By Katie Marie
Carbon capture and storage (CCS) is increasingly seen as vital to the efforts of decarbonizing the economy in order to keep global warming below 1.5°C. Yet one of the main challenges that has prevented the expansion of this tool is cost.
“Carbon capture and storage works, but the challenge is to make it economical,” said Sherif Fakher ’16, assistant professor in the Department of Petroleum and Energy Engineering. “Right now, there are carbon capture facilities in operation, especially in Europe, but they’re very costly to build and operate. They are also not capturing enough CO2.”
The cost of direct air capture, the process of scrubbing carbon directly from the atmosphere rather than from concentrated emissions points, is difficult to estimate. The technology has never been deployed on a large scale. Researchers looking into it have cited figures ranging from $100 to $1,000 per ton of CO2 removed.
“Once you’ve actually captured enough CO2, there is also the challenge of storing it,” Fakher said. “This is usually done underground, but CO2 is quite acidic. It reacts with certain types of rock and can cause dissolution or the formation of new minerals underground.”
Oil and gas reservoirs exist in layers of rock underground, and CO2 can be pumped into these layers for storage. When injecting CO2 to store it, another problem is that it tends to concentrate in the highly porous layers of this rock, limiting the total space available for storage.
Fakher and his students are testing the effectiveness of low-cost alternative materials throughout each stage of the CCS process, examining the interactions between CO2 and different materials and rock types to enhance storage. “We’re taking a comprehensive view, looking at not only how much carbon we can capture on the surface but also how we can maximize storage capacity underground,” Fakher said.
One way to increase underground storage capacity is to maintain wellbore integrity by ensuring that CO2 does not contact the underground cement. This is done by injecting a plugging agent to prevent direct carbon dioxide-cement communication, Fakher noted.
“We’re trying to capture carbon using fly ash, literally the ash that flies out when you burn coal,” said Fakher. “It comes out of your grill when barbecuing, but it’s also produced by industrial processes like cement manufacturing, so it’s very cheap. In carbon capture, it’s quite common to refine fly ash into something called a zeolite, but we’re trying to use the fly ash as is.”
Fakher and his team are experimenting with combining the fly ash used in carbon capture and another chemical so that the ash itself can act as the plugging agent and increase storage underground. “The technique is novel, and a big challenge is that coal from different sources produces fly ash with varying compositions. There is no universal recipe, so we’re testing the ability to store CO2 using fly ash from Egypt in a variety of ways. We have a lot of work to do,” he said.
CCS is important in the fight against climate change because it will give humanity more time. Energy transitions have historically been complicated, lengthy processes. After all, it took the world 100 years to transition from using biomass to coal as its primary energy source.
Even as we rapidly scale up the role of low-carbon power sources in our energy mix, fossil fuels will continue to dominate for decades to come. Finding ways to reduce the carbon footprint of existing fossil fuel infrastructure will be crucial to keeping society running while capping global emissions at the level needed to prevent global warming above 1.5°C.
“Oil and gas are powering almost the entire world right now, even with the rapid growth in renewable energy sources,” said Fakher. “These fuel sources will play a big role in the energy sector in the future. The key is not to run away from the problem but to solve it. The oil and gas industry is investing billions of dollars in reducing its emissions, and the main way to do this is through CCS.”
If CO2 can be more effectively captured, there is the potential to not just store it but also use it. A myriad of industrial processes utilize CO2 as an input, from oil and gas companies to manufacturers of fizzy drinks. “If CO2 can be captured cheaply, it can be sold to buyers in the chemical and cement industries, for example,” Fakher explained. “We are thinking of CO2 now as a problem, but it is also a commodity that has value.”