Systems and methods for recovering helium from feed streams containing carbon dioxide
Systems and methods are provided for recovering helium from a feed comprising helium, carbon dioxide, and at least one intermediate component having a volatility between those of helium and carbon dioxide. In particular, processes of the present invention comprise separating the carbon dioxide and the components of intermediate volatility from the helium at a temperature greater than −82.7° C. to form a helium-rich product stream, wherein the concentration of at least one of the intermediate components in the helium-rich product stream is lower than its concentration in the feed stream, and wherein at least part of the separation is effected by contacting a vapor with a liquid.
1. A method for recovering helium from a feed stream comprising helium, at least 50 mol % carbon dioxide, and one or more intermediate components having volatilities between those of carbon dioxide and helium, the method comprising:
(a) cooling the feed stream;
(b) separating the feed stream into a first helium-enriched stream and a first CO 2 -enriched stream in a distillation column;
(c) feeding a liquid stream comprising CO 2 to the top of the distillation column, thereby washing at least a portion of the one or more intermediate components into the first CO2-enriched stream; and
(d) separating the first helium-enriched stream to form a helium-rich product stream and a helium-lean stream,
wherein the concentration of at least one of the intermediate components in the helium-rich product stream is lower than its concentration in the feed stream, wherein at least part of the separation in step (b) is effected by contacting a vapor with a liquid, wherein at least part of the feed stream enters the distillation column at an intermediate stage, and wherein the temperature at the coldest part of method steps (a) through (d) is greater than −56.6° C.
2. The method of claim 1 , wherein at least part of the method takes place at a temperature below ambient temperature.
3. The method of claim 1 , further comprising the steps of:
(e) splitting the first CO 2 -enriched stream into two or more derivative CO 2 -enriched streams;
(f) heating at least one of the two or more derivative CO 2 -enriched streams; and
(g) compressing and combining the two or more derivative CO 2 -enriched streams to form a CO 2 -rich product stream.
4. The method of claim 1 , wherein the feed stream is dried to a water dew point of less than or equal to −40° C. prior to cooling the feed stream.
5. The method of claim 1 , wherein the helium-lean stream is recycled and fed to the distillation column.
6. The method of claim 5 , wherein the recycled helium-lean stream is combined with the feed stream before being fed to the distillation column.
7. The method of claim 1 , wherein the feed stream is separated in step (b) in a distillation column having a first reboiler, wherein a first liquid stream is withdrawn from the bottom of the distillation column, heated and at least partially vaporized, and at least the vapor portion of the heated first liquid stream is returned to the bottom of the distillation column.
8. The method of claim 3 , further comprising separating at least one of the two or more derivative CO 2 -enriched streams into a liquid fraction and a vapor fraction and feeding the liquid fraction to the top of the distillation column.
9. The method of claim 8 , wherein the derivative CO 2 -enriched stream is heated prior to separating the stream into the liquid fraction and the vapor fraction and wherein the liquid fraction is cooled prior to entering the top of the distillation column.
10. The method of claim 1 or claim 9 , wherein the helium-rich product stream comprises at least 90 mol % helium.
11. The method of claim 1 , wherein the helium-rich product stream comprises at least 60 mol % helium.
12. The method of claim 3 , wherein the CO 2 -rich product stream comprises at least 90 mol % CO 2 .
13. The method of claim 1 , wherein the feed stream comprises a gas.
14. The method of claim 1 , wherein the feed stream comprises a liquid.
15. The method of claim 1 , wherein the feed stream comprises a supercritical fluid.
16. The method of claim 1 , wherein the pressure of the feed stream is greater than about 35 bar.