Daniel Schrag gets visitors all the time—graduate students in despair over their dissertations, fellow faculty members dropping by to chat about the Cretaceous sulfur cycle or some equally abstruse topic, or visiting scientists collaborating with him on one of the scores of scholarly papers he has churned out in a career that has earned him a professorship in Harvard’s department of earth and planetary sciences and a MacArthur genius grant.
The two men who stopped by his office one afternoon three years ago were not interested in professorial chitchat, however. Frank Smith and Jim Croyle are hard-nosed businessmen, and they wanted Schrag’s advice on a major investment. Smith and Croyle are cofounders of SCS Energy, a power plant development company in nearby Concord, Massachusetts, and they were planning to spend 5 billion dollars on a radical new type of coal-based power plant called PurGen One. Burning coal accounts for about 40 percent of all carbon emissions worldwide, but this plant would emit essentially no carbon at all. Smith and Croyle had read some of Schrag’s papers about carbon capture and sequestration, or CCS—a technique for keeping globe-warming carbon dioxide out of the air by burying it—and they were ready to put it into action. “I was kind of surprised,” Schrag admits. “I told them, ‘I’d love it if you’d sequester carbon. But how would you make money?’”
Coal is plentiful around the world, especially in three of the most energy-intensive economies: the United States, India, and China. It would be tough to abandon it entirely. On the other hand, capturing the carbon from a coal-burning plant and pumping it underground is expensive. Such “clean coal” technology could cost 50 percent more than regular, dirty coal-generated power, wiping out much of the black rock’s economic appeal. Schrag politely brought up all the reasons why CCS might never be commercially viable, but Croyle and Smith just kept talking. They didn’t seem to care how much money it took to get started. “They knew the project depended on making a profit,” Schrag says, “and they thought they had figured out the way to do it.”
As the two investors explained their plan, Schrag grew increasingly excited: They had come up with a breakthrough in clean-coal power generation that just might work. PurGen would transform raw coal into cleaner-burning hydrogen and fire its generators with that instead, in a process that would also yield valuable by-products. Croyle and Smith already had a few potential sites in mind (they later decided on a heavily industrial section of Linden, New Jersey), and they were convinced they could have their plant up and running by 2016, largely by using off-the-shelf technology. The project could mark the beginning of a transformation in the way we produce electricity. We could drastically cut back on human-generated carbon emissions without giving up on an energy source that could last us a century or more.
If all Croyle and Smith had to offer was the idea of turning coal into hydrogen, Schrag would not have been impressed. The basic technology for turning coal into other fuels, known as gasification, has been around since the 1920s. During South Africa’s apartheid period, for example, the country could not import oil, so it gasified locally abundant coal to make gasoline. Creating hydrogen requires merely tweaking the process. To do so, explains PurGen project manager Tim Bauer, coal is ground up and heated under pressure in the presence of oxygen. The right mix of heat, pressure, and chemistry keeps the coal from burning; instead, it undergoes a series of reactions that give rise to a mix of gases, including hydrogen, carbon monoxide, nitrogen, and sulfur dioxide. The solids left over at the end are recycled back into the pressure vessel, where more gases are extracted until all that is left are “clinkers”—inert, glassy cinders that can be added to concrete to strengthen it. The gases, meanwhile, are combined with steam, which changes the carbon monoxide to carbon dioxide that can be extracted, liquefied, and buried.
Processing coal this way is substantially more complicated than burning it whole, which is why Schrag initially assumed that SCS Energy’s plan would be a money loser. “Even regular coal-fired power plants are generally terrible investments,” Bauer says. They cost billions of dollars to build but make money only part of the time. During the day, when people are using computers, appliances, electric machinery, and so on, the plants can sell all the power they can churn out. At night, though, demand goes way down—especially in winter, when air conditioners are turned off.
Here is where the cleverness that sparked Schrag’s interest comes in. At an estimated $5.2 billion to construct, PurGen will be twice as expensive as a conventional coal plant. But what the SCS people realized is that while coal is pretty much good for only one thing, the hydrogen locked inside the coal has multiple uses. In particular, it can be a feedstock to make ammonia and urea, which are used to manufacture fertilizer. So the PurGen plant will be two plants in one: a hydrogen-burning power plant churning out electricity when demand is high, and a chemical plant making hydrogen-based ammonia and urea when electricity demand is low. And sulfur dioxide extracted from the coal will be converted into sulfuric acid and sold as well. As a result, PurGen should yield substantially more income than a conventional 750-megawatt coal power plant could. “It puts the capital investment to work 24 hours a day,” Schrag says.
And churning out ammonia and urea is only one potential source of extra income. Hydrogen has plenty of other applications. It can be used to generate electricity in fuel cells, for example, which could become a significant source of energy for transportation and distributed power in the coming decades. At present, most commercially produced hydrogen is derived from natural gas in a process that “has an awful carbon footprint,” Bauer says. Any serious attempt to tax or cap carbon emissions would make PurGen’s hydrogen much more attractive to the chemical industry than the conventional sort.
Strictly speaking, PurGen will not be entirely emission-free. When you burn hydrogen in pure oxygen, the only by-product is water; when you burn it in air, as PurGen will, you also get nitrogen oxides. The urea plant will create some particulate emissions too. Bauer says all of these will fall well within state and federal pollution guidelines. The big advantage of PurGen, though, is that it avoids the copious carbon emissions that normally come with burning coal.
The captured CO2 will be liquefied on site and pumped through a two-foot-diameter pipeline that will snake south through the waters of the Arthur Kill, turn eastward through Raritan Bay out into the Atlantic Ocean, and arrive, about 140 miles later, at a natural repository of Lower Cretaceous sandstone more than 8,000 feet below the seafloor. The formation is huge, stretching from Long Island to Georgia. It is highly permeable, making it easy to pump the CO2 in, and is capped by layers of impermeable shale with a total thickness of about a mile, making it hard for the CO2 to get back out. “There’s no way that CO2 is going to leak out in a million years,” Schrag says.
SCS acknowledges that even with sharply reduced emissions, coal is inherently dirty. No matter how you burn it, you still have to mine it—dumping West Virginia mountaintops into nearby rivers, gouging huge scars into the earth in Montana or Wyoming, and exposing miners to the risk of injury or death. “We take these issues seriously,” Bauer says, “which is why we’ve pledged not to use mountaintop-removal coal.” Instead, the company will use high-sulfur coal—mined mostly in Pennsylvania, Ohio, and West Virginia—and will then pull the sulfur out as part of the CCS process.