Optimum design and exergy analysis of a novel cryogenic air separation process with LNG (liquefied natural gas) cold energy utilization

A novel cryogenic air separation process with LNG (liquefied natural gas) cold energy utilization that produces liquid nitrogen and oxygen is proposed and analyzed. Air separation process problems such as process configuration complexity, extreme operating conditions and high operating costs are covered. In this process heat from the top vapor stream of the column is recovered and exchanged with heat in the bottom liquid and feed streams. It is noted that column operating pressure can be decreased compared with the high pressure portion of the air separation systems. In fact, the high and low pressure columns are combined here to exchange nitrogen latent heat with oxygen latent heat. This significantly reduces the energy input to the main compressor located before the column. Also, to completely utilize the cold energy of the LNG and to offset some of the consumed power, a power generation cycle is integrated with the process. This cycle utilizes pure oxygen from the air separation unit. The cryogenic air separation process is simulated and the main parameters are analyzed. It is shown that the energy consumption for the proposed air separation process with LNG cold recovery is about 38.5% lower compared for a convectional cryogenic air separation process. The energy and exergy efficiencies increase by 59.4% and 67.1%, respectively.