Remote, small-scale, ‘greener’ routes of ammonia production

The techno-economic feasibility of low-carbon–based ammonia (NH ₃ ) production has been explored in this study. Black coal and a eucalyptus-based biomass, available in the vicinity of a carbon dioxide (CO ₂ ) sequestration site, have been chosen as the two carbon-based feedstocks. The scale of the production of NH ₃ has been chosen to match the production of a bulk industrial Ammonium Nitrate/Fuel Oil (ANFO) explosives manufacturing facility. The production of NH ₃ from any carbon-based feedstock implicitly involves a CO ₂ -removal step; therefore, only CO ₂ pressurisation to the supercritical state is required before transporting it to the storage location. In order to gain a better understanding of the economic and environmental trade-offs, two representative flowsheets have been modelled in Aspen Plus ^® simulation software for the two feedstocks. A Natural Gas (NG)-based NH ₃ process has also been modelled for comparison. Material and energy balance data from the Aspen Plus ^® simulation has been used to predict the economics and carbon footprint of NH ₃ production from different feedstocks. A cradle-to-gate Life Cycle Assessment (LCA) has been performed to predict the environmental hotspots. A genetic algorithm based Multi-objective Optimisation (MOO) has generated Pareto plots that represent the minimum cost of NH ₃ production against different CO ₂ footprints. For a similar CO ₂ footprint, the coal-based NH ₃ process has been found to be more economic than the biomass-based process. However, the biomass-based process has the potential to be carbon negative by capturing the biogenic CO ₂ , which is not possible in a coal-based process. The cost of carbon capture in coal-based NH ₃ production has been estimated to be between 11 and 19 US$/tCO ₂ ^eq , which is significantly lower than the cost of CO ₂ capture from coal-based power generation (usually reported to be in the range of 40–60 US$/tCO ₂ ).