Thermodynamic, life cycle, and techno-economic assessment of an autothermal supercritical water gasification system for direct processing raw pig manure: Hydrogen generation and ammonia recovery

Supercritical water gasification (SCWG) exhibits an excellent potential for the conversion from pig manure (PM) to H2. However, the low solid content characteristic of raw PM and ammonia discharge significantly constrain the thermodynamic efficiency of SCWG. To address these limitations, a novel SCWG system was designed for simultaneous autothermal H2 production and ammonia recovery from raw PM. Thermodynamic analysis, life cycle, and techno-economic were carried out to assess system performance. Results indicated that the novel system exhibited exceptional adaptability to variations in concentration and mass flow of raw PM, with autothermal H2 production achieved even at low concentration of 10 %. Raw PM was converted into high-concentration slurries through pulping operations, thereby reducing exergy losses of gasification, heat exchange, and cooling units. Further, the system implemented an efficient ammonia recovery utilizing steam generated during the pulping stage. Under a typical scenario, energy efficiency, exergy efficiency, GWPs, and EP of the novel system reached 50.34 %, 45.99 %, 0.005 kgCO2-eq/kgH2, and 0.07 kgNO3--eq/kg H2, respectively. The levelized hydrogen cost of the new system was 15.81 CNY/kg. This study provides a valuable solution for autothermal SCWG of low-solid-content and high-nitrogen-content feedstocks to produce H2 and recover ammonia.