Performance Analysis of Ammonia Solid Oxide Fuel Cells Integrated System with Various Designations of Waste Heat Recovery

Abstract

Maritime transportation, which is the primary mode of transportation, carries out more than 80% of world trade by volume. Thus, it is significantly contributing to air pollution and climate change resulting in a negative effect on human health and the environment. The International Maritime Organization (IMO) has adopted various regulations and requirements in response to this issue and limit greenhouse gas emissions (GHGs), control airborne pollutants, and protect future environment. These standards and objectives have encouraged the use of innovative technology, renewable energy, and decarbonized or low-carbon alternative fuels in global maritime shipping. Ammonia has recently gained attention as a promising marine fuel for reducing CO2 and SOx emissions, resulting in minimal climate change and green future energy. Since ammonia can be efficiently produced and stored using renewable energy sources, ammonia has become an efficient energy vector. Because it is inexpensive, portable, less flammable than other fuels, and relatively safe due to detectable odor leakage, it is a viable fuel for fuel cells. This thesis presents studies on the possibility of using ammonia for SOFC system and the performances of direct ammonia Solid Oxide Fuel Cells (SOFC) in various waste heat recovery combined systems with application targeted for 3800 kW marine vessels. The three different designations of ammonia SOFC-waste heat recovery systems are established and proposed. The process simulation software named ASPEN-HYSYS V12.1 (AspenTech, Massachusetts, USA) are used to estimate the thermodynamic properties and operating parameters of all components. The effectiveness of various viable waste heat recovery systems and cycles, such as gas turbine (GT), Steam Rankine Cycle (SRC), Organic Rankine Cycle (ORC), Kalina Cycle (KC), Waste heat boiler (WHB), Proton Exchange Membrane Fuel cells (PEMFC), ammonia reforming and hydrogen purification system are employed for harvesting waste heat from the exhaust gas of SOFC, has been analyzed and evaluated in terms of thermodynamic performances. The energy efficiency of designation 1,2,3 were obtained at 64.53%, 60.4% and 60.69%, respectively which are all higher than SOFC-stand-alone system. Besides, the combination of SOFC and PEMFC in proposed designation 3 is expected to overcome disadvantage of SOFC on start-up and maneuvering period of vessels. The numerical study results of the ammonia SOFC system were compared and revealed a good agreement with reported results in the literature. The results demonstrated that employing a suitable waste heat recovery system will significantly contribute to the output power and energy, exergy efficiency of an entire integrated system. In an effort to discover a method to further improve fuel cells power output and thermodynamic performances, this thesis also investigated the effects of operating factors that have an impact on the performance of the integrated systems such as current density of SOFC, fuel utilization factor, working fluid of organic Rankine cycles, working parameter of Steam Rankine Cycle, distribution ratio of ammonia supply to SOFC and PEMFC, and etc. The variety range of current density was set from 930 A/m2 to 1830 A/m2 to examine the response of output power and efficiencies of systems. The ORC’s working fluids also carefully examined and selected in consideration of each application characteristics. The studies in this thesis have effectively evaluated the benefits of using various viable waste heat recovery systems for the direct ammonia SOFC combined to increase the output power and thermal efficiency of system. The use of ammonia SOFC for marine vessels is also recognized as an effective method to meet the emission IMO’s regulations of emission control that limitation to be found in previous researches.