Steady And Dynamic Simulation For The Air Separation Process With18000Nm³/h Of N₂

Air separation unit has been mainly employed to separate the oxygen, nitrogenand argon in the air. Due to the broad application of air separation products in thepetroleum, chemical engineering, metallurgy, pharmaceutical industry and so on, theair separation unit has become an industry with broad development prospects. Atpresent, the most commonly used technology to separate components in the air is thecryogenic technology. The streams in the system interrelate and interact with eachother and the mass and energy exchange is complicated. To implement the accuratesimulation of air separation process is of great importance for the design of theprocess and to guide the production operation.In recent years, with the continuous development and the widespread applicationof chemical process simulation softwares, like Aspen PLUS, Aspen HYSYS, PROIIand ChemCAD, the steady state simulation and optimization design for the airseparation process have been very mature. However, the dynamic simulation of the airseparation process is also meaningful. The dynamic simulation can investigate thecontrol system of the unit and predict the adjustment direction after a surge hasoccurred in the process as well as train and mentor the start-up process to save thestart-up time and reduce consumption. According to the author’s knowledge, there arefew reports about the dynamic simulation of the air separation process.HYSYS was employed to do the steady and dynamic simulation for the airseparation process with18000Nm3/h of N2. The process is made up of five systems:they are air filtration system, air compressor system, air precooling system, airpurification system and air separation system. First, the steady state simulation wasdone for the air compressor system and the air separation system, the operationparameters and the output of the products were determined. Second, the LNGexchanger and distillation column parameters were determined and then dynamicsimulations were made and the dynamic characteristics were studied for theexchanger and the distillation column.1) Aspen MUSE was used to design the LNGexchanger in the process to determine its size, layer stacking pattern and the inlet andoutlet arrangement. Based on the results obtained, partitioned the exchanger into several zones to achieve the dynamic simulation by HYSYS, and then analyzed theheat transmission inside the exchanger.2) Equipment parameters were input and thecontrol instruments were installed for the distillation column and then the dynamicsimulation for the distillation column was conducted. The products output and theinside parameters changes along with the surges of the feed rate are studied toevaluate the availability of the control scheme. Finally, dynamic simulation was madefor the air separation process and the system stability was studied with the feed rateand pressure fluctuations.