A number of commercial or industrial processes produce CO2 as a byproduct. Examples include natural gas processing, steam reforming of methane, enhanced oil recovery, gas recycling, and power generation. As a specific illustration in the case of a power plant, a flue gas is produced when coal or other types of fuel are burned in air. The heat released by combustion generates steam, which drives a turbine generator for producing electric power. Hot combustion gases exiting the boiler include nitrogen and smaller concentrations of water vapor and carbon dioxide. Other constituents, formed from impurities in coal, include sulfur dioxide, nitrogen oxides, and particulate matter (fly ash). Such pollutants must be removed to meet environmental standards. In many instances, it is highly desirable to capture or otherwise separate the CO2 from the gas mixture to prevent the release of CO2 into the environment.
Many current CO2 absorption processes involve aqueous amine-based solvents, where the solvent is brought into contact with the exhaust gases to capture CO2 from them. In addition, experiments are in progress to test the efficacy of non-aqueous aminosiloxane solvents for CO2 capture. These processes result in primarily two different streams—a clean gas stream and a CO2-rich solvent stream. In many current setups, the CO2-rich solvent stream is recovered and regenerated.
To reduce the volumes of solvent being utilized for CO2 recovery processes, desorption systems are also utilized at the end of an absorption cycle to separate CO2 and recover the solvent from the CO2-rich solvent stream. Examples of desorption systems include, but are not limited to, stripping columns, and the like.
However, systems that include CO2-absorption as well as CO2-desorption processes are typically capital intensive; and their complexity can result in high maintenance costs. In the case of using non-aqueous aminosiloxane solvents, some of the cost relates to the relatively high viscosity of the solvent after it has absorbed CO2. Moreover, some of the solvents are relatively expensive to manufacture, and replacing solvent lost during the treatment process can have adverse economic effects. Other costs relate to the energy required in heating and cooling the absorbent fluid during the various thermal cycles in the overall process. Moreover, excessive exposure to heat during the absorption/desorption processes can degrade some of the newer, non-aqueous aminosiloxane solvents.
With these observations and concerns in mind, additional improvements in separating carbon dioxide from flue gas and other exhaust streams would be welcome in the art. The new processes should increase the efficiency of the overall process, e.g., by relying on lower process temperatures. The processes should also recover relatively high amounts of the treatment solvents.