Could Electrons Be Used to Clean Up Coal Emissions?
How a laser developed for nuclear fusion may be repurposed to scrub coal emissions.
Image: Dergenaue/Wikimedia Commons
By 2008 John Sethian, a leading plasma physicist at the Naval Research Laboratory in Washington, DC, had been working on nuclear fusion—the holy grail of clean energy—for close to a decade.
He and his team had recently built a potential game-changer: a laser that was durable and highly precise, allowing researchers to fire energy at a bundle of isotopes in hopes of starting a reaction that produced more energy than it consumed. Plans had been drawn up for a reactor based on the new laser, and a long-term test of the system was scheduled.
But just as they were on the verge of a breakthrough, Sethian's fusion program's funding was killed in the 2009 fiscal year during routine budget cuts.
For Sethian, this represented the end of a lot of hard work. Fusion—compressing atomic nuclei with such force that they produce more power than they take in—involves such extremes of precision and force that years of intense research can go into any single component. But after the initial disappointment, he and his team started hunting for a new use for their invention.
"We were left with very durable electron beam technology nobody ever had before," Sethian said. "You gotta be able to do something with it."
As it turns out, Sethian's laser technology could still be a step toward cleaning toxic emissions from coal power plants. Specifically, NOx.
NOx is nasty stuff. Made up of nitrogen oxide and nitric oxide, it enters our atmosphere mainly from automobiles, causing acid rain, smog, ozone, and a host of other grim effects. (NOx is among the chief targets of the exhaust-scrubbing catalytic converters that have been installed in all vehicles since 1975, leading to visibly improved air quality in car-heavy regions like Los Angeles.) It's also one of the most concerning emissions at coal plants.
Up to now, the most common ways of limiting NOx have involved introducing other chemicals—like platinum plates in automobiles or ammonia gas in power plants—to catalyze the compounds into less immediately harmful ones. This introduces inefficiencies, and in the latter case produces highly explosive ammonium nitrate, often used as a fertilizer.
In theory, a plant could clean its own emissions using pure physics instead of chemistry
But if you could scrub NOx without any additional ingredients, the process would be vastly cheaper and more efficient. In theory, a plant could clean its own emissions using pure physics instead of chemistry.
Back at the Naval Research Laboratory, Sethian's team had been working on a nuclear fusion approach called inertial confinement fusion. It works (or would work) by compressing a 5mm pellet of hydrogen isotopes deuterium and tritium, using an array of powerful pulsing lasers.
Most lasers aren't consistent enough to strike at the pellet directly, though—the National Ignition Facility, for example, fires its beams into a pencil eraser-sized container called a hohlraum, which in turn emits x-rays that then compress the pellet.
Sethian and his team developed a super-smooth Krypton Fluoride laser that could repeatedly fire at the pellet directly, powered by pulsed electron beams that could survive the intense forces generated over thousands of shots.
A few years after his program lost its funding, Sethian and co. began publishing papers on the possible use of their laser in treating NOx.
Electron energy had been used this way before, but only with continuous beams that still required the addition of ammonia. Sethian's team claims the pulsed electron beam technology they developed can be used to scrub up to 98 percent of NOx without any additional agents or byproducts.
The new approach involves firing short—around 20 billionths of a second long—bursts of electrons directly into coal or gas emissions. By introducing just the right amount of electron energy in precisely timed shots, the NOx compounds break up and recombine into their inert constituents: nitrogen and oxygen, stuff you're breathing now.
That means no ammonia to add, no ammonium nitrate to transport, and a more efficient process overall that actually leads to less NOx anyway.
"It just goes into this box and comes out clean," says Sethian.
Various sources of possible funding, including the Department of Energy, passed on the idea before entrepreneur Steve Kennedy took notice. He'd already been speaking to people in the energy industry about ways to cut costs, and they'd told him that the best thing he could do would be to find a way of cutting operational costs in meeting ever-tightening emissions regulations.
Zerronox, which now owns the rights to the NRL's pulsed electron beam technology, is the company Kennedy formed in partnership with an unnamed energy provider in order to establish the technology at a real power plant.
So far, pulsed electron beams have only been tested in the lab. Gases from a bona fide coal burning power plant include additional elements that complicate the process, and further testing is required before the approach is field-ready. Physical limitations of the technology mean automobiles, the largest contributors of NOx, probably won't get a pulsed electron beam retrofit, but current models show an upward scalability to power plants of 600 megawatt capacity, enough to power roughly 4,300 homes. The pulses can be dialed in to match the varying output of a given plant, or to keep to the emissions requirements of a given locality.
Sethian estimates it'll take about two years to get the kinks worked out in an operational prototype. The plan involves installing a pulsed electron beam array along a series of ducts to zap slugs of boiler exhaust before they reach the plant's smoke stack.
Reducing NOx emissions is great of course, but the best technology like this can do is polish some dirt off of an essentially filthy industry. Meanwhile, fusion is one of the most exciting areas of research today.
By wielding the same nuclear forces that power main stage stars like our sun, scientists think they may soon build machines that can generate what is essentially clean and free energy. Physicists are telling us that we're achingly close to what might count among the most significant developments in human history—free energy—and while weapons budgets continue to soar, relatively modest programs are targeted for cuts.
So why did the fusion project get cut off just as it had reached a tipping point?
So why did Sethian's project get cut off just as it had reached a potential tipping point in the search for free, clean, nearly limitless energy be cut from the national budget?
You can always point a finger at the oil and gas industries, which are a powerful influence in government. But another possible explanation is that the High Average Power Laser research done by Sethian's team at NRL was oriented specifically at generating fusion power, while facilities like the National Ignition Facility are explicitly oriented toward nuclear weapons research, a front the US government has continued prioritizing despite its non-proliferation rhetoric.
Sethian declined to discuss the issue. "We're not going to get into the politics of all that, but nevertheless let's just say it ended, not our first choice," he said.
In any case, for almost ten years, the HAPL program cost some $190 million to pursue free and clean energy. Nuclear weapons research and maintenance costs over similar time-frames, by contrast, go into the hundreds of billions.
We may never see the awakening in world leadership that makes clean energy a true priority, and failing some magic bullet technology that satisfies all the bottom lines at play, any greener shade of future is likely to be approached in small, incremental steps. Many scientists haven't given up on the dream, even if their work must focus, for the time being, on more earthly goals.
"The fusion aspects of my program are, I like to say, dormant, not dead," says Sethian. "Me personally, I've devoted my career either to working on the ultimate clean energy source that doesn't exist yet, to cleaning up an energy source that does exist."