Microwave induced destruction of impurities from biogas and nitrogen oxides from engine exhaust

Abstract

Granulated Activated Carbon (GAC) is used to remove hydrogen sulfide (H 2 S) from the biogas produced in an anaerobic digester. The cleaned biogas is then combusted in a reciprocating engine. The exhaust of the engine is passed through a heat exchanger and then through GAC in an adsorber to adsorb nitrogen oxides (NOx) and any sulfur oxides (SOx). The GACs containing NOx, H 2 S, and SOx, are transported to a microwave reactor, mixed, and exposed to microwave energy. The H 2 S and NOx are desorbed from the GAC and chemically combined to produce nitrogen, carbon dioxide, sulfur and water. Unreacted nitrogen oxides or hydrogen sulfide are transported to a second reactor containing carbon media to be reacted by a further microwave process. Sulfur is removed with a filter as a solid and the remaining inert components are vented to the atmosphere. The GAC is regenerated and reused to remove additional H 2 S and NOx.

1 . An apparatus for decomposing hydrogen sulfide and nitrogen oxides adsorbed in carbon media, comprising:
 a first microwave reactor having a source of microwave energy;   wherein said first microwave reactor is configured to receive a first carbon media containing hydrogen sulfide and nitrogen oxides;   a source of sweep gas connected to said first microwave reactor;   wherein sweep gas flows from said sweep gas source through said first microwave reactor;   wherein hydrogen sulfide and nitrogen oxides are desorbed from said first carbon media in said first microwave reactor when exposed to microwave energy;   wherein said nitrogen oxides react with hydrogen sulfide when exposed to microwave energy to form nitrogen, water and sulfur; and   wherein nitrogen, water and sulfur are removed from said first microwave reactor in said sweep gas.   
   
   
       2 . An apparatus as recited in  claim 1 , further comprising:
 a second microwave reactor fluidly connected to said first microwave reactor;   wherein said second microwave reactor has a source of microwave energy;   a second carbon media positioned in said second reactor;   means for filtering sulfur fluidly connected to said second reactor;   wherein said sweep gas flows from said sweep gas source through said first microwave reactor, through said second reactor and through said filtering means.   
   
   
       3 . An apparatus as recited in  claim 2 :
 wherein a portion of said hydrogen sulfide is unreacted in said first microwave reactor;   wherein unreacted hydrogen sulfide is transported by the sweep gas from said first microwave reactor to said second microwave reactor; and   wherein hydrogen sulfide is reduced to sulfur and hydrogen when exposed to microwave energy in said second microwave reactor.   
   
   
       4 . An apparatus as recited in  claim 2 :
 wherein a portion of said nitrogen oxides are unreacted in said first microwave reactor;   wherein unreacted nitrogen oxides are transported by said sweep gas from said first microwave reactor to said second microwave reactor; and   wherein nitrogen oxides react with said second carbon media to form nitrogen and carbon dioxide when exposed to microwave energy in said second microwave reactor.   
   
   
       5 . An apparatus as recited in  claim 2 , further comprising:
 a biogas adsorber having first carbon media positioned in a biogas stream to adsorb hydrogen sulfide;   wherein said biogas is combusted in an engine;   an exhaust gas adsorber positioned in the exhaust stream of said engine;   said exhaust gas adsorber having first carbon media to adsorb nitrogen oxides; and   wherein said first carbon media from said biogas adsorber is combined with said first carbon media in said exhaust gas adsorber and positioned in said first microwave reactor.   
   
   
       6 . An apparatus as recited in  claim 5 :
 wherein said biogas adsorber is configured as a container to transport first carbon media to said first microwave reactor; and   wherein said exhaust gas adsorber is configured as a container to transport first carbon media to said first microwave reactor.   
   
   
       7 . An apparatus as recited in  claim 5 , further comprising a heat exchanger positioned between said engine and said exhaust gas adsorber. 
   
   
       8 . An apparatus as recited in  claim 2 , wherein said means for filtering sulfur comprises a particulate filter. 
   
   
       9 . An apparatus to remove hydrogen sulfide from biogas and remove nitrogen oxides from the exhaust of an engine fueled by the biogas comprising:
 a first adsorber having first carbon media configured to remove hydrogen sulfide from a flow of biogas;   a second adsorber having first carbon media configured to remove nitrogen oxides from the exhaust of an engine fueled by said biogas;   a first microwave reactor configured to receive first carbon media from said first adsorber and said second adsorber;   wherein said first microwave reactor has a source of microwave energy;   a source of sweep gas fluidly connected to said first microwave reactor;   wherein sweep gas flows from said sweep gas source through said first microwave reactor;   wherein hydrogen sulfide and nitrogen oxides are desorbed from said first carbon media in said first microwave reactor when exposed to microwave energy;   wherein said nitrogen oxides react with hydrogen sulfide when exposed to microwave energy in said first microwave reactor to form nitrogen, water and sulfur; and   wherein said nitrogen, water and sulfur flow from said first microwave reactor in said sweep gas.   
   
   
       10 . An apparatus as recited in  claim 9 , further comprising:
 a second microwave reactor fluidly coupled to said first microwave reactor;   a source of microwave energy coupled to said second microwave reactor;   a second carbon media positioned in said second microwave reactor;   a particulate filter fluidly connected to said second reactor;   wherein said filter is configured to remove sulfur from said sweep gas; and   wherein said sweep gas flows from said first microwave reactor, through said second reactor and through said filter.   
   
   
       11 . An apparatus as recited in  claim 10 :
 wherein a portion of said hydrogen sulfide is unreacted in said first microwave reactor;   wherein unreacted hydrogen sulfide is transported by the sweep gas from said first microwave reactor to said second microwave reactor; and   wherein hydrogen sulfide is reduced to sulfur and hydrogen when exposed to microwave energy in said second microwave reactor.   
   
   
       12 . An apparatus as recited in  claim 10 :
 wherein a portion of said nitrogen oxides are unreacted in said first microwave reactor;   wherein unreacted nitrogen oxides are transported by said sweep gas from said first microwave reactor to said second microwave reactor; and   wherein nitrogen oxides react with said second carbon media to form nitrogen and carbon dioxide when exposed to microwave energy in said second microwave reactor.   
   
   
       13 . An apparatus as recited in  claim 9 :
 wherein said first adsorber is configured as a container to transport first carbon media to said first microwave reactor; and   wherein said second adsorber is configured as a container to transport first carbon media to said first microwave reactor.   
   
   
       14 . An apparatus as recited in  claim 9 , further comprising a heat exchanger positioned between said engine and said second adsorber.