Removal of sulfur oxides from stack gas

Claim 2

IN THE SCRUBBING OF COMBUSTION GASES WITH AQUEOUS AMMONICAL SOLUTION FOR REMOVAL OF CONTAINED SULFUR OXIDES, THE IMPROVEMENT WHICH COMPRISES EFFECTING ABSORPTION OF SO2 BY THE AMMONIACAL SCRUBBING LIQUOR UNDER CONTROLLED CONDITIONS OF CONCENTRATIONS OF COMPONENTS AT THE ABSORPTION TEMPERATURE SUCH THAT THE LOGARITHM (TO THE BASE 10) OF THE PRODUCT OF THE PARTIAL VAPOR PRESSURES OF SO2, NH3 AND H2O AT ALL REGIONS WITHIN THE SCRUBBING AND PRIOR TO DISCHARGE OF THE VAPOR EFFLUENT THEREFROM INTO THE ATMOSPHERE DOES NOT EXCEED THE NUMERICAL VALUE: 31.24-(17,300/T), WHEREIN THE SAID PARTIAL PRESSURE ARE EXPRESSED IN MILLIMETERS OF MECURY AND T IS THE ABSOLUTE TEMPERATURES IN DEGREES RANKINE.

Claim 3

The method as defined in claim 1 wherein the combustion gas is saturated with water vapor prior to its initial contact with ammoniacal scrub liquor.

Claim 4

cooling and saturating the solids-free gas to a temperature in the range of 100* - 120*F by water washing, and in so doing reducing the concentration of hydrogen chloride to less that 10 ppm,

Claim 5

cooling and saturating the solids-free gas to a temperature in the range of 100* - 120*F by water washing, and in so doing reducing the concentration of hydrogen chloride to less that 10 ppm,

Claim 6

contacting the cooled gas with aqueous ammoniacal liquor in successive treating stages under controlled conditions such that the concentrations respectively of ammonia, sulfur dioxide and water at the prevailing temperature in all areas of such contact are such that the logarithm (to the base 10) of the product of these partial pressures (expressed in mm Hg) at the temperature prevailing in each such area lies below and to the left of the line graph IIa in FIG. 2 of the accompanying drawings; and reheating the remaining gas after the last said liquid contacting stage to a temperature in the range of about 50*F above the temperature prevailing during the said last liquid contacting stage, prior to discharge of said gas into the atmosphere.

Claim 7

contacting the cooled gas with aqueous ammoniacal liquor in successive treating stages under controlled conditions such that the concentrations respectively of ammonia, sulfur dioxide and water at the prevailing temperature in all areas of such contact are such that the logarithm (to the base 10) of the product of these partial pressures (expressed in mm Hg) at the temperature prevailing in each such area lies below and to the left of the line graph IIa in FIG. 2 of the accompanying drawings; and reheating the remaining gas after the last said liquid contacting stage to a temperature in the range of about 50*F above the temperature prevailing during the said last liquid contacting stage, prior to discharge of said gas into the atmosphere.

Claim 8

The method as defined in claim 1 wherein the hydrogen chloride content of the combustion gases is reduced to less than about 10 ppm prior to their initial contact with the ammoniacal solution.

Claim 9

The improvement as defined in claim 1 wherein said ammoniacal scrubbing liquid comprises ammonium sulfite and ammonium bisulfite.

Claim 10

The improvement as defined in claim 1 wherein the absorption of SO2 by the ammoniacal liquid is carried out in several stages and the defined controlled conditions are maintained in all such absorption stages and in all regions traversed by the vapors prior to discharge of the vapor effluent into the atmosphere.

Claim 11

The improvement as defined in claim 2 wherein prior to discharge of the vapor effluent into the atmosphere, it is reheated to a temperature in the range of 35* to 70*F above the absorption temperature.

Claim 12

The improvement as defined in claim 5 wherein the effluent vapor from the uppermost stage substantially freed of SO2, is reheated to a temperature in the range of 35* to 70*F above absorption temperature of the uppermost stage prior to discharge into the atmosphere.

Claim 15

The method as defined in claim 1 wherein insulation is provided at the boundaries of at least a portion of the path traversed by the vapor effluent from the scrubber to the atmosphere.

Claim 16

The method as defined in claim 1 wherein insulation is provided at least in part at the walls bounding the scrubber.