation plant, according to the 12 examples of eco-efficient economy in Sweden

The waste comes from households and businesses in Western Sweden. In the economic downturn spare capacity has arisen, creating opportunities to deal with waste that would otherwise have gone to landfill. Efficient energy recovery means a sharp reduction in greenhouse gas emissions.

Renova Company is the leading environmental company in Western Sweden in the waste and
recycling industry. Renova has several plants. In 2008 they treated nearly 700 000 tons of waste, of which 450 000 tons went for incineration with energy recovery. The company is currently expanding its waste co-generation plant with the addition of a fourth incineration line.

The amount of waste is directly affected by the trends in society, and has increased by an average of 2-3 percent every year since 1900. The amount of waste falls sharply during the prevailing economic downturn, but rises again as soon as the economy picks up. Construction of the fourth boiler will safeguard waste management and environmentally friendly energy production in Western Sweden for the future.

Large investment

With an investment of over 600 million Swedish Kronor(nearly 90 million dollars), the fourth incineration line which includes complete equipment for flue-gas treatment, an important process for eliminating dioxin, is expected to be completed in 2010.

Renova is making further investments of around 100 million(about 15 million dollars) annually to ensure that the plant contains the best equipment for environment. The focus right now is on removing sulphur from the flue gases even more effectively in the existing plant.

Energy equivalent to a supertanker every year

The waste burnt at Renova provides electricity equivalent to the annual consumption of 60 000 apartments, as well as heating and hot water for 120 000 apartments. The plant contributes energy which is equivalent to more than 120 000 tons of oil per year. This helps avoid large quantity of emissions of greenhouse gas.

Sweden’s northwestern neighbor, Norway, now buys incineration capacity in the Renova plant to deal with waste that would otherwise have gone to landfill.

How the process takes place

When the waste is burnt in one of the furnaces, the energy released from the waste, is converted to steam in the steam boilers. Then the steam goes to the steam turbine, which drives a generator where electricity is produced. Thermal energy is harnessed in the condenser after the turbine and supplied to the district heating network. Using flue gas condensation and absorption heat pumps, the heat in the flue gases can also be extracted-this too is supplied to the district heating network.

Each ton of waste burned can obtain a total of 3,3 MWh in the form of electricity and district heating. That is the amount consumed in heating a fairly large detached house for two months. A total of 1,3 TWh of energy can be delivered by the plants every year.

Three stage treatment

The flue gases are treated in three stages. First the dust-borne particles are separated in an electric filter. The acidic gases are then scrubbed and condensed in a wet treatment stage to remove further dust particles and acidic gases.

The third stage is a fabric filter that removes almost all dioxin and additionally ensures that the sulphur levels are reduced from 200 mg/cubic meter to less than 50 mg/cubic meter. A fourth stage in the process – catalyst treatment – is now being built, alongside the new incineration line.

The net result is that Renova’s waste co-generation plant easily meets present and future EU requirements for treatment.

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