MCFC-Based System for Active CO2 Capture From Flue Gases

Abstract

Carbon dioxide emissions reduction in the atmosphere is the major driver of technological innovations, in particular in energy and industrial sectors. Those sectors are dominated by the use of fossil fuels whose main concern on the combustion gases is the presence of CO2. Their emission in atmosphere accumulates Carbon, the main cause of global warming. The only way to continue to make reference to fossil fuel in the medium-long term and to avoid the carbon accumulation in the atmosphere is to use technologies capable to capture and sequester the carbon in the flue gases (CCS). In the sector of electricity production, several technologies have been proposed for the capture CO2, including absorption, adsorption, cryogenic distillation or membrane separation. All of them offer flexibility and easiness of application, but they need external energy to operate. On the other hand, particular interest is reversed to those technological options that are able to remove CO2 without energy consumption; even more attention is reserved to those technologies which, suitably integrated with other conversion systems, can produce electrical energy at the same time, so increasing the electricity production with respect to the original plant. They are defined active systems and one of these is represented by Molten Carbonate Fuel Cells (MCFCs). In fact, MCFCs are fuel cell capable to concentrate CO2 at anode exhaust, making easier its capture, separation and storage and in parallel to contribute to the electricity production. In this paper, a comprehensive model of the MCFC is used to assess the opportunity related to its use as a CO2 remover from a flue gas as a CCS active device, without energy penalties related to traditional carbon capture methods (MEA, pre and post-combustion, oxy-combustion, etc.). Hence, it has been integrated in a wider system with auxiliary components: compressors to overcome pressure drops, steam generator (also using heat recovered from MCFC exhausts) for fuel dilution, fresh air integration in cathode inlet section, heat exchangers for thermal management and recovery. A CO2 compression and drying section has been considered and represented as a multi-step intercooled compression. The so-defined system can be used as a plug-in device able to be coupled to flue gases with different compositions and thermodynamic operating parameters (temperature, pressure, flow rates). Finally, it has been applied to a case study (a Natural Gas Combined Cycle power plant - NGCC) and the performance of the MCFC in terms of CO2 removal capacity, electrical power generation and size have been evaluated as well the energetic and environmental impact on the reference NGCC power plant.