Innovative air turbine captures industrial waste gases and turns them into electricity

Air motors are ideal for this application as they are incredibly robust and have excellent power density. Dubbed the Green Energy Turbine (GET), the device uses two stages to maximise the amount of energy recovered from the waste gases. The turbine and electrical generator are a compact unit and share a single driveshaft. As gas flows into the turbine, it passes through a series of nozzles to accelerate the flow. This high pressure then turns the turbine blades, which are connected to the shaft. This, in turn, drives a generator at the same speed to produce electricity. Chief operating officer of Deprag, Dr. Rolf Pfeiffer, says: "In many industrial procedures, unused process gas escapes into the atmosphere. Our basic idea was to tap these gases to generate energy. "In a small, local energy recovery plant our progressive turbine generator can convert even tiny amounts of residual gas into electric power." During development it was decided that the use of gears was to be avoided due to cost and maintenance. But this proved to be a major challenge for the developers. The physical characteristics and the small diameter of the turbine rotors resulted in a relatively high rotational speed for the turbine, and therefore the generator. This set clear limitations in terms of material properties. As no standard generator was small enough or constructed from suitable material to withstand the continual loads at the calculated rotational speed of around 40,000rpm, it meant Deprag developed the electric generator itself from scratch. The result is a compact unit consisting of a turbine and a generator that is not much bigger than a shoe box, so can easily be located and implemented for what the company call an instant 'plug and earn'. The company has identified a number of potential applications including the cooling process in smelting plants. Melting tanks are normally cooled by compressed air which flows through cooling channels to absorb heat. Normally, the compressed air is then released into the atmosphere, but with the GET turbine generator, the compressed air can be reused profitably. Another example is where natural gas is pumped thousands of kilometres at high pressure from producing countries to the consumer. In order to feed it into the regional networks, which operate at a lower pressure, the pipe-pressure must be reduced and the gas decompressed. The utility companies reduce the gas pressure once again before it 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. The ecological benefits of this sort of energy recovery also pay off financially and the company say the investment costs should also remain affordable. Dr Pfeiffer concludes: "It is certainly imaginable that in the future we will be able to offer the turbine generator unit for 10kW for less than €10,000 at a corresponding volume."