Techno-economic and life cycle greenhouse gas assessment of green ammonia produced by low-pressure Haber-Bosch process

Abstract

Green ammonia can be used as an energy storage carrier and a sustainable chemical. To improve the competitiveness of green ammonia, two power-to-ammonia (PtA) processes integrated with low-pressure (LP) and ultra-low-pressure (ULP) Haber-Bosch (HB) techniques were designed and optimized based on technical, economic, and environmental performances. The effects of multiple variables were studied. The LP technique is preferred over the ULP technique because the latter has a more complex configuration and a slightly higher levelized cost. The systematic energy efficiency excluding or including the cold energy of liquid ammonia reaches 68.71 % or 73.75 %, respectively. The unit power consumption of green ammonia is as low as 7.64 kWh/kg. The plant scale should not be <10 t/h. Based on the electricity price for energy storage (0.041 €/kWh), the equivalent operating hours should exceed 5000 h to achieve profitability. The life cycle greenhouse gas emission of green ammonia derived from wind power under the Chinese scenario is 257–316 kgCO₂e/t. The life cycle ammonia emissions with NH₃ recovery from the purge gas is <0.06 kgNH₃/t. This study indicates that the PtA technology can efficiently store intermittent electricity with cold energy utilization and effectively decarbonize the ammonia industry.