Düdingen has a population of around 8,000. Since autumn 2015, the municipality in the Sense District, canton of Fribourg, has been bringing a new district heating network into operation in stages. One year on, all the municipal buildings and around 180 households have been connected to the system. The combined heat and power system is operated by the Western Swiss energy supply company Celsius Groupe E.
Decentralised heat and electricity production
The heating network in Düdingen has a central energy system that is unique worldwide: as well as a standard wood-burning furnace, a Schmid AG hot-air turbine has been installed that produces electricity as well as heat. The power plant closes a gap in the market, as in this size class, the supply of decentralised heating and power using the native, CO2-neutral energy source of wood was to date only possible using gasification that requires substantial preparation of the fuel and high technical capabilities on the part of the operators. The energy plant used in Düdingen is suited to the supply of heating networks serving typically around 180 households, and the electricity produced can supply the requirements of around 250 households. Plants of this kind can make a contribution towards the implementation of the Federal Council’s Energy Strategy 2050, which has led the Swiss Federal Office of Energy (SFOE) to support the wood-fired power plant as a showcase Project.
Innovative hot-air turbines
Schmid AG, who have specialised in biomass heating systems for 80 years, spent seven years developing the power plant together with various partners. The hot-air turbine consists of a standard grate-fired furnace for a wide range of unprocessed fuels. The wood furnace is fitted with an air-exhaust gas heat exchanger, and the air heated here is discharged via two turbines that produce electricity. The excess warmth is then diverted off to an air-water heat exchanger.
“One of the major advantages of the hot-air turbine compared to conventional combined heat and power systems for timber biomasses (e.g. steam turbines, ORC plants, wood gasifiers) is that we are working with a very low-risk medium, hot air,” says Philipp Lüscher CEO of Schmid AG. “Unlike systems that are operated with superheated steam or thermal oil, the risk of accidents is kept to a minimum. Hot air as a medium also allows for simpler system technology and therefore low maintenance costs. Another substantial plus compared with carburettor systems is the use of unprocessed small-diameter wood, which can be used with a moisture content of up to 55%, without any pretreatment. This has a considerable positive effect on the fuel costs of heating plants of this kind.”
Use in Switzerland and abroad
The example of Schmid AG shows how Swiss SMEs can prove their competitiveness with their cleantech innovations.
A wood-fired heating plant with hot-air turbines can achieve an excellent overall efficiency level of 77%. The use of the latest electrostatic precipitators reduces the impact on the environment from dust pollution to a minimum.
Philipp Lüscher is aware of many locations in Switzerland that would be ideal for the installation of a hot-air turbine. This cleantech innovation from the Swiss family firm has also attracted considerable interest from countries such as Austria, Italy and Japan, and the export promotion organisation Switzerland Global Enterprise (S-GE) has supported Schmid AG in entering the North American market and their development of the hot-air turbines.