(771h) An Energetic Analysis of CO2 Capture On a Gas Turbine Combining Flue Gas Recirculation and Membrane Separation

Post combustion Carbon Capture and Storage (CCS) is currently intensively investigated as a key issue for the mitigation of greenhouse gases emissions. A very large number of studies is dedicated to coal power plants. The objective of this study is to evaluate the possibilities and limitations of a hybrid process for CO₂ capture on a gas turbine, based on a combination of flue gas recycle and membrane separation.

Membrane processes are effectively known to offer attractive performances in terms of energy efficiency, as soon as concentrated and/or high pressure mixtures have to be treated. Two different flow schemes have been simulated and compared: flue gas recycle with air combustion and flue gas recycle with an oxygen enriched feed mixture.

The energy requirement of the different processes, expressed in GJ (thermal basis) per ton of recovered CO₂, and the size of the membrane capture process (expressed in m² of membrane area) have been systematically estimated. Based on a feed compression strategy, the simulations are achieved for four different membrane characteristics, covering a broad range of currently commercially available and hypothetical materials, with 0.9 CO₂ purity in the permeate side and 0.9 CO₂ capture ratio specifications.

For air combustion scheme, the results show that the best performances, logically obtained with the most selective membrane (a = 200), induce an energy requirement of more than 8 GJ/ton. This value is much larger than the 3.5 GJ/ton needed for the reference post-combustion capture process (absorption in MEA). A completely different picture is obtained if an Oxygen Enriched Air (OEA) strategy is applied. In that case, energy requirements down to 2.6 GJ/ton can be attained. Interestingly, the membrane selectivity performances (tested between a = 50 and a = 200 here) play a key role on the overall energy requirement. This situation differs from the direct “end of pipe” post-combustion carbon capture, where no significant improvement on the energy requirement is observed as soon as the membrane selectivity reaches a value of a= 50. Thus, the search for highly selective membranes, far above the performances of the actual membrane materials, is of major interest for the gas turbine / membrane capture process investigated in this study. Additionally, moderate inlet pressure values (12-22 bar), together with moderate oxygen purities (45-53 %) are needed for optimal OEA conditions.  The promising results reported for the OEA combustion strategy call for a more in depth analysis of this hybrid process. Several unexplored issues could be investigated in future works.