New process marries solar, natural gas

Matthew L. Wald / New York Times News Service /


Published Apr 14, 2013 at 05:00AM / Updated Nov 19, 2013 at 12:31AM

Using the sun’s heat to break open the molecules of natural gas, researchers hope to reduce emissions produced by gas by as much as 20 percent. But there are still a lot of kinks to work out before it’s commercially viable.

WASHINGTON — The Energy Department is preparing to test a new way for solar power to make electricity: using the sun’s heat to increase the energy content of natural gas.

Researchers at the Pacific Northwest National Laboratory in Richland, Wash., hope by this summer to carry out the test, which entails a process that could cut the amount of natural gas used — and the greenhouse gasses emitted — by 20 percent.

“We can reduce carbon dioxide emissions, and the consumer doesn’t get hit,” said Robert Wegeng, the researcher in charge of the project.

The system is a marriage of chemical and mechanical engineering. The process will work anywhere it is sunny, according to researchers, although it might be more valuable in places where natural gas is relatively expensive, or where a company making electricity would be paid for generating less carbon dioxide.

The project, financed with $4.5 million in federal stimulus money, is still in development, and experts say the technology’s costs have yet to be established. The process also is several major steps away from commercial viability.

Using the sun’s heat to make electricity is hardly new; as far back as 2007, companies were building plants with parabolic mirrors to boil water into steam and turn a turbine. In Australia, Areva built a plant that helps reduce the amount of coal needed to make electricity by using solar power to preheat the water that the burning coal boiled into steam.

The new system captures solar energy in a chemical form, using the sun’s heat to break open the molecules of natural gas (four hydrogen atoms and one carbon atom) and water (two hydrogen atoms and one oxygen atom) and reshuffle them into something that burns better: carbon monoxide and pure hydrogen. The result also has carbon dioxide, which is inert.

The mixture, called synthesis gas, is a common building block in the chemical industry, but it requires energy to make it, usually from burning natural gas. In the Pacific Northwest design, that energy comes from the sun. Sunlight falls on a mirrored dish that looks a bit like an upturned umbrella, and focuses on a spot where the umbrella handle would be. It heats water and natural gas to 700 degrees Celsius, about 1,300 degrees Fahrenheit. A catalyst breaks the molecules up and the atoms are reassembled.

Laboratory officials say they have improved the efficiency of the process. But they also have introduced a second innovation: Before the synthesis gas is sent to a turbine for burning, a new kind of heat exchanger extracts some heat from it. That heat is added to the chemical reactor, further improving the efficiency of the solar side of the process.

If the system starts with 1 million BTUs of natural gas, the standard unit for pricing, then the synthesis gas has a value of about 1.25 million BTUs. That means turning $4 of gas into $5.

Michael Webber, an associate professor of mechanical engineering at the University of Texas at Austin and a co-director of the clean energy incubator there, cautioned that there were still a lot of “engineering kinks to sort out.” He called the resulting gas “a wonderful fuel, but it’s a pain in the neck to make.”

The technology might be economical in a place like Japan, where natural gas prices are higher, he said. “We might as well master the technology and sell it to them,” he said.

Researchers hope they can find other improvements that will probably be necessary to win commercial acceptance of the technology in North America, where gas prices are low. Wegeng also said that mass production would drive down prices of the necessary components.

Unlike other forms of solar energy, the hybrid solar/gas plant is intended to supply steady levels of electricity.

“When the sun is shining, you get this solar augment to the fuel,” said Wegeng. If clouds roll in, or if the sun sets, then the turbine can burn ordinary natural gas and produce the same amount of electricity. “You’re just using more natural gas,” he said.