Ron Kotrba, Biomass Magazine
Power plants featuring organic Rankine cycle (ORC) systems, such as this 8-megawatt biomass plant in Maine, feature many advantages over steam turbine power generation. PHOTO: TURBODEN
Afundamental principle of distillation, whether for beverage alcohol production or petroleum refining, is that most liquids have different boiling points. Alcohol boils at 173 degrees Fahrenheit, and water at 212 degrees, so to make alcohol, distillers employ temperatures between those two points in order to evaporate the alcohol, and then condense it back into liquid form—sans water. Now, imagine standing outside on a cool autumn day with a cold, closed jar of unknown liquid. It’s 58 degrees outside, and the jar is much colder than that. When you open the jar and expose the liquid to the 58-degree air, it starts to boil.
This is the basis of the organic Rankine cycle (ORC)—a thermodynamic cycle using an organic, high-molecular mass fluid instead of water to produce power from low-grade heat. “ORC is literally a refrigeration cycle in reverse,” says John Fox, managing director of ElectraTherm.