Thermo-environomic evaluation of the ammonia production
Within the global challenge of sustainable energy supply and greenhouse gas emissions mitigation, carbon capture and storage (CCS) and the deployment of renewable resources are considered as promising solutions. In this context, the production of ammonia mainly used in the fertilizer industry that is responsible for a large part of the global CO2 emissions is analyzed in detail in this study. Considering natural gas and biomass as a resource and the option for CO2 capture and storage, different process configurations are systematically compared with regard to energetic, economic and environmental considerations. A consistent thermo-environonomic optimization approach combining flowsheeting, process integration techniques, economic performance evaluation, life cycle assessment and multi-objective optimization is applied for the conceptual process design and the assessment of the competitiveness and the trade-offs. It is highlighted that the quality of the process integration is a key factor for improving the process performance by valorizing the heat excess through electricity cogeneration. Including CO2 mitigation in the ammonia production allows to reduce the emissions, but leads to a slight efficiency decrease due to the additional energy consumption for the compression. For the natural gas fed process yielding an energy efficiency around 65%, the overall life cycle emissions can however be reduced to 0.79kgCO2/kgNH3 with CO2 capture compared to 1.6kgCO2/kgNH3 without capture and to -1.79kgCO2/kgNH3 for the biomass process having an energy efficiency of 50%. The economic competitiveness highly depends on the resource price and the introduction of a carbon tax. This study reveals the potential of the decarbonization of the fertilizer industry.