Air compression is the main energy consumption process in cryogenic air separation units (ASUs), while compression waste heat occupies over 60% of the total compression power. However, the compression waste heat has not yet been recovered in existing ASUs, implying a great potential for energy efficiency improvement. In this paper, an organic Rankine-vapor compression cycle (ORVC) assisted three-stage air compression system (ORVC-ACS) is proposed. The compression waste heat is recovered by the ORVC to generate cooling capacity to precool the inlet air of the air compressors, which thus reduces its compression power consumption. Humidity constraint is specially considered in the thermodynamic model as the heat source is pressurized humid air. The feed air conditions (i.e., temperature and humidity) and operation parameters (i.e., the compressed air temperatures, evaporation temperatures and condensation temperature) are first investigated and optimized to study their effects on system performance. The operating ranges of the feed air and operation parameters are further analyzed and identified to ensure no condensed water during the air compressor operation. The optimization results show that the maximum energy saving ratio (ESR) of the ORVC-ACS reaches 4.2%, corresponding to a total annual energy saving of 7500 MWh for a 60,000-Nm³/h scale ASUs. It is found that the proposed ORVC-ACS is able to work under the feed air temperature range of 5.35–22.5 °C and relative humidity range of 0–0.8. In addition, economic and environmental assessment shows that a discounted pay-back period of 3.1 years and annual carbon-dioxide emission reduction of 5400 t are attainable with the proposed ORVC-ACS, indicating that it is economic viable with excellent decarbonization potential. This work would provide guidance for practical compression system operation in cryogenic ASUs.

空气压缩是低温空气分离装置（ASU）的主要能耗过程，而压缩废热占总压缩功率的60％以上。但是，现有的ASU中尚未回收压缩废热，这意味着提高能源效率的巨大潜力。本文提出了一种有机朗肯蒸气压缩循环（ORVC）辅助的三级空气压缩系统（ORVC-ACS）。压缩废热由ORVC回收，以产生冷却能力以预冷空气压缩机的进气，从而降低其压缩功率消耗。由于热源是加压湿空气，因此在热力学模型中特别考虑了湿度限制。进风条件（即温度和湿度）和运行参数（即 首先研究和优化压缩空气温度，蒸发温度和冷凝温度，以研究它们对系统性能的影响。进料空气的运行范围和运行参数会被进一步分析和确定，以确保在空气压缩机运行期间没有冷凝水。优化结果表明，最大节能率（ORVC-ACS的ESR达到4.2％，对应于60,000-Nm ³ / h规模的ASU每年总共节省7500 MWh 。发现建议的ORVC-ACS能够在5.35–22.5°C的进风温度范围和0–0.8的相对湿度范围内工作。此外，经济和环境评估表明，拟议的ORVC-ACS可以实现3.1年的折现投资回收期和每年减少5400吨的二氧化碳排放，这表明脱碳潜力在经济上可行。这项工作将为低温ASU中的实际压缩系统操作提供指导。