Most existing heat-harvesting technologies are efficient only at temperatures above 150 °C, and much waste heat just isn’t that hot. Now Ener-G-Rotors, based in Schenectady, NY, is developing technology that can use heat between 65 and 150 °C. [338-453 Kelvin] The company expects to convert 10 to 15 percent of low-temperature waste heat into electricity, delivering a payback in two years or less in most case. This efficiency would be the red box in the graph. It would likely be equivalent to ZT 2-20.
Ener-G-Rotors’ technology is based on the Rankine cycle, in which heated fluid flowing through a tube heats a pressurized fluid in a second tube via a heat exchanger. The second tube is a closed loop; the so-called working fluid flowing through it (a refrigerant with a low boiling point, in the case of Ener-G-Rotors) vaporizes and travels into a larger space called an expander. There, as the name would imply, it expands, exerting a mechanical force that can be converted into electricity.
Instead of turning a turbine, the expanding vapor in Ener-G-Rotors’ system turns the gerotor, which is really two concentric rotors. The inner rotor attaches to an axle, and the outer rotor is a kind of collar around it. The rotors have mismatched gear teeth, and when vapor passing between them forces them apart, the gears mesh, turning the rotor.
The company claims that the rotor design is far simpler than that of a turbine, making it potentially easier and cheaper to manufacture, as well as more durable. And the company says that it has invented a proprietary way of mounting the rotor on rolling bearings that makes its movement nearly frictionless.
Reducing the friction means that the rotor turns more easily, so the gas doesn’t need to exert as much force to generate electricity. That’s why the system can work at lower temperatures, which impart less energy to the gas.
Ener-G-Rotors initially plans to target industries, such as chemicals, paper, oil, and food, that use plenty of energy and also release a tremendous amount of waste heat, Newell says. Later, the company also hopes to participate in solar-thermal and geothermal projects, and to target consumers with a one-kilowatt system.
The company is installing its first beta unit, a five-kilowatt system, in a combined heat-and-power plant at Harbec Plastics. It is also installing betas at a steam plant for New York utility Consolidated Edison and at a landfill-gas-burning plant for the New York State Energy Research and Development Authority.
If the betas pan out, Ener-G-Rotors plans to expand to a 50-kilowatt demonstration, which is much smaller than the scale that most of its competitors are targeting.
United Technologies, which makes aircraft, aerospace systems, and air conditioning, and smaller companies such as ElectraTherm, are also pursuing low-temperature technologies–and they already have systems installed.
ElectraTherm combines traditional components with patented, cutting-edge technology to create electricity from waste heat. ElectraTherm power systems use a closed-loop organic Rankine cycle (ORC) to create pressure by boiling EPA-approved chemical working fluids into gas. The gas expands in a one way system and turns a patented Twin Screw Expander, which drives a generator to ultimately put out electricity.
– Lowest heat requirement in the industry: 200º F [366K]
– Flexible and scalable from 25kW-1MW
– One third the cost of turbine generators
The heat2power system is based on the use of one or more cylinders for the regeneration of waste heat. These cylinders can be in replacement of the combustion cylinders inside an existing engine or as an add-on module that is connected to the engine by means of a gear set or a belt drive. Also is it possible to have no mechanical linkage between combustion engine and regeneration unit in case the power from the regeneration unit is taken off electrically. The thermal power is extracted from the exhaust of the internal combustion engine by means of a heat exchanger.
The heat2power concept main characterics :
* Fuel savings of about 15 to 35% under ALL driving conditions
* Reduction of CO2 emissions of about 15 to 35% (under same conditions and with same fuel)
* Regeneration system possible as Add-in and as Add-on solution
* Engine block and architecture remain the same and so does the associated tooling
* Gasoline-Otto/heat2power hybrid Engine costs approximately 30% more than a comparable turbocharged gasoline engine
(That is cheaper than a Diesel engine but with comparable fuel efficiency) Diesel/heat2power hybrid Engine increases fuel economy