Simultaneous removal of nitrogen oxides and sulfur oxides from combustion gases

Claim 2

A dry solids process for the simultaneous removal of SO x and NO x from diluent gases containing them wherein So x is removed by absorption substantially as a sulfide and NO x is removed by reduction which comprises: a. contacting the diluent gases in an SO x and NO x removal zone with a solid catalyst/absorbent comprising partially reduced iron oxide and ferric oxide at a temperature of at least about 370° C in the presence of an amount of a reducing agent selected from carbon monoxide, hydrogen, and a mixture thereof sufficient to provide a net reducing atmosphere in the SO x and NO x removal zone, thereby removing SO x by absorption on the catalyst/absorbent substantially as ferrous sulfide and removing NO x by reduction; and b. separating the resulting ferrous sulfide containing catalyst/absorbent from the diluent gases reduced in SO x and NO x content.

Claim 3

A process according to claim 1 further defined by maintaining an amount of ferric oxide in the catalyst/absorbent at least sufficient to oxidize the excess reducing agent.

Claim 4

A process according to claim 1 wherein the catalyst/absorbent is supported on a particulate matrix.

Claim 5

A process according to claim 3 wherein the particulate matrix is a substance selected from alumina and a mixture of alumina and silica.

Claim 6

A process according to claim 1 wherein the reducing agent is a mixture comprising carbon monoxide and hydrogen.

Claim 7

A process according to claim 1 wherein SO x is SO 2 , NO x is NO, and the gases containing them are effluent gases produced by combustion of a fossil fuel.

Claim 8

A process according to claim 1 wherein the temperature in the SO x and NO x removal zone is in the range of from about 370° C to about 540° C.

Claim 9

A process according to claim 1 further defined by contacting at least a portion of the separated ferrous sulfide containing catalyst/absorbent with an oxidizing gas in a regeneration zone at a temperature of at least about 650° C, thereby regenerating the catalyst/absorbent by conversion of the iron compounds contained therein substantially to ferric oxide, and recycling the regenerated catalyst/absorbent to the SO x and NO x removal zone.

Claim 10

A process according to claim 8 wherein the oxidizing gas is air.

Claim 11

A process according to claim 8 wherein the temperature in the regeneration zone is in the range of from about 650° C to about 760° C.

Claim 12

A process according to claim 8 further defined by maintaining an amount of ferric oxide in the catalyst/absorbent at least sufficient to oxidize the excess reducing agent.

Claim 13

A dry solids process for the simultaneous removal of SO x and NO x from diluent gases containing them to provide a gas suitable for discharge into the atmosphere and wherein SO x is removed substantially as a sulfide and NO x is removed by reduction, which process comprises: a. contacting the diluent gases in an SO x and NO x removal zone with a dispersed bed of a solid catalyst/absorbent comprising partially reduced iron oxide and ferric oxide supported on a particulate matrix at a temperature of at least about 370° C in the presence of a reducing agent selected from carbon monoxide, hydrogen, and mixtures thereof in an amount sufficient to provide a net reducing atmosphere in said removal zone, thereby simultaneously removing from said diluent gases SO x by absorption on the catalyst/absorbent substantially as ferrous sulfide and NO x by reduction; b. separating the resulting ferrous sulfide containing catalyst/absorbent from the diluent gases reduced in SO x and NO x content; c. recycling a first portion of the separated ferrous sulfide containing catalyst/absorbent to the SO x and NO x removal zone; d. contacting a second portion of the separated ferrous sulfide containing catalyst/absorbent with an oxidizing gas in a regeneration zone at a temperature of at least about 650° C, thereby converting the iron compounds contained therein to ferric oxide; e. recycling regenerated catalyst/absorbent from step (d) to the SO x and NO x removal zone; and f. maintaining an amount of ferric oxide in the catalyst/absorbent recycle stream at least sufficient to oxidize excess reducing agent in the SO x and NO x removal zone.

Claim 14

A dry solids process for the simultaneous removal of SO x and NO x from diluent gases containing them to provide a gas suitable for discharge into the atmosphere and wherein SO x is removed substantially as a sulfide and NO x is removed by reduction, which process comprises: a. contacting the diluent gases in an SO x and NO x removal zone with a dispersed bed of a solid catalyst/absorbent comprising partially reduced iron oxide and ferric oxide supported on a particulate matrix at a temperature of at least about 370° C in the presence of a reducing agent selected from carbon monoxide, hydrogen, and mixtures thereof in an amount sufficient to provide a net reducing atmosphere in said removal zone, thereby simultaneously removing from said diluent gases SO x by absorption on the catalyst/absorbent substantially as ferrous sulfide and NO x by reduction; b. separating the resulting ferrous sulfide containing catalyst/absorbent from the diluent gases reduced in SO x and NO x content; c. recycling a first portion of the separated ferrous sulfide containing catalyst/absorbent to the SO x and NO x removal zone; d. contacting a second portion of the separated ferrous sulfide containing catalyst/absorbent with an oxidizing gas in a regeneration zone at a temperature of at least about 650° C, thereby converting the iron compounds contained therein to ferric oxide; e. recycling regenerated catalyst/absorbent from step (d) to the SO x and NO x removal zone; and f. maintaining an amount of ferric oxide in the catalyst/absorbent recycle stream at least sufficient to oxidize excess reducing agent in the SO x and NO x removal zone.

Claim 15

A process according to claim 12 wherein the temperature in the SO x and NO x removal zone is in the range of from about 370° C to about 540° C and the temperature in the regeneration zone is in the range of from about 650° C to about 760° C.

Claim 16

A process according to claim 12 further defined by maintaining an amount of ferrous sulfide in the catalyst/absorbent in the SO x and NO x removal zone to provide a net exothermic reaction in the subsequent regeneration step.