Solvent absorption is the benchmark process for removing carbon dioxide and indeed other acid gases from industrial processes. An example is shown in the figure for a post combustion gas application (low pressure) using an amine solvent.
Solvent absorption uses either a chemical or physical absorbent medium, or solvent, to selectively absorb the carbon dioxide from the feed gas stream in a vessel or absorption tower which is packed with a high surface area packing material. The gas stream leaves the absorption tower with the required low concentration of carbon dioxide and the solvent which has become ‘rich’ in carbon dioxide, is fed to a regeneration tower or ‘stripper’ where the CO2 is recovered as a pure stream through the application of either temperature or pressure changes.
The ‘lean’ solvent, with low levels of carbon dioxide is then, after exchanging heat with the stripper feed to conserve energy, fed back to the absorber to close the loop on the process.
This process can be carried out with a range of solvents and at a range of processing conditions (pressures, temperatures and concentrations of carbon dioxide). The most common solvents for conventional absorption/stripping processes are amines.
Amine-based solvents are volatile and prone to instability in the presence of oxygen, SOx and NOx, resulting in unwanted environmental emissions and increased costs through water wash columns and the need for a constant amine make-up supply. In addition, amine-based solvent systems require a substantial amount of energy for regeneration which, in the case of capture from a power station, significantly reduces the power output.
UNO MK 3 was born from a need to find a solution to reducing CO2 emissions at a lower cost and without creating any additional environmental impact. The precipitating potassium carbonate (K2CO3) system presents great potential to provide this solution as outlined below in the key features.