C arbon capture and sequestration (or storage)—known as CCS—is a process that involves capturing man-made carbon dioxide (CO 2 ) at its source and storing it to avoid its release to the atmosphere. (CCS is sometimes referred to as CCUS—carbon capture, utilization , and storage.) CCS could reduce the amount of CO 2 emitted to the atmosphere from the burning of fossil fuels at power plants and other large industrial facilities. An integrated CCS system would include three main steps: (1) capturing and separating CO 2 from other gases; (2) purifying, compressing, and transporting the captured CO 2 to the sequestration site; and (3) injecting the CO 2 in underground geological reservoirs (the process is explained more fully below in " CCS Primer "). In recent years, utilization as part of CCUS increasingly has been viewed as a potentially important component of the process. Utilization refers to the beneficial use of CO 2 as a means of mitigating CO 2 emissions and converting it to chemicals, cements, plastics, and other products. (This report uses the term CCS except in cases where utilization is specifically discussed.) The U.S. Department of Energy (DOE) has long supported research and development (R&D) on CCS within its Fossil Energy Research and Development portfolio (FER&D). Since FY2010, Congress has provided more than $5 billion in total appropriations for CCS activities within DOE FER&D (not including the one-time appropriation of $3.4 billion provided for CCS in the American Recovery and Reinvestment Act of 2009, P.L. 111-5 ). In its FY2018 and FY2019 budget requests, the Trump Administration proposed to reduce FER&D funding compared to previous years. The Trump Administration's proposal differs from the policy trends of the previous two Administrations, which supported R&D on CCS and emphasized the development of large-scale demonstration projects—nearly first-of-their-kind ventures using technologies developed at a pilot or smaller scale that have been ramped up to commercial scale—to evaluate how CCS might be deployed commercially. Congress did not accept the Administration's FY2018 request for DOE FER&D and instead increased funding by nearly $59 million (9%) compared to FY2017. In 2018 Congress also enacted legislation (Title II, Section 4119 of P.L. 115-123 ) that would increase the tax credit for capturing and sequestering or utilizing CO 2 , leading many observers to predict increased CCS activity as a result. This report includes a primer on the CCS (and carbon utilization) process and discusses the current state of CCS in the United States, as well as the DOE program for CCS R&D and CCS-related legislation in the 115 th Congress. An integrated CCS system would include three main steps: (1) capturing and separating CO 2 from other gases; (2) purifying, compressing, and transporting the captured CO 2 to the sequestration site; and (3) injecting the CO 2 in subsurface geological reservoirs. The most technologically challenging and costly step in the process is the capture step, which is capital-intensive to build and requires a considerable amount of energy to operate (the amount of energy a power plant uses to capture and compress CO 2 is that much less electricity the plant can deliver to its customers; this is sometimes referred to as the energy penalty or the parasitic load ). Figure 1 shows the CCS process schematically from source to storage. The transport and injection/storage steps of the CCS process are not technologically challenging per se, as compared to the capture step. Carbon dioxide pipelines are in use for EOR in regions of the United States today, and large quantities of fluids have been injected into the deep subsurface for a variety of purposes for decades, such as disposal of wastewater from oil and gas operations or of municipal wastewater. However, the transport and capture steps still face challenges, including economic and regulatory issues, rights-of-way, and questions regarding the permanence of CO 2 sequestration in deep geological reservoirs, as well as ownership and liability for the stored CO 2 , among others. The first step in CCS is to capture CO 2 at the source and separate it from other gases. Currently, three main approaches are available to capture CO 2 from large-scale industrial facilities or power plants: (1) post-combustion capture, (2) precombustion capture, and (3) oxy-fuel combustion capture. For power plants, current commercial CO 2 capture systems theoretically could operate at 85%-95% capture efficiency—meaning that 85% to 95% of all the CO 2 produced during the combustion process could be captured before it goes up the stack into the atmosphere. In a worst-case scenario, energy penalty in the capture phase of the CCS process may increase the cost of electricity by 80% and reduce an electricity-generating plant's net capacity by 20%. Further, as much as 70%-90% of the total cost for CCS is associated with the capture and compression phases of CCS. Other estimates indicate that the energy penalty could be lower, resulting in smaller impacts to subsequent electricity costs. A detailed description and assessment of these capture technologies is provided in CRS Report R41325, Carbon Capture: A Technology Assessment , by [author name scrubbed]. The process of post-combustion capture involves extracting CO 2 from the flue gas—the mix of gases produced that goes up the exhaust stack—following combustion of fossil fuels or biomass. Several commercially available technologies, some involving absorption using chemical solvents (such as an amine , see Figure 2 ), can in principle be used to capture large quantities of CO 2 from flue gases. In a vessel called an absorber, the flue gas is "scrubbed" with an amine solution, typically capturing 85% to 90% of the CO 2 . The CO 2 -laden solvent is then pumped to a second vessel, called a regenerator, where heat is applied (in the form of steam) to release the CO 2 . The resulting stream of concentrated CO 2 is then compressed and piped to a storage site, while the depleted solvent is recycled back to the absorber. Other than the Petra Nova plant (discussed in " Petra Nova: The First (and Only) Large U.S. Power Plant with CCS "), no large U.S. commercial electricity-generating plants currently capture large volumes of CO 2 (i.e., over 1 million tons per year). As the Petra Nova project indicates, the post-combustion capture process includes proven technologies that are commercially available today. The process of precombustion capture separates CO 2 from the fuel by combining the fuel with air and/or steam to produce hydrogen for combustion and a separate CO 2 stream that could be stored. For coal-fueled plants, this is accomplished by reacting coal with steam and oxygen at high temperature and pressure, a process called partial oxidation, or gasification ( Figure 3 ). The result is a gaseous fuel consisting mainly of carbon monoxide and hydrogen—a mixture known as synthesis gas, or syngas—which can be burned to generate electricity. After particulate impurities are removed from the syngas, a two-stage "shift reactor" converts the carbon monoxide to CO 2 via a reaction with steam (H 2 O). The result is a mixture of CO 2 and hydrogen. A chemical solvent, such as the widely used commercial product Selexol (which employs a glycol-based solvent), then captures the CO 2 , leaving a stream of nearly pure hydrogen that is burned in a combined cycle power plant to generate electricity—this is known as an integrated gasification combined-cycle plant (IGCC)—as depicted in Figure 3 . One example of precombustion capture technology in operation today is at the Great Plains Synfuels Plant in Beulah, ND. The Great Plains plant produces synthetic natural gas from lignite coal through a gasification process, and the natural gas is shipped out of the facility for sale in the natural gas market. The process also produces a stream of high-purity CO 2 , which is piped northward into Canada for use in enhanced oil recovery (EOR) at the Weyburn oil field. The process of oxy-fuel combustion capture uses pure oxygen instead of air for combustion and produces a flue gas that is mostly CO 2 and water, which are easily separable, after which the CO 2 can be compressed, transported, and stored ( Figure 4 ). Oxy-fuel combustion requires an oxygen production step, which would likely involve a cryogenic process (shown as the air separation unit in Figure 4 ). The advantage of using pure oxygen is that it eliminates the large amount of nitrogen in the flue gas stream. Currently oxy-fuel combustion projects are at the lab- or bench-scale ranging up to verification testing at a pilot scale. After the CO 2 capture step, the gas is purified and compressed to produce a concentrated stream for transport. Pipelines are the most common method for transporting CO 2 in the United States. Currently, approximately 4,500 miles of pipelines transport CO 2 in the United States, predominately to oil fields, where it is used for EOR. Transporting CO 2 in pipelines is similar to transporting fuels such as natural gas and oil; it requires attention to design, monitoring for leaks, and protection against overpressure, especially in populated areas. Typically, CO 2 would be compressed prior to transportation into a supercritical state, making it dense like a liquid but fluid like a gas. Using ships may be feasible when CO 2 must be transported over large distances or overseas. Liquefied natural gas, propane, and butane are routinely shipped by marine tankers on a large scale worldwide.