Composition in the form of briquettes comprising burnt calcium-magnesium compounds, method for obtaining same, and use thereof
10718034 ยท 2020-07-21
Assignee
Inventors
Cpc classification
C22B1/245
CHEMISTRY; METALLURGY
C04B18/021
CHEMISTRY; METALLURGY
C04B2111/00758
CHEMISTRY; METALLURGY
C04B18/021
CHEMISTRY; METALLURGY
International classification
C04B18/02
CHEMISTRY; METALLURGY
C22B1/245
CHEMISTRY; METALLURGY
Abstract
A composition based on quick calcium-magnesium compounds in the form of briquettes is shown, as well as a method for the preparation and use thereof. The composition of the briquettes contains quicklime in the form of milled particles at a concentration of at least 10% by weight and at most 100% by weight relative to the weight of the composition. The compositions in the form of briquettes have a Shatter test index of less than 10%.
Claims
1. Composition in the form of briquettes comprising at least one quick calcium-magnesium compound, said composition having at least 40% by weight of CaO+MgO equivalent, relative to the weight of said composition, characterised in that said calcium-magnesium compound comprises quicklime in the form of milled particles at a concentration of at least 10% by weight and at most 100% by weight relative to the total weight of said composition, said milled particles containing at least 30% by weight of particles having a particle she smaller than 100 m and having a value t.sub.60 less than 5 min, said composition in the form of briquettes having a Shatter test index of less than 10%, said Shatter test index being the percentage by weight of fines under 10 mm generated after 4 drops from 2m starting from 10 kg of product, the fines being quantified by sieving through a screen with square mesh of 10 mm after 4 drops from 2m.
2. Composition in the form of briquettes according to claim 1, wherein said briquettes have a maximum size of at least 20 mm.
3. Composition in the form of briquettes according to claim 1, wherein said briquettes have a maximum size of at most 50 mm.
4. Composition in the form of briquettes according to claim 1, wherein said briquettes are raw briquettes and have a BET specific surface area of greater than or equal to 1 m.sup.2/g, said specific area being measured using nitrogen absorption manometry after vacuum degassing at 190C for at least 2 hours and calculated in accordance with BET method described in standard ISO 9277:2010E.
5. Composition in the form of briquettes according to claim 1, wherein said briquettes are burnt briquettes and have a BET specific surface area of greater than or equal to 0.4 m.sup.2/g.
6. Composition in the form of briquettes according, to claim 1, wherein said briquettes have a porosity of greater than or equal to 20%.
7. Composition in the form of briquettes according to claim 1, wherein said quicklime in the form of milled particles is present at a concentration of at least 15% by weight relative to the total weight of said composition.
8. Composition in the form of briquettes according to claim 1, wherein said quicklime in the form of milled particles is present at a concentration of at most 90% by weight-relative to the total weight of said composition.
9. Composition in the form of briquettes according to claim 1, further comprising a binder or a lubricant with a content of between 0.10 and 1% by weight relative to the total weight of said composition.
10. Composition in the form of briquettes according to claim 1, wherein said briquettes have an average weight per briquette of at least 5 g.
11. Composition in the form of briquettes according to claim 1, wherein said briquettes have an average weight per briquette of less than or equal to 100 g.
12. Composition in the form of briquettes according to claim 1, wherein said briquettes have an apparent density of between 2 g/cm.sup.3 and 3.0 g/cm.sup.3.
13. Composition in the form of briquettes according to claim 1, characterised in that said quick calcium-magnesium compound further comprises fine particles of calcium-magnesium compound selected from fine particles rejected during screening for the production of pebbles of said quick calcium-magnesium compound, calcium-magnesium filter dust and mixtures thereof, at a concentration of at least 10% by weight and at most 90% by weight relative to the total weight of said composition.
14. Composition in the form of briquettes according to claim 1, characterised in that said composition also comprises one or more iron-based compound(s) at a concentration of at least 3% by weight and at most 60% by weight expressed as Fe.sub.2O.sub.3 equivalent relative to the total weight of said composition.
15. Composition in the form of briquettes according to claim 1, packaged in types of containers with a contents volume of greater than 1 m.sup.3.
16. Composition in the form of briquettes according to claim 1, wherein the briquettes are raw briquettes with a Shatter test index of less than 8%.
17. Composition in the form of briquettes according to claim 1, wherein the briquettes are burnt briquettes with a Shatter test index of less than 6%.
Description
(1) Other characteristics, details and advantages of the invention will be included in the description provided below, by way of non-limiting example and with reference to the figures and examples.
(2)
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(6)
(7) The present invention relates to a method for briquetting a composition comprising at least one quick calco-magnesian compound comprising quicklime in the form of milled particles at a concentration of at least 10% by weight and at most 100% by weight relative to the total weight of said composition.
(8) The briquetting method according to the invention comprises a supply of a substantially homogeneous pulverulent mixture comprising at least one quick calco-magnesian compound.
(9) Depending on the intended use of the briquettes, it is possible to add additives, such as, for example, in the case of use in the iron and steel industry, fluxes, such as B.sub.2O.sub.3, NaO.sub.3, calcium aluminate, calcium silicate, a calcium ferrite such as Ca.sub.2Fe.sub.2O.sub.3 or CaFe.sub.2O.sub.4, metallic Al, metallic Mg, metallic Fe, metallic Mn, metallic Mo, metallic Zn, metallic Cu, elemental Si, CaF.sub.2, C, Cac.sub.2, alloys such as CaSi, Ca Mg, CaFe, FeMn, FeSi, FeSiMn, FeMo; TiO.sub.2, a molybdenum-based oxide, a copper-based oxide, a zinc-based oxide, a molybdenum-based hydroxide, a copper-based hydroxide, a zinc-based hydroxide and mixtures thereof.
(10) The substantially homogeneous pulverulent mixture is fed into a roller press of a briquetter, also occasionally referred to as a tangential press, for example a Komarek, Sahut Konreur, Hosokawa Bepex, Koppern press.
(11) In the roller press, the substantially homogeneous pulverulent mixture is compressed, optionally in the presence of a binder or a lubricant, preferably provided in the form of powder or concentrated aqueous suspension, more particularly selected from the group consisting of binders of mineral origin such as cements, clays, silicates, binders of plant or animal origin, such as celluloses, starches, gums, alginates, pectin, glues, binders of synthetic origin, such as polymers, waxes, liquid lubricants such as mineral oils or silicones, solid lubricants such as talc, graphite, paraffins, stearates, in particular calcium stearate, magnesium stearate, and mixtures thereof, preferably calcium stearate and/or magnesium stearate, with a content of between 0.1 and 1% by weight, preferably between 0.15 and 0.6% by weight, more preferably between 0.2 and 0.5% by weight relative to the total weight of said mixture.
(12) During use, the rollers of the roller press develop linear speeds on the periphery of the rollers of between 10 and 100 cm/s, preferably between 20 and 80 cm/s, and linear pressures of between 60 and 160 kN/cm, preferably between 80 and 140 kN/cm, and even more preferably between 80 and 120 kN/cm.
(13) By considering an angle of degree on which the linear pressure is applied on the surface of the sleeves, it is possible to calculate a surface pressure which is equal to the linear pressure divided by (.Math.D )/360 where D is the diameter of the sleeves expressed in cm. The surface pressure is between 300 and 500 MPa, preferably between 300 and 450 MPa, and more preferably between 350 and 450 MPa.
(14) At the end of compression, the calco-magnesian composition in the form of raw briquettes is obtained and the latter are collected.
(15) In a preferred embodiment of the method according to the present invention, the collected raw briquettes are thermally treated at a temperature of between 700 C. and 1200 C., preferably between 700 C. et 1000 C., preferably between 800 C. and 1000 C. for a predetermined period of time.
(16) The raw briquettes are then taken into a high-temperature furnace where they undergo thermal treatment at a temperature of less than or equal to 1200 C., preferably less than or equal to 1000 C. They are then cooled and collected in the form of burnt briquettes in order to, among other things, improve their ageing resistance and their strength when dropped.
(17) The period of thermal treatment is related to the temperature of the thermal treatment (the higher the temperature, the shorter the period) and the thickness of the bed of briquettes (the time increases with the thickness of the bed in order to allow time for the heat to diffuse inside the bed). Thus, under monolayer conditions, the thermal treatment is preferably performed at around 900 C., for example for a predetermined duration of between 3 and 20 minutes, preferably greater than or equal to 5 minutes and less than or equal to 15 minutes, more particularly greater than or equal to 7 minutes and less than or equal to 13 minutes, resulting in burnt briquettes being formed and obtained. Under monolayer conditions, each temperature decrease of 50 C. in the thermal treatment results in the thermal treatment duration being doubled.
(18) When the thermal treatment is performed under multi-layer conditions, i.e. the briquettes are in the form of a static bed of briquettes of a certain thickness, it is understood that the thermal treatment period needs to be increased in order to allow time for the heat to penetrate the core of the bed of briquettes. By way of illustration, for a bed thickness of 100 mm, the thermal treatment is preferably performed at around 900 C. for a predetermined duration of between 6 and 40 minutes, preferably greater than or equal to 10 minutes and less than or equal to 30 minutes, more particularly greater than or equal to 14 minutes and less than or equal to 26 minutes. By way of example, thermal treatment for a duration of 10 to 20 minutes at 900 C. is sufficient for a layer of briquettes of up to 100 to 150 mm thick inside the furnace. Typically, the duration of thermal treatment needs to be doubled in order to achieve a 50 C. decrease in temperature.
(19) The quick calco-magnesian compound is advantageously a soft- or medium-burnt calco-magnesian compound, preferably soft-burnt.
(20) In a very particular embodiment of the present invention, wherein the raw briquettes contain an iron-based compound which is an iron oxide-based compound, the method further comprises a step wherein said collected raw briquettes are subjected to thermal treatment at a temperature of between 900 C. and 1200 C., preferably between 1050 C. and 1200 C., particularly at around 1100 C. for a predetermined duration resulting in burnt briquettes being formed and obtained, wherein the iron oxide-based compound is converted, at least partially, to calcium ferrites.
(21) The raw briquettes are then taken into a high-temperature furnace where they undergo thermal treatment at a temperature of less than or equal to 1200 C. They are then cooled and collected in the form of burnt briquettes in order to, among other things, encourage the formation of calcium ferrites, sought for applications in the iron and steel industry, and improve their ageing resistance as well as their strength when dropped.
(22) The period of thermal treatment is related to the temperature of the thermal treatment (the higher the temperature, the shorter the period) and the thickness of the bed of briquettes (the time increases with the thickness of the bed in order to allow time for the heat to diffuse inside the bed). Thus, under monolayer conditions, the thermal treatment is preferably performed at around 1100 C., for a predetermined duration of between 3 and 20 minutes, preferably greater than or equal to 5 minutes and less than or equal to 15 minutes, more particularly greater than or equal to 7 minutes and less than or equal to 13 minutes, resulting in burnt briquettes being obtained, wherein said active iron oxide is converted to calcium ferrite. Under monolayer conditions, each temperature decrease of 50 C. in the thermal treatment results in the thermal treatment duration being doubled.
(23) When the thermal treatment is performed under multi-layer conditions, i.e. the briquettes are in the form of a static bed of briquettes of a certain thickness, it is understood that the thermal treatment period needs to be increased in order to allow time for the heat to penetrate the core of the bed of briquettes. By way of illustration, for a bed thickness of 100 mm, the thermal treatment is preferably performed at around 1100 C. for a predetermined duration of between 6 and 40 minutes, preferably greater than or equal to 10 minutes and less than or equal to 30 minutes, more particularly greater than or equal to 14 minutes and less than or equal to 26 minutes.
(24) In order to perform these thermal treatments, a horizontal furnace such as, for example, a tunnel furnace, a continuous furnace, a bogie furnace, a roller furnace or a mesh belt conveyor furnace may be used. Alternatively, any other type of conventional furnace can be used, though should not result in the integrity of the compacts being altered, for example due to excessive attrition. Cooling may either be performed conventionally in the downstream section of the furnace or outside the furnace, for example in a vertical counterflow cooler for cooling air or even in a fluid bed cooler using cooling air in the case of quenching.
(25) In a particular embodiment, cooling at the end of thermal treatment is performed rapidly in less than 15 minutes, preferably in less than 10 minutes, in a fluidised bed by means of the cooling air.
(26) In a preferred embodiment according to the present invention, the method comprises, before said provision of a substantially homogeneous pulverulent mixture,
(27) a) feeding a mixer with said at least one quick calco-magnesian compound and
(28) b) mixing for a predetermined period, long enough to obtain a substantially homogeneous pulverulent mixture of said at least one quick calco-magnesian compound.
(29) In a variant of the invention, the substantially homogeneous mixture based on calco-magnesian compound comprises at least 10% by weight of milled quicklime particles, preferably at least 20% by weight, more particularly at least 30% by weight and at most 100% by weight relative to the total weight of said mixture.
(30) The raw briquettes are advantageously based on quicklime (optionally dolomitic) in the form of particles rejected at screening when manufacturing pebbles and quicklime in the form of milled particles.
(31) They are also characterised by a mass content of calcium and magnesium of at least 40%, preferably at least 60%, preferably at least 70% and at most 100%, preferably 95%, expressed as CaO and MgO equivalent. The chemical analysis is performed using XRF.
(32) The % by weight of CaO+MgO and Fe.sub.2O.sub.3 equivalent is determined via X-ray fluorescence spectroscopy (XRF) as described in standard EN 15309. The semi-quantitative chemical analysis via XRF to determine the relative mass concentration of the elements whose atomic mass is between 16 (oxygen) and 228 (uranium), is performed using samples milled at 80 m and shaped into pellets. The samples are introduced into a PANalytical/MagiX PRO PW2540 device, operating with wavelength dispersion. Measurement is taken with a power of 50 kV and 80 mA, with a Duplex detector.
(33) The results of the analysis provide the content of calcium, magnesium and iron and these measurements are reported by weight of CaO and MgO equivalent and by weight of Fe.sub.2O.sub.3 equivalent.
(34) They preferentially contain 0.1 to 1% of lubricant, for example stearate such as calcium or magnesium stearate, preferably 0.2 to 0.5% by weight.
(35) They come in the form of briquettes (typically shaped like soap bars, ovoids, chippings, etc. known to those skilled in the art and are produced using tangential roller presses) and have a size of at least 10 mm, preferably at least 15 mm and at most 50 mm, preferably at most 40 mm, preferably at most 30 mm, so that they can pass through a square mesh screen.
(36) The raw briquettes of the composition have good mechanical strength characterised by a Shatter Test Index (STI, i.e., the mass percentage of fines smaller than 10 mm after four 2-metre drops, less than 8%, preferentially less than 6%, 5%, 4%.
(37) They are also characterised by a BET specific surface area of greater than or equal to 1 m.sup.2/g, preferably 1.2 m.sup.2/g, preferably 1.4 m.sup.2/g.
(38) The porosity of the raw briquettes is greater than or equal to 20%, preferably greater than or equal to 22%, more preferably greater than or equal to 24%.
(39) The raw briquettes have an apparent density of between 2.0 and 3.0, preferably between 2.2 and 2.8.
(40) The raw briquettes have good ageing resistance. Thus, when they are exposed to a humic atmosphere containing, for example, 5 to 15 g/m.sup.3 of absolute humidity, their mechanical properties (STI) only deteriorate after more than 1.5% mass increase, preferably 2% mass increase, and even more preferably 2.5% mass increase, following the hydration reaction of the quicklime CaO in slaked lime Ca(OH)2.
(41) The burnt briquettes from the present invention have a Shatter Test Index (STI, i.e., the mass percentage of fines smaller than 10 mm after four 2-metre drops, less than 6%, preferentially less than 4%, 3%, 2%. Indeed, in certain embodiments of the method according to the present invention, the burnt briquettes have a Shatter test index of less than 8%, sometimes less than 6%, less than 4%, less than 3%, or even around 2%.
(42) They are also characterised by a BET specific surface area bigger than or equal to 0.4 m.sup.2/g, preferably bigger than or equal to 0.6 m.sup.2/g, more preferably bigger than or equal to 0.8 m.sup.2/g.
(43) Porosity is greater than or equal to 20%, preferably greater than or equal to 22%, more preferably greater than or equal to 24%.
(44) The burnt briquettes have an apparent density of between 2.0 and 3.0, preferably between 2.2 and 2.8.
(45) The burnt briquettes have good ageing resistance. Thus, when they are exposed to a humic atmosphere containing, for example, 5 to 15 g/m.sup.3 of absolute humidity, their mechanical properties (STI) only deteriorate after more than 4% mass increase, preferably 4.5% mass increase, and even more preferably 5% mass increase, following the hydration reaction of the quicklime CaO in slaked lime Ca(OH).sub.2.
EXAMPLES
Example 1
Briquettes of Quicklime, Originating from Milled Quicklime Fines
(46) The milled quicklime fines were prepared using soft-burnt pebble quicklime produced in a parallel flow regenerative shaft kiln. Grinding is performed in a hammer mill fitted with a 2-mm screen and a recirculation loop for sizes larger than 2 mm. These milled quicklime fines contain 71% of particles larger than 90 m, 37% of particles larger than 500 m, 21% of particles larger than 1 mm and 1% of particles between 2 and 3 mm. The t.sub.60 value of the water reactivity test is 0.9 min. The BET specific surface area (measured using nitrogen adsorption manometry after vacuum degassing at 190 C. for at least two hours and calculated in accordance with the multipoint BET method as described in standard ISO 9277:2010E) is 1.7 m.sup.2/g. These milled quicklime fines contain 95.7% of CaO and 0.8% of MgO by weight.
(47) A Gericke GCM450 powder mixer with a capacity of 10 dm.sup.3 is used, fitted with standard blades with a radius of 7 cm used in rotation at 350 revolutions per minute (i.e. 2.6 m/s). This mixer is used in continuous mode to prepare a mixture containing:
(48) 99.75% by weight of these milled quicklime fines,
(49) 0.25% by weight of calcium stearate powder.
(50) The total flow rate of the powder is 300 kg/h and the dwell time is 3.5 s. The mixture obtained is very substantially homogeneous.
(51) A tangential press fitted with sleeves with a diameter of 604 mm and a width of 145 mm is used to produce briquettes with a target volume of 7.2 cm.sup.3 in the shape of a soap bar (4 rows of 67 pockets per sleeve, i.e. 268 pockets per sleeve) and can develop a linear pressure of up to 120 kN/cm.
(52) Taking 10 tonnes of the mixture, the tangential press is loaded and compacting takes place at a speed of 12 revolutions per minute (i.e. a linear speed of 38 cm/s) at a linear pressure of 120 kN/cm (i.e. a calculated surface pressure of 455 MPa for an angle of 0.5 degrees).
(53) Almost 8.5 tonnes of briquettes with an average volume of 8.2 cm.sup.3, an average weight of 19 g and an average density of 2.3 are obtained. These briquettes have a length of around 36 mm, a width of around 26 mm and a thickness of around 15.5 mm. These briquettes develop a BET specific surface area of 1.6 m.sup.2/g and a total mercury pore volume (determined using mercury intrusion porosimetry as per section 1 of standard ISO 15901-1:2005E, which involves dividing the difference between the skeletal density, measured at 30000 psia, and the apparent density, measured at 0.51 psia, by the skeletal density) of 26%.
(54) The reactivity of the briquettes to water is determined by adding 150 g of these briquettes, previously milled into the form of fines with a size of between 0 and 1 mm, to 600 cm.sup.3 of water at 20 C. The t.sub.60 value is 1.1 min.
(55) A Shatter Test is performed using 10 kg of these briquettes by successively dropping them from 2 m, four times. The quantity of the fines smaller than 10 mm generated after these four drops is then weighed. A Shatter Test Index of 3.5% is obtained.
Example 2
Briquettes of Quicklime, Originating from a Mixture of Soft-Burnt Milled Quicklime Fines and Screened Quicklime Fines
(56) The milled quicklime fines are those from example 1. The screened quicklime fines were recovered at the end of screening through a 3-mm screen from the unsorted material at the outlet of a rotary kiln fitted with a preheater. These screened quicklime fines contain 74% of particles larger than 90 m, 60% of particles larger than 500 m, 47% of particles larger than 1 mm and 18% of particles of between 2 and 3 mm. The t.sub.60 value of the water reactivity test is 4 min. The BET specific surface area is 1.2 m.sup.2/g. These screened quicklime fines contain 97.1% of CaO and 0.7% of MgO by weight.
(57) The mixture, created according to the method in example 1, is formed from:
(58) 0.25% by weight of calcium stearate powder,
(59) 99.75% by weight of a 50:50 mixture by weight of these milled quicklime fines and of these screened quicklime fines.
(60) Briquettes are produced from this mixture according to the method in example 1. Almost 10 tonnes of briquettes with an average volume of 8.3 cm.sup.3, an average weight of 19.2 g and an average density of 2.3 are obtained. These briquettes have a length of around 36 mm, a width of around 26 mm and a thickness of around 15.6 mm. These briquettes develop a BET specific surface area of 1.4 m.sup.2/g and have a total mercury pore volume of 26%.
(61) The reactivity of the briquettes to water is determined by adding 150 g of these briquettes, previously milled into the form of fines with a size of between 0 and 1 mm, to 600 cm.sup.3 of water at 20 C. The t.sub.60 value is 1.8 min.
(62) A Shatter Test is performed using 10 kg of these briquettes by successively dropping them from 2 m, four times. The quantity of the fines smaller than 10 mm generated after these four drops is then weighed. A Shatter Test Index of 4.0% is obtained.
Example 3
Briquettes of Dolomitic Quicklime, Originating from a Mixture of Soft-Burnt Milled Quicklime Fines and Burnt Dolomite Fines
(63) The milled quicklime fines are those from example 1. The milled dolomite fines were prepared using soft-burnt pebble quicklime produced in a parallel flow regenerative shaft kiln. Milling was performed in a hammer mill. These milled burnt dolomite fines contain 91% of particles larger than 90 m, 44% of particles larger than 500 m, 31% of particles larger than 1 mm and 17% particles larger than 2 mm and 8% of particles of between 3 and 5 mm. The t.sub.70 value of the water reactivity test is 3.1 min. The BET specific surface area is 2.8 m.sup.2/g. These milled burnt dolomite fines contain 58.5% of CaO and 38.4% of MgO by weight.
(64) The mixture, created according to the method in example 1, is formed from:
(65) 0.25% by weight of calcium stearate powder,
(66) 99.75% by weight of a 70:30 mixture by weight of these milled quicklime fines and of these milled burnt dolomite fines.
(67) Briquettes are produced from this mixture according to the method in example 1. Almost 10 tonnes of briquettes with an average volume of 8.1 cm.sup.3, an average weight of 19.1 g and an average density of 2.3 are obtained. These briquettes have a length of around 36 mm, a width of around 26 mm and a thickness of around 15.5 mm. These briquettes develop a BET specific surface area of 2.2 m.sup.2/g and have a total mercury pore volume of 27%.
(68) A Shatter Test is performed using 10 kg of these briquettes by successively dropping them from 2 m, four times. The quantity of the fines smaller than 10 mm generated after these four drops is then weighed. A Shatter Test Index of 4.9% is obtained.
Example 4
Briquettes of Quicklime, Originating from a Mixture of Soft-Burnt Milled Quicklime Fines and Iron Oxide Fines
(69) The milled quicklime fines are those from example 1. The iron oxide fines originate from the milling of an Fe.sub.2O.sub.3 hematite iron ore passing through a 150-m screen and are characterised using a Coulter laser particle size analyser (based on light diffraction and as per the theories of Fraunhofer and Mie) by a d.sub.10 of 0.5 m, a d.sub.50 of 12.3 m and a d.sub.90 of 35.7 m. These iron oxide fines contain 64.6% of Fe.
(70) The mixture, created according to the method in example 1, is formed from:
(71) 0.25% by weight of calcium stearate powder,
(72) 99.75% by weight of an 80:20 mixture by weight of these milled quicklime fines and of these iron oxide fines.
(73) Briquettes are produced from this mixture according to the method in example 1. Almost 10 tonnes of briquettes with an average volume of 8.5 cm.sup.3, an average weight of 22.3 g and an average density of 2.6 are obtained. These briquettes have a length of around 36 mm, a width of around 26 mm and a thickness of around 16.1 mm. These briquettes develop a BET specific surface area of 1.6 m.sup.2/g and have a total mercury pore volume of 25%.
(74) The reactivity of the briquettes to water is determined by adding 166.7 g of these briquettes, previously milled into the form of fines with a size of between 0 and 1 mm, to 600 cm.sup.3 of water at 20 C. The 166.7 g of briquettes correspond to 150 g of quicklime. The t.sub.60 value is 1.2 min.
(75) A Shatter Test is performed using 10 kg of these briquettes by successively dropping them from 2 m, four times. The quantity of the fines smaller than 10 mm generated after these four drops is then weighed. A Shatter Test Index of 3.9% is obtained.
Example 5
Briquettes of Quicklime, Originating from Milled Quicklime Fines, Thermally Treated
(76) Using a tonne of briquettes from example 1, arranged in boxes so that the thickness of the briquette bed is 100 mm, thermal treatment of 20 min at 900 C. was performed, with up- and down-ramps in temperature of around 40 C. per minute.
(77) Briquettes with an average volume of 8.2 cm.sup.3, an average weight of 19 g and an average density of 2.3 are obtained. These briquettes have a length of around 36 mm, a width of around 26 mm and a thickness of around 15.5 mm. These briquettes develop a BET specific surface area of 1.3 m.sup.2/g and have a total mercury pore volume of 27%.
(78) The reactivity of the briquettes to water is determined by adding 150 g of these briquettes, previously milled into the form of fines with a size of between 0 and 1 mm, to 600 cm.sup.3 of water at 20 C. The t.sub.60 value is 1.0 min.
(79) A Shatter Test is performed using 10 kg of these briquettes by successively dropping them from 2 m, four times. The quantity of the fines smaller than 10 mm generated after these four drops is then weighed. A Shatter Test Index of 3.3% is obtained.
Example 6
Briquettes of Quicklime, Originating from a Mixture of Soft-Burnt Milled Quicklime Fines and Iron Oxide Fines, Thermally Treated
(80) Using a tonne of Briquettes from example 4, arranged in boxes so that the thickness of the briquette bed is 100 mm, thermal treatment of 20 min at 1100 C. was performed, with up ramps and down ramps in temperature of around 50 C. per minute.
(81) Briquettes with an average volume of 8.5 cm.sup.3, an average weight of 22.2 g and an average density of 2.6 are obtained. These briquettes have a length of around 36 mm, a width of around 26 mm and a thickness of around 16.1 mm. These briquettes develop a BET specific surface area of 0.9 m.sup.2/g and have a total mercury pore volume of 27%.
(82) The reactivity of the briquettes to water is determined by adding 178.2 g of these briquettes, previously milled into the form of fines with a size of between 0 and 1 mm, to 600 cm.sup.3 of water at 20 C. The 178.2 g of briquettes correspond to 150 g of free lime (i.e. not in the form of calcium ferrites). The t.sub.60 value is 1.5 min.
(83) A Shatter Test is performed using 10 kg of these briquettes by successively dropping them from 2 m, four times. The quantity of the fines smaller than 10 mm generated after these four drops is then weighed. A Shatter Test Index of 1.2% is obtained.
Comparative Example 1
Briquettes of Quicklime, Originating from Screened Quicklime Fines
(84) The screened quicklime fines are those from example 2. The mixture, created according to the method in example 1, is formed from:
(85) 99.75% by weight of these screened quicklime fines,
(86) 0.25% by weight of calcium stearate powder.
(87) Briquettes are produced from this mixture according to the method in example 1. Almost 10 tonnes of briquettes with an average volume of 8.3 cm.sup.3, an average weight of 19.4 g and an average density of 2.3 are obtained. These briquettes have a length of around 36 mm, a width of around 26 mm and a thickness of around 15.6 mm. These briquettes develop a BET specific surface area of 1.2 m.sup.2/g and have a total mercury pore volume of 26%.
(88) A Shatter Test is performed using 10 kg of these briquettes by successively dropping them from 2 m, four times. The quantity of the fines smaller than 10 mm generated after these four drops is then weighed. A Shatter Test Index of 11.2% is obtained.
Comparative Example 2
Briquettes of Burnt Dolomite, Originating from Milled Burnt Dolomite Fines
(89) The milled burnt dolomite fines are those from example 3. The mixture, created according to the method in example 1, is formed from:
(90) 99.75% by weight of these milled burnt dolomite fines,
(91) 0.25% by weight of calcium stearate powder.
(92) Briquettes are produced from this mixture according to the method in example 1. Almost 10 tonnes of briquettes with an average volume of 8.4 cm.sup.3, an average weight of 19.9 g and an average density of 2.3 are obtained. These briquettes have a length of around 36 mm, a width of around 26 mm and a thickness of around 16.0 mm. These briquettes develop a BET specific surface area of 2.6 m.sup.2/g and have a total mercury pore volume of 26%.
(93) A Shatter Test is performed using 10 kg of these briquettes by successively dropping them from 2 m, four times. The quantity of the fines smaller than 10 mm generated after these four drops is then weighed. A Shatter Test Index of 14.3% is obtained.
Examples 7 to 14
(94) Raw briquettes are produced according to the invention with milled quicklime containing particles sized between 0 and 2 mm, but with different particle size profiles and contents of iron oxide with sizes smaller than 100 m expressed as Fe.sub.2O.sub.3 equivalent ranging from 10% to 60%. The iron oxide used in these examples is characterised by a d.sub.10 of 0.5 m, d.sub.50 of 12.3 m and d.sub.90 of 35.7 m. In each example, the milled quicklime particles sized between 0 and 2 mm have at least 30% of particles that are smaller than 90 m.
(95) Raw briquettes of the same composition were thermally treated at 1100 C. or 1200 C. for 20 minutes in order to obtain burnt briquettes with different contents of quicklime and iron-based compounds. The composition of the briquettes and the thermal treatment performed are shown in Table 1. For these raw and burnt briquettes, several tests were performed and described below using
(96)
(97) the evolution of the BET specific surface area (SSA) based on the content of iron-based compound expressed as Fe.sub.2O.sub.3 equivalent for raw briquettes;
(98) the evolution of porosity using petroleum intrusion based on the content of iron-based compound expressed as Fe.sub.2O.sub.3 equivalent for raw briquettes;
(99) the evolution of the BET specific surface area (SSA) based on the content of iron-based compound as Fe.sub.2O.sub.3 equivalent for burnt briquettes having been subjected to thermal treatment (TT) of 1100 C. for 20 minutes; and
(100) the evolution of porosity based on the content of iron-based compound as Fe.sub.2O.sub.3 equivalent for burnt briquettes having been subjected to thermal treatment (TT) of 1100 C. for 20 minutes.
(101) As can be seen, these porosity and surface area evolutions decreased slightly, in a linear manner, with the content of iron-based compound for raw and burnt briquettes. Burnt briquettes have a smaller specific surface area than raw briquettes, although they have higher porosity for identical contents of iron-based compound.
(102)
(103) the evolution of the Shatter test index for raw briquettes, based on the contents of iron-based compound expressed as Fe.sub.2O.sub.3 equivalent; and
(104) the evolution of the Shatter test index for burnt briquettes having been thermally treated at a temperature of 1100 C. for 20 minutes, based on the contents of iron-based compound expressed as Fe.sub.2O.sub.3 equivalent.
(105) As can be seen, the Shatter test indices are less than 20% for raw briquettes with contents of iron-based compound expressed as Fe.sub.2O.sub.3 equivalent of less than 40%, whereas for burnt briquettes all Shatter test indices are less than 10%, or even 6%.
(106)
(107) As can be seen, the calcium ferrite conversion yield begins to decrease for contents of iron oxide expressed as Fe.sub.2O.sub.3 equivalent of greater than 40%.
(108)
(109) As can be seen, the contents of calcium ferrites in the burnt briquettes increase with the content of iron oxide in the raw briquettes. Nevertheless, this evolution reaches a maximum of 50% in content of calcium ferrite for contents of iron oxide in the raw briquettes in a range of between 40 and 45%, before decreasing to contents of calcium ferrites of around 40% for contents of iron oxide in raw briquettes of 60%.
(110) Nevertheless, it is possible to increase the yield of conversion from iron oxide to calcium ferrites to above 90% and to obtain contents of calcium ferrite in the burnt briquettes to above 50%, or even above 70%, for example by increasing the temperature of the thermal treatment to up to 1200 C. or by optimising the milling of the quicklime so as to increase the proportion of particles of quicklime smaller than 90 m, or a combination of one and the other. Several examples were carried out and measured and presented in table 1.
(111) TABLE-US-00001 TABLE 1 % of calcium Conversion to ferrites in Fe.sub.2O.sub.3 Heat calcium the burnt Examples equivalent % treatment T Type of CaO ferrites % briquette Ex. 7 20% 1200 C CaO < 2 mm, of 95% 31% which 30% < 90 m Ex. 8 30% 1200 C. CaO < 2 mm, of 98% 47% which 30% < 90 m Ex. 9 40% 1200 C. CaO < 2 mm, of 98% 58% which 30% < 90 m Ex. 10 50% 1200 C. CaO < 2 mm, of 97% 74% which 30% < 90 m Ex. 11 50% 1100 C. 50% of (CaO < 90% 65% 2 mm, of which 30% < 90 m) + 50% of CaO < 90 m Ex. 12 50% 1100 C. 100% of CaO < 96% 73% 90 m Ex. 13 50% 1200 C. 50% of (CaO < 99% 76% 2 mm, of which 30% < 90 M) + 50% of CaO < 90 m Ex. 14 50% 1100 C. CaO < 2 mm, of 61% 43% which 30% < 90 m
Comparative Example 3
(112) The Shatter test indices were compared with the compressive force on several samples of raw briquettes to establish the correlation between the Shatter test index and the compressive force. The raw briquettes tested included quicklime with a particle size of 0 to 3 mm with different contents of iron oxide, from 0 to 60% by weight and different contents of lubricant ranging from 0.125 to 0.5% by weight, relative to the total weight of the briquettes. The parameters of the briquetting process were also modified to ensure that the population for establishing correlation was broad enough.
(113) As can be seen in
(114) It is understood that the present invention is in no way limited to the embodiments described above and that many modifications can be made to said embodiments without departing from the scope of the appended claims.