Green Ammonia Synthesis in a Multi-RES System

Green ammonia is a promising hydrogen carrier and an excellent candidate for the decarbonization of the transport sector. Despite the synthesis process (Haber Bosch, HB) being well known and widely applied in conventional natural gas-fed plants, much effort is required for the coupling with Variable Renewable Energy Sources (V-RES). V-RES intermittency does not meet the limited partial load transient capability of the conventional ammonia process unless large electricity and thermal storage are installed. For that, V-RES may be complemented with biomass-based processes, to have multiple sources of hydrogen supply for the constant-load HB synthesis. This study investigates a multi-RES system for green ammonia production, combining solar-powered high-temperature electrolysis and lignocellulosic oxy-steam gasification. The co-existence of the two processes for hydrogen production allows minimum variations of the HB load, backup hydrogen production, improved thermal integration and the reduction of VRES generator size. The proposed system is investigated with a thermochemical 0D modelling approach, and the discussion of simulation results is based on the 3E (energy-economic-environment) indicators set. The Specific Energy consumption falls in the range of 8.76-10.65 MWh/tonNH3, the Levelized cost of Ammonia is approximately 970-1230 €/tonNH3 based on current costs of technology and raw feeding materials, and the CO2 reduction ranges from -65% to 100% (totally green ammonia) while the raw water withdrawal index is on average 3.27 tonH2O/tonNH3.