Emission control system

1. A method of treating mercury contaminated gas comprising:

a. introducing a dilute aqueous hydrogen halide comprising 0.25 to 4% hydrogen halide selected from HBr and HI into a mercury contaminated gas stream containing a quantity of particulate matter at an introduction rate sufficient to create a concentration of at least 0.1 ppmvd;

b. wherein greater than 50% of all particulate matter in the mercury contaminated gas stream is a native particulate matter;

c. contacting a quantity of active halide with the native particulate matter;

d. creating a doped particulate matter;

e. coating a filtration media with the doped particulate matter; and

f. passing a portion of the mercury contaminated gas stream through the doped particulate matter on the filtration media.

2. The method of claim 1 wherein the hydrogen halide is HBr.

3. The method of claim 1 wherein the introducing of a hydrogen halide selected from HBr and HI occurs at a point where the mercury contaminated gas stream is less than 750° F.

4. The method of claim 1 wherein the introducing of a hydrogen halide selected from HBr and HI occurs at a point where the mercury contaminated gas stream is greater than 180° F.

5. The method of claim 1 wherein the mercury contaminated gas stream is a byproduct of the combustion of coal having a chlorine content of less than 300 ppm by weight and a mercury content greater than 50 ppb by weight.

6. The method of claim 1 wherein the introducing of a hydrogen halide selected from HBr and HI is at an introduction rate creating a concentration of at most 15 ppmvd.

7. A method of treating mercury contaminated gas comprising:

a. introducing a mercury contaminated gas into a conduit;

b. wherein the conduit comprises HBr susceptible materials;

c. wherein the mercury contaminated gas has an initial quantity of mercury;

d. wherein the conduit has an inner surface;

e. injecting a quantity of dilute aqueous HBr comprising 0.25 to 4% into the conduit;

f. wherein the injection of the quantity of dilute aqueous HBr is through a plurality of nozzles at an HBr injection rate sufficient to create a HBr concentration of at least 0.1 ppmvd;

g. wherein a spray pattern of the plurality of nozzles covers a majority of a cross-section of the conduit;

h. wherein there is no substantial accumulation of aqueous HBr on the inner surface; and

i. contacting the mercury contaminated gas with a media thereby removing at least 50% of the initial quantity of mercury from the mercury contaminated gas.

8. The method of claim 7 wherein the injection of the quantity of dilute aqueous HBr occurs at a point where the mercury contaminated gas is between 180° F. and 750° F.

9. The method of claim 7 wherein the plurality of nozzles is a plurality of dual fluid nozzles and the quantity of dilute aqueous HBr has an HBr concentration greater than 0.25%.

10. The method of claim 7 wherein the injection of the quantity of dilute aqueous HBr is through a plurality of nozzles at an HBr injection rate creating a HBr concentration of at most 10 ppmvd.

11. A method of treating mercury contaminated gas comprising:

a. introducing active bromine into a treatment zone wherein the active bromine comprises a dilute aqueous HBr solution comprising 0.25 to 4% HBr;

b. passing a mercury contaminated gas through the treatment zone;

c. wherein the mercury contaminated gas contains nitrogen;

d. wherein a residence time of the active bromine in the treatment zone is at least 1.1 times that of a residence time of the nitrogen in the treatment zone; and

e. removing at least 50% of the mercury contained in the mercury contaminated gas stream from the mercury contaminated gas stream with a particulate control device.

12. The method of claim 11 wherein the introducing active bromine into the treatment zone is at an introduction rate that creates an active bromine concentration of between 0.1 ppmvd and 10 ppmvd.