Is Carbon Capture Part of the Low-carbon Solution?
by Bob Shively, Enerdynamics President and Lead Facilitator
Carbon capture refers to the process of chemically capturing the greenhouse gas carbon dioxide (CO2) from biomass or fossil-fueled power plants, industrial facilities, or directly from air. Once the carbon is captured, it is compressed and transported via ship or pipeline either for permanent storage or to locations where it can be used for other purposes. Because the complete process includes capture, utilization, and storage, it is commonly called CCUS. If all the carbon captured is going to be stored, the process may just be called CCS for carbon capture and storage. When the carbon is permanently stored underground it is also sometimes called carbon capture and sequestration.
The Role of CCUS
Most projections of how the world can move to a low- or zero-carbon economy identify CCUS as a key technology. It can be retrofitted to existing power plants and industrial facilities and can potentially be used to address greenhouse gas emissions from “hard-to-abate” activities such a production of cement, steel, or chemicals. It can also be used to create clean hydrogen by limiting the greenhouse gas emissions associated with hydrogen production and be used to remove CO2 from the air through a process called direct air capture. The International Energy Agency (IEA) Net Zero Energy (NZE) Scenario calls for over 1,000 Megatons (Mt) of CO2 capture capacity by the year 2030. This requires rapid development of new projects, as the current level of annual CO2 capture is only 45 Mt. [1] This article considers the application of CCUS to power plants.
The Amager Bakke waste-to-energy plant in Copenhagen, Denmark, that captures CO2 from the exhaust
How CCUS Works
CO2 is captured from power plants in one of three ways:
Post-combustion
In the post-combustion process, CO2 is captured from the exhaust gases following the combustion of fossil fuel or biofuel. The CO2 is captured by passing the exhaust gas through chemical solvents such as amines. The resulting CO2 stream is at low pressure and must be compressed to pipeline pressures for removal from the plant site. The compression process results in a large auxiliary power load that reduces the net output from the power plant by as much as 20% to 30%. This method is already used in various industrial applications. For power production, it is primarily applicable to new or existing pulverized coal and gas combustion power plants. A few of these power plants exist today and more are in the planning or engineering stages.
Pre-combustion
In the pre-combustion process, CO2 is trapped prior to combustion of fossil fuel. This involves two steps – partially burning the fossil fuel with steam and oxygen in a gasifier to form a synthetic gas and then processing the syngas in a water-gas-shift reactor to create a mix of CO2 and hydrogen gas. The CO2 is captured at a high pressure, which makes it less costly to prepare the gas for removal from the plant site. This process is envisioned to be used for new power plants. Research and development are ongoing to integrate this technology into advanced gas turbine power plants. No commercial power plants currently use this technology.
Oxyfuel combustion
In the oxyfuel combustion process, fossil fuel is burned in enriched oxygen diluted with recycled CO2 or water, instead of air. The resulting exhaust gas consists mainly of CO2 and water. This allows the CO2 to be captured by condensing the water in the exhaust stream. Because the CO2 in the exhaust stream is at a high concentration, it requires less energy to condense for removal from the plant. A key additional expense for this method is separating high purity oxygen from air. Research is ongoing to apply this methodology to new and existing coal power plants. No commercial power plants currently use this technology.
CO2 Removal, Utilization, and Storage
Once the CO2 has been captured, it is liquified and removed from the plant site by high-pressure pipelines. These are similar to gas or oil pipelines. About 5,000 miles of CO2 pipelines already exist in the U.S., primarily linking natural CO2 sources to oil fields for enhanced oil recovery [2]. New CO2 pipelines are required for newly implemented CCUS projects.
If CCUS becomes widespread, most of the captured CO2 must be permanently stored since opportunities for utilization are limited. This process is also known as carbon sequestration. Carbon may be sequestered in biological processes such as storage of carbonates in bogs, peats, or swamps. But in most cases, it is envisioned that it will be stored in underground geologic formations such as depleted oil and gas reservoirs, coal mines, or deep aquifers.
The Current Status of CCUS
While recognized as an important component of the transition to a low- or zero-carbon economy, CCUS is still in the early stages of development. As a new, yet relatively complex technology, it is only commercially viable in limited applications without government support. Governments including China, the European Union, Japan, the United Kingdom, and the U.S. all have programs to foster development of CCUS in power plants. But real operating experience is limited. The Boundary Dam Power Station in Saskatchewan was the first power plant in the world to utilize carbon capture at commercial scale starting in 2014. As expected, operators have worked to overcome numerous issues with new technology. A second power plant, Petra Nova in Texas, began operation in 2017. The carbon capture component of the plant was shut down in 2020 due to loss of economic markets for the captured CO2 along with technology issues, but carbon capture was restarted in October 2023. Lastly, the Taizhou power plant with CCUS in the Jiangsu Province of China began operation in June of 2023. More projects are in the planning stages. In addition to developing the carbon capture technology, much work remains to be done in building the necessary pipeline network to move the CO2 to site for utilization or storge and to develop and permit storage facilities.
Whether CCUS proves an important part of the energy transition mix remains to be seen since significant development is still required. Some in the energy industry believe our dollars are better spent elsewhere. But others disagree. The Wyoming Integrated Test Center provides a demonstration center for testing carbon capture technologies at the Dry Fork Station power plant. The center’s Stakeholder Relations Director Jason Beggers states that utilities are watching their results closely. According to Beggers, “We think carbon capture on post-combustion processes is a lot closer than the naysayers would lead you to believe. A lot of stars have to align to make these projects work, but we are getting close, and I have all the confidence that we’ll have the technology sooner rather than later.” [3]
