Sulfur dioxide scrubbing process

Claim 2

A CONTINUOUS PROCESS FOR REMOVING SULFUR DIOXIDE FROM A SULFUR-DIOXIDE BEARING GAS STREAM COMPRISING THE STEPS OF: A. PASSING THE GAS STREAM INTO AND THROUGH A SCRUBBING ZONE AND THERE SCRUBBING THE GAS BY CONTACT WITH AN AQUEOUS ALKALINE HYDROXIDE SCRUBBING LIQUID TO CONVERT AT LEAST PART OF THE SULFUR-DIOXIDE CONTENT OF THE STREAM TO ALKALINE SULFITE AND SULFATE IONS IN SOLUTION IN THE SCRUBBING LIQUID; B. INTRODUCING A PORTION OF SAID SCRUBBING LIQUID WITH SAID ALKALINE SULFITE AND SULFATE IONS INTO A FIRST ZONE AND THERE MIXING IT WITH SOLUBILIZED CALCIUM IONS IN THE PRESENCE OF FINELY DIVIDED CALCIUM SULFITE AND CALCIUM SULFATE CRYSTALS TO EFFECT A REACTION BETWEEN SAID ALKALINE SULFITE AND SULFATE IONS AND SAID CALCIUM IONS TO PRECIPITATE ADDITIONAL CALCIUM SULFITE AND CALCIUM SULFATE SOLIDS CONCOMITANTLY WITH THE REGENERATION OF THE AQUEOUS SCRUBBING LIQUID BY THE FORMATION OF ALKALINE HYDROXIDE THEREIN; C. SEPARATING SAID PRECIPITATED CALCIUM SULFITE AND SULFATE SOLIDS FROM SAID AQUEOUS SCRUBBING LIQUID; D. RETURNING AT LEAST A PORTION OF SAID SEPARATED CALCIUM SULFITE AND SULFATE SOLIDS TO SAID FIRST MIXING ZONE; E. REDUCING THE CALCIUM ION CONTENT OF SAID REGENERATED SCRUBBING LIQUID BY INTRODUCING SAID LIQUID INTO SECOND ZONE AND THERE MIXING IT WITH CARBONATE IONS IN THE PRESENCE OF CALCIUM CARBONATE SOLIDS TO PRECIPITATE ADDITIONAL CALCIUM AS CALIUM CARBONATE; AND F. SEPARATING SAID AQUEOUS SCRUBBING LIQUID FROM SAID CALCIUM CARBONATE AND INTRODUCING SAID REGENERATED LIQUID INTO SAID SCRUBBING ZONE TO CONTACT THE SULFUR-DIOXIDE BEARING GAS STREAM THEREIN.

Claim 3

The process of claim 1 wherein said scrubbing liquid is a sodium-based solution.

Claim 4

The process of claim 2 wherein said sodium-based solution is sodium hydroxide.

Claim 5

The process according to claim 3 wherein the sodium hydroxide scrubbing solution is formed in said first zone with slaked lime which furnishes said soluble calcium ions.

Claim 6

The process according to claim 1 wherein the separation of said precipitated calcium sulfite and calcium sulfate solids is accomplished in a third zone.

Claim 7

The process of claim 5 wherein at least a portion of said precipitated calcium carbonate in the second zone is returned for mixing with the aqueous scrubbing liquid effluent in said first zone.

Claim 8

The process according to claim 5 wherein said returned portion of said separated calcium sulfite and sulfate solids contains an amount of calcium sulfate sufficient to desupersaturate the spent scrubbing liquid.

Claim 9

The process of claim 1 further including the step of contacting the spent scrubbing liquid stream with oxygen-bearing material thereby to oxidize at least a portion of the sulfites to sulfates.

Claim 10

The process of claim 2 wherein the gas stream to the scrubbing zone is first quenched with aN aqueous solution to about 50*C prior to being scrubbed.

Claim 11

The process of claim 1 wherein said soluble calcium ions are furnished by slaked lime which is supplied to said mixing zone.

Claim 12

The process of claim 1 including the step of contacting said regenerated aqueous scrubbing liquid with carbon-dioxide to reduce the calcium ion concentration thereof by producing a calcium carbonate precipitate.

Claim 13

The process of claim 1 wherein said carbonate ions are furnished by sodium carbonate which is supplied to said second zone.

Claim 14

The process of claim 1 including making up for liquid losses in the system by adding cooling tower blow-down liquid containing dissolved calcium sulfate salts and subsequently precipitatively removing at least some of said salts in said second zone.

Claim 15

The process of claim 1 including dewatering said separated calcium sulfite and calcium sulfate to form a filter cake and then washing the same with blow-down liquid from a cooling tower, thereby to retain dissolved calcium sulfate salts from said blow-down liquid in said filter cake.

Claim 16

The process of claim 1 further including the step of separately introducing an oxygen-bearing material into said scrubbing liquid that contains said alkaline sulfite and sulfate ions to oxidize a portion of the sulfite ions to sulfate ions.

Claim 17

The process of claim 15 wherein said oxygen-bearing material is introduced prior to said first mixing zone.

Claim 18

A CONTINUOUS PROCESS FOR REMOVING SULFUR DIOXIDE FROM A SULFUR-DIOXIDE BEARING GAS STREAM COMPRISING THE STEPS OF: A. PASSING THE GAS STREAM INTO AND THROUGH A SCRUBBING ZONE AND THERE SCRUBBING THE GAS BY CONTACT WITH AN AQUEOUS ALKALINE HYDROXIDE SCRUBBING LIQUID TO CONVERT AT LEAST PART OF THE SULFUR-DIOXIDE CONTENT OF THE STREAM TO ALKALINE SULFITE AND SULFAATE IONS IN SOLUTION IN THE SCRUBBING LIQUID; B. SEPARATELY INTRODUCING AN OXYGEN-BEARING MATERIAL INTO SAID SCRUBBING LIQUID SOLUTION THAT CONTAIN SAID ALKALINE SULFITE AND SULFATE IONS TO OXIDIZE A PORTION OF THE SULFITE IONS TO SULFATE IONS; C. THEN IN A FIRST ZONE, MIXING AT LEAST A PORTION OF THE RESULTANT SAID SOLUTION WITH SOLUBILIZED CALCIUM IONS IN THE PRESENCE OF FINELY DIVIDED CALCIUM SULFITE AND CALCIUM SULFATE CRYSTALS TO EFFECT A REACTION BETWEEN SAID ALKALINE SULFITE AND SULFATE IONS AN SAID CALCIUM IONS TO PRECIPITATE ADDITIONAL CALCIUM SULFITE AND CALCIUM SULFATE SOLIDS CONCOMITANTLY WITH THE REGENERATION OF THE AQUEOUS SCRUBBING LIQUID BY THE FORMATION OF ALKALINE HYDROXIDE THERIN; D. SEPARATING SAID PRECIPITED CALCIUM SULFITE AND CALCIUM SULFATE SOLIDS FROM SAID AQUEOUS SCRUBBING LIQUID; E. RETURNING AT LEAST A PORTION OF SAID SEPARATED CALCIUM SULFITE AND SULFATE SOLIDS TO SAID FIRST MIXING ZONE; F. REDUCING THE CALCIUM ION CONTENT OF SAID REGENERATED SCRUBBING LIQUID BY INTRODUCING SAID LIQUID INTO A SECOND ZONE AND THERE MIXING IT WITH CARBONATE IONS IN THE PRESENCE OF CALCIUM CARBONATE SOLIDS TO PRECIPITATE ADDITIONAL CALCIUM AS CALCIUM CARBONATE; AND G. SEPARATING SAID AQUEOUS SCRUBBING LIQUID FROM SAID CALCIUM CARBONATE AND INTRODUCING SAID REGENERATED LIQUID INTO SAID SCRUBBING ZONE TO CONTACT THE SULFURDIOXIDE BEARING GAS STREAM THEREIN.

Claim 19

A CONTINUOUS PROCESS FOR REMOVING SULFUR DIOXIDE FROM A SULFUR-DIOXIDE BEARING GAS STREAM COMPRISING THE STEPS OF: A. PASSING THE GAS STREAM INTO AND THROUGH A SCRUBBING ZONE AND THERE SCRUBBING THE GAS BY CONTACT WITH AN AQUEOUS ALKALINE HYDROXIDE SCRUBBING LIQUID TO CONVERT AT LEAST PART OF THE SULFUR-DIOXIDE CONTENT OF THE STREAM TO ALKALINE SULFITE AND SULFAATE IONS IN SOLUTION IN THE SCRUBBING LIQUID; B. SEPARATELY INTRODUCING AN OXYGEN-BEARING MATERIAL INTO SAID SCRUBBING LIQUID SOLUTION THAT CONTAIN SAID ALKALINE SULFITE AND SULFATE IONS TO OXIDIZE A PORTION OF THE SULFITE IONS TO SULFATE IONS; C. THEN IN A FIRST ZONE, MIXING AT LEAST A PORTION OF THE RESULTANT SAID SOLUTION WITH SOLUBILIZED CALCIUM IONS IN THE PRESENCE OF FINELY DIVIDED CALCIUM SULFITE AND CALCIUM SULFATE CRYSTALS TO EFFECT A REACTION BETWEEN SAID ALKALINE SULFITE AND SULFATE IONS AN SAID CALCIUM IONS TO PRECIPITATE ADDITIONAL CALCIUM SULFITE AND CALCIUM SULFATE SOLIDS CONCOMITANTLY WITH THE REGENERATION OF THE AQUEOUS SCRUBBING LIQUID BY THE FORMATION OF ALKALINE HYDROXIDE THERIN; D. SEPARATING SAID PRECIPITED CALCIUM SULFITE AND CALCIUM SULFATE SOLIDS FROM SAID AQUEOUS SCRUBBING LIQUID; E. RETURNING AT LEAST A PORTION OF SAID SEPARATED CALCIUM SULFITE AND SULFATE SOLIDS TO SAID FIRST MIXING ZONE; F. REDUCING THE CALCIUM ION CONTENT OF SAID REGENERATED SCRUBBING LIQUID BY INTRODUCING SAID LIQUID INTO A SECOND ZONE AND THERE MIXING IT WITH CARBONATE IONS IN THE PRESENCE OF CALCIUM CARBONATE SOLIDS TO PRECIPITATE ADDITIONAL CALCIUM AS CALCIUM CARBONATE; AND G. SEPARATING SAID AQUEOUS SCRUBBING LIQUID FROM SAID CALCIUM CARBONATE AND INTRODUCING SAID REGENERATED LIQUID INTO SAID SCRUBBING ZONE TO CONTACT THE SULFURDIOXIDE BEARING GAS STREAM THEREIN.

Claim 20

The process of claim 17 wherein said scrubbing liquid is sodium hydroxide solution.

Claim 21

The process according to claim 18 wherein the sodium hydroxide scrubbing solution is mixed in said first zone with slaked lime which furnishes said soluble calcium ions.

Claim 22

The process according to claim 19 wherein said separation of the precipitated calcium sulfite and calcium sulfate solids is accomplished in a third zone.

Claim 23

The process of claim 19 wherein at least a portion of the precipitated calcium carbonate in the second zone is returned for mixing with the material in said first zone.

Claim 24

The process of claim 17 wherein said carbonate ions in said second zone are furnished by sodium carbonate which is supplied to said second zone.

Claim 25

The process of claIm 1 wherein said scrubbing liquid introduced to said first zone contains substantial amounts of sulfate and wherein substantial amounts of sulfate are included in said regenerated liquid that is returned to said scrubbing zone.