Performance Analysis of an Alkaline Water Electrolysis–Cryogenic Air Separation–Ammonia Synthesis System Based on Multi-Stage Compression Power Optimization

Driven by the increasing demand for renewable energy integration and low-carbon transformation in the chemical industry, the production of green hydrogen from renewable electricity for subsequent ammonia synthesis has emerged as an important route for green ammonia production. However, the process still relies on the high-pressure Haber–Bosch synthesis loop, typically operating at 200–300 bar, where multi-stage compression, recycle gas treatment, and low-temperature condensation separation strongly influence energy consumption and feedstock utilization. In this study, a steady-state Aspen Plus (V15) model integrating an Alkaline Water Electrolysis Unit (AWE), cryogenic air separation for nitrogen production, and an ammonia synthesis loop was established for a liquid ammonia plant with an annual capacity of approximately 600,000 t. Under base-case conditions, the specific energy consumption of liquid ammonia production was 10.28 kWh/kg-NH3, while the hydrogen and nitrogen elemental utilization rates reached 87.73% and 88.92%, respectively, both higher than those of conventional coal- and natural gas-based ammonia routes. Increasing the compression stages from 2 to 5 reduced the fresh syngas compression work by 6.69%, although the energy-saving benefit became marginal beyond four stages. A purge ratio of 1–2% achieved a reasonable balance between recycle compression work and hydrogen/nitrogen purge loss, while the preferred condensation temperature range for improved NH3 recovery was −20 °C to −25 °C.