Sorbents for the oxidation and removal of mercury
First Claim
1. A method for reducing mercury in mercury-containing gas to a desired level, the method comprising:
- preparing a sorbent having a sorbent composition;
wherein preparing the sorbent comprises reacting a base activated carbon with at least one promoter selected from the group consisting of molecular halogens, halides, and combinations thereof to yield a promoted halogenated carbon comprising active sites wherein the active sites comprise halide covalently-bound to the base-activated carbon;
injecting the sorbent into a mercury-containing gas stream at at least one sorbent injection location and at a sorbent injection rate, wherein the mercury-containing gas stream is a combustion gas or a gasification gas, and wherein the composition of the mercury-containing gas may vary with time;
optionally co-injecting an alkaline sorbent into the mercury-containing gas stream at at least one alkaline injection location and at an alkaline injection rate;
collecting greater than 70 wt % of the mercury in the mercury-containing gas on the sorbent to produce a cleaned gas;
monitoring the mercury content of the cleaned gas; and
controlling, in response to the monitored mercury content of the cleaned gas, which may vary with the composition of the mercury-containing gas and operating conditions, the sorbent injection rate, the alkaline injection rate, the sorbent composition, or a combination thereof so that the mercury content of the cleaned gas is maintained at substantially the desired level with minimal operating cost.
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Accused Products
Abstract
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.
140 Citations
30 Claims
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1. A method for reducing mercury in mercury-containing gas to a desired level, the method comprising:
- preparing a sorbent having a sorbent composition;
wherein preparing the sorbent comprises reacting a base activated carbon with at least one promoter selected from the group consisting of molecular halogens, halides, and combinations thereof to yield a promoted halogenated carbon comprising active sites wherein the active sites comprise halide covalently-bound to the base-activated carbon; injecting the sorbent into a mercury-containing gas stream at at least one sorbent injection location and at a sorbent injection rate, wherein the mercury-containing gas stream is a combustion gas or a gasification gas, and wherein the composition of the mercury-containing gas may vary with time; optionally co-injecting an alkaline sorbent into the mercury-containing gas stream at at least one alkaline injection location and at an alkaline injection rate; collecting greater than 70 wt % of the mercury in the mercury-containing gas on the sorbent to produce a cleaned gas; monitoring the mercury content of the cleaned gas; and controlling, in response to the monitored mercury content of the cleaned gas, which may vary with the composition of the mercury-containing gas and operating conditions, the sorbent injection rate, the alkaline injection rate, the sorbent composition, or a combination thereof so that the mercury content of the cleaned gas is maintained at substantially the desired level with minimal operating cost. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
- preparing a sorbent having a sorbent composition;
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30. A method for removing mercury from a mercury-containing gas stream to produce a cleaned gas stream having a desired mercury level, the method comprising,
reacting an activated carbon with at least one promoter selected from molecular halogens, Group V halides, Group VT halides, hydrohalides, and combinations thereof and optionally at least one secondary component selected from Group V halides, Group VI halides, hydrohalides, and combinations thereof to produce a halogenated carbon sorbent comprising carbocation reactive sites that are capable of accepting electrons from neutral mercury atoms thereby forming oxidized mercury species that bind to the surface of the halogenated sorbent, wherein the halogenated carbon sorbent comprises a promoter to carbon ratio and optionally, a secondary component to carbon ratio; -
injecting the halogenated carbon sorbent into a mercury-containing gas stream at a sorbent injection rate, wherein the mercury containing gas comprises flue gas, synthesis gas, fuel gas, or a combination thereof and wherein the composition of the mercury-containing gas stream may vary with time; injecting an alkaline sorbent into the mercury-containing gas stream at an alkaline injection rate, wherein the alkaline sorbent is capable of adsorbing oxidized mercury gas and of removing contaminants from the mercury-containing gas stream capable of consuming carbocation reactive sites of the halogenated carbon sorbent; allowing the sorbents to interact with the mercury-containing gas stream for a residence time to produce a cleaned gas; removing the halogenated sorbent from the cleaned gas; monitoring the mercury content of the cleaned gas; and maintaining the desired mercury level of the cleaned gas by optimizing the sorbent injection rate, the promoter to carbon ratio of the sorbent, the optional secondary component to carbon ratio of the sorbent, the alkaline injection rate, or a combination thereof such that operating costs for removing mercury from the mercury-containing gas stream are minimized.
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Specification