Green urea fertiliser manufacture by integrating water electrolysis with oxyfuel combustion: A life cycle assessment of carbon emissions

Nitrogen fertilisers account for 2% of global carbon emissions and urea is the most widely used of them. We propose a new production pathway that lowers carbon emissions by utilising green hydrogen and oxygen produced by the electrolysis of water. The hydrogen would be used to produce ammonia, a precursor for urea. The oxygen would be used for oxyfuel combustion of biomass to generate carbon dioxide, which would be reacted with the ammonia to produce green urea. Urea produced in New Zealand by this route would produce 23% less carbon emissions than urea produced by steam-methane reforming of natural gas, and a 41% reduction if grid electricity was 100% renewable. Urea produced by biomass gasification showed even lower emissions, 39% lower than urea derived from natural gas. However, the novel oxyfuel-electrolysis route required 69% less biomass feedstock than the biomass gasification route.