Highly Efficient Removal of Mercury from Industrial Flue Gas

It is estimated that 144-189 megagrams (158-207 tons) of mercury are emitted annually into the atmosphere by anthropogenic sources in the United States. Approximately 87 percent of the mercury is from combustion point sources and 10 percent is from manufacturing point sources. The combustion point sources can be broken down further into four classes: (1) coal-fired utility boilers, (2) municipal waste combustion, (3) commercial/industrial boilers, and (4) medical waste incinerators. It is not economically feasible to remove the trace mercury before it enters the process; the easiest location for mercury capture is the flue gas discharges. Wet scrubbing is used in 20-30 percent of U.S. coal-fired plants. In most cases, the systems are designed mainly for solid particle or SOx removal. As a serendipitous side benefit, organic and inorganic materials that easily dissolve in water, such as HgCl2, also are removed from the flue gas. However, a large fraction of the mercury in the flue gas is elemental mercury (Hg0), which is not fully removed by a simple wet scrubbing system and is expelled into the environment. The goal of this Phase I research project is to develop a technology that can remove all forms of mercury from flue gases, allowing the "trapped" Hg to be easily separated from the scrubber water in a form that passes all required Toxicity Characteristic Leaching Procedure (TCLP) protocols and be easily adapted to existing plant equipment, reducing capital and implementation costs. Frontier Geosciences, Inc., has discovered a method in which the scrubber water is chemically modified to remove and complex Hg, no matter what form, from industrial flue gases. It is proposed that Hg is extracted into the scrubber water using an inert solid chemical modifier. Once in solution, the Hg is complexed and precipitated by an organic binding agent. The intended organic binding agent has been shown to complex Hg greater than 99.9999 percent in aqueous solution, and the resulting precipitate passes TCLP testing. The combined waste solids then can be removed by an industry standard filter system and the scrubber water immediately recycled back into the treatment system. This will minimize water consumption and possibly allow the regeneration of the inert solid chemical modifier with minimal equipment modification.