Study on Phase-Change Materials to Make Power Generation Cleaner

Xingchao Wang (left), Chunjian Pan (center) and Joshua Charles are conducting research in Lehigh’s Energy Research Center on hydrated salts that have the potential to improve the efficiency of power plants that use waterless air-cooled condensers to condense steam. (Credit: Lehigh University)

A competitive award was given to Joshua Charles, a Ph.D. student in mechanical engineering for his research into the application of phase change materials to help enhance the efficiency of power plants and decrease the amount of pollutants they discharge.

Charles is also a part-time research scientist at Lehigh’s Energy Research Center, and has received a scholarship from the Air Pollution and Educational Research Grant Program (APERG), which is administered by the Mid-Atlantic States Section of the Air and Waste Management Association.

The scholarship is awarded to doctoral and post-doctoral students who are undertaking research associated to air quality and air pollution. The title of Charles’s project is “Low Temperature Phase Change Materials for Application Resulting in the Reduction of Airborne Pollutants from Fossil Power Plants.”

Phase change materials (PCMs) absorb thermal energy as latent heat at a moderately constant temperature as they melt. Then as they freeze, they emit thermal energy, or heat. Charles is researching hydrated salts, which melt at room temperature and freeze as temperatures fall during the night.

His research aims to help enhance the efficiency of power plants that use waterless air-cooled condensers (ACCs) to condense the steam from the turbines that produce electricity.

Thermoelectric power plants boil water to form the steam that spins the turbines to produce electricity. The steam turns to water upon cooling and returns to the boiler. The cooling water used in this step signifies the power plant’s largest water withdrawal.

Cooling is usually achieved with cold water, but this has certain challenges. Freshwater supplies around the world are dwindling, says Sudhakar Neti, professor emeritus of mechanical engineering and mechanics and one of Charles’s advisers. Approximately, two-fifths of fresh water in the US, for instance, is utilized to cool the steam from power plants.

Another fact is that fresh water is in short supply in dry regions. Thirdly, in “once through” power plants, cooling water is used once and then released back into the environment, usually into a river, where its heat can cause harm to fish and other aquatic life.

ACCs use air to cool steam after it powers the turbines. They use considerably less water compared to water-cooled power plants but they cool steam less efficiently, particularly in regions with high ambient air temperatures.

Due to this inefficiency, power plants using ACCs require extra fuel per kilowatt-hour of power generated and are more costly to operate.

Charles is eager to enhance the cooling efficiency of ACCs by supplementing them with PCMs. In a lab in Lehigh’s Energy Research Center (ERC), he has constructed a cycling testing machine that can test 200 g of hydrated salt, melting and refreezing the material once every two hours for 12 cycles per day. Across a nine-month period, the machine will replicate the effects of eight years of use of the material in a power plant.

Charles is working with numerous different variations of the salt, incorporating a nucleation agent in an effort to enhance the PCM’s performance and extend its useful life in a power plant.

We’ve done 300 cycles - about a month’s worth—on some of the materials. So far, in all three materials, we’ve seen no loss in performance.

Joshua Charles

The three-year project is funded by the federal Advanced Research Projects Agency-Energy, or ARPA-E. Lehigh is a subcontractor on the grant, which was awarded to Advanced Cooling Technologies of Lancaster, Pa. The University of Missouri is also participating.

ERC director Carlos Romero and Neti are the project’s chief investigators at Lehigh, which is supervising material development and corrosion testing. Several other Lehigh students are working on other aspects of the project, including graduate students Xingchao Wang, Chunjian Pan and Fengxiang Nie and undergraduate Anika Chakravarti.

The ERC maintains research projects in power plants, energy efficiency and pollutant emissions control, renewable energy, clean fuel utilization, and crosscutting technology research and development.

The researchers anticipate scaling up the PCM cooling technology that Charles is testing, building first a 1-kWh prototype and then a 200-kWh prototype prior to testing the final product in a power plant.

The goal is to create PCMs that take heat from the steam after it has passed through the turbines, store that heat during the day and then reject, or discharge it at night, when air temperatures drop.

Charles earned an M.S. in mechanical engineering from Lehigh in 2011 after finishing a B.S. in physics from Mansfield University of Pennsylvania.

His earlier research at Lehigh was related to the countrywide efforts to decrease pollution from coal-fired power plants. For his M.S. thesis, Charles explored the capture and sequestration of carbon dioxide, a greenhouse gas discharged by power plants. He also completed a project with Air Products and advised utility operators in North Dakota and Virginia.

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