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
  • C04B2/02—Lime
  • C04B2/04—Slaking
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C13/00—Disintegrating by mills having rotary beater elements ; Hammer mills
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
  • B02C23/18—Adding fluid, other than for crushing or disintegrating by fluid energy
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F11/00—Compounds of calcium, strontium, or barium
  • C01F11/02—Oxides or hydroxides
• • 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
  • C04B2/02—Lime
  • C04B2/04—Slaking
  • C04B2/08—Devices therefor
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/50—Agglomerated particles

Definitions

• the present invention relates to equipment that is suitable for the dry hydration of calcium oxide, i.e. for converting calcium oxide into calcium hydroxide, and for treating the raw materials and the product.
• the invention also relates to a process of performing the dry hydration, particularly by utilizing said equipment.
• Lime i.e.. calcium oxide
• lime is used, among others in the manufacture of cement and mortar. It is sensitive to reacting with water, whereby, calcium hydroxide is formed, which is also called slaked lime. The reaction is then as follows:
• reaction is vigorous, and enough heat is generated, among others to ignite flammable substances.
• the formed calcium hydroxide is also sensitive to further reaction, forming calcium carbonate.
• the reaction is vigorous and heat is generated, whereby the hydration of lime has conventionally been carried out by means of slowly rotating kneaders by simultaneously adding to the reaction vessel burnt lime, i.e. calcium oxide, and water in small batches.
• Conventional lime hydration methods include the so-called wet process (wherein burnt lime is added to an excess of water) and the so-called dry hydration method (wherein the amount of water stoichiometrically required by the hydration reaction is added to the burnt lime).
• the Finnish patent FI 103964 describes a wet hydration process, wherein slaked lime is conducted into excess water into decomposing equipment provided with opposed cylinder rotors, and the aqueous suspension that contains calcium hydroxide exiting the equipment is allowed to settle in a separate container for the time required for the reaction to take place.
• calcium hydroxide is formed in the form of fine powder.
• a problem of such fine-ground calcium hydroxide powder is, among others the difficulty of transportation due to the volume of the powder.
• a further problem with wet hydration methods is their poor controllability.
• the Finnish patent FI 120733 describes a hydration method, where the amount of water is reduced compared to the previous solution.
• calcium oxide is conducted to an impact disintegrator, where also a small amount of water is conducted in order to moisten the particles generated in the disintegration.
• the equipment used in the method also contains a screw conveyor used to knead the reacting material. Also in this case the reacting material is conveyed to a separate container, where the reaction is completed. The remaining portion of the amount of water required for the slaking is conducted to this container.
• EP 1087832 describes a similar dry hydration method, where the hydration is carried out in 3- 20 minutes in an open vessel using a slightly larger amount of water than required stoichiometrically. Consequently, this is a slow reaction, where the end product is able to absorb carbon dioxide from the ambient air, thus deteriorating the quality of the product.
• An object of the present invention is to provide equipment suitable for the dry hydration of calcium oxide. It is also an object of the invention is to provide a dry hydration process that utilizes this equipment.
• a particular object of the invention is to provide equipment and a process that yield homogeneous slaked lime (i.e. calcium hydroxide product) that is not dependent on any variations in the raw material (i.e. burnt lime).
• homogeneous slaked lime i.e. calcium hydroxide product
• a second particular object of the invention is to provide a process by which calcium oxide can form agglomerates, on the surface of which there is provided calcium hydroxide and by the disintegration of which smaller calcium hydroxide particles are obtained.
• Said calcium hydroxide product can thus be either in the form of agglomerates or disintegrated particles.
• Agglomerates are fine-sized and porous and they have a large specific surface area (particularly 15 ⁇ 0m 2 /g). If they are disintegrated, particles are obtained having an average diameter of ⁇ 100nm.
• the present invention is based on the observation that burnt lime (CaO) reacts most effectively when the raw material containing it is disintegrated into smaller particles simultaneously with reacting it in a fluid formed by water mist and steam.
• the fresh surfaces of calcium oxide that are generated in the disintegration immediately receive a protective and reactive aqueous coating after being formed, whereas the original surfaces receive impacts that activate them, causing at least a partial disintegration of the layers that were formed among others on the surfaces of the raw material.
• the vigorous nature of the reaction is limited by the formation of new surfaces, and not by the amount of water (or the air humidity) or the mixing speed.
• the calcium oxide on the fresh surfaces as well as the aqueous coating surrounding these surfaces thus, immediately react, forming calcium hydroxide (Ca(OH) 2 ), first in the form of a film, which in turn functions as a reaction substrate for the formation of the crystal.
• the present invention relates to equipment suitable for the dry hydration of calcium oxide particles, containing a pre-treatment section for calcium oxide, a processing space that is suitable for the completion of the slaking reaction, as well as optionally one or more auxiliary parts, particularly to facilitate the runnability and controllability of the equipment.
• the pre-treatment section preferably contains a rotor section, a stator section, and a water mist generator, whereas the processing space preferably contains a screw section formed by two screws with a speed of rotation adjustable according to the process conditions.
• the invention also relates to a process, wherein said equipment is utilized, and wherein the calcium oxide particles are reacted into hydroxide, particularly at their surfaces, by using only the stoichiometric amount of water required by said reaction.
• the end product of the process is either the calcium hydroxide agglomerate or a smaller hydroxide particle produced from the same by disintegration.
• the amount of water bound to the surface and the pore structure of the calcium oxide particle corresponds to the amount of water used in the hydroxide- generating chemical reaction
• the course of the reaction, the amount of water to be fed, as well as the equipment adjustments can be controlled based on the maximum temperature. Since burnt lime is obtained from a natural product, which is certainly not pure, and since flaws also happen during the burning, the theoretical maximum temperature is not reached, but using the present invention a point very close to this can be achieved.
• the calcium hydroxide particles are internally porous.
• the process controlled by the control mechanism produces also homogeneous porosity.
• the porosity achieved by pilot devices has been 20-40 m /g, more generally -30 m7g.
• Such agglomerates also constitute a product that is easy to transport based on its particle size. The grinding fineness cannot be taken to nano levels, but particles of the micron level have to be maintained.
• the target level is c/c 8-10 ⁇ .
• the obtained Ca(OH) 2 agglomerate forms a powder with a surface area of 15-40 m 2 /g.
• Such a dry powder (-0.6 g/cm 3 ) is easy to transport to the desired destination of use, both in terms of economy and safety. It will also not react uncontrollably or prematurely into calcium carbonate, because no excess water has been added thereto.
• the agglomerates of the powder can be disintegrated by active elutriation, whereby particles of the size ⁇ 100 nm (average diameter) are obtained, expressed in spherical terms.
• the equipment of the invention functions so that the calcium oxide (CaO) is optionally first crushed, whereafter it is conducted to the actual pre-treatment where it is ground in a fluid containing aqueous mist and steam.
• the amount of water is thus the amount required by the chemical reaction of CaO, and this water attaches to the CaO particle surface.
• the obtained CaO in fluid form is conducted to the processing space of the equipment, having two screws, by means of which the hydroxide formation can be advanced as desired, particularly by adjusting their speed of rotation in relation to the progression of the process.
• the invention provides considerable advantages.
• the large surfaces of the agglomerates are utilized, making it possible to avoid their disintegration into nano-sized particles until a desired stage, also resulting in the possibility of quick utilization.
• the agglomerate form and size of the product as well as its bulk density enable economic transportation.
• the pre-treatment, processing, and auxiliary devices that are included in the equipment of the invention constitute economic production equipment, having a smaller size than conventional equipment, whereby the process implemented by the same is also simpler and quicker to implement.
• the combination of the rotor and the control stator is a functional sub-unit, wherein the high rotational speed of the rotor enables the use of rotors with a small diameter, and the turning sides of the stator can be used to control the radial velocities and the magnitude of impact on the particle (see Fig. 2).
• high-speed motors it is thus easy to reach rotational speeds of 20000 rpm by said rotor.
• Screw processing has, in turn, been developed so that it does not essentially mix the calcium oxide to be processed, whereby the end product will be an agglomerate composed of thin Ca(OH) 2 "threads".
• the double-screw processing space essential for the invention provides good adjustment and agglomeration conditions also for the use of attrition.
• the equipment of the invention can be used for producing several Ca(OH) 2 -based products.
• Fig. 1 is a diagram of the equipment according to an embodiment of the invention, which is suitable for reacting calcium oxide particles into hydroxide, at least on the surfaces thereof.
• Fig. 2 is a more detailed diagram of the stator section of the pre-treatment section of the equipment according to an embodiment of the invention (and its connection to the rotor section), wherein Fig. 2A shows the positions of the rotor blade and the turning stator blade with respect to each other; Fig. 2B shows the possible blade positions of the turning stator blade; and Fig. 2C shows the differences between the turning and stationary blades of the stator.
• Fig. 3 is a diagram of the equipment according to a particularly preferred embodiment of the invention, illustrating some of the auxiliary parts of the equipment that are described below, and their positions in the complete equipment.
• Fig. 4 is a SEM image of the calcium hydroxide agglomerate produced according to the invention, whereby Fig. 4A shows several agglomerates and Fig. 4B shows a close-up of a single agglomerate.
• the present invention relates to equipment for reacting calcium oxide particles (CaO particles) into hydroxide (Ca(OH 2 )), containing
• pre-treatment section 1 for calcium oxide wherein raw material (particles of ⁇ 20 mm) containing oxide can be treated into particles of a desired size, and which preferably is in the form of an impact disintegrator;
• the CaO particles obtained from the raw material in the pre-treatment section 1 are ground particularly into a micron grade, for example into particles with an average diameter of 1-20 ⁇ ⁇ .
• the CaO particles receive water on their surfaces and, at least partly, inside their pore structure.
• the equipment of the invention is operated based on the principle that the calcium oxide particles obtained from the optional raw material disintegration stage are conducted to the first actual processing stage, i.e. to the pre-treatment section 1 of the equipment, where they are ground in a fluid containing aqueous mist (and steam).
• the amount of water is then the just amount required by the chemical reaction of CaO, and mainly attaches to the surfaces of the CaO particles.
• the obtained CaO fluid (together with the aqueous mist and steam) is conducted to the processing space 2 of the equipment, its conditions being adjusted so as to advance the formation of hydroxide and to obtain the desired product properties.
• the auxiliary parts of the equipment can be used to adjust the particle sizes of the materials, the process conditions, or the properties, such as purity, of the formed product.
• the water brought onto the oxide surface immediately reacts with the oxide, forming a film that partly functions as a reaction substrate for the formation of the calcium hydroxide crystal, and partly detaches.
• the detachment is probably a result of attrition caused by strong turbulence. More surface of CaO is thus revealed for the quick reaction to continue. Due to the water supplied to the particles, the reaction mixture is now in the form of a fluid.
• the calcium oxide particles are porous.
• the formed hydroxide crystals at least partly penetrate into the calcium oxide particle, whereby the oxide structure is partly disintegrated and the porosity of the particle even increases. In this way, hydroxide agglomerates are obtained, having a small surface area with respect to the amount of product.
• Agglomerate in this context means a porous particle with an average diameter of >2 ⁇ , preferably 2-20 ⁇ , its porosity, measured by nitrogen absorption, being 20-40m 2 /g.
• the present invention also relates to such a continuous process of reacting calcium oxide particles into hydroxide, wherein said equipment is used.
• calcium oxide particles are added to the pre-treatment section 1 of said equipment, water or water vapour is sprayed into the same space in an amount that is stoichiometric with respect to the amount required by the formation of hydroxide or, more preferably in an amount that is 1.03-1.5-fold (compared to the stoichiometric amount), whereby calcium hydroxide is formed at least on the particle surfaces, and the thus formed particle-water fluid is conveyed to the processing space 2 of the equipment, wherein the hydroxide formation reaction is completed and the hydroxide is allowed to agglomerate.
• the lime slaking is carried out in almost dry conditions in the process, particularly by using the device described above.
• the agglomerates formed in the reaction are thereafter disintegrated into smaller particles in the way described hereinafter.
• the end product of the process is, thus, either a calcium hydroxide particle or agglomerate.
• the pre-treatment section 1 of the equipment contains the following auxiliary parts:
• the equipment includes one rotor section 1 1 (with rotor blades 1 la), which functions by accelerating the calcium oxide particles (in water vapour) in the outermost rotor of section 11 to a suitable velocity, preferably being 200-900 m/s. Its rotational speed and direction are adjustable, preferably so that the radial velocity (blade velocity) is adjusted to a value of 200-900 m/s, more preferably 200-300 m/s, and most suitably 300 m/s.
• the equipment includes one stator section 12 containing stator blades 12a,b, which preferably have a V-shape and are arranged in circles, particularly so that the outermost circle has a turning blade 12a, by means of which the blade angle can be adjusted, while the other blades 12b are stationary.
• This stator section 12 operates so that the CaO particles accelerated from the rotor section 1 1 are collided with said stator blades 12a,b at a suitably adjusted collision angle (see Fig 2).
• the rotor 11 and stator section 12 when combined so that particles can be conducted from the rotor section 1 1 to the stator section 12, are suited for grinding calcium oxide particles.
• the water vapour generator 13 such as a nozzle, can be used to spray water into this pre- treatment section 1, which thus functions both as a grinder and a pre-hydration space.
• the large speed of rotation of the rotors enables the use of rotors with a small diameter (such as 250-600 mm), and the turning blades 12a of the stator can be used for controlling the radial velocities and the magnitude of impact on the particle.
• high-speed motors are preferably used in the equipment of the invention, by means of which the rotors are accelerated to rotation speeds as high as 9000 rpm, or even 20000 rpm.
• the CaO particles remain in this pre-treatment section 1 for approximately ⁇ 1 s, generally 0.01-0.1 s.
• the ground and pre-hydrated slurry (i.e. fluid) formed in the pre-treatment section 1 of the equipment is conducted to the processing space 2 with a screw section 21 formed by two screws, preferably a twin-screw screw conveyor 21, particularly a conveyor 21 formed by two helix screws.
• a screw section 21 formed by two screws, preferably a twin-screw screw conveyor 21, particularly a conveyor 21 formed by two helix screws.
• the water bound to the surfaces and pore structure of the calcium oxide particles causes a chemical reaction, whereby the hydroxide formation reaction is completed essentially without mixing the slurry fed thereto.
• the progress of said reaction can be advanced by raising the temperature, for example to >100°C, preferably to 100-300°C, most suitably to 100-295°C.
• minor attrition is also created between the CaO particles, advancing the reaction. This attrition is adjusted by adjusting the rotation speed of the two screws in the screw section 21.
• the end product is an agglomerate formed by thin fibrils (or Ca(OH) 2 "threads") (thus corresponding to a threadlike ball).
• the agglomerates form a powder with a surface area of 15-40 m 2 /g.
• Such dry powder ⁇ 0.6 g/cm3 is easy to transport to the desired location of use, both in terms of economy and safety. It will not react uncontrollably or prematurely into calcium carbonate, because no water has been added thereto.
• the calcium hydroxide (Ca(OH) 2 ) obtained by the present invention is, however, in an at least partly reacted form, and as an agglomerate powder having a surface area of 20-40 m 2 /g and bulk density of 0.6 g/cnv', and the average diameter of the particles contained in it is 2-20 ⁇ . Because of the variation in the amount of grits in the raw material to be processed (i.e.
• the temperature in the processing space 2 is preferably allowed to rise to a level of >100°C, more preferably 100-310 °C, particularly 1 10-300 °C, and most suitably about 290 °C.
• the formed calcium hydroxide agglomerates are either conveyed from the processing space 2 elsewhere for further processing or are further processed on site, for example by disintegrating them into a smaller size, as described below. They can also be recovered and stored, and used later on as such, for example for the purification of flue gases, as described in EP 1087832.
• the raw material can be processed. Because a natural product (such as limestone) containing calcium oxide is used as the raw material, being available in different sizes, it is according to an embodiment subjected to crushing before the actual processing. This stage is particularly carried out if the average diameter of the raw material particles is >20 mm. Metals can also be removed therefrom.
• auxiliary parts are selected for the equipment from a group that includes:
• - raw material treatment means 3 preferably located before the pre-treatment section 1 in the equipment, and in turn containing, for example:
• - or metal stripping means 4 preferably located before the pre-treatment section 2 in the equipment; however, so that they do not interrupt the flow of material to be processed in the equipment, and which include
• limestone with a diameter of ⁇ 20 mm is used, it is, however, processed as such, without separate crushing.
• CaO containers 5 required for the storage of the raw material containing calcium oxide specifically in connection with said equipment, whereby they are preferably located right before the particle crusher 31, if used, and in another case, right before the pre-treatment section 1.
• the agglomerates formed in the pre-treatment 1 and processing section 2 of the equipment mentioned above can be disintegrated by an active elutriation.
• the elutriation takes place in a fluid space, preferably with 20-40 g/L of solid matter. This elutriation yields particles with a size of ⁇ 100 nm (the average diameter), expressed in spherical terms. These disintegrated particles are in fluid form before an optional separation.
• a preferred way of elutriating is the wet grinding by the opposed cylinder rotor method.
• Another economic alternative is the use of a combination of a pressure roll and said opposed cylinder rotor method for the powder.
• additives must, however, be added to the material to be processed, their selection and properties being defined by the further use of the Ca(OH) 2 .
• one of the optional auxiliary parts of the equipment is
• the elutriation section 6 preferably works on the opposed cylinder rotor principle and is capable of homogenizing the agglomerates, whereby the re-growth of the particles of the created reaction products is prevented.
• the particles are brought to a colloidal size (typically 10-500 nm), whereby they are very stable.
• optional auxiliary parts for the equipment are selected from a group capable of advancing the operation or control of the pre-treatment section 1, these parts including:
• a water dosing device 14 for adjusting the amount of water mist to be fed into the reaction mix, preferably being located in connection with the water mist generator 13 of the pre-treatment section 1;
• optional auxiliary parts for the equipment are selected from a group capable of advancing the control of the processing space 2, these parts including:
• - temperature measuring means 22 preferably located in the processing section 2, more preferably in or below its screw section 21, which are in connection with the rotor 11 and stator section 12 of the pre-treatment equipment 1, most suitably via their adjusting means 1 , so that the temperature of the calcium oxide to be processed can be measured in the screw section 21 and used to control the rotational speed of the rotors and the blade angles of the stator; or
• the durability of the obtained agglomerates was analyzed during a storage period of 6 months, whereby the surface area in the Ca(OH) 2 powder decreased ⁇ 20% (about 15%).
• the decrease in surface area did not, however, decrease the surface area of the nano- particles created in the dry or wet grinding of the agglomerate powder. It remained in an area corresponding to the surface area of ⁇ 100 nm particles.
• the surface area of the powder did, however, decrease 23-19 m 2 /g during a longer storage period of 12 months.
• the equipment of the invention was used to hydrate calcium oxide (CaO) in laboratory conditions, using 0.32 kg of water / kg of water, whereby calcium hydroxide agglomerates were obtained (Ca(OH) 2 , see Fig. 4). A part of them was directly subjected to a particle size measurement, whereas a part was disintegrated into smaller particles before the measurement.
• CaO calcium oxide
• the particle size was measured by nitrogen absorption measurement, directly, without disintegrating the agglomerates, yielding a result of an average diameter of 50-70nm (converted into a spherical form).
• Ca(OH) 2 agglomerate powder (24 m 2 /g) was elutriated in an aqueous solution and disintegrated by a laboratory device of the disintegrator type, its rotational speed being 20000 rpm and the collision speed 350 m/s.
• the solids content of the slurry was about 10% and it remained as a slurry for about 1 h. During this time, no observable amounts of agglomerates or particles were separated.
• the particle size of the Ca(OH) 2 particles was again measured by nitrogen absorption measurement, yielding a result of an average diameter of ⁇ 100nm (converted into a spherical form).

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Citations (6)

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• 2012
  • 2012-12-12 FI FI20126295A patent/FI20126295A/fi not_active IP Right Cessation
• 2013
  • 2013-12-12 EP EP13863554.5A patent/EP2931674A4/en not_active Withdrawn
  • 2013-12-12 WO PCT/FI2013/051160 patent/WO2014091081A1/en active Application Filing

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