CA1302049C - Method and system for simultaneously scrubbing cement kiln exhaustgas and producing useful by-products therefrom - Google Patents
Method and system for simultaneously scrubbing cement kiln exhaustgas and producing useful by-products therefromInfo
- Publication number
- CA1302049C CA1302049C CA000542492A CA542492A CA1302049C CA 1302049 C CA1302049 C CA 1302049C CA 000542492 A CA000542492 A CA 000542492A CA 542492 A CA542492 A CA 542492A CA 1302049 C CA1302049 C CA 1302049C
- Authority
- CA
- Canada
- Prior art keywords
- alkali
- slurry
- solution
- alkaline earth
- earth metal
- 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 - Lifetime
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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
- B01D53/60—Simultaneously removing sulfur oxides and nitrogen oxides
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B7/00—Hydraulic cements
- C04B7/36—Manufacture of hydraulic cements in general
- C04B7/60—Methods for eliminating alkali metals or compounds thereof, e.g. from the raw materials or during the burning process; methods for eliminating other harmful components
Abstract
Abstract of the Disclosure This invention provides a method and system for simultaneously scrubbing acidic exhaust gases and removing alkali and alkaline earth metal salts from waste dust from a cement plant or the like thereby producing useful products from what would otherwise be wasted. In essence the two wastes are combined in water and the resulting solution and precipitate separated in a tank. The solu-tion is useful both to cool incoming waste gas and as a fertilizer, whilst the precipitate is suitable as kiln feed stock.
Description
~L3~ 9 Backqround of the Invention This invention relates to the treatment of kiln dust and exhaust fumes from a cement facility to convert the former into a useful product while removing pollutants from the latter.
. Dust collection facilities operating at cement or lime producing kilns remove particulate matter from the kiln exhaust. This particulate matter includes calcium carbonate, calcium oxide, and the oxides and carbonates of other metals, depending on. the com~osltion of t~e feed stock to the kiln. Two elements ~requentl~v present in the kiln dust are potassium and sodium. These elements limi.t or prevent the reuse of the kiln dust as kiln feed stock, since they interfere with.the properties o~ the final pro-duct, and the dust is therefore discarded. These dust collection facilities do not remove sufficient gaseous pollutants from the exhaust.stream and separate scrubbers must be provided if they are to be prevented from entering the atmosphere.~
The use of alkali or alkaline earth materials, as solids or in a slurry or in a solution, for ~crubbing tremoving sulfur ~nd nitrogen o~ides) of exhaust gas has been known ~or years (see discussion in Canadian Patent Application No~ 521,8i9, f~led 30 October, 1986). For example, Mehlmann (1985, Zement-Kalk-Gips Edition B) ~escribes the use of hydrated or pulverized limestone at temperatures up to`ll00CJ or of spray dryLng with hydrated lime; and ~yer (19790 EPA-600/7-79-167b) describes the use of lime to scrub exhaust gas from a heating plant. Limestone may be .. . . ...
~3~21~
included in the charge of fluidized bed furnaces for the same purpose. In general the oxides of carbon, sulfur, and nitrogen, present in exhaust gas, when reacted with water, produce acids, including sulfuric, sulfurous, nitric, and carbonic~ The presence and amounts of each depend on the oxides present, the availability of oxygen, and the reaction conditions~ When these acids are reacted with the oxides, hydroxides, or carbonates of alkali or alkaline ea th metals, salts of the components are formed.
For example, sulfuric acid will react with the calcium carbonate present in limestone to yield calcium sulfate.
The principal object of the present invention is to provide a method and apparatus to eliminate the dust disposal problem present in cement plants and simultane-ously to reduce gaseous and particulate emissions and to be able to do so C05t effectively, including the conver-sion of otherwise waste products into useful products.
Brief Summary of the Invention This invention provides a process that removes a significant portion of the potassium, sodium and sulfur in kiln dust, so that the dust may be reused as kiln feed;
and at the same time uses the kiIn dust as a reactant for removing the oxides of sulfur, nitrogen and carbon from the exhaust stream.
More specifically, the process will react cement kiln dust or lime kiln dust with acid, produced from the acidic oxides of sulfur, nitrogen and carbon in exhaust gas, to dissolve some components of the dust and renaer the remaining undissolved solids reuseable as process feed stock; scrub a portion of the oxides of sulfur, nitrogen and carbon from the exhaust stream and make them available for reaction with kiln dust; produce as a by~product alkali and alkaline earth metal salts composed of the scrubbed exhaust gas sulfur, nitrogen and carbon oxides and materials derived from the kiln dust; and utilize heat in the exhaust stream to reduce the water content of the ~L3t~}2G~4~
process stream containing the dissolved alkali and alka-line earth metal salts.
In accordance with the invention, there is pro-vided a method of simultaneously scrubbing an exhaust gas stream having acidic oxides and treating dust having alkali and alkaline earth metal compounds as solids, com-prising the steps of: (a) mixing the dust with water ~o form an alkaline (p~ greater than 7) solution and ~b) passing the gas stream into the said alkaline solution, whereby the said solution and gas react to form an alkali and alkaline earth metal salt solution and a precipitate of alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds.
Preferred methods include cooling and/or dehumidify-ing the gas ~tream prior to passing the same into the alkaline solution; utilizing the alkali and alka-line earth metal salt solution for the purpose of such cooling and/or dehumidifying; utilizing said precipitate together with insoluble silicates, aluminates and iron compounds to add to the feed stock of a cement plant to produce cement; utilizing the heat of the gas to remove water from the alkali and alkaline earth metal salt solu-tion aforesaid; utilizing the dissolved solids contents of the alkali salt solution as a fertilizer; and obtaining the exhaust gas stream and dust from the kiln of a cement plant.
In accordance with one aspect of the invention, there is provided a m~thod of converting dust from a cement kiln containing alkali and alkaline earth metal compounds as solids into a product suitable for adding to the feed stock for said kiln, comprising the steps of (a) dissolving the soluble portion of the dust in water to form an alkaline solution, and (b) passing exhaust gas from the kiln lnto the said solution, whereby the solution and gas react to form an alkali and alkaline earth metal salt solution and a precipitate of alkali and alkaline 3l3~Z~
earth metal salts with insoluble silicates, aluminates and iron compounds suitable for adding to the feed stock for the kiln. Preferably, thè gas is cooled and dehumidified prior to being passed into the alkaline solution, utiliz-ing the latter for such purpose, and water is evaporated from the alkali salt solution by heat from the gas.
In a preferred aspect there is provided a method of simultaneously scrubbing acidic oxides of sulfur, nitrogen and carbon from the hot exhaust stream ~rom a cement kiln and utilizing acids derived therefrom to pxoduce useful products from the carbonates and oxides of alkali and alkaline earth metals contained as solids in cement kiln dust comprising said carbonates and oxides and insoluble silicates, aluminates and iron compounds. The method comprises mixing the dust with water to form a slurry comprisiny undissolved solids and a solution of the soluble compounds in the dust. The gas stream is passed into the slurry whereby the acidic oxides contained therein will react with water to produce acids. The latter will react with the carbonates and oxides of alkali and alkaline earth metals to yield a solution of alkali and alkaline earth metal salts comprising principally the cationic components, calcium, potassium, magnesium and sodium, and anionic components, carbonate, sulfate and nitrate, and a precipitate o~ alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds. After passing through the slurry, the gas of the gas stream emerges as a scrubbed exhaust.
In accordance with a further aspect of the inven-tion, there is provided a method of simultaneously con-verting dust from a c~ment kiln containing alkali and alkaline earth metal compounds as solids into a product suitable for adding to the feed stock for the kiln, scrub-bing the exhaust gas stream from the kiln and producing alkali and alkaline earth metal salts suitable for use as fertilizer, comprising the steps of (a) dissolving the dust in water to form an alkaline solution, and (b) pass-ing exhaust gas from said kiln into the said solution, whereby said solution and gas react to scrub the latter '~
~ ~1 ~3~?;~
- 4a -and at the same time form an alkali and alkaline earth metal salt solution and a precipitate of alkali and alka-line earth metal salts with insoluble silicates, alumi-nates and iron compounds suitable for adding to the feed stock for said kiln, and, lastly, evaporating wate~ from the alkali and alkaline earth metal salt solution to pro-duce a concentrated solution or a precipitate suitable ~or use as fertilizer.
The invention also provides a system for simultaneously scrubbing acidic oxides of sulfur, nitrogen, and carbon from the hot exhaust gas stream from a cement kiln and utilizing acids derived therefrom to produce useful products from the carbonates and oxides of alkali and alkaline earth metal salts contained as solids in cement kiln dust, principally calcium carbonate, potassium carbonate, magnesium carbonate, sodium carbonate, calcium oxide, potassium oxide, and magnesium oxide, comprising said carbonates and oxides and insoluble silicates, aluminates and iron compounds. Such system comprises a means for mixing the cement kiln dust with water to form a slurry comprising undissolved solids and a solution of the soluble compounds in the cement kiln dust. There is a reaction chamber and a means for delivering the exhaust ~as stream into the reaction chamber and a means for delivering the slurry into the reaction chamber.
There is also a means for scrubbing the exhaust gas stream comprising means for contacting the exhaust gas stream with the slurry within the reaction chamber in a manner to cause the acidic oxides contained in the exhaust gas stream to react with water in the slurry to produce acids, and to cause the acids to react with carbonates and o~ides of alkali and alkaline earth metals salts comprising principally cationic components calcium, potassium, magnesium and sodium, and anionic components carbonate, sulfate and nitrate, and precipitates of alkali and alkaline earth metal sal~s with insoluble silicates, aluminates and iron compounds. There is also a means for removing scrubbed exhaust gas from the reaction chamber, means for removing a li~uid suspension of soluble compounds and undissolved solids '~
- 4b -from the reaction chamber, means for separating a solution of solub].e compounds ~rom undissolved solids and means for ~vaporating water from the solution of soluble compounds.
The invention also includes apparatus for simul-taneously scrubbing a gas stream containing acidic oxides and treating dust from a cement kiln or the like contain-ing alkali and alkaline earth metal salts, comprising a treatment tank, means for feeding a mixture of water and dust into the latter, means for feeding additional water into the said tank further to dilute the mixture afore-said, means for passing the gas into the mixture to react therewith and to thereby produce an aqueous solution of its water soluble components to form therewith a slurry of acidic oxides and alkali and alkaline earth metal salts ~j .
~3~J2~
and any remaining insoluble compounds, a precipitation tank, means for conveying the slurry from the treatment tank to the precipitation tank wherein the slurry is sepa-rated into solids and liquid, the former dropping toward the base of the tank beneath the latter which remains in the upper part thereof, means for removing the said solids from the base of the precipitation tank and means for removing the said liquid from the upper part of the pre-cipitation tank.
In a presently preferred embodiment, the appara-tus further comprises a heat exchanger, means for passing the said gas through the heat exchanger prior to being ~ed into the treatment tank and means ~or passing liquid removed frvm the precipitation tank through the heat exchanger, whereby the incoming gas stream is cooled and the said liquid simultaneously heated to remove the water therefrom.
Still further objects/ features and advantages of the invention will be apparent from the following detailed description of a presently preferred embodiment thereof taken in conjunction with the accompanying drawings.
~rief Description of the Drawinqs In the drawings, Fig. 1 is a schematic representation of one appa-ratus for practicing the invention;
Fig. 2 is a graph illustrating the effectiveness of removal of potassium and sulfur oxides from kiln dust during reaction with exhaust gas oxides according to the invention.
Detailed Description of Preferred Embodiment The invention comprises method and means for sup-plying alkali and alkaline earth me al compounds as solids, the kiln dust, water, and exhaust gas, and the method and apparatus for first combining and reacting the same and then separating the resulting components.
~3~ 4~
Briefly, the acidic gas and alkaline solids are mixed with water in a treatment tank and react to form a slurry. A settling tank is provided for the separation of precipitated and undissolved solids from the solution of water and dissolved solids in the slurry. A heat exchanger~crystallization unit is also provided and util-izes the heat, including latent heat, in the exhaust stream to evaporate water from the solution o dissolved salts in the slurry to provide cooling of the exhaust gas for use in the above process. ~eat for evaporation of water from the solution of dissolved salts is also obtained from the hot waste dust, the hydration reaction between dust and water, and energy obtained from compres-sion of the exhaust gas.
Referring to Fig. 1, a slurry, exiting at 8 from a dust and water mixing tank ~not shown), composed o alkali and alkaline earth metal salt solids and water, is pumped via pipe 10 into the treatment tank 12, along with additional water through inlet 14 from a suitable source (not shown) to produce a dilute slurry 16. Exhaust gas~
from a cement kiln or boiler (not shown) enters heat exchanger 22 through inlet 18 from which it emerges as cooled exhaust. Condensed exhaust gas moisture is col- -lected in the heat exchanger 22 and conveyed to the treat-ment tank 12 through pipe 44. The exhaust then travels to compressor 20 through pipe 23 and is delivered via pipe 24 to distribution pipes 26 in the bottom of the treatment tank 12. To prevent settling of the solids to the bottom of treatment tank 12 the slurry may be stirred or recir-culated by suitable means, for exa~ple by recirculation pump 27.
The exhaust gas bubbles through slurry 16 of alkaline solids and water to emerge from the tank tap as scrubbed exhaust 28~ Slurry 16, as a mixture o~ treated solid, water, and dissolved materials, is pumped by pump 32 via pipe 30 to the settling tank 3~ where the settled ~3~
solids 36 are pumped out by pump 38 and the water 37 laden with dissolved salts is pumped to heat exchanger 22 to provide cooling for the input exhaust gas. The water from salt solution 37 is evaporated to a vapor and release~ via pipe 40 to the atmosphere or the water is evaporated and then condensed to a liquid to recapture the latent heat for reuse. The salts from the salt solution 37 are con-centrated and/or precipitated and collected from the heat exchanger via pipe 42. The cationic components of the collected salts are principally calcium, potassium, magne-sium, and sodium. The anionic components of the salts are principally sulfate, carbonate and nitrate. The actual composition of the salts will depend on the init~al compo-sition of the kiln dust to be treated and on the composi-tion of the exhaust gas.
The heat exchanger 22 is a dual purpose heat exchanger-crystallization unit of a known type which will extract heat from the exhaust gas and use that heat, including latent heat derived from condensation of the exhaust gas moisture to evaporate water.
The Apparatus The whole system i5 created from well known parts combined by standard methods. For example, typically tbe treatment tank may have a volume of one million gallons and be provided with gas distribution and stirring means;
the settling tank may have a volume of 100 thousand gallons, both being constructed from stainless steel, or other suitable materials, such as rubber, which can toler-ate highly alkaline or acidic solutions.
Workin~ Principle The basic working principle in this invention is recombination and reaction of two waste streams produced during burning to provide mutual neutralization of the waste streams, production of a valuable and useful by-product, and utilization of low grade heat energy. The two waste streams are the gaseous oxides which produce ~3~ZC~
acidic solutions in water and the waste particulate matter from cement kilns, which produce basic solutions in water.
After partial dissolution in water, the two wastes react to neutralize each other. In the case of cement kiln dust, which contains excess potassium and/or sodium and sulfate, the process provides for dissolution of a significant proportion of the remaining undissolved solids which include calcium and magnesium salts. The resultin~ solids are therefore suitable for use as process feed stock. The potassium sulfate and other salts removed from the heat exchanger-crystallization unit are suitable as fertilizer or as a source of material for extraction of chemicals. At the same time, the exhaust gas passing through the slurry in ~he treatment tank is cleansed of a signiEicant portion of the oxides of sulfur and nitrogen, by forming sulfates and nitrates.
~xampie The discussion that follows is an example of use of the process in a moderate size wet process cement pro-ducing facility.
Exhaust gas from the kiln baghouse, fed through duct 18, is introduced to heat exchanger 22 at a rate of 200,000 actual cubic feet per minute by compressor 20~
The exhaust gas is vari-able in composition, but contains roughly 29~ water, 25~ carbon dioxide, 36% nitrogen, 10%
oxygen and 400 to 600 ppm nitrogen oxides and 200 ppm sul-fur dioxide. In heat exchanger 22 the exhaust gas is cooled and water is condensed, resulting in a 35% to 40%
decrease in flow volume. The exhaust gas is then drawn by compressor 20 through pipe 23 for delivery through pipe 24 to distribution pipes 26 and allowed to react with slurry 16 where most of the oxides of sulfur and nitrogen are remo~ed. In lab scale trials 99% of the SO2 was removed from the exhaust stream.
Kiln dust is introduced to treatment tank 12 at a rate of eight to ~welve tons per hour dry weight~ Water ~3~
g is added to produce a dilute slurry of up to 95~ water content. The slurry water content is determined by the initial concentration of potassium and sodium in the waste dust and on the desired concentration in the material to I be returned to the kiln feed system. After reaction with the exhaust gas, the slurry of treated dust is pumped at a rate of approximately 200 gallons per minute to settling tank 34. In this tank the solids settle to form a slurry of approximately 35% water and 65% solids, beneath a solu-tion of water and soluble salts dissolved during treat-ment. The slurry is pumped by pump 38 from tank 34 and combined with process feed for a cement plant at a rate of approximately 7.8 tons per hour of solids. The water I solution is pumped through outlet 37 to heat exchanger 22 at approximately 200 gallons per minute to provide coolinq for the exhaust gaS and to evaporate the water therefrom to produce the by-product salts. The by-product salts, removed via pipe 42, are produced at a rate of approxi-mately eight to twelve tons per day. The by-product salts include potassium sulfate, calcium carbonate, and other salts with cationic components incuding potassium, calcium, magnesium, and sodium and anionic components including carbonate, sulfate, and nitrate. ~ portion of the nitrate oxidizes the sulfite to sulfate.
Referring to Fig. 2, the results of two experi-ments (KD-18 and KD-20) are displayed, showing that extraction of the alkali and alkaline earth metal salts from the dust results in the treated dust being acceptable as kiln feed stock. That is, the level of potassium salts falls from approximately 3~ to less than 1-1/2~, and the level of sulfate falls from approximately 6% to 3~ or below. It should bej noted that in the examples illus-trated in Fig. 2 a full charge of dust was loaded ini-tially into the treatment tank and then the introduction of gas commenced. This accounts for the slopes of the graph during days A through M. This reduction in ~3~
potassium, sodium, and sulfate concentration in the dust, from initial untreatad to final treatecl material is greater than 50%. Samples A-M refer to successive days during which samples were taken from a continuous treat-ment process.
The impact of addition of treated dust on raw feed composition is shown in the following table showing the percentage of each oxide in normal kiln feed for both Type I and Type II cement production. The figures con-tained in the columns labeled "100 TPD Dust Added to Feed"
and "200 TPD Dust added to Feed" show dramatically the slight impact on composition of the feed resulting from the addition of 100 tons per day and 200 tons per day re ~//
/
/
3L3~4~
TABLE
Impact of Treated Dust on Kiln Feecl Composition Normal 100 TPD ~ust200 TPD Dust Type I Feed Added to FeedAdded to Feed SiO2 12.99 12.99 12.99 Al2O3 3.57 3-59 3.61 23 1.45 1.53 1.61 CaO 43.49 43.62 43.75 MgO 2.83 2.81 2.78 SO3 * 0.18 0.23 0.2~
K2O 0.93 0.94 0.96 Loss 35.83 35.45 35.07 Si Ratio 2.58 2.54 2.49 Al/Fe 2.46 2.35 3.24 SiO2 13.24 13.23 1~,22 A12O3 3.33 3.35 ~.38 23 1.77 2.03 2.09 CaO 43.09 43.23 43.38 MgO 2.66 2.64 2.62 SO3 * 0.19 0.24 0.29 K2O 0.68 0.70 0.72 Loss 35.20 34.85 ~ 34.49 Si Ratio 2.49 2.46 2.42 Al/Fe 1.69 1.65 1.62 *Sulfate expressed as SO3 These results demonstrate that the major change in kiln dust composition is the removal of SO3 and K2O and that the unremoved K2O and SO3 do not significantly alter the composition o~ the raw feed.
While there has herein been disclosed and described a presently preferred method and apparatus for practicing the invention, it will nevertheless be under-stood that the same is by way of illustration and not by way of limitation, and it i5 intended that the scope of the invention be limited only by ~he proper interpretation to be afforded the appended claims.
.
, .
. Dust collection facilities operating at cement or lime producing kilns remove particulate matter from the kiln exhaust. This particulate matter includes calcium carbonate, calcium oxide, and the oxides and carbonates of other metals, depending on. the com~osltion of t~e feed stock to the kiln. Two elements ~requentl~v present in the kiln dust are potassium and sodium. These elements limi.t or prevent the reuse of the kiln dust as kiln feed stock, since they interfere with.the properties o~ the final pro-duct, and the dust is therefore discarded. These dust collection facilities do not remove sufficient gaseous pollutants from the exhaust.stream and separate scrubbers must be provided if they are to be prevented from entering the atmosphere.~
The use of alkali or alkaline earth materials, as solids or in a slurry or in a solution, for ~crubbing tremoving sulfur ~nd nitrogen o~ides) of exhaust gas has been known ~or years (see discussion in Canadian Patent Application No~ 521,8i9, f~led 30 October, 1986). For example, Mehlmann (1985, Zement-Kalk-Gips Edition B) ~escribes the use of hydrated or pulverized limestone at temperatures up to`ll00CJ or of spray dryLng with hydrated lime; and ~yer (19790 EPA-600/7-79-167b) describes the use of lime to scrub exhaust gas from a heating plant. Limestone may be .. . . ...
~3~21~
included in the charge of fluidized bed furnaces for the same purpose. In general the oxides of carbon, sulfur, and nitrogen, present in exhaust gas, when reacted with water, produce acids, including sulfuric, sulfurous, nitric, and carbonic~ The presence and amounts of each depend on the oxides present, the availability of oxygen, and the reaction conditions~ When these acids are reacted with the oxides, hydroxides, or carbonates of alkali or alkaline ea th metals, salts of the components are formed.
For example, sulfuric acid will react with the calcium carbonate present in limestone to yield calcium sulfate.
The principal object of the present invention is to provide a method and apparatus to eliminate the dust disposal problem present in cement plants and simultane-ously to reduce gaseous and particulate emissions and to be able to do so C05t effectively, including the conver-sion of otherwise waste products into useful products.
Brief Summary of the Invention This invention provides a process that removes a significant portion of the potassium, sodium and sulfur in kiln dust, so that the dust may be reused as kiln feed;
and at the same time uses the kiIn dust as a reactant for removing the oxides of sulfur, nitrogen and carbon from the exhaust stream.
More specifically, the process will react cement kiln dust or lime kiln dust with acid, produced from the acidic oxides of sulfur, nitrogen and carbon in exhaust gas, to dissolve some components of the dust and renaer the remaining undissolved solids reuseable as process feed stock; scrub a portion of the oxides of sulfur, nitrogen and carbon from the exhaust stream and make them available for reaction with kiln dust; produce as a by~product alkali and alkaline earth metal salts composed of the scrubbed exhaust gas sulfur, nitrogen and carbon oxides and materials derived from the kiln dust; and utilize heat in the exhaust stream to reduce the water content of the ~L3t~}2G~4~
process stream containing the dissolved alkali and alka-line earth metal salts.
In accordance with the invention, there is pro-vided a method of simultaneously scrubbing an exhaust gas stream having acidic oxides and treating dust having alkali and alkaline earth metal compounds as solids, com-prising the steps of: (a) mixing the dust with water ~o form an alkaline (p~ greater than 7) solution and ~b) passing the gas stream into the said alkaline solution, whereby the said solution and gas react to form an alkali and alkaline earth metal salt solution and a precipitate of alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds.
Preferred methods include cooling and/or dehumidify-ing the gas ~tream prior to passing the same into the alkaline solution; utilizing the alkali and alka-line earth metal salt solution for the purpose of such cooling and/or dehumidifying; utilizing said precipitate together with insoluble silicates, aluminates and iron compounds to add to the feed stock of a cement plant to produce cement; utilizing the heat of the gas to remove water from the alkali and alkaline earth metal salt solu-tion aforesaid; utilizing the dissolved solids contents of the alkali salt solution as a fertilizer; and obtaining the exhaust gas stream and dust from the kiln of a cement plant.
In accordance with one aspect of the invention, there is provided a m~thod of converting dust from a cement kiln containing alkali and alkaline earth metal compounds as solids into a product suitable for adding to the feed stock for said kiln, comprising the steps of (a) dissolving the soluble portion of the dust in water to form an alkaline solution, and (b) passing exhaust gas from the kiln lnto the said solution, whereby the solution and gas react to form an alkali and alkaline earth metal salt solution and a precipitate of alkali and alkaline 3l3~Z~
earth metal salts with insoluble silicates, aluminates and iron compounds suitable for adding to the feed stock for the kiln. Preferably, thè gas is cooled and dehumidified prior to being passed into the alkaline solution, utiliz-ing the latter for such purpose, and water is evaporated from the alkali salt solution by heat from the gas.
In a preferred aspect there is provided a method of simultaneously scrubbing acidic oxides of sulfur, nitrogen and carbon from the hot exhaust stream ~rom a cement kiln and utilizing acids derived therefrom to pxoduce useful products from the carbonates and oxides of alkali and alkaline earth metals contained as solids in cement kiln dust comprising said carbonates and oxides and insoluble silicates, aluminates and iron compounds. The method comprises mixing the dust with water to form a slurry comprisiny undissolved solids and a solution of the soluble compounds in the dust. The gas stream is passed into the slurry whereby the acidic oxides contained therein will react with water to produce acids. The latter will react with the carbonates and oxides of alkali and alkaline earth metals to yield a solution of alkali and alkaline earth metal salts comprising principally the cationic components, calcium, potassium, magnesium and sodium, and anionic components, carbonate, sulfate and nitrate, and a precipitate o~ alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds. After passing through the slurry, the gas of the gas stream emerges as a scrubbed exhaust.
In accordance with a further aspect of the inven-tion, there is provided a method of simultaneously con-verting dust from a c~ment kiln containing alkali and alkaline earth metal compounds as solids into a product suitable for adding to the feed stock for the kiln, scrub-bing the exhaust gas stream from the kiln and producing alkali and alkaline earth metal salts suitable for use as fertilizer, comprising the steps of (a) dissolving the dust in water to form an alkaline solution, and (b) pass-ing exhaust gas from said kiln into the said solution, whereby said solution and gas react to scrub the latter '~
~ ~1 ~3~?;~
- 4a -and at the same time form an alkali and alkaline earth metal salt solution and a precipitate of alkali and alka-line earth metal salts with insoluble silicates, alumi-nates and iron compounds suitable for adding to the feed stock for said kiln, and, lastly, evaporating wate~ from the alkali and alkaline earth metal salt solution to pro-duce a concentrated solution or a precipitate suitable ~or use as fertilizer.
The invention also provides a system for simultaneously scrubbing acidic oxides of sulfur, nitrogen, and carbon from the hot exhaust gas stream from a cement kiln and utilizing acids derived therefrom to produce useful products from the carbonates and oxides of alkali and alkaline earth metal salts contained as solids in cement kiln dust, principally calcium carbonate, potassium carbonate, magnesium carbonate, sodium carbonate, calcium oxide, potassium oxide, and magnesium oxide, comprising said carbonates and oxides and insoluble silicates, aluminates and iron compounds. Such system comprises a means for mixing the cement kiln dust with water to form a slurry comprising undissolved solids and a solution of the soluble compounds in the cement kiln dust. There is a reaction chamber and a means for delivering the exhaust ~as stream into the reaction chamber and a means for delivering the slurry into the reaction chamber.
There is also a means for scrubbing the exhaust gas stream comprising means for contacting the exhaust gas stream with the slurry within the reaction chamber in a manner to cause the acidic oxides contained in the exhaust gas stream to react with water in the slurry to produce acids, and to cause the acids to react with carbonates and o~ides of alkali and alkaline earth metals salts comprising principally cationic components calcium, potassium, magnesium and sodium, and anionic components carbonate, sulfate and nitrate, and precipitates of alkali and alkaline earth metal sal~s with insoluble silicates, aluminates and iron compounds. There is also a means for removing scrubbed exhaust gas from the reaction chamber, means for removing a li~uid suspension of soluble compounds and undissolved solids '~
- 4b -from the reaction chamber, means for separating a solution of solub].e compounds ~rom undissolved solids and means for ~vaporating water from the solution of soluble compounds.
The invention also includes apparatus for simul-taneously scrubbing a gas stream containing acidic oxides and treating dust from a cement kiln or the like contain-ing alkali and alkaline earth metal salts, comprising a treatment tank, means for feeding a mixture of water and dust into the latter, means for feeding additional water into the said tank further to dilute the mixture afore-said, means for passing the gas into the mixture to react therewith and to thereby produce an aqueous solution of its water soluble components to form therewith a slurry of acidic oxides and alkali and alkaline earth metal salts ~j .
~3~J2~
and any remaining insoluble compounds, a precipitation tank, means for conveying the slurry from the treatment tank to the precipitation tank wherein the slurry is sepa-rated into solids and liquid, the former dropping toward the base of the tank beneath the latter which remains in the upper part thereof, means for removing the said solids from the base of the precipitation tank and means for removing the said liquid from the upper part of the pre-cipitation tank.
In a presently preferred embodiment, the appara-tus further comprises a heat exchanger, means for passing the said gas through the heat exchanger prior to being ~ed into the treatment tank and means ~or passing liquid removed frvm the precipitation tank through the heat exchanger, whereby the incoming gas stream is cooled and the said liquid simultaneously heated to remove the water therefrom.
Still further objects/ features and advantages of the invention will be apparent from the following detailed description of a presently preferred embodiment thereof taken in conjunction with the accompanying drawings.
~rief Description of the Drawinqs In the drawings, Fig. 1 is a schematic representation of one appa-ratus for practicing the invention;
Fig. 2 is a graph illustrating the effectiveness of removal of potassium and sulfur oxides from kiln dust during reaction with exhaust gas oxides according to the invention.
Detailed Description of Preferred Embodiment The invention comprises method and means for sup-plying alkali and alkaline earth me al compounds as solids, the kiln dust, water, and exhaust gas, and the method and apparatus for first combining and reacting the same and then separating the resulting components.
~3~ 4~
Briefly, the acidic gas and alkaline solids are mixed with water in a treatment tank and react to form a slurry. A settling tank is provided for the separation of precipitated and undissolved solids from the solution of water and dissolved solids in the slurry. A heat exchanger~crystallization unit is also provided and util-izes the heat, including latent heat, in the exhaust stream to evaporate water from the solution o dissolved salts in the slurry to provide cooling of the exhaust gas for use in the above process. ~eat for evaporation of water from the solution of dissolved salts is also obtained from the hot waste dust, the hydration reaction between dust and water, and energy obtained from compres-sion of the exhaust gas.
Referring to Fig. 1, a slurry, exiting at 8 from a dust and water mixing tank ~not shown), composed o alkali and alkaline earth metal salt solids and water, is pumped via pipe 10 into the treatment tank 12, along with additional water through inlet 14 from a suitable source (not shown) to produce a dilute slurry 16. Exhaust gas~
from a cement kiln or boiler (not shown) enters heat exchanger 22 through inlet 18 from which it emerges as cooled exhaust. Condensed exhaust gas moisture is col- -lected in the heat exchanger 22 and conveyed to the treat-ment tank 12 through pipe 44. The exhaust then travels to compressor 20 through pipe 23 and is delivered via pipe 24 to distribution pipes 26 in the bottom of the treatment tank 12. To prevent settling of the solids to the bottom of treatment tank 12 the slurry may be stirred or recir-culated by suitable means, for exa~ple by recirculation pump 27.
The exhaust gas bubbles through slurry 16 of alkaline solids and water to emerge from the tank tap as scrubbed exhaust 28~ Slurry 16, as a mixture o~ treated solid, water, and dissolved materials, is pumped by pump 32 via pipe 30 to the settling tank 3~ where the settled ~3~
solids 36 are pumped out by pump 38 and the water 37 laden with dissolved salts is pumped to heat exchanger 22 to provide cooling for the input exhaust gas. The water from salt solution 37 is evaporated to a vapor and release~ via pipe 40 to the atmosphere or the water is evaporated and then condensed to a liquid to recapture the latent heat for reuse. The salts from the salt solution 37 are con-centrated and/or precipitated and collected from the heat exchanger via pipe 42. The cationic components of the collected salts are principally calcium, potassium, magne-sium, and sodium. The anionic components of the salts are principally sulfate, carbonate and nitrate. The actual composition of the salts will depend on the init~al compo-sition of the kiln dust to be treated and on the composi-tion of the exhaust gas.
The heat exchanger 22 is a dual purpose heat exchanger-crystallization unit of a known type which will extract heat from the exhaust gas and use that heat, including latent heat derived from condensation of the exhaust gas moisture to evaporate water.
The Apparatus The whole system i5 created from well known parts combined by standard methods. For example, typically tbe treatment tank may have a volume of one million gallons and be provided with gas distribution and stirring means;
the settling tank may have a volume of 100 thousand gallons, both being constructed from stainless steel, or other suitable materials, such as rubber, which can toler-ate highly alkaline or acidic solutions.
Workin~ Principle The basic working principle in this invention is recombination and reaction of two waste streams produced during burning to provide mutual neutralization of the waste streams, production of a valuable and useful by-product, and utilization of low grade heat energy. The two waste streams are the gaseous oxides which produce ~3~ZC~
acidic solutions in water and the waste particulate matter from cement kilns, which produce basic solutions in water.
After partial dissolution in water, the two wastes react to neutralize each other. In the case of cement kiln dust, which contains excess potassium and/or sodium and sulfate, the process provides for dissolution of a significant proportion of the remaining undissolved solids which include calcium and magnesium salts. The resultin~ solids are therefore suitable for use as process feed stock. The potassium sulfate and other salts removed from the heat exchanger-crystallization unit are suitable as fertilizer or as a source of material for extraction of chemicals. At the same time, the exhaust gas passing through the slurry in ~he treatment tank is cleansed of a signiEicant portion of the oxides of sulfur and nitrogen, by forming sulfates and nitrates.
~xampie The discussion that follows is an example of use of the process in a moderate size wet process cement pro-ducing facility.
Exhaust gas from the kiln baghouse, fed through duct 18, is introduced to heat exchanger 22 at a rate of 200,000 actual cubic feet per minute by compressor 20~
The exhaust gas is vari-able in composition, but contains roughly 29~ water, 25~ carbon dioxide, 36% nitrogen, 10%
oxygen and 400 to 600 ppm nitrogen oxides and 200 ppm sul-fur dioxide. In heat exchanger 22 the exhaust gas is cooled and water is condensed, resulting in a 35% to 40%
decrease in flow volume. The exhaust gas is then drawn by compressor 20 through pipe 23 for delivery through pipe 24 to distribution pipes 26 and allowed to react with slurry 16 where most of the oxides of sulfur and nitrogen are remo~ed. In lab scale trials 99% of the SO2 was removed from the exhaust stream.
Kiln dust is introduced to treatment tank 12 at a rate of eight to ~welve tons per hour dry weight~ Water ~3~
g is added to produce a dilute slurry of up to 95~ water content. The slurry water content is determined by the initial concentration of potassium and sodium in the waste dust and on the desired concentration in the material to I be returned to the kiln feed system. After reaction with the exhaust gas, the slurry of treated dust is pumped at a rate of approximately 200 gallons per minute to settling tank 34. In this tank the solids settle to form a slurry of approximately 35% water and 65% solids, beneath a solu-tion of water and soluble salts dissolved during treat-ment. The slurry is pumped by pump 38 from tank 34 and combined with process feed for a cement plant at a rate of approximately 7.8 tons per hour of solids. The water I solution is pumped through outlet 37 to heat exchanger 22 at approximately 200 gallons per minute to provide coolinq for the exhaust gaS and to evaporate the water therefrom to produce the by-product salts. The by-product salts, removed via pipe 42, are produced at a rate of approxi-mately eight to twelve tons per day. The by-product salts include potassium sulfate, calcium carbonate, and other salts with cationic components incuding potassium, calcium, magnesium, and sodium and anionic components including carbonate, sulfate, and nitrate. ~ portion of the nitrate oxidizes the sulfite to sulfate.
Referring to Fig. 2, the results of two experi-ments (KD-18 and KD-20) are displayed, showing that extraction of the alkali and alkaline earth metal salts from the dust results in the treated dust being acceptable as kiln feed stock. That is, the level of potassium salts falls from approximately 3~ to less than 1-1/2~, and the level of sulfate falls from approximately 6% to 3~ or below. It should bej noted that in the examples illus-trated in Fig. 2 a full charge of dust was loaded ini-tially into the treatment tank and then the introduction of gas commenced. This accounts for the slopes of the graph during days A through M. This reduction in ~3~
potassium, sodium, and sulfate concentration in the dust, from initial untreatad to final treatecl material is greater than 50%. Samples A-M refer to successive days during which samples were taken from a continuous treat-ment process.
The impact of addition of treated dust on raw feed composition is shown in the following table showing the percentage of each oxide in normal kiln feed for both Type I and Type II cement production. The figures con-tained in the columns labeled "100 TPD Dust Added to Feed"
and "200 TPD Dust added to Feed" show dramatically the slight impact on composition of the feed resulting from the addition of 100 tons per day and 200 tons per day re ~//
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TABLE
Impact of Treated Dust on Kiln Feecl Composition Normal 100 TPD ~ust200 TPD Dust Type I Feed Added to FeedAdded to Feed SiO2 12.99 12.99 12.99 Al2O3 3.57 3-59 3.61 23 1.45 1.53 1.61 CaO 43.49 43.62 43.75 MgO 2.83 2.81 2.78 SO3 * 0.18 0.23 0.2~
K2O 0.93 0.94 0.96 Loss 35.83 35.45 35.07 Si Ratio 2.58 2.54 2.49 Al/Fe 2.46 2.35 3.24 SiO2 13.24 13.23 1~,22 A12O3 3.33 3.35 ~.38 23 1.77 2.03 2.09 CaO 43.09 43.23 43.38 MgO 2.66 2.64 2.62 SO3 * 0.19 0.24 0.29 K2O 0.68 0.70 0.72 Loss 35.20 34.85 ~ 34.49 Si Ratio 2.49 2.46 2.42 Al/Fe 1.69 1.65 1.62 *Sulfate expressed as SO3 These results demonstrate that the major change in kiln dust composition is the removal of SO3 and K2O and that the unremoved K2O and SO3 do not significantly alter the composition o~ the raw feed.
While there has herein been disclosed and described a presently preferred method and apparatus for practicing the invention, it will nevertheless be under-stood that the same is by way of illustration and not by way of limitation, and it i5 intended that the scope of the invention be limited only by ~he proper interpretation to be afforded the appended claims.
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Claims (38)
1. A method of simultaneously scrubbing acidic oxides of sulfur, nitrogen and carbon from the hot exhaust stream from a cement kiln and utilizing acids derived therefrom to produce useful products from the carbonates and oxides of alkali and alkaline earth metals contained as solids in cement kiln dust comprising said carbonates and oxides and insoluble silicates, aluminates and iron compounds, which comprises (a) mixing said dust with water to form a slurry comprising undissolved solids and a solution of the soluble compounds in said dust, and (b) passing said gas stream into said slurry whereby said acidic oxides contained therein will react with water to produce acids, the latter will react with said carbonates and oxides of alkali and alkaline earth metals to yield a solution of alkali and alkaline earth metal salts compris-ing principally the cationic components, calcium, potassium, magnesium and sodium, and anionic components, carbonate, sulfate and nitrate, and a precipitate of alkali and alkaline earth metal salts with insoluble sili-cates, aluminates and iron compounds, and the gas of said gas stream after passing through said slurry emerges as scrubbed exhaust.
2. The method of claim 1 wherein said solution of alkali and alkaline earth metal salts is separated from said precipitate and insoluble silicates, aluminates and iron compounds by allowing the latter to settle therefrom.
3. The method of claim 1 including the step of transferring said solution of alkali and alkaline earth metal salts and said precipitate with said insolubles to a settling tank wherein said salt solution is separated from said precipitate and insoluble silicates, aluminates and iron compounds by allowing the latter to settle therefrom.
4. The method of claim 3 including the step of passing the separated salt solution through a heat exchanger wherein it extracts heat from said exhaust gas before the latter is passed into said slurry.
5. The method of claim 1 wherein said gas stream is dehumidified by cooling prior to said passing step.
6. The method of claim 5 wherein said solution of alkali and alkaline earth metal salts is used to cool and dehumidify said gas stream.
7. The method of claim 1 wherein said precipitate together with insoluble silicates, aluminates and iron compounds is added to the feed stock of a cement plant to produce cement.
8. The method of claim 6 wherein heat from said exhaust gas stream is used to remove water from said solution of alkali and alkaline earth metal salts.
9. The method of claim 8 wherein said heat is derived in part from each of the hot exhaust gas, the latent heat of moisture in said exhaust, the hydration reaction between dust and water and from compressing said gas prior to said passing step.
10. The method of claim 1 wherein the dissolved solids contained in said solution of alkali and alkaline earth metal salts are suitable for use as a fertilizer.
11. A system for simultaneously scrubbing acidic oxides of sulfur, nitrogen, and carbon from the hot exhaust gas stream from a cement kiln and utilizing acids derived therefrom to produce useful products from the carbonates and oxides of alkali and alkaline earth metal salts contained as solids in cement kiln dust, principally calcium carbonate, potassium carbonate, magnesium carbonate, sodium carbonate, calcium oxide, potassium oxide, and magnesium oxide, comprising said carbonates and oxides and insoluble silicates, aluminates and iron compounds, said system comprising:
means for mixing said cement kiln dust with water to form a slurry comprising undissolved solids and a solution of the soluble compounds in said cement kiln dust, and a reaction chamber; and means for delivering said exhaust gas stream into said reaction chamber; and means for delivering said slurry into said reaction chamber; and means for scrubbing said exhaust gas stream comprising means for contacting said exhaust gas stream with said slurry within said reaction chamber in a manner to cause said acidic oxides contained in said exhaust gas stream to react with water in said slurry to produce acids, and to cause said acids to react with said carbonates and oxides of alkali and alkaline earth metal salts comprising principally cationic components calcium, potassium, magnesium and sodium, and anionic components carbonate, sulfate and nitrate, and precipitates of alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds, and means for removing scrubbed exhaust gas from said reaction chamber; and means for removing a liquid suspension of soluble compounds and undissolved solids from said reaction chamber; and means for separating a solution of soluble compounds from undissolved solids; and means for evaporating water from said solution of soluble compounds.
means for mixing said cement kiln dust with water to form a slurry comprising undissolved solids and a solution of the soluble compounds in said cement kiln dust, and a reaction chamber; and means for delivering said exhaust gas stream into said reaction chamber; and means for delivering said slurry into said reaction chamber; and means for scrubbing said exhaust gas stream comprising means for contacting said exhaust gas stream with said slurry within said reaction chamber in a manner to cause said acidic oxides contained in said exhaust gas stream to react with water in said slurry to produce acids, and to cause said acids to react with said carbonates and oxides of alkali and alkaline earth metal salts comprising principally cationic components calcium, potassium, magnesium and sodium, and anionic components carbonate, sulfate and nitrate, and precipitates of alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds, and means for removing scrubbed exhaust gas from said reaction chamber; and means for removing a liquid suspension of soluble compounds and undissolved solids from said reaction chamber; and means for separating a solution of soluble compounds from undissolved solids; and means for evaporating water from said solution of soluble compounds.
12. The system according to claim 11 including means for separating a solution of alkali and alkaline earth metal salts from - 14a -said precipitate and insoluble silicates, aluminates and iron compounds.
13. The system according to claim 12 wherein said means for separating comprises:
a settling tank and means for transferring said solution of alkali and alkaline earth metal salts and said precipitate with said insolubles thereto wherein said salt solution is separated from said precipitate and insoluble silicates, aluminates and iron compounds by allowing the latter to settle therefrom.
a settling tank and means for transferring said solution of alkali and alkaline earth metal salts and said precipitate with said insolubles thereto wherein said salt solution is separated from said precipitate and insoluble silicates, aluminates and iron compounds by allowing the latter to settle therefrom.
14. The system according to claim 12 including a heat exchanger, means for passing the separated solution of alkali and alkaline earth metal salts and said hot exhaust stream prior to its passage into said slurry through said heat exchanger, and means for collecting water condensed from said gas in said heat exchanger and conveying it into said means for mixing with said dust and water for mixture with said dust.
15. The system according to claim 13 including a heat exchanger and means for passing the separated solution of alkali and alkaline earth metal salts and said hot exhaust gas through the heat exchanger before said gas is passed into said slurry whereby said solution extracts heat from said gas before the latter is passed into said slurry.
16. A system for simultaneously scrubbing acidic oxides of sulfur, nitrogen and carbon from the hot exhaust stream from a cement kiln and utilizing acids derived therefrom to produce useful products from the carbonates and oxides of alkali and alkaline earth metals contained as solids in cement kiln dust comprising said carbonates and oxides and insoluble silicates, aluminates and iron compounds, comprising:
a treatment tank, means for feeding water and cement kiln dust into said tank, said water and dust comprising a slurry of undissolved solids and a solution of the soluble compounds in said dust, conduits for passing said gas stream into said slurry whereby said acidic oxides contained therein will react with the water to produce acids and the latter will react with said carbonates and oxides of alkali and alka-line earth metals to yield a solution of alkali and alka-line earth metal salts comprising principally the cationic components, calcium, potassium, magnesium and sodium, and anionic components, carbonate, sulfate and nitrate, and a precipitate of alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds, said gas after passage through said slurry emerging as scrubbed exhaust, a precipitation tank, conduit means placing said treatment tank in com-munication with said precipitation tank, pump means for conveying said slurry through said conduit means from said treatment tank into said precipi-tation tank where-in said slurry is separated into solids and liquid, the former dropping toward the base of said tank beneath the latter which remains in the upper part thereof, means for removing said solids from the base of said precipitation tank, and means for removing said liquid from the upper part of said precipitation tank.
a treatment tank, means for feeding water and cement kiln dust into said tank, said water and dust comprising a slurry of undissolved solids and a solution of the soluble compounds in said dust, conduits for passing said gas stream into said slurry whereby said acidic oxides contained therein will react with the water to produce acids and the latter will react with said carbonates and oxides of alkali and alka-line earth metals to yield a solution of alkali and alka-line earth metal salts comprising principally the cationic components, calcium, potassium, magnesium and sodium, and anionic components, carbonate, sulfate and nitrate, and a precipitate of alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds, said gas after passage through said slurry emerging as scrubbed exhaust, a precipitation tank, conduit means placing said treatment tank in com-munication with said precipitation tank, pump means for conveying said slurry through said conduit means from said treatment tank into said precipi-tation tank where-in said slurry is separated into solids and liquid, the former dropping toward the base of said tank beneath the latter which remains in the upper part thereof, means for removing said solids from the base of said precipitation tank, and means for removing said liquid from the upper part of said precipitation tank.
17. The system according to claim 16 further com-prising a heat exchanger, conduit means for passing said hot gas stream through said heat exchanger prior to being fed into said treatment tank and means for passing liquid removed from said pre-cipitation tank through said heat exchanger, whereby said gas is cooled and said liquid heated to evaporate water therefrom.
18. The system according to claim 16 further com-prising means for agitating the slurry in said treatment tank to prevent settling of the solids.
19. The system according to claim 18 wherein said agitating means comprises a pump and conduit means placing said pump in communication with said treatment tank for recirculating slurry out from and back into said treatment tank.
20. The system according to claim 17 further com-prising means for supplementing the heat provided by said gas for evaporating water from said liquid.
21. The system according to claim 20 wherein said supplementing means comprises means for compressing said gas prior to passing it into said treatment tank.
22. The system according to claim 17 further including means for collecting water condensed from said exhaust gas in said heat exchanger and means for conveying said water into said treatment tank for mixing with said dust.
23. The method of claim 1 including the step of agitating said solution of alkali and alkaline earth metal salts and precipitate to prevent settling of the solids during said reactions.
24. A method of simultaneously scrubbing acidic oxides of sulfur, nitrogen and carbon from the hot exhaust stream from a cement kiln or boiler and utilizing acids derived therefrom to produce useful products from cement kiln dust containing as solids carbonates and oxides of alkali and alkaline earth metals along with insoluble silicates, aluminates and iron compounds, which comprises (a) mixing said dust with water to form a slurry comprising the undissolved components and a solution of the soluble components in said dust, and (b) reacting said gas stream with said slurry whereby said acidic oxides contained in said stream will react with water to produce acids, the latter will react with said carbonates and oxides of alkali and alkaline earth metals to yield a solution of alkali and alkaline earth metal salts comprising principally the cationic components, calcium, potassium, magnesium and sodium, and anionic components, carbonate, sulfate and nitrate, and a precipitate of alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds, the gas of said gas stream after contact with said slurry emerging as scrubbed exhaust.
25. the method of claim 24 wherein said gas stream is passed through said slurry to react therewith.
26. The method of claim 25 including the step of agitating said slurry to prevent settling of the solids during said reactions.
27. The method of claim 26 wherein said slurry is agitated by stirring.
28. The method of claim 26 wherein said slurry is agitated by recirculation.
29. The method of claim 24 including the step of separating said solution of alkali and alkaline earth metal salts from said precipitate and insoluble silicates, aluminates and iron compounds.
30. The method of claim 29 wherein said separating step comprises allowing said precipitate and insoluble silicates, aluminates and iron compounds to settle out of said solution.
31. The method of claim 30 wherein said solution of alkali and alkaline earth metal salts and said precipitate with said insolubles are transferred to a settling tank wherein said salt solution is separated from said precipitate and insoluble silicates, aluminates and iron compounds by allowing the latter to settle therefrom.
32. The method of claim 29 wherein said separated precipitate together with insoluble silicates, aluminates and iron compounds is added to the feed stock of a cement plant to produce cement.
33. The method of claim 24 including the step of cooling and dehumidifying said gas stream prior to passing it into contact with said slurry.
34. The method of claim 29 including the further step of using said separated solution to cool and dehumidify said gas stream prior to passing said gas stream into contact with said slurry.
35. The method of claim 34 including the step of using heat from the gaseous components of said exhaust gas stream to evaporate water from said separated solution of alkali and alkaline earth metal salts to produce a precipitate useful as fertilizer.
36. The method of claim 35 wherein said heat is derived in part from each of the hot exhaust gas, the latent heat of moisture in said exhaust, the hydration reaction between dust and water and from compressing said gas prior to said passing step.
37. The method of claim 34 wherein said separated solution and exhaust gas stream are passed through a heat exchanger wherein said solution extracts heat from said exhaust gas before the latter is passed into contact with said slurry.
38. The method of claim 35 wherein said separated solution and exhaust gas stream are passed through a heat exchanger wherein heat from the gaseous components of said stream evaporates water from said separated solution.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/890,991 US4708855A (en) | 1985-11-07 | 1986-07-25 | Method and system for exhaust gas stream scrubbing |
| US890,991 | 1986-07-25 | ||
| US06/904,719 US4716027A (en) | 1986-07-25 | 1986-09-05 | Method for simultaneously scrubbing cement kiln exhaust gas and producing useful by-products therefrom |
| US904,719 | 1986-09-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1302049C true CA1302049C (en) | 1992-06-02 |
Family
ID=27128966
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000542492A Expired - Lifetime CA1302049C (en) | 1986-07-25 | 1987-07-20 | Method and system for simultaneously scrubbing cement kiln exhaustgas and producing useful by-products therefrom |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1302049C (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115212713A (en) * | 2022-05-30 | 2022-10-21 | 湖北工业大学 | Carbon sequestration and emission reduction method for wet grinding kiln ash of cement plant |
| CN115555350A (en) * | 2022-07-04 | 2023-01-03 | 万昊远 | Dust removal purification equipment is used in fertilizer production |
-
1987
- 1987-07-20 CA CA000542492A patent/CA1302049C/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115212713A (en) * | 2022-05-30 | 2022-10-21 | 湖北工业大学 | Carbon sequestration and emission reduction method for wet grinding kiln ash of cement plant |
| CN115212713B (en) * | 2022-05-30 | 2024-03-26 | 湖北工业大学 | Method for carbon fixation and emission reduction of wet mill kiln ash of cement plant |
| CN115555350A (en) * | 2022-07-04 | 2023-01-03 | 万昊远 | Dust removal purification equipment is used in fertilizer production |
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