Techno-Economic Analysis of Ammonia-to-Power Systems for Marine Applications

The drive to decarbonize the maritime sector has prompted the exploration of alternative carbon-free fuels, with ammonia emerging as a viable solution that com-bines the promising characteristics of hydrogen while overcoming its storage challenges. Beyond serving as a hydrogen carrier, ammonia’s combustion performance is a critical factor, forming the basis of research into ammonia-to-power conversion systems. This study investigates the dual role of ammonia as both a fuel and a hydrogen carrier, evaluating the performance of internal combustion engines (ICEs) and proton exchange membrane fuel cells (PEMFCs) as power generators.
The goal of this study is to design a system capable of delivering a gross power output of 2 MW. The ICE operates on ammonia/hydrogen blends, while the PEMFC consumes high-purity hydrogen, requiring ammonia concentrations below 0.1 ppm to avoid potential membrane damage. Both systems are integrated with an ammonia decomposition unit, which utilizes a packed bed membrane reactor for efficient hydrogen production and extraction in a single step. System simulations are conducted in Aspen Plus®, supplemented by additional software tools for models not available in the primary package.
ICE modeling is carried out using Ansys Chemkin Pro, offering preliminary in-sights into engine performance and exhaust emissions with simpler approaches than advanced computational tools. Although ammonia and hydrogen combustion is car-bon-free, it generates pollutants such as ammonia, nitric oxide, and nitrous oxide, which must be properly managed. Based on modeling results, a hydrogen fraction of 20 vol.% is selected, delivering the required power output under stoichiometric conditions, optimizing emissions of NOx and ammonia.
PEMFC modeling is performed in MATLAB, where the electrochemical model is developed to assess power production, cell efficiency, and cooling requirements. Unlike ICEs, the low operating temperature of PEMFCs necessitates efficient heat management. The chosen operating current density of 0.75 A/cm2 strikes a balance between power generation and system efficiency. The model is validated against commercially available fuel cell stacks to ensure accuracy.
The ammonia decomposition reactor is also modeled in MATLAB, incorporating kinetic and membrane permeation models fitted to experimental data. The PEMFC and ammonia cracking models are linked with Aspen Plus® via user-defined models, while the ICE results are incorporated through built-in Aspen Plus® models, allowing for a comprehensive system design and balance-of-plant.
The final component of the study is the techno-economic analysis, which evaluates the key cost drivers in the hydrogen production process. The generator systems are designed based on standalone performance, with the upstream hydrogen pro-duction process optimized for cost minimization. Economic findings reveal that ammonia contributes 86% to the hydrogen production cost in the PEMFC case and 76% in the ICE case, with corresponding hydrogen production costs of 3.66 €/kgH2 for the PEMFC and 3.4 €/kgH2 for the ICE, according to the optimization outcome. The PEMFC is 8% more expensive due to the increased ammonia requirements for the endothermic process. The remaining costs are divided between operational expenditures and capital expenditures.
In terms of electricity production, the PEMFC yields a cost of 445.75 €/MWh with an electrical efficiency of 43.5%, while the ICE generates electricity at a cost of 228.08 €/MWh with a higher efficiency of nearly 50%. This price disparity is primarily due to the significantly higher operational costs in the PEMFC case—87% greater than the ICE—along with increased balance-of-plant energy demands. Although both systems consume the same amount of ammonia, the higher auxiliary loads in the PEMFC system lead to lower overall efficiency. The PEMFC delivers a net electrical power output of 1.76 MW, whereas the ICE provides 2.02 MW. The study also evaluates the impact of key cost factors such as ammonia pricing, the lifetime, and cost of membranes and catalysts for ammonia cracking. Given ammonia’s significant role as the primary cost driver, its price heavily influences hydrogen production costs, with the analysis examining a range of optimistic to realistic green ammonia costs.