Owners of industrial processing facilities and fossil fuel-fired power plants have something in common: the potential for capturing carbon dioxide (CO2) at the source, also known as point-source carbon capture.
There are three generally accepted categorizations of this type of carbon capture—pre-combustion, post-combustion, and oxy-combustion.
Pre-combustion
Pre-combustion carbon capture techniques utilize gasification (for solid fuel, such as coal) or reforming processes (for gases, like natural gas) to first create a syngas and then capture the CO2 that would otherwise be generated and expelled in the combustion process. The fuel is effectively depleted of carbon prior to combustion so minimal CO2 is produced when it burns. An example of this technology is Integrated Gasification Combined Cycle (IGCC) power plant design. One of the advantages of pre-combustion capture is that the CO2 is under higher partial pressure making capture easier relative to post-combustion. However, IGCC is an expensive and complicated process.
Post-combustion
Post-combustion carbon capture uses legacy combustion technology like burners and combustion turbines and conventional fuels such as coal or natural gas. CO2 in the combustion exhaust is then separated using one of multiple technologies. Amine-based solvents in tall absorption towers have been the traditional approach but membrane processes and novel adsorbents are promising emerging technologies. Because this is taking place downstream of primary power generation or other industrial processes, facilities that were not originally designed to include carbon capture are more likely to lean towards a post-combustion technology retrofit for CO2 capture.
Oxy-combustion
Finally, point-source carbon capture may be achieved utilizing a third method called oxy-combustion, which has a slightly less revealing name. The process works by isolating oxygen from air using an air separation unit (ASU) followed by combusting a conventional fuel source in mostly pure oxygen. By removing most of the nitrogen (N2) from the air, the resulting combustion exhaust stream contains a much higher concentration of CO2 (and other pollutants), making it much more efficient to capture using post-combustion technologies referenced above. An additional benefit of removing N2 from combustion is the suppression of nitrogen dioxide (NO2) emissions, a gas that has 273 times the global warming impact of CO2.
Captured CO2 can be used in other applications or compressed and stored. Transportation infrastructure and suitable locations for storage are among several determining factors for how the CO2 is handled. Whichever point source method may be used, owners have options that they can explore to reduce emissions and help meet their decarbonization goals.
Article originally published on the POWER Engineers website.
