APPLICATIONS OF TECHNOLOGY:

• Removing mercury from waste gas streams

ADVANTAGES:

• An order of magnitude less expensive than powdered activated carbon (PAC)
• High removal efficiency

ABSTRACT:

Shih-ger Chang and colleagues have developed a method for removing mercury from waste gas streams that is calculated to be an order of magnitude less expensive than its least expensive competitor - powdered activated carbon (PAC). 

In the Berkeley Lab process a low concentration of bromine gas is injected into a waste gas stream.  The bromine converts the elemental mercury vapor to its water soluble oxidized form.  Unlike the elemental mercury, the oxidized mercury can then be removed efficiently by dissolution in an aqueous gas absorber or by the adsorption on sorbents in a baghouse or electrostatic precipitator.

Assuming that the flue gas contains 3 ppb of mercury with 60% of that initially in elemental form, and that a wet SO₂ scrubber is 90% efficient in removing the oxidized mercury, an 80% removal efficiency can be achieved in 10.8 seconds with a bromine concentration of 30 ppm, in 8 seconds with a bromine concentration of 40 ppm, and in 6.2 seconds with a bromine concentration of 50 ppm.

The small quantities of the unreacted bromine and reaction byproducts that remain are highly water soluble and can be captured by wet SO₂ scrubbers.  It is expected that current and proposed US Environmental Protection Agency emission standards can be met readily using the Berkeley Lab technique.  The Berkeley Lab group is also researching compounds other than bromine that look very promising.

STATUS:

• Published Patent Application WO2006075999 available at www.wipo.int. Available for licensing or collaborative research.

REFERENCE NUMBER: IB-1900