WO2012054409A1 - Production of calcined lime from natural chalk material in a rotary kiln - Google Patents
Production of calcined lime from natural chalk material in a rotary kiln Download PDFInfo
- Publication number
- WO2012054409A1 WO2012054409A1 PCT/US2011/056604 US2011056604W WO2012054409A1 WO 2012054409 A1 WO2012054409 A1 WO 2012054409A1 US 2011056604 W US2011056604 W US 2011056604W WO 2012054409 A1 WO2012054409 A1 WO 2012054409A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- kiln
- additive
- chalk
- area
- nodulization
- Prior art date
Links
- 239000000463 material Substances 0.000 title claims description 58
- 235000008733 Citrus aurantifolia Nutrition 0.000 title claims description 19
- 235000011941 Tilia x europaea Nutrition 0.000 title claims description 19
- 239000004571 lime Substances 0.000 title claims description 19
- 238000004519 manufacturing process Methods 0.000 title description 6
- 239000000654 additive Substances 0.000 claims abstract description 33
- 238000000034 method Methods 0.000 claims abstract description 30
- 230000000996 additive effect Effects 0.000 claims abstract description 27
- 238000001354 calcination Methods 0.000 claims abstract description 22
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 claims abstract description 13
- 239000007787 solid Substances 0.000 claims description 11
- 235000019738 Limestone Nutrition 0.000 claims description 10
- 239000006028 limestone Substances 0.000 claims description 10
- 238000001035 drying Methods 0.000 claims description 6
- 229910000019 calcium carbonate Inorganic materials 0.000 claims description 5
- 239000000428 dust Substances 0.000 claims description 5
- 238000012216 screening Methods 0.000 claims description 5
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical group [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 4
- 229910052783 alkali metal Inorganic materials 0.000 claims description 3
- -1 alkaline earth metal salt Chemical class 0.000 claims description 3
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 2
- 150000001340 alkali metals Chemical class 0.000 claims description 2
- 229910052784 alkaline earth metal Inorganic materials 0.000 claims description 2
- 229910052708 sodium Inorganic materials 0.000 claims description 2
- 239000011734 sodium Substances 0.000 claims description 2
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 2
- 238000007599 discharging Methods 0.000 claims 2
- XAEFZNCEHLXOMS-UHFFFAOYSA-M potassium benzoate Chemical compound [K+].[O-]C(=O)C1=CC=CC=C1 XAEFZNCEHLXOMS-UHFFFAOYSA-M 0.000 claims 1
- 239000000843 powder Substances 0.000 abstract description 3
- 239000007789 gas Substances 0.000 description 15
- 239000000047 product Substances 0.000 description 9
- 238000005054 agglomeration Methods 0.000 description 5
- 230000002776 aggregation Effects 0.000 description 5
- 239000003513 alkali Substances 0.000 description 5
- 235000010216 calcium carbonate Nutrition 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- 230000007704 transition Effects 0.000 description 4
- 239000000292 calcium oxide Substances 0.000 description 3
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 239000008187 granular material Substances 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 239000007858 starting material Substances 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 229910021532 Calcite Inorganic materials 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000012717 electrostatic precipitator Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 159000000001 potassium salts Chemical class 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 239000011435 rock Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- 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
- C04B2/00—Lime, magnesia or dolomite
- C04B2/10—Preheating, burning calcining or cooling
- C04B2/104—Ingredients added before or during the burning process
-
- 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
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/03—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on magnesium oxide, calcium oxide or oxide mixtures derived from dolomite
- C04B35/057—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on magnesium oxide, calcium oxide or oxide mixtures derived from dolomite based on calcium oxide
-
- 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
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
- C04B35/62605—Treating the starting powders individually or as mixtures
- C04B35/62695—Granulation or pelletising
-
- 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
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
- C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
- C04B35/6303—Inorganic additives
-
- 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
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/64—Burning or sintering processes
-
- 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
- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
- C04B2235/30—Constituents and secondary phases not being of a fibrous nature
- C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
- C04B2235/3201—Alkali metal oxides or oxide-forming salts thereof
-
- 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
- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
- C04B2235/30—Constituents and secondary phases not being of a fibrous nature
- C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
- C04B2235/3205—Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
- C04B2235/3208—Calcium oxide or oxide-forming salts thereof, e.g. lime
Definitions
- the present invention is broadly concerned with processing naturally occurring chalk or a fine limestone material into a lime product.
- the above and other objectives are generally achieved by producing a granulated or nodulized lime product utilizing a rotary kiln.
- the resulting product is suitable for the vast majority of existing lime markets.
- the present invention utilizes chalk processing steps that include drying, preheating, agglomeration, calcination and cooling to form from a micron sized chalk starting material a granulated or nodulized lime product having a preferred diameter top size ranging from about 3mm to about 50 mm, and most preferably from about 6mm to about 20mm that is suitable for further processing.
- the desired size or size range of the granulated lime product will be determined by the practitioner of the invention, and increasing the amount of additive material used according to the invention will increase the top size of the granulated lime product.
- Numerous equipment configurations can be utilized to perform the above steps but all rely on a rotary kiln to support the high temperature agglomeration and calcination.
- the rotary kiln if sufficiently sized, can support all of the processing steps except the cooling step.
- the drying and all or a portion of the preheating of the natural chalk starting material may be performed outside of a rotary kiln to reduce the required rotary kiln size.
- the natural chalk material is introduced to the rotary kiln along with a comparatively small quantity of an additive material comprising of an alkali metal salt or an alkaline metal salt or a compound demonstrating similar behavior as described farther that serves to promote nodulization of the chalk.
- the chalk nodules undergo final calcination in the rotary kiln and are then discharged into a cooling device.
- the alkali or alkaline metal salt additive has the property of becoming sticky prior to melting, and further of becoming sticky at temperatures below the temperature at which the calcination of the chalk will commence.
- the calcination temperature of the natural chalk will vary according to the desired final product properties, but will generall range from about 900° C to about 1 100° C.
- the stickiness of the alkali or alkaline metal salt will promote, at suitable temperatures, the agglomeration of the chalk grains to produce larger nodules.
- the alkali or alkaline metal salt further promotes agglomeration of the natural chalk in a rotary kiln environment in that under normal operating conditions a portion of the additive material will vaporize under the kiln flame, travel in counter- current direction to the direction of movement of the chalk material through the kiln to a cooler portion of the kiln (typically the preheating portion of the kiln). Upon entering the cooler portion of the kiln, the alkali vapor condenses onto the surfaces of the chalk solids, thereby enabling further contribution to the nodulization process and minimizing the quantity of additive material that must be used.
- Figure 1 depicts pertinent portions of a natural chalk processing system according to the present invention.
- natural chalk to be processed is fed to optional dryer and preheater 11 via a feeder such as feed screw 12.
- the function of dryer and preheater 11 may be alternately performed by the rotary kiln.
- dryer and preheater 11 is a flash dryer, although other preheating systems such as a hammer mill dryer may e utilized.
- Dryer and preheater 11 has an initial chalk drying area 13 and a subsequent chalk preheating area 14.
- the chalk material is fed into the bottom of flash dryer's shaft via feed screw 12 and is carried upwards (moving in the direction of arrow C) in the hot drying gas (moving in the direction of arrow D), which in the present case is exhaust gas from rotary kiln 20, although exhaust gas from another thermal process may be utilized or alternatively the hot gas can be produced in a combustion chamber.
- the flash dryer thoroughly disperses the material in the hot gas.
- the predried natural chalk entrained in a preheating gas is directed to an optional first separator 16, which is preferably a cyclone type separator, which is configured to separate the predried chalk from the preheating gas.
- the separated chalk is thereafter directed to rotary kiln 20 via conduit 21.
- the separated preheating gas in which there may be entrained chalk dust, is directed to an optional second separator (not shown) such as a baghouse or electrostatic precipitator, to separate the dust from the gas and direct the separated dust to rotary kiln 20.
- Natural chalk treated by the instant process typically consists of minute individual calcite crystals in the order of 1 micron or less in size. Chalk is a form of carbonate rocks containing 97.5 - 98.5wt% calcium carbonate. The instant process can be used on other fine, primarily (>80wt%) calcium carbonate, limestone materials containing a significant fine fraction (at least 90wt% of the total material) of material that has a diameter of less than 1 mm- specifically lime kiln dust exhausted from a lime kiln.
- the process of the present invention can also be utilized to calcine other limestone material that previously was not easily processed.
- limestone screening fines is a waste material from a lime manufacturing process that typically contains about 95 wt% of material having a diameter of 6mm or less. This material is not easily calcined because it also contains a quantity (at least 10 wt percent) of fines material that has a diameter of less than 74 microns resulting in extremely dusty conditions under normal processing techniques.
- the process of the present invention will granulize limestone screening fines containing a fines fraction thereby allowing for efficient calcination of these fines in a rotary kiln.
- the chalk moves from material inlet 24 to material outlet 25 in counter- current direction to the direction of movement of the hot gases in the kiln, the movement of the gas and material being shown by arrows A and B respectively.
- the hot gases are generated by flame 22 inside the kiln, which in turn is generated by fuel that enters the kiln at point 23.
- a rotary kiln is well known in the art, and is a cylindrical vessel, inclined slightly to the horizontal, and rotated slowly about its axis. The material to be processed is fed into the upper material entry end of the cylinder. As the kiln rotates, material gradually moves down towards the lower material exit end, and in the process will undergo a certain amount of stirring and mixing.
- a drying zone there may be up to four temperature zones or areas: a drying zone, a preheating zone, a transition/nodulization zone and a calcining zone, with the transition/nodulization zone and the calcining zone being necessary to the present invention.
- a preheating zone there may be up to four temperature zones or areas: a drying zone, a preheating zone, a transition/nodulization zone and a calcining zone, with the transition/nodulization zone and the calcining zone being necessary to the present invention.
- a transition/nodulization zone and the calcining zone being necessary to the present invention.
- Zone I in which the temperature in a chalk process will range from about 225 °C to about 700 °C, is the preheating zone. To a certain extent the dimensions of the preheating area can be shortened, or as indicated above eliminated, depending on the extent of material preheating, if any, that takes place external to the kiln.
- Zone II in which the temperature in a chalk process will range from about 700°C to about 900°C, is the transition/nodulization area.
- Zone III in which the temperature in a chalk process will range from about 900°C to about 1100°C, is the calcination area in which the rapid calcination of chalk to form calcium oxide begins, The calcined material is then directed to a cooler (not shown) such as a grate cooler or an attached tube cooler.
- a cooler such as a grate cooler or an attached tube cooler.
- the calcination of natural chalk in a rotary kiln is greatly facilitated and in fact made practical by nodulizing the natural chalk during the course of its treatment in the rotary kiln in the presence of a specified additive.
- the additive is preferably added by homogeneously mixing it to the chalk material, either with the feed prior to entry into the kiln, such as inserting the additive into material feed screw 12 at point 30 so that it mixes with the chalk material prior to the chalk entering the dryer/preheater 1 1, or at an earlier point in the process, such as at point 31 wherein the additive is inserted into the feed conduit leading directly into the kiln.
- the additives that are utilized in the present invention to promote nodulization of the chalk must not be harmful to the properties of the end lime material or have significant environmental drawbacks. Moreover, these additives must have the property of becoming sticky, viscous, or tacky (hereafter
- the additives are preferably alkali metal or alkaline earth metal salts, more preferably sodium or potassium salts and most preferably sodium carbonate.
- the additives are generally added to/combined with the chalk in an amount that generally ranges from about 0.05 wt% to about 0.5 wt%, and most preferably about 0.2 wt% to about 0.5 wt%, based on the weight of the natural chalk being added to the kiln.
- the size of the end granules is controlled by the amount of additive utilized. Although amounts above about 0.5 wt% of the additive may be used, larger amounts may promote the formation of ever increasingly larger granules of chalk and may also contribute to the formation of coatings in the kiln.
- the additive will tend to become sticky in Zone II, the transitional area of the kiln, where it starts to promote nodulization of the chalk material.
- the majority of the additives will be incorporated with and will exit the kiln with the lime product.
- typically a very small amount of the additive will vaporize near the flame end of the kiln.
- the vaporized additive will be carried by the heating gases through the kiln in a direction counter-current to the movement of the material through the kiln and will recondense on the material in the lower temperature environment of Zone I, the preheating area, thereby forming a partial circulation of the alkali to improve its distribution and effectiveness for agglomeration.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Structural Engineering (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Muffle Furnaces And Rotary Kilns (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Furnace Details (AREA)
- Processing Of Solid Wastes (AREA)
Abstract
Disclosed is a method for calcining a natural chalk powder within a rotary kiln. The powder is inserted into the kiln accompanied by an additive that promotes nodulization of the powder to thereby facilitate the treatment of the chalk powder within the rotary kiln. The nodulization takes place at temperatures less than the calcining temperatures of the chalk and prior to the nodulized chalk being calcined within the kiln.
Description
PRODUCTION OF CALCINED LIME FROM NATURAL CHALK MATERIAL IN A
ROTARY KILN Field Of The Invention
The present invention is broadly concerned with processing naturally occurring chalk or a fine limestone material into a lime product.
Background Of The Invention
There are vast deposits of naturally occurring chalk in Russia, the northwestern part of Europe and in South America, such as Peru. Such chalk is composed mostly of calcium carbonate with minor amounts of silt and clay, and is potentially an excellent material for the production of lime. Unlike limestone, the normal feed for lime production, such naturally occurring chalk is typically characterized by a fine grain size on the order of several microns. This grain size makes it disadvantageous to process the chalk in normal limestone processing systems such as shaft kilns and long kilns, where, for example, in the latter processing naturally occurring chalk using normal processing techniques results in extremely dusty conditions while consuming large amounts of fuel. In addition, attempts at utilizing gas suspension calciners that are designed specifically to handle fine grain materials have also been unsuccessful due to the poor flow properties of the fine chalk grains at elevated temperatures during the conversion to calcium oxide. This chalk exhibits very high reactivity such that the recarbonization (CaO +CO2→ CaCO3) in the upper stages of a gas suspension system yields catastrophic buildup in the preheater preventing continuous stable operation.
It is an object therefore of the present invention to produce a lime product from natural chalk that is suitable for lime markets. Brief Description Of The Invention
The above and other objectives are generally achieved by producing a granulated or nodulized lime product utilizing a rotary kiln. The resulting product is suitable for the vast majority of existing lime markets. The present invention utilizes chalk processing steps that include drying, preheating, agglomeration, calcination and cooling to form from a micron sized chalk starting material a granulated or nodulized lime product having a preferred diameter top size ranging from about 3mm to about 50 mm, and most preferably from about 6mm to about 20mm that is suitable for further processing. Ultimately, it is understood that the desired size or size range of the granulated lime product will be determined by the practitioner of the invention, and increasing the amount of additive material used according to the invention will increase the top size of the granulated lime product. Numerous equipment configurations can be utilized to perform the above steps but all rely on a rotary kiln to support the high temperature agglomeration and calcination. The rotary kiln, if sufficiently sized, can support all of the processing steps except the cooling step.
Alternatively and preferably the drying and all or a portion of the preheating of the natural chalk starting material may be performed outside of a rotary kiln to reduce the required rotary kiln size. The natural chalk material is introduced to the rotary kiln along with a comparatively small quantity of an additive material comprising of an alkali metal salt or an alkaline metal salt or a compound demonstrating similar behavior as described farther that serves to promote nodulization of the chalk. The chalk nodules undergo final calcination in the rotary kiln and are then discharged into a cooling device.
The alkali or alkaline metal salt additive has the property of becoming sticky prior to melting, and further of becoming sticky at temperatures below the temperature at which the calcination of the chalk will commence. The calcination temperature of the natural chalk will vary according to the desired final product properties, but will generall range from about 900° C to about 1 100° C.
The stickiness of the alkali or alkaline metal salt will promote, at suitable temperatures, the agglomeration of the chalk grains to produce larger nodules. In addition it has been discovered that the alkali or alkaline metal salt further promotes agglomeration of the natural chalk in a rotary kiln environment in that under normal operating conditions a portion of the additive material will vaporize under the kiln flame, travel in counter- current direction to the direction of movement of the chalk material through the kiln to a cooler portion of the kiln (typically the preheating portion of the kiln). Upon entering the cooler portion of the kiln, the alkali vapor condenses onto the surfaces of the chalk solids, thereby enabling further contribution to the nodulization process and minimizing the quantity of additive material that must be used.
Description of the Drawing
Figure 1 depicts pertinent portions of a natural chalk processing system according to the present invention.
Detailed Description of the Invention
With reference to the Figure, natural chalk to be processed is fed to optional dryer and preheater 11 via a feeder such as feed screw 12. The function of dryer and preheater 11 may be alternately performed by the rotary kiln. In the presently depicted embodiment, dryer and preheater 11 is a flash dryer, although other preheating systems such as a hammer mill dryer may e utilized. Dryer and preheater 11 has an initial chalk drying area 13 and a subsequent chalk preheating area 14. The chalk material is fed into the bottom of flash dryer's shaft via feed screw 12 and is carried upwards (moving in the direction of arrow C) in the hot drying gas (moving in the direction of arrow D), which in the present case is exhaust gas from rotary kiln 20, although exhaust gas from another thermal process may be utilized or alternatively the hot gas can be produced in a combustion chamber. The flash dryer thoroughly disperses the material in the hot gas. The predried natural chalk entrained in a preheating gas is directed to an optional first separator 16, which is preferably a cyclone type separator, which is configured to separate the predried chalk from the preheating gas. The separated chalk is thereafter directed to rotary kiln 20 via conduit 21. The separated preheating gas, in which there
may be entrained chalk dust, is directed to an optional second separator (not shown) such as a baghouse or electrostatic precipitator, to separate the dust from the gas and direct the separated dust to rotary kiln 20. Natural chalk treated by the instant process typically consists of minute individual calcite crystals in the order of 1 micron or less in size. Chalk is a form of carbonate rocks containing 97.5 - 98.5wt% calcium carbonate. The instant process can be used on other fine, primarily (>80wt%) calcium carbonate, limestone materials containing a significant fine fraction (at least 90wt% of the total material) of material that has a diameter of less than 1 mm- specifically lime kiln dust exhausted from a lime kiln.
The process of the present invention can also be utilized to calcine other limestone material that previously was not easily processed. For example, limestone screening fines is a waste material from a lime manufacturing process that typically contains about 95 wt% of material having a diameter of 6mm or less. This material is not easily calcined because it also contains a quantity (at least 10 wt percent) of fines material that has a diameter of less than 74 microns resulting in extremely dusty conditions under normal processing techniques. The process of the present invention will granulize limestone screening fines containing a fines fraction thereby allowing for efficient calcination of these fines in a rotary kiln.
In the rotary kiln the chalk moves from material inlet 24 to material outlet 25 in counter- current direction to the direction of movement of the hot gases in the kiln, the movement of the gas and material being shown by arrows A and B respectively. The hot gases are generated by flame 22 inside the kiln, which in turn is generated by fuel that enters the kiln at point 23. A rotary kiln is well known in the art, and is a cylindrical vessel, inclined slightly to the horizontal, and rotated slowly about its axis. The material to be processed is fed into the upper material entry end of the cylinder. As the kiln rotates, material gradually moves down towards the lower material exit end, and in the process will undergo a certain amount of stirring and mixing.
In the rotary kiln utilized in the present invention there may be up to four temperature zones or areas: a drying zone, a preheating zone, a transition/nodulization zone and a calcining zone, with the transition/nodulization zone and the calcining zone being necessary to the present invention. In the depicted embodiment of the invention there are three zones:
Zone I, in which the temperature in a chalk process will range from about 225 °C to about 700 °C, is the preheating zone. To a certain extent the dimensions of the preheating area can be shortened, or as indicated above eliminated, depending on the extent of material preheating, if any, that takes place external to the kiln.
Zone II, in which the temperature in a chalk process will range from about 700°C to about 900°C, is the transition/nodulization area. Through the use of selected additives in the chalk calcining process, as described below, the nodulization of the chalk particles will take place in this area of the kiln.
Zone III, in which the temperature in a chalk process will range from about 900°C to about 1100°C, is the calcination area in which the rapid calcination of chalk to form calcium oxide begins, The calcined material is then directed to a cooler (not shown) such as a grate cooler or an attached tube cooler.
The calcination of natural chalk in a rotary kiln is greatly facilitated and in fact made practical by nodulizing the natural chalk during the course of its treatment in the rotary kiln in the presence of a specified additive. The additive is preferably added by homogeneously mixing it to the chalk material, either with the feed prior to entry into the kiln, such as inserting the additive into material feed screw 12 at point 30 so that it mixes with the chalk material prior to the chalk entering the dryer/preheater 1 1, or at an earlier point in the process, such as at point 31 wherein the additive is inserted into the feed conduit leading directly into the kiln. The additives that are utilized in the present invention to promote nodulization of the chalk must not be harmful to the properties of the end lime material or have significant environmental drawbacks. Moreover, these additives must have the property of becoming sticky, viscous, or tacky (hereafter
"sticky") at temperatures that are less than the rapid calcination temperatures of the natural chalk, and more specifically at temperatures below, preferably about 50°C to
about 200CC below, the temperatures at which rapid calcination of the chalk material commences. The additives are preferably alkali metal or alkaline earth metal salts, more preferably sodium or potassium salts and most preferably sodium carbonate. The additives are generally added to/combined with the chalk in an amount that generally ranges from about 0.05 wt% to about 0.5 wt%, and most preferably about 0.2 wt% to about 0.5 wt%, based on the weight of the natural chalk being added to the kiln. The size of the end granules is controlled by the amount of additive utilized. Although amounts above about 0.5 wt% of the additive may be used, larger amounts may promote the formation of ever increasingly larger granules of chalk and may also contribute to the formation of coatings in the kiln.
The additive will tend to become sticky in Zone II, the transitional area of the kiln, where it starts to promote nodulization of the chalk material. The majority of the additives will be incorporated with and will exit the kiln with the lime product. However, typically a very small amount of the additive will vaporize near the flame end of the kiln. The vaporized additive will be carried by the heating gases through the kiln in a direction counter-current to the movement of the material through the kiln and will recondense on the material in the lower temperature environment of Zone I, the preheating area, thereby forming a partial circulation of the alkali to improve its distribution and effectiveness for agglomeration.
In rotary kiln 20 natural chalk in primarily powder form is fed into the kiln at elevated material feed end 24 and the process heat enters at lower material exiting end 25. As the chalk moves through the kiln due to its rotation and the effects of gravity, it passes through three distinct areas within the kiln which are temperature dependent and progress in sequence from the coolest to the hottest area of the kiln, namely, initial preheating Zone I, transition area Zone II and calcination area Zone III, The calcined material will exit at lower end 25 as product 26 and is transferred to a cooler (not shown). Typical rotary kiln production rates will range from 200 mtpd to 1600 mtpd.
The residence time of the chalk material in the kiln will typically range between 1 and 3 hours.
Claims
1. A method for nodulizing and calcining a calcium carbonate material within a rotary kiln having a solid charging end and a solid exit end comprising:
inserting the material and an additive that promotes nodulization of the material into the kiln at the solid charging end;
directing the material and the additive to an area within the kiln having temperatures at which the additive becomes sticky and promotes nodulization of the material;
directing the nodulized material to an area within the kiln having temperatures at which there is rapid calcination in the nodulized material; and
discharging the calcined nodules from the kiln at solids exit end.
2. The method of claim 1 wherein the nodulization takes place at a temperature that ranges from about 50 0 to about 200 0 less than the temperature at which the material undergoes rapid calcination.
3. The method of claim 1 wherein the material and the additive are homogenously mixed prior to being inserted into the kiln.
4. The method of claim 1 wherein the material is first directed to a preheating area of the kiln that is adjacent to the solids charging end of the kiln wherein the material is heat treated at temperatures less than the temperatures in the area of the kiln in which nodulization occurs.
5. The method of claim 1 wherein the material is first dried in a drying area of the kiln that is adjacent to the solids charging end of the kiln and thereafter preheated in a preheating area of the kiln .
6. The method of claim 1 wherein the additive is an alkali metal or alkaline earth metal salt.
7. The method of claim 6 wherein the additive is a sodium or potassium salt.
8. The method of claim 7 wherein the additive is sodium carbonate.
9. The method of claim 8 wherein the additive is added to the material in an amount that ranges from about 0.05 wt% to about 0.5 wt%, based on the weight of the natural chalk being added to the kiln.
10. The method of claim 9 wherein the additive is added to the material in an amount that ranges from about 0.2 wt% to about 0.5 wt%.
11. The method of claim 1 wherein the material is natural chalk powder.
12. The method of claim 1 wherein the material is lime kiln dust exhausted from a lime kiln.
13. A method for nodulizing and calcining limestone screening fines that contain about 10 wt% of material having a diameter of 74 microns or less within a rotary kiln having a solid charging end and a solid exit end comprising: inserting at the solid charging end of a rotary kiln the limestone screening fines and an additive that promotes nodulization of the limestone screening fines;
directing the fines and the additive through the kiln to the an area having temperatures at which the additive becomes sticky and the nodulization takes place;
directing the nodulized fines through the kiln to the an area having temperatures at which the rapid calcination of the nodulized fines takes place; and
discharging the calcined nodules from the kiln at solids exit end.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EA201300478A EA201300478A1 (en) | 2010-10-22 | 2011-10-18 | MANUFACTURING OF BONDED LIME FROM NATURAL CHALK IN A ROTATING KILN |
EP11834948.9A EP2630085A4 (en) | 2010-10-22 | 2011-10-18 | Production of calcined lime from natural chalk material in a rotary kiln |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US12/910,190 US20120100050A1 (en) | 2010-10-22 | 2010-10-22 | Production of calcined lime from natural chalk material in a rotary kiln |
US12/910,190 | 2010-10-22 |
Publications (1)
Publication Number | Publication Date |
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WO2012054409A1 true WO2012054409A1 (en) | 2012-04-26 |
Family
ID=45973184
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/US2011/056604 WO2012054409A1 (en) | 2010-10-22 | 2011-10-18 | Production of calcined lime from natural chalk material in a rotary kiln |
Country Status (4)
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US (1) | US20120100050A1 (en) |
EP (1) | EP2630085A4 (en) |
EA (1) | EA201300478A1 (en) |
WO (1) | WO2012054409A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2016108778A1 (en) * | 2014-12-29 | 2016-07-07 | YAŞAR, Muzaffer | Calcium oxide compound with high purity |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
ES2498738B1 (en) * | 2013-03-22 | 2015-06-30 | Domeco Maquinaria Y Sistemas Para El Reciclaje S.L. | A facility for the elaboration of quicklime |
CN106977118B (en) * | 2017-03-30 | 2020-02-14 | 鞍钢集团朝阳钢铁有限公司 | Method for calcining lime by converter gas for rotary kiln |
CN108502909A (en) * | 2018-06-19 | 2018-09-07 | 郑小华 | A kind of powdery highly active calcium oxide and its production technology |
CN115490440B (en) * | 2021-06-17 | 2023-05-05 | 太原钢铁(集团)有限公司 | Operation method for calcining limestone with large particle size ratio |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US1379157A (en) * | 1920-05-08 | 1921-05-24 | William H Alton | Art of treating calcium carbonate |
US5919038A (en) * | 1996-02-29 | 1999-07-06 | Fuller Company | Method for the calcination of calcium carbonate bearing materials |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB594729A (en) * | 1945-05-02 | 1947-11-18 | Norman Victor Sydney Knibbs | Improvements in or relating to the production of quicklime |
US4421594A (en) * | 1981-08-24 | 1983-12-20 | Bildjukevich Viktor L | Method of and apparatus for producing granulated products from a suspension |
RU2116988C1 (en) * | 1996-07-09 | 1998-08-10 | Санкт-Петербургский государственный технологический институт (технический университет) | Mixture for production of water resistant lime clinker |
-
2010
- 2010-10-22 US US12/910,190 patent/US20120100050A1/en not_active Abandoned
-
2011
- 2011-10-18 EA EA201300478A patent/EA201300478A1/en unknown
- 2011-10-18 EP EP11834948.9A patent/EP2630085A4/en not_active Withdrawn
- 2011-10-18 WO PCT/US2011/056604 patent/WO2012054409A1/en active Application Filing
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US1379157A (en) * | 1920-05-08 | 1921-05-24 | William H Alton | Art of treating calcium carbonate |
US5919038A (en) * | 1996-02-29 | 1999-07-06 | Fuller Company | Method for the calcination of calcium carbonate bearing materials |
Non-Patent Citations (1)
Title |
---|
See also references of EP2630085A4 * |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2016108778A1 (en) * | 2014-12-29 | 2016-07-07 | YAŞAR, Muzaffer | Calcium oxide compound with high purity |
JP2018501180A (en) * | 2014-12-29 | 2018-01-18 | エリフ ガンガー レイスGUNGOR REIS, Elif | High purity calcium oxide compound |
US10617136B2 (en) | 2014-12-29 | 2020-04-14 | Arkim Kimyevi Maddeler Sanayi Ve Ticaret Anonim Sirketi | Calcium oxide compound with high purity |
Also Published As
Publication number | Publication date |
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EA201300478A1 (en) | 2013-10-30 |
US20120100050A1 (en) | 2012-04-26 |
EP2630085A1 (en) | 2013-08-28 |
EP2630085A4 (en) | 2014-03-12 |
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