AU611478B2

AU611478B2 - Method for simultaneously scrubbing an exhaust gas stream and producing useful or benign products therefrom

Info

Publication number: AU611478B2
Application number: AU22302/88A
Authority: AU
Inventors: Garrett Louis Morrison
Original assignee: Passamaquoddy Tribe
Current assignee: Passamaquoddy Tribe
Priority date: 1986-09-05
Filing date: 1988-09-15
Publication date: 1991-06-13
Anticipated expiration: 2007-09-04
Also published as: GB2210035B; NZ225964A; CA1311343C; GB8821734D0; FI884278A; NO884101L; FI884278A0; PL274651A1; ZA886879B; CN1013642B; NO884101D0; DK513988D0; IT1223827B; SE8803286L; CN1035959A; BR8804771A; SE8803286D0; JPH01148330A; AT395543B; BE1001118A5

Description

KLN/9228W IIII I C I k

COMMOI

P

114 78 S F Ref: 71199 FORM NWEALTH OF AUSTRALIA ATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class oQ 0 a 00 0o 0 0 0 Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name and Address of Applicant: o'0 0 0 0 00 0 Passamaquoddy Tribe, a sovereign Indian Tribe recognized by the Government of the United States of America Indian Township Reseyration Princeton, Maine 04668, and Pleasant Point Reservation Perry, Maine 04667 UNITED STATES OF AMERICA Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Address for Service: 0 00 0 0 0 0o 000 0 0 Complete Specification for the invention entitled: Method for Simultaneously Scrubbing an Exhaust Cas Stream and Producing Useful or Benign Products Therefrom The following statement is a full description of tnis invention, Including the best method of performing it known to mr/us 5845/8 a. 0 a 0 0 o 00 a a 000, a. aa a a 0 ~0 0 a a a a a a a aa a a 0 a a a ad 0 a a 0 Ode a Odt.d a a 1 A~- This invention relates to method and apparatus for scrubbing pollutants from an exhaust gas stream be it from a boiler installation or a cement kiln whereby the materials reacted with the stream are rendered at least benign and in many cases converted by the reaction into useful products.

Backoround of the Invention Scrubbing of exhaust gas pollutants is generally costly, having significant environmental returns but little or no economic returns unless it is possible to convert by the scrubbing otherwise waste products 'nto useful products. The cost of the initial equipment is high, Furthermore, the materials for scrubbing, such as the oxides, carbonates, or hydroxides of alkali and/or 1s alkaline earth metals are a continuing expense. In addition, disposal of the reaction products derived from reaction of the scrubbing materials with the exhaust gas adds to the continuing cost, especially if the products contain toxic components.

20 The use of alkali or alkaline earth materials, as solids or in a slurry or in a solution, for scrubbing (removing sulfur and nitrogen oxides) of exhaust gas has been known for years. For example, mehlmann (1985, Zement-Kalk-Gips Edition B) describes the usc of hydrated 25 or pulverized limestone at temeratures up to 11000C, or of spray drying with hydrated lime; p~an-~Limestone may be included in the charge of fl~uidized 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 ZA,, with the oxides, hydroxides, or carbonates of alkali or 2 alkaline earth metals, salts of the components are formed.

For example, sulfuric acid will react with the calcium carbonate present in limestone to yield calcium sulfate.

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 composition of the feed stock to the kiln. Two elements frequently present in the kiln dust are potassium and sodium. These elements limit oo or prevent the reuse of the kiln dust as kiln feed stock, since they interfere with the properties of the final product, and the dust is therefore discarded. These dust Qo a 0 collection facilities do not remove sufficient gaseous pollutants from the exhaust stream and separate scrubbers °0 must be provided if they are to be prevented from entering the atmosphere.

Turning now to boiler installations, a growing number of which are fueled by combustion of biologic mate- 20 rials (hereinafter collectively "biomass"), including wood, peat, or crop residue, where there is little or no o production of sulfur oxides and therefore no scrubbing of the gaseous components of the exhaust is needed or done, On the other hand, the ash produced from these operations 0 25 contains significant alkali and alkaline earth metal °.00 salts, occurring commonly as the oxide, or, if wetted and/or reacted with carbon dioxide, as the hydroxide or the carbonate, or perhaps as hydrated salts of these.

I have discovered that cffnt l r- rn "amv~a t -k 4 ash from boiler installations, where alkali and alkaline earth metal oxides, hydroxides, and/or carbonates are a significant proportion of the ash, can be used in a process for scrubbing exhaust gas in place of the usual materials above referred to, thus making use of an otherwise waste product as a substitute for expensive LIA, materials which must be purchased, 3- Other waste materials are also usable for this purpose. Industrial or municipal waste, incinerator ash or by-products which contain potassium or sodium or other soluble salts which, when dissolved in water yield a basic (high pH) solution and when recovered from the waste or by-product, provide an economic benefit are also suitable.

In the following specification and claims, ash derived from burning biomass material and industrial or municipal wastes or other by-products, usable in the process herein described and claimed, are collectively 0:0 identified by the generic term, "ah" eiit u=tc a Unfortunately, the insoluble portion of reacted 15 ash, must usually still be disposed, of as waste, for 0 .example, in most boiler applications, it will not be usable for any other purpose. The waste ma terial,.

however, will no longer be a caustic material and should, 0 .o in most cases, be disposable as benign commor, fill or 0 0 20 could, in some landfills, be used as cover matertal. In some cases, where the composition of the residue and 00 0 transport costs permit, it may also be used as cement kiln raw feed. In some other situations the insoluble portion of the scrubbing material could be used, as it is now, for 00 25 production of calcium sulfate or gypsum, or as a mineral filler.

in cases where the facility producing the ash does not itself also have a boiler installation producing an exhaust of high sulfur content in need of scrubbing, the ash could be transported to other boiler installations which have such a problem, or to installations where use of a higher sulfur content fuel would provide an economic benefit. in addition, because ash derived from biomass material generally contains potassium and other alkali and alkaline earth metal salts recoverable by utilization of QA/V the exhaust gas heat or other waste heat sources, the -4resulting alkali and alkaline earth metal salts can be a valuable by-product of the process.

Brief Summary of the Invention There is disclosed herein a method of scrubbing the hot exhaust gas stream from a boiler installation or a cement kiln containing pollutants compri-sing one or more of the acidic oxides of sulfur, nitrogen and carbon and compounds of any of the halogens by reacting therewith ash wherein: the ash comprises particulate matter or solutions thereof containing as solids one or more of alkali and alkaline earth metal salts which, when mixed with water, will produce a basic (pH greater than 7) solution, mixing said particulate matter or solution thereof with water to produce a said basic solution with any insoll:ble components contained in said particulate matter, and contacting said exhaust gas stream with said basic solution thereby causing said pollutants contained therein to react with the water therein to produce acids, and 00 further causing the latter to react with any oxides, hydroxides and 00 0 carbonates of alkali and alkaline earth metals therein derived from said 00~ particulate matter or solution thereof to yield a solution of one or more 0200 of:- alkali and alkaline earth metal .alts comprising principally the 00 .0 cationic alkaline earth metal components calcium and magnesium, and alkali metal components, namely, compounds of potassium and sodium, and anionic salt components, namely, carbonate, sulfate, sulfite, nitrate and nitrite, O00 and compounds of the halogens, along with a precipitate of alkali and alkaline oarth metal salts with any insoluble components of the particulate 000matter or solution thereof, and 0 .0 finally causing said exhaust gas stream, after contacting said 0 0 solution or slurry, to emerge as scrubbed exhaust.

o There is further disclosed herein apparatus suitable for use in the 3O0 above method, comprising: 0 00 0(a) means for mixing said ash with water to form a slurry comprising undissolved solids and a solution of the soluble compounds in said ash, and means for contacting said gas stream with 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 soli~ltion of alkali and alkaline earth metal salts comprising principally the cationic components. calcium, L

,A

*E H /A'l potassium, magnesium and sodium, and anionic components, carbonate, sulfate and nitrate, and a precipitate of alkali and alkaline earthi metal salts with insoluble silicates, aluminates and iron compounds, whereby the gas of said gas stream after contacting said slurry emerges as scrubbed exhaust.

There is further disclosed herein apparatus suitable for use in the above method, comprising: a treatment tank, means for feeding water and said ash into said tank, said water and ash comprising a slurry of undissolved solids and a solution of the soluble compounds in said ash, conduits for passing said gas stream into said slurry whereby ald 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 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, carbonaii, sulfate '0 and nitrate, and a precipitate of alkali and alkaline earth metal salts o0 with insoluble silicates, aluminates and iron compounds, said gas after passage through said slurry emerging as scrubbed exhaust, 0o a precipitation tank, conduit means placing said treatment tank in communication with said precipitation tank, punmp means for conveying said slurry through said conduit means from said treatment tank into said precipitation tank wherein said slurry 00 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 00'Z means for removing said liquid from the upper part of said precipitation tank.

There is further disclosed herein a method of treatment of an exhaust gas stream containing as pollutants at least one of the halogens, acidic halogen compounds, and acidic oxides of sulfur, nitrogen ind carbon whose temperature exceeds the dew point of the gas, to produce scrubbed exhaust and useful or benign by-products, said method comprising: K 42 -6 providing a basic aqueous slurry of ash, said ash containing alkali and alkaline earth metal oxides, hydroxides or carbonates, contacting the exhaust gas stream with the slurry in a manner to scrub said exhaust gas stream and to cause the pollutants therein to react with the water in the slurry to produce acids, I allowing said acids to react with any oxides, hydroxides and carbonates of alkali and alkaline earth metal in said slurry, thereby to produce a solution containing soluble alkali metal salts and a precipitate of any insoluble alkali and alkaline earth metal salts comprising at least one of halogen compounds, carbonate, sulfate, sulfite, nitrate, and nitrite of calcium, magnesium, potassium and sodium in said slurry, recovering said precipitate from said solution, evaporating said solution freed of said precipitate, 000 etal recovering in solid form any soluble alkali and alkaline earth 00 meta salts present in said solution, and expelling the scrubbed exhaust gas stream.

In preferred methods, the exhaust gas stream Is contacted with the ash by passing the same through the said basic solution; the method Includes: the step of separating the salt solution of alkali and alkaline 26a earth metal salts from the said precipitate and Insoluble components, the 00 step of transferring the said salt solution prc-Aipitate and Insoluble components to a separation system wherein the said salt solution is separated from the precipitate and insoluble components, the step of passing the separated salt solution through a heat exchanger wherein It extracts from the exhaust gas stream before the latter is contacted with 0 the said basic solution; the exhaust gas stream is dehumidified by cooling prior to the contacting step; the salt solution Is used to both cool and 0 0 dehumidify the exhaust gas stream, and heat from the exhaust gas stream Is 0 used to remove water from the separated salt solution, In a most preferred method the heat for removing water from the separated salt solution is derived in part from one or more of the hot exhaust gas of said stream, the latent heat of vaporization of any moisture contained in said exhaust gas stream, the hydration reaction between the ash a~id water and from compressing said gas prior to said contacting step.

grief esi.ttion of the9 Drawingis A preferred form of the present invention will now be described byJ 6Away of example with reference to the accompanying drawings, wherein: Fig. 1 is a schematic representation of one apparatus for practicing the invention.

Fig. 2 is graph illustrating the effectiveness of removal of potassium and sulfur oxides from kiln dust during reaction with exhaust gas oxides according to the invention.

Fig. 3 is a flow diagram showing the mode of operation of the apparatus shown in Fig. 1.

Detailed Description of Preferred Apparatus and Method Referring to Figs. 1 and 3, a slurry composed of neutralizing material (cement dust or ash) and water exiting at 1 from an ash and water mixing tank 35, is pumped via pipe 2 into the treatment tank 3, along with additional water through inlet 4 from a suitable source (not shown) to produce a dilute slurry 5. The ash is trucked in from a source such as a 0 15, generating plant fired by biomass or an incinerator fired by waste Smaterial. In a cement plant, cement dust Is already present as a waste material. Exhaust gas from a cement kiln, incinerator or boiler (not )shown) containing one or more of the oxides of sulfur, nitrogen, carbon, 0 0and/or compounds of halogens and their oxides, enters heat exchanger 6 0200 through Inlet 7 from which It emerges as cooled exhaust. Condensed exhaust 0 0 gas moisture is collected in the heat texchanger 6 and conveyed to the treatment tan-k 3 through pipe 8, The exhaust then travels to compressor 9 through pipe 10 and is delivered via pipe 11 to distribution pipes 12 in Sthe bottom of the treatment tank 3. To prevent settling of the solids to Z 50 the bottom of treatment tank 3, the slurry may be stirred or recirculated 00by suitable means, for example by recirculation pump 13.

00,00,The exhaust gas contacts the neutralizing material by bubbling through slurry 5 of ash or cement dust and water to emerge from the tank top as scrubbed exhaust KEH4. 7o& -7- 14. Slurry 5, as a mixture of treated solid, water, and dissolved materials, is pumped by pump 15 via pipe 16 to the settling tank 17 where the settled solids 18 are pumped out by pump 19 and the waiter 20 laden with dissolved salts is pumped to heat exchanger 6 -to provide cooling for the input exhaust gas. The water from salt solution 20 is evaporated to a vapor and released via pipe 21 to the atmosphere, or the water is evaporated and then condpnsed to a liquid to recapture the latent heat for reuse. The salts from the salt zsolution 20 are concentrated and/or precipitated and collzcted from the heat exchanger via pipe 22. The cati~nic components of the collected salts are principally calcium, potassium, magnesium, and sodium. The anionic,- components of the S 15 salts are principally sulfate, carbonate and nitrate, The o actual composition of the salts will depend on the initial composition of the ash to be treated and on the composition of the exhaust gas.

The operation of the novel system for carzrying o 20 out the invention will be more completely apparent from a consideration of the flow diagram of Fig. 3 wherein the 0. 0 components are diagrammatically shown in, somewhat greater detail.

in aDistilled Water for use in the system is stored n adistilled water storage tank 23 from which it may be 2 pumpud as needed to other locations by pumps 24 and drained when desired to drain 25. Distilled water from the heat exchanger 6 is fed to the tank 23 through line 21, The salt solution 20 from settling tank 17 is pumped by pump 26 through pipe 38 to the heat exchanger 6 and through pipe 39 to coils 40 as shown at the upper left-hand side of the drawing of Fig. 3. There it is concentrated, the vapor being either released to atmosphere or fed through pipe 21 to the distilled water storage tank 23. Solids from the bottom of~ settling tank 17 may be withdrawn by pump 19 and fed to dilution tank 28 where they are diluted 8by water from tank 23 and stirred by stirrer 37 and thence removed by pump 29 to a second settling tank 30 from which the settled solids 31 are pumped by puinp 32. in the case of use of the invention in a cement plant, these settled solids are usable as raw feed for the kiln; in the case of a boiler installation, wherein ash has been used as the neutralizing agent, the solids, which are now benign, go to waste removal facilities.

Tank 30 at this point also contains solution 33 which is pumped by pump 34 to the primary mixing tank (not shown in Fig. 1) wherein it is added to the cement o dust or ash along with water to produce a slurry of the 44 desired consistency which is then pumped by pump 42 into 44treatment tank 3 to be reacted with the exhaust gas stream entering through line 11 and exiting, after neutralization, through outlet 14 to the stack. As previously dev-cribed, 'the slurry and precipitating solids are 44444continuously agitated in tank 3 by being recirculated by pumps 13, As can be seen from the schematic, additional S 20 Water can be added to the slurry in tank 3 from source 4 as well as from other parts of the system through the pip- Ing shown. The exhaust gas stream is bubbled through the 0 slurry through ports 12 to react with the acid solution a 00 41 1produced by mixing the cement dust or ash with water.

in the case of ash derived from biomass burning systems, tho ash may contain unburned carbon which, In some situations, Will float in water. The process illustrated can be modified, if desired, to allow removal of the carbon. Water 20 having unburned carbon is pumped from the surface of the settling tank to be filtered or otherwise treated to remove the carbon and is then returned to the process. if necessary, the solution cont~aining dissolved alkali and alkaline earth metal salts maiy be removed by piping (not shown) to be f iltered or otherwise cla..ansed of particulate Matter at a particulate 9 removal component. The solution is the weyed to the heat exchanger 6.

The heat exchanger 6 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 is created from well known parts combined by standard methods. For example, typically the treatment tank may have a volume of one million gallons (3,800,000 liters) and be provided with gas distribution and stirring means; the settling tank may have a volume of 1,00 thousand gallons (380,000 liters), both being copstructed from stainless steel, or other suitable materials, such as rubber, which can tolerate highly alkao line or acidic solutions. Other components are also o conventional, including necessary pumps, motors and piping to convey the material from place to place within the syscoo tern and a suitable heat exchanger.

working Principle The basic working principle in this invention is recombination and reaction of two wastes produced during burning to provide mutual neutralization of the waste....

one waste stream comprises the gasses and gasoous oxidh which produce acidic solutions in water and the other particulate matter, namely ash from a biomass or industrial or municipal waste burning facility or cement dust from a cement kiln, which produces basic solutions in water.

After partial dissolution in water, the two wastes react to neutralize each other, In the case of the ash, the process provides for reaction of or removal of the caustic components, thus rendoring what remains as neutral solids suitable for disposal as non-hazardous waste. At the same time, the exhaust gas pass4ng through the slurry in the treatment tank is cleansed of a significarbonates of alkali and alkaline earth metals therein derived from said particulate matter or solution thereof to yield a solution of one or more of:- alkali and alkaline earth metal salts comprising principally the cant portion of the compounds of the halogens and oxides of sulfur, nitrogen and halogens by forming salts of these components.

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 resulting solids are therefore suitable for use process feed stock. The potassium sulfate and other salts removed from the heat exchangercrystallization unit are suitable as fertilizer or as a source of material for extraction of chemicals, At the same time, the exhaiust gas passing through the slurry in the treatment tank is cleansed of a significant portion of the oxides of sulfur and nitrogen, by forming sulfates and nitrates.

Vxqmple Using Ash as Particulate Matter ExhausL gas from, e.g. a boiler, may be fed through duct 7, to heat exchanger 6 at a, rate of 200,000 Cubic feet (6000 in 3 per minute by compressor 9. The exhaust gas is variable in comnposition, but may contain roughly 10% water, 15% carbon dioxide, 65% nitrogen, oxygen and 500 to 10Q0 ppm nitrogen oxides and 100 to IL000 ppm sulfur dioxide. In heat exchanger 6 the exhaust gas is cooled and water is condensed, resulting in a decrease in flow volume. The exhaust gas is then drawn by compressor 9 through pipe 10 for delivery through pipe 11 to distribut:,,on pipes 12 and allowed to react with slurry where the halogens and the oxides of sulfur, nitrogen, carbon and halogens are reacted.

Ash may be introduced to treatment tank 3, for example, at a rate of eight to twelve tons (7200 to 10,800 kg) per hour dry weight. water is added to produce a dilute slurry of up -to 95% w~ter clontent. The slurry water coatent is determined by the initial concentration of alkali and alkaline eatth metal salts or other metal uu pLu ipiae or 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, 3/ 11 salts in the ash and on the desired degree of removal of these salts from the residue.

After reaction with the exhaust gas, the slurry of treated ash is pumped at a rate of approximately 200 gallons (760 liters) per minute to settling tank 17. In this tank the solids settle to form a slurry of approximately 35% water and 65% solids, beneath a solution of water and soluble salts dissolved during treatment. The water solution is pumped through outlet 20 to heat exchanger 6 at approximately 200 gallons (760 liters) per minute to provide cooling for the exhaust gas and to evaporate the water therefrom to produce the by-product salts.

Any floating carbon can be removed as previously °o explained. The by-product salts, removed via pipe 22, are produced at a rate of approximately five to twenty tops (4500 to 18,000 kg) 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 o 20 carbonate, sulfate, and nitrate. A portion of the nitrate oxidizes the sulfite to sulfate.

Example Using Cement Dust The discussion that follows is an example of use Sof the process in a moderate size wet process cement producing facility.

Exhaust gas from the kiln baghouse, fed through duct 7, is introduced to heat exchanger 6 at a rate of S200,000 actual cubic feet per minute by compressor 9. The exhaust gas is variable in composition, but contains roughly 29% water, 25% carbon dioxide, 36% nitrogen, oxygen and 400 to 600 ppm nitrogen oxides and 200 ppm sulfur dioxide. In heat exchanger 6 the exhaust gas is cooled and water is condensed, resulting in a 35% to decrease in flow volume. The exhaust gas is then drawn by compressor 9 through pipe 10 for delivery through pipe 11 to distribution pipes 12 and allowed to react with slurry i'.4 I I 12 where most of the oxides of sulfur and nitrogen are removed. In lab scale trials 99% of the SO 2 was removed from the exhaust stream.

Kiln dust is introduced to treatment tank 3 at a rate of eight to twelve tons per hour dry weight. Water 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 10 be returned to the kiln feed system. After reaction with the exhaust gas, the slurry of treated dust is pumped at a o rate of approximately 200 gallons per minute to settling S. tank 17. In this tank the solids settle to form a slurry o"o i of approximately 35% water and 65% solids, beneath a solution of water and soluble salts dissolved during treatment. The slurry is pumped by pump 19 from tank 17 o and combined with process feed for a cement plant at a rate of approximately 7.8 tons per hour of solids. The water solution is pumped through outlet 20 to heat S° 20 exchanger 6 at approximately 200 gallons per minute to provide cooling for the exhaust gas and to evaporate the water therefrom to produce the by-product salts. The byo. product salts, removed via pipe 22, are produced at a rate S o Iof approximately eight to twelve tons per day. The byproduct salts include potassium sulfate, calcium carbonate, and other salts with cationic components including potassium, calcium, magnesium, and sodium and anionic components including carbonate, sulfat'e, rad nitrate. A portion of the nitrate oxidizes the sulfite to sulfate.

Referring to Fig. 2, the results of two experiments (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 and the 5845/8 13 00 0 o 0 0 0 o 0a 0 00 00 00 0 0 o 0 0 0 0 00 0. 0 o 0 0 0q 0 0 0 0 0 0 00 00 0 0Q 0 000000 0 0 o 0 level of sulfate falls from approximately 6% to 3% or below. It should be noted that in the examples illustrated in Fig. 2 a full charge of dust was loaded in"ially into the treatment tank anA then the introduction of gas commenced. This accounts for the slopes of the graph during days A through M. '?his reduction in potassium, sodium, and sulfate concentration in the dust, from initial untreated to final treated material is greater than 50%. Samples A-M refer to successive days during which samples were taken from a continuous treat- 10 ment process.

The impact of addition of treated dust on raw feed composition is shown in the following table showing the percentage oi each oxide in normal kiln feed for both Type I and Type 1I cement production. The figures con- 15 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 respectively, of treated dust to the normal feed.

Lt-CIU-UI ~iUi OnUIrions. wnen these acids are reacted ~Nwith the oxides, hydroxides, or carbonates of alkali or 14

TABLL'

Impact of Treated Dust on Kiln Feed Composition 00 0 0 0 0 o 00 0040 0 0 00 o p 0 *0 0 0 00 00 0 0 0 0 0 00 0 0 0 o 00 00 0 0 90 Type I 2 A1 2 0 3 Fe 2 0 3 CaO NgO S03*

K

2 0 Loss Si Ratio Al/Fe Normal Feed 12.99 3 .57 1.45 43 .49 2.83 0.18 0.93 35.83 2.58 2.46 100 TPD Dust Added to Feed 12.99 3.59 1.53 43.62 2.81 0.23 0.94 35.45 2.54 2.35 200 TPD Dust Added to Feed 12.99 3.61 1.61 43.75 2.78 0.28 0.96 35.07 2.49 3.24 0400 00 0o 0 0 0 0 0 0 0 Type II S10 Ai 2 0 3 Fe 2

O

3 CaO MgO S03*

K

2 0 Loss Si Ratio AI./Fe 13.24 3 .33 1.77 43.09 2.66 0.19 0.68 35.20 2.49 1.69 13.23 3.35 2.03 43.23 2.64 0.24 0.70 34.85 2.46 1.65 13.22 3,38 2.09 38 2,62 0.29 0.72 34.49 2.42 1.62 *Sulfate expressed as S03 JO an otnerwise waste product as a substitute for expensive materials which must be purchased.

I C I i u~ar.~ 15 These results demonstrate that the major change in kiln dust composition is the removal of SO 3 and K 2 0 and that the unremoved K 2 0 and SO 3 do not significantly alter the composition of 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 understood that the same is by way of illustration and not by way of limitation, and it is intended that the scope of 10 the invention be limited only by the proper interpretation to be afforded the appended claims.

00 0 0 0 a 0 0 0e 0 00 40 0 0 0 0 0 O 0 0 0 00 0 00 0 0 0 0 00 0 00 00 0 o 0 o o

Claims

1. A method of scrubbing the hot exhaust gas stream from a boiler installation or a cement kiln containing pollutants comprising one or more of the acidic oxides of sulfur, nitrogen and carbon and compounds of any of the halogens by reacting therewith ash wherein: the ash comprises particulate matter or solutions thereof containing as solids one or more of alkali and alkaline earth metal salts which, when mixed with water, will produce a basic (pH greater than 7) solution, mixing said particulate matter or solution thereof with water to produce a said basic solution with any Insoluble components contained in said particulate matter, and contacting said exhaust gas stream with said basic solution thereby causing said pollutants contained therein to react with the water therein to produce acids, and further causing the latter to react with any oxides, hydroxides and carbonates of alkali and alkaline earth metals therein derived from said particulate matter or solution thereof to yield a solution of one or more of:- alkali and alkaline earth metal salts comprising principally the cationic alkaline earth metal components calcium and magnesium, and alkali metal components, namely, compounds of potassium and sodium, and anionic salt components, namely, carbonate, sulfate, sulfite, nitrate and nitrite, and compounds of the halogens, along with a precipitate of alkali and alkaline earth metal salts with any insoluble components of the particulate matter or solution thereof, and finally causing said exhaust gas stream, after contacting said solution or slurry, to emerge as scrubbed exhaust.

2. The method of claim 1 wherein said exhaust gas stream is contacted with said ash by passing the same through said basic solution.

3. The method of ary one of claims 1 or 2 including the step of separating said solution of alkali and alkaline earth metal salts from said precipitate and insoluble components.

4. The method of claim 1 or claim 2 including the step of transferring said solution of alkali and alkaline earth metal salts and said precipitate and insoluble components to a separation system wherein said salt solution is separated from said precipitate and insoluble components, The method of claim 4 including the step of passing the separated salt solution through a heat exchanger wherein it extracts heat L_ K 27 -17 stream is dehumidified by cooling prior to said contacting step. 17 from said exhaust gas stream before the latter is contacted with said basic solution.

6. The method of any one of claims 1 to 5 wherein said exhaust gas stream is dehumidified by cooling prior to said contacting step.

7. The method of claim 6 wherein said salt solution is used to cool and de'humidify said exhaust gas stream.

8. The method of claim 7 wherein heat from said exhaust gas stream is used to remove water from said separated salt solution.

9. The method of clai:n 8 wherein said heat is derived in part from one or more of the hot exhaust gas of said stream, the latent heat of vaporization of any moisture contained In said exhaust gas stream, the hydration reaction between the ash and water and from compressing said gas prior to said contacting step. .o i10. Apparatus suitable for carrying out the method of any one of o. claims 1 to 9, comprising: o° means for mixing said ash with water to form a slurry comprising o undissolved solids and a solution of the soluble compounds in said ash, and means for contacting said gas stream with said slurry whereby said acidic oxides contained therein will react with water to produce acids, o 0 0 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 o and nitrate, and a precipitate of alkali and alkaline earth metal salts with insoluble silicates, aluminates and iron compounds, Sg whereby the gas of said gas stream after contacting said slurry o emerges as scrubbed exhaust.

11. Apparatus according to claim 10 including means for separating S said solution of alkali and alkaline earth metal salts from said o 0. 0° precipitate and insoluble silicates, aluminates and iron compounds.

12. Apparatus according to claim 11 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 KE 7091 L- C- ~1 18 silicates, alumlna'es and iron compounds by allowing the latter to settle therefrom.

13. Apparatus according to claim 11 Including a heat exchanger, means for passing the separated solution of alkali and alkaline earth metal salts and said hot exhaust stream prior to contacting 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 ash and water for mixture with said ash.

14. Apparatus according to claim 12 Including 8 a heat exchanger, and means for passing the separated solution of alkali and alkaline earth metal salts and said hot exhaust gas therethrough before the latter contacts said slurry whereby said solution extracts heat from said gas before the latter contacts said slurry, 0

15. Apparatius suitable for carrying out the method of any one oF 0 claims I to 9, comprising: 0 o a treatment tan\, o o means for feeding water and said ash Into said tank, said water and ash comprising a slurry of undissolved solids and a solution of the soluble compounds In said ash, conduits for passing said gas stream Into said slurry whereby oo said acidic oxides contained therein will react with the water to produce Q o o acids and the latter will react with said carbonates and oxides of alkali and alkaline earth metals to yield a solution of alkali and alkaline earth 00 0 0 metal salts comprising principally the cationic components, calcium, potassium, magnesium and sodium, and anionic components, carbonate, sulfate and nitrate, and a precipitate of alkall and alkaline earth metal salts o 0° 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 communicatlon with said precipitation tank, pump means for conveying said slurry through said conduit means from said treatment tank into said precipitation tank wherein said slurry i .KEH/27091 -19- 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.

16. Apparatus according to claim 15, further comprising: 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 precipitation tank through said heat exchanger, o whereby said gas is cooled and sair liquid heated to evaporate '.water therefrom, mas17. Apparatus according to claim 15 or claim 16 further comprising mansfor agitating the slurry in said treatment tank to prevent settling 0 0 f the solids, 18, Apparatus according to claim 17 wherein saidJ agitating means o 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, 0 19. Apparatus according to claim 16, further comprising means for supplementing the heat provided by said gas for evaporating water from said 0 Q liquid, Apparatus according to claim 19 wherein said supplementing means 0~ comprises means for compressing said gas prior to passinig it Into said 0000 ml xturi

21. Apparatus according to claim 16 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 ash,

22. A method of treatment of an exhaust gas stream containing. as pollutants at least one of the halogens, acidic halogen compounds, and acidic oxides of sulfur, nitrogen and carbon whose temperature exceeds the 9 1 pipe 21 to the distilled water storage tank 23. Solids I from the bottom of settling tank 17 may be withdrawn by pump 19 and fed to dilution tank 28 where they are diluted 20 dew point of the gas, to produce scrubbed exhaust and useful or benign by-products, said method comprising: providing a basic aqueous slurry of ash, said ash containing alkali and alkaline earth metal oxides, hydroxides or carbonates, contacting the exhaust gas stream with the slurry in a manner to scrub said exhaust gas stream and to cause the pollutants therein to react with the water In the slurry to produce acids, allowing said acids to react with any oxides, hydroxides and carbonates of alkali and alkaline earth metal In said slurry, thereby to produce a solution containing soluble alkali metal salts and a precipitate of any insoluble alkali and alkaline earth metal salts comprising at least one of halogen compounds, carbonate, sulfate, sulfite, nitrate, and nitrite of calcium, magnesium, potassium and sodium in said slurry, recovering said precipitate from said solution, evaporating said solution freed of said precipitate, recovering in solid form any soluble alkali and alkaline earth metal salts present in said solution, and expelling the scrubbed exhaust gas stream. 23,. A method according to claim 22 wherein potassium and sodium are the prime reactants in said ash that combine with sulfur compounds in the flue gas to produce a solution containing alkall metal sulfates, and a precipitate comprising alkaline earth carbonates is formed from carbon dioxide scrubbed from the flue gas. o 24, A method according to claim 22 wherein said acids react to o Oo neutralize said oxides, hydroxides and carbonates. A method according to claim 22 wherein said soluble alkali and alkaline earth metal salts are recovered by crystalllzation. o. 26. A method according to claim 22 wherein water vapor obtained from evaporating said solution is condensed to form distilled water which is returned as needed for use in said method.

27. A method according to claim 22 wherein the heat for evaporating said solution is derived in part from each of the exhaust gas stream, the latent heat of moisture in said gas stream, the hydration reaction between ash and water, and from compressing said gas stream prior to reacting it with said slurry. 28, A method according to claim 22 wherein said contacting of said basic slurry and said exhaust gas stream is effected by bubbling said gas stream through said slurry. S"KEH/1Z091 may be removed by piping (not shown) to be filtered or otherwise cleansed of particulate matter at a particulate I 21

29. A method according to claim 22 comprising in addition cooling said exhaust gas stream in a manner to remove and recover heat therefrom prior to contacting said gas stream with said slurry, and evaporating said solution freed of said precipitate using only said recovered heat. The method according to claim 29 wherein said dissolved solids are recovered by crystallization.

31. The method according to claim 29 further comprising evaporating liquid from the liquid solution containing dissolved solids and recondensing the evaporated liquid.

32. A method of scrubbing the hot exhaust gas stream from a boiler installation or a cement kiln containing pollutants comprising one or more of the acidic oxides of sulfur, nitrogen and carbon and compounds of any of the halogens by reacting therewith ash substantially as hereinbefore described with reference to any one of the Examples.

33. A method of scrubbing the hot exhaust gas stream from a boiler installation or a cement kiln containing pollutants comprising one or more of the acidic oxides of sulfur, nitrogen and carbon and compounds of any of the halogens by reacting therewith ash substantially as hereinbefore described with reference to the accompanying drawings,

34. Apparatus for scrubbing the hot exhaust gas stream from a boiler installation or a cement kil; containing pollutants comprising one or more of the acidic oxides of sulfur, nitrogen and carbon and compounds of any of the halogens by reacting therewith ash substantially as hereinbefore described with reference to the accompanying drawings. A method of treatment of an exhaust gas stream substantially as hereinbefore described with reference to the accompanying drawings. DATED this FIFTH day of MARCH 1991 Passamaquoddy Tribe, a sovereign Indian Tribe recognized by the Governmers of the United States of America Patent Attorneys for the Applicant SPRUSON FERGUSON Ei KEi* s