In the city of Zurich, waste heat from waste incineration has been used to supply district heating networks for over 100 years.
The expansion of the Hagenholz waste incineration plant is set to provide more than twice as much usable thermal energy for district heating networks.
The ability to heat significantly more buildings with climate-friendly district heating will save some 44,000 additional tonnes of CO₂ every year.
Hagenholz, in the north of Zurich, is one of the largest waste incineration plants in Switzerland. Every year, it recovers around 240,000 tonnes of combustible waste that cannot be recycled. This equates to around 48 million 35-litre rubbish bags. The waste incineration plant currently operates two ‘incineration lines’. These are technical installations in which the waste is recovered and incinerated in several stages.
Due to population growth and a construction boom, the canton of Zurich is not expecting the volume of waste to decline, despite efforts to prevent waste. To ensure safe and environmentally friendly disposal, the city of Zurich is expanding the Hagenholz waste incineration plant. In September 2023, the electorate approved the corresponding loan with 90 per cent of votes in favour. The waste incineration plant is set to receive a third incineration line. This will enable it to increase its capacity by 50 per cent to 360,000 tonnes per year, ensuring it is well placed to process the volumes of waste generated efficiently in the long term, too.
Waste incineration produces heat. To ensure that this does not simply go up in smoke, it has been used in the city of Zurich to heat buildings and produce electricity since the 1920s. The first district heating network was built around the former Josefstrasse waste incineration plant in what used to be the industrial district in the heart of Zurich. The waste heat from the Hagenholz waste incineration plant has been supplying the city of Zurich’s other district heating networks, which are now operated by ewz, since it opened in 1969. It is an important energy source because it generates climate-friendly heat evenly. In addition to the construction of the third incineration line, the thermal output of the existing lines will also be increased. For this purpose, heat pumps will extract additional heat from the flue gas produced during combustion. Increasing the incineration capacity by 50 per cent will double the heat output.
44,000 tonnes of CO₂ saved
ewz will make good use of the additional waste heat. The analysis revealed that the district heating network can be consolidated with additional connections in the existing network area. At the same time, the third incineration line will allow the expansion of existing networks and the construction of new ones. “This will enable us to connect even more buildings in the city of Zurich to the district heating network,” says Philipp Brunner, Project Manager for Thermal Networks Strategy at ewz. “This will benefit the climate, as district heating is much more environmentally friendly than the oil and gas heating systems that are still installed in many places today.” According to ewz, expanding the district heating network will save some 44,000 additional tonnes of CO₂ per year – roughly equivalent to the emissions caused by 20,000 people flying from Zurich to New York and back.
Secure supply thanks to heat storage
The additional thermal energy from the Hagenholz waste incineration plant will allow more neighbourhoods to be connected to the district heating network in the future. The district heating areas of Zurich Centre, Zurich West and Zurich South have been connected since the commissioning of the district heating transmission line from the Hagenholz plant via Strickhof and the Milchbucktunnel under the Limmat River to the Josefstrasse energy centre. Another transmission line will go out to Wiedikon. What’s more, the district heating network will receive a large new heat storage facility, probably on the premises of the Hagenholz waste incineration plant. With a volume of 10,000 cubic metres – roughly equivalent to the capacity of sixteen 25-metre swimming pools – it will be five times larger than the storage capacity currently available in the district heating network. This will allow even more excess thermal energy to be stored temporarily and made available when consumption is particularly high.
The existing bunker will be extended by approx. 45 m to the south. The buildings marked in red are to be added to the Hagenholz waste incineration plant. The third line furnace and boiler can be installed in the existing incineration building. For the necessary connections, electrical rooms and ancillary spaces, a service wing will be added to the incineration building to the north, to go with the existing wing on the south side. The third line flue gas cleaning facility will not fit inside the existing building, which is why the building needs to be extended to the west.
Construction began in 2024 and is expected to be completed by 2027. “We are aiming to light the first furnace in the new incineration line in November 2026,” says Philipp Brunner. “The full heat output from the three incineration lines and flue gas heat recovery should be available one year after that.” This will enable the Hagenholz waste incineration plant to continue to recover waste from the Zurich region in a climate-friendly manner and at the same time contribute to the city’s net-zero target, which envisages carbon-free heat supply by 2040.
Further information on the project status and the net-zero target can be found in the brochure (in German).
The recovery or incineration of waste produces CO₂. However, according to current Swiss legislation, waste heat from waste incineration plants is considered climate-friendly if waste incineration is unavoidable due to current technological limitations. This is justified by the fact that this method reduces the demand for energy – especially that from fossil sources, which generate even more CO₂. In the medium and long term, the aim is also to capture and store CO₂ for the long term. The federal government has imposed an obligation on waste incineration plant operators to commission at least one plant that allows this carbon capture by 2030. The intention behind this is to encourage the necessary technical development.
