(401ae) Membranes for CO2 Capture from Low Concentration Sources: A Technical and Economic Feasibility Study

Authors: 
Han, Y., The Ohio State University
Ho, W. S. W., The Ohio State University
In the past decade, membranes and membrane processes have been studied extensively for carbon capture from various gas sources in the energy sector, such as syngas (~35% CO2) from an integrated gasification combined cycle, flue gas (11 – 15% CO2) in coal-fired power plants, and gas turbine flue gas (~4% CO2) of a natural gas combined cycle. However, there are other more challenging candidates for carbon capture where the CO2 concentration is low but the total CO2 emission is large. In this presentation, a first-of-a-kind membrane process is proposed for carbon capture from low CO2 concentration (~1%) sources. The low CO2 concentration sources have included the treated flue gas in coal-fired power plants in which 90% CO2 has been removed by a primary carbon capture unit, e.g., membrane or aqueous amine absorption, as well as coal mine gas streams. The low CO2 concentration feed gas is passed to a 2-stage enriching membrane cascade where the CO2 is sequentially enriched to 95% purity. Vacuum is pulled on the permeate sides of both membrane stages to provide the transmembrane driving force. The techno-economic analysis shows that a high CO2/N2 selectivity is crucial to achieve the 95% CO2 purity. If the CO2 permeance is higher than 1000 GPU (1 GPU = 10-6 cm3 (STP)·cm-2·s-1·cmHg-1), a minimum selectivity of 80 is required. A high selectivity of about 200 is preferred from a cost and energy standpoint. Further increasing the selectivity shows little benefit. By using the state-of-the-art amine-containing facilitated transport membrane with a CO2 permeance of 1100 GPU and a CO2/N2 selectivity of 200, a capture cost of $294.7/tonne CO2 (in the 2011 dollar basis) can be achieved for 90% CO2 recovery. This corresponds to an increase in the cost of electricity of 21.2%. The membrane process is feasible for CO2 mitigation with a feed CO2 concentration spectrum of 0.6 – 2.0%. If the feed CO2 concentration falls within this range, 90% CO2 recovery and 95% purity can be achieved with similar total capital and operational expenditures. It is also found that the 90% CO2 removal may not be the most economic option for low CO2 concentration sources. Reducing the CO2 recovery leads to a smaller energy penalty, and a lowest capture cost is reached at 70% recovery. These cost calculations in the 2011 dollar basis have included both membrane module installation cost and 20% process contingency.