Modeling And Optimization For Nitrogen Liquefaction With Subcooling And Air Separation Unit From Air

Abstract

Nitrogen liquefaction is an energy-intensive process which is used in several industries like polymer industry, aerospace engineering, air separation unit, sewage treatment plant, electronic industry, agricultural science, petroleum and reservoir engineering, mining engineering, bioscience engineering, nanotechnology, separation process technology, storage technology, civil and construction engineering, fuel cell, catalysis, power systems, pharmaceutical technology, ceramic technology, solar energy systems, molecular dynamic simulation etc. Also, nitrogen can be utilized for the manufacture of ammonia or start tipping on an ammonia plant, protection of materials from bacterial and fungal disorders. Therefore, liquefaction of nitrogen is an important process for various process industries. Generally, liquefaction of nitrogen involves various methods like reverse stirling cycle, LINDE-HAMPSON cycle, Joule Thompson effect and etc. This research is focused on the production of generation of liquid nitrogen from air using Air Separation Unit (ASU) followed by multistage subcooling system. Modeling of this process was carried out using Aspen Plus® and then optimized using Design Expert®. The final composition of liquid nitrogen varies from 78.558 tons/day to 234.7108 tons/day, which increases linearly, while the conversion of 78.558% to 78.224%, which decreases exponentially. The effect of parameters used in the Design Expert ® were split fraction (f) and air flowrate (a). The values of (f) and (a) were fixed using User Defined Method, Central Composite Method and D-Optimal Method. User Defined Method confirms that when the air flowrate was 299.99 tons/day with a split fraction of nitrogen from ASU unit is 0.59, the production of liquid nitrogen is 132.1815 tons/day. While for Central Composite Method and D-optimal Method, when the air flowrates were 300 and 299.99 with split fraction of 0.6 and 0.59 respectively then the production of liquid nitrogen were 128.8224 and 139.975 respectively. Out of these three response methodology methods D-Optimal Methods reveals the most appropriate method since it infers the maximum nitrogen production or generation. The range for the production or generation of liquid nitrogen validates with the results of Aspen Plus ®. So it can be confirmed that the results obtained from Aspen Plus ® are realistic in nature.