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Viessmann biogas purification technology helps to make CNG fuel from sewage

Schmack Carbotech, part of the Viessmann Group, has been awarded a contract to provide a gas upgrading plant at one of the world's largest underground wastewater treatment plants.

Through a process of purification, the facility will produce around 180 million kWh of natural gas quality biomethane annually from the metropolitan area of Stockholm's sewage, covering up to 40% of its annual compressed natural gas (CNG) fuel needs.

The Henriksdal plant, owned by municipal water, wastewater and waste management company Stockholm Vatten AB, currently treats wastewater from around 1 million inhabitants, extracting biogas from sewage sludge. This will now be purified and upgraded to natural gas quality using the pressure swing adsorption (PSA) process. This method of gas upgrading is characterised by low power consumption, efficient heat extraction and a high methane yield.

The company built a similar plant for upgrading biogas from organic waste in Sofielund, Stockholm earlier this year.

The facility has a capacity to upgrade 3,000m³/h of raw biogas. The gas that is produced has a methane content of 97% after purification and is used as biofuel in natural gas vehicles. The need for CNG in Sweden is comparatively high, as 60% of public buses already use fuel from renewable energy sources such as biogas, bioethanol or biodiesel.

The demand for and acceptance of environmentally friendly technologies is high in Sweden: 40% of newly registered cars are powered by biogas or electricity. By using biofuels in its public transport system, Stockholm saves 130,000 tonnes of environmentally harmful CO2 per year.

The Carbotech plants in Sofielund and Henriksdal will enable almost 17% of Sweden's natural gas vehicles to run on climate-neutral fuel in the future.