Sulfur dioxide removal by absorption and fractionation

Claim 1

A process for removing sulfur dioxide from a gaseous feed stream comprising water, sulfur dioxide and carbon dioxide which comprises the steps of: (a) contacting the gaseous feed stream with a sulfur dioxide lean absorbent stream comprising water in an absorption zone operated at conditions effective to produce a sulfur dioxide rich absorbent stream comprising carbon dioxide and an off-gas stream containing less sulfur dioxide than the gaseous feed stream; (b) passing the sulfur dioxide rich absorbent stream into a first intermediate point of a first fractionation column having a rectification section and a stripping section and operated at conditions effective to cause the separation of water and sulfur dioxide by fractionation including (1) a bottom temperature within 20 Fahrenheit degrees of the boiling point of water at the pressure imposed at the bottom of the first fractionation column, and (2) the retention of liquid sulfur dioxide on fractionation trays located above the first intermediate point and the retention of liquid water on fractionation trays located below the first intermediate point; (c) passing at least a portion of a sulfur dioxide lean water stream removed as a bottoms product of the first fractionation column into the absorption zone as the sulfur dioxide lean absorbent stream; (d) removing a first liquid sidecut stream comprising sulfur dioxide from the first fractionation column at a second, higher intermediate point; (e) partially condensing an overhead vapor stream comprising sulfur dioxide and carbon dioxide withdrawn from the first fractionation column to form a first condensate stream comprising sulfur dioxide and a first vapor stream comprising carbon dioxide and sulfur dioxide; (f) admixing the first vapor stream with a hereinafter described second vapor stream and partially condensing the resultant admixture to form a third vapor stream comprising sulfur dioxide and carbon dioxide and a second condensate stream comprising sulfur dioxide; (g) passing the first and the second condensate streams into the first fractionation column as reflux liquid; (h) passing the third vapor stream into the absorption zone and contacting the third vapor stream with the sulfur dioxide lean absorbent stream; (i) passing the first liquid sidecut stream into a first intermediate point of a second fractionation column having a rectification section and a stripping section and operated at conditions effective to cause the separation of water and sulfur dioxide by fractionation including the retention of liquid sulfur dioxide on fractionation trays located above the first intermediate point; (j) removing a second liquid sidecut stream comprising anhydrous sulfur dioxide from the second fractionation column at a second, higher intermediate point; (k) passing a bottoms liquid product stream comprising water and sulfur dioxide and removed as a bottoms product of the second fractionation column into the first fractionation column; (l) partially condensing an overhead vapor stream comprising sulfur dioxide and carbon dioxide and removed from the second fractionation column to form reflux liquid returned to the second fractionation column and a fourth vapor stream comprising sulfur dioxide and carbon dioxide; and, (m) admixing the fourth vapor stream with the first vapor stream as the previously specified second vapor stream.