Design and Analysis of Dual-Bed Helium-Purifier operating at 80K Temperature for Helium Refrigerator/Liquefier

Abstract

The Helium Refrigerator/Liquefier (HRL) plant is normally operated with helium gas having purity better than 99.999 % by volume which is equivalent to having < 10 PPM (parts per million) impure gas in the helium stream. In the process of gas transfer or due to some other processes before reaching to cold box of helium plant, impurity level sometimes can reach to as high as 500 PPM averaging to about 100 PPM. These impurities consist of mainly gases present in the air, hydrocarbons and Hz and traces of Ne. These gases condense at significantly higher temperature compared to the LHe temperature (4.5 K). If such high level of impurity enters the process equipment placed inside the cold box of the HRL, then it can condense and choke the pipe lines and valves leading to large pressure drop and inefficient liquefaction process. Some time, condensed and frozen impurity can destroy the blades of turbines of HRL. Hence, to be on safer side generally, internal purifiers are placed at two temperature levels (at 80 K and 20 K) inside the cold box to take care the operational problem due to impurities. But, for HRL operating for significantly longer duration and producing larger liquid helium for application, these internal purifiers are not sufficient. Hence, externally, a dual-bed purifier operating at 80 K is used, which can be used for continuous operation of purification process. As most of the impurity gases are O2, N2 and Ar, adsorption purification process operating at 80K can be sufficient to remove these major impurities. When one bed is saturated, the other bed is used for purification, while the earlier bed is put in regeneration mode and kept ready for next adsorption process and this is done alternately for both beds, such that, purification process is continuous. Activated charcoals will be used to adsorb impure gases from cold helium gas at ~80 K and ~14 bar. The nominal flow rate of helium gas is ~120 g/s for the actual size purifier bed. Necessary filters, piping and valves will be worked out.
Following activities will be involved
1. Study the large scale helium plant and its components and design and analysis work done for 80K internal purifier bed for HRL
2. Study the literatures related to O2, N2 and Ar removal from helium stream using adsorber beds and operations related to it.
3. Design the purifier beds, filter elements and the associated piping and valve sizing.
4. Do the analysis and sizing of beds, such that operation can be continuous.
5. Do the detailed thermo hydraulic analysis of the system.
6. Make drawings of the system.
7. Make the report for the above work.