Sorbents for the oxidation and removal of mercury
View Patent ↗A promoted activated carbon sorbent is described that is highly effective for the removal of mercury from flue gas streams. The sorbent comprises a new modified carbon form containing reactive forms of halogen and halides. Optional components may be added to increase reactivity and mercury capacity. These may be added directly with the sorbent, or to the flue gas to enhance sorbent performance and/or mercury capture. Mercury removal efficiencies obtained exceed conventional methods. The sorbent can be regenerated and reused. Sorbent treatment and preparation methods are also described. New methods for in-flight preparation, introduction, and control of the active sorbent into the mercury contaminated gas stream are described.
1. A method for separating mercury from a mercury containing gas comprising:
(a) promoting at least a portion of a particulate sorbent material comprising activated carbon by chemically reacting the sorbent material with a bromine containing promoter to form a promoted brominated sorbent, wherein the bromine containing promoter is in gaseous form, vapor form, or non-aqueous liquid form, and wherein the activated carbon contains graphene sheets having carbene species edge sites which react with the bromine containing promoter to form a carbocation paired with a bromide anion in the promoted brominated sorbent for oxidation of the mercury;
(b) chemically reacting elemental mercury in the mercury containing gas with the promoted brominated sorbent to form a mercury/sorbent chemical composition; and
(c) separating particulates from the mercury containing gas, the particulates including ash and the mercury/sorbent chemical composition.
2. A method according to claim 1 , wherein the bromine containing promoter is in gaseous form.
3. A method according to claim 1 , wherein the bromine containing promoter is in an organic solvent.
4. A method according to claim 1 , wherein the carbocation paired with a bromide anion chemically react with elemental mercury form the mercury/sorbent composition.
5. A method according to claim 1 , wherein at least a portion of the basic binding sites of the activated carbon reacts with oxidized mercury in the mercury containing gas to form another mercury/sorbent chemical composition.
6. A method according to claim 1 , wherein the step of separating particulates from the mercury containing gas comprises separating in a particulate separator comprising one or more electrostatic precipitators.
7. A method according to claim 1 , further comprising a step of regenerating a promoted brominated sorbent from the mercury/sorbent chemical composition for reuse.
8. A method according to claim 7 , further comprising injecting the regenerated promoted brominated sorbent into a mercury containing gas.
9. A method according to claim 1 , further comprising injecting an alkali component into the mercury containing gas for protecting mercury binding sites and capturing oxidized mercury.
10. A method according to claim 9 , wherein the alkali component comprises an oxide, hydroxide, carbonate, phosphate of an alkali or alkaline earth element.
11. A method according to claim 1 , further comprising adding a second halogen or halide promoter to the promoted halogen containing sorbent.
12. A method according to claim 11 , wherein the second halogen or halide promoter comprises HI, HBr, HCl, Group V element with halogen, or Group VI element with halogen.
13. A method according to claim 1 , further comprising adding a stabilizing agent to the promoted brominated sorbent.
14. A method according to claim 13 , wherein the stabilizing agent comprises at least one of S, Se, H 2 S, SO 2 , H 2 Se, Se0 2 , CS 2 , P 2 S 5 , or mixtures thereof.
15. A method according to claim 1 , wherein the step of promoting at least a portion of the available sorbent material occurs at least partially outside of the mercury containing gas.
16. A method according to claim 1 , wherein the promoted brominated sorbent combines with at least 70% of the mercury present in the mercury containing gas.
17. A method according to claim 1 , further comprising injecting the particulate sorbent material at a sorbent material injection rate and injecting separately the bromine containing promoter into a gas stream whereby in-flight reaction produces the promoted brominated sorbent, wherein the promoter is reacted in the gas phase or as a vapor, wherein the promoter is added at from about 1 to about 30 grams per 100 grams of the sorbent material.
18. A method according to claim 17 , wherein the gas stream is a mercury containing gas.
19. A method according to claim 18 , wherein the gas stream is a transport gas.
20. A method according to claim 17 , wherein the promoter injection rate and the sorbent injection rate into the gas are determined at least in part on the monitored mercury content of the cleaned gas.
21. A method according to claim 1 , wherein the composition of the promoted sorbent is controlled by the mercury content of the cleaned gas stream.
22. A method according to claim 1 , wherein the bromine containing promoter comprises at least one of HBr, PBr 3 , or Br 2 .
23. A method according to claim 1 , wherein the bromine containing promoter comprises molecular bromine.
24. A method according to claim 1 , wherein the bromine containing promoter comprises a bromine compound.
25. A method according to claim 1 , wherein the bromine containing promoter comprises a Group V or Group VI bromide.