Low-pressure microwave-assisted Ammonia synthesis: Evaluation of novel separation technologies, plant-wide process design, and techno-economic analysis

Opeyemi Ogunniyan, Md Emdadul Haque, Yuxin Wang, Debangsu Bhattacharyya and John Hu

Applied Energy, 2024, vol. 373, issue C, No S0306261924012601

Abstract: Ammonia, essential for agriculture, chemical industries, and energy storage, is traditionally synthesized through the Haber-Bosch (HB) process. This established process requires high pressures (up to 300 bar) and temperatures (400–500 °C), thus generally limiting its feasibility to large-scale operations with high capital investment. This study investigates a novel low-pressure (6.5–35.5 bar) microwave-assisted ammonia synthesis process as an alternative to the HB process. Since the ammonia reaction is equilibrium-limited, single-pass conversion is limited, thus requiring separation of ammonia from the unreacted reactants for recycling. However, conventional condensation separation used in the HB process is not suitable for this novel process due to the low operating pressure. This work evaluates four potential separation technologies: cryogenic distillation, cryogenic flash separation, absorption with water as the solvent, and membrane separation. A model of the microwave reactor is developed with kinetic parameters estimated from in-house experimental data. Different configurations of plant-wide models with production capacity of 60,000 t_NH3/year are developed using Aspen Plus. Economic performance is assessed by using two economic measures- minimum selling price (MSP) and levelized cost of ammonia (LCOA). The cryogenic flash separation is found to result in the best economic performance. Optimization results show that the catalyst cost significantly impacts the optimal number of reactors needed. Interestingly, it is observed that the highest single-pass conversion does not necessarily yield the best process economics. The range of MSP improvement through optimization spanned from 0.84% to 16.2% for various case studies. Notably, the optimized case achieved an MSP of $0.113/kWh, that is close to $0.111/kWh obtained using the conventional thermo-catalytic HB process under same boundary conditions for the feed.

Keywords: Ammonia; Low pressure; Microwave; Economics; Optimization (search for similar items in EconPapers)
Date: 2024
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DOI: 10.1016/j.apenergy.2024.123877

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