US company tapping waste heat for electricity generation

22 November 2008

A US company is in the process of harnessing waste heat, which is produced as a result of some other process and is not utilised, for electricity generation.

Ener-G-Rotors, based in Schenectdy, New York, is in the process of developing technology that will harness this waste heat that is usually generated in relatively low temperature ranges between 65 and 150 degrees centigrade.

The company says that most existing heat-harvesting technologies are efficient at temperatures only above 150 degrees centigrade. Therefore, it plans to replace the turbine that generates electricity in a typical generator with a device called a gerotor.

The company claims that this device is "near frictionless." The technology is based on the Rankine cycle, in which heated fluid flowing through a tube heats a pressurised fluid in a second tube via a heat exchanger.

The second tube is a closed loop. The working fluid flowing through it, in the case of Ener-G-Rotors, a refrigerant with a low boiling point, vaporises and travels into a larger space called an expander, where it expands, exerting a mechanical force that is converted into electricity.

The expanding vapour in Ener-G-Rotors' system turns the gerotor, which are two concentric rotors. The inner rotor is attached to an axle, while the outer rotor is like a collar around it. The rotors have mismatched gear teeth, which the vapour passing between forces apart, causing the gears to mesh, and thereby turning the rotor.