Method and device for the cryogenic separation of a methane-rich flow
A method and device for the cryogenic separation of a methane-rich flow is provided.
1. A method for the cryogenic separation of a methane-rich feed flow also comprising carbon dioxide and a second impurity selected from the group consisting of nitrogen, oxygen, and a combination thereof, said method comprising the steps of:
i) sending the methane-rich feed flow to an adsorption purification unit to produce a carbon dioxide-lean flow having less carbon dioxide relative to the methane-rich feed flow;
ii) cooling at least part of the carbon dioxide-lean flow to produce a cooled flow;
iii) sending at least part of the cooled flow to a distillation column;
iv) withdrawing a methane-rich product flow from the distillation column, the methane-rich product flow being richer in methane relative to the methane-rich feed flow;
v) withdrawing a flow rich in the second impurity from the distillation column, the flow rich in the second impurity being richer in the second impurity relative to the methane-rich feed flow,
vi) vaporizing at least part of the methane-rich product flow;
vii) regenerating the adsorption purification unit using a regeneration fluid comprising at least part of the vaporized methane-rich product flow, such that a second product stream comp sing methane and carbon dioxide is produced;
viii) monitoring the carbon dioxide content of the second product stream; and
ix) maintaining the carbon dioxide content of the second product stream within a given threshold.
2. The method of claim 1 , wherein the carbon dioxide-lean flow is cooled upstream of the column by means of at least one fluid withdrawn from the column.
3. The method of claim 2 , wherein the fluid withdrawn from the column is the flow rich in nitrogen and/or oxygen.
4. The method of claim 2 , wherein the fluid withdrawn from the column is the methane-rich product flow.
5. method of claim 4 , wherein the methane-rich product flow is withdrawn in liquid form.
6. The method of claim 5 , wherein the methane-rich product flow is vaporized by heat exchange with the carbon dioxide-lean flow.
7. The method of claim 1 , wherein the carbon dioxide content of the second product is kept substantially constant.
8. The method of claim 7 , wherein the carbon dioxide content of the second product is kept substantially constant by mixing therewith part of the vaporized methane-rich product flow taken upstream of the adsorption purification unit.
9. The method of claim 1 , wherein cooling is at least partially maintained by vaporizing a liquid nitrogen flow coming from an external source.
10. The method of claim 9 , wherein liquid nitrogen vaporizes by heat exchange with the carbon dioxide-lean flow.
11. The method of claim 9 , further comprising a condenser at the top of the distillation column, and wherein liquid nitrogen vaporizes in said condenser.
12. The method of claim 1 , wherein cooling is at least partially maintained by a refrigerating cycle.
13. The method of claim 1 , wherein the methane-rich product flow is produced in gaseous form.
14. The method of claim 1 , wherein the methane-rich product flow is produced in liquid form.
15. The method of claim 1 , further comprising a reboiler at the bottom of the distillation column, wherein the reboiler is heated.
16. The method of claim 15 , wherein the reboiler is heated with at least part of the flow to be separated.
17. The method of claim 1 , wherein the methane-rich product flow withdrawn from the distillation column contains at least 98% methane.
18. The method of claim 1 , wherein the methane-rich product flow withdrawn from the distillation column contains at least 99% methane.
19. The method of claim 1 , wherein the methane-rich feed flow contains between 75% and 95% methane.
20. The method of claim 1 , wherein the methane-rich feed flow contains between 3% and 25% in total of nitrogen and/or oxygen.
21. The method of claim 1 , wherein step ix) further comprises adding a methane rich fluid to the second product stream.
22. The method of claim 21 , wherein the methane rich fluid comprises the methane-rich product flow.
23. The method of claim 21 , wherein the methane rich fluid comprises the methane-rich product flow vaporized from step vi).
24. The method of claim 1 , wherein step ix) further comprises the steps of mixing a portion of the methane-rich product flow with the second product stream without passing the portion of the methane-rich product flow through the adsorption purification unit.
25. The method of claim 1 , wherein the second product stream has an increased amount of carbon dioxide as compared to the vaporized methane-rich product flow.