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1. Introduction Luca Riboldi and Olav Bolland / Energy Procedia 114 (2017) 2390 – 2400 2391 Carbon capture and storage (CCS) is a key tool in the global commitment to tackle climate change. Absorption, whether chemical or physical, is commonly regarded as the most mature technology for CO2 capture. Nevertheless, absorption suffers from some drawbacks, such as high energy requirements and corrosion of process equipment. Adsorption is considered a promising alternative, especially when the regeneration process is carried out through a pressure reduction (i.e. pressure swing adsorption - PSA), with potential for reducing energy penalty, environmental impact [1] and cost of CO2 capture [2,3]. A significant research effort has been already undertaken in order to develop PSA technology for CO2 capture applications. A wide range of adsorbent materials has been synthesized and studied [4–7]. However, material science is still very active and newly-discovered adsorbents are currently under investigation. With regard to the engineering of the process, PSA cycles have been studied in depth [8,9]. Some key criteria to define the most efficient way to use and regenerate adsorbents can be already pinpointed. Further work is ongoing, focusing on decreasing the relative energy consumption and on the process optimization. The literature is less comprehensive with regard to the integration of PSA processes into the power plants and the relative system performance. Some analyses at a system level have been published lately [10–14], touching upon these topics and giving some indications on strengths and weaknesses of PSA in the contexts investigated. This work aims to wrap up all this information, so to provide a thorough insight on the current viability of PSA as CO2 capture technology into power plants. The analyses presented are based on the expertise gained with modeling and simulation of those systems [15] and include considerations on the adsorbent materials, the process configurations and the integration strategies. Such holistic approach, taking into account different domains and their mutual influence, is missing in the literature and provides a systematic overview on the topic, putting in the right context the specific advancements achieved. The analyses encompass both post- and pre-combustion process frameworks. The final outcome is an evaluation on the current status and the prospects of PSA for CO2 sequestration in power plants. 2. Post-combustion analysis The first case analyzed is post-combustion CO2 capture in thermal power plants. The focus is mainly on coal-fired power plants. 2.1. Adsorbent materials Zeolites are the natural candidate adsorbents for a PSA process in a post-combustion process framework. Zeolites exhibit good CO2 adsorption capacity and selectivity at low pressures and moderate temperatures, and demonstrated to outperform activated carbons in post-combustion operating conditions [16,17]. For the typical CO2 partial pressures of flue gases, zeolite 13X and NaY showed to be the most effective [18]. Some studies suggest to use zeolite 5A because of its higher volumetric capacities and less severe heat effect of adsorption [19], although these advantages may apply more to thermal swing processes [20]. A main drawback of zeolites is linked to their hydrophilic nature. The presence of water vapor, an inevitable component of flue gas, negatively affects the capacity of these adsorbents and reduces the availability of the active surface area. Metal organic frameworks (MOFs) are a potential alternative. Extremely promising CO2 adsorption capacities have been demonstrated in the MOFs with the highest surface area, even in the presence of water vapor [21]. High adsorptive selectivity has also begun to emerge in materials MOFs furnished with functionalized surfaces [22]. However, additional research effort needs to be undertaken to ensure the MOFs applicability. Many issues are yet to be addressed, including: the effect of impurities components (O2, CO, CH4, SOx, NOx) in the feed, the practical aspects of employing a PSA process [22], the stability over multiple adsorption/desorption cycles [4] and the material formulation and mechanical stability [23]. Amine-functionalized adsorbents display large CO2 adsorption capacity at low pressure levels, high CO2 selectivity (especially over N2) and robustness toward water. These characteristics make them promising candidates for post-combustion applications. However, issues like very sharp adsorption isotherms, high energy requirement for regeneration and possible amine degradation at high temperature question their actual applicability in common PSA-based systems [8].PDF Image | Pressure Swing Adsorption (PSA) as CO2 Capture Technology
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