(554f) Capital and Energy Considerations in CO2 Capture by Sorption

The state of the art post-combustion CO2 capture processes for coal-based power plants include absorption processes based on amines and chilled ammonia. Because of the high heats of reaction, the amine based processes need up to 30% of power plant's output for CO2 capture and compression. After adding the energy needed for the reaction to the energy required for chilling the feed, the overall energy required for the chilled ammonia process is not substantially lower than the amine process.

The heats of adsorption for physical sorption are typically 20-30% of the heats of reaction for the amine processes. The heats of reaction for chemical sorption, using supported carbonates and amines as sorbents, are similar to the heats of reaction for amines though the overall energy requirement may be lower as the latent of vaporization for water in the amine solution does not have to be provided for the sorbent-based processes.

Processes based on both the physical sorbents as well as chemical sorbents offer potential for lower capital and energy requirement compared to the amine-based processes and a number of processes based on both have been proposed. This paper will present a systems analysis to evaluate overall energy and sorbent requirement for processes based on both the physical and chemical sorption. The analysis will attempt to answer questions such as whether a sorbent with lower heat of sorption and lower CO2 capacity is better than a sorbent with higher heat of sorption and higher CO2 capacity. Another question to be answered is whether a sorbent based on chemical sorption has a potential for lower energy requirement than the amine and carbonate based absorption processes. Suitable materials of construction for various sorbent based processes will be suggested and preliminary capital cost estimates for processes based on both the physical sorbents as well as chemical sorbents will be presented.