PNNL

Abstract

Solvent-based absorption using aqueous amines is the most mature and scalable technology for post-combustion carbon capture, but aqueous amines are subject to high energy and capital investment costs. Those costs can be significantly reduced by considering water-lean solvents and advanced process configurations, as both approaches can minimize the circulation, condensation and vaporization of water in the system. Even though advanced process configurations have been intensively studied for aqueous amines, few discussions can be found in the open literature for configurations associated with water-lean solvents. In order to fill the gap, the present study focuses on the process designs towards lower carbon capture cost enabled by water-lean solvents. N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (EEMPA), a single-component water-lean solvent developed at PNNL, was selected as an archetypical water-lean solvent for the study. A primary thermodynamic package was developed for the H2O-CO2-EEMPA system based on property data measured experimentally. Process models were developed in Aspen Plus for 90% CO2 capture in a 550 MW supercritical pulverized coal power plant. Sensitivity studies were conducted to determine the optimal operating conditions. Techno-economic analyses were performed to compare seven process configurations including simple stripper, two-stage flash, lean vapor compression, inter-heated column, advanced flash stripper, low-pressure steam heater, and advanced heat integration. The results showed a two-stage flash configuration, with EEMPA, could have a carbon capture cost of $47.1/tonne CO2 (in 2011 US dollars). This estimated cost is 19% lower than the industrial benchmark, Cansolv. While considerable capture cost reductions have been proven for aqueous amine using lean vapor compressor and advanced flash stripper, those configurations were shown to have negligible impacts with water-lean solvents due to differences in solvent’s physical properties.