(57g) Technical and Economic Feasibility Study of Membranes for Carbon Capture from Low CO2 Concentration Sources

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.