Waste heat recovery from waste water
In order to increase the share of renewable energy production in existing district heating systems (DH systems), alternative heat sources must be integrated and new technical concepts developed (Lund, H., (2014)). Especially for low-temperature systems and urban development areas, the decentralised use of the heat energy contained in waste water represents a new and innovative form of heat recovery.
In 2021, a pilot plant for waste heat recovery from wastewater will therefore be realised in Vienna’s 23rd district near the “Liesing” railway station, which will regularly feed into a secondary district heating network from 2022. The technical concept of the pilot plant is based on the discharge of wastewater from the main sewer (heat source) and heat removal through heat exchangers at a low-temperature level (8-20°C). In a further step, heat pumps are used to increase the temperature. The concept is specifically designed to integrate waste heat from sewers with a minimum flow rate of 15 litres/sec into district heating systems with flow temperatures between 70 and 90°C. The pilot plant and the sewer are connected to a heat pump.
The pilot plant and the duct will be characterised by the following technical parameters:
- Waste water flow between 15 and 160 litres/sec,
- two heat pump systems with a total heat output of approx. 1.3 MWth.
The functionality of the pilot plant will be tested for more than 6 months under different operating conditions, taking into account aspects of sector coupling. Based on the performance of the plant (e.g. efficiency of heat pumps and heat exchangers) and the resulting operating costs, a technical and economic guideline for the optimised planning, realisation and operation of such plants will be developed.
Contribution picture: External heat exchanger outside the canal, for mechanically treated wastewater, in the immediate vicinity of the heat pump/energy centre (source: Fa. Rabmer Greentech GmbH, technology partner Thermowatt), common from 500 kW capacity upwards.