In the series about Carbon Capture and Storage, here is another short technical flyer about how the partial pressure of the Carbon Dioxide we are capturing affects the cost of the facilities. The good news is that technologies are advancing and scaling well and costs are reducing. For a world with carbon emissions, this mitigation is available now whilst we continue to scale up renewables.
Partial pressure influences CO2 capture costs, because it affects the size of process equipment, capture plant energy requirements, and applicable capture technologies.
Partial pressure is directly proportional to concentration, i.e. P=CRT, where P=pressure in atm, C – concentration in moles/L, R=ideal gas constant, and T=temperature in Kelvin.
The higher the pressure, the easier CO2 will be captured, and the process will be cheaper due to less energy consumption and smaller capture equipment. For the high partial pressures physical solvents are more suitable. They hold CO2 in solution through physical mechanisms rather than chemical reactions, and as such the solution of CO2 is weaker and easier to break by heating, so less energy (or heat) is needed.
At low CO2 partial pressures, chemical solvents are usually required to capture the CO2 stream. A significant amount of heat is needed to release captured CO2.
Higher CO2 partial pressures could be achieved when the concentration (or fraction) of CO2 is higher, or the overall gas pressure is higher, or both.
It is possible, but expensive, to compress the flue gas to increase the CO2 partial pressure. For a given CO2 source, it is unusual to control or change CO2 partial pressure. More often, CO2 partial pressure is taken as it is.
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