Systems Optimization for the Production, Utilization, and Distribution of Green Ammonia

Abstract

Ammonia is arguably one of the most important industrial chemicals; however, it is also responsible for over 1% of the global CO2 emissions because of the conventional Haber-Bosch process’s reliance on fossil fuels. Therefore, research efforts in recent years have focused on seeking more sustainable ways of producing ammonia. The most widely considered approach is to replace the traditional fossil-based hydrogen generation process with water electrolysis driven by renewable electricity. Besides its conventional use as a fertilizer, ammonia can also serve as a carbon-free fuel, for example, for heavy-duty transportation or long-term grid-scale energy storage. As such, sustainable ammonia can play a key role in the decarbonization of multiple industries. This thesis research focuses on the development of mathematical models to aid in the integrated design and operation of green ammonia systems, covering the whole value chain from production to distribution to utilization. We first develop an optimization framework for designing a sustainable ammonia-based agricultural system that synergistically integrates ammonia production from renewable resources and effective measures for nitrogen management. A multiscale time representation and a tailored data-driven surrogate model are applied to reduce the problem size and approximate the model nonlinearity. A computational case study is conducted using real-world data, where the results indicate the trade-off between cost and nitrogen loss. We then explore the use of green ammonia to exploit offshore wind energy on the ocean. A comprehensive techno-economic analysis is performed to determine the minimum achievable levelized costs of ammonia for various scenarios. The results indicate that the proposed approach has the promise to be cost-competitive, especially when considering expected cost reductions in offshore wind turbines in the foreseeable future. Finally, we investigate the design of green corridors for sustainable maritime transportation, where green ammonia is considered as an alternative, sulfur- and carbon-free marine fuel. The proposed optimization model is applied to real-world case studies to assess the potential benefit and cost of establishing global green corridors. This work is further extended to a multiperiod and two-echelon supply chain study incorporating the long-term planning for establishing the green shipping corridors over multiple years and providing a roadmap for marine decarbonization. Overall, this thesis provides insights into the effective design and operation of green ammonia systems for sustainable agricultural, energy, offshore wind, and maritime transportation applications.