A cryogenic air separation process that generates nitrogen has different process configurations depending on the utilization of either a cold heat supply method or a distillation method. Each method presents different initial investment costs, operating costs and energy efficiencies. Therefore, an accurate estimation of the energy efficiency as well as the cost is an important factor in selecting an appropriate process and in designing the most efficient equipment. Accordingly, the current study formulated criteria that can be applied to select the most efficient process. Processes using liquid nitrogen and an expansion turbine representing different cold heat supply methods were analyzed and evaluated to compare the exergy efficiency. In addition, the exergy efficiency of structure packing and sieve tray distillation method was also compared based on the experimental results.