CA1181928A - Process for removal of oxides from waste gases - Google Patents
Process for removal of oxides from waste gasesInfo
- Publication number
- CA1181928A CA1181928A CA000411689A CA411689A CA1181928A CA 1181928 A CA1181928 A CA 1181928A CA 000411689 A CA000411689 A CA 000411689A CA 411689 A CA411689 A CA 411689A CA 1181928 A CA1181928 A CA 1181928A
- Authority
- CA
- Canada
- Prior art keywords
- liquor
- trona
- sorbent
- sodium
- alkaline
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/48—Sulfur compounds
- B01D53/50—Sulfur oxides
- B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Biomedical Technology (AREA)
- Environmental & Geological Engineering (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Treating Waste Gases (AREA)
Abstract
ABSTRACT
A process For removing sulfur oxides from waste gas is provided. The gas is contacted with d sorbent selected from trona and activated sodium car-bonate and, utilizing an alkaline ammonia liquor so as to reduce the flow rates and loss of alkalinity, the spent sorbent is regenerated with an alka-line earth metal oxide or hydroxide.
A process For removing sulfur oxides from waste gas is provided. The gas is contacted with d sorbent selected from trona and activated sodium car-bonate and, utilizing an alkaline ammonia liquor so as to reduce the flow rates and loss of alkalinity, the spent sorbent is regenerated with an alka-line earth metal oxide or hydroxide.
Description
PROCESS FOR REMOVAL OF SULFUR OXIDES FROM WASTE GASES
Background of the Invention This invention relates to a process for absorbLng sulfur oxldes from industrial waste gases with a solid sorbent and regenerating the solid sorbent for reuse.
In the combustlon of fossil fuels, and in many industrial processes, a serious problem is presented by the combustion of the sulfur-containing components therein. The noxious sulfur o.Kides produced are Rn environmental pollutant and in recent years considerable effort has been made to remove the sulfur o~ldes from the combustion gasses exhausted to the atmosphere. Several methods for removing such oxides are known. For example, U.SO Patent 3,852~410 issued to Rivers et al., and U~S. Patent 3,846,535 issued to Fonseca, are illustrative. To applicant's knowledge, however, all prior art processes have certain disadvantages and, consequently, an improved method for economically and reliably removing sulfur oxides from gaseous mixtures would be desirable, and is hereln provided.
Brief Su~mary of the Invention Briefly, the process of the invention comprises treating the waste gas containing sulfur oxides (which is princlpally and hereinafter for convenience referred to as sulfur dioxide) with a solid sorbent selected from the class consisting of activated sodium carbonate1 trona and mixtures thereof which can remove 90 percent or more of the sulfur dioxide. Trona is the mineral name for Na2C03.NaHC03;2H20. Activated sodium carbonate can be formed from sodlum bicarbonate, trona or a mixture of the two, by calcining at a temperature between about 70C and about 200C. For sodium bicarbonate having a characteristic partlcle dimension of about 50 microns, a calcination period l,~
~3~ 3 of dbout 10 to about 30 minutes, at d temperature o-f about 150C ~lill suf-fice. rhe clean gas is vented ancl the resul-tant urlreactec~ solids, so~i Utll sulfites~ sulfa-tes ancl mixtures ~hereof, dre dissolved in a haxic amlllorli~
liquor that is all(dlinc enou(Jh to convert carbonic dCi~ to bicarb()nate, to fonn soluble sodiulll ccml)ounds. Carbondtiorl o-F lhe resultc~rlt licluor fonlls socliwn pre~cipitate containin~ bicarbonate, trona, or mixtures thereof.
The precipitate is separated from the carborldted li4uor dnd the liquor ~reated wi~h d precipitdn~ compouncl selected frorn the class consisting of alkaline edrth metal hyclroxides, oxides and mix-tures ~hereof to Fo~ in-soluble alkaline earth metal sulFates, sulfites and rnixtures thereof. Suit-able alkaline earth metals inclucle calcium, bariurn and strontiurrl. After removing ~he solids, the liquor is recycled to treat spent sorbent.
The presence of ammonia in the process provides severdl distinct advantages. For one, it permi~s the use of lower flow rdtes in the regenerd~
tion loop of the process. Another important advantage is that since it does not degrade chemically o~ biologically to any significant extent~ there is little loss of ammonia in the system, which accordingly reduces the amount of materials utilized in the process. Moreover, since the ammonia does not act as a reducing agent in the regeneratiorl loop or in the solid waste disposal 20 area the sulfites andJor sulfates present are not reduced to noxious sulfur canpounds as, for example, hydrogen sulfide which can present serious health and disposal problemsO
Brief Description of the ~rawing The drawing is a schematic flow diagram of the process of the inven-tion..
Detailed Descrlptlon of the Inventlon .
Referring no~ to the drawing, a flue gas contalning sulfur dloxide is fed v:La conduit 2 to a gas-solid contactor 4. Contactor 4, which can take many forms (e.g., fixed bed, moving bed, fluidized bed, etc.), is suitably a baghouse collector employing tube type fabric filter dust collecting surfaces preloaded with a suitable sorbent, which is introduced into contactor 4 via conduit 6. Alternately, the sorbent may be introduced into the gas stream upstream of the Contactor. On passing through the contactor 4, the sulfur dioxide in the flue gas reacts with the sodium containing sorbent to produce ] sodlum sul~te and sulfate, leaving a flue gas substantlally free of any sulfur dixoide and which is vented from contactor 4 via condult 8.
A sollds product is removed from contactor 4 via conduit 10 and transferred to a spent sorbent storage vessel 12. At this point, the solids product will comprise unused sorbent initially in gas-solid contactor 4 plus soluble (sodium) sulfite and/or sulfate resulting from the reaction of the sorbent with the sulfur dioxide in the flue gase. The solids product is transferred to mixing tank 16 via conduit 14 where it is admixed with an alkaline recycle liquor containing ammonia from line 18 and makeup chemicals which can include NH4Cl, (NH4)2S04, Na2C03, N 2 4~
various mixtures of the above. In mixing tank 16, the soluble sulfite and/or sulfate which were formed by the reaction of the sulfur dioxide with the sorbent are dissolved. The liquor from mixing tank 16 is transferred via conduit 22 to a fly ash filter 24 where any fly ash is removed and dlsposed of via conduit 26. Conduit 26 may go to reaction tank 64 when not all of the sodium sulfite or sulfate from the spent sorbent storage vessel 12 dissolves in mixing tank 16. The fly ash free liquor leaves ftlter 24 via conduit 28, ls introduced into carbonator 30, and is reacted with C02, introduced into carbonator 30 via condult 32. Bicarbonate ions are formed which are transferred via conduit 36 to crystallizer 38 and converted to solid sodium bicarbonate which crystallizes ou-t oF solution. Excess C02 leaves carbonalor 30 Vid conduil ~'~
For ventiny to the atmosphere or, iF preferred, to the c'ledn gas stack via conduit 8. 'I'he sodium bicarbona-te ancl/or trona crys~a'lli~ecl in cr~stallizer 38 is transferred Vid conduit 40 to sodium bicarbonate filter 42~ Carbon dioxide may also be addecl to -the crystalli~er 38 ~o drive l;he crystal'liza~ior of sodium bicarbonate toward completion. The sodium bicarbonate recovered fronl Filter 42 is transferred via conduit 46 to drier/ca'lciner 4~ ~Ihere it isdried and calcined to an active form oF sodiurn bicarbona~e and transferred via conduit 52 to regenerated sorbent stordge vessel 54. Alternatively, trona Ina~
be formed in crystalli~er 38, It may be dried or dried and calcined to an active Form oF sodium carbonate in drier/calciner 4~ and transferred Vid conduit 52 to regenerated sorben~ storage vessel 54.
The liquid from filter 42 passes via conduit 44 lnto carbon dioxide stripper 56 where it is contacted countercurrently with a stripping 9dS (eO9., steam) introduced in the lower portion of stripper 56 via conduit 58. A por-tion of the C02, other undissolved gases and any remaining stripping gas is vented froln stripper 56 via conduit 60. This C02 containing gas may be added to carbonator 30 or crystallizer 38. The C02 stripped liquor frorn stripper 56 is introduced~ via conduit 62, into a reaction vessel 64 where it is contacted 20 with precipitant preferably lime introduced via line 66. In reaction tank 64, the precipitant, e.g. lime, reacts with the solub1e sodium sulfite and/or sulfate to produce insoluble calciùm sulfate and/or calcium sulfite and regenerate the alkaline liquor. The mixture in reaction tank 64 is transferred via conduit 68 to a sludge dewatering vessel 70 where the insoluble calcium sulfate and/or sulfite is disposed of via conduit 72, the liquid from vessel 70 being recycled~ as noted above, to mixing tank 16 via conduit 18~ r As can be seen from the drawing, the process is comprised of two basic steps, a sorption step and a regeneration step. In the sorption step, the sulfur dioxide in the f1ue 9dS is contacted with -the sorbent an~ converted into soluble sulfate and/or sul-fi-te compounds. In the reyenerdtion step or loop, the sulfur species is ultimately purgecl from the process as an insoluhle sulFur compound dnd the sorbent is regenera-ted For reuse in the sorption slep.
The sorbent is preFerably a sodium carbona-te obt~ine(i by calcinin(~ d sodiuln-containing compound such as sodium bicarbonate, trona or a rllixture thereof at a temperature of from about 70 to about 200C. It has heen Found that while sodium carbonate which has been produceci by crystalliza~ion directly from solution does not act as an efFective sorbent in the process of the present invention, calcined sodium carbonate produced by calcinin~ sodiu bicarbonate or trona, makes an excellent sorbent and is easily obtained b~
cdlcining the precipitdted sodiurn bicarbonate produced in crystalli~er 3~
To remove the soluble sulFites and/or sulfates frorn the sys~em, d precipitant oF an alkàline earth metal hydroxide, oxide or mixture thereof is employed. Thus, for example, the process can employ an oxide or hydroxide oF
calcium, bariurn or strontium or rnix~ures~ The preFerred alkaline earth metal is cdlcium.
As noted above with regard to the description of the drawing, the process, with advantagel employs à carbon dioxide stripper. The stripper, 20 which can be any gas-liquid countercurrent contactor, serves to remove excessC0~ from the process which would otherwise be precipitated as calcium carbon-ate in vessel 64, thereby increasin3 the use o-F lime in the process. The C02 stripper ~as can include steam or an oxygen-containing gaseous rnedium such as, For example, air.
As pointed out above, the process of the present invention utilizes ammonia in the liquor in mixing tank 16. The ultimate source of alkalinity in the process is supplied by the precipitant (hereinaFter For convenienGe reFerred to as lime~ added to the reaction tank 64. However, without the use of some medium to transFer alkalinity ~rom the solid phase ~lirne) to the liquid phase, the alkalini-ty oF the solution woul~ be rdp-i~ le~'lete~ ~lurinthe carbonation step. Accor~in~lly, for d yiven circul~-ion r~le in lhe system, pro(luction of so~ium bicdrbondte in ~he carbon~t(Jr ~ould be yrea~
reduce~. -rhis would necessitate dn i ncredsed pUlllp i ny or recircu'lalion rale in the system -to the point where the process could become economicdlly not ~'C~dSi-b'le. The arnmonia serves the funccion of effectiny the a'lka'linity trarlsf'erfrom the lime to the liqui(l phase ancl can thus be consiclered an "a'lkdlinity carrier". This alkalini-ty c~lrrier has an acid Form (ammoniurn ion) an(l a base ~orrn, (amlnonia), being in the base Form as it leaYes reaction tank ~4. The lo clear liquid which is removed -From ash fi'lter ~4 and which is used l;o ~issolve the gds-solid contactor so'lids froln contactor 4 is pumped to -the carborlator 30 where -the liquid phase alkalinity oF the carrier is now exchan~ed For li~ui~
phase bicarbonate alkalinity~ This liquid phase bicarbonate alkalirlity is no~
converted to the solid pha$e alkalinity of the sodium bicarbonate in the crystalli~er. The alkalinity carrier in the clear liquid from crystallizer 3 is now in the acid form, i.e., ammonium ion. Upon entering reaçtion tank 64, the ammonium ion once again contacts the solid phase alkalinity provided by the lime, and is converted into the basic form (ammonia) and the cycle repeated.
It ~ill be apparent that the alkalinity carrier can be added as the base, as ammonid, or in the acid Form of its respective salts. Thus, For example, the ammonia can be added in the -Form oF ammonium sulfate, amnlonium chloride or thP like.
The 'limits for ammonia may be determined from the following consider-ations. As an alkalinity carrier, it is desirable to maxirnize its concentra~
tion.
The limitation on ammonia concentration is the vapor pressure of am-monia. This is tlreatest at high ternperature and pH. An upper limit is the totdl solution vapor pressure (water, dmmonia, and C02) of the solution e4llal to Five atmosphere absolute (60 psig)~
The following examples will serve to illustrate the preferred emt~odi-ments oF the invention.
Exclm~
Flue gas containing 700 lb. mo1e/hr. of S02 is treated with 760 lb.
mole/hr. of activated sodium carbonate and reacts ~ith 90 percent of the sul~
fur dioxide in the flue gas. The resulting solids are collected in a bag house. The solids From the baghouse are dissolved using 1350 gal~/rnin. o-F d recirculated liquor containing 2.6 m ammonia and 6.5 m sodium, and other dissolved species such as chlorides, sulfites, sulfates, carbonates, calciuln, etc. Also, makeup soda ash is dissolved into the liquor at the rate of 35.0 lb. mole/hr. The resulting liquor is ~hen carbonated with 760 lb~
mole/hr. of C02 from a combination of clean flue gas, and C02 recycled from other parts o~ the process. Excess C0~ is combined with the cleaned flue gas. Makeup ammonia is also added to the liquor at a rate of 25.4 lb~
mole/hr, in the carbonator tower. The resulting hot, carbonated liquor is ~cooled to 95F ~o precipitate 1520 lb. mole/hr. oF sodium bicarbonate. The sodium bicarbonate solids are separated from the liquorg dried and calcined at 20 300F to for~ an activated sodium carbonate which is recycled to -the baghouse to treat the flue gas. The separaced liquor is passed through a C02 stripping column to remove ~0 lb. mole/hr. of carbon dioxide from the liquor. The liquor leaving the C02 stripping column is treated with 660 lb. mo1e/hr. of lime in a reaction tank to precipitate calcium sulfi-te and/or ca1cium sulfate solids. These solids are separated fr~n the slurry leaving the reaction tank and constitute the waste productO The separated liquor is recycled dS noted above to dissolve the baghouse solids.
The fo'llowing Examples II, when run in accordarlce ~ith tne general procedure of Exdnlple I, but in the absence of an alkalinity cdrrier as indi cated in ttle following table~ demonstrate that the circu'iation ra-tfl ~lould be increased at least a thousandfold (iF even technically feasib'le) over the 1350 9pl11 circlllation rate o~ Example I.
molali ~, rnoles/K ~ Circu'lation Rate rnmonia ~ c~rn II 0 1,350,000t While the foregoin~ description is illustrative of -the preferred embodimenks of the process of the invention, numerous obvious vdrid~ions an(i modi~'ications will be apparent to one of ordinary skill, and accordingly, i~
is intended that the invenkion be limited only by the appended claims~
Background of the Invention This invention relates to a process for absorbLng sulfur oxldes from industrial waste gases with a solid sorbent and regenerating the solid sorbent for reuse.
In the combustlon of fossil fuels, and in many industrial processes, a serious problem is presented by the combustion of the sulfur-containing components therein. The noxious sulfur o.Kides produced are Rn environmental pollutant and in recent years considerable effort has been made to remove the sulfur o~ldes from the combustion gasses exhausted to the atmosphere. Several methods for removing such oxides are known. For example, U.SO Patent 3,852~410 issued to Rivers et al., and U~S. Patent 3,846,535 issued to Fonseca, are illustrative. To applicant's knowledge, however, all prior art processes have certain disadvantages and, consequently, an improved method for economically and reliably removing sulfur oxides from gaseous mixtures would be desirable, and is hereln provided.
Brief Su~mary of the Invention Briefly, the process of the invention comprises treating the waste gas containing sulfur oxides (which is princlpally and hereinafter for convenience referred to as sulfur dioxide) with a solid sorbent selected from the class consisting of activated sodium carbonate1 trona and mixtures thereof which can remove 90 percent or more of the sulfur dioxide. Trona is the mineral name for Na2C03.NaHC03;2H20. Activated sodium carbonate can be formed from sodlum bicarbonate, trona or a mixture of the two, by calcining at a temperature between about 70C and about 200C. For sodium bicarbonate having a characteristic partlcle dimension of about 50 microns, a calcination period l,~
~3~ 3 of dbout 10 to about 30 minutes, at d temperature o-f about 150C ~lill suf-fice. rhe clean gas is vented ancl the resul-tant urlreactec~ solids, so~i Utll sulfites~ sulfa-tes ancl mixtures ~hereof, dre dissolved in a haxic amlllorli~
liquor that is all(dlinc enou(Jh to convert carbonic dCi~ to bicarb()nate, to fonn soluble sodiulll ccml)ounds. Carbondtiorl o-F lhe resultc~rlt licluor fonlls socliwn pre~cipitate containin~ bicarbonate, trona, or mixtures thereof.
The precipitate is separated from the carborldted li4uor dnd the liquor ~reated wi~h d precipitdn~ compouncl selected frorn the class consisting of alkaline edrth metal hyclroxides, oxides and mix-tures ~hereof to Fo~ in-soluble alkaline earth metal sulFates, sulfites and rnixtures thereof. Suit-able alkaline earth metals inclucle calcium, bariurn and strontiurrl. After removing ~he solids, the liquor is recycled to treat spent sorbent.
The presence of ammonia in the process provides severdl distinct advantages. For one, it permi~s the use of lower flow rdtes in the regenerd~
tion loop of the process. Another important advantage is that since it does not degrade chemically o~ biologically to any significant extent~ there is little loss of ammonia in the system, which accordingly reduces the amount of materials utilized in the process. Moreover, since the ammonia does not act as a reducing agent in the regeneratiorl loop or in the solid waste disposal 20 area the sulfites andJor sulfates present are not reduced to noxious sulfur canpounds as, for example, hydrogen sulfide which can present serious health and disposal problemsO
Brief Description of the ~rawing The drawing is a schematic flow diagram of the process of the inven-tion..
Detailed Descrlptlon of the Inventlon .
Referring no~ to the drawing, a flue gas contalning sulfur dloxide is fed v:La conduit 2 to a gas-solid contactor 4. Contactor 4, which can take many forms (e.g., fixed bed, moving bed, fluidized bed, etc.), is suitably a baghouse collector employing tube type fabric filter dust collecting surfaces preloaded with a suitable sorbent, which is introduced into contactor 4 via conduit 6. Alternately, the sorbent may be introduced into the gas stream upstream of the Contactor. On passing through the contactor 4, the sulfur dioxide in the flue gas reacts with the sodium containing sorbent to produce ] sodlum sul~te and sulfate, leaving a flue gas substantlally free of any sulfur dixoide and which is vented from contactor 4 via condult 8.
A sollds product is removed from contactor 4 via conduit 10 and transferred to a spent sorbent storage vessel 12. At this point, the solids product will comprise unused sorbent initially in gas-solid contactor 4 plus soluble (sodium) sulfite and/or sulfate resulting from the reaction of the sorbent with the sulfur dioxide in the flue gase. The solids product is transferred to mixing tank 16 via conduit 14 where it is admixed with an alkaline recycle liquor containing ammonia from line 18 and makeup chemicals which can include NH4Cl, (NH4)2S04, Na2C03, N 2 4~
various mixtures of the above. In mixing tank 16, the soluble sulfite and/or sulfate which were formed by the reaction of the sulfur dioxide with the sorbent are dissolved. The liquor from mixing tank 16 is transferred via conduit 22 to a fly ash filter 24 where any fly ash is removed and dlsposed of via conduit 26. Conduit 26 may go to reaction tank 64 when not all of the sodium sulfite or sulfate from the spent sorbent storage vessel 12 dissolves in mixing tank 16. The fly ash free liquor leaves ftlter 24 via conduit 28, ls introduced into carbonator 30, and is reacted with C02, introduced into carbonator 30 via condult 32. Bicarbonate ions are formed which are transferred via conduit 36 to crystallizer 38 and converted to solid sodium bicarbonate which crystallizes ou-t oF solution. Excess C02 leaves carbonalor 30 Vid conduil ~'~
For ventiny to the atmosphere or, iF preferred, to the c'ledn gas stack via conduit 8. 'I'he sodium bicarbona-te ancl/or trona crys~a'lli~ecl in cr~stallizer 38 is transferred Vid conduit 40 to sodium bicarbonate filter 42~ Carbon dioxide may also be addecl to -the crystalli~er 38 ~o drive l;he crystal'liza~ior of sodium bicarbonate toward completion. The sodium bicarbonate recovered fronl Filter 42 is transferred via conduit 46 to drier/ca'lciner 4~ ~Ihere it isdried and calcined to an active form oF sodiurn bicarbona~e and transferred via conduit 52 to regenerated sorbent stordge vessel 54. Alternatively, trona Ina~
be formed in crystalli~er 38, It may be dried or dried and calcined to an active Form oF sodium carbonate in drier/calciner 4~ and transferred Vid conduit 52 to regenerated sorben~ storage vessel 54.
The liquid from filter 42 passes via conduit 44 lnto carbon dioxide stripper 56 where it is contacted countercurrently with a stripping 9dS (eO9., steam) introduced in the lower portion of stripper 56 via conduit 58. A por-tion of the C02, other undissolved gases and any remaining stripping gas is vented froln stripper 56 via conduit 60. This C02 containing gas may be added to carbonator 30 or crystallizer 38. The C02 stripped liquor frorn stripper 56 is introduced~ via conduit 62, into a reaction vessel 64 where it is contacted 20 with precipitant preferably lime introduced via line 66. In reaction tank 64, the precipitant, e.g. lime, reacts with the solub1e sodium sulfite and/or sulfate to produce insoluble calciùm sulfate and/or calcium sulfite and regenerate the alkaline liquor. The mixture in reaction tank 64 is transferred via conduit 68 to a sludge dewatering vessel 70 where the insoluble calcium sulfate and/or sulfite is disposed of via conduit 72, the liquid from vessel 70 being recycled~ as noted above, to mixing tank 16 via conduit 18~ r As can be seen from the drawing, the process is comprised of two basic steps, a sorption step and a regeneration step. In the sorption step, the sulfur dioxide in the f1ue 9dS is contacted with -the sorbent an~ converted into soluble sulfate and/or sul-fi-te compounds. In the reyenerdtion step or loop, the sulfur species is ultimately purgecl from the process as an insoluhle sulFur compound dnd the sorbent is regenera-ted For reuse in the sorption slep.
The sorbent is preFerably a sodium carbona-te obt~ine(i by calcinin(~ d sodiuln-containing compound such as sodium bicarbonate, trona or a rllixture thereof at a temperature of from about 70 to about 200C. It has heen Found that while sodium carbonate which has been produceci by crystalliza~ion directly from solution does not act as an efFective sorbent in the process of the present invention, calcined sodium carbonate produced by calcinin~ sodiu bicarbonate or trona, makes an excellent sorbent and is easily obtained b~
cdlcining the precipitdted sodiurn bicarbonate produced in crystalli~er 3~
To remove the soluble sulFites and/or sulfates frorn the sys~em, d precipitant oF an alkàline earth metal hydroxide, oxide or mixture thereof is employed. Thus, for example, the process can employ an oxide or hydroxide oF
calcium, bariurn or strontium or rnix~ures~ The preFerred alkaline earth metal is cdlcium.
As noted above with regard to the description of the drawing, the process, with advantagel employs à carbon dioxide stripper. The stripper, 20 which can be any gas-liquid countercurrent contactor, serves to remove excessC0~ from the process which would otherwise be precipitated as calcium carbon-ate in vessel 64, thereby increasin3 the use o-F lime in the process. The C02 stripper ~as can include steam or an oxygen-containing gaseous rnedium such as, For example, air.
As pointed out above, the process of the present invention utilizes ammonia in the liquor in mixing tank 16. The ultimate source of alkalinity in the process is supplied by the precipitant (hereinaFter For convenienGe reFerred to as lime~ added to the reaction tank 64. However, without the use of some medium to transFer alkalinity ~rom the solid phase ~lirne) to the liquid phase, the alkalini-ty oF the solution woul~ be rdp-i~ le~'lete~ ~lurinthe carbonation step. Accor~in~lly, for d yiven circul~-ion r~le in lhe system, pro(luction of so~ium bicdrbondte in ~he carbon~t(Jr ~ould be yrea~
reduce~. -rhis would necessitate dn i ncredsed pUlllp i ny or recircu'lalion rale in the system -to the point where the process could become economicdlly not ~'C~dSi-b'le. The arnmonia serves the funccion of effectiny the a'lka'linity trarlsf'erfrom the lime to the liqui(l phase ancl can thus be consiclered an "a'lkdlinity carrier". This alkalini-ty c~lrrier has an acid Form (ammoniurn ion) an(l a base ~orrn, (amlnonia), being in the base Form as it leaYes reaction tank ~4. The lo clear liquid which is removed -From ash fi'lter ~4 and which is used l;o ~issolve the gds-solid contactor so'lids froln contactor 4 is pumped to -the carborlator 30 where -the liquid phase alkalinity oF the carrier is now exchan~ed For li~ui~
phase bicarbonate alkalinity~ This liquid phase bicarbonate alkalirlity is no~
converted to the solid pha$e alkalinity of the sodium bicarbonate in the crystalli~er. The alkalinity carrier in the clear liquid from crystallizer 3 is now in the acid form, i.e., ammonium ion. Upon entering reaçtion tank 64, the ammonium ion once again contacts the solid phase alkalinity provided by the lime, and is converted into the basic form (ammonia) and the cycle repeated.
It ~ill be apparent that the alkalinity carrier can be added as the base, as ammonid, or in the acid Form of its respective salts. Thus, For example, the ammonia can be added in the -Form oF ammonium sulfate, amnlonium chloride or thP like.
The 'limits for ammonia may be determined from the following consider-ations. As an alkalinity carrier, it is desirable to maxirnize its concentra~
tion.
The limitation on ammonia concentration is the vapor pressure of am-monia. This is tlreatest at high ternperature and pH. An upper limit is the totdl solution vapor pressure (water, dmmonia, and C02) of the solution e4llal to Five atmosphere absolute (60 psig)~
The following examples will serve to illustrate the preferred emt~odi-ments oF the invention.
Exclm~
Flue gas containing 700 lb. mo1e/hr. of S02 is treated with 760 lb.
mole/hr. of activated sodium carbonate and reacts ~ith 90 percent of the sul~
fur dioxide in the flue gas. The resulting solids are collected in a bag house. The solids From the baghouse are dissolved using 1350 gal~/rnin. o-F d recirculated liquor containing 2.6 m ammonia and 6.5 m sodium, and other dissolved species such as chlorides, sulfites, sulfates, carbonates, calciuln, etc. Also, makeup soda ash is dissolved into the liquor at the rate of 35.0 lb. mole/hr. The resulting liquor is ~hen carbonated with 760 lb~
mole/hr. of C02 from a combination of clean flue gas, and C02 recycled from other parts o~ the process. Excess C0~ is combined with the cleaned flue gas. Makeup ammonia is also added to the liquor at a rate of 25.4 lb~
mole/hr, in the carbonator tower. The resulting hot, carbonated liquor is ~cooled to 95F ~o precipitate 1520 lb. mole/hr. oF sodium bicarbonate. The sodium bicarbonate solids are separated from the liquorg dried and calcined at 20 300F to for~ an activated sodium carbonate which is recycled to -the baghouse to treat the flue gas. The separaced liquor is passed through a C02 stripping column to remove ~0 lb. mole/hr. of carbon dioxide from the liquor. The liquor leaving the C02 stripping column is treated with 660 lb. mo1e/hr. of lime in a reaction tank to precipitate calcium sulfi-te and/or ca1cium sulfate solids. These solids are separated fr~n the slurry leaving the reaction tank and constitute the waste productO The separated liquor is recycled dS noted above to dissolve the baghouse solids.
The fo'llowing Examples II, when run in accordarlce ~ith tne general procedure of Exdnlple I, but in the absence of an alkalinity cdrrier as indi cated in ttle following table~ demonstrate that the circu'iation ra-tfl ~lould be increased at least a thousandfold (iF even technically feasib'le) over the 1350 9pl11 circlllation rate o~ Example I.
molali ~, rnoles/K ~ Circu'lation Rate rnmonia ~ c~rn II 0 1,350,000t While the foregoin~ description is illustrative of -the preferred embodimenks of the process of the invention, numerous obvious vdrid~ions an(i modi~'ications will be apparent to one of ordinary skill, and accordingly, i~
is intended that the invenkion be limited only by the appended claims~
Claims (8)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for the removal of sulfur oxide from industrial waste gas containing same comprising:
(a) contacting said gas with a solid sorbent selected from activated sodium carbonate, trona and mixtures, thereof, in an amount sufficient to react with substantially all of the sulfur oxide present in said gas to form solids of unre-acted sorbent, sodium sulfite, sulfate, and mixtures thereof, and a waste gas substantially free of sulfur oxide;
(b) venting the resultant waste gas from the process, dis-solving said solids in an alkaline ammonia liquor to form soluble sodium compounds;
(c) carbonating the resultant alkaline sodium liquor from step (b) and cooling to a temperature sufficient to form sodium bicarbonate or trona crystals;
(d) separating the sodium bicarbonate or trona crystals from the liquor of step (c) and drying said trona and recycling to step (a) or heating said bicarbonate and trona crystals for a time and at a temperature sufficient to form acti-vated sodium carbonate, and recycling said activated sodium carbonate to step (a); and (e) removing carbon dioxide from the cooled liquor of step (c), adding a precipitant selected from the class consisting of alkaline earth metal hydroxides, oxides and mixtures there-of, to the resultant liquor to render it alkaline and form insoluble solids comprising alkaline earth metal sulfates, sulfites and mixtures thereof, separating said solids and recycling the resultant alkaline liquor to step (b).
(a) contacting said gas with a solid sorbent selected from activated sodium carbonate, trona and mixtures, thereof, in an amount sufficient to react with substantially all of the sulfur oxide present in said gas to form solids of unre-acted sorbent, sodium sulfite, sulfate, and mixtures thereof, and a waste gas substantially free of sulfur oxide;
(b) venting the resultant waste gas from the process, dis-solving said solids in an alkaline ammonia liquor to form soluble sodium compounds;
(c) carbonating the resultant alkaline sodium liquor from step (b) and cooling to a temperature sufficient to form sodium bicarbonate or trona crystals;
(d) separating the sodium bicarbonate or trona crystals from the liquor of step (c) and drying said trona and recycling to step (a) or heating said bicarbonate and trona crystals for a time and at a temperature sufficient to form acti-vated sodium carbonate, and recycling said activated sodium carbonate to step (a); and (e) removing carbon dioxide from the cooled liquor of step (c), adding a precipitant selected from the class consisting of alkaline earth metal hydroxides, oxides and mixtures there-of, to the resultant liquor to render it alkaline and form insoluble solids comprising alkaline earth metal sulfates, sulfites and mixtures thereof, separating said solids and recycling the resultant alkaline liquor to step (b).
2. The method of Claim 1 wherein said sorbent comprises trona.
3. The method of Claim 1 wherein said sorbent comprises activated sodium carbonate.
4. The method of Claim 1 wherein said precipitant comprises calcium oxide.
5. The method of Claim 1 wherein said precipitant comprises calcium hyroxide.
6. The method of Claim 1 wherein ammonium sulfate or ammonium chlo-ride is employed to provide the ammonia.
7. The method of Claim 1 wherein an activated sodium carbonate sor-bent is employed with a lime precipitant.
8. The method of Claim 2 wherein CO2 is added in the crystal-lization to drive the crystallization of the sodium bicarbonate to completion.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US30335981A | 1981-09-18 | 1981-09-18 | |
| US303,359 | 1981-09-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1181928A true CA1181928A (en) | 1985-02-05 |
Family
ID=23171733
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000411689A Expired CA1181928A (en) | 1981-09-18 | 1982-09-17 | Process for removal of oxides from waste gases |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5864118A (en) |
| AU (1) | AU548689B2 (en) |
| CA (1) | CA1181928A (en) |
| DE (1) | DE3233201C2 (en) |
| FR (1) | FR2513141A1 (en) |
| GB (1) | GB2106489B (en) |
| IN (1) | IN159058B (en) |
| ZA (1) | ZA826566B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2740354B1 (en) * | 1995-10-31 | 1997-11-28 | Rhone Poulenc Chimie | PROCESS FOR THE TREATMENT OF FUMES BASED ON SULFUR OXIDES |
| FR2740362B1 (en) * | 1995-10-31 | 1997-11-28 | Rhone Poulenc Chimie | PROCESS FOR THE PREPARATION OF SODIUM BICARBONATE AND ITS USE IN THE TREATMENT OF SMOKE |
| US7531154B2 (en) | 2005-08-18 | 2009-05-12 | Solvay Chemicals | Method of removing sulfur dioxide from a flue gas stream |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3846535A (en) * | 1972-09-05 | 1974-11-05 | Continental Oil Co | Method for absorbing sulfur oxides from gaseous mixtures and regenerating the absorbent |
| US3823676A (en) * | 1972-10-10 | 1974-07-16 | Warren Cook Chem Inc | Method of reducing sulphur dioxide emissions from coal |
| US3852410A (en) * | 1972-12-07 | 1974-12-03 | American Air Filter Co | Sulfur dioxide and particulate contaminant removal from industrial stack gases |
-
1982
- 1982-08-27 AU AU87800/82A patent/AU548689B2/en not_active Ceased
- 1982-09-07 DE DE3233201A patent/DE3233201C2/en not_active Expired
- 1982-09-08 ZA ZA826566A patent/ZA826566B/en unknown
- 1982-09-15 GB GB08226295A patent/GB2106489B/en not_active Expired
- 1982-09-16 JP JP57161559A patent/JPS5864118A/en active Granted
- 1982-09-17 FR FR8215716A patent/FR2513141A1/en active Granted
- 1982-09-17 CA CA000411689A patent/CA1181928A/en not_active Expired
-
1983
- 1983-07-08 IN IN849/CAL/83A patent/IN159058B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| GB2106489A (en) | 1983-04-13 |
| DE3233201C2 (en) | 1986-04-24 |
| JPS5864118A (en) | 1983-04-16 |
| GB2106489B (en) | 1984-10-24 |
| DE3233201A1 (en) | 1983-04-14 |
| IN159058B (en) | 1987-03-14 |
| FR2513141B1 (en) | 1985-03-15 |
| AU548689B2 (en) | 1986-01-02 |
| ZA826566B (en) | 1983-07-27 |
| FR2513141A1 (en) | 1983-03-25 |
| AU8780082A (en) | 1983-03-24 |
| JPS6141247B2 (en) | 1986-09-13 |
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