Plant-wide modeling and techno-economic optimization of a low-pressure microwave-assisted ammonia synthesis process with adsorption separation

• Published in: International journal of hydrogen energy Vol. 86; no. C; pp. 300 - 315
• Main Authors: Ogunniyan, Opeyemi, Haque, Md Emdadul, Wang, Yuxin, Hu, Jianli, Bhattacharyya, Debangsu
• Format: Journal Article
• Language: English
• Published: United Kingdom Elsevier Ltd 11.10.2024; Elsevier
• Subjects: Adsorption; Ammonia; Dynamic model; Economics; Microwave; Optimization; Economics; Microwave; Ammonia; Adsorption; Dynamic model; Optimization
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2024.08.383

Ammonia production has traditionally been done by using the Haber-Bosch process, that operates at extremely high pressure (200–300 bar), has a large carbon footprint, and requires significant energy. For ammonia to be used as a hydrogen carrier, it is desired that it is produced by using modular technologies under benign conditions, yet the economics remain commercially viable. This paper investigates a novel technology for ammonia synthesis by using a microwave-assisted low-pressure reactor. Microwave reactors are compact and can be readily modularized and started/shutdown thus making them ideal to be integrated with the electric grid or with regional/local renewable-based electric generation facilities. For separation of unreacted reactants from the product ammonia, if the traditional condensation separation technology used in the high-pressure Haber-Bosch process is used, then the separation process needs to be operated under cryogenic condition thus adversely affecting the economics. A solid sorbent based separation technology is investigated in this paper. A kinetic model for the microwave-catalytic synthesis process is used. An isotherm model is developed for MgCl2–Si adsorbent and used for modeling the dynamic adsorption-desorption cycle. A plant-wide model with heat and mass integration is developed. An economic model is developed and used for economic optimization by using an equation-oriented approach. Since the adsorption-desorption process is dynamic, for techno-economic optimization, a reduced order model for the key performance measures of the adsorption-desorption process as a function of its input and decision variable is developed under cyclic steady-state conditions. For the optimized MW-assisted process, the levelized cost of ammonia is $772/mt as opposed to $808/mt for the conventional Haber-Bosch process for a hydrogen price of $2.07/kg. The MW-assisted process is found to be economically viable in the US market if the hydrogen price is below $4/kg. •Plant-wide model of a novel MW-assisted ammonia synthesis process is developed.•A solid-sorbent based separation technology is investigated for separation.•A reduced model based approach is developed for optimizing the adsorption process.•For the optimized process, the levelized cost of ammonia is found to be $772/mt.•The technology is found to be economically viable for H2 price below $4/kg.