Now more than ever, those in the power industry, manufacturers, oil and gas producers, and others are looking for ways to make operations more environmentally sustainable. One area that has increasingly caught the interest of researchers, regulators, and those in industry is carbon capture technology. Here, we offer a simple explanation of how carbon capture and sequestration works, and explore the impact of carbon capture on water and energy resources.
What is carbon sequestration and why is it important?
By definition, carbon capture is the removal of carbon dioxide (CO2) from the atmosphere. This process occurs naturally through CO2 absorption by oceans or plant life, and through human intervention in a process known as carbon capture and sequestration (CCS). The focus of this article is on the latter, which involves the use of technologies that capture, transport, and store carbon emissions as a means of combatting climate change due to greenhouse gases.
Carbon sequestration technologies
The most common type of CCS is point-source carbon capture, where CO2 is separated out from other gases produced by industrial processes right at the source of emission. This is typically achieved by outfitting industrial smokestacks with carbon capture equipment of some kind, such as scrubbers or filters. Another method, known as direct air capture (DAC), works by filtering atmospheric air in bulk to remove CO2. Still in a relatively early phase of development, DAC technologies are costly and in limited use at this time. Recent developments, however, like the late 2021 opening of a large DAC facility in Iceland and the recent development of a low-cost zeolite DAC process, are signaling future growth.
Regardless of the method used, the captured carbon must be stored in some way so as to prevent it from making its way back into the atmosphere where it can do harm by contributing to global warming. Today, the process for storing captured CO2 gas starts with first pressurizing it to form a liquid, then injecting it into porous underground rock formations. Often, liquid or gas injection is done in connection with enhanced oil recovery (EOR) operations, where the injected stream is used push oil toward an extraction well. While geological injection remains the most common storage approach, researchers are currently working to develop processes for reusing captured CO2, so there may well be other storage options available in coming years.
Trends and outlook
Today, many see carbon sequestration as an important tool in meeting net-zero carbon emissions goals. The US Department of Energy, along with some energy producers and industrial facilities, have continued to invest heavily in CCS strategies for the past several years. Many energy producers are taking proactive action to develop and implement new carbon capture technologies, and major producers are beginning implement CCS across the cement, concrete, iron, steel, oil, gas, and mining industries.
While there’s plenty of reason to expect that CCS will grow in the years to come, not everyone is convinced that carbon capture should play a central role in future sustainability efforts. To be sure, CCS does have high capital, energy and water costs, while costs for renewable energy are declining. In light of these factors, some feel that investment in gross emissions reduction strategies is a better use of resources than mitigation strategies like CCS. Still, so long as a significant share of our energy is derived from fossil fuels, it is likely that the world will see growth in both mitigation and emissions reduction strategies in the decades to come—it just remains to be seen what the balance will look like.
Carbon sequestration’s impact on energy and water
For all its benefits, carbon sequestration can consume a lot of energy and water resources, meaning that CCS can have a sizeable carbon footprint of its own. This is because CCS strategies require significant amounts of energy to run all the equipment needed to separate, compress, and transport CO2 for storage. When used at large power plants, CCS can consume as much as half a facility’s normal output. And, given that 84% of the world’s energy comes from fossil fuels, it is likely that the added demand of CCS will mean more combustion, and more carbon. Unless the facility is powered by a source of clean energy, a CCS strategy could even result in little to no net carbon reduction.
CO2 capture can also be costly in terms of water use. Many common types of CCS equipment use water directly, such as for preparation and regeneration of solvent mixtures used to separate CO2 from flue gas. On this front, emerging adsorption and membrane technologies may help to reduce water use. While these types of advancements may make it easier and more cost-effective for facilities to adopt CCS in the future, the larger share of its water footprint is due to its high energy consumption. This is because energy and water use are closely intertwined, as large quantities of water are required for cooling, mining, and other activities associated with energy production. While the exact footprint varies depending upon the CCS technology used, one study estimates that it takes between 0.74 to 575 cubic meters of water to sequester each metric ton of CO2, causing some researchers to recommend against the use of CCS in water-scarce areas.
The water footprint is highest for power generation facilities that rely on older technologies, such as once-through cooling systems, which draw and discharge large volumes of water from surface waterways. With the tightening of regulations, and the increasing costs of sourcing freshwater, as well as rising costs for treating and discharging wastewater, facilities stand to benefit from learning about water reduction strategies. For electrical generation applications, this can include cooling system optimization, or recycling process or wastewater streams, for example. Like CCS itself, such changes may require significant capital investment, but may well be worth it as costs for carbon emissions and wastewater discharge continue to rise as expected.
