Carbon capture and storage (CCS) is an innovative technique used to mitigate greenhouse gas emissions from industrial processes. CCS works by sequestering CO2 within geologic formations deep underground for long-term safe storage.
CO2 captured from flue gas is then stored in underground rock formations such as depleted oil and gas reservoirs or saline aquifers, making a convenient location available worldwide for storage purposes.
Capture
Carbon capture and storage (CCS) provides an effective means of mitigating carbon emissions from coal- and gas-fired power generation, steel mills, cement plants, petrochemical facilities and other facilities, with greenhouse-gas emitting activities, by diverting their emissions away from entering the atmosphere. When at its best, CCS helps mask harmful effects while permitting those facilities to continue operations indefinitely.
After post-combustion capture, CO2 is separated from other gases produced and compressed for transport before being sent directly to storage via pipelines or ships. There it will remain stored safely rather than being released back into the atmosphere.
There are various strategies available to us for extracting CO2 from the air, from machines that scavenge CO2 directly from the atmosphere to trees and algae which do so naturally. Each technique has their own set of advantages and disadvantages and are still in development stages.
Compression
Compression is key to lowering the cost of carbon capture regardless of which technology is chosen, both in terms of liquefaction and transportation of CO2. For CCS technologies that employ supercritical steam vessels as their capture medium or pipeline transport using molecular sieves for dehydrating.
This step consumes energy and adds cost to carbon capture. Furthermore, solvent regeneration may produce harmful air pollutants like ammonia. Furthermore, absorption carbon capture increases fossil fuel usage on site while special pipelines must be built and maintained for it; making CCS implementation even more complex for stationary sources like power plants.
Transport
Carbon capture projects involve transporting CO2 from industrial clusters to storage sites such as deep geological formations using pipelines or ships.
Pipelines are currently the primary means of transporting carbon dioxide (CO2). To minimize energy losses during transport, carbon dioxide must usually be compressed into liquid form before entering pipelines for transportation. Pipeline operators must verify the purity and compliance with temperature and pressure specifications prior to beginning transport of CO2.
At the storage site, CO2 is injected into deep geological formations like used oil and gas reservoirs or coal beds for injection. This step is sometimes known as utilization; in today’s context of CCS projects this usually refers to CO2 injection for enhanced oil recovery (EOR). As this does not result in reduced emissions or net climate benefits it should not be considered part of CCS.
Injection
CO2 captured from fossil fuel power plants or ethanol facilities is injected underground, creating a permanent carbon store and helping reduce greenhouse gas levels in the atmosphere. Carbon Capture and Storage (CCS) technologies use this strategy as one component of their overall emissions reduction strategies, leading to lower greenhouse gas levels overall.
CO2 injection into oil fields or deep-salt formations occurs at depth where natural temperatures and fluid pressure increase naturally, creating an environment in which supercritical CO2 becomes more buoyant than any other liquid present in its pore space, leading to structural trapping.
Injection sites are defined by their integrity, which ensures that CO2 remains within an specified volume and does not leak out of it. Commercial-scale CCS projects inject CO2 at locations like Norway’s Sleipner and Weyburn-Midale carbon storage complexes as well as Michigan’s Antrim saline reservoir for injection.
Storage
CO2 can be permanently stored underground by injecting it into deep underground rock formations similar to how oil and natural gas are stored, using similar techniques as used for oil storage. Potential locations for CO2 storage could include saline aquifers, depleted oil/natural gas reservoirs, unmineable coal beds or basalt formations.
Carbon dioxide captured can also be utilized to produce fuels, building materials and enhance oil recovery – this practice is known as utilization (CCUS – carbon capture, use and storage). Different uses have varying impacts on climate change.
CCS projects with storage may qualify for California Low Carbon Fuel Standard credits; however, for them to qualify they must be located there. As of September 2017, 13 CCS power and industrial plants were in operation with 26 more in construction or advanced development status – potentially meeting 14 percent of global emission reduction needs by 2050 through this technology.