Semester
Summer
Date of Graduation
2024
Document Type
Dissertation
Degree Type
PhD
College
Statler College of Engineering and Mineral Resources
Department
Chemical and Biomedical Engineering
Committee Chair
Debangsu Bhattacharyya
Committee Co-Chair
Jianli Hu
Committee Member
Jianli Hu
Committee Member
Wenyuan Li
Committee Member
Nagasree Garapati
Committee Member
Christina Wildfire
Abstract
Ammonia, which plays a crucial role in agriculture, chemical production, and energy storage applications, has traditionally been produced using the Haber-Bosch (HB) process. However, this well-established technology has significant drawbacks. The HB process requires extremely high pressures (up to 300 bar) and temperatures (400-500°C), making it feasible only for large-scale operations with substantial capital investment. Additionally, the high energy consumption of the HB process contributes significantly to greenhouse gas emissions, raising concerns about its environmental sustainability. This dissertation extensively explores a new low-pressure microwave-assisted process for synthesizing ammonia, demonstrating its economic viability and potential cost-effectiveness compared to the traditional method, especially when combined with solid-sorbent separation. Ideal pressure range and production scale for efficient and economically feasible ammonia production are identified using this method. A novel, low-pressure (6.5-35.5 bar) microwave (MW)-assisted ammonia synthesis process is thoroughly investigated in this dissertation as a potential game-changer for sustainable ammonia production. The research investigates process design, techno-economic optimization, separation strategies, catalyst performance evaluation, and the underlying mechanisms governing the MW reactor.
The economic feasibility of the proposed MW-assisted ammonia synthesis technology is investigated. A critical part of this investigation involves the development of a comprehensive kinetic model for the MW reactor. This model serves as the basis for developing plant-wide models in Aspen Plus, which is needed to evaluate the overall performance and economic feasibility of the proposed process. Furthermore, various product separation techniques applicable to the low-pressure MW process are explored. While the conventional condensation separation utilized in the HB process is unsuitable due to the lower operating pressure, alternative approaches are investigated. Among these, cryogenic flash separation emerges as the most promising option from an economic standpoint. It was realized that the highest single-pass conversion in the MW reactor does not necessarily translate to the most economically viable process configuration. Through optimization techniques, it is demonstrated that catalyst cost plays a significant role in determining the optimal number of reactors needed. This highlights the importance of considering not just conversion rates but also the overall process economics when designing and optimizing the MW-assisted ammonia synthesis process. By using a minimum selling price (MSP) and levelized cost of ammonia (LCOA) as key economic metrics, the study shows that the optimized MW process achieves an MSP competitive with the conventional HB process under identical feedstock conditions. This finding signifies a crucial step toward establishing the MW-assisted technology as a commercially viable alternative.
The integration of solid-sorbent based separation with the MW-assisted ammonia synthesis process is investigated. This approach offers potential advantages in terms of energy efficiency and overall process economics. A dynamic adsorption-desorption model is developed to accurately capture the behavior of the solid sorbent material during the separation cycle. This model is then combined with a heat and mass integrated plant-wide model, creating a comprehensive framework for techno-economic optimization. Techno-economic optimization demonstrates that the MW-assisted process with solid-sorbent separation exhibits a lower levelized cost of ammonia compared to the HB process, especially for hydrogen prices below $4/kg.
The crucial role of catalysts in the MW-assisted process is studied. The study investigates the commercial viability of the technology by exploring the performance of novel Fe-based and Ru-based catalysts. To ensure optimal design and operation of the integrated process, a two-stage optimization approach is implemented. This approach involves evaluating the interplay between various factors such as catalyst performance, operating pressure, and minimum viable production scale. The optimization study identifies an optimal pressure range of 15-20 bar for the MW-assisted process. This finding provides valuable guidance for designing and operating the MW reactor for efficient ammonia production. Additionally, the research reveals that the MW-assisted process becomes economically infeasible at production scales below 18 tons per day. This highlights the importance of scaling up the technology to achieve economic viability in larger-scale ammonia production applications.
An E-field microwave reactor model is developed, incorporating a validated reduced order model for accurate and efficient MW power absorption calculations. The simulations shows the crucial role of MW power in reactor temperature control and highlight the importance of advanced modeling techniques for understanding the interplay between microwave radiation and catalysts.
Recommended Citation
Ogunniyan, Opeyemi Aduragbemi, "Modeling and Techno-Economic Optimization of Microwave Assisted Ammonia Synthesis Processes" (2024). Graduate Theses, Dissertations, and Problem Reports. 12565.
https://researchrepository.wvu.edu/etd/12565
Embargo Reason
Publication Pending