CA2079687A1 - Process and apparatus for producing concentrated aqueous slurries and spray dried particulate products - Google Patents
Process and apparatus for producing concentrated aqueous slurries and spray dried particulate productsInfo
- Publication number
- CA2079687A1 CA2079687A1 CA002079687A CA2079687A CA2079687A1 CA 2079687 A1 CA2079687 A1 CA 2079687A1 CA 002079687 A CA002079687 A CA 002079687A CA 2079687 A CA2079687 A CA 2079687A CA 2079687 A1 CA2079687 A1 CA 2079687A1
- Authority
- CA
- Canada
- Prior art keywords
- slurry
- spray dryer
- hot gases
- gases
- heat
- 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.)
- Abandoned
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B3/00—Drying solid materials or objects by processes involving the application of heat
- F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
- F26B3/10—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour carrying the materials or objects to be dried with it
- F26B3/12—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour carrying the materials or objects to be dried with it in the form of a spray, i.e. sprayed or dispersed emulsions or suspensions
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D1/00—Evaporating
- B01D1/16—Evaporating by spraying
- B01D1/18—Evaporating by spraying to obtain dry solids
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/06—Flash distillation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/048—Purification of waste water by evaporation
-
- 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
- C04B33/00—Clay-wares
- C04B33/02—Preparing or treating the raw materials individually or as batches
- C04B33/04—Clay; Kaolin
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
- C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
- C09C1/40—Compounds of aluminium
- C09C1/42—Clays
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
- C09C3/00—Treatment in general of inorganic materials, other than fibrous fillers, to enhance their pigmenting or filling properties
- C09C3/04—Physical treatment, e.g. grinding, treatment with ultrasonic vibrations
- C09C3/043—Drying, calcination
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B23/00—Heating arrangements
- F26B23/001—Heating arrangements using waste heat
- F26B23/002—Heating arrangements using waste heat recovered from dryer exhaust gases
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
- C01P2006/82—Compositional purity water content
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S159/00—Concentrating evaporators
- Y10S159/32—Indirect heat exchange
Abstract
An improved process and apparatus for producing concentrated kaolin slurries and spray dried kaolin particulates through the use of an arrangement where an evaporation system for producing concentrated slurries is coupled with a spray dryer such that off gases from the spray dryer are used to supply heat energy to the spray dryer and to the evaporation system.
Description
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P~C)CESS AND APPARATUS FOR P}IODUCING CONC'ENTEIATED AQUEOUS
SLURRIES AND SPRAY DRIED PARTICUY.ATE PRODUCTS
Field o:E the In~ention This invention is directed t:o an improved process and apparatus for producing concentrated mineral bearinfj aqueous slurries and particula~e products obtained ~y spray drying such slurries. More specifically, the presen-t invention provides a novel method and apparatus for producing concentrated aqueous clurries and spray drled particulate products, especially kaolin clay particulates which significantly reduces the amount of energy required in the process and enhances operation of the production facility.
The present invention provides an improved process and means fox producing concentrated kaolin slurries and spray driQd kaolin particulates through the use of an arrangement where an evaporation system for producing concentrated slurries is coupled with a spray dryer su~h that off gases from the spray dryer are used to supply heat energy to the spray dryer and to the evaporation systemO ~n one aspect, the invention relates to means whereby the dew point and the heat content of the spray dryer off gases are increased such that the temperature of the evaporating system can be increased, the volume of slurry circulation decreased and the area of heat exchangers reduced. In another aspect, the in~ention relates to means for red~cing or eliminating the o~ygen content of the spray dryer gases.
In still another aspect, the invention relates to impro~ed means whereby concentrated kaolin slurries and spray dried kaolin products are produced while minimizing heat consumption and energy by recycling part of the spray dryer off gases to the spray dryer as a source of heat and utilizing part of the spray dryer off gases for heating a fluid providing a source of heat to the evaporative system.
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Back~ound of the Invention Kaolin clay was one of the firs-t lnorganic materials to be dried commercially on a large scale uslng spray dryers. To prepare pure kaolin for the paper, pain~
plastics, rubher, and ceramic ind~lstries, crude kaolin f~o~
a mine is milled, crushed, and then slurried with water and chemical dispersants. A fine clay slip containiny about 25 solids is formed. The slip is floccula-ted with acid, further chemically treated to omprove its quality~
centrifugated and then filtered to obtain a slurry of abo~
60% solids content. In conven~ional processing the 60~
slurry is spray dried to produce a particulate proc~uct containing less than one percent free moisture and about 14% crystal bound water.
Two main products dominate the current kaolin product market. The first is a dry particulate product and the second is a near 70~ solids content kaolin slurry Individual customer preference for these products depends on factors which are not relevant to the present invention~
Howe~er, it is essential that a kaolin supplier be capable of producing near 70~ slurries and dry products at minimum cost.
Since the production of these products ls accomplished by removing water from the kaolin clay slurries, and since this is accomplished by heating and evaporating water from the raw produc-t, the amount of heat required to operate such a process is of primary concern to manufacturers of these products. Therafore, a number of different techniques have been p~eviously considered to save energy.
U.S. Patent No. 1,746,294 discloses a process for the continuous calcination of gypsum wherein waste heat from a preheater furnace may be put into a steam jacke~
surrounding a calcinating chamber or used to heat steam supplied to the jacket.
U.S. Patent 4,246,039 discloses a kaolin clay process wherein a suspension of hydrated kaolin fed to an RE~ACE~NTSHE~
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electrofilter is preheated by direct heat: e~change with hot gases from a c,lay calciner used to remove water of hydration from the kaolin.
It is also known to utilize calciner off gases to supply heat to a spray dryer. For example, U.S. Patent 3,776,688 describes the operation of a rotatiny kiln plant for producing cement accordiny to a wet processO The capacity of the kiln is increased, and heat econorny improved, by drying part of the cement slurry in a spray dryer and introducing the spray dried material into the kiln. The spray drying is performed using exhaust gasks from the kiln in an integrated operation.
U.S. Patent 2,815,292 discloses a method for dewatering clay wherein waste gases from a dryer are lS delivered to a heat exchanger for heat.ing a cold clay slip prior to dewatering.
U.S. Patent 4,642,904 describes a process for drying a clay slurry which includes: dewatering an aqueous clay slurry by filtration, contacting the partially dewatered slurry with hot d~ying gases in an evaporative dryer~
condensing part of the evaporated water and using the condensate to preheat aqueous clay slurry before and after being filtered.
U.S. Patent 4,687,5~6 describes a method for concentrating a kaolin slurry whereby a beneficiated clay slurry is concentrated by evaporating water from the slurry by passing the slurry through one or more non-contact evaporative heat exchangers.
U.S. Patents 4,717,559 and 4,962,279 disclose a kaolin calciner waste heat and feed recovery system wherein hot exhaust gas from the calciner is added to and delivered with a hot air stream from a combus~or to a spray drierO
Hot gases from the spray dry r may also be used to heat water in a scrubber and the heated water is used to heat the feed to a filtration process.
Notwithstanding the various efforts and techniaues to conserve energy in the production of concentrated slurries REPLACEMEN~SHEET
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described below, none of the prior techniques considered the process and apparatus of the presen~ invention or provided the degree of savings alld enhanced production o the present invention.
Summary of the Invention One object of this invention is ~o provide an improved process for concentrating kaolin slurries and produciny dry kaolin particulate products which includes, a single or multistage evaporation system where a feed slurry is delivered to a-t least one non-evaporative heat transfer surface and then to a flash chamber. The evaporation system is used in combination with a spray dryer and part of the off gases from the spray dryer are recycled to the spray dryer to substitute for part of the cold air intake to the spray dryer heat source and a second part of the off gases from the spray dryer are used as a source of heat to the slurry concentra-ting evapora-tion system.
Another object of this invention is to provide improved means for simultaneously concentratiny solids in an aqueous slurry by evaporating water therefrom that includes at least one non-evaporative heat transfer surface followed by a flash chamber where the aqueous slurry i.s passed first to the non-evaporative heat transfer surface for heating under sufficient pressure to maintain a liquid state and then to the flash chamber. The concentrated slurry is spray dried to produce a particulate product, or taken in part as concentrated slurry product, or in par-t recycled to the non-svapora~e heat exchanger. Off gases from the spray dryer are, in part, used as a source of hea~
for ~he aqueous slurry concentrator. Part of the spray dryer off gases are also recycled to the spray dryer as a source of heat.
It is a further object of this invention to provide improved means for simultaneously producing concentrated RFPIACEMEN~ SHEET
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slurrles and spray dried solids from an aqueous slurry by evaporating water therefrom which includes at least two non-evaporati~e heat e~changer and flash chamber assemblies wherein a slurry product of the first heat exchanger and flash chamber assembly is passed to a second non-evaporative heat e~changer that may be heated optionally by recompressed vapor from the firs1: or second stage assembly and/or by heat recovered from spray dryer off gases or live steam. The heated slurry issuing from the second non--evaporative heat exchanger is then delivered to a flashchamber water vapor separator. Concentrated slurry product from the second flash chamber is taken as feed to the spray dryer or, may be taken in part, as a concentrated slurry product.
It is a still further object of this invention to provide at reduced equipment cost, improved means for simultaneously producing concentrated slurri~s and spray dried solids contained in an aqueous slurry by evaporating water from the slurry which includes more than one non-evaporative heat exchanger and flash chamber assemblies wherein a slurry product of a first heat exchanger and flash chamber assembly is passed to a second non-evaporative heat exchanger that may be heated optionally by recompressed vapor from the first stage assembly and/or by heat recovered from the spray dryer off gases. The heated slurry issuin~ from the second non-evaporative heat exchanger is passed to a flash chamber water vapor separator. Concentrated slurry product from the second flash chamber is taken as feed to the spray dryer or, may be taken in part as a concentrated slurry product.
It is another object of this in~ention, when used in a process for the production of concentrated kaolin slurries and spray dried kaolin particulates, to provide means whereby the heat content of the spray dryer off gases is increased by increasing the temperature of the spray dryer off gases used to substitute for part of the cold air ~E~ACEMENTSHEET
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intake to the spray dryer heater and -to supply heat to the a~ueous slurry concentra-tor means.
It is a still further object of this invention, which is directed towards improved processing means for removing water from kaolin slurries, to simultaneously produce concentrated slurry products and spray dried kaolin particulates whereby an evaporative slurry concentrator system is coupled with a spray d~yer such that off gasss from the spray dryer are used to supply thermal energy to a spray dryer and to the slurry c:oncentrator system.
One specific object of the present invention is to provide means to control the oxygen content of gases delivered to the spray dryer which necessarily contact the material being spray dried.
lS It is a still further object of this invention to provide means for removing water from kaolin slurries with a reduced heat consumption whereby an aqueous slurry concentration system is coupled with a spray dryer such that off gases from the spray dryer are used to supply thermal energy to the spray dryer and to the aqueous slurry concentra~ion system. The amount of off gases used to supply heat to the spray dryer being such that only sufficient cold fresh air need be introduced to the combustion system as is necessary to assure efficient fuel combustion.
In accordance with the present invention, an aqueous beneficiated clay slurry is concentrated from a solids content of about 50 to 60~ to a solids content of about 70%
by passing the aqueous slurry through one or mora non-contact heat exchanger/~lash chamber evaporative systems toproduce an a~ueous concentrate of about 70~ solids. The 70~
solids concentrate may be taken as product or he converted to a dry product by direct contact with heated gases in a spray dryer. An energy efficient process having equipman~
cost savings is achieved by recycling part of the spray dryer off gases directly to the spray dryer and part to FlE~PlACli~MEN~ SHEEl ~ .
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supply thermal energy to the aqueous slurry concentrating system.
The present invention will be more fully unders-tood following review of the drawings appended hereto and thL~
following detailed description of certaln preferred embodiments.
Brief DescriPtion of the ~rawinqs, Fig. 1 is a flow sheet diagrammatic illustration o a process of this invention in an emhodiment which may be operated to concentrate an aqueous feed slurry and to produce particulate product by spray drying the concentrated aqueous slurry;
Fig. 2 is a flow sheet diagrammatic illustratlon similar to Fig. 1 but showing an alternate embodiment of the process of this invention for concentrating an aqueous fesd slurry and spray drying the concentrated feed slurry to produce particulate product;
Fig. 3 is a flow sheet diagrammatic illustration of another alternate embodiment of the process of the present invention;
Fig. 4 is a flow sheet diagrammatic illustration of still another embodiment of the process of the present invention;
Fig. 5 is a schematic sectional view of a hea~
exchanger which may be utilized in the feed slurry evaporation system of the present invention;
Fig. 6 is a schematic sectional view of a flash chamber which may be utilized in the evaporation system of this invention;
Fig. 7 is a diagrammatic sectional view of a heat recovery unit which may be utili~ed in the practice of the present invention;
Fig. 8 is a graph showing the heat consumption requirements as a function of the amount of spray dryer exhaust gases recycled to the spray dryer in the practice of the present invention;
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Fig. 9 is a graph showing the heat savings obtainable in a process according to the present invention ove:r a process for producing an equivalent particulate produc~ ln a production facility having no feed slurry evaporati~n capability and without recycling spray dryer off gases te the spray dryer;
Fig. 10 is a graph showing how, in a speci.flc application of this ~nvention, the ma~imum temperature of the liquid obtained from the heat: recovery unit increases as the quantity of recycled spray dryer off gases increases from 0 to 62%;
- Fig. 11 is a graph showing the declining relationship between the volume of the aqueous slurry circulation rate passing through the heat e~changer as a function of the percent of exhaust gas recycled from the spray dryer; and Fig. 12 is a graph showing the declining relationship between the area of a non-evaporative heat exchanger required to produce a slurry having 70% solids content as a function of the percent of exhaust gases recycled from the spray dryer.
D~tailed Description of Certain Preferred Embodi~ents of the Inv~tion The present invention will, by specific example, now be described in detail with reference to the drawings wherein like reference numerals represent like parts throughout.
Apparatus for praoticing a preferred embodiment of the process of the present invention is diagrammatically illustrated in Fig. 1. With referenc~ to Fig. 1, there is shown a process and appratus for producing spray dried kaolin particulates from a 60~ solids kaolin feed slur.r~
delivered through a line 10 to a slurry concentrating system generally designated by the reference numeral 22 and including a heat e~changer 26 and a flash evaporator 27. An aqueous feed slurry is delivered from the feed line 10 t3 REPIACEMFNTSHEE~
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the heat exchanger 26 by a pump 24 and then, after e~itiny the heat exchanger 26 to the flash evaporator 27.
As more fully shown by Figu:re 5 of the drawings, the heat exchanger 26 is comprised of a clo~ed housing with internal chambers providing a heat transfer surface(s) 20 heated by a fluid delivered by line 46 to raise the temperature of the slurry. The i.nternal chambers of the heat exchanger 26 may be formed in conventional manner by an assembly of tubes or spac~d plates providing separa~e flow passages for the slurry and the heated fluid. The pressure internal of the chamber is controlled at a level where the slurry is maintained in a llquid sta~e and boiling is avoided. The heated slurry is then moved to the flash evaporator which includes a chamber maintained a-t a pressure less than the boiling point pressure of the slurry in orcler to rapidly evaporate water and separate the water vapor from the heated slurry. Due to the evaporation of water vapor, the slurry drawn frorn the flash evaporator is a more concentrated slurry, for example, on the order of a 70% solids content clurry.
The concentrated slurry is withdrawn from the slurry concentration system 22 by means of a pump 25 and line 29 which delivers the concentrated slurry to a spray dryer generally designated by the reference numeral 30. The pump 25 delivers the concentrated slurry by means of a line 31 to a rotary atomizing wheel 32 provided adjacent the top of a spray dryer chamber 33. Part of the concentrated slurry exiting the 1ash evaporator 27 is conveyed to the spray dryer 30 by the pump 25 and part is recirculated with additional fePd slurry by means of the pump 24 in the slurry concentration system 22.
Heat~d gases are also provided to the spray dr~er chamber 33 by means of a supply duct 41 delivering heated gas~s from a burner 40. Burner 40 is supplied with a combustible mixture of air and uel to provide the heated gases delivered to the spray dryer. As will be described more fully below, "off-gases" from the spray dryer, i.e.
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hot gases withdrawn from the spray dryer, are also delivered or recirculated through the supply duc~ 410 Internally of the spray dryer chamber 33, the concentrated slurry is sprayed by the rotary atomizing wheel 32 into the hot atmosphere or drying medium internally of the chamber 33. Small particles of the concentrated slurry provided by the rotary atomizer wheel are dried by the hot gases to produce a desired particulate material which is removed from the spray dryer in the orm of a powder and delivered by a duct 34 to a particle separator 35 wherein a ma,jor portion of the particulate product is removed at 36. A
gaseous effluent which is still at a relatively high temperature is removed from the particle separator 35 by line 37. A part of the hot gaseous effluent is delivered through a line 38 to a second particle separator 39l.
Another part of the hot gases withdrawn from the particle separator 35 is delivered along line 45 to a heat recovery unit 28. The yaseous effl~lent taken from the particl-e separator 35 is comprised of hot off-gases withdrawn from the spray dryer 30 and remain at a sufficiently high temperature to warrant utilization of the th~rmal energy contained therein and thus, the hot gases taken along line 38 are recycled to the spray dryer and the thermal energy of the hot gases taken along line 45 i5 recovered by heat recovery unit 28 for use in heat exchanger 26.
More specifically, additional partîculate product which may remain in the hot gases delivered by line 38 are separated by particle separator 39 and returned for removal with the particulate product from particle separator 35 at 36. The hot gases delivered to the particle separator 39 by line 38 are withdrawn through a duct 42 by blower 44 and delivered with hot gases provided by the burner 40 to the supply duct 41 delivering hot gases to the spray dryer 30.
The hot off gases withdrawn by line 34 from the spray dryer 30 are thus recycled through the particle separators 35 and 39 and duct 42 to supplement the hot gases provided by the burner 40 and reduce the total requirement of fuel and air ~E~ACE~ENTSHEET
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to main-tain operation of the spray dr~er 30 at a desir~d temperature. Although the duct 42 is schematically shown as deliveriny off gases to ~he burner 40, the off gases are separated from the gases of combustion internally of the burner so as not to reduce e-fficiency of the combustor, but~
are delivered or added to -the hot: gases flowing from the burner through the supply duct ~l. The duct 42 could be joined with the supply duct ~1 downstream from the burner 40. However, it is preferred to deliver the off gases f:r.om the line 42 adjacent a combustor in order to take advantage of the use of a single blower such as the blower ~4 f O:L
moving both the recycled off gases from duct 42 as well as the hot gases provided by the combustor.
The other part or portion of the hot off gases from the spray dryer delivered to the heat recovery unit 28 b~
line 45 heat a liquid, typically water which is delivered by a pump 23 in line 46 to the heat exchanger 26. The water is returned from heat exchanger 26 by return line 48 to the heat recovery unit 28. the liquid circulated -through the heat exchanger 26 and the heat recovery unit 28 is heated mainly by condensing water vapor in the reco~ery unit 280 The condensate exits the system via a condensate bleed off 47. The hot off gases from the spray dryer are drawn to the heat recovery unit 28 and exhausted by means of an exhaust.
fan 49.
With rPference to the apparatus illustrated in Fig.
l the process of the present invention is practiced by delive.ring a feed slurry through the feed line 10 to the slurry concentration system 22 where a portion of the water vapor is evaporated -to provide a concentrated slurry which in turn is delivered by pump 25 and line 31 to the spray dryer 30. The concentrated slurry is spray dried in~ernally of the chamber 33 from which the hot gases and dry particulate product are withdrawn and deli~ered to the particle separators 35 and 39. The particulate product is withdrawn rom the particle separators and the hot gases withdrawn from the spray dryer are separated to provide a RE~ACEMENTSHEET
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first portlon which is returned along llnes 3a and 42 and recycled through the spray dryer 30 and another por~1on which is delivered along the lin0 45 to the heat recovery uni-t 28 and utilized to heat a liquid circulated by the pump 23 to the heat exchanger 26.
An alternate apparatus for practicing the process of the present inventlon is diagrammatically illustrated :in Fig. 2. A number of the component:s of the apparatus of FiyD
2 may be the same as components previously discussed in the description of the apparatus of Fig. 1 and the same reference numerals as used in Fig. 1 are used to identi.fy those same or similar components in Fig. 2. The slurry concentrating apparatus of Fig. 2 includes a first stage slurry concentrating system generally designated by the lS reference numeral 12 which includes a first heat exchanyer 16 and flash evaporator 17 and a second stage slurly concentrating system generally designated by the reference numeral 22 which includes a second heat exchanger 26 and second flash evaporator chamber 27. Concentrated slurry withdrawn from the second stage slurry concentrating system 22 by line 29 and pump 25 is delivered by line 31 to a sprya nozzle 13 located internally of the spray dryer chamber 33. Hot ~ases from a burner 40 are delivered by line 41 to a gas distributor housing 11 provided at the top of the spray dryer 30. The spray nozzle 13, like the rotary atomizer wheel 32 of Figure 1 is an atomizing device whirh serves to spray small particles of the slurry fed by line 31 internally of the spray dryer chamber 33. However, in Fig~ 2, the spray nozzle 13 is directed upwardly toward the gas distribution chamber 11 to pro~ide a continuous fountain type spray of the particles or droplets of the liquid feed material which are dried or reacted -to provide a desired particulate material by the hot gases forced downward from the gas distribution chamber 11.
Th~ process of the present invention is practiced with the apparatus illustrated in Fig. 2 by delivaring an aqueous feed slurry, for example, a kaolin slurry having RE~ACEMENT5HEEr wo 9~/14530 2 ~ $ 7 ! .
50~ solid6 content, by feed line 10 ~o the first stage slurry concentrating system 12. The feed sl~rry is partially mixed with a previously concentrated slurry recirculating in the firs-t stage and delivered ~o the heat e~changer 16 by pump 14 where the slurry is heated at arl increased pressure to maintain the slurry in a liquid state and then moved to the flash evaporator chamber which .is maintained at a reduced pressure to rapidly separate water vapor from the heated slurry. The slurry is then withdrawr from the first stage slurry concentra~ion system 12 by means of a pump 15 and line 19 which delivers the sl~rry along line 21 to the second stage slurry concentrating system ~2. In the second stage slurry concentrating system 22, the slurry is mixed with previously treated slur:ry recirculated in the system 22 by pump 24 and delivered to a heat exchanger 26 having a solids content of approximately 69-% due to treatment in the first slur concentrating system 12 and mixture with the previously treated slurry in the second concentrating system 22. Th~
slurry is heated under increased pressure in the heat exchanger 26 and then moved to the flash evaporator chamber maintained under reduced pressure in the evaporator 27 to rapidly separate water vapor from the heated slurry..
Concentrated slurry, now having a solids content of approximately 70% is withdrawn from the second stage slurry concentrating system 22 by means of a pump 25 and line 29 which delivers the concentrated slurry to the spray dryer 30. The pump 25 delivers the concentrated slurry by means of line 31 to the spray nozzle 13 where the slurry is sprayed upwardly as small liquid droplets or particles and dried by hot gases forced downwardly from the gas distribution chamber 11 to dry the particles and provide a kaolin particulate product.
As previously described in the discussion of the apparatus of Fig. 1, the hot gases and particulate product are withdrawn from the spray dryer 30 by line 34 and delivered to particle separators 35 and 39 where a RE~ACEMENTSHEET
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particulate product, in this case kaoli~ particuLates having a water content of approximately 2~ are recovered~
The hot off gases from the spray dryer 30 are ~7ithdrawn along line 37 from the particle separator 3S and a portlo~
of the hot off yases are delivered along line 38 to the particle separator 39 where they are recycled by blower 4 and line 42 with hot gases from the burner ~0 to the ga.c, distribution chamber 11 of the spray dryer 30. A protion of the hot gases withdrawn from the particle separator 35 are also delivered along line 45 to the heat recovery uni.t 28 to heat water circulated by pump :23 and line ~6 to the heat e~changer 26 of the second stage slurry concentrating system 22 and then returned along line ~8. The apparatus o Fig. 2 thus provides similar energy savings by recovering or reusing thermal energy in the o~f gases from the spray dryer 30 as are realized with the apparatus o Fig. 1 and also provides an additional benefit in terms of energy savings.
The additional benefit is relaized in the two stage slurry concentrating system. As previously discussed, thermal energy from the hot spray dryer off gases is utilized in the second stage slurry concentrating system 22 to heat slurry in the heat exchanger 26.
The first stage heat exchanger 16 is heated by steam provided along a ine 6 with the condensate being withdrawn along line 9. A line 7 and compressor 8 are provided between the second stage flash evaporator 27 and the first stage steam feed line 6 to compress the hot water vapor removed from the flash evaporator 27 and deliver the same as an admi~ture to the steam delivered along line 6. The two stage slurry concentrating system of Fig. 2 thus takes further advantage of the thermal energy recovered from the hot spray dryer off ga~es and delivered to the heat exchanger 26 by oompressing water vapor withdrawn from the ~5 flash evaporator 27 and mixing the same with steam to provide an add:itional thermal eneryy input for the first stage heat exchanger 16.
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The apparatus illustrated by Flg. 3 is similar to the apparatus of Fig. 1 but includes a concentrated slurry product withdrawal line 50 connected to the spray dryer feed line 31. A valve 51 is provided to -the concentrated slurry product withdrawal line 50 to permit the selective withdrawal of a concentrated slurry product from the spray dryer feed lina 31 while simultaneously fe~d:lng concentrated slurry to the spray dryPr 30. If there is no requirement or a concentrated slurry product, the valve S1 may be closed to supply concentrated slurry from the slurry concentration system 22 to the spray dryer 30. The apparatus illustrated in Fig. 3 may be operated, :for example, by providing an aqueous feed slurry of approxima~ely 60-~ solids content to the feed line 10, withdrawing a concentrated 70~ sollds content slurry from the line 50 while simultaneously providing a 70~ solids concentrated slurry product to the rotary atomizer wheal 32 and recovering from the particle separators 35 and 39 a particulate product having approxima~ely 0.1% wate:r content.
The apparatus illustrated in Fig. 4 is also similar to the apparatus illustrated in Fig. 1 with the exceptian that separate feed slurry lines 10 and 10' are provi.ded for the slurry concentrating system 22 and the spray dryer 30 and the pump 24 delivers concentrated slurry from the system 22 to a concantrated slurry product withdrawal lin~
52. The apparatus of Fig. 4 may be operated by providing an aqueous feed slurry of approximately 60~ solids content to the feed line 10 for circulation in the slurry concentrating system 22, heating the feed slurry in the heat exchanger 26 and evaporating water vapor in the flash evaporator 27 to produce a concentrated slurry product Qf approximately 70~ solids content which may be withdrawn along lines 29 and S2. A similar, or the same, 60~ solids content aqueous feed slurry is also delivered by the eed line 10', pump 25' and line 31 to a rotary atomi~er wheel 32 provided internally of the spray dryer chamber 33 for RE~ACEMENTSHE~
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processing to recover a particulate product frorn the particle separators 35 and 39 having approximately 0~1 water content. Although separate products, a concentrated slurry and a particula~e produc:t are withdrawn from the apparatus of Fig. 4, the process of ~the invention Ls nevertheless operated as an integrated process wi~h respect to the advantages provided by the present invention in-tha-t the thermal energy of the hot gases withdrawn from the particle separator 35 is recovered by recycling a portion of the hot gases through the spray dryer 30 and utilizirlg another portion as a source of heat providing thermal energy to the heat exchanger 26.
Examples A number of examples u~ilizing the apparatus of FigO
1 to practice the process of the present invention have been conducted. The design and process conditiorls controlled during operation of the process for each of -the examples are summarized in Table 1.
These examples are for operations at a constant spray dryex inlet temperature of 550C
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WO92/14~30 2 With reference to Table 1, line 2 identifies data sets .1-5 which are equivalent to five clifferent examples of operating the apparatus of Figure :L to produce a concentrated kaolin slurry and a kaolin particulate produc~ With particular reference to lines 24 and 8 of Table 1, the examples 1-5 us:ing different rat.ios o:f recycling off gas from the spray dryer from 0% recycle in Examples 1 and 2 up to 62~ recycle in Example 5. With reference to line 8, Example 1 was run using a 60~ solids feed without subjecting the feed slurry to a .slurry concentration step. In Examples 2~5, a 60~ contents feec1 slurry was first subjected to a concentration step enhancing the solids content to 70~.
Additional data relati.ve to the examples or data set numbers 1-5 of Table 1 is set forth in Tahle 2.
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With reference to Table 2, data set numbPrs 3-5 are directly related to the data set numbers or E~amples 3-5 of Table 1 where the apparatus was operated at 29.3, ~1.0 and 62-~ recycle of spray dryer gases using a feed slurry ha~ing S 70~ solids content in the feed to the spray dryer. Data set number 1, as previously mentioned, used a feed slurry having 60~ solids content in the feed to the spray dryer~
The example represented by data set 5 which was operated with 62~ recycling of the spray clryer off gases represents the stoichiometric amount of recycle such tha-t the only cold or fresh air introduced to the system is-that quantity of air supplied to tha burner ~0 to assure and maintain efficient fuel combustion. Operation at 62-~ recycle results in a near zero oxygen content of the spray dryer off gases and a minimum heat e~changer area requirement as shown by Fig. 11. Note that a near linear reduction in heat exchanger area requirement is obtained between 5~ and 30 recycle.
In all operations of this invention, there must be a recycle of at least a part of the spray dryer off gases to the spray dryer inlet, and, further, there must be at least sufficient ambient cold air intake to the spray dryer heat source to provide sufficient oxygen for efficient fue1 combustion in the burner. In the examples of thi.s specification, as established for a kaolin processing operation, a spray dryer inlet temperature of 550C ~as used. At this gas inlet temperature, a ma~imum of 62~ of the spray dryer off gases can be recycled to the spray dryer as shown by dataset number five, Table 1. Operation at 62% recycle r~sults in essentially an oxygen free drying operation. As shown in Tables 1 and 2, the process of this invention may be operated using a spray dryer inlet temperature of 550C~ while providing more ambient cold air intake than is sufficient to provide oxygen sufficient for efficient combustion of the required fuel.
Alternately, as may be dictated by specific properties of a material beiny processed, the process of ~lEPLAC;EMFNl'SHEEr ' '': ' ' ''', ~''' ' ' , ~
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this invention may be operated at spray dryer in:Let temperatures greater -than or lecis than 550C as shown 1.n Table 1. If the inlet tempera-ture is lowered, relative.~ly more spray dryer of f gases may be recycled. I f the in:l.e~
temperature is raised, relatively less spray dryer ~kf gases can ~e recycled wh.ile obt:aining the objectives of this invention.
The energy saving ad~antages offered by the process of the present invention are clearly indicated in Tables :l and 2 whera a 40.2% heat savings is attained in Exampl.e 5 over the comparative base case of Example 1 when the process is operated to recycle about 6~% of the spray d:ryer off gases to the spray dryer. The energy savings attainab:le.
by using the process o the present invention are dramatically illustrated in Fig. 7 wherein the heat;
consumption measured in terms of KCAL/KG water evaporated.
as listed in Table 2 at line 39 is plotted against the corresponding amount of recycle for each of the exa~ples as listed in Table 1 at line 24. By definition herein, the percentage of spray dryer off gas recycled to the spray dryer is expressed as the KG/H dry gas recycle divided by the KG/H total dry gas rate times 100 Fig. 8 is a graph plottiny the heat savings reali.ze~
in each of the E~amples 2-5 as listed in Table 2, line 4Q
ralative to the amount of spray dryer off gases recycled t:-the spray dryer~ Fig. 9 is a graph plotting the recove:ry temperatures for Examples 1-5 as listed in Table 1, at line 49 against the amount of spray dryer of f gases that are recycled to the spray dryer and clearly illus~ates how the maximum recovery temperature increases from 57.4C at 0 recycle to 80.3C at 62% recycle.
Fig. 10 is a yraph illustrating how-the volume slurry circulation rate in M3/H (Table ~, line 21) is substantially reduced with an increase in the amount and temperature of spray dryer.off gases recycled to the spray dryer.
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Fig. 11 is a graph dramatically il:Lustrating ho~ ~he surface area of a heat transfer surface such as that ~/hich would be utilized in the heat e~changer 26 may be reduced with an increase in the amoun-t of spray dryer off ga.ses recycled to a spray dryer while providing the same heat recovery requirement. This is particularly si~nlficant f:rom a capital expenditure point of view since the heat exchangers used in processes to which the present inventi.on is directed typically involve relatively e~pensive tubula:Y:
or plate type heat transfer arrays and the expenditure for.
such apparatus may be reduced by reducing the size of the to-tal surface area required to effect effi.cient heat recovery. Such a reduction in the total surface area required to effect the efficient heat exchange may be attained by recycling spray dryer off gases to the sp:ray dryer in accordance with the process of the preserlt invention as clearly illustrated by Fig. 11~
In addition to the eneryy and capital expenditu.re savings, the apparatus and process of the present invent.io.r also provides an additional benefit in terms of particulate product quality. In processing kaolin, organic additiv~es are provided to raw kaolin slurries for the purpose of improving the material for subsequent processing. Howevex, the organic additive materials tend to discolor and produce off-color particulates whe~ heated in an oxygen containing atmosphere. That is, the quantity of oxygen introduced to a spray dryer chamber for purposes of drying atomized slurry particles may adversely effect the color quality of the particulates recovered from the spray dryer. The process and apparatus of applicants' invention avoids this quality problem sinca the amount of air introduced to the burner 40 may be oontrolled and limited to only that quantity of oxygen ontaining air that is essential for efficient combustion of the fuel delivered to the burnerO
The requirement for a specific temperature of the hot gases suppli2d to the spray dryer - said temperature in R~AC~MNTSHEET
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general being lower than -the tempera~ure of the combustion gases arising from the combLIstion of the fuel with only the amount of air re~uired for efficient combustion -.is met b~
mi~ing a part of the spray dryer offgases into sald combustion gases. The mass flow of dry gases thus introduced into the system then rnust also leave the system at the only exhaust point, the heat recovery unit exhaust 49. Due to the mixing of combustion gases and recycled gases, the exhaust flow contains part of the gases initially present in the system and thus the gas composition in the system gradually is shifted from that of the initial gas to that of the combustion gases being introduced through the burner 40. If, for e~ample, the operation of the burner results in combustion gases essentially fre,e of oxygen.
Although specific embodiments of the invention and several alternative processes and apparatus have been disclosed, the present invention is not to be construed as limited to the particular embodiments and forms disclosed herein since the foregoing description is to be regarded as illustrative rather than restrictive and it should be understood that modifications and variations in details of the above described embodiments of the invantion may be made without departing from the spirit and scope of the invention as defined by the claims appended hereto.
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P~C)CESS AND APPARATUS FOR P}IODUCING CONC'ENTEIATED AQUEOUS
SLURRIES AND SPRAY DRIED PARTICUY.ATE PRODUCTS
Field o:E the In~ention This invention is directed t:o an improved process and apparatus for producing concentrated mineral bearinfj aqueous slurries and particula~e products obtained ~y spray drying such slurries. More specifically, the presen-t invention provides a novel method and apparatus for producing concentrated aqueous clurries and spray drled particulate products, especially kaolin clay particulates which significantly reduces the amount of energy required in the process and enhances operation of the production facility.
The present invention provides an improved process and means fox producing concentrated kaolin slurries and spray driQd kaolin particulates through the use of an arrangement where an evaporation system for producing concentrated slurries is coupled with a spray dryer su~h that off gases from the spray dryer are used to supply heat energy to the spray dryer and to the evaporation systemO ~n one aspect, the invention relates to means whereby the dew point and the heat content of the spray dryer off gases are increased such that the temperature of the evaporating system can be increased, the volume of slurry circulation decreased and the area of heat exchangers reduced. In another aspect, the in~ention relates to means for red~cing or eliminating the o~ygen content of the spray dryer gases.
In still another aspect, the invention relates to impro~ed means whereby concentrated kaolin slurries and spray dried kaolin products are produced while minimizing heat consumption and energy by recycling part of the spray dryer off gases to the spray dryer as a source of heat and utilizing part of the spray dryer off gases for heating a fluid providing a source of heat to the evaporative system.
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Back~ound of the Invention Kaolin clay was one of the firs-t lnorganic materials to be dried commercially on a large scale uslng spray dryers. To prepare pure kaolin for the paper, pain~
plastics, rubher, and ceramic ind~lstries, crude kaolin f~o~
a mine is milled, crushed, and then slurried with water and chemical dispersants. A fine clay slip containiny about 25 solids is formed. The slip is floccula-ted with acid, further chemically treated to omprove its quality~
centrifugated and then filtered to obtain a slurry of abo~
60% solids content. In conven~ional processing the 60~
slurry is spray dried to produce a particulate proc~uct containing less than one percent free moisture and about 14% crystal bound water.
Two main products dominate the current kaolin product market. The first is a dry particulate product and the second is a near 70~ solids content kaolin slurry Individual customer preference for these products depends on factors which are not relevant to the present invention~
Howe~er, it is essential that a kaolin supplier be capable of producing near 70~ slurries and dry products at minimum cost.
Since the production of these products ls accomplished by removing water from the kaolin clay slurries, and since this is accomplished by heating and evaporating water from the raw produc-t, the amount of heat required to operate such a process is of primary concern to manufacturers of these products. Therafore, a number of different techniques have been p~eviously considered to save energy.
U.S. Patent No. 1,746,294 discloses a process for the continuous calcination of gypsum wherein waste heat from a preheater furnace may be put into a steam jacke~
surrounding a calcinating chamber or used to heat steam supplied to the jacket.
U.S. Patent 4,246,039 discloses a kaolin clay process wherein a suspension of hydrated kaolin fed to an RE~ACE~NTSHE~
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electrofilter is preheated by direct heat: e~change with hot gases from a c,lay calciner used to remove water of hydration from the kaolin.
It is also known to utilize calciner off gases to supply heat to a spray dryer. For example, U.S. Patent 3,776,688 describes the operation of a rotatiny kiln plant for producing cement accordiny to a wet processO The capacity of the kiln is increased, and heat econorny improved, by drying part of the cement slurry in a spray dryer and introducing the spray dried material into the kiln. The spray drying is performed using exhaust gasks from the kiln in an integrated operation.
U.S. Patent 2,815,292 discloses a method for dewatering clay wherein waste gases from a dryer are lS delivered to a heat exchanger for heat.ing a cold clay slip prior to dewatering.
U.S. Patent 4,642,904 describes a process for drying a clay slurry which includes: dewatering an aqueous clay slurry by filtration, contacting the partially dewatered slurry with hot d~ying gases in an evaporative dryer~
condensing part of the evaporated water and using the condensate to preheat aqueous clay slurry before and after being filtered.
U.S. Patent 4,687,5~6 describes a method for concentrating a kaolin slurry whereby a beneficiated clay slurry is concentrated by evaporating water from the slurry by passing the slurry through one or more non-contact evaporative heat exchangers.
U.S. Patents 4,717,559 and 4,962,279 disclose a kaolin calciner waste heat and feed recovery system wherein hot exhaust gas from the calciner is added to and delivered with a hot air stream from a combus~or to a spray drierO
Hot gases from the spray dry r may also be used to heat water in a scrubber and the heated water is used to heat the feed to a filtration process.
Notwithstanding the various efforts and techniaues to conserve energy in the production of concentrated slurries REPLACEMEN~SHEET
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described below, none of the prior techniques considered the process and apparatus of the presen~ invention or provided the degree of savings alld enhanced production o the present invention.
Summary of the Invention One object of this invention is ~o provide an improved process for concentrating kaolin slurries and produciny dry kaolin particulate products which includes, a single or multistage evaporation system where a feed slurry is delivered to a-t least one non-evaporative heat transfer surface and then to a flash chamber. The evaporation system is used in combination with a spray dryer and part of the off gases from the spray dryer are recycled to the spray dryer to substitute for part of the cold air intake to the spray dryer heat source and a second part of the off gases from the spray dryer are used as a source of heat to the slurry concentra-ting evapora-tion system.
Another object of this invention is to provide improved means for simultaneously concentratiny solids in an aqueous slurry by evaporating water therefrom that includes at least one non-evaporative heat transfer surface followed by a flash chamber where the aqueous slurry i.s passed first to the non-evaporative heat transfer surface for heating under sufficient pressure to maintain a liquid state and then to the flash chamber. The concentrated slurry is spray dried to produce a particulate product, or taken in part as concentrated slurry product, or in par-t recycled to the non-svapora~e heat exchanger. Off gases from the spray dryer are, in part, used as a source of hea~
for ~he aqueous slurry concentrator. Part of the spray dryer off gases are also recycled to the spray dryer as a source of heat.
It is a further object of this invention to provide improved means for simultaneously producing concentrated RFPIACEMEN~ SHEET
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slurrles and spray dried solids from an aqueous slurry by evaporating water therefrom which includes at least two non-evaporati~e heat e~changer and flash chamber assemblies wherein a slurry product of the first heat exchanger and flash chamber assembly is passed to a second non-evaporative heat e~changer that may be heated optionally by recompressed vapor from the firs1: or second stage assembly and/or by heat recovered from spray dryer off gases or live steam. The heated slurry issuing from the second non--evaporative heat exchanger is then delivered to a flashchamber water vapor separator. Concentrated slurry product from the second flash chamber is taken as feed to the spray dryer or, may be taken in part, as a concentrated slurry product.
It is a still further object of this invention to provide at reduced equipment cost, improved means for simultaneously producing concentrated slurri~s and spray dried solids contained in an aqueous slurry by evaporating water from the slurry which includes more than one non-evaporative heat exchanger and flash chamber assemblies wherein a slurry product of a first heat exchanger and flash chamber assembly is passed to a second non-evaporative heat exchanger that may be heated optionally by recompressed vapor from the first stage assembly and/or by heat recovered from the spray dryer off gases. The heated slurry issuin~ from the second non-evaporative heat exchanger is passed to a flash chamber water vapor separator. Concentrated slurry product from the second flash chamber is taken as feed to the spray dryer or, may be taken in part as a concentrated slurry product.
It is another object of this in~ention, when used in a process for the production of concentrated kaolin slurries and spray dried kaolin particulates, to provide means whereby the heat content of the spray dryer off gases is increased by increasing the temperature of the spray dryer off gases used to substitute for part of the cold air ~E~ACEMENTSHEET
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intake to the spray dryer heater and -to supply heat to the a~ueous slurry concentra-tor means.
It is a still further object of this invention, which is directed towards improved processing means for removing water from kaolin slurries, to simultaneously produce concentrated slurry products and spray dried kaolin particulates whereby an evaporative slurry concentrator system is coupled with a spray d~yer such that off gasss from the spray dryer are used to supply thermal energy to a spray dryer and to the slurry c:oncentrator system.
One specific object of the present invention is to provide means to control the oxygen content of gases delivered to the spray dryer which necessarily contact the material being spray dried.
lS It is a still further object of this invention to provide means for removing water from kaolin slurries with a reduced heat consumption whereby an aqueous slurry concentration system is coupled with a spray dryer such that off gases from the spray dryer are used to supply thermal energy to the spray dryer and to the aqueous slurry concentra~ion system. The amount of off gases used to supply heat to the spray dryer being such that only sufficient cold fresh air need be introduced to the combustion system as is necessary to assure efficient fuel combustion.
In accordance with the present invention, an aqueous beneficiated clay slurry is concentrated from a solids content of about 50 to 60~ to a solids content of about 70%
by passing the aqueous slurry through one or mora non-contact heat exchanger/~lash chamber evaporative systems toproduce an a~ueous concentrate of about 70~ solids. The 70~
solids concentrate may be taken as product or he converted to a dry product by direct contact with heated gases in a spray dryer. An energy efficient process having equipman~
cost savings is achieved by recycling part of the spray dryer off gases directly to the spray dryer and part to FlE~PlACli~MEN~ SHEEl ~ .
;~092/145~0 2 Q 7 9 ~ ~3 ~ PcrJDK~u~
supply thermal energy to the aqueous slurry concentrating system.
The present invention will be more fully unders-tood following review of the drawings appended hereto and thL~
following detailed description of certaln preferred embodiments.
Brief DescriPtion of the ~rawinqs, Fig. 1 is a flow sheet diagrammatic illustration o a process of this invention in an emhodiment which may be operated to concentrate an aqueous feed slurry and to produce particulate product by spray drying the concentrated aqueous slurry;
Fig. 2 is a flow sheet diagrammatic illustratlon similar to Fig. 1 but showing an alternate embodiment of the process of this invention for concentrating an aqueous fesd slurry and spray drying the concentrated feed slurry to produce particulate product;
Fig. 3 is a flow sheet diagrammatic illustration of another alternate embodiment of the process of the present invention;
Fig. 4 is a flow sheet diagrammatic illustration of still another embodiment of the process of the present invention;
Fig. 5 is a schematic sectional view of a hea~
exchanger which may be utilized in the feed slurry evaporation system of the present invention;
Fig. 6 is a schematic sectional view of a flash chamber which may be utilized in the evaporation system of this invention;
Fig. 7 is a diagrammatic sectional view of a heat recovery unit which may be utili~ed in the practice of the present invention;
Fig. 8 is a graph showing the heat consumption requirements as a function of the amount of spray dryer exhaust gases recycled to the spray dryer in the practice of the present invention;
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Fig. 9 is a graph showing the heat savings obtainable in a process according to the present invention ove:r a process for producing an equivalent particulate produc~ ln a production facility having no feed slurry evaporati~n capability and without recycling spray dryer off gases te the spray dryer;
Fig. 10 is a graph showing how, in a speci.flc application of this ~nvention, the ma~imum temperature of the liquid obtained from the heat: recovery unit increases as the quantity of recycled spray dryer off gases increases from 0 to 62%;
- Fig. 11 is a graph showing the declining relationship between the volume of the aqueous slurry circulation rate passing through the heat e~changer as a function of the percent of exhaust gas recycled from the spray dryer; and Fig. 12 is a graph showing the declining relationship between the area of a non-evaporative heat exchanger required to produce a slurry having 70% solids content as a function of the percent of exhaust gases recycled from the spray dryer.
D~tailed Description of Certain Preferred Embodi~ents of the Inv~tion The present invention will, by specific example, now be described in detail with reference to the drawings wherein like reference numerals represent like parts throughout.
Apparatus for praoticing a preferred embodiment of the process of the present invention is diagrammatically illustrated in Fig. 1. With referenc~ to Fig. 1, there is shown a process and appratus for producing spray dried kaolin particulates from a 60~ solids kaolin feed slur.r~
delivered through a line 10 to a slurry concentrating system generally designated by the reference numeral 22 and including a heat e~changer 26 and a flash evaporator 27. An aqueous feed slurry is delivered from the feed line 10 t3 REPIACEMFNTSHEE~
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the heat exchanger 26 by a pump 24 and then, after e~itiny the heat exchanger 26 to the flash evaporator 27.
As more fully shown by Figu:re 5 of the drawings, the heat exchanger 26 is comprised of a clo~ed housing with internal chambers providing a heat transfer surface(s) 20 heated by a fluid delivered by line 46 to raise the temperature of the slurry. The i.nternal chambers of the heat exchanger 26 may be formed in conventional manner by an assembly of tubes or spac~d plates providing separa~e flow passages for the slurry and the heated fluid. The pressure internal of the chamber is controlled at a level where the slurry is maintained in a llquid sta~e and boiling is avoided. The heated slurry is then moved to the flash evaporator which includes a chamber maintained a-t a pressure less than the boiling point pressure of the slurry in orcler to rapidly evaporate water and separate the water vapor from the heated slurry. Due to the evaporation of water vapor, the slurry drawn frorn the flash evaporator is a more concentrated slurry, for example, on the order of a 70% solids content clurry.
The concentrated slurry is withdrawn from the slurry concentration system 22 by means of a pump 25 and line 29 which delivers the concentrated slurry to a spray dryer generally designated by the reference numeral 30. The pump 25 delivers the concentrated slurry by means of a line 31 to a rotary atomizing wheel 32 provided adjacent the top of a spray dryer chamber 33. Part of the concentrated slurry exiting the 1ash evaporator 27 is conveyed to the spray dryer 30 by the pump 25 and part is recirculated with additional fePd slurry by means of the pump 24 in the slurry concentration system 22.
Heat~d gases are also provided to the spray dr~er chamber 33 by means of a supply duct 41 delivering heated gas~s from a burner 40. Burner 40 is supplied with a combustible mixture of air and uel to provide the heated gases delivered to the spray dryer. As will be described more fully below, "off-gases" from the spray dryer, i.e.
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hot gases withdrawn from the spray dryer, are also delivered or recirculated through the supply duc~ 410 Internally of the spray dryer chamber 33, the concentrated slurry is sprayed by the rotary atomizing wheel 32 into the hot atmosphere or drying medium internally of the chamber 33. Small particles of the concentrated slurry provided by the rotary atomizer wheel are dried by the hot gases to produce a desired particulate material which is removed from the spray dryer in the orm of a powder and delivered by a duct 34 to a particle separator 35 wherein a ma,jor portion of the particulate product is removed at 36. A
gaseous effluent which is still at a relatively high temperature is removed from the particle separator 35 by line 37. A part of the hot gaseous effluent is delivered through a line 38 to a second particle separator 39l.
Another part of the hot gases withdrawn from the particle separator 35 is delivered along line 45 to a heat recovery unit 28. The yaseous effl~lent taken from the particl-e separator 35 is comprised of hot off-gases withdrawn from the spray dryer 30 and remain at a sufficiently high temperature to warrant utilization of the th~rmal energy contained therein and thus, the hot gases taken along line 38 are recycled to the spray dryer and the thermal energy of the hot gases taken along line 45 i5 recovered by heat recovery unit 28 for use in heat exchanger 26.
More specifically, additional partîculate product which may remain in the hot gases delivered by line 38 are separated by particle separator 39 and returned for removal with the particulate product from particle separator 35 at 36. The hot gases delivered to the particle separator 39 by line 38 are withdrawn through a duct 42 by blower 44 and delivered with hot gases provided by the burner 40 to the supply duct 41 delivering hot gases to the spray dryer 30.
The hot off gases withdrawn by line 34 from the spray dryer 30 are thus recycled through the particle separators 35 and 39 and duct 42 to supplement the hot gases provided by the burner 40 and reduce the total requirement of fuel and air ~E~ACE~ENTSHEET
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to main-tain operation of the spray dr~er 30 at a desir~d temperature. Although the duct 42 is schematically shown as deliveriny off gases to ~he burner 40, the off gases are separated from the gases of combustion internally of the burner so as not to reduce e-fficiency of the combustor, but~
are delivered or added to -the hot: gases flowing from the burner through the supply duct ~l. The duct 42 could be joined with the supply duct ~1 downstream from the burner 40. However, it is preferred to deliver the off gases f:r.om the line 42 adjacent a combustor in order to take advantage of the use of a single blower such as the blower ~4 f O:L
moving both the recycled off gases from duct 42 as well as the hot gases provided by the combustor.
The other part or portion of the hot off gases from the spray dryer delivered to the heat recovery unit 28 b~
line 45 heat a liquid, typically water which is delivered by a pump 23 in line 46 to the heat exchanger 26. The water is returned from heat exchanger 26 by return line 48 to the heat recovery unit 28. the liquid circulated -through the heat exchanger 26 and the heat recovery unit 28 is heated mainly by condensing water vapor in the reco~ery unit 280 The condensate exits the system via a condensate bleed off 47. The hot off gases from the spray dryer are drawn to the heat recovery unit 28 and exhausted by means of an exhaust.
fan 49.
With rPference to the apparatus illustrated in Fig.
l the process of the present invention is practiced by delive.ring a feed slurry through the feed line 10 to the slurry concentration system 22 where a portion of the water vapor is evaporated -to provide a concentrated slurry which in turn is delivered by pump 25 and line 31 to the spray dryer 30. The concentrated slurry is spray dried in~ernally of the chamber 33 from which the hot gases and dry particulate product are withdrawn and deli~ered to the particle separators 35 and 39. The particulate product is withdrawn rom the particle separators and the hot gases withdrawn from the spray dryer are separated to provide a RE~ACEMENTSHEET
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first portlon which is returned along llnes 3a and 42 and recycled through the spray dryer 30 and another por~1on which is delivered along the lin0 45 to the heat recovery uni-t 28 and utilized to heat a liquid circulated by the pump 23 to the heat exchanger 26.
An alternate apparatus for practicing the process of the present inventlon is diagrammatically illustrated :in Fig. 2. A number of the component:s of the apparatus of FiyD
2 may be the same as components previously discussed in the description of the apparatus of Fig. 1 and the same reference numerals as used in Fig. 1 are used to identi.fy those same or similar components in Fig. 2. The slurry concentrating apparatus of Fig. 2 includes a first stage slurry concentrating system generally designated by the lS reference numeral 12 which includes a first heat exchanyer 16 and flash evaporator 17 and a second stage slurly concentrating system generally designated by the reference numeral 22 which includes a second heat exchanger 26 and second flash evaporator chamber 27. Concentrated slurry withdrawn from the second stage slurry concentrating system 22 by line 29 and pump 25 is delivered by line 31 to a sprya nozzle 13 located internally of the spray dryer chamber 33. Hot ~ases from a burner 40 are delivered by line 41 to a gas distributor housing 11 provided at the top of the spray dryer 30. The spray nozzle 13, like the rotary atomizer wheel 32 of Figure 1 is an atomizing device whirh serves to spray small particles of the slurry fed by line 31 internally of the spray dryer chamber 33. However, in Fig~ 2, the spray nozzle 13 is directed upwardly toward the gas distribution chamber 11 to pro~ide a continuous fountain type spray of the particles or droplets of the liquid feed material which are dried or reacted -to provide a desired particulate material by the hot gases forced downward from the gas distribution chamber 11.
Th~ process of the present invention is practiced with the apparatus illustrated in Fig. 2 by delivaring an aqueous feed slurry, for example, a kaolin slurry having RE~ACEMENT5HEEr wo 9~/14530 2 ~ $ 7 ! .
50~ solid6 content, by feed line 10 ~o the first stage slurry concentrating system 12. The feed sl~rry is partially mixed with a previously concentrated slurry recirculating in the firs-t stage and delivered ~o the heat e~changer 16 by pump 14 where the slurry is heated at arl increased pressure to maintain the slurry in a liquid state and then moved to the flash evaporator chamber which .is maintained at a reduced pressure to rapidly separate water vapor from the heated slurry. The slurry is then withdrawr from the first stage slurry concentra~ion system 12 by means of a pump 15 and line 19 which delivers the sl~rry along line 21 to the second stage slurry concentrating system ~2. In the second stage slurry concentrating system 22, the slurry is mixed with previously treated slur:ry recirculated in the system 22 by pump 24 and delivered to a heat exchanger 26 having a solids content of approximately 69-% due to treatment in the first slur concentrating system 12 and mixture with the previously treated slurry in the second concentrating system 22. Th~
slurry is heated under increased pressure in the heat exchanger 26 and then moved to the flash evaporator chamber maintained under reduced pressure in the evaporator 27 to rapidly separate water vapor from the heated slurry..
Concentrated slurry, now having a solids content of approximately 70% is withdrawn from the second stage slurry concentrating system 22 by means of a pump 25 and line 29 which delivers the concentrated slurry to the spray dryer 30. The pump 25 delivers the concentrated slurry by means of line 31 to the spray nozzle 13 where the slurry is sprayed upwardly as small liquid droplets or particles and dried by hot gases forced downwardly from the gas distribution chamber 11 to dry the particles and provide a kaolin particulate product.
As previously described in the discussion of the apparatus of Fig. 1, the hot gases and particulate product are withdrawn from the spray dryer 30 by line 34 and delivered to particle separators 35 and 39 where a RE~ACEMENTSHEET
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particulate product, in this case kaoli~ particuLates having a water content of approximately 2~ are recovered~
The hot off gases from the spray dryer 30 are ~7ithdrawn along line 37 from the particle separator 3S and a portlo~
of the hot off yases are delivered along line 38 to the particle separator 39 where they are recycled by blower 4 and line 42 with hot gases from the burner ~0 to the ga.c, distribution chamber 11 of the spray dryer 30. A protion of the hot gases withdrawn from the particle separator 35 are also delivered along line 45 to the heat recovery uni.t 28 to heat water circulated by pump :23 and line ~6 to the heat e~changer 26 of the second stage slurry concentrating system 22 and then returned along line ~8. The apparatus o Fig. 2 thus provides similar energy savings by recovering or reusing thermal energy in the o~f gases from the spray dryer 30 as are realized with the apparatus o Fig. 1 and also provides an additional benefit in terms of energy savings.
The additional benefit is relaized in the two stage slurry concentrating system. As previously discussed, thermal energy from the hot spray dryer off gases is utilized in the second stage slurry concentrating system 22 to heat slurry in the heat exchanger 26.
The first stage heat exchanger 16 is heated by steam provided along a ine 6 with the condensate being withdrawn along line 9. A line 7 and compressor 8 are provided between the second stage flash evaporator 27 and the first stage steam feed line 6 to compress the hot water vapor removed from the flash evaporator 27 and deliver the same as an admi~ture to the steam delivered along line 6. The two stage slurry concentrating system of Fig. 2 thus takes further advantage of the thermal energy recovered from the hot spray dryer off ga~es and delivered to the heat exchanger 26 by oompressing water vapor withdrawn from the ~5 flash evaporator 27 and mixing the same with steam to provide an add:itional thermal eneryy input for the first stage heat exchanger 16.
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The apparatus illustrated by Flg. 3 is similar to the apparatus of Fig. 1 but includes a concentrated slurry product withdrawal line 50 connected to the spray dryer feed line 31. A valve 51 is provided to -the concentrated slurry product withdrawal line 50 to permit the selective withdrawal of a concentrated slurry product from the spray dryer feed lina 31 while simultaneously fe~d:lng concentrated slurry to the spray dryPr 30. If there is no requirement or a concentrated slurry product, the valve S1 may be closed to supply concentrated slurry from the slurry concentration system 22 to the spray dryer 30. The apparatus illustrated in Fig. 3 may be operated, :for example, by providing an aqueous feed slurry of approxima~ely 60-~ solids content to the feed line 10, withdrawing a concentrated 70~ sollds content slurry from the line 50 while simultaneously providing a 70~ solids concentrated slurry product to the rotary atomizer wheal 32 and recovering from the particle separators 35 and 39 a particulate product having approxima~ely 0.1% wate:r content.
The apparatus illustrated in Fig. 4 is also similar to the apparatus illustrated in Fig. 1 with the exceptian that separate feed slurry lines 10 and 10' are provi.ded for the slurry concentrating system 22 and the spray dryer 30 and the pump 24 delivers concentrated slurry from the system 22 to a concantrated slurry product withdrawal lin~
52. The apparatus of Fig. 4 may be operated by providing an aqueous feed slurry of approximately 60~ solids content to the feed line 10 for circulation in the slurry concentrating system 22, heating the feed slurry in the heat exchanger 26 and evaporating water vapor in the flash evaporator 27 to produce a concentrated slurry product Qf approximately 70~ solids content which may be withdrawn along lines 29 and S2. A similar, or the same, 60~ solids content aqueous feed slurry is also delivered by the eed line 10', pump 25' and line 31 to a rotary atomi~er wheel 32 provided internally of the spray dryer chamber 33 for RE~ACEMENTSHE~
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processing to recover a particulate product frorn the particle separators 35 and 39 having approximately 0~1 water content. Although separate products, a concentrated slurry and a particula~e produc:t are withdrawn from the apparatus of Fig. 4, the process of ~the invention Ls nevertheless operated as an integrated process wi~h respect to the advantages provided by the present invention in-tha-t the thermal energy of the hot gases withdrawn from the particle separator 35 is recovered by recycling a portion of the hot gases through the spray dryer 30 and utilizirlg another portion as a source of heat providing thermal energy to the heat exchanger 26.
Examples A number of examples u~ilizing the apparatus of FigO
1 to practice the process of the present invention have been conducted. The design and process conditiorls controlled during operation of the process for each of -the examples are summarized in Table 1.
These examples are for operations at a constant spray dryex inlet temperature of 550C
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WO92/14~30 2 With reference to Table 1, line 2 identifies data sets .1-5 which are equivalent to five clifferent examples of operating the apparatus of Figure :L to produce a concentrated kaolin slurry and a kaolin particulate produc~ With particular reference to lines 24 and 8 of Table 1, the examples 1-5 us:ing different rat.ios o:f recycling off gas from the spray dryer from 0% recycle in Examples 1 and 2 up to 62~ recycle in Example 5. With reference to line 8, Example 1 was run using a 60~ solids feed without subjecting the feed slurry to a .slurry concentration step. In Examples 2~5, a 60~ contents feec1 slurry was first subjected to a concentration step enhancing the solids content to 70~.
Additional data relati.ve to the examples or data set numbers 1-5 of Table 1 is set forth in Tahle 2.
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With reference to Table 2, data set numbPrs 3-5 are directly related to the data set numbers or E~amples 3-5 of Table 1 where the apparatus was operated at 29.3, ~1.0 and 62-~ recycle of spray dryer gases using a feed slurry ha~ing S 70~ solids content in the feed to the spray dryer. Data set number 1, as previously mentioned, used a feed slurry having 60~ solids content in the feed to the spray dryer~
The example represented by data set 5 which was operated with 62~ recycling of the spray clryer off gases represents the stoichiometric amount of recycle such tha-t the only cold or fresh air introduced to the system is-that quantity of air supplied to tha burner ~0 to assure and maintain efficient fuel combustion. Operation at 62-~ recycle results in a near zero oxygen content of the spray dryer off gases and a minimum heat e~changer area requirement as shown by Fig. 11. Note that a near linear reduction in heat exchanger area requirement is obtained between 5~ and 30 recycle.
In all operations of this invention, there must be a recycle of at least a part of the spray dryer off gases to the spray dryer inlet, and, further, there must be at least sufficient ambient cold air intake to the spray dryer heat source to provide sufficient oxygen for efficient fue1 combustion in the burner. In the examples of thi.s specification, as established for a kaolin processing operation, a spray dryer inlet temperature of 550C ~as used. At this gas inlet temperature, a ma~imum of 62~ of the spray dryer off gases can be recycled to the spray dryer as shown by dataset number five, Table 1. Operation at 62% recycle r~sults in essentially an oxygen free drying operation. As shown in Tables 1 and 2, the process of this invention may be operated using a spray dryer inlet temperature of 550C~ while providing more ambient cold air intake than is sufficient to provide oxygen sufficient for efficient combustion of the required fuel.
Alternately, as may be dictated by specific properties of a material beiny processed, the process of ~lEPLAC;EMFNl'SHEEr ' '': ' ' ''', ~''' ' ' , ~
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this invention may be operated at spray dryer in:Let temperatures greater -than or lecis than 550C as shown 1.n Table 1. If the inlet tempera-ture is lowered, relative.~ly more spray dryer of f gases may be recycled. I f the in:l.e~
temperature is raised, relatively less spray dryer ~kf gases can ~e recycled wh.ile obt:aining the objectives of this invention.
The energy saving ad~antages offered by the process of the present invention are clearly indicated in Tables :l and 2 whera a 40.2% heat savings is attained in Exampl.e 5 over the comparative base case of Example 1 when the process is operated to recycle about 6~% of the spray d:ryer off gases to the spray dryer. The energy savings attainab:le.
by using the process o the present invention are dramatically illustrated in Fig. 7 wherein the heat;
consumption measured in terms of KCAL/KG water evaporated.
as listed in Table 2 at line 39 is plotted against the corresponding amount of recycle for each of the exa~ples as listed in Table 1 at line 24. By definition herein, the percentage of spray dryer off gas recycled to the spray dryer is expressed as the KG/H dry gas recycle divided by the KG/H total dry gas rate times 100 Fig. 8 is a graph plottiny the heat savings reali.ze~
in each of the E~amples 2-5 as listed in Table 2, line 4Q
ralative to the amount of spray dryer off gases recycled t:-the spray dryer~ Fig. 9 is a graph plotting the recove:ry temperatures for Examples 1-5 as listed in Table 1, at line 49 against the amount of spray dryer of f gases that are recycled to the spray dryer and clearly illus~ates how the maximum recovery temperature increases from 57.4C at 0 recycle to 80.3C at 62% recycle.
Fig. 10 is a yraph illustrating how-the volume slurry circulation rate in M3/H (Table ~, line 21) is substantially reduced with an increase in the amount and temperature of spray dryer.off gases recycled to the spray dryer.
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Fig. 11 is a graph dramatically il:Lustrating ho~ ~he surface area of a heat transfer surface such as that ~/hich would be utilized in the heat e~changer 26 may be reduced with an increase in the amoun-t of spray dryer off ga.ses recycled to a spray dryer while providing the same heat recovery requirement. This is particularly si~nlficant f:rom a capital expenditure point of view since the heat exchangers used in processes to which the present inventi.on is directed typically involve relatively e~pensive tubula:Y:
or plate type heat transfer arrays and the expenditure for.
such apparatus may be reduced by reducing the size of the to-tal surface area required to effect effi.cient heat recovery. Such a reduction in the total surface area required to effect the efficient heat exchange may be attained by recycling spray dryer off gases to the sp:ray dryer in accordance with the process of the preserlt invention as clearly illustrated by Fig. 11~
In addition to the eneryy and capital expenditu.re savings, the apparatus and process of the present invent.io.r also provides an additional benefit in terms of particulate product quality. In processing kaolin, organic additiv~es are provided to raw kaolin slurries for the purpose of improving the material for subsequent processing. Howevex, the organic additive materials tend to discolor and produce off-color particulates whe~ heated in an oxygen containing atmosphere. That is, the quantity of oxygen introduced to a spray dryer chamber for purposes of drying atomized slurry particles may adversely effect the color quality of the particulates recovered from the spray dryer. The process and apparatus of applicants' invention avoids this quality problem sinca the amount of air introduced to the burner 40 may be oontrolled and limited to only that quantity of oxygen ontaining air that is essential for efficient combustion of the fuel delivered to the burnerO
The requirement for a specific temperature of the hot gases suppli2d to the spray dryer - said temperature in R~AC~MNTSHEET
.
.. , ~ . .
W09~/l4530 2 ~ 7 ~ Pcr/~Jn~
general being lower than -the tempera~ure of the combustion gases arising from the combLIstion of the fuel with only the amount of air re~uired for efficient combustion -.is met b~
mi~ing a part of the spray dryer offgases into sald combustion gases. The mass flow of dry gases thus introduced into the system then rnust also leave the system at the only exhaust point, the heat recovery unit exhaust 49. Due to the mixing of combustion gases and recycled gases, the exhaust flow contains part of the gases initially present in the system and thus the gas composition in the system gradually is shifted from that of the initial gas to that of the combustion gases being introduced through the burner 40. If, for e~ample, the operation of the burner results in combustion gases essentially fre,e of oxygen.
Although specific embodiments of the invention and several alternative processes and apparatus have been disclosed, the present invention is not to be construed as limited to the particular embodiments and forms disclosed herein since the foregoing description is to be regarded as illustrative rather than restrictive and it should be understood that modifications and variations in details of the above described embodiments of the invantion may be made without departing from the spirit and scope of the invention as defined by the claims appended hereto.
RE~ACEMENTS~EET
Claims (9)
1. A process for producing a concentrated aqueous slurry and a particulate product comprising the steps of:
delivering a feed slurry to an evaporation system including at least one heat exchanger heated by a fluid and a heat recovery unit for heating said fluid, evaporating water from said feed slurry in said evaporation system to provide a concentrated aqueous slurry, providing hot gases of combustion by burning a fuel with an oxygen containing gas in a burner, delivering said hot gases to a spray dryer, feeding said concentrated aqueous slurry to an atomizing device in said spray dryer and atomizing said slurry, drying atomized particles of said concentrated slurry in said spray dryer, withdrawing said particles and hot gases from said spray dryer and delivering hot gases together with particles entrained therein to a particle separator, withdrawing said particles from said particle separator as a particulate product, withdrawing said hot gases from said particle separator, delivering a first portion of said hot gases withdrawn from said particle separator together with hot gases provided by said burner to sid spray dryer, and delivering a second portion of said hot gases withdrawn from said particle separator to said heat recovery unit of said evaporation system.
delivering a feed slurry to an evaporation system including at least one heat exchanger heated by a fluid and a heat recovery unit for heating said fluid, evaporating water from said feed slurry in said evaporation system to provide a concentrated aqueous slurry, providing hot gases of combustion by burning a fuel with an oxygen containing gas in a burner, delivering said hot gases to a spray dryer, feeding said concentrated aqueous slurry to an atomizing device in said spray dryer and atomizing said slurry, drying atomized particles of said concentrated slurry in said spray dryer, withdrawing said particles and hot gases from said spray dryer and delivering hot gases together with particles entrained therein to a particle separator, withdrawing said particles from said particle separator as a particulate product, withdrawing said hot gases from said particle separator, delivering a first portion of said hot gases withdrawn from said particle separator together with hot gases provided by said burner to sid spray dryer, and delivering a second portion of said hot gases withdrawn from said particle separator to said heat recovery unit of said evaporation system.
2. The process defined by claim 1, wherein said heat exchanger includes a non-evaporative heat transfer surface heated by said fluid, said evaporation system includes a flash chamber, and said process further includes the steps of: heating said feed slurry on said heat transfer surface under pressure to maintain said feed slurry in a liquid state, moving said heated feed slurry to said flash chamber, and separating water vapor from said heated feed slurry under reduced pressure in said flash chamber.
3. The process defined by claim 1, wherein said evaporation system includes a first and a second heat exchanger and flash chamber assemblies, said feed slurry is first delivered to said first heat exchanger and flash chamber asssembly and then delivered to said second heat exchanger and flash chamber assembly, and said second heat exchanger is heated by a fluid heated by said heat recovery unit.
4. The process defined by claim 1, wherein said first portion of hot gases withdrawn from said particle separator are recycled to said spray dryer in a percentage amount greater than zero but not greater than 62%.
5. The process defined by claim 1, wherein said particulate product is of a clay origin.
6. The process defined by claim 1, wherein said particulate product is Kaolin.
7. A process for producing a spray dried particulate product comprising the steps of:
providing hot gases of combustion by burning a fuel with an oxygen containing gas in a burner, delivering said hot gases to a spray dryer, feeding an aqueous mineral containing slurry to an atomizing device in said spray dryer, atomizing said slurry and drying said slurry by exposure to said hot gases in said spray dryer to produce dried particles of said mineral, withdrawing said particles and hot gases from said spray dryer and delivering said particles and hot gases to a particle separator, withdrawing said particles from said particle separator as a product of said process, and delivering a portion of said hot gases withdrawn from said particle separator together with hot gases provided by said burner to said spray dryer, whereby at least a portion of said hat gases delivered to said spray dryer are recycled and the oxygen content of said hot gases delivered to said spray dryer from said burner is minimized.
providing hot gases of combustion by burning a fuel with an oxygen containing gas in a burner, delivering said hot gases to a spray dryer, feeding an aqueous mineral containing slurry to an atomizing device in said spray dryer, atomizing said slurry and drying said slurry by exposure to said hot gases in said spray dryer to produce dried particles of said mineral, withdrawing said particles and hot gases from said spray dryer and delivering said particles and hot gases to a particle separator, withdrawing said particles from said particle separator as a product of said process, and delivering a portion of said hot gases withdrawn from said particle separator together with hot gases provided by said burner to said spray dryer, whereby at least a portion of said hat gases delivered to said spray dryer are recycled and the oxygen content of said hot gases delivered to said spray dryer from said burner is minimized.
8. The process defined by claim 7, wherein said oxygen containing gas provided to said burner is air and said process further includes the step of controlling the quantity of air supplied to said burner to provide a minimum quantity of oxygen required for efficient combustion of the fuel supplied to the burner.
9. Apparatus for producing a concentrated aqueous slurry comprising:
a spray dryer, means for delivering hot gases to dry atomized particles in said spray dryer, an evaporation system including at least one. non evaporative heat transfer surface heated by a fluid, a heat recovery unit for heating said fluid, and a flash chamber, means for withdrawing hot gases from said spray dryer and delivering said hot gases to said heat recovery unit to heat said fluid, means for delivering a feed slurry to said non-evaporative heat transfer surface under pressure to heat said feed slurry and maintain said feed slurry in a liquid state, and means for delivering said heated slurry to said flash chamber under reduced pressure to separate water vapor from said heated slurry.
a spray dryer, means for delivering hot gases to dry atomized particles in said spray dryer, an evaporation system including at least one. non evaporative heat transfer surface heated by a fluid, a heat recovery unit for heating said fluid, and a flash chamber, means for withdrawing hot gases from said spray dryer and delivering said hot gases to said heat recovery unit to heat said fluid, means for delivering a feed slurry to said non-evaporative heat transfer surface under pressure to heat said feed slurry and maintain said feed slurry in a liquid state, and means for delivering said heated slurry to said flash chamber under reduced pressure to separate water vapor from said heated slurry.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/656,269 US5248387A (en) | 1991-02-15 | 1991-02-15 | Process for producing concentrated aqueous slurries and spray dried particulate products |
| US656.269 | 1991-02-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2079687A1 true CA2079687A1 (en) | 1992-08-16 |
Family
ID=24632336
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002079687A Abandoned CA2079687A1 (en) | 1991-02-15 | 1992-02-11 | Process and apparatus for producing concentrated aqueous slurries and spray dried particulate products |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5248387A (en) |
| AU (1) | AU1321192A (en) |
| CA (1) | CA2079687A1 (en) |
| GB (1) | GB2259458A (en) |
| WO (1) | WO1992014530A1 (en) |
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| DK131493D0 (en) * | 1993-11-23 | 1993-11-23 | Anhydro As | PROCEDURE FOR SPRAYING AIR SUSPENSION |
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| IT1281915B1 (en) * | 1995-08-04 | 1998-03-03 | Bruno Pietrella | PROCESS OF PURIFICATION, REGENERATION AND REUSE OF INDUSTRIAL SEWAGE |
| CA2178575A1 (en) * | 1996-06-07 | 1997-12-08 | Kebir Ratnani | Spout-fluid bed dryer and granulator for the treatment of animal manure |
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| IT1295225B1 (en) * | 1997-10-14 | 1999-05-04 | Magneti Marelli Spa | METHOD AND PLANT FOR THE PRODUCTION OF SALT GRAINS WITH PREFIXED GRANULOMETRIC DIMENSIONS. |
| US6368658B1 (en) * | 1999-04-19 | 2002-04-09 | Scimed Life Systems, Inc. | Coating medical devices using air suspension |
| US6730349B2 (en) * | 1999-04-19 | 2004-05-04 | Scimed Life Systems, Inc. | Mechanical and acoustical suspension coating of medical implants |
| US6253463B1 (en) * | 1999-04-26 | 2001-07-03 | Niro A/S | Method of spray drying |
| FI106633B (en) * | 1999-07-29 | 2001-03-15 | Outokumpu Oy | A device for heating a fluid containing solid material |
| US6463675B1 (en) * | 1999-09-29 | 2002-10-15 | Niro A/S | Process and a plant for spray drying |
| AUPQ540200A0 (en) * | 2000-02-02 | 2000-02-24 | Aquadyne Incorporated | Water distillation systems |
| US6402824B1 (en) | 2000-05-26 | 2002-06-11 | J. M. Huber Corporation | Processes for preparing precipitated calcium carbonate compositions and the products thereof |
| CZ20031556A3 (en) * | 2000-11-06 | 2004-03-17 | Cabot Corporation | Modified oxides of valve metals with reduced content of oxygen |
| ES2191539B1 (en) * | 2001-08-16 | 2005-02-01 | Esmalglass, S.A. | PROCESS FOR MANUFACTURE OF FRIED, CORRESPONDING INSTALLATION AND FRITAS SO OBTAINED. |
| DE10358015A1 (en) * | 2003-12-11 | 2005-07-14 | Gea Wiegand Gmbh | evaporation |
| US7275644B2 (en) | 2004-10-12 | 2007-10-02 | Great River Energy | Apparatus and method of separating and concentrating organic and/or non-organic material |
| US8062410B2 (en) | 2004-10-12 | 2011-11-22 | Great River Energy | Apparatus and method of enhancing the quality of high-moisture materials and separating and concentrating organic and/or non-organic material contained therein |
| US8579999B2 (en) | 2004-10-12 | 2013-11-12 | Great River Energy | Method of enhancing the quality of high-moisture materials using system heat sources |
| US7987613B2 (en) * | 2004-10-12 | 2011-08-02 | Great River Energy | Control system for particulate material drying apparatus and process |
| US8523963B2 (en) | 2004-10-12 | 2013-09-03 | Great River Energy | Apparatus for heat treatment of particulate materials |
| WO2006105189A1 (en) * | 2005-03-31 | 2006-10-05 | Imerys Kaolin, Inc. | Aggregated particulate minerals, compositions comprising aggregated calcium carbonate, methods of making and uses thereof |
| CA2636351C (en) * | 2006-01-13 | 2014-04-15 | Certainteed Gypsum, Inc. | System and method for the production of alpha type gypsum using heat recovery |
| US8388926B2 (en) | 2006-01-13 | 2013-03-05 | Certainteed Gypsum, Inc. | System and method for the production of gypsum using heat recovery |
| US20080152782A1 (en) * | 2006-12-15 | 2008-06-26 | Georgios Avgoustopoulos | Waste treatment process |
| US8097128B1 (en) | 2007-06-01 | 2012-01-17 | Sherry Raymond C | Method and apparatus for purifying water |
| GB2465361A (en) * | 2008-11-13 | 2010-05-19 | Thomas John Stubbing | Material drying or processing method and apparatus comprising a venturi |
| US8496787B2 (en) * | 2009-07-26 | 2013-07-30 | Michael John Lord | Method and apparatus for effluent free sea water desalination |
| CN102294124B (en) * | 2010-06-23 | 2013-06-05 | 中国科学院工程热物理研究所 | Spray drying method and device based on absorption heat pipe |
| KR20170109912A (en) * | 2016-03-22 | 2017-10-10 | 삼성에스디아이 주식회사 | Apparatus for drying electrode plate |
| UA126678C2 (en) | 2017-03-03 | 2023-01-11 | Даґлас Текнікал Лімітед | Apparatus and method for continuously drying bulk goods, in particular wood chips and/or wood fibers comprising a hot gas cyclone |
| WO2018157948A1 (en) | 2017-03-03 | 2018-09-07 | Douglas Technical Limited | Apparatus and method for continuously drying bulk goods, in particular wood chips and/or wood fibers comprising a solid fired hot gas generator |
| US11248845B2 (en) | 2017-03-03 | 2022-02-15 | Douglas Technical Limited | Apparatus and method for continuously drying bulk goods, in particular wood chips and/or wood fibers comprising a heat exchanger |
| EP3635312A1 (en) * | 2017-06-06 | 2020-04-15 | Douglas Technical Limited | Apparatus and method for continuously drying bulk goods |
| CN107213846A (en) * | 2017-07-07 | 2017-09-29 | 西安建筑科技大学 | A kind of granulation of net gas and smoke processing system and technique for ceramic industry |
| CN109624134B (en) * | 2017-10-09 | 2021-02-23 | 中国石油化工股份有限公司 | Styrene butadiene rubber drying device and method for reducing waste gas emission |
| IT201700114724A1 (en) * | 2017-10-11 | 2019-04-11 | Pozzi Leopoldo S R L | PLANT AND METHOD FOR THE TREATMENT OF BARBOTTINA |
| CN108823409B (en) * | 2018-06-29 | 2020-05-05 | 东北大学 | System and method for recovering waste heat of liquid magnesium chloride generated in titanium sponge preparation process |
| CN109173321B (en) * | 2018-08-21 | 2021-01-26 | 无锡华翔化纤有限公司 | Polyester fiber production is with section boiling crystallization desiccator |
| CN112704890B (en) * | 2020-11-05 | 2023-02-28 | 中国恩菲工程技术有限公司 | Liquid feeding device and liquid feeding control method |
| CN114247166B (en) * | 2021-12-27 | 2023-01-13 | 江苏帕特斯环保科技有限公司 | Horizontal spraying flash evaporation granulating device and process thereof |
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| US2189083A (en) * | 1937-10-23 | 1940-02-06 | Lancaster Iron Works Inc | Disposal process for the treatment of weak ammoniacal waste liquors from coal distilation plants |
| US2756029A (en) * | 1952-02-19 | 1956-07-24 | Freeport Sulphur Co | Heating systems for water containing dissolved scale-forming solids |
| US2815292A (en) * | 1953-06-30 | 1957-12-03 | Thiele Kaolin Co | Method for dewatering clay |
| US3423173A (en) * | 1965-12-08 | 1969-01-21 | Armour Agricultural Chem Co | Spray concentration of wet process orthophosphoric acid to polyphosphoric acid |
| DE1729232B1 (en) * | 1967-12-20 | 1971-07-15 | Knapsack Ag | Process and device for the production of salts from thin solutions or suspensions containing the latter |
| US4171243A (en) * | 1975-06-17 | 1979-10-16 | The Chemithon Corporation | Spray drying method |
| US4246039A (en) * | 1979-01-08 | 1981-01-20 | Engelhard Minerals & Chemicals Corporation | Kaolin clay processing |
| US4473438A (en) * | 1981-05-04 | 1984-09-25 | Witco Chemical Corporation | Spray drying method |
| US4687546B1 (en) * | 1985-07-19 | 1996-06-04 | Anglo American Clays Corp | Method of concentrating slurried kaolin |
| US4642904A (en) * | 1985-08-01 | 1987-02-17 | Georgia Krolin Company, Inc. | Energy conserving process for drying a clay slurry |
| US4962279A (en) * | 1986-06-03 | 1990-10-09 | Ecc America Inc. | Kaolin calciner waste heat and feed recovery process |
-
1991
- 1991-02-15 US US07/656,269 patent/US5248387A/en not_active Expired - Fee Related
-
1992
- 1992-02-11 WO PCT/DK1992/000042 patent/WO1992014530A1/en not_active Application Discontinuation
- 1992-02-11 CA CA002079687A patent/CA2079687A1/en not_active Abandoned
- 1992-02-11 GB GB9222577A patent/GB2259458A/en not_active Withdrawn
- 1992-02-11 AU AU13211/92A patent/AU1321192A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO1992014530A1 (en) | 1992-09-03 |
| GB9222577D0 (en) | 1992-12-16 |
| AU1321192A (en) | 1992-09-15 |
| GB2259458A (en) | 1993-03-17 |
| US5248387A (en) | 1993-09-28 |
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