Potential of CO2 capture from flue gases by physicochemical and biological methods: a comparative study

Abstract We compare the industrial viability of two emerging technologies for CO2 capture from flue gases, i.e., adsorption in porous commercial zeolites and biomass production by microalgae. Our study is organized in two steps: first, the best system is selected (either zeolite type or microalgae strain). Second, their performance is quantified and their advantages at real conditions discussed. For the physicochemical process, we find that commercial zeolite MFI is the best choice for CO2 capture from a typical industrial flue gas emission. Numerical dual PSA cycle simulations at ambient conditions yield 8 kg m-3 bed h-1 and an energy consumption of 0.987 MJ per kg of captured CO2. As regards the biological process, evaluation of several microalgae strains in continuous mode using low-cost resources (waste water, fertilizers, flue gases), results in Scenedesmus almeriensis as the most promising strain. The maximal capacity of CO2 capture at laboratory conditions was 0.1 kg m-3 h-1, allowing to produce up to 0.06 of kg m-3 h-1 of biomass (3% maximal photosynthetic efficiency). Although this is a significantly lower value, the produced biomass, being composed by carbohydrates, entails an overall economic yield of 0.6 € m-3·day. To demonstrate reliability at large scale, experiments were performed in a 100 m2 pilot raceway reactor under outdoor conditions. We measured 54 g of CO2/m2·day (= 197 tn/ha·year) and a biomass productivity of 21 g/m2·day (= 75 tn/ha·year). The energy consumption approaches to 0.48 MJ/kgCO2, lower than zeolites adsorption. Still, zeolites can be advantageous as they offer higher productivity, lower energy consumption than amines-based methods, and possibility of producing added-value chemical products, such as methanol, CO or CH4.