Authors

Abstract

Ammonia (NH3) is conventionally produced using fossil natural gas (NG) for hydrogen production through steam reformation and synthesis in the Haber-Bosch (HB) process. The global conventional ammonia production contributes more than 420 million tons of CO2 emissions annually. In this work, we investigated the techno-economics and well-to-plant-gate (WTG) greenhouse gas (GHG) emissions of conventional NG-based, carbon-capturing, nuclear-powered, and renewable ammonia production by developing an engineering process model for each. Carbon-capturing ammonia production refers to the NG-based ammonia production while capturing CO2 and transporting it via pipelines for storage or utilization. Nuclear-powered and renewable ammonia production represents an alternative ammonia production through water electrolysis, air separation, and the HB process using carbon-free energy sources. Nuclear and renewable energy sources are assumed to be used for nuclear-powered and renewable ammonia production, respectively. Sensitivity analyses are performed for CO2 pipeline transport distances, potential carbon capture tax credits, and clean H-2 production cost. Carbon-capturing ammonia production reduces WTG GHG emissions by 55-70% compared to conventional NG-based ammonia production methods. Nuclear-powered and renewable ammonia production almost eliminate GHG emissions since energy supply is either zero carbon or near-zero carbon. However, when $4.16-4.83 per kg is the cost assumed for clean H-2 production using state-of-the-art electrolysis technologies, the levelized costs of nuclear-powered and renewable ammonia are calculated to be $0.92-1.06 per kg NH3, which are approximately four times higher than the conventional NG-based ammonia production cost. The cost of CO2 emission avoidance is estimated in the range of $266-318 per metric ton of CO2 for nuclear-powered and renewable ammonia production. The clean H-2 production cost is the major contributor to the levelized costs of nuclear-powered and renewable ammonia production. A lower production cost, near $1 per kg H-2, for clean H-2 is required for nuclear-powered and renewable ammonia production to be cost-competitive with conventional NG-based ammonia production.