Abstract Flue gas enters a wet scrubber where it comes in contact with a circulating aqueous solution containing from 1 to 10 weight percent of an amine, such as diethanolamine, monoethanolamine, or mixtures thereof, at pH of about 4 to 8, for example about 7. As the solution removes SOx (SO2 and SO3) from the flue gas, the pH drops slightly, for example, to about 6.0. At this predetermined point the solution is considered ''''spent'''' and is withdrawn for regeneration. Regeneration is performed in two steps. The first step adjusts pH to about 5.5 to 11, preferably about 7 to 10 by addition of supernatant from the second regeneration step which provides calcium ions, or alternatively supplemental calcium ion can be provided by adding calcium hydroxide directly to the first step, and some calcium sulfite precipitates at this point. The second step removes the sulfur values picked up from the flue gas in the scrubber by addition of calcium hydroxide to raise the pH of solution to about 10 to 12. These ''''reaction products'''' are removed in the form of calcium sulfite and calcium sulfate. This two-step regeneration makes possible the exclusion of calcium ion from the scrubber and minimizes calcium ion at all times in all the liquid systems, thereby preventing the troublesome accumulation of scale normally associated with calcium base scrubbing.
A PROCESS OF SOX REMOVAL FROM FLUE GAS COMPRISING: STEP A. OF TREATING SAID FLUE GAS WITH AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF ABOUT 1 TO 10 WEIGHT PERCENT OF AN AMINE HAVING A PKA OF ABOUT 7 T 11, THE AQUEOUS PHASE HAVING A PH OF ABOUT 4 TO 8 ENTERING THIS STEP (A); STEP B. OF WITHDRAWING A PORTION OF AT LEAST PARTIALLY SPENT SOLUTION FROM STEP (A) AND RECIRCULATING SAID PORTION TO STEP (A) FLUE GAS TREATMENT; STEP C. OF WITHDRAWING AT LEAST A PORTION OF THE REMAINING AT LEAST PARTIALLY SPENT SOLUTION FROM STEP (A) AND TREATING THE SAME WITH CALCIUM IONS IN A PROPORTION WHICH IS STOICHIOMETRICALLY NOT GREATER THAN THE SULFITE ION CONTENT THEREOF TO PRECIPITATE CALCIUM SULFITE; STEP D. OF WITHDRAWING A PORTION OF LIQUOR FROM STEP (C) AND RECIRCULATING SAID PORTION TO STEP (A) FLUE GAS TREATMENT; STEP E. OR WITHDRAWING ALL OR ANOTHER PORTION OF THE REMAINING LIQUOR FROM STEP (C) TOGETHER WITH FROM NONE TO ALL OF THE CALCIUM SULFITE SOLIDS FROM STEP (C) AND TREATING THE SULFATE IONS AND ANY REMAINING SULFITE IONS CONTAINED THEREIN WITH AT LEAST A STOICHIOMETRICALLY EQUIVALENT PROPORTION OF CALCIUM HYDROXIDE TO PRECIPITATE THE CALCIUM SALTS THEREOF; AND STEP F. SEPARATING THE SOLID CALCIUM SALTS FORMED IN STEP (E) FROM AT LEAST A MAJOR PROPORTION OF THE AQUEOUS PHASE RESULTING FROM STEP (E) AND RECIRCULATING SAID SEPARATED AQUEOUS PHASE AND THE CALCIUM IONS CONTAINED THEREIN TO STEP (C).
Claim 2
Dependent Claim
243 words
A PROCESS OF SOX REMOVAL FROM FLUE GAS COMPRISING: STEP A. OF TREATING SAID FLUE GAS WITH AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF ABOUT 1 TO 10 WEIGHT PERCENT OF AN AMINE HAVING A PKA OF ABOUT 7 T 11, THE AQUEOUS PHASE HAVING A PH OF ABOUT 4 TO 8 ENTERING THIS STEP (A); STEP B. OF WITHDRAWING A PORTION OF AT LEAST PARTIALLY SPENT SOLUTION FROM STEP (A) AND RECIRCULATING SAID PORTION TO STEP (A) FLUE GAS TREATMENT; STEP C. OF WITHDRAWING AT LEAST A PORTION OF THE REMAINING AT LEAST PARTIALLY SPENT SOLUTION FROM STEP (A) AND TREATING THE SAME WITH CALCIUM IONS IN A PROPORTION WHICH IS STOICHIOMETRICALLY NOT GREATER THAN THE SULFITE ION CONTENT THEREOF TO PRECIPITATE CALCIUM SULFITE; STEP D. OF WITHDRAWING A PORTION OF LIQUOR FROM STEP (C) AND RECIRCULATING SAID PORTION TO STEP (A) FLUE GAS TREATMENT; STEP E. OR WITHDRAWING ALL OR ANOTHER PORTION OF THE REMAINING LIQUOR FROM STEP (C) TOGETHER WITH FROM NONE TO ALL OF THE CALCIUM SULFITE SOLIDS FROM STEP (C) AND TREATING THE SULFATE IONS AND ANY REMAINING SULFITE IONS CONTAINED THEREIN WITH AT LEAST A STOICHIOMETRICALLY EQUIVALENT PROPORTION OF CALCIUM HYDROXIDE TO PRECIPITATE THE CALCIUM SALTS THEREOF; AND STEP F. SEPARATING THE SOLID CALCIUM SALTS FORMED IN STEP (E) FROM AT LEAST A MAJOR PROPORTION OF THE AQUEOUS PHASE RESULTING FROM STEP (E) AND RECIRCULATING SAID SEPARATED AQUEOUS PHASE AND THE CALCIUM IONS CONTAINED THEREIN TO STEP (C).
Claim 3
Dependent Claim
26 words
A process as in claim 1 wherein substantially all of the calcium ions used in step (c) are supplied by the aqueous phase from step (f).
Claim 4
Dependent Claim
30 words
A process as in claim 1 wherein calcium hydroxide is added in step (c) to supplement the calcium ions supplied to step (c) by the aqueous phase from step (f).
Claim 5
Dependent Claim
16 words
A process as in claim 1 wherein the amine comprises a monoethanolamine, diethanolamine or mixtures thereof.
Claim 6
Dependent Claim
30 words
A process as in claim 4 wherein sufficient calcium hydroxide is added in step (e) such that the pH of the supernatant from step (c) is about 5.5 to 11.
Claim 7
Dependent Claim
34 words
A process as in claim 4 wherein the calcium sulfite solids precipItated in step (c) are separated from the liquor so that the liquor going to step (e) contains substantially no calcium sulfite solids.
Claim 8
Dependent Claim
23 words
A process as in claim 4 wherein substantially all of the calcium sulfite solids precipitated in step (c) are added to step (e).
Claim 9
Dependent Claim
11 words
A process as in claim 7 wherein the amine is diethanolamine.
Claim 10
Dependent Claim
23 words
A process as in claim 1 wherein the calcium salts are precipitated in step (e) at a pH of about 10 to 12.