Megawatts to methane – a deep drop in emissions reduction transition for existing regional gas-based ammonia plants

Abstract

Synthetic ammonia production sustains food production for more than half of the world’s population. Many regional ammonia plants convert all ammonia to ammonium nitrate fertiliser. With these, all carbon in the feed ends up as carbon dioxide (CO₂), with around 2 tonnes of CO₂ released per tonne of ammonia produced using natural gas. Conveniently, ammonia plants produce a substantial pre-concentrated CO₂ stream. Ammonia plants are high-capex, long-life assets that operate for 40+ years. With the energy transition, replacing such assets is very high cost and will dramatically impact the cost of food production. Further, green energy is highly variable, leading to the need for additional supply side assets to stabilise energy supply. This paper outlines a transition approach for a 30% CO₂ reduction (also a 43% case) to extend the useful life of these assets while re-using much of the plant, with the ability to turn on/off the green energy with minimal disruption for stable operation. The example plant is based on a typical 750 tpd ammonia gas Steam Methane Reforming (SMR) plant. The approach considers adding and integrating green power and biogas into this plant to reduce net reportable CO₂ emissions. Methanation of CO₂ has been demonstrated in several projects and is considered key in developing a transition pathway for an existing gas-based plant, extending its operational life and flexibility to operate with varying degrees of variable green energy supply. Further, whilst Synthetic Natural Gas (SNG) is used in this case, the approach can be beneficially applied with methanol and other Power-to-X opportunities.