Ormat and DOE to Validate Electricity Generation from Oilfield Heat
25 January 2007
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| Ormat binary geothermal power generation system. Click to enlarge. |
Ormat Technologies, Inc., a geothermal and recovered energy business, has signed a shared-cost Cooperative Research and Development Agreement (CRADA) with the US Department of Energy (DOE) to validate the feasibility of using geothermal power generation technology for the production of commercial electricity using hot water produced during the process of oilfield production.
The project will be conducted at the DOE Rocky Mountain Oil Test Center (RMOTC), near Casper Wyoming, and will use an Ormat Organic Rankine Cycle (ORC) power generation system to produce commercial electricity.
The test will use a commercial, air-cooled, skid-mounted standard design Ormat Organic Rankine Cycle system. Ormat will supply the ORC power unit at its own expense while the DOE will install and operate the facility for a 12-month period. Ormat and the DOE will share the total cost of the test and the study, with Ormat bearing approximately two thirds of the less than $1M total investment.
Presently there are two large unutilized sources of hot water at the RMOTC Naval Petroleum Reserve No. 3, which produces water in excess of 190°F (88°C) and at flow rates sufficient for power generation of approximately 200 kW.
The project will consist of the installation, testing and evaluation of a binary geothermal power unit in the field near these hot water sources. The ORC power unit will be interconnected into the field electrical system and the energy produced will be used by RMOTC and monitored for reliability quality.
The binary power unit brings a geothermal fluid—here, the hot water—through pipelines to heat exchangers in the Ormat Energy Converter (vaporizer and preheater). In these heat exchangers the geothermal fluid heats (preheater) and vaporizes (vaporizer) a secondary working fluid, which is typically an organic fluid with a low boiling point.
The vapors drive a turbine which powers a generator and then are condensed in a condenser. The condensed fluid is then recycled back into the heat exchangers by a pump, completing the cycle within the closed system. The cooled geothermal fluid is re-injected into the reservoir.
The Ormat ORC unit that will be used in the study is similar to the 250 kW air-cooled unit that has been producing electricity from 210°F (99°C) geothermal water for more than six years at an Austrian resort. Additionally, there are similar units in Nevada and Thailand that have been in continuous commercial operation and without overhaul, since 1984 and 1989, respectively.
A 70 kW Ormat ORC power system was also used in a project co-sponsored by the US Bureau of Reclamation, Ormat and others. This ORC unit operated for 16 years using water with temperatures as low as 154°F (68°C) to produce electricity.
Some 8,000 similar wells were identified in Texas, by Prof Richard Erdlac of the University of Texas of the Permian Basin, and the US DOE Geothermal Research Project Office. Ormat is now assessing the feasibility of utilizing some of these wells to support on site power generation by employing Ormat’s factory integrated sub-megawatt geothermal power units.
Even though the heat in the form of hot water is essentially free in this case, it is presented at a relatively low temperature (low exergy/anergy ratio).
This means that per unit of electrical energy produced, you have to invest perhaps 2x as much as in a conventional power station, because the heat exchangers have to be bigger and the turbine and pump more efficient.
Posted by: Rafael Seidl | 25 January 2007 at 11:17 AM
I wonder how much the efficiency of such systems is affected by environmental temperature.
Posted by: Paul Dietz | 25 January 2007 at 12:28 PM
You could probably get a better return on investment burning cow poop.
Posted by: Dezakin | 25 January 2007 at 01:45 PM
Paul -
exergy, i.e. the technically usable fraction of heat, is defined relative to the temperature of the heat sink. With an air-cooled design such as this one, the exergy of the geofluid will be especially low on hot summer days when demand for electrically powered air conditioning is highest.
The situation could be improved on by concentrating the heat of the geofluid with a heat pump, perhaps a free-piston Vuilleumier engine powered by solar radiation concentrated by a heliostat array. Many geothermal power plants cover relatively large areas, with insulated pipes connecting individual wellheads to the central electricity generation facility, therefore any heat pumps should ideally be installed at the wellhead.
Posted by: Rafael Seidl | 25 January 2007 at 02:33 PM
If we multiply the 500,000 oil wells in the US by 200 kw we get 100 GW of potential power. This is about the same amount of power we get from nukes.
Posted by: tom deplume | 26 January 2007 at 09:47 AM
Rafael:
Whoa! I've never caught you in a technical blunder before, Raphael, but this one's a doozy!
The net efficiency of work extraction from geothermal heat cannot be improved through use of a heat pump. If it could be, it would be possible to build a perpetual motion machine of the second type.
Posted by: Roger Arnold | 26 January 2007 at 04:46 PM
Roger -
as indicated, an additional source of high-temperature heat would be required to drive a Vuilleumier machine. If you're not familiar with these, please look them up on e.g. Wikipedia.
Raising the temperature of the heat in the geofluid does not, of course, magically increase the eNergy it contains. However, it does increase its eXergy, which means you can sharply reduce losses due to the inevitable imperfections in any real-world process. Moreover, the energy required to drive the heat pump is added to that presented to the turbine.
None of this in any way, shape or form constitutes a perpetual motion machine of either type. Only a more detailed analysis would show if adding solar-powered heat pumps to a geothermal power station would be worthwhile in economic terms.
Posted by: Rafael Seidl | 27 January 2007 at 09:14 AM
I am wondering if equipment could be used to drill these older oil wells deeper so as to reach hotter rock. It would seem to me that the expense for the drilling could be recovered by the larger amount of heat energy extracted if the temperatures could reach high enough to vaporize the water. Why use a binary cycle if a greater depth would negate this requirement?
Perhaps there are wells already drilled that are close enough together so that drilling deeper and fracturing the rock between the two wells for the water to steam conversion process could be used.
Why settle for low power Geothermal generation when there could be much greater amounts available with limited modifications to the wells.
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Posted by: Adrian Akau | 01 February 2007 at 07:33 PM