The sludge from the treatment process is digested anaerobically (without oxygen). This produces a source of renewable energy, biogas, with a methane content of about 60 per cent. The energy content of digested biogas is approximately 6.42 kWh/Nm3. Although the treatment plant’s gas engines are capable of running on biogas, it is better for operational reliability to first scrub the gas with active carbon filters. For example, the filters can remove silicone left over from cosmetics.
The plant operator Helsinki Region Environmental Services HSY is part of the City of Helsinki Climate Partners network. HSY is a joint municipal authority, and it aims to reach carbon neutrality by 2030. The production of renewable energy plays an important role in achieving this goal.
Gas engines turn biogas into power and heat
Sarlin has delivered to Viikinmäki three TCG 2020 V16 biogas engines and one V12 biogas engine, the gas scrubbing system, and two ORC systems that convert the heat energy of the engine exhaust into electricity. The ORC systems produced 1.32 GWh of electricity in 2018. Gas is stored in a local 4,000 m3 container to ensure a steady gas supply for the engines. The gas supply is controlled by automation.
In 2018, almost 15 million cubic metres of biogas was produced, of which 14 million cubic metres was used by the gas engines and the rest to fire boilers. Flaring was only required in exceptional situations where excess gas was produced during maintenance.
“The CHP station of the HSY Viikinmäki water treatment plant is exemplary,” says Vesa Saarinen, Product Manager at Sarlin. The station is highly efficient in converting biogas into energy. The station performs well, and its energy production is profitable. “The current production figures are a fantastic performance by the Viikinmäki power station team. At HSY, the TCG engines have an extremely high utilisation rate, further supported by the ORC systems.”
