CA1097486A - Process and apparatus for reducing the so.sub.2 content of a hot flue gas - Google Patents
Process and apparatus for reducing the so.sub.2 content of a hot flue gasInfo
- Publication number
- CA1097486A CA1097486A CA275,844A CA275844A CA1097486A CA 1097486 A CA1097486 A CA 1097486A CA 275844 A CA275844 A CA 275844A CA 1097486 A CA1097486 A CA 1097486A
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- Prior art keywords
- flue gas
- drying zone
- zone
- scrubbing
- drying
- Prior art date
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- Expired
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Abstract
ABSTRACT OF THE DISCLOSURE
In a process and apparatus for reducing the sulfur dioxide content of a hot flue gas, it is known to bring a lime slurry into contact with the gas to remove sulfur dioxide there-from and leave a highly liquid waste sludge product the dis-posal of which is a serious problem. In this invention, during the contact, the lime slurry flows from a scrubbing zone to a drying zone while the gas flows from the drying zone to the scrubbing zone, with the result that the waste sludge product is efficiently dewatered to a low moisture content by evapora-tion in the drying zone from the heat of the incoming flue gas and is thereby made easily disposable and exceptionally suitable for use as landfill.
In a process and apparatus for reducing the sulfur dioxide content of a hot flue gas, it is known to bring a lime slurry into contact with the gas to remove sulfur dioxide there-from and leave a highly liquid waste sludge product the dis-posal of which is a serious problem. In this invention, during the contact, the lime slurry flows from a scrubbing zone to a drying zone while the gas flows from the drying zone to the scrubbing zone, with the result that the waste sludge product is efficiently dewatered to a low moisture content by evapora-tion in the drying zone from the heat of the incoming flue gas and is thereby made easily disposable and exceptionally suitable for use as landfill.
Description
~974~6 This invention relates to a process and an apparatus for reducing the sulur dioxide content of a hoi flue gas.
A tubular rotating scrubber for removing sulfur di-oxide from stack gases by tumbling contact of a li.me slurry has been described in the following U~S.A. publications and various oral presentations of similar context:
tl) Lewis, C.J., "New Concept for Scrubbing Gases", Brick and Clay Record, June
A tubular rotating scrubber for removing sulfur di-oxide from stack gases by tumbling contact of a li.me slurry has been described in the following U~S.A. publications and various oral presentations of similar context:
tl) Lewis, C.J., "New Concept for Scrubbing Gases", Brick and Clay Record, June
(2) Lewis, CoJo, "Lime, Limestone Employed in New Gas Scrubbing Concept", Pi~ and Quarry, July 1973;
(3) Lewis, C.Jo, "Aqueous Lime Scrubber Simplifies Sulfur Dioxide Removal", lS R~o ~ , July 1974.
The Lewis system eectively removes sulfur dioxide rom a 1ue gas, but the waste sludge produot normally contains rom about 50 to 80 per cent by weight of free moisture. This sludge poses a waste solids disposal problem because of its semi-solid nature and substantial quantity. An aim o this invention is to provide a process and a scrubber ~or removing sulfur dioxide from flue gas which minimizes the amount of free moisture in the waste productO
According to the inven~ion, there is provided a pro--~ 25 cess for reducing the sulur dioxide content of a hot flue gas, comprising continuously contacting the flue gas with a counter-current stream of lime slurry in contiguous scrubbing and dry-ing zones whereby sulur dioxide is removed rom the 1ue ~
. .
.: ~ ' :
7~
by said lime slurry in the scrubbing zone and the wa~te sludge product formed is simultaneously dewatered by evaporation in the drying zone downstream of said scrubbing zone by contact with the incoming flue gas, the free moisturo content of said dewatered sludge leaving said drying zone b~ing controlled to be from 5 to 25 weight percent.
We also provide a flue gas s~rubber for reducing the sulfur dioxide content of~a hot flue gas, compri~ing an elongat-ed tubular drum rotatably drivabl2 about it longitudinal ~xis and having a scrubbing zone ext~nding inwar~ly from one end ther~of contiguous with a drying zone ~xtending lnwardly from the other-end thereof, said.drum including slurry retain1ng means at the interface of said zones, a gas inlet di~posed at the drying zone end for introducing hot ~lue gas int~ th~ drum ~or flow through it from the drylng zon~ end tQ the scrub~ing zone end, a gas outlet at the scrubbing zon~ end, slurry fe~ding means on the drum for intrGducing lime slurry into the drum for flow through it from the scrubbing zonz en~ to the drying.zone end, kumbling means in the scrubbing zone for intimately mixing the slurry with the ga~ to caus~ the 31urry to combine with sulfur dioxide components of tho gas and be tran~formed int~ a waste slu~g~ product, and collecting m~an~ ~t the drying zone end o~ the drum for ~onducting the waste Blu~e product out of th~ drum after it has been d~watered ~y evaporatio~ fr~m aonta~t in the drying zone with the hot flue gas introduced at the dry-ing zone end and flowing through the drying zone, the drying zone and gas inlet being so arranged that tho d~watered wast~
sludge product is disoharged with a moistur~ content of about 5 to 25 percent w~ight.
0 Pre~erably, ~he moisture oon~en~ of the waste sludge .
~a79L~6 product is reduced to about 5 to 15 per cent by wei~ht.
Agitating and substantially smooth nodulizing portions ~f the drying zone may advantageously be separated by a low annular baffle or dam. An advantageous axample of the scrub-ber of this invention has a drum which is about 75 to 10~ feet long with a diameter of about 10 to 15 feet; the scrubbing zone is about 30 to 50 feet long with the remainder of the drum comprising the drying zone.
In order that the invention may be more fully under-stood, it will now be described in conjunction with the accom-panyings drawings, in which:
Fig. 1 is a diagrammatic side view in elevation partially in cross section of a scrubber installation which in-corporates one embodiment of a scrubber capable of carrying out the process of this invention;
Fig. 2 is a cross-sectional view taken through FigO
1 along the line 2-2; and Fig. 3 is another cross-~ectional view taken through Fig. 1 along the line 3-3.
In Fig. 1 is shown flue ga~ scrubber system 30 incor-porating an elongated tubular drum 32 mounted to rotate about a slightly inclined longitudinal axis 34. ~he inclination is, for example, 1/8 inch per foot. Tubular drum 32 is about 88 feet long with an internal diameter of about 11 feet. The - 25 ~Qn~btng 5ection 36 is about 40 feet long and a drying section 38 comprises the remainder of drum 32, The drying section 38 includes an agitating portion 40 and a substantially smooth nodulizing portion 42 adjacent the exit 44. Drum 32 is rotated by pinion gear 46 engaged by bull gear 48 mounted to the out-;~~` 30 side of the drum 32. Electric motor 50 connected to pinion a741~6 gear 46 supplies the rotating force. The drum 32 is rotatably supported or cradled in tires 47 mounted to engage rim 49.
Although two such tire and rim support systems are shown in Fig. 1, more such ~lpport sys~ oould be used dep~rg on thelength o~ drum to be supported and rotated.
Lime, or limestone, slurry 19 is introduced in the direction of arrow 52 through supply pipe 54 into entrance 56 of scrubbing section 36. Slurry 19 is prepared in a mixing tank 57 into which lime or limestone is fed from storage tower 58 and water is introduced through piping 60 in amounts regulat-ed ~y automatic control valve 62. Flue gases designated by arrow 16 axe introduced through inlet duct 64 and bonnet 66 into the end 68 of drying section 38 and flow through drum 32. The treated gases 70 flow out of the end 72 of scrubbing section 36 and through bonnet 74, outlet duct 76 and fan 78 to exhaust to atmosphere. SO2 gas sampler and control unit 77 is connected to exhaust gas duct 76, This unit controls the sulfur dioxide content in the treated gas that is esaaping into the atmosphere by increasing or decreasing the amount of slurry volume through regulation of slurry flow control valve 53 mounted in slurry supply line 54.
Scrubbing section 36 includes tumbling means 80 in-cluding a cage 8~ to which chain assembly 84 is connected. Cage 82 is removably inserted within scr~bbing section 36 to facil-itate cleaning. Chain assembly 84 is connected to cage 82 fortumbling and agitating slurry 19 into intimate contact with flue gas 16 to remove the sulfur dioxide from it and to form waste pxoduct 86, which passes through drying section 38 as later de-scribed. Cage 82 includes longitudinal ribs which are formed ` 30 as scoops 88, as shown in Fig 2, which dispexse and distribute ~L~97486 slurry 19 throughout the interior of scrubbing section 36 during drum rotation. Scoops 88 and chain assembly 84 tumble lime slurry 19 within the flow of flue gas 16 to intimately mix and react them with each other to scrub and substantially remove sulfur dioxide components from gas 16 before it flows ou~ of end 72 of scrubbing section 36 in the form of treated or scrubbed gas 70 which.is exhausted to the atmosphere. The scrubber system 30 reduaes the sulfur dioxide content, for example, from about 2000-4000 ppm in flue gas 16 to about 500 ppm or less in treated gas 70.
Scrubbing section 36 is separatad from drying section 38 by annular dam 92 which ensures that a substantial height of slurry 19 is retained within scrubbing section 36.
Drying section 38 include~ an agitating portion 40 and a substantially smooth or nodulizing portion 42 separated from each other by another annular dam 98. The nodulizing portion 42 retains waste product 86 wit~in drying section 38 for a su~fici-ent time to be ncdulized and to ba dri~ by ~lue gas 16, which flows through the entire length o~ ~ m 32. ~ot flue gases 16 are rem~ved from stack 104 : 20 by inlet duct 64 connected ~elow ~ran~se sealing baffle 106. Stack io4 is, for example, the flue for boiler iO8 and conducts a flow of flue gases having a substantial sulfur dioxide content when coal or fuel oil of high sulfur content is burned in boiler 108.
An anchored agitating chain assembly 110 is mounted in agitating portion 40 of drying section 38. Agitation chain 110 is of an inclined aonfiguration and is connected, for example, as shown in Figs. 1 and 3 to help agitate w~t waste product 86 throughout the flow of hot flue gas 16 to help lower the moisture content of waste product 86 before it flows . 30 out of exit 44 of drying saction 38. The chain assembly 110 --6~
:
741~6 keepc scale from building up on the inside of drum 32 by its constant innerwall contact. In addition, the chains are used as supplemental heat conductors to the waste product 86 since they will conduct the heat from the flue gas 16. Waste product 5 86 has a free moisture content of, for example, from about 50 to 80 per cent by weight as it passes from scrubbing section 36 to drying section 38. The hot flue gases 16 introduced through duct 64 are at about 400F. and remarkably reduce the moisture content of waste product 86 passing through drying 1~ section 38, The water transfer to the flue gas 16 as it passes through drying section 38 remarkably reduces the temperature of the flue gas 16 before it reaches scrubbing section 36.
~ emperature sensor 112 disposed within drying section 38 is connected through control system 114 to spray pipe 116 ; 15 in n~dulizing portion 4~ to maint:ain dried waste product 102 at a temperature of about 170F. and a free moisture content of about 5 to 25, especially 5 to 15, per cent by weight as it is discharged in the direction oi~ arrow 118 into colleating hopper 120. Waste product 102 i8 removed through collecting 20 and discharging system 122 and transported away from the scrubbing system by truck 124.
The only controlled variable in the drying section 38 is the free moisture content of the discharged solids 102.
The desired free moisture content is estimated to be between 25 about 5 and 25 weight per cent. A moisture content of less than 5 per cent tends to create fugitive dusting in the solids handling systems. A moisture aontent much in excess of 25 per cent causes the solids to be excessively fluid in additdon to increasing the amount of solids for disposal.
3Q The free moisture content of the ~ischarged solids 102.
.
. . . .
, ~ .: . : .: :.
.
:: .
is controlled by an empirical correlation between the moisture content and the solids temperature. Solids temperature at the point 44 at which solids leave the drying section 38 is :
monitored by an infrared temperature sensor 112. An output signal from this sensor controls the addition of water to the drying section 38 via a spray pipe 116O Thus, once the entire scrubber system has been started, a solids discharge temperature corresponding to the desired free moisture content is selected. ;~
This moisture content is then maintained by the automatically controlled addition of water to the drying section 38.
The flue gas scrubber as described herein, because of its method of operation`-in which hot flue gas is continuous-ly contacted with a countercurrent stream of lime slurry in con-tiguous scrubbing and drying zones, is r~markably efficient, not only for removing the sulfur dioxide from the flue gas but also from the standpoint of energy conser~ation. The sulfur dioxide is effectively removed in a scrubbing zone by the lime slurry and the waste produat sludge whiah i9 formed is simultaneously dewatered in the drying zone, downstream of the scrubbing zone in the airection of flow of the lime slurry, upon contact with the incoming hot flue gas, The flue gas enters the drying zone at from about 350 to 550JF. and leave~
the scrubbing zone at from about 120 to 180F. Fly ash pxesent in the incoming hot flue gas is also removed, in the drying as well as the scrubbing zone, and discharged in the dewatered sludge, which leaves the drying zone at from about 100 to 200~F. Thus a readily disposable waste product, suit-ably with a free moisture content of about S to 25 weight per cent, is obtained with no additional energy consumptionO
This waste product is also readily adaptable for use ~97~6 as landfill. A prior process for producing landfill from scrubber sludge is described in a brochure entitled "Poz-o-TecG~" distributed by IU Conversion Systems, Inc., Philadelphia, Pennsylvania. As described in that brochure~ the "Poz-O-Tec~' system treats hot flue gas, after electrostatic precipitation of its fly ash content, in a sulphur dioxide scrubber, and the resultant sludge is then dewatered by thickening and filtra-tion steps and recombined with the separated fly ash and other additives in the production of wet stabilized material suitable for landfill.
In the process of the present invention such a land-fill product can be produced in a single step. The sulfur di-oxide and fly ash are effectively removed from flue gas in the novel process of the present invention and the sludge which forms is simultaneously dewatered in the drying zone thereof.
This process affords the ability to discharge a solid waste product of whatever moisture content may be desired, for example, from about 5 to 25 weight per cent as already set forth hereinbefore. Such solid waste is eminently suitable for use as landfill. Other substances such as boiler bottom ash may be incorporated in the solid--waste if desired for the use as landfill.
The Lewis system eectively removes sulfur dioxide rom a 1ue gas, but the waste sludge produot normally contains rom about 50 to 80 per cent by weight of free moisture. This sludge poses a waste solids disposal problem because of its semi-solid nature and substantial quantity. An aim o this invention is to provide a process and a scrubber ~or removing sulfur dioxide from flue gas which minimizes the amount of free moisture in the waste productO
According to the inven~ion, there is provided a pro--~ 25 cess for reducing the sulur dioxide content of a hot flue gas, comprising continuously contacting the flue gas with a counter-current stream of lime slurry in contiguous scrubbing and dry-ing zones whereby sulur dioxide is removed rom the 1ue ~
. .
.: ~ ' :
7~
by said lime slurry in the scrubbing zone and the wa~te sludge product formed is simultaneously dewatered by evaporation in the drying zone downstream of said scrubbing zone by contact with the incoming flue gas, the free moisturo content of said dewatered sludge leaving said drying zone b~ing controlled to be from 5 to 25 weight percent.
We also provide a flue gas s~rubber for reducing the sulfur dioxide content of~a hot flue gas, compri~ing an elongat-ed tubular drum rotatably drivabl2 about it longitudinal ~xis and having a scrubbing zone ext~nding inwar~ly from one end ther~of contiguous with a drying zone ~xtending lnwardly from the other-end thereof, said.drum including slurry retain1ng means at the interface of said zones, a gas inlet di~posed at the drying zone end for introducing hot ~lue gas int~ th~ drum ~or flow through it from the drylng zon~ end tQ the scrub~ing zone end, a gas outlet at the scrubbing zon~ end, slurry fe~ding means on the drum for intrGducing lime slurry into the drum for flow through it from the scrubbing zonz en~ to the drying.zone end, kumbling means in the scrubbing zone for intimately mixing the slurry with the ga~ to caus~ the 31urry to combine with sulfur dioxide components of tho gas and be tran~formed int~ a waste slu~g~ product, and collecting m~an~ ~t the drying zone end o~ the drum for ~onducting the waste Blu~e product out of th~ drum after it has been d~watered ~y evaporatio~ fr~m aonta~t in the drying zone with the hot flue gas introduced at the dry-ing zone end and flowing through the drying zone, the drying zone and gas inlet being so arranged that tho d~watered wast~
sludge product is disoharged with a moistur~ content of about 5 to 25 percent w~ight.
0 Pre~erably, ~he moisture oon~en~ of the waste sludge .
~a79L~6 product is reduced to about 5 to 15 per cent by wei~ht.
Agitating and substantially smooth nodulizing portions ~f the drying zone may advantageously be separated by a low annular baffle or dam. An advantageous axample of the scrub-ber of this invention has a drum which is about 75 to 10~ feet long with a diameter of about 10 to 15 feet; the scrubbing zone is about 30 to 50 feet long with the remainder of the drum comprising the drying zone.
In order that the invention may be more fully under-stood, it will now be described in conjunction with the accom-panyings drawings, in which:
Fig. 1 is a diagrammatic side view in elevation partially in cross section of a scrubber installation which in-corporates one embodiment of a scrubber capable of carrying out the process of this invention;
Fig. 2 is a cross-sectional view taken through FigO
1 along the line 2-2; and Fig. 3 is another cross-~ectional view taken through Fig. 1 along the line 3-3.
In Fig. 1 is shown flue ga~ scrubber system 30 incor-porating an elongated tubular drum 32 mounted to rotate about a slightly inclined longitudinal axis 34. ~he inclination is, for example, 1/8 inch per foot. Tubular drum 32 is about 88 feet long with an internal diameter of about 11 feet. The - 25 ~Qn~btng 5ection 36 is about 40 feet long and a drying section 38 comprises the remainder of drum 32, The drying section 38 includes an agitating portion 40 and a substantially smooth nodulizing portion 42 adjacent the exit 44. Drum 32 is rotated by pinion gear 46 engaged by bull gear 48 mounted to the out-;~~` 30 side of the drum 32. Electric motor 50 connected to pinion a741~6 gear 46 supplies the rotating force. The drum 32 is rotatably supported or cradled in tires 47 mounted to engage rim 49.
Although two such tire and rim support systems are shown in Fig. 1, more such ~lpport sys~ oould be used dep~rg on thelength o~ drum to be supported and rotated.
Lime, or limestone, slurry 19 is introduced in the direction of arrow 52 through supply pipe 54 into entrance 56 of scrubbing section 36. Slurry 19 is prepared in a mixing tank 57 into which lime or limestone is fed from storage tower 58 and water is introduced through piping 60 in amounts regulat-ed ~y automatic control valve 62. Flue gases designated by arrow 16 axe introduced through inlet duct 64 and bonnet 66 into the end 68 of drying section 38 and flow through drum 32. The treated gases 70 flow out of the end 72 of scrubbing section 36 and through bonnet 74, outlet duct 76 and fan 78 to exhaust to atmosphere. SO2 gas sampler and control unit 77 is connected to exhaust gas duct 76, This unit controls the sulfur dioxide content in the treated gas that is esaaping into the atmosphere by increasing or decreasing the amount of slurry volume through regulation of slurry flow control valve 53 mounted in slurry supply line 54.
Scrubbing section 36 includes tumbling means 80 in-cluding a cage 8~ to which chain assembly 84 is connected. Cage 82 is removably inserted within scr~bbing section 36 to facil-itate cleaning. Chain assembly 84 is connected to cage 82 fortumbling and agitating slurry 19 into intimate contact with flue gas 16 to remove the sulfur dioxide from it and to form waste pxoduct 86, which passes through drying section 38 as later de-scribed. Cage 82 includes longitudinal ribs which are formed ` 30 as scoops 88, as shown in Fig 2, which dispexse and distribute ~L~97486 slurry 19 throughout the interior of scrubbing section 36 during drum rotation. Scoops 88 and chain assembly 84 tumble lime slurry 19 within the flow of flue gas 16 to intimately mix and react them with each other to scrub and substantially remove sulfur dioxide components from gas 16 before it flows ou~ of end 72 of scrubbing section 36 in the form of treated or scrubbed gas 70 which.is exhausted to the atmosphere. The scrubber system 30 reduaes the sulfur dioxide content, for example, from about 2000-4000 ppm in flue gas 16 to about 500 ppm or less in treated gas 70.
Scrubbing section 36 is separatad from drying section 38 by annular dam 92 which ensures that a substantial height of slurry 19 is retained within scrubbing section 36.
Drying section 38 include~ an agitating portion 40 and a substantially smooth or nodulizing portion 42 separated from each other by another annular dam 98. The nodulizing portion 42 retains waste product 86 wit~in drying section 38 for a su~fici-ent time to be ncdulized and to ba dri~ by ~lue gas 16, which flows through the entire length o~ ~ m 32. ~ot flue gases 16 are rem~ved from stack 104 : 20 by inlet duct 64 connected ~elow ~ran~se sealing baffle 106. Stack io4 is, for example, the flue for boiler iO8 and conducts a flow of flue gases having a substantial sulfur dioxide content when coal or fuel oil of high sulfur content is burned in boiler 108.
An anchored agitating chain assembly 110 is mounted in agitating portion 40 of drying section 38. Agitation chain 110 is of an inclined aonfiguration and is connected, for example, as shown in Figs. 1 and 3 to help agitate w~t waste product 86 throughout the flow of hot flue gas 16 to help lower the moisture content of waste product 86 before it flows . 30 out of exit 44 of drying saction 38. The chain assembly 110 --6~
:
741~6 keepc scale from building up on the inside of drum 32 by its constant innerwall contact. In addition, the chains are used as supplemental heat conductors to the waste product 86 since they will conduct the heat from the flue gas 16. Waste product 5 86 has a free moisture content of, for example, from about 50 to 80 per cent by weight as it passes from scrubbing section 36 to drying section 38. The hot flue gases 16 introduced through duct 64 are at about 400F. and remarkably reduce the moisture content of waste product 86 passing through drying 1~ section 38, The water transfer to the flue gas 16 as it passes through drying section 38 remarkably reduces the temperature of the flue gas 16 before it reaches scrubbing section 36.
~ emperature sensor 112 disposed within drying section 38 is connected through control system 114 to spray pipe 116 ; 15 in n~dulizing portion 4~ to maint:ain dried waste product 102 at a temperature of about 170F. and a free moisture content of about 5 to 25, especially 5 to 15, per cent by weight as it is discharged in the direction oi~ arrow 118 into colleating hopper 120. Waste product 102 i8 removed through collecting 20 and discharging system 122 and transported away from the scrubbing system by truck 124.
The only controlled variable in the drying section 38 is the free moisture content of the discharged solids 102.
The desired free moisture content is estimated to be between 25 about 5 and 25 weight per cent. A moisture content of less than 5 per cent tends to create fugitive dusting in the solids handling systems. A moisture aontent much in excess of 25 per cent causes the solids to be excessively fluid in additdon to increasing the amount of solids for disposal.
3Q The free moisture content of the ~ischarged solids 102.
.
. . . .
, ~ .: . : .: :.
.
:: .
is controlled by an empirical correlation between the moisture content and the solids temperature. Solids temperature at the point 44 at which solids leave the drying section 38 is :
monitored by an infrared temperature sensor 112. An output signal from this sensor controls the addition of water to the drying section 38 via a spray pipe 116O Thus, once the entire scrubber system has been started, a solids discharge temperature corresponding to the desired free moisture content is selected. ;~
This moisture content is then maintained by the automatically controlled addition of water to the drying section 38.
The flue gas scrubber as described herein, because of its method of operation`-in which hot flue gas is continuous-ly contacted with a countercurrent stream of lime slurry in con-tiguous scrubbing and drying zones, is r~markably efficient, not only for removing the sulfur dioxide from the flue gas but also from the standpoint of energy conser~ation. The sulfur dioxide is effectively removed in a scrubbing zone by the lime slurry and the waste produat sludge whiah i9 formed is simultaneously dewatered in the drying zone, downstream of the scrubbing zone in the airection of flow of the lime slurry, upon contact with the incoming hot flue gas, The flue gas enters the drying zone at from about 350 to 550JF. and leave~
the scrubbing zone at from about 120 to 180F. Fly ash pxesent in the incoming hot flue gas is also removed, in the drying as well as the scrubbing zone, and discharged in the dewatered sludge, which leaves the drying zone at from about 100 to 200~F. Thus a readily disposable waste product, suit-ably with a free moisture content of about S to 25 weight per cent, is obtained with no additional energy consumptionO
This waste product is also readily adaptable for use ~97~6 as landfill. A prior process for producing landfill from scrubber sludge is described in a brochure entitled "Poz-o-TecG~" distributed by IU Conversion Systems, Inc., Philadelphia, Pennsylvania. As described in that brochure~ the "Poz-O-Tec~' system treats hot flue gas, after electrostatic precipitation of its fly ash content, in a sulphur dioxide scrubber, and the resultant sludge is then dewatered by thickening and filtra-tion steps and recombined with the separated fly ash and other additives in the production of wet stabilized material suitable for landfill.
In the process of the present invention such a land-fill product can be produced in a single step. The sulfur di-oxide and fly ash are effectively removed from flue gas in the novel process of the present invention and the sludge which forms is simultaneously dewatered in the drying zone thereof.
This process affords the ability to discharge a solid waste product of whatever moisture content may be desired, for example, from about 5 to 25 weight per cent as already set forth hereinbefore. Such solid waste is eminently suitable for use as landfill. Other substances such as boiler bottom ash may be incorporated in the solid--waste if desired for the use as landfill.
Claims (13)
1, A process for reducing the sulfur dioxide content of a hot flue gas, comprising continuously contacting the flue gas with a countercurrent stream of lime slurry in contiguous scrubbing and drying zones whereby sulfur dioxide is removed from the flue gas by said lime slurry in the scrubbing zone and the waste sludge product formed is simultaneously dewatered by evaporation in the drying zone downstream of said scrubbing zone by contact with the incoming flue gas, the free moisture content of said dewatered sludge leaving said drying zone being controlled to be from about 5 to 25 weight per cent.
2. A process according to claim 1, wherein said moisture content is maintained by controlled addition of water in said drying zone.
3. A process according to claim 1, wherein said flue gas enters said drying zone at from about 350 to 550°F. and leaves said scrubbing zone at from about 120 to 180°F,
4. A process according to claim 1, wherein said de-watered sludge leaves said drying zone at a temperature of from about 100 to 200°F,
5. A process according to claim 1, wherein said flue gas enters said drying zone with a sulfur dioxide content of from about 2000 to 4000 ppm and leaves said scrubbing zone with a sulfur dioxide content of about 500 ppm or less.
6. A process according to claim 1, wherein fly ash is removed from said flue gas by said slurry in said scrub-bing and drying zones and is incorporated in the dewatered waste sludge product to form landfill therewith.
7. A process according to claim 6, wherein boiler bottom ash is added to the landfill formed by the incorpor-ation of the fly ash in the dewatered waste sludge product.
8. A flue gas scrubber for reducing the sulfur dioxide content of a hot flue gas, comprising an elongated tubular drum rotatably drivable about its longitudinal axis and having a scrubbing zone extending inwardly from one end thereof contiguous with a drying zone extending inwardly from the other end thereof, said drum including slurry retaining means at the interface of said zones, a gas inlet disposed at the drying zone end for introducing hot flue gas into the drum for flow through it from the drying zone end to the scrubbing zone end, a gas outlet at the scrubbing zone end, slurry feeding means on the drum for introducing lime slurry into the drum for flow through it from the scrubbing zone end to the drying zone end, tumbling means in the scrubbing zone for intimately mixing the slurry with the gas to cause the slurry to combine with sulfur dioxide components of the gas and be transformed into a waste sludge product, and collecting means at the drying zone end of the drum for conducting the waste sludge product out of the drum after it has been dewatered by evaporation from contact in the drying zone with the hot flue gas introduced at the drying zone end and flowing through the drying zone, the drying zone and gas inlet being so arranged that the dewatered waste sludge product is discharged with a moisture content of about 5 to 25 per cent by weight.
9. A flue gas scrubber according to claim 8, wherein the longitudinal axis of the tubular drum slopes slightly downwardly from the scrubbing zone end to the drying zone end to cause the slurry and waste sludge product to flow through the tubular drum.
10. A flue gas scrubber according to claim 8, wherein liquid-spraying means and temperature-sensing means are disposed within the end of the drying zone and are connected by control means for controlling the moisture content of the discharged waste sludge product,
11. A flue gas scrubber according to claim 8, wherein the drying zone includes an agitating portion disposed adjacent the scrubbing zone and a substantially smooth portion disposed adjacent the drying zone end.
12. A flue gas scrubber according to claim 11, wherein an annular dam is disposed between the agitating and substantially smooth portions of the drying zone.
13. A flue gas scrubber according to claim 8, wherein the slurry retaining means is an annular dam.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA275,844A CA1097486A (en) | 1977-04-07 | 1977-04-07 | Process and apparatus for reducing the so.sub.2 content of a hot flue gas |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA275,844A CA1097486A (en) | 1977-04-07 | 1977-04-07 | Process and apparatus for reducing the so.sub.2 content of a hot flue gas |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1097486A true CA1097486A (en) | 1981-03-17 |
Family
ID=4108353
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA275,844A Expired CA1097486A (en) | 1977-04-07 | 1977-04-07 | Process and apparatus for reducing the so.sub.2 content of a hot flue gas |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1097486A (en) |
-
1977
- 1977-04-07 CA CA275,844A patent/CA1097486A/en not_active Expired
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