09 Dec 2015 [Just appeared]
Tim De Chant
It’s another steamy day on the outskirts of Houston, Texas. The temperatures are hovering just above 90˚ F, and my car’s air conditioning is struggling to keep up. The engine, probably laboring under the strain of the AC compressor, is groaning loudly as I hurtle down a backroad past cattle ranches and cotton fields. I’m on my way to see a promising first step in what might be our best hope for reversing climate change—not just reducing our carbon emissions, but removing CO2 from the atmosphere.
Suburban Houston is perhaps the least likely place to kick off the carbon-negative revolution. Sprawling over hundreds of square miles of south Texas’s coastal plains, the metropolitan region is bound together by cheap gas and massive ten-lane expressways flanked by three-lane access roads that feed strip mall after strip mall, each less distinguishable than the last, their parking lots brimming with full-size trucks and SUVs.
But soon, over the long horizon, under a hazy, cotton-candy sky, the near future resolves itself. Rising beneath the four towering smoke stacks of W.A. Parish—the nation’s largest fossil fuel plant—is a more modest tangle of beams and pipes known as Petra Nova. When finished, NRG’s newest five-acre chemistry kit will draw a portion of the exhaust from Unit 8, a 610-megawatt coal-fired electric generator, remove 90% of its carbon dioxide, compress the greenhouse gas, and send it to be stored in an oilfield some 80 miles to the southwest.
Unit 8 at NRG’s W.A. Parish plant will soon be hooked up to a carbon capture system.
Petra Nova will capture 1.6 million tons of CO2 annually, and by itself, it’s not going to do much to alleviate climate change. But the technology it uses could someday—soon perhaps—transform the dirtiest coal power plants into terraforming machines that could rein in today’s runaway CO2 levels.
In other words, by the end of this century, this coal plant, or one very much like it, could be saving the planet. But can we build enough of them in time?
The road to the Petra Nova field office is lined with imposing steel cubes and half-finished metal frames. Cherry pickers hoist workers to dizzying heights as portable generators and compressors thrum below. I park my car and step out into the sweltering sun where I’m greeted by John Ragan, president of both NRG’s Gulf Coast region and the company’s Carbon360 business group. Ragan is a veteran of the Gulf Coast oil and gas industry, and even in his crisp white shirt and pressed slacks he seems perfectly comfortable in the heat, humidity, and organized chaos that define Southern construction sites. After a brief chat inside the mercifully air conditioned field office, we head out for a tour of the plant with Ragan, Jim Tharp, senior director at NRG overseeing construction here, and Dave Knox, senior director of communications for the company.
John Ragan, president of NRG’s Carbon360 business group, explains how Petra Nova’s CO2 scrubber will work once it’s assembled.
Coal-fired power plants may seem imposingly complex from the roadside, but they’re surprisingly simple. Pulverized coal is fed into the boiler and burned, turning water into steam which powers a turbine that turns a generator. Even the pollution control equipment is straightforward. In one chamber, giant bags—similar to those in a vacuum cleaner—trap particulates from the exhaust gas. In another, limestone slurry is mixed with the exhaust to react with sulfur dioxide, which produces gypsum.
Carbon capture systems are just as simple. At Petra Nova, exhaust gas flows into a 320-foot-tall tower packed with a dense thicket of metal that’s drenched in an amine solution. The CO2 reacts with water and the NH2 of the amine to produce bicarbonate (HCO3–). The solution is then pumped to a 180-foot-tall regenerator—delivered from Korea last week in one piece—which heats up the amine to release the CO2. The gas is then compressed and injected underground into an oil field to push out more crude. (When the goal isn’t oil production, it’s stored in deep saline aquifers.)
Exhaust gas from W.A. Parish’s Unit 8 flows through a duct to the CO2 scrubber where it reacts with an amine solution. CO2 is then released from the amine solution in the regenerator, which is powered by a natural gas power plant.
Work on Petra Nova started in 2009 after the company was awarded a $167 million grant from the Department of Energy, a little more than 10% of the demonstration plant’s estimated $1 billion price tag. “That really gave us the momentum to move forward,” Ragan says.
That momentum would soon be tested. In the early days of the Obama administration, when Democrats still controlled the House of Representatives and had a simple majority in the Senate, it was a foregone conclusion that CO2 emissions would be regulated in some fashion, most likely through a cap-and-trade program where utilities and other polluters could swap or buy emissions permits to stay under a legally mandated cap. A bill was introduced in the House, but it never made it to the Senate floor.
“When we started planning this, everyone assumed there would eventually be a price on carbon. Then there wasn’t,” Ragan says. “Our CEO David Crane told us to figure out how to make this work without a price on carbon.”
John Ward, managing director of Vivid Economics, a London-based consultancy, says that the lack of a price on carbon has scuttled a lot of similar projects. “A large part of what’s holding carbon capture and storage back is around the carbon price,” he says. For the technology to succeed, he adds, the price needs to be “sufficiently strong and reliable to make really quite significant capital investments.”
For NRG, the trick was finding someone willing to pay for the excess CO2. This being Texas, there was a nearby oilfield that could use the gas to squeeze more crude from the rock. The partnership will make Petra Nova profitable, but burning the extra oil it helps extract will counter the climate benefit of the CO2 it stores.
The Petra Nova demonstration plant, then, represents something of a hedge. For now, without regulatory or economic incentives to capture the carbon simply for storage, the project doesn’t make financial sense for NRG. But Ragan believes that’s likely to change. “We’re going to live in a carbon constrained world,” he says. “We have to do something with our existing coal power plants.”
From Neutral to Negative
There is something else that power companies can do with their existing coal power plants, and that’s burn biomass. While burning coal releases CO2 inhaled by plants millions of years ago, burning fresh biomass captures CO2 that’s circulating today. The idea isn’t new—power companies have been burning biomass for more than 20 years. Currently, there’s about 16.1 GW of biomass generating capacity in the U.S., or about 1.4% of the total. Some of that is burned in pure biomass plants, the rest in so-called co-fired plants that mix biomass with fossil fuels.
From a climate perspective, biomass energy is appealing because it burns plants, which suck CO2 out of the atmosphere as a part of everyday life. We don’t need to build specialized structures to capture CO2—we can let plants do it for us.
Wood pellets are frequently used as sources of biomass for power plants.
When done right, burning biomass is almost carbon neutral, where the amount of CO2 it emits is balanced by the CO2 plants absorb. The caveat is that the biomass has to be appropriately harvested or grown, with a focus on organic waste and quick-growing plants. Slow-growing hardwoods and old growth forests are definitely out of the question. “If you cut down a 100 year old rainforest, then it could take up to 400 years to pay back that debt, to make up for all that biomass that was standing perfectly happy in the Amazon,” says Daniel Kammen, director of the Renewable and Appropriate Energy Laboratory at the University of California, Berkeley. Biomass harvested for energy also has to be replaced with new plantings—if not, then burning biomass is worse than coal.
It’s tempting to think of biomass as an easy fix—that we could switch the grid from fossil fuels to biomass—but it would place enormous demands on both human ingenuity and life on Earth. “We would need something like a quarter of all the net primary production, the total plant growth on the Earth’s surface,” says Chris Field, director of the Carnegie Institution’s Department of Global Ecology. “That’s completely unrealistic.”
“But what’s a meaningful level?” he continues. “Would a meaningful level be at one, two, five percent of the global energy system? I think the answer is that we’re looking at a 21st century energy system that’s likely to have lots and lots of components so that contributions of a few percent will be meaningful. There’s every reason to think that biomass should be considered at that kind of scale.”
Even utilizing 5% of all plant growth—about 12.3 gigatons, an amount approaching the productivity of the world’s farms—won’t do much to tamp down carbon emissions. In fact, biomass is not quite carbon neutral because it still has to be harvested and hauled before it’s combusted, and right now, both require fossil fuels. On balance, burning biomass still releases CO2, just less than burning coal.
But the good news is that biomass power plants, just like their coal cousins, release their CO2 in conveniently concentrated streams of hot gas. And as projects like Petra Nova and others are demonstrating, we know how to capture and store CO2 from those emissions.
So to start removing CO2 from the atmosphere—and possibly begin reversing climate change—all we have to do is combine them. “The innovation is putting the two together,” Kammen says.
Best of Both Worlds
Scrubbing CO2 from power plant emissions is based on old technology. The amine-based process used at Petra Nova and other carbon capture and sequestration (CCS) plants has been around for for a long time. “It was patented in the 1930s,” says Howard Herzog, a senior research engineer at MIT’s Energy Initiative. “The process has improved since then, but the fundamentals are basically the same. You’ve got something that’s been around 80 years and developed. A lot of the issues have been worked out.”
The idea to combine bioenergy with CCS had emerged early in the 1990s, and the original goal was to make coal power stations carbon neutral. A little later in the decade, other scientists started exploring how to remove CO2 directly from the atmosphere. It wasn’t until 2001, when Kenneth Möllersten, an engineer with the Swedish Energy Agency, and Jinyue Yan, a professor at the Swedish Royal Institute of Technology, put two and two together. Rather than push the limits of chemistry to capture CO2 from the open air, they realized that we could let trees, grasses, and other plants do the hard work. All we’d need to do is collect and burn them, capture the CO2, and find somewhere to store it for a long, long time.
A crane lowers a piece of the CO2 scrubber into place at Petra Nova.
Burying the CO2 from power plants deep underground has some inherent benefits. Unlike forests, which are also excellent long-term carbon sinks, stored CO2 can’t easily be rereleased. Once buried, it isn’t likely to surface for thousands, perhaps millions, of years. Today, we have no way of guaranteeing that a forest will be left standing for that long. Plus, all plants eventually die and decay, releasing their carbon. Bioenergy with CCS is a best-of-both-worlds approach. With it, we can take advantage of plants’ natural ability to capture CO2 and then use a proven technology to lock those emissions away.
“Neither piece of what we’re talking about, individually, is technically hard,” Kammen says. “But then when you start looking at it as a system, then it gets interesting.”
Searching for Supplies
Recently, Kammen and a handful of his students decided to see if, by 2050, they could reduce carbon emissions by 145% below 1990s levels for a chunk of North America known as the Western Interconnection—the regional power grid that supplies the Western U.S., the Canadian provinces of Alberta and British Columbia, and a chunk of Baja California in Mexico. Essentially, they would be transforming a region from one that produced CO2 pollution into one that would remove it from the atmosphere.
They started their simulation by replacing nearly all fossil fuel power sources with renewables, including wind, solar, hydro, and geothermal. Then they ramped up biomass energy with CCS, also known as BECCS, to provide an always-on source of power that also removed CO2 from the atmosphere. By 2050, they were using nearly all available biomass supplies, which included everything from trash to orchard waste and wood from fast growing trees.
Biomass energy’s insatiable demand for combustible material is usually where it hits a roadblock. There’s only so much biomass to go around, and collecting and trucking it to various power plants will require entirely new supply chains that don’t currently exist. “It becomes increasingly expensive to supply large quantities of biomass as opposed to smaller quantities,” says Ed Rubin, a professor of engineering and public policy at Carnegie Mellon University. “Most biomass facilities are relatively small—an order of magnitude or sometimes two orders of magnitude smaller than a typical coal fired plan. It’s a supply issue.”
The current cost of supplying biomass is what’s kept NRG from co-firing any of their 19 coal plants with biomass. “We have explored biomass options at a number of plants across our fleet,” says Knox, the senior director of communications. “The problem we have encountered is getting a guaranteed and consistent supply that is close enough to the plant that you do not add to your carbon footprint through carbon-intensive trucking of the biomass.”
There’s also the danger that if BECCS is a runaway success it will start eating into food supplies. “We’re going to have to feed 9–10 billion people by 2050,” says Pete Smith, a professor of plant and soil science at the University of Aberdeen. “People are asking, is this the best use of land when we’ve got all these additional mouths to feed?”
Still, there are sources of biomass that can be used responsibly. “The clearest pool of biomass that’s available is waste products in agriculture and forestry,” says Field, the Carnegie Institution director. “That’s hundreds of millions of tons. It’s not a trivial quantity, but it’s not enough to dominate energy system. Whether there’s more biomass available really depends on one thing, critically: how much we’re able to increase agricultural yields in years ahead.”
Kammen’s study lists a variety of biomass options that wouldn’t eat into the food supply, from municipal waste to sawdust and dead corn stalks. At its most aggressive, the simulation also relies on wood and switchgrass grown specifically for BECCS, but those represent only a little more than 10% of the total biomass energy.
The post-harvest remains of corn stalks, known as corn stover, is a potential source of biomass.
Still, to roll out BECCS on a wide scale, the demands for land could be massive, especially if only dedicated crops were used. “This would be on an order of magnitude of several hundred megahectares of land,” says Sabine Fuss, head of sustainable resource management and global change at Mercator Research Institute on Global Commons and Climate Change in Berlin. A paper published this week by Smith, Fuss, and others suggests that relying on dedicated crops—no municipal, agricultural, or forestry waste—would consume between 320–970 megahectares of land. Currently, there are about 1,600 megahectares, or about 4 billion acres, of land under cultivation.
Then there’s the issue of transporting the resulting CO2 to a storage location. “We need an infrastructure in place to do that,” Smith says. “That’s probably an infrastructure on the size that we currently use to move gas and oil.”
Those are big hurdles, but none of the experts I spoke with saw them as insurmountable. “This is something that we could, in limited amounts, do yesterday.” Kammen says. “We’re already doing all of it, just not in a coordinated way.”
Key Piece of the Puzzle
NRG expects their Petra Nova carbon capture project to be operational sometime next year, which means it will have taken about six years to move from planning to completion. In terms of large capital projects based on new technology, that’s relatively quick, and as more are built, we’ll probably get faster at it.
But can we build them quickly enough? Nearly everyone I spoke with said the optimal time to to deploy BECCS was yesterday. Realistically, though, Petra Nova’s timeline seems about right. “It’s probably instructive to look backwards a bit before you look forward to see how quickly other kinds of technologies have been deployed absent a true wartime footing,” Rubin says. New natural gas power plants, he says, take about three to four years to build, while new coal plants take about eight to ten.
Start to finish, Petra Nova will take about six years to plan, engineer, and build.
The International Energy Agency estimates that about $4 trillion will have to be spent building CCS facilities between now and 2050. That may seem like a vast sum, but consider that countries around the world currently subsidize fossil fuels at more than quadruple that amount, or about $490 billion every year. If that figure holds constant for the next 35 years, we’ll have spent $17 trillion of public money supporting oil and gas. (They receive the vast amount of subsidies—coal only gets about $3 billion per year.)
We may not have to build entirely new power plants, either, but just add CCS to existing ones. Here again, the Petra Nova retrofit can be instructive. “One way you could ease into a BECCS environment is looking at coal fired power plants and beginning to increase the fraction of biomass you burn in those,” Field says. Many coal plants can already burn small amounts of biomass with few if any modifications. “If you’re cofiring those with biomass, that provides a possibility of a carbon negative component of a system that you can scale in in a very gradual way so you’re beginning to make a difference right away. You could think about having thousands of power plants that are running 5–10% biomass in a way that really begins to change the equation and doesn’t require building any new power plants.”
But, Kammen is quick to caution, “we’re not going to solve the climate story with BECCS.” Pete Smith agrees, seeing “BECCS, rather than a magic bullet, being another piece—and maybe another significant piece—of a jigsaw of future possibilities.”
We’ll still have to move most of our power supply to renewables like wind and solar, but BECCS seems too promising to overlook. “The big upside of BECCS is that you have something which solar, wind, and geothermal can’t get you, and that is an ability to make up for our past emissions and draw carbon numbers down,” Kammen says. “We’re so far above a reasonable trajectory that we’re going to need carbon negative.”
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