A Techno-Economic Model for Renewable Ammonia By Electrochemical Synthesis with Proton Conductive Membrane

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Abstract

Ammonia as a renewable liquid fuel has increased global interest for long term energy storage and as a principal chemical candidate in overcoming the challenging practical issues such as storage and transport associated with hydrogen. It is known the Haber-Bosch method of producing ammonia is based on fossil fuels and has a high energy consumption as a result of operating temperatures and pressures of special concern. A techno-economic study is presented for the electrochemical synthesis of ammonia with proton conducting membrane at near ambient pressure. Different coupling pathways were investigated for production of hydrogen and generation of nitrogen to assess the savings per ton of ammonia. The ammonia production rate is 142 ton/day based on 26 ton/day and 120 ton/day of hydrogen and nitrogen feeds respectively. The pathway for the electrochemical synthesis of ammonia that uses electrolysis of hydrogen and cryogenic nitrogen generation was found to be potentially viable. Hydrogen production via this pathway accounted for less than 40% of the total CapEx and OpEx yearly costs per ton of ammonia. Additionally, the profitability metrics yielded a discounted rate of return of 8%, net present value of $40 MM and 4 to 6 years payback period. The tonnage of ammonia is greatly impacted by conversion rate, cost of electricity, and chemical conversion efficiency. Sensitivity studies revealed a competitive ammonia cost below $1000 per ton can be maintained if electricity prices are less than 0.01c/kWh. Electrolyte development and electro-catalyst tuning to reach higher ammonia conversion rates at improved current densities should be the direction of future research work.

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