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US 5,695,726 AGranted
Removal of mercury and cadmium and their compounds from incinerator flue gases
AssigneeBeco Engineering Company
InventorBernard J. Lerner
Life of this patent
Estimating the term…
Abstract
Toxic metal vapor phase compounds, and in particular, mercury and cadmium, are removed from waste incinerator combustion gases by contact with dry alkaline material and dry activated carbon followed by solids separation. The resulting gas is subjected to quench/wet scrubbing with recycle hydrochloric acid solution formed in situ by absorption of HCl from the gas. Blowdown liquid withdrawn from the recycle acid liquor, may be recycled to the incinerator or further treated by neutralization, precipitation, and filtration of the precipitated toxic metals.
Claims37
A process useful for reducing toxic emissions of mercury, cadmium and thallium in waste exhaust gases from a waste incineration zone, which process comprises:
- contacting a first stream comprising waste exhaust gases containing a toxic metal chloride of one or more of mercury, cadmium or thallium and HCl with (a) substantially dry, alkaline solid material selected from the group consisting of a hydroxide, carbonate, or bicarbonate of an alkali metal or alkaline earth metal for removal of HCl, and (b) substantially dry, solid adsorbent material having a high surface area above about 100 square meters per gram for removal of a major portion of said toxic metal chloride, to form a second stream comprising exhaust gases containing residual toxic metal chlorides and residual HCl, spent alkaline solids, spent adsorbent and fly ash,
- passing said second stream to a solids separation zone for removal of particulate matter comprising spent alkaline solids and spent adsorbent to form a third stream substantially free of fly ash, spent alkaline solids and spent adsorbent,
- passing said third stream comprising exhaust gases containing residual toxic metal chlorides and residual HCl to a wet scrubber zone, contacting said third stream in said wet scrubber zone with a liquid consisting essentially of aqueous hydrochloric acid for absorption of residual toxic metal compounds and HCl from said third stream, said aqueous hydrochloric acid having been generated in said wet scrubber zone and recirculated for contact with said third stream, passing a portion of said recirculated aqueous hydrochloric acid to said incineration zone,
- and withdrawing a substantially toxic metal-free gas stream.
1 more element
The process of 8, wherein said waste exhaust gases are cooled in a waste heat boiler.
The process of 17, wherein said absorbent is fuller's earth.
A process useful for reducing toxic emissions of mercury, cadmium and thallium resulting from incineration of waste, which process comprises:
- passing wastes to a waste incineration zone to form waste exhaust gases containing HCl and at least one of a toxic metal chloride of mercury, cadmium or thallium,
- cooling said waste exhaust gases withdrawn from said incineration zone to form a cooled first stream,
- contacting said cooled first stream with (a) substantially dry, alkaline solid material selected from the group consisting of a hydroxide, carbonate, or bicarbonate of an alkali metal or alkaline earth metal for removal of HCl, and (b) substantially dry, solid adsorbent material having a surface area above about 100 square meters per gram for removal of a major portion of said toxic metal chloride to form a second stream comprising exhaust gases containing residual toxic metal chlorides, residual HCl, spent alkaline solids, spent adsorbent and fly ash,
- passing said second stream to a solids separation zone for removal of particulate matter comprising spent alkaline solids and spent adsorbent to form a third stream substantially free of fly ash, spent alkaline solids and spent adsorbent,
- passing said third stream comprising exhaust gases containing residual toxic metal chlorides and residual HCl to a quench/scrubber zone, contacting said third stream in said quench/scrubber zone with a liquid consisting essentially of aqueous hydrochloric acid for absorption of residual toxic metal compounds and HCl from said third stream, said quench/scrubber zone being operated without addition of extraneous alkaline neutralizing agent to said quench/wet scrubber zone, said aqueous hydrochloric acid having been generated in said quench/scrubber zone and recirculated for contact with said third stream, passing a portion of said recirculated aqueous hydrochloric acid to said incineration zone,
- withdrawing a gas stream from said quench/wet scrubber zone and passing said withdrawn gas stream to a second scrubbing zone to remove residual hydrochloric acid from said withdrawn gas stream,
- and withdrawing a liquid stream from said quench/scrubber zone containing toxic metal.
4 more elements
A process useful for reducing toxic emissions of mercury, cadmium and thallium resulting from incineration of waste or coal, which process comprises
- passing waste or coal feed to an incineration zone, said feed containing at least one of mercury, cadmium or thallium and insufficient chlorine to convert said mercury, cadmium or thallium to the corresponding chloride,
- adding hydrochloric acid or a hydrochloric acid-generating material to said incineration zone in an amount at least sufficient to convert the mercury, cadmium and thallium present in said feed to chloride form during incineration in said waste incineration zone,
- cooling said waste exhaust gases withdrawn from said incineration zone and contacting said cooled gas stream with:
- (a) substantially dry, alkaline solid material selected from the group consisting of a hydroxide, carbonate, or bicarbonate of an alkali metal or alkaline earth metal, and
- (b) substantially dry, solid adsorbent material, said solid adsorbent material having a surface area above about 100 square meters per gram,
- and passing the resulting gas stream to a solids separation zone for removal of particulate matter, comprising spent alkaline solids and spent adsorbent to form a third stream substantially free of fly ash, spent alkaline solids and spent adsorbent,
- passing said third stream comprising exhaust gases containing residual toxic metal chlorides and residual HCl to a wet scrubber zone, contacting said third stream in said wet scrubber zone with a liquid consisting essentially of aqueous hydrochloric acid for absorption of residual toxic metal compounds and HCl from said third stream and without addition of an alkaline neutralizing agent to said wet scrubber zone, said aqueous hydrochloric acid having been generated in said wet scrubber zone and recirculated for contact with said third stream, passing a portion of said recirculated aqueous hydrochloric acid to said incineration zone,
- and withdrawing a substantially toxic metal-free gas stream.
5 more elements
Dependencies are inferred from the claim text.