Carbon sequestration is the separation and storage of carbon dioxide CO2 and other greenhouse gases (GHGs) that would otherwise be emitted to the atmosphere. GHGs can be captured at the point of emission or they can be removed from the air. The captured gases can be used, stored in underground reservoirs or possibly the deep oceans, or converted to rocklike mineral carbonates and other products. There is a wide range of sequestration possibilities to be explored, but a clear priority for near-term deployment is to capture a stream of CO2 from a large, stationary emission point source and sequester it in an underground formation. Carbon sequestration holds the potential to provide deep reductions in greenhouse gas emissions since a little less than half of total U.S. GHG emissions are from large point sources of CO2. Research is ongoing to develop a clearer picture of domestic geologic sequestration storage capacity, but it is likely that domestic formations have at least enough capacity to store several centuries’ worth of point source emissions. Technologies aimed at capturing and utilizing methane emissions from energy production and conversion systems can be applied to carbon sequestration and will reduce an important GHG emission. Mobile and dispersed GHG emissions can be offset by enhanced carbon uptake in terrestrial ecosystems, and research into CO2 conversion and other advanced sequestration concepts will expand the range of sequestration.
DOE established the carbon sequestration program in 1997.2 The program, which is administered within the Office of Fossil Energy (FE) by the National Energy Technology Laboratory (NETL), seeks to move sequestration technologies forward so that their potential can be realized and they can play a major role in meeting any future needs for the reduction of GHG emissions. This program utilizes an annual Carbon Sequestration Technology Roadmap and Program Plan to identify research pathways that are expected to lead to commercially viable sequestration systems and sets forth a plan of action for sequestration research. Table I-1 is a toplevel roadmap for core R&D and infrastructure development. The overarching program goal is 90 percent CO2 capture with 99 percent storage permanence at no more than a 10 percent increase in the cost of energy services by 2012.
The goal of the core R&D program is to advance sequestration science and develop new sequestration technologies and approaches to the point of precommercial deployment. The core program is a portfolio of work including costshared, industry-led technology development projects, research grants, and research conducted in-house at NETL. The core program is divided into the following six areas.
CO2capture. CO2 exhausted from fossil-fuel-fired energy systems is typically too dilute, at too low a pressure, or too contaminated with impurities to be directly stored or converted to a stable, carbon-based product. The aim of CO2 capture research is to produce a CO2-rich stream at high pressure. The research is categorized into three pathways: postcombustion, precombustion, and oxyfuels.
Carbon storage. Carbon storage is defined as the placement of CO2 into a repository in such a way that it will remain stored (or sequestered) permanently. It includes three distinct subareas: geologic sequestration, terrestrial sequestration, and ocean sequestration.
Trapping within a geologic formation is the primary method for storing CO2. A layer, or cap, of impermeable rock overlies the porous rock into which the CO2 is injected and prevents upward flow of CO2.
Because the surface of sandstone and other rocks preferentially adheres to saline water in preference to CO2, if there is enough saline water within a pore (75-90 percent of the pore volume), the water will form a capillary plug that traps the residual CO2 within the pore space.
When CO2 comes in contact with the saline water it dissolves into solution.
Over longer periods of time (thousands of years), dissolved CO2 reacts with minerals to form solid carbonates. This process is known as mineralization.
Preferential adsorption of CO2 onto coal and other organic-rich reservoirs takes place as a function of reservoir pressure.
Monitoring, Mitigation, and Verification (MM&V). Monitoring and verification for geologic sequestration has three components: (1) modeling, which facilitates the understanding of the forces that influence the behavior of CO2 in a reservoir; (2) plume tracking, the ability to see the injected CO2 and its behavior; and (3) leak detection systems, which serve as a backstop for modeling and plume tracking. MM&V for terrestrial ecosystems also has three components: organic matter measurement, soil carbon measurement, and modeling.
Non-CO2GHG Control. Because some non-CO2 GHGs (e.g., methane, N2O, and gases having high global warming potential) have significant economic value, they can often be captured or avoided at relatively low net cost. This area of the core sequestration program is focused on fugitive methane emissions, whereby non-CO2 GHG abatement is integrated with energy production, conversion, and use. Landfill gas and coal mine methane are two top-priority opportunities.
Breakthrough Concepts. R&D on breakthrough concepts is