Storing emissions from hard-to-abate sectors
Carbon capture and storage (CCS) is the process of capturing CO
2, typically from an industrial source, either before it is released into the atmosphere or after release, via direct air capture (DAC). The captured CO2 is compressed into liquid or solid form, which can then be transported to storage locations deep underground such as depleted oil fields, saline aquifers, or other porous geological formations. This process is known as sequestration.
How does Carbon Capture and Storage work?
CO2 can be captured at the source via three methods: post-combustion, pre-combustion, and oxyfuel. Post-combustion capture uses absorption-, adsorption-, or membrane-based ‘scrubbing’ to remove CO2 from the flue gases emitted by fossil fuel combustion. Pre-combustion capture removes the carbon dioxide before combustion. Here, steam methane reforming or gasification of fuels such as coal or biomass produces syngas. The syngas then undergoes a water-gas shift reaction that converts carbon monoxide and water to hydrogen and carbon dioxide. The carbon dioxide concentration is high and can be separated, leaving hydrogen as fuel. This is the first step in producing blue hydrogen from coal or natural gas.
Finally, Oxyfuel technology burns fuel using pure oxygen, or a mixture of oxygen and re-circulated flue gas, instead of air. The many advantages of Oxyfuel combustion over air include reduced fuel consumption, higher possible flame temperature, less heat loss, greater concentration of CO2 (making sequestration easier), greater condensability of the flue gas (easing compression separation), ability to capture the heat of condensation, and 75% reduction of overall flue gas.
Carbon Capture Utilization and Storage is a necessary bridge between the reality of today’s energy system and the increasingly urgent need to reduce emissions.
Why is CCS Important to Energy Transition?
Although CCS is still expensive and new, it is considered an essential way to mitigate greenhouse gas accumulation from fossil fuel use while the world transitions to cleaner energy sources. Until recently, liquefaction via compression was the only viable
CCS option. However, newer solidification technologies are being developed involving the use of liquid metal electrocatalysts (for instance, gallium alloy), which enable conversion of the CO2 to a solid at room temperature. The challenge
is scaling up CCS technologies, old and new.
CCS is a good currently available way to reduce emissions from hard-to-abate industries such as cement and steel factories. Cement-related CO2 emissions are about 7% of total annual energy and industry emissions. CCS can ameliorate a cement plant’s emissions at several points. Cement plants make cement by heating raw materials (mostly limestone and gypsum) in a rotary kiln at very high temperature, emitting CO2 at several stages of the process. Traditionally, emissions from the kiln’s fuel are combined with emissions from the limestone’s calcination process into a single-flue gas stream that exits the plant. CCS post-combustion technology can be retrofitted to existing cement plants to scrub the flue gas. Because CO2 concentration is so high (14-33% by volume) in the cement plant’s flue gas, it’s more easily and efficiently captured than from an equivalently sized natural gas plant (about 3%) or coal-fired plant (about 15%)
CO2 is needed at industrial sites making fertilizers, plastics and rubber; and it has numerous applications throughout the food and beverage industry, and in the medical industry. CO2 can also be used to enrich greenhouse air to increase plant yields. Installations that traditionally emit large amounts of carbon dioxide are candidates for CCS technology, either retrofitted or as part of new plant construction. There are currently 27 large-scale CCS projects operating around the world, with many more expected.
What are the developing CCS technologies?
Direct Air Capture (DAC) captures carbon directly from the atmosphere, using giant fans to draw in air and then bonding the CO2 to chemical sorbents via adsorption or absorption. When the sorbent is saturated, it is heated to 80-100°C to
release the captured CO2 for storage. Because CO2 in the atmosphere is widely dispersed (only about 0.04% of air), removing it via DAC requires much more energy than removing CO2 at the source, where it is far more
concentrated, so DAC is much more expensive.
Although there are only 19 DAC plants currently in operation, Both the International Energy Agency (IEC) and the United States Department of Energy see DAC as a crucial component of a multi-pronged strategy to meet net zero goals. Meeting net zero goals will require a very large and swift ramp-up of DAC, as well as refinement of DAC technology and a reduction of capture costs.
Compression technology is central to all CCS, including DAC. MAN Energy Solutions supplies compressors for large-scale CCS projects around the world, including the ‘Porthos’ project in the Netherlands, where two of their RG 25-4 and one RG 31-4 type compressor trains will pressurize CO2 for transport and injection below the North Sea.
Learn more about the future of MAN’s CCS compression solutions