Okay, so this isn’t quite as sexy as a 100 MPG hybrid hummer, but Raser just announced that its new Hatch Geothermal Power Plant is up and running in Utah. Normally, geothermal plants take years to start production, but Raser took only 5 months to power up this plant.
How did they do it? Basically, the plant uses an organic Rankine cycle (ORC), with parts modified from industrial air conditioners. Using off-the-shelf, mass produced components reduces the time needed to construct a plant and results in significant cost savings. The ORC method also makes it possible to extract geothermal energy that is unavailable through other processes.
Gizmag.com has an excellent article about Raser’s process. Here is an excerpt that explains the process Raser uses in a little more detail:
In a binary cycle closed loop geothermal plant, the hot brine pulled from the earth is passed through a large tank that contains an evaporator. The heat from the brine causes a low-boiling-point working fluid in the evaporator to flash into vapor, much in the same way water is boiled to flash into steam. Raser isn’t giving away which working fluid they are using, but ORC systems often use common refrigerants such as monochlorodifluoromethane, normally called R-22, which is nontoxic, noncorrosive, nonflammable, extensively used in household refrigerators and window air conditioners and has a boiling point of -41°F (-44.4ºC), at atmospheric pressure.
The vaporized working fluid, which is now at high pressure, leaves the evaporator and is fed directly into a high efficiency turbine, driving in this case a 250 Kw generator. With most of the energy removed from the vapor, as it drives the turbine, a partially liquefied working fluid is exhausted from the turbine into a second tank that contains a condenser heat exchanger. The exchanger removes any remaining heat and returns the working fluid to a fully liquid state. From there the closed loop is completed by a small pump that takes the refrigerant from the condenser back to the evaporator.
The whole process is similar to the way a conventional coal-fired or nuclear power plant generates electricity, only the working fluid is different. In fact, up to 80 percent of the world’s electricity is generated using the Rankine cycle to heat water into high pressure steam, which drives a turbine and, in turn, an electrical generator.
The Raser plant uses 50 binary generator modules supplied by UTC Power, combined in parallel, to give a net output power of 10 MW. The total capacity is about 14 MW, but 3 to 4 MW are required to run the pumps pulling the water up from the hot reservoirs and then back down. In cooler months, when environmental factors will help cool the secondary fluid, the net output will be more like 11 MW.
Not quite as sexy as a Hummer, but I agree with Tate: the real story with Raser is geothermal.