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DeVex 15.20 steam expansion engine
New type of ORC expansion machine under development

Electricity from unused waste heat

With a new technology, the efficient use of waste heat flows at temperatures between 200 and 500 degrees Celsius for electricity generation could in future be far more common than has previously been the case. With the support of the German Federal Ministry of Economics and Technology, DEVETEC GmbH is developing a system which can be extended in a modular fashion. As with conventional ORC power plants, the working media are organic fluids with a low boiling point. However, unlike in these plants, newly developed expansion machines are used instead of turbines or screw-type engines. A pilot system is already being tested in a Saarland power plant, in combination with a coalmine gas engine.

This steam expansion engine's distinguishing feature is that with its system and engine concept, it can be used for different temperature ranges and different ORC media. Due to the relative simplicity of the system technology, it requires significantly fewer components than the existing solutions on the market. Thus, an ORC system can be made more cheaply, new market segments and areas of application can be opened up and economically profitable systems can be operated. The team of developers also promise high efficiency. "Depending on the process temperature, an efficiency of up to 20% can be achieved," explains Joachim Meyer, CEO of DEVETEC GmbH. The output of the individual modules is between 100 and 200 kW. The application concept envisages combining individual modules to obtain the required output.

Low-temperature heat flows are plentiful, e.g. from CHP plants, hardening plants, foundries, paper production, industrial bakeries or steel refinement. Geothermal and solar thermal energy also provide heat sources which can be used for electricity generation once suitable temperatures are reached. Increasingly, these heat flows are being used in heating networks. However, there is often a lack of adequate infrastructure and in summer there are often too few consumers. In the worst case scenario, the waste heat is actively eliminated, e.g. via cooling towers.


Until this technology is ready for mass production, a number of developmental steps still need to be taken. This further development is to draw on experience gathered with prototypes and from pilot system tests, in order to obtain products which can be mass-produced. The project team aims to complete research work by the end of 2013. "The machines should be available as modular systems for different performance classes," says Meyer. "Due to the low module costs and overall efficiency which is more than 60% higher than that of comparable turbine solutions, we expect payback times of four to five years." According to Meyer, the target market for the ORC expansion machine encompasses energy contracting companies and manufacturers of biogas, landfill gas and coalmine gas systems, as well as other alternative energy generation systems and energy-intensive industrial companies.

Background: ORC power plants

Essentially, the principle of an ORC process resembles that of a conventional steam power plant:

A heat source evaporates a medium, thus producing steam pressure which performs work in a displacement machine. The steam, which is thus depressurised, is liquefied in a condenser and, by means of a feed pump, fed back to the heat exchanger, which then transfers the heat source's thermal energy to the fluid once more.

One decisive difference with regard to conventional power plants is that instead of water, an organic fluid (e.g. ethanol) with a very low evaporating temperature is used. Thus, it is currently possible to make efficient use of heat flows from around 100 °C.


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