Life cycle assessment of molten carbonate fuel cell system for power plants

Abstract

This study evaluated the environmental impacts of a 2.5 MW molten carbonate fuel cell (MCFC) system on impact categories such as climate change (CC), abiotic resource depletion (ARD), acidification (AC), and eutrophication (EU) using a life cycle assessment (LCA) methodology with the functional unit of 1 kWh electricity. Because MCFC systems produce electricity and heat simultaneously, the allocation was performed based on the amounts of exergy contents between electricity and heat (0.636 and 0.364, respectively). The impact on CC, expressed in global warming potential (GWP), was estimated as 3.53E-01 kg CO2 eq./kWh, while the impact on ARD was 1.90E-03 kg Sb eq./kWh, the impact on AC was 3.05E-04 kg SO2 eq./kWh, and the impact on EU was 1.35E-05 kg PO43− eq./kWh. The main cause for the impact on CC was found to be the reforming of liquefied natural gas in the operation stage. For the other categories (ARD, AC, and EU), the contributions of the operation stage were also over 80%. A comparison of the MCFC system with the Korean grid mix showed that the environmental impacts of the grid mix were larger than those of the MCFC system. Several improvement strategies were simulated to reduce the GWPs. First, to improve the efficiency of the heat exchanger, instead of using the heat generated by the MCFC system to produce high-temperature steam as is currently done, the generated heat was proposed to be used to produce medium or low-temperature water. This change reduced the GWPs of the MCFC by approximately 1.72E-02 kg CO2 eq./kWh. Second, this study simulated with an improved electricity production efficiency, with an increase from its current level (45%) to the theoretical maximum value of 60%. This improvement achieved a reduction of approximately 4.00E-02 kg CO2 eq./kWh. Finally, the electricity production efficiency was further increased using unreacted hydrogen, resulting in a reduction of 2.70E-02 kg CO2 eq./kWh.