Capturing carbon dioxide from power plants is, at least theoretically, a good way to reduce one of the top gases that contributes to climate change.
But in reality, it’s hard – and so far, inefficient.
Carbon capture pilot projects across the country have come and gone. But even though it’s technically over, the pilot project at one power plant in Central Kentucky remains. There, University of Kentucky researchers continue to test technology they say is cheaper and more efficient than others being tested around the country.
At Louisville Gas & Electric and Kentucky Utilities’ E.W. Brown Plant, near Danville, there’s a six-story open structure attached to one of the plant’s units. It’s a scaffolding-like maze of yellow, blue and silver metal.
Kunlei Liu stands under it, wearing a hardhat and safety glasses, ready to explain the intricate workings of the device.
Liu is an engineer with the University of Kentucky’s Center for Applied Energy Research, and this is a carbon capture system. Or to be more specific, this is a carbon capture pilot system, attached to Unit 3 of the Brown Plant. It captures some of the carbon dioxide that would normally come from burning coal in the unit, and uses a complicated process to separate that CO2 from the other gases.
Liu points to the apparatus.
“What we’re doing and what we built over here, is we take the flue gas off the [Flue Gas Desulfurization Unit] on the top of the duct over there,” he said. “Then we bring it all the way over here just to get it in our CO2 capture plant.”
The carbon dioxide pumped out by coal-fired power plants is contributing directly to climate change. And in the future, though the power plants might still burn coal, industries want a way to do that while emitting less CO2.
So all over the country, scientists are trying to perfect the technology. Since 2008, Congress appropriated more than $7 billion for the research at the Department of Energy — and some of that money went to projects like this one in Kentucky.
Liu’s system was announced in 2014, and it was meant to test a new way of separating carbon dioxide. He says it worked.
One of the biggest problems with carbon capture systems now is that they’re inefficient. The systems use so much energy that a power plant has to burn more coal just to power them. The technology at Brown uses two different techniques to extract the carbon dioxide, and also reuses some of the heat that would otherwise be lost.
“The CO2 capture always requires the energy,” Liu said. “What we’re trying to do is heat integration — to take the energy that’s a low quality to use it to regenerate the solvent.”
Carbon capture usually involves spraying some sort of liquid solvent onto the power plant’s flue gas, which contains carbon dioxide. The liquid absorbs the CO2. Then the solvent is regenerated with a heated vessel, the carbon capture pops off with a higher purity, and it’s compressed and disposed of.
The University of Kentucky’s project follows the same basic steps. But it actually works to make the power plant more efficient, even as it removes carbon dioxide. Here are three key factors:
- The project integrates some of the heat that’s being typically rejected from the carbon capture system back into the power plant and capture system. By reusing some of that heat that would otherwise be lost, it makes the plant more efficient.
- The full-scale system proposes to use two different techniques to extract carbon dioxide from the solvent. Most similar systems only use one: the solvent containing the CO2 is regenerated in a heated vessel, where the CO2 is separated from the solvent. This system also passes air over the solvent in a second vessel. This air-based regeneration removes additional CO2 from the solvent for recycling.
- Some of the low-level heat produced by the full-scale carbon capture system will be channeled into a drying system that dehumidifies the cooling air in the power plant’s cooling tower. This increases the power generation of the plant and increases efficiency.
UK concluded the technology was a success last year, reporting it captured 90 percent of the CO2 that went through its system. And the system at Brown performed better than most, in terms of efficiency. But it’s expensive; at best, this system will end up working out to a cost of about $40 per ton of carbon dioxide.
Even though there are lots of people pulling for it, the billions of dollars of cost overruns at the country’s few full-scale carbon capture systems makes Pat Knight of Synapse Energy Economics — a Boston-based energy consulting firm — pessimistic about the prospects.
“The idea that coal CCS could be economically viable without some sort of incredibly high carbon tax seems like a stretch to me,” he said.
Synapse is a Boston-based energy consulting firm. Knight pointed to two projects in particular: the Kemper coal plant in Mississippi that’s so far three years behind schedule and $3 billion over budget, and the Edwardsport plant in Indiana, which was more than $1.5 billion over budget.
Knight said there are two ways to make carbon capture – or CCS – systems make sense from a financial standpoint. One is to find a market for the carbon dioxide these systems are capturing, like how some places are using it for enhanced oil recovery. The other is making it too expensive for coal plants to operate without it, like through a carbon tax.
But Knight said the biggest hurdle is just that there are other, cheaper ways to generate electricity with less carbon dioxide. He said in some places, wind and solar are actually the least-cost option, and they don’t generate any carbon dioxide.
"Even if there were a regional or even nationwide carbon tax or carbon cap, it seems unlikely that installing carbon sequestration devices at the existing coal plants would be economically feasible, compared to all the other options that are available for providing electricity to Kentucky," Knight said.
Back at the Brown plant, Kunlei Lui said he doesn’t know if carbon capture will ever take off. But predicting that isn’t his job. He’s an engineer, and he’s determined to test the technology and get it as efficient as possible.
So far, the project has cost more than $21 million, including private and public money. The University of Kentucky, LG&E, KU and the other partners intend to continue it, hopefully trying out larger and larger systems. If the market ever calls for carbon capture systems on coal-fired power plants, they want to be ready.
