Carbon capture and storage

Carbon capture and storage (CCS) is a process in which a relatively pure stream of carbon dioxide (CO2) from industrial sources is separated, treated and transported to a long-term storage location.: 2221  For example, the carbon dioxide stream that is to be captured can result from burning fossil fuels or biomass. Usually the CO2 is captured from large point sources, such as a chemical plant or biomass plant, and then stored in an underground geological formation. The aim is to reduce greenhouse gas emissions and thus mitigate climate change. CO2 can be captured directly from an industrial source, such as a cement kiln, using a variety of technologies; including absorption, adsorption, chemical looping, membrane gas separation or gas hydration. As of 2022[update], about one thousandth of global CO2 emissions are captured by CCS, and most projects are for fossil gas processing.: 32  The technology has a success rate of between 50-68% of captured carbon, and aspirations of a 90% or 100% capture rate have not been achieved. Opponents point out that many CCS projects have failed to deliver on promised emissions reductions. Additionally, opponents argue that carbon capture and storage is only a justification for indefinite fossil fuel usage disguised as marginal emission reductions. Carbon capture and utilization (CCU) and CCS are sometimes discussed collectively as carbon capture, utilization, and sequestration (CCUS). This is because CCS is a relatively expensive process yielding a product which is often too cheap. Hence, carbon capture makes economically more sense where the carbon price is high enough, such as in much of Europe, or when combined with a utilization process where the cheap CO2 can be used to produce high-value chemicals to offset the high costs of capture operations. Storage of the CO2 is either in deep geological formations, or in the form of mineral carbonates. Pyrogenic carbon capture and storage (PyCCS) is also being researched. Geological formations are currently considered the most promising sequestration sites. The US National Energy Technology Laboratory (NETL) reported that North America has enough storage capacity for more than 900 years worth of CO2 at current production rates. A general problem is that long-term predictions about submarine or underground storage security are very difficult and uncertain, and there is still the risk that some CO2 might leak into the atmosphere. Despite this, a recent evaluation estimates the risk of substantial leakage to be fairly low.[when?]