The deep-cooling oxygen plant is now widely industrialized because of its highest production capacity and the highest purity of separated gas of all other oxygen plants. The deep-cooling oxygen plant is an air-liquefaction separator that uses compressed air to swell the throttle, obtain the cold, devolatilize the air, and then distill the devolatilized air at low temperature to obtain gases such as oxygen, nitrogen, argon, etc.
Expanders are widely used because they are energetically more advantageous to obtain cold than throttling expansion of compressed gas. At present, turbo-expanders are widely used in the production of oxygen by the deep-cooling method. In oxygen plants, a turbo-expander accounts for 80-90% of the total cold production.
High-strength aluminum alloys are used for the working wheels of a turbo-expander since they rotate at such cryogenic temperatures as -186℃ to -175℃ at high rotational speeds (18 300-18 600r/min). Recently, with the improvement of the mechanical properties of casting materials by the development of casting technology, many researches have been carried out to fabricate efficient closed working wheels by the casting method. What is important here is to choose proper material for working wheels.
Sok Sun Hak, a researcher at the Faculty of Material Science and Technology, proposed a new method for optimizing the alloy composition and heat treatment process parameters of turbo-expander working wheel materials by using quality index and quality engineering techniques, and obtained the optimum parameters.
The additive amount of RE is 0.1%, and the optimum heat treatment process is to perform solid solution treatment before aging heat treatment at 155℃ for 8h. The mechanical properties of this case were excellent, with yield strength of 287MPa, tensile strength of 380MPa and elongation of 12.7%.
This improvement in the mechanical properties ensured stable operation of working wheels in a large oxygen plant and made it possible to increase their lifecycle by three times as much as that of existing ones.