Low temperature wet air oxidation
There are disclosed systems and processes that substantially prevent scaling in the treatment of a spent carbon material in a wet air oxidation (WAO) system.
1. A treatment process comprising:
directing a feed stream comprising spent carbon and an amount of a scale forming contaminant therein through a heat exchanger to control temperature of the feed stream to a temperature lower than a solubility temperature limit of the amount of the scale forming contaminant;
adding an oxidant to the feed stream in an amount of at least about 20 vol. %;
directing the feed stream to a wet air oxidation unit for regeneration of the spent carbon therein;
performing a wet air oxidation process on at least a portion of the feed stream in the wet air oxidation unit for a residence time of at least about 1 hour, to produce a treated material comprising a regenerated carbon material and an offgas comprising a residual oxygen concentration of at least 3 vol. %; and
directing the treated material from the wet air oxidation unit through the heat exchanger to control the temperature of the feed stream in the heat exchanger.
2. The process of claim 1 , comprising performing the wet air oxidation process at a temperature of from about 150° C. to 200° C.
3. The process of claim 1 , comprising performing the wet air oxidation process at a pressure of about from about 150-900 psig.
4. The process of claim 3 , comprising performing the wet air oxidation process at a pressure of about from about 150-500 prig.
5. The process of claim 1 , comprising performing the wet air oxidation process for a residence time of about 3 hours to about 8 hours.
6. The process of claim 1 , wherein the wet air oxidation process produces an offgas with a residual oxygen concentration of about 5% to about 15% by volume.
7. The process of claim 6 , wherein the wet air oxidation process produces an offgas with a residual oxygen concentration of about 10% by volume to about 12% by volume.
8. The process of claim 1 , wherein the treated material comprises a temperature lower than the solubility temperature limit of the amount of the scale forming contaminant.
9. The process of claim 1 , wherein the scale forming contaminant comprises at least one of aluminum, calcium, carbonate, iron, magnesium, phosphorus, sulfate, and combinations thereof.
10. The process of claim 9 , wherein the scale forming contaminant comprises calcium.
11. The process of claim 10 , wherein the scale forming contaminant comprises calcium sulfate.
12. The process of claim 1 , wherein the heat exchanger comprises a double pipe heat exchanger.
13. The process of claim 1 , wherein the feed stream is derived from at least one of a powdered activated carbon treatment (PACT) system or a granular activated carbon (GAC) system.
14. The process of claim 1 , wherein the spent carbon comprises spent powdered activated carbon.
15. The process of claim 1 , further comprising separating the offgas from the regenerated carbon material.
16. The process of claim 1 , wherein the feed stream comprises an amount of biological solids.
17. The process of claim 1 , comprising performing the wet air oxidation process at a temperature of about 200° C. or less.
18. The process of claim 13 , further comprising returning the regenerated carbon material to the at least one of the PACT and the GAC system for carbon reuse.
19. The process of claim 1 , further comprising directly transferring the treated material to a post-treatment process.
20. The process of claim 19 , further comprising transferring the regenerated carbon material to a source of the feed stream for carbon reuse.