Centrifuge process for dewatering oil sands tailings
A process for dewatering oil sands tailings is provided, comprising providing a tailings feed having a solids content in the range of about 10 wt % to about 45 wt %; adding a flocculant to the tailings feed and mixing the tailings feed and flocculant to form flocs; and centrifuging the flocculated tailings feed to produce a centrate having a solids content of less than about 3 wt % and a cake having a solids content of at least about 50 wt %.
1. A process for dewatering fluid fine tailings, comprising:
a) providing a fluid fine tailings feed having a solids content in a range of about 10 wt % to about 45 wt %;
b) adding an pre-centrifuge additive consisting of a coagulant selected from the group consisting of gypsum, alum and lime, and a flocculant, the coagulant being added to the fluid fine tailings feed and mixed to form a coagulant-treated tailings feed and the flocculant being added to the coagulant-treated tailings feed and mixed to form flocs and produce a flocculated tailings feed; and
c) feeding the flocculated tailings feed to at least one centrifuge and centrifuging the flocculated tailings feed to produce a centrifuge centrate having a solids content of less than about 3 wt % and a centrifuge cake having a solids content of at least about 50 wt %;
whereby the addition of coagulant prior to the addition of flocculant increases the throughput of flocculated tailings through the centrifuge.
2. The process of claim 1 , wherein the coagulant and the fluid fine tailings feed are mixed in an agitated feed tank to cause the solids to agglomerate.
3. The process of claim 1 , wherein the coagulant is added to the fluid fine tailings feed in-line.
4. The process of claim 1 , further comprising diluting the coagulant with water prior to adding it to the fluid fine tailings feed.
5. The process of claim 1 , wherein the dosage of coagulant ranges from about 300 grams to about 1,500 grams per tonne of solids in the fluid fine tailings feed.
6. The process of claim 1 , wherein the coagulant comprises gypsum.
7. The process of claim 1 , wherein the solids content of the fluid fine tailings feed is in a range of about 30 wt % to about 45 wt %.
8. The process of claim 1 , wherein in step (b), the flocculant and coagulant-treated tailings feed are mixed in a static mixer having no moving parts or a dynamic mixer having at least one moving part.
9. The process of claim 8 , wherein the flocculant and the coagulant-treated tailings feed are mixed in a static mixer having no moving parts.
10. The process of claim 9 , wherein the static mixer having no moving parts is a T mixer.
11. The process of claim 8 , wherein the flocculant and the coagulant-treated tailings feed are mixed in a dynamic mixer having at least one moving part.
12. The process of claim 11 , wherein the flocculant is added to the coagulant-treated tailings feed in-line prior to mixing in the dynamic mixer having at least one moving part.
13. The process of claim 1 , further comprising diluting the flocculant prior to adding it to the coagulant-treated tailings feed.
14. The process of claim 13 , wherein the flocculant is a 0.2 to 2% by weight aqueous solution.
15. The process of claim 13 , wherein the flocculant is a 0.2 to 0.4% by weight aqueous solution.
16. The process of claim 1 , wherein the flocculant is an anionic, nonionic, cationic or amphoteric polymer.
17. The process of claim 16 , wherein the dosage of flocculant ranges from about 400 grams to about 2000 grams per tonne of solids in the fluid fine tailings feed.
18. The process of claim 16 , wherein the flocculant comprises a polyacrylamide anionic flocculant.
19. The process of claim 1 , wherein in step (b), the flocculant is added to and mixed with the coagulant-treated tailings feed in a centrifuge.
20. The process of claim 1 , wherein the flocculated tailings feed is centrifuged in a solid bowl decanter centrifuge.
21. The process of claim 1 , wherein the fluid fine tailings are optionally diluted with dilution water to produce the fluid fine tailings feed having a solids content in the range of about 10 wt % to about 45 wt %.
22. The process of claim 21 , wherein after step (c), the centrifuge centrate is returned to a tailings pond or recycled as dilution water.
23. The process of claim 1 , wherein after step (c), the centrifuge cake is disposed in an area using a dry stacking mode of disposal.
24. The process of claim 1 , wherein the fluid fine tailings are mature fine tailings (MFT).
25. The process as claimed in claim 1 , wherein the process is performed at ambient temperature.
26. The process as claimed in claim 1 , further comprising:
(e) dewatering the centrifuge cake by consolidation, drying and/or desiccation using 1 to 2 meter lifts.
27. The process as claimed in claim 1 , further comprising:
(e) dewatering the centrifuge cake by consolidation, drying and/or desiccation using greater than 2 meter lifts.
28. The process as claimed in claim 1 , further comprising:
(e) adding a cake strengthening additive to the centrifuge cake.
29. The process as claimed in claim 28 , wherein the cake strengthening additive is selected from the group consisting of Portland cement, fly ash, overburden, gypsum and lime.
30. The process as claimed in claim 1 , wherein the flocculant is a water soluble polymer having a molecular weight ranging between about 1,000 kD to about 50,000 kD and an intrinsic viscosity of at least 3 dl/g.
31. The process as claimed in claim 1 , wherein the coagulant comprises gypsum and the flocculant comprises a polyacrylamide anionic flocculant.