(70e) Implications of Flue Gas Components on the Performance of Sorbents

Carbon sequestration is a viable scheme to mitigate carbon dioxide (CO₂) emissions from large point sources, such as power generators that burn fossil fuels.  Although both the capture and storage steps are important, the most costly step is the capture one.  The Fossil Energy Program in the U.S. Department of Energy has prompted the investigation of various techniques to capture carbon dioxide from coal-burning power generation point sources.  A solid sorbent method, a category of post-combustion carbon capture, is a regenerable scheme where the CO₂ is removed from the flue gas stream by a sorbent and then regenerated.  The technique can use an amine-based absorbent where the amine can be immobilized onto a support or encapsulated within a porous substrate.  The sorbent becomes fully loaded once the CO₂ capacity of the sorbent is achieved.  In a transport type of system, the spent sorbent is thermally regenerated in another vessel and recycled back to the absorption scrubbing unit. 

With respect to CO₂ capture, loading capacity and regenerative heat duty are important parameters that define the technical/economic relevance of the sorbent.  However, other components within the flue gas could have a direct impact on these parameters.  The moisture of the flue gas can be important not only as it may be a reactant in certain CO₂–amine reactions, but by itself, it could possibly absorb onto the sorbent material, and thus cause an additional need for energy in the regeneration step.  Depending on the requirement of upstream scrubbing of the flue gas in a flue gas desulfurization unit, the sorbent can be exposed to upwards of 15 vol% moisture in the flue gas.  Additionally, if the flue gas emanates from the combustion of coal, it is eminent that the sorbent will need to contend with the trace gaseous components of sulfur dioxide and nitric oxides.  Results of packed bed studies with an immobilized amine sorbent will be discussed.  Gas mixtures simulated those of flue gas and the conditions for regeneration.  The role of moisture in the absorption and regeneration steps will be described and its impact on CO₂ capacity and the regenerative heat duty will be addressed.