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Innovative research project by DEPRAG sends a signal: Generating electricity from small amounts of process gas
New turbine generator is an important component in the fight against climate change
There are a variety of different approaches. Many industrial processes release and waste surplus energy. The recovery of untapped energy potential is therefore a crucial part of the fight against global warming. An ambitious energy recovery research project, which is funded by the German Federal Ministry of Economics and Technology under a resolution by the Deutsche Bundestag (Germany's parliament), is soon to start production at DEPRAG SCHULZ GMBH & CO. Managing Director Dr. Eng. Rolf Pfeiffer explains the underlying concept: "In many industrial processes, process gas escapes unused into the atmosphere. Our basic idea was to tap these gases for the further generation of energy." Energy recovery from process gases, however, is not a new concept. Rolf Pfeiffer: "What is new with our development is that it enables the conversion of even small amounts of residual energy in the range of 5 to 20 kilowatts into electricity using a small, compact and decentralised energy recovery unit."
As a result of the extensive research, the first prototypes of the innovative DEPRAG turbine generator are now finished in the development lab. The patent has been registered; test series with the prototypes have been successfully concluded. Dr. Eng. Rolf Pfeiffer says: "We can now go into production with our product and are looking for partners who want to use this innovative system for energy recovery in their facilities. Our recovery system can be used in a variety of applications to convert process gases into electricity or even to utilise unused surplus heat."
In the initial studies, the DEPRAG team under development manager Gerd Zinn determined that the new energy recovery system should be a small, simple, and robust system for the 5 to 20 kW range. The use of gears was to be avoided based upon costs and maintenance. But this proved to be a major challenge for the developers. The physical characteristics and the small diameter of the turbine rotors result in a relatively high speed for the turbine and thus for the generator.
The strength properties of the suitable materials set clear limitations. No standard generator was small enough and constructed from suitable materials to meet the demands for fatigue strength at the the calculated rotational speed of around 40,000 revolutions/minute. That meant it was necessary for them to develop a suitable electric generator themselves. The engineers were particularly focused on the fatigue strength of the rotor. The result of the intensive development work was a compact total system in two versions, based on a permanent magnet synchronous induction machine for the generation of electricity.
And that is what the prototype from DEPRAG looks like: a compact unit made from a microexpansion turbine with an electrical generator which produces electricity from gas. not including the associated electrical control box, the turbine generator is not much bigger than a shoebox and, following the plug & earn principle, can be used locally where gas is either released unused by the industrial process or where a high level of pressure is reduced to a lower value. To date, released pressure energy is seldom used to generate electricity, thus wasting an ecologically valuable energy potential.
The innovative DEPRAG turbine generator converts the surplus energy contained in working gases into usable energy. Gas flows into the turbine, is pressed through jets, and is accelerated. When it meets the blades of the turbine and is diverted, it releases its energy. The kinetic energy is converted to electrical energy in the generator. In this innovative system, the turbine and electric generator represent a compact unit, and have one shared drive shaft. The result: when the turbine rotates, the generator's rotor rotates at the same time - electrical energy is generated!
Energy recovery with the DEPRAG turbine generator can be applied in many areas of industry. In the smelting of metals, for example, the melting tanks are cooled by compressed air. The compressed air flows through cooling channels and absorbs heat. Normally, it is then released into the atmosphere without being used. With the new turbine generator, what is actually a waste product can be reused profitably. The energy absorbed from the heat can be converted to electricity by the microexpansion turbine and the integrated generator and fed into the power grid.
To date in large biogas plants and cogeneration units, residual energy has been converted to electricity based on the ORC (organic Rankine cycle) process, however the power range of these installations is between 200 and 1,500 kW. But today, it is smaller biogas plants and cogeneration units that are increasingly being built. The electrical efficiency of such plants can be effectively optimised with the new turbine generator by also allowing smaller amounts of waste heat to be used efficiently in an ORC recovery process. Thus, the overall efficiency of these plants can potentially be increased to more than 45%. In accordance with the German Renewable Energy Act (EEG), a technology bonus of 2 cents/kWh will be earned for the whole plant.
Natural gas is pumped thousands of kilometres at high pressure from producing countries to the consumer. In order to introduce it into the regional networks, which operate at a lower pressure, the pressure must be reduced, and the gas must be decompressed. The utility companies reduce the gas pressure once again before the natural gas reaches private homes. In the transformation of pressures in the gas pipelines, energy is lost in gas distribution technology which could, in the view of DEPRAG engineers, be converted to electrical energy without major effort using the turbine generator.
Managing Director Dr. Eng. Rolf Pfeiffer sees great market potential for the DEPRAG turbine generator. He summarises the advantages: "Even smaller amounts of residual energy can be converted to electricity at a reasonable price with the compact recovery system." The ecological benefits of this sort of energy recovery also pay off financially. The feed-in tariff in accordance with the Renewable Energy Act (EEG) offers an additional incentive. The investment costs should also remain affordable. Dr. Eng. Rolf Pfeiffer says: "It is certainly imaginable that in the future we will be able to offer the turbine generator unit for 10 kW for less than 10,000 euros at a corresponding volume."
DEPRAG SCHULZ GMBH & CO. is one of the market leaders in the field of innovative air motors. Based in Amberg, Germany, the company has 600 employees in over 50 countries. DEFRAG has always considered innovation and the continuing improvement of existing product lines to be the best answer to today's challenges.
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