Argon production method and apparatus
A method and apparatus for producing a purified liquid argon product in which liquid argon having oxygen impurities is produced in a cryogenic air separation plant by separating argon from oxygen within an argon column. An impure liquid argon stream, composed of part of the liquid argon, is purified in an adsorbent bed by adsorbing the oxygen impurities in an adsorbent to produce a purified liquid argon stream that constitutes the purified liquid argon product. During adsorption, the adsorbent bed is maintained at a reduced temperature with a coolant to prevent vaporization of the liquid argon. The bed is then regenerated by draining residual liquid argon from the adsorbent bed, introducing the residual liquid argon back into the air separation plant and then desorbing the oxygen impurities with a regeneration gas. After regeneration, the adsorbent bed is refilled with purified liquid argon prior to being brought back on-line.
1. A method of producing a purified liquid argon product comprising the steps of:
separating argon from oxygen in an argon column within a cryogenic air separation plant wherein the argon column is configured to produce an impure liquid argon stream having oxygen impurities;
introducing a portion of the impure liquid argon stream having oxygen impurities into an adsorbent bed;
adsorbing the oxygen impurities from the impure liquid argon stream in an adsorption process having an adsorbent to produce a purified liquid argon stream constituting the purified liquid argon product;
subjecting the adsorbent bed to an alternating cycle having an on-line phase where oxygen impurities are adsorbed from the portion of the liquid argon stream having oxygen impurities within the adsorbent bed and an off-line phase where the adsorbent contained in the adsorbent bed is regenerated;
indirectly exchanging heat from the adsorbent bed to a coolant stream during the on-line phase of the alternating cycle to provide the adsorbent bed at a reduced temperature that is sufficient to prevent vaporization of the liquid argon stream and the liquid argon product stream;
terminating the step of introducing a portion of the impure liquid argon stream having oxygen impurities into the adsorbent bed during the off-line phase of the alternating cycle;
draining the adsorbent bed of residual liquid argon contained in the adsorbent bed during the off-line phase of the alternating cycle to produce a residual liquid argon stream;
directing the residual liquid argon stream into the argon column or a low pressure column of the cryogenic air separation plant as a liquid or a vapor or a mixture of liquid and vapor;
regenerating the adsorbent by removing the oxygen impurities from the adsorbent;
refilling the adsorbent bed with the purified liquid argon product; and
re-subjecting the adsorbent bed to the on-line phase of the alternating cycle by introducing the impure liquid argon stream having oxygen impurities into the adsorbent bed.
2. The method of claim 1 , wherein the adsorbent is a molecular sieve and the adsorption process is a temperature swing adsorption process and wherein the step of regenerating the adsorbent further comprises the steps of terminating indirect heat exchange between the adsorbent bed and the coolant stream and passing a heated regeneration gas stream through the adsorbent bed to desorb the adsorbed oxygen impurities.
3. The method of claim 2 , wherein the regeneration gas is formed from part of a nitrogen-rich vapor column overhead stream from the lower pressure column of the cryogenic air separation plant after having been at least partially warmed in a main heat exchanger of the cryogenic air separation plant.
4. The method of claim 1 , wherein the coolant stream is formed from shelf liquid produced in a high pressure column of the cryogenic air separation plant.
5. The method of claim 2 , further comprising the step of resuming the indirect heat exchange between the adsorbent bed and the coolant stream prior to the step of refilling the adsorbent bed with the purified argon liquid product.
6. The method of claim 1 , wherein the step of adsorbing the oxygen impurities from the impure liquid argon stream to produce a purified liquid argon stream further comprises producing the purified liquid argon stream and a subsidiary liquid argon stream, and wherein the subsidiary liquid argon stream is introduced into a storage tank.
7. The method of claim 6 , further comprising the steps of:
removing a portion of the liquid argon from the storage tank;
vaporizing the liquid argon removed from the storage tank to form a displacement gas stream; and
introducing the displacement gas stream into the adsorbent bed during the off-line phase of the alternating cycle to assist in draining the residual liquid argon stream from the adsorbent bed.