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From problem to resource

Green advisor

From problem to prominence as a resource

Every day some 1.3 million tonnes of waste are generated by human activity around the world. Almost every town and city offers residents waste management and storage services, but relentlessly rising amounts of waste are having an ever greater impact on the environment. Fortunately, new technical solutions are helping to create more sustainable waste management systems by turning non-recyclable materials into a valuable energy resource.

Important political issue

Today the waste-to-energy industry, which generates electricity and heat by incinerating waste, is expanding all over the world. Burning one tonne of waste in this way has the potential to generate up to 800 kilowatt hours of electricity and 2,200 kilowatt hours of heat. Waste management has become an important political issue and the focus of legislation initiatives both in the Nordic countries and at EU level. Strong forces are at work to reduce landfill waste in Europe, for example by outlawing the disposal of unsorted combustible refuse and organic materials in landfills.

Jakob Sahlén, Energy Recycling Advisor for Avfall Sverige, the industry organisation for Sweden’s waste management and recycling sectors, is in no doubt about the benefits to society of waste-to-energy plants that produce electricity and heat:

“Some of the waste burned in these plants is so called source-sorted waste from homes and industry. This is waste that it has not been possible to recycle, either because of people’s unwillingness to do so, or the way local waste collection systems are designed. These plants also incinerate and destroy waste containing hazardous or undesirable substances that we do not want to see returned to the production chain. These, too, are converted into an important energy resource.”

ÅF assignment in Finland

The Finnish company Tammervoima Oy has awarded ÅF an engineering, procurement, and construction management (EPCM) contract in connection with the new Tarastenjärvi waste-to-energy cogeneration plant planned for Tampere, Finland. “The EPCM contract means ÅF is responsible for everything from technical project planning and procurement services to construction and site operation,” explains Peter Kling, an ÅF Section Manager with experience of EPCM work.

The plant will receive 150,000 tonnes of municipal waste a year and generate 310 GWh of district heat and 90 GWh of electricity for the surrounding region. Landfill gas from the existing waste treatment facility in Tarastenjärvi will be led through a new pipeline to be used in the combustion process. The plant will be the first in Finland to use environmentally harmful methane gas in this way, as a complementary fuel in energy production.

According to Tammervoima Oy, reasons for choosing ÅF included ÅFs experience with similar projects. “ÅF made us a cost-effective offer and had excellent references within the waste-to-energy area. It was important for us to choose a company that had experience with similar projects,” says Mika Pekkinen from Tammervoima Oy.

From waste to electricity and district heating

How does the waste-to-energy process in Tampere actually work? The waste is brought by road to the plant and deposited in a 9,000 cubic-metre bunker – big enough to receive 70-90 full lorry loads a day.

From there it is transported to the cogeneration plant’s grate furnace. Here, at temperatures in excess of 1,000°C, all the combustible waste is incinerated, leaving non-combustible fractions such as metals to be collected for subsequent processing and recycling.

Not even the heat from the flue gas generated during the incineration process is wasted. Instead, the gas is used to turn water in the pipes into superheated steam, which is then led to a steam turbine that drives an electric generator. Even after passing through the turbine, the steam still contains a lot of heat; this can be transferred to the district heating network via heat exchangers.

After all the energy has been extracted from the waste, various processes are used to clean the flue gases. In the last step of the flue gas treatment the flue gases are condensed and heat is extracted to be used as additional district heating. The condensate water is not released as wastewater, but is re-used in the plant’s own internal processes.

Reduced environmental impact

Work on the Tarastenjärvi plant will be complete by the end of 2015. From 2016 onwards the region’s waste need no longer go to landfill, but can be used to supply local residents with electricity and district heat. “Finland’s historical reliance on landfills means that the need for waste-to-energy plants in the country is particularly important. And waste incineration also reduces Finland’s dependence on fossil fuels,” Jakob Sahlén concludes.

Waste – a historical challenge

Dealing with waste has always been a headache for cities. In the 1800s waste management was a haphazard affair; all manner of garbage was simply dumped in streets, rivers and streams. The march of industrialisation and the surge in urban populations precipitated huge problems for health and hygiene – and led to an urgent need for society to devise measures to meet the challenge.

By the early 1900s the concept of recycling had begun to gain ground. Waste was sorted into fractions and re-used as road fill, manure or in new products. However, a few decades later, as stricter controls came into force, it was felt that incineration or landfill provided better solutions for disposing of the waste generated by new patterns of consumption.

A new idea – from waste to energy

By the late 1970s and 1980s the negative impact of waste on the environment was becoming obvious. Waste decomposing in the landfills posed a particular problem, not least in the form of methane gas that contributed to an accelerating greenhouse effect. As a result of the 1970s oil crisis, attention once again turned to the potential of waste as an important resource and a domestic alternative to oil. This coincided with an expansion of district heating networks as an alternative to individual heating systems.  

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