“Every time we consume 100 units of energy, we send back 260”.
For the past six months alone, wastewater treatment plant Lynetten in Copenhagen has produced record amounts of energy from wastewater. At the same time, the plant has reduced its energy consumption.
One of the areas where energy consumption has been reduced is in connection with stirring and oxidisation of the water. A novel discovery cut energy consumption in half by blowing in air from the tubes that lie at the bottom of the reservoirs.
However, the most important change is found in terms of energy production. Based on the sludge separation in connection with treatment of the wastewater, more than 3 million cubic meters of biogas has been produced for the Copenhagen city gas net during the first six months of 2016. This covers approximately 1/3 of consumption in Copenhagen. At the same time, the dry sludge is incinerated in Lynetten’s own incineration plant, which has produced 18,740 MWh of district heating, also during the first six months of this year.
A fluid-bed incinerator has been installed together with a modern flue gas cleaning system at Lynetten. Furthermore, a flue gas condensation step has been added. Thereby, the process of sludge disposal has been turned from an energy consuming to an energy producing process. There is much more surplus heat available to the district heating system and there is a lot of biogas available.
The main part of the high temperature heat from the boiler is first used for pre-drying of sludge and the rest of it, plus the energy from the condensation, is used for district heating. The additional surplus heat capacity is used in the local low temperature district heating network.
Detailed analysis showed that the best solution for the whole society was be to clean the surplus biogas and use it directly to produce city gas, which today is produced by mixing natural gas with air.
Source: State of Green (Energy Supply, Danish newspaper Politiken and Ramboll)