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Deprag develops new compact turbine generators

article image Deprag GET turbine generator

Deprag Schulz GmbH u. Co began an ambitious research project into the field of energy recovery in 2010. Sponsored by the German Federal Ministry for Economics and Technology, the project is based on the idea that gas is released into the atmosphere in many industrial processes. The aim was to utilise these gases as an energy source.

The recovery of energy from process gases is not a new concept. However, according to Dr. -Ing. Rolf Pfeiffer, the new aspect of the Deprag development was that their small compact decentralised energy recovery system could also convert small amounts of residual energy in the power range of 5 to 20 kW into electricity.

Prof. Dr. Ing. A.P. Weiß from the East Bavarian University of Applied Sciences Amberg-Weiden sees a great potential for this system in the future. He explains that compressed air systems could be boosted by the use of this decentralised storage of surplus renewable energy. With the innovative GET turbine generator from Deprag, the CAES (Compressed Air Energy Storage) temporary storage of wind or solar energy even in small kW ranges could present a new scope of application for compressed air technology.

Deprag has completed the development of their initial prototype of the innovative Deprag GET turbine generator for the power range 3-50 kW in sizes of 5 kW, 20 kW and 50 kW. These design sizes are individually configured to each process.

It is necessary to define the specific processing parameters, namely the type of medium, inlet pressure, outlet pressure, mass flow, inlet and outlet temperature for the fluid mechanic layout and design of the turbine generator. The specialists at Deprag also require a description of the application and processing conditions in order to integrate the GET turbine into the existing production process.

The Deprag turbine generator can be used in both open and closed processes, and designed for use with diverse mediums such as compressed air, natural gas, CO2, steam, R245fa, SES36 and Cyclopentan.

Dr.-Ing. Rolf Pfeiffer comments that Deprag’s energy recovery system is suitable for use in a multitude of applications to convert direct process gas into energy or by integrating the GET unit into an ORC process indirectly to utilise unused surplus heat.

From the very start of their research, Head of Development Gerd Zinn’s team discovered that the new energy recovery system had to be a small, simple and robust system in the power range between 5 and 20 kW; they also wanted to forego the use of a gearing after deliberations concerning cost and maintenance. This proved however to be the greatest challenge to the developers because the physical realities and the small diameter of the turbine rotors result in a relatively high speed of the turbine and therefore, also of the generator. The mechanical properties of the suited materials set definite limits on the developers. No available standard generator was small enough or fulfilled the requirements for durability to be able to withstand the calculated speeds of approx 40,000 rpm. Consequently it was necessary for them to develop a new electric generator themselves.

The durability of the rotor was the focal point for the engineers. Intensive research finally resulted in a compact complete system based on a permanently excited synchronous motor for the generation of power.

The Deprag turbine generator

A compact unit consisting of a micro expansion turbine with an electric generator that generates electricity from gas, the turbine generator is not much larger than a shoebox without its control cabinet, and can be installed anywhere gas pressure shifts from a high level to a lower level. Previously this released pressure energy has rarely been utilised to recover power and the ecologically valuable energy potential has therefore been needlessly wasted.

The innovative Deprag GET turbine generator changes the energy contained in the working fluid into electricity. Gas flows into the turbine and is ‘pressed’ through jets and accelerated. When it reaches the blades of the rotors and is deflected, it releases its energy. The kinetic energy is transformed into electrical energy in the generator. In this innovative design the turbine and electric generator form a single compact unit and share the same shaft. Therefore, when the turbine turns, the rotor of the generator also rotates.


Energy recovery using Deprag turbine generators is suitable for many application areas. When smelting metals such as aluminium and copper, 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. With the new micro expansion turbine and integrated generator this is changed into electricity and fed into the power network.

In biogas and thermal power stations the GET turbine can be utilised by a method based on the ORC process (Organic Rankine Cycle) to convert residual energy into power. The electrical efficiency of plants can be successfully optimised by allowing small volumes of waste heat to be utilised economically in an ORC recovery process.

To further increase efficiency of biogas plants methane can be fed into the natural gas network and energy can be stored or transported. A large part of biogas is methane and carbon dioxide. A prerequisite for the feed-in is that the carbon dioxide is removed from the biogas. Usually this occurs in those processing plants where carbon dioxide is present at the end stage at relatively high pressure and temperature levels. A large amount of the stored energy can be recovered using the turbine generator.


Deprag has also developed a comprehensive range of accessories. The recovery units up to 15 kW combine the components rectifier, inverted rectifier and ballast circuit in a compact housing. An external load resistor is directly controlled by this unit. If the turbine is not creating power the feed-in converter switches off and does not use any electricity from the supply network. As soon as the turbine generator is generating power again the recovery unit automatically switches back on.

The feed-in systems for 25-50 kW are specifically developed performance electronics for high speed generators. Along with specific measurement and cooling concepts, additional add-on functions and safety functions such as network monitoring and braking resistors can be taken into account.

To increase time between maintenance intervals the engineers have now developed a re-greasing unit, which automatically re-greases the turbine bearings. The compact greasing pump is designed for independent operation with a battery and does not require an external electricity supply though it can be connected to a control panel with 24V.

One of the market leaders in the manufacture of air motors, Deprag is currently focussed on turbine technology. The owner managed family business has around 600 employees and is represented in over 50 countries. 

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