ElectraTherm’s Green Machine
Fifty percent of all fuel burned by American industry is wasted as heat. ElectraTherm Inc. in Reno, Nevada, U.S.A., has developed and is now marketing its Green Machine Waste Energy Generator that could capture this wasted energy and convert it into electricity. In the United States, ElectraTherm’s products could recover this lost energy to generate the equivalent of the electric output of a 92 500 MW gas-fired, combinedcycle plant, and do it without additional carbon dioxide or other emissions.
The Green Machine can convert low-temperature heat, as low as 93.3°C for fluids and 149°C for gases, into electricity for on-site consumption, or supply it to the power grid. For example, waste heat as low as 93.3°C given off by common boilers or chillers in office buildings could be used. It can produce power from many sources including industrial waste heat from fuel-fired furnaces, kilns, boilers, ovens, dryers, incinerators and so forth without consuming any fuel or producing any polluting emissions. Other smaller geothermal resources include tens of thousands of oil and gas wells in the United States and Canada, as well as waste engine heat, biomass and solar thermal sources.
The ElectraTherm technology features a closed-loop Organic Rankine Cycle (ORC) to boil the working fluid into a gas using surplus heat captured by the evaporator. The gas is then expanded in a one-way, closed piping system. The expanding gas turns a patented Twin Screw Expander with two small, screw-shaped rotors to drive a generator. The vapor is cooled and condensed back into a liquid in the condenser. The working fluid, a liquid refrigerant, is pumped to higher pressure and returned to the evaporator to repeat the process. The Waste Heat Generator uses a nonflammable, ecofriendly refrigerant approved by the EPA that was selected for its high performance at low temperatures.
According to ElectraTherm, the Twin Screw Expander operates with improved efficiency and reliability compared to conventional turbo expanders, but at about 10% of the price. It can operate in caustic environments that would damage high-speed turbines and turboexpanders.
Running at about one-tenth the rotational speed of turboexpanders, there is less friction and greater lobe strength than any other twin-screw rotor profiles. There are no expensive gearboxes or electronics as needed by high-speed turbines. By allowing wet vapor into the closed-loop system, which is not possible with turbines, the patented lubrication system does not need a traditional oil pump, tank, lines and filter. With few moving parts, long-term maintenance is also much less. All this adds up to a system price advantage of 35 to 50% over traditional turbine-driven, small-scale power systems.
Built on skids, ElectraTherm systems are easy to transport and install as single units or in clusters. The technology is modular and scalable with capacities from 50 up to 500 kW. Larger units connected in parallel could be used to rapidly construct multimegawatt plants at larger geothermal resources. Installation is plug-and-play.
ElectraTherm Inc. and its partner, Gulf Coast Green Energy, are using the ElectraTherm Green Machine to produce clean electricity at two projects funded by the Research Partnership to Secure Energy for America. The first Electra-Therm Green Machine was installed at Southern Methodist University’s Geothermal Laboratory in 2008. This, the world’s first commercially viable waste heat generator, exceeded its 50 kW rating by 20%. The other one will use heat captured in geothermal brine, a common byproduct of drilling for oil.
ElectraTherm also offers its Gas Pressure Reduction Generator (GPRG) using the same Twin Screw Expander technology. Developed for the oil and gas industry, the GPRG uses the energy contained in the pressure drop of any gas to produce noncombustable, fuel-free, emission-free electricity. This includes gas pressure reduction stations used to reduce pressure from distribution pipeline levels to low pressures before being delivered to consumers.
ElectraTherm technology uses the released pressure to generate carbon-free electricity.
The technology can also use the geo-pressure of natural gas on offshore oil platforms to produce enough electricity to satisfy the demands of the platform through the controlled expansion of a small amount of the gas flow. Because an offshore satellite platform typically requires less than 30 kW, ElectraTherm’s scaled technology is far more cost-effective than traditional radial inflow or axial turbomachinery. These systems can also produce 25 kW to 1.5 MW of fuel-free, emission-free electricity.
ElectraTherm sees other applications for its technology. One of which is to recover wasted heat from coal-fired power plants. Coal-fired power plants account for roughly half of the electricity produced in the United States and have been responsible for 83% of the carbon dioxide emitted by all power plants since 1990. The only practical way to reduce carbon dioxide emissions from coal is to increase efficiency by getting more electrical energy out of each pound of coal, something that can be accomplished, without additional emissions, by ElectraTherm’s technology.
ElectraTherm’s technology could also capture jacket water, engine exhaust or a combination of both from stationary internal combustion engines. This includes engines used for gas compression, pumping, power generation, cogeneration, irrigation or inert gas production. Automated control systems permit unattended operation for low operation and maintenance costs. Again, small sizes could mean cost-effective results.