The Process And Rectification Simulation Analysis Of Full Low-pressure Air Separation Plant

Simulation analysis would be done against to the rectification process with the most common full low-pressure air units used in home country. The process is full rectification low-pressure process adopted with molecular sieve adsorption, compressor turbo-expander, full rectification argon production without hydrogen and oxygen external compression.The rectification process is: most of the clean air, left from the air purification system, flows into the major heat exchangers in the cold box. It is cold by the back air. The air close to the dew point flows into the lower column bottom to complete the first rectification. In the rectification column, the rising vapor contacts completely with the descending liquid, after heat and mass transfer, nitrogen's concentration in the rising vapor is more and more high. The pure nitrogen flows into the reboiler-condenser to be condensed, while the liquid oxygen in reboiler-condenser to be gasified. A part of the liquid nitrogen refluxes to lower column, the other flows into upper column after sub-cooled and throttled, with the exception of a few liquid nitrogen taken as manufacture. The liquid air in lower column flows into upper column, too, after sub-cooled and throttled. After the second rectification in the upper column, the product, nitrogen, oxygen, and waste nitrogen would be got.Simulated calculation is the promise and key of the process design. This paper is based on the soft ASPEN PLUS and HYSYS, containing the model and simulation calculation. The method of increasing the output and recovered rate is generalized by debugging the program. The recovered rate of oxygen and argon can reach to more than 99% and 80%. And the emphasis work is researching the characteristic of argon enrichment area in up-column. It is approved that each compotation in up-column cannot be independent. They are interconnected and interrelationship, their alteration is dynamic. According to this information, the optimally position of argon fraction can be found in up-column. When this position is fixed, if the work condition is change a little, it can be regulated to the optimally status by setting the operability variable. The other major work in this paper is optimizing the process. A expansion air sub-cooler is added followed the expansion heat exchanger. It is result that the temperature of the expansion dropping to 85K, making the work condition steadily and increasing the extraction rate of argon, and providing a viability program.