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Goodbye smokestacks: Startup invents zero-emission fossil fuel power

May 24, 2017
Science

Between the energy hub of Houston, Texas, and the Gulf Coast lies a sprawling petropolis: a sea of refineries and oil storage tanks, power lines, and smokestacks, all dedicated to converting fossil fuels into dollars. They are the reason why the Houston area emits more carbon dioxide (CO2) than anyplace else in the United States.

But here, on the eastern edge of that CO2 hot spot, a new fossil fuel power plant showcases a potential remedy for Houston's outsized greenhouse gas footprint. The facility looks suspiciously like its forebears, a complex the size of two U.S. football fields, chock-a-block with snaking pipes and pumps. It has a turbine and a combustor. But there is one thing it doesn't need: smokestacks.

Zero-emission fossil fuel power sounds like an oxymoron. But when that 25-megawatt demonstration plant is fired up later this year, it will burn natural gas in pure oxygen. The result: a stream of nearly pure CO2, which can be piped away and stored underground or blasted into depleted oil reservoirs to free more oil, a process called enhanced oil recovery (EOR). Either way, the CO2 will be sequestered from the atmosphere and the climate.

That has long been the hope for carbon capture and storage (CCS), a strategy that climate experts say will be necessary if the world is to make any headway in limiting climate change. But CCS systems bolted to conventional fossil fuel plants have struggled to take off because CO2 makes up only a small fraction of their exhaust. Capturing it saps up to 30% of a power plant's energy and drives up the cost of electricity.

In contrast, NET Power, the startup backing the new plant, says it expects to produce emission-free power at about $0.06 per kilowatt-hour. That's about the same cost as power from a state-of-the-art natural gas-fired plant—and cheaper than most renewable energy. The key to its efficiency is a new thermodynamic cycle that swaps CO2 for the steam that drives turbines in conventional plants. Invented by an unlikely trio—a retired British engineer and a pair of technology geeks who had tired of their day jobs—the scheme may soon get a bigger test. If the prototype lives up to hopes, NET Power says, it will forge ahead with a full-scale, 300-megawatt power plant—enough to power more than 200,000 homes—which could open in 2021 at a cost of about $300 million. Both the company and CCS experts hope that the technology will then proliferate. "This is a game-changer if they achieve 100% of their goals," says John Thompson, a carbon capture expert at the Clean Air Task Force, an environmental nonprofit with an office in Carbondale, Illinois.

In 2009, contacted Rodney Allam, a chemical engineer who had run European R&D operations for Air Products, an industrial giant in the United Kingdom. Later, in 2012, Allam won a share of the $600,000 Global Energy Prize, sponsored by the Russian energy industry, for his work on industrial gas production. But at the time, he was mostly retired, concentrating on his fishing, lawn bowling, and gardening.

Palmer and Brown hired Allam as a consultant. Inspired by some Russian research from the 1930s, Allam thought he saw a way to radically reinvent the staid steam cycle. Forget about boilers, he thought. He would drive everything with the CO2 itself, making an ally out of his enemy. "The only way you could proceed was to develop a totally new power system," Allam says.

Allam envisioned the CO2 circulating in a loop, cycling between a gas and what's called a supercritical fluid. At high pressure and temperature, supercritical CO2 expands to fill a container like a gas but flows like a liquid.

For decades, engineers have worked on Brayton cycles—thermodynamic loops that take advantage of the properties of supercritical fluids, which could be air or CO2. Supercritical fluids offer advantages: Because they are fluids, a pump can pressurize them, which takes far less energy than a compressor needs to pressurize a gas. And because of the fluidlike gas's extra density, it can efficiently gain or shed heat at heat exchangers.

Full version of the article is available by the link - http://www.sciencemag.org/news/2017/05/goodbye-smokestacks-startup-invents-zero-emission-fossil-fuel-power?utm_source=sciencemagazine&utm_medium=facebook-text&utm_campaign=netpower-13213 

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