(421b) Comparative Techno-Economic and Life Cycle Analysis of Conventional Ammonia with Carbon-Capture and Low-Carbon Hydrogen-Based Ammonia

Conventional ammonia production employs fossil resources, mostly natural gas (NG), as hydrogen feedstock and accounts for more than 420 million tons of global CO₂ emissions per annum. To reduce the carbon intensity of ammonia production, alternative pathways have been studied. In this work, we investigate and compare techno-economic performances and well-to-plant-gate (WTG) GHG emissions of various ammonia production pathways, including conventional NG-based, carbon-capture, and low-carbon hydrogen-based production. Conventional NG-based ammonia refers to the ammonia produced using fossil NG through steam methane reforming and Haber-Bosch (HB) processes. Carbon-capture ammonia represents the NG-based ammonia produced while capturing process and combustion CO₂ emissions and transporting them via pipelines for CO₂ utilization. Low-carbon hydrogen-based ammonia refers to the alternative ammonia produced from carbon-free sources through water electrolysis, air separation, and HB processes using nuclear or renewable power. Most of the previous studies did not perform techno-economic and life cycle assessment for all these pathways by developing engineering process models. Also, there is a lack of studies that investigate techno-economic performances and life cycle GHG emissions of various ammonia production pathways in the United States.

In this work, we develop detailed engineering process models for each production pathway using Aspen Plus to perform techno-economic and life cycle assessment. Sensitivity analyses are conducted for uncertain parameters such as CO₂ pipeline transport distances, carbon capture tax credits, and low-carbon H₂ production costs. The results show that carbon-capture ammonia reduces WTG GHG emissions by 55–70% compared to conventional ammonia. Also, low-carbon hydrogen-based ammonia almost eliminates WTG GHG emissions because zero-carbon or near-zero carbon energy sources are employed. However, when more than $4/kg of H₂ prices are considered for low-carbon H₂ produced using state-of-the-art electrolysis technologies, the levelized costs of low-carbon hydrogen-based ammonia are calculated to be $0.92–$1.06 per kg NH₃, which are about four times higher than conventional ammonia production cost. We identify that low-carbon H₂ production cost is a key cost driver for low-carbon hydrogen-based ammonia. A cheaper low-carbon H₂ production cost such as $1/kg H₂ is needed for low-carbon hydrogen-based ammonia to be cost-competitive with conventional ammonia.