A number of efforts are currently being employed across industries to harvest energy typically lost during production operations. A number of these projects involve energizing low-power devices, such as sensors, through capture of wasted energy from vibrations or heat dissipation. But that still leaves a massive amount of energy being released by industrial systems that remain uncaptured for greater use.
To help address this, the German Federal Ministry of Economics and Technology is funding a project at Deprag Schulz GmbH & Co. (a supplier of air 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’s new project does add a new twist. The Deprag Schulz project involves converting small amounts of residual energy (5 -20 kilowatts) directly into electricity using a small generator.
Because no standard generator was small enough or employed suitable materials for use as the core of the energy unit (calculated rotational speed of the generator is around 40,000 rpm), Deprag Schulz had to develop an electric generator specifically for this purpose. The result is a turbine generator based on a permanent magnet synchronous induction machine for the generation of electricity.
The prototype from Deprag Schulz is a compact unit made from a microexpansion turbine with an electrical generator which produces electricity from gas. The core turbine generator unit, not including the electrical control box, is not much bigger than a shoebox and 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.
Here’s how the turbine generator works: Gas flows into the turbine and is pressed through jets to accelerate its movement. When it meets the blades of the turbine and is diverted, it releases energy. This kinetic energy is then converted to electrical energy in the generator.
The key to the design of this prototype is that the turbine and electric generator have one shared drive shaft. This means that, when the turbine rotates, the generator’s rotor rotates at the same time and electrical energy is generated.
As an application example for this turbine generator, the tanks used in smelting of metals are cooled by compressed air. The compressed air flows through cooling channels and absorbs heat. Typically, this air is then released into the atmosphere without being used. With the turbine generator, the energy absorbed from the heat can be converted to electricity by passing it through the microexpansion turbine and the integrated generator and then feeding the resulting power back into the grid.