The Boc Group, Inc.

Robert James Ferrell

Neeraj Saxena

Shuen-Cheng Hwang

Naresh J Suchak

James K Tseng

Wenchang Ji

Arthur I Shirley

Mark H Anderson

Piotr J Sadkowski

Thulasidas Chellppannair

Lev Davydov

Chester Gorski

The present invention relates to a process for removing nitrogen oxides, sulfur oxides, mercury and mercuric oxide from gas streams such as furnace or utility boiler flue gas streams, particularly those derived from coal-fired utility boilers, or from a gas stream from another pollutant abatement process. Ozone will react with the impurities in the gas stream to form mercuric oxide and higher oxides of nitrogen which can be removed by scrubber means. Additionally, and alternatively, the present invention provides for the use of ozone and ultraviolet radiation to remove nitrogen oxides, sulfur oxides and mercury from gas streams.

Process for the removal of impurities from gas streams

The present invention relates to a process for removing nitrogen oxides, sulfur dioxides and mercury from gas streams such as furnace or utility boiler flue gas streams, particularly those derived from coal-fired utility boilers. A stream containing relatively low concentration of ozone from an ozone concentrator is feed to a barrier discharge reactor. Nitrogen oxides and mercury in the flue gas are oxidized by oxygen and hydroxyl radicals formed in the reactor. The flue gas is then directed to a reactor duct along with the ozone at a greater concentration wherein the remaining nitrogen oxides and mercury in the gas stream will react with the ozone to form nitric acid, nitric acid precursors, mixtures thereof and mercuric oxide. These impurities can then be removed from the gas stream by use of an aqueous scrubber, a wet electrostatic precipitator, a dry scrubber or a semi-dry scrubber.

Sulfur compounds present as sulfides and mercaptans in spent caustic streams from refinery and petrochemical processes are oxidized by contacting them with an oxygen-containing gas in a packed column recycle reactor.

Method for treating spent caustic streams

An ozone-oxygen gas stream produced by passing oxygen into an ozone generator is introduced into a membrane separation unit containing an ozone-permeable membrane. Ozone-enriched gas passes through the membrane and is recovered or it contacts a liquid or gas stream which contains ozone-reactive substances, thereby oxidizing the substances. The oxygen-enriched gas stream produced on the feed side of the membrane by permeation of ozone through the membrane is recycled to the ozone generator. Prior to being recycled, the oxygen-enriched stream may be purified to remove gaseous impurities which permeate through the membrane from the liquid or gas stream being treated.

Ozone purification process

Nitrogen oxides are removed from a waste gas stream by contacting the waste gas stream with ammonia, thereby reducing the nitrogen oxides to nitrogen. Residual nitrogen oxides and unreacted ammonia in the waste gas stream leaving the nitrogen oxides reducing step are oxidized to nitrogen pentoxide or nitric acid by contacting this gas stream with ozone. Contact of the ozone and waste gas is preferably carried out in the presence of an aqueous solution at a pH above about 9 and at a temperature above about 75&deg; C., and this step is preferably carried out in the presence of an ammonia-oxidizing catalyst.

Reduction of toxic substances in waste gas emissions

An ozone-oxygen gas stream is introduced into feed side of a membrane separation unit containing an elastomeric polymer membrane. Ozone-enriched gas passes through the membrane to a permeate zone and is contacted with an ozone-reactive substance-containing gas stream in the permeate zone, thereby oxidizing the substances or is removed from the permeate zone. Removal of the ozone-enriched gas from the permeate zone may be effected by purging the permeate zone with an inert gas and/or evacuating the permeate zone. Ozone-enriched gas removed from the permeate zone may be mixed with a liquid or gas stream which contains ozone-reactive substances in, for example, a venturi device, thereby oxidizing the substances.

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Rutherford, NJ, United States of America

Robert James Ferrell