PNNL carbon capture process, image credit: PNNL

Carbon Capture For Less Than $40 A Ton? It’s Possible, Says PNNL

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Scientists at Pacific Northwest National Laboratory say they have have discovered a way to capture carbon dioxide as it’s emitted from power plants and factories, such as iron and steel manufacturing facilities, that costs less than $40 a ton.

Let’s be clear right up front. We aren’t talking about direct carbon capture here, the process of removing carbon dioxide that is already in the atmosphere. There are companies working on that technology, such as ClimeWorks, but it can cost $200 a ton or more. That sort of process may become critical in the future, after the world has figured out how to stop spewing carbon dioxide into the environment. PNNL says the average cost of capturing carbon dioxide from flue gases is around $57 per metric ton.

The PNNL system recognizes that energy generation and industrial processes will continue burning fossil fuels for the foreseeable future. Its technology can capture nearly 90% of the carbon dioxide in flue gases and sequester it before it gets into the atmosphere in the first place. Globally, industrial processes are responsible for 31% of total greenhouse gas emissions and electricity generation accounts for 27%, according to Bill Gates in his climate book. Combined, they dwarf the 16% of total greenhouse gas emissions that comes from the transportation sector. For all the technical and scientific details, please see the research paper published this week in the Journal of Cleaner Production.

Carbon Capture For Flue Gases

Even if the electric grid were powered primarily by wind and solar, there would still need to be natural gas plants to maintain grid stability, or to provide backup when the wind isn’t blowing or the sun isn’t shining, PNNL’s Casie Davidson tells CNBC. “We have the technology to be able to capture carbon dioxide from those industrial point sources. And sitting around waiting for 20 years until we have the next-generation steel technology that doesn’t generate carbon dioxide emissions doesn’t make a lot of sense,” Davidson said.,

“Imagine you’re trying to separate a grape out of a big bowl of spaghetti or you’re trying to separate the grape out of a swimming pool of spaghetti. You still get a grape, but you have got to do a lot more work in the swimming pool than in the bowl,” Davidson explained. “But from a from a climate change perspective, the atmosphere doesn’t care whether that grape came out of the bowl of spaghetti or the swimming pool of spaghetti — it has the same impact. From a societal perspective, capturing it before it ever gets out there, when it’s $39 a ton to capture, versus capturing it when it’s already in the atmosphere for $200-plus a ton, makes a lot more sense.”

Carbon Capture Using Solvents

PNNL’s technique uses solvent chemistry, explained David J. Heldebrant, a chief scientist at PNNL who is leading this research. The dirty gas comes out of the power plant or factory and is moved into a very large chamber. At the same time, a liquid is sprayed down from the top of the chamber. The gas rises and the liquid falls and the two substances mix. Treated gas leaves out of the top of the chamber and liquid containing the CO2 is siphoned away. That liquid is heated until the CO2 is released as a gas. The CO2 is compressed for transportation and storage. The remaining liquid, with the CO2 gas removed, is cooled and sent back to the first stage of the process.

The PNNL system is cheaper than other carbon capture systems because its it operates with 2% water, as opposed to as much as 70% water with other carbon capture technologies. It takes a long time and a lot of energy to boil water, so by removing the water from the system, the carbon capture process becomes much cheaper. “It’s like heating oil on your pan versus boiling water,” Heldebrant said. “The oil gets to temperature much more quickly. So just think of it as we’ve replaced the water with essentially something like an oil.”

Even with this innovation, a carbon capture system takes a lot of energy. That energy comes from the power plant where the carbon capture system is attached, Yuan Jiang, a chemical engineer at PNNL who works with Heldebrant, told CNBC. An installed carbon capture machine will use as much as 30% of the energy that a power plant generates to remove 90% of the carbon dioxide. To get back to full energy capacity, the power plant would have to burn more energy. Even so, the technique ultimately translates to a net carbon dioxide reduction of 87% on a per-megawatt net power generation basis, Heldebrant and Jiang told CNBC.

Creating A Financial Incentive

These carbon capture systems are large and expensive. Adding one to a conventional generating station can cost $750 million. Without strict government mandates or financial incentives, power plant or factory owner operators will have little reason to spend that money. In an effort to make this technology more economically attractive, PNNL researchers have developed a smaller modular reactor that would pump one to two percent of the solvent from the carbon capture system into another smaller modular reactor and use it to make a product that companies can sell.

“If we can give an economic incentive — if they can convert just 1 percent of the carbon dioxide that they’re capturing in one of these big facilities” — the factories can “sell enough of things like methanol, or methane, or other types of carbonate products to at least provide a financial incentive, so they would actually want to build the capture unit in the first place,” Heldebrant told CNBC.

They’re starting with methanol, which currently costs $1.20 per gallon. That means 20 gallons of methanol produced would pay for a metric ton of carbon dioxide to be captured. For some sense of scale, the United States emitted 4.7 billion metric tons of carbon dioxide in 2020, according to the most recent data available from the EPA.

“We chose methanol because it’s probably the third or fourth largest chemical made by man,” Heldebrant said. Methanol is used in hundreds of common products, including plastics, paints, car parts, and construction materials, according to the Methanol Institute. It can also be a source of energy for trucks, buses, ships, fuel cells, boilers, and cook stoves.

“If we can start replacing fossil produced methanol with carbon dioxide derived methanol, that can at least start being a part of a carbon negative chemical approach to manufacture fuels and chemicals, as opposed to carbon positive by just taking synthesis gas from fossil fuels,” Heldebrant said. Converting carbon dioxide to methanol does not consume a lot of energy, Jiang told CNBC, but it does require hydrogen, which itself takes energy to produce. But hydrogen can be made in processes that are powered by renewable energy, Jiang said.

Sequestering Carbon

While some small percentage of the carbon dioxide could be siphoned off to make a product, like methanol, the rest will have to be sequestered. According to Todd Schaef, a PNNL scientist who works on sequestration, the volumes of carbon dioxide that will need to be sequestered are “staggering.”

In his research, Schaef injected carbon dioxide 830 meters into basaltic rock beneath the surface of the Earth. Two years later, the carbon dioxide had reacted with the rock and converted to a carbonate, permanently storing it underground. “That carbon dioxide reacted with the rock and it made a solid so that gas no longer exists,” Schaef said. “These minerals are stable on geologic timescales. Millions and millions of years.”

Climate activists oppose carbon capture technology. They say focusing on removing carbon dioxide from fossil-fuel emissions instead of reducing or eliminating them entirely simply delays the necessary transition. It’s a “touchy topic,” Schaef acknowledged. “It comes up at almost every conference I go to.” But he says it is counterproductive not to sequester the carbon dioxide that’s already been emitted and will continue to be emitted for as long as it takes before the transition to zero carbon power generation and industrial processes takes place.

“Whether you want to admit it or not, there are going to be countries that use fossil fuels,” Schaef said. While global use of coal-fired power plants is markedly lower than it was a few years ago, there are still more than 2,400 coal-fired generating facilities in the world with 189 more under construction. “When the wind doesn’t blow, when the rivers aren’t running, when the sun’s not shining, we need some type of option that lets us keep the lights on. And I know it’s hard for some to understand, but we have to have that gas powered option. We can sequester that carbon dioxide. We can capture and sequester it,” Schaef says.

The Takeaway

In essence, what the people at PNNL are saying is, let’s not allow the perfect to be the enemy of the good. Yes, in an ideal world, we would stop extracting and burning fossil fuels tomorrow. But in the real world, we need strategies to manage the carbon emissions that will continue to occur. Economics being central to all human activity, if there is a way to remove a significant amount of carbon dioxide from flue gases affordably and use the process to create marketable byproducts, that sounds like a pretty good outcome while we wait for the perfect to arrive.

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Steve Hanley

Steve writes about the interface between technology and sustainability from his home in Florida or anywhere else The Force may lead him. He is proud to be "woke" and doesn't really give a damn why the glass broke. He believes passionately in what Socrates said 3000 years ago: "The secret to change is to focus all of your energy not on fighting the old but on building the new." You can follow him on Substack and LinkedIn but not on Fakebook or any social media platforms controlled by narcissistic yahoos.

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