Energy Harvesting Design AdvancesEnergy Harvesting Design Advances

Many of these projects involve energizing low-powerdevices, such as sensors, through capture of wasted energy from vibrations orheat dissipation. But that still leaves a massive amount of energy being released by industrial systems that remains uncaptured for greater use.

To help address this, the German Federal Ministry of Economics andTechnology is funding a project at Deprag Schulz GmbH & Co. (a supplier ofair motors) to capture excess process gas for energy generation. Of course,energy recovery from excess process gas in not a new idea, but Deprag Schulz'snew project does add a new twist. The Deprag Schulz project involves convertingsmall amounts of residual energy (5 to 20 kW) directly into electricity using a small generator.

Because no standard generator was small enough or employed suitablematerials for use as the core of the energy unit (calculated rotational speedof the generator is around 40,000 rpm), Deprag Schulz had todevelop an electric generator specifically for this purpose. The result is a turbinegenerator based on a permanent magnet synchronous induction machine for thegeneration of electricity.

The prototype from Deprag Schulz is a compact unit made from amicroexpansion turbine with an electrical generator which produces electricityfrom gas. The core turbine generator unit, not including the electrical controlbox, is not much bigger than a shoebox and can be used locally where gas iseither released unused by the industrial process or where a high level ofpressure is reduced to a lower value.

Here's how the turbine generator works: Gas flows into the turbine and ispressed through jets to accelerate its movement. When it meets the blades ofthe turbine and is diverted, it releases energy. This kinetic energy isthen converted to electrical energy in the generator.

The key to the design of this prototype is that the turbine and electricgenerator have one shared drive shaft. This means that, when the turbinerotates, the generator's rotor rotates at the same time and electrical energyis generated.

As an application example for this turbine generator, the tanks used insmelting of metals are cooled by compressed air. The compressed air flowsthrough cooling channels and absorbs heat. Typically, this air is then releasedinto the atmosphere without being used. With the turbine generator, the energyabsorbed from the heat can be converted to electricity by passing it throughthe microexpansion turbine and the integrated generator and then feeding theresulting power back into the grid.