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NREL Tackling Industry Challenges, Improving Low-Temperature Resource Power Output

March 21, 2011

True or false? Oil and gas fields have loads of geothermal resources that can be used to run power plants.

You might be inclined to say "false"… and you'd be wrong. In fact, oil and gas fields in the United States produce 25 billion barrels of hot water (co-produced low-temperature geothermal resources) annually that can be used to produce electricity for field use or sold to the grid. These co-produced low-temperature geothermal resources have the potential to help diminish greenhouse gas emissions and extend the economic life of oil and gas fields.

NREL is working to address the challenges currently related to low-temperature geothermal power production units as part of a three-way agreement between NREL, the U.S. Department of Energy's Geothermal Technologies Program (GTP), and the Rocky Mountain Oilfield Testing Center (RMOTC), just north of Casper, Wyoming.

NREL will track operational data from two 280 kilowatt (kW) Organic Rankine Cycle units (one already installed and one to be installed) at RMOTC's Naval Petroleum Reserve No. 3 (Teapot Dome Oil Field) site to identify power output improvements through the year and power output improvements in warm climates. The unit currently being operated uses 92°C co-produced low-temperature geothermal water to produce electricity and has produced more than 1,918 megawatt hours of power from 10.9 million barrels of co-produced hot water, with an online percentage of 97% since operations began in September 2008.

With results this impressive, why improve? Because there are numerous challenges to successfully using co-produced low-temperature geothermal technologies for power production—after all, the RMOTC unit wasn't always so successful. The unit was actually shut down from for approximately 6 months during its operational period due to operator learning curve issues and resulting system failures.

In the coming months, NREL will install real-time data monitoring systems, which will include sensors that monitor:

  • Temperatures, pressures, and flows of brine and working fluids
  • Power output to the grid
  • Consumed parasitic power
  • Ambient weather conditions and the effect on power output.

Baseline data and long-term data will be collected and stored. Non-proprietary data, including levelized cost of electricity, base load power offset, and system efficiency, will be available to the public through GTP's National Geothermal Data System and a Web page of real-time data that NREL is developing to help GTP meet its goal of achieving development and widespread deployment of economically viable, innovative, and scalable technologies that can capture a significant portion of the low-temperature geothermal resource base over the next 20 years.

Hybrid Cooling Retrofit

Along these same lines, NREL will use the collected data to work with RMOTC on system improvements to one of the units by focusing on hybrid cooling technology. Because air-cooled geothermal plants, like the one at RMOTC, commonly have a decrease in power output during the hottest periods of the day in the summer months, NREL researchers have been modeling and evaluating commercially available hybrid cooling systems that can be retrofitted to one of the RMOTC units to mitigate the decrease in net power output. The retrofit will incorporate a nozzle spray system to pre-cool the air to the air-cooled condenser during the hottest periods of the day during the summer, increasing the power output during those hot periods while using minimal amounts of water. In fact, modeling indicates that the addition of a spray system to handle 30% of the total condenser load during the hot periods of the day could improve power production output by nearly 36%.

NREL's recently released technical report, "Hybrid Cooling Systems for Low-Temperature Geothermal Power Production," details the results of research to identify and analyze alternative heat rejection strategies that allow air-cooled geothermal power plants to both maintain a high electrical power output during periods of high ambient air dry-bulb temperatures and minimize plant water consumption. Download the report to learn more about the analysis and results. 

Promoting Low-Temperature Technologies

"These technologies are a great compliment to the research that NREL is working on to characterize low-temperature resources in the United States," says project leader Neil Popovich. "Additionally, low-temperature technologies can make use of existing wells with known geothermal water resources as opposed to the exploration and drilling requirements of other geothermal resources, making them less risky for geothermal development."

NREL will continue their work with RMOTC through summer 2011.

"We plan to use the results of our data collection and retrofitting to promote the use of low- temperature geothermal power production technologies by using real data and analysis to inform the public about the benefits of these technologies as well as tackle the challenges industry currently faces," says Popovich.

Download the GTP fact sheet or visit the website to learn more about co-produced low-temperature geothermal resources.

—Devin Egan