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    • 专利摘要:
    Figure 1 A method for producing high porosity slaked lime comprising a step of feeding a quicklime, a step of feeding water into a feed zone of a hydrator, a step of quenching said quicklime in an extinction zone of said hydrator and a maturation step in a maturation zone of the hydrator to form a slaked lime. Figure 1
    公开号:BE1022687B1
    申请号:E2016/5181
    申请日:2016-03-11
    公开日:2016-07-18
    发明作者:Stephan Chini；Marion Lorgouilloux；Olivier Nyssen；Olivier Francoisse
    申请人:S.A. Lhoist Recherche Et Developpement；
    IPC主号:
    专利说明:

    "METHOD OF MANUFACTURING HIGH-POROSITY OFF-CHAIN LIMITS AND PRODUCTS SO OBTAINED"
    The present invention relates to a high porosity slaked lime manufacturing process comprising a lime feed step, a water supply step in a feed zone of a hydrator, a step of quenching said lime live in an extinction zone of said hydrator and a maturation step in a maturation zone of said hydrator to form slaked lime.
    By quicklime is meant a mineral solid whose chemical composition is mainly calcium oxide, CaO. Quicklime is generally obtained by calcination of limestone (mainly CaCO3).
    The quicklime may also contain impurities such as magnesium oxide MgO, sulfur oxide, SO 3, silica, SiO 2, or even alumina, Al 2 O 3, ..., the sum of which is at a content of a few %. The impurities are expressed here in their oxide form, but they can of course appear in different phases. Quicklime usually also contains some residual limestone, called incinerated residues.
    Suitable quicklime according to the present invention may comprise MgO in an amount, expressed as MgO, in the range of 0.5 to 10% by weight, preferably 5% or less by weight, preferably equal to or less than 3% by weight, more preferably equal to or less than 1% by weight relative to the total weight of quicklime.
    The CO 2 content of the quicklime (representing, inter alia, the unburned limestone) is preferably equal to or less than 3% by weight, preferably equal to or less than 2%, more preferably equal to or less than 1% by weight per relative to the weight of quicklime.
    The content of SO 3 (sulfur expressed as SO 3 equivalent) of quicklime is equal to or less than 1% by weight, preferably equal to or less than 0.5% by weight, better still equal to or less than 0.2% by weight. relative to the weight of quicklime.
    As a rule, to form slaked lime, quicklime is put in the presence of water. Calcium oxide in lime reacts rapidly with water to form calcium dihydroxide Ca (OH) 2, in the form of slaked lime or hydrated lime, in a reaction known as the quenching or hydration reaction that is very exothermic. In what follows, calcium dihydroxide will simply be called calcium hydroxide.
    The slaked lime can therefore contain the same impurities as the quicklime from which it is produced.
    The slaked lime may also include calcium oxide, which may not have been fully hydrated during the quenching step, or calcium carbonate CaCO 3. Calcium carbonate can originate from the original limestone (incinerated) from which the slaked lime is obtained (via calcium oxide) or be the result of a partial carbonation reaction of the slaked lime by contact with an atmosphere containing CO 2.
    The amount of calcium oxide in the slaked lime according to the present invention is generally equal to or less than 3% by weight, preferably equal to or less than 2% by weight and advantageously equal to or less than 1% by weight relative to to the total weight of the slaked lime. The amount of CO 2 in the slaked lime (mainly in the form of CaCO 3) according to the present invention is equal to or less than 4.5% by weight, preferably equal to or less than 3% by weight, more preferably equal to or less than 2% by weight, based on the total weight of the slaked lime according to the present invention. One of the most common industrial processes for the production of slaked lime is called "dry quenching" which produces standard slaked lime with a BET specific surface area of between 12 and 20 m2 / g. water is added to the hydrator in a quantity limited to that which is necessary to completely hydrate the quicklime, taking into account that some will evaporate during the extinction reaction, due to the exothermic nature of this reaction. At the exit of the hydrator, the slaked lime thus produced is already in a powdery state and generally comprises less than 2% by weight, or even less than 1.5% by weight of moisture.
    The quenching reaction is therefore carried out in the hydrator, in which the quicklime is introduced upstream of the quenching direction, which means the direction along which the lime is transported along and into the hydrator . The slaked lime is removed downstream of the extinguishing direction. Transport means, such as a horizontal axis equipped with mixing blades, for example, allow the transport of lime along the direction of extinction in the hydrator, from the supply of quicklime to the withdrawal. slaked lime. The means of transport also allow a homogeneous mixture of lime undergoing hydration and thus improve the contact between water and lime in the hydrator and avoid the formation of hot spots.
    A hydrator can be divided into three large consecutive areas. The first is called the feed or mixing zone and is the part of the hydrator located upstream of the extinction direction, in which quicklime and water are introduced and mixed together. The second zone, referred to as the quench zone, represents that part of the hydrator in which the quenching reaction occurs essentially, which means, in which most of the quicklime CaO is chemically converted to slaked lime Ca ( OH) 2 and in which the majority of the steam is generated, in particular because of this exothermic reaction. The third zone, called ripening zone or finishing area, is located downstream of the extinction direction and is the part of the hydrator that ensures that the particles are completely extinguished and that allows the homogenization of the residual moisture content. slaked lime.
    Different types of hydration and hydration processes exist, depending on the properties of the quicklime used, but also depending on the expected yield of the quenching reaction and the desired properties of the resulting slaked lime.
    In order to achieve a good hydration yield, several parameters must be taken into consideration, such as the residence time of the lime in the hydrator, the reactivity to the water of the quicklime, the location of the supply of quicklime along the hydrator, but also the amount of water in relation to the amount of lime.
    The reactivity to water of quicklime is generally characterized and measured by the procedure indicated in the European standard EN459-2 and is often quantified by the value t60, corresponding to the time required to reach a temperature of 60 ° C for a volume water of 600 cm3 initially at 20 ° C, with the addition of 150 g of quicklime.
    During the hydration of quicklime, more or less fine particles are produced, depending on the particle size of the starting quicklime that is introduced, but also depending on the speed of the hydration reaction, this the latter being explosive and generating small, cracked and fragmented particles. A well-controlled reaction therefore makes it possible to produce the desired particle size (from fine particles to the production of lime grains, corresponding to particles agglomerated together) as well as the desired porosity. In this perspective, the temperature within the hydration or quench zone is also a key factor governing the hydration reaction.
    In the past, conventional slaked lime, namely having a BET surface area of between 12 and 20 m 2 / g / was generally produced in single-stage hydrators. However, with this kind of hydrator, particularly because of the short residence time of the lime inside the hydrator, it was difficult to correctly adjust the amount of water to be added so as to obtain lime entirely off, while remaining within the desired humidity range to prevent clogging and collapse during the extinguishing process.
    One of the major developments in the dry extinction process was the arrival of multi-stage moisturizers, with two or more stages, usually three stories, usually superimposed.
    In a three-stage hydrator, for example, the first stage is generally used to introduce and mix water and lime, and part of the hydration reaction can begin. Most of the quenching reaction occurs in the second stage, where water mixed with lime and not yet consumed by the hydration reaction reacts with lime and where most of the steam is generated. The last floor is usually used for maturation of the slaked lime (which means to ensure that the particles are completely extinguished). The multi-stage hydrator is therefore more flexible, in particular because it allows a longer residence time of the lime inside the hydrator, but also because the treatment parameters (such as the mixing speed, the design of the blades, the level of the weir, ...) can be adjusted in each floor independently, thus allowing a certain degree of adaptation of the process to different grades of quicklime and more flexibility concerning the water / lime ratio used for hydration.
    In a particular three-stage hydrator, the mixing zone is located in the first stage, the extinction zone in the second stage and the ripening zone in the third stage.
    Such a process is known from the prior art, such as that described in "Lime and Limestone, Chemistry and Technology, Production and Uses", J.A.H. Oates, 1998, pp. 216-218.
    Standard slaked lime produced by the processes mentioned above are generally used in many industrial applications, such as water treatment, sludge conditioning, gas treatment, agriculture, construction, etc.
    For some of these applications, the properties of slaked lime are particularly critical for good performance. For example, in the treatment of flue gases, lime is used as an absorber of several gaseous pollutants. However, such lime, once it has captured these pollutants, becomes a by-product that must be processed or recycled. As a result, manufacturers are looking for high-performance products to reduce the amount of by-products that are expensive to process. Thus, in recent years, more and more products and manufacturing processes have been developed in order to control the properties of slaked lime, in particular the size of its particles, its pore volume and its specific surface, so to improve their capture performance.
    One way of increasing the performance of lime is to increase the proportion of hydrated lime that will actually come into contact with the pollutants to be captured, increasing the specific surface area and the pore volume of the hydrated lime. It has led in recent decades to the production of slaked lime with a high specific surface in which the quenching reaction is carried out in the presence of alcohol.
    Relevant examples are described in US5492685, which relates to a hydrated lime having a high specific surface area and a small particle size, prepared by hydration of lime with an aqueous hydration solution of an organic solvent (such as alcohol) and preferably by washing the resulting hydrate with an aqueous solution of an organic solvent before drying. The resulting high surface area hydrated lime according to this document are described as being excellent sorbents for SO 2 removal from the flue gases and have specific surface areas which are generally greater than 35 m 2 / g, preferably greater than 55 m2 / g or even up to 85 m2 / g.
    To achieve these high specific surfaces, water alcohol ratios above 5: 1 are used, particularly with highly reactive quicklime.
    In the process described for the manufacture of hydrated lime having a high specific surface, an intimate mixture between the hydration solution and the lime is important. High speed, intensive mixing is very useful, and is described as necessary with very reactive lime, for good heat transfer. For extremely reactive lime, this document teaches a cooling step of the mixing tank. Another approach that is described is to use a split water jet to minimize the rapid increase in temperature when a very reactive lime is processed. The alcohol or other solvent in the hydration solution is described as delaying the kinetics of quenching, and maintains the temperature of the hydration mixture below the boiling point of the water (thereby preventing or reducing the degree of hydration in the gas phase, which inhibits the development of the specific surface).
    Several plants are described for carrying out the described process, in which in each case the temperature control, the control of the mixing conditions, the preheating steps and the residence time are essential to achieve the desired properties of the final product.
    By the alcohol process, in which the quicklime is extinguished in the presence of a large amount of alcohol, hydrated lime is prepared characterized by a small particle size distribution (less than 20 μm), a large specific surface area (greater than 30 m2 / g) and a low water content, but which nevertheless contains alcohol (the complete elimination of the latter being impossible). In addition, this process requires an expensive installation, because it is necessary to recycle as much alcohol used.
    As a result, other types of slaked lime, with a high specific surface area and a high pore volume have been developed. One way, which has been further studied, is described in WO 97/14650.
    WO 97/14650 discloses a Ca (OH) 2 particle composition and a method of making the composition. The composition consists essentially of dry particles of calcium hydroxide having a moisture content of less than 2 percent by weight of the total composition, a specific surface area greater than 30 m 2 / g, a total pore volume of nitrogen desorption, and at least 0.1 cm 3 / g for pores having a diameter of less than 1000 Angstroms. The lime composition is described as providing excellent performance for the treatment of flue gases in installations with a bag filter.
    As can be seen in this document, it is also possible, without adding any organic additive, to achieve a high specific surface area and a high pore volume by controlling the parameters governing the quenching process.
    However, the document describes a laboratory or pilot scale production, and a process in which the operation is simply represented by boxes. In addition, in recent decades, environmental legislation has generally been considerably strengthened, in terms of the amount of pollutant allowed in the flue gases and in terms of by-product treatment, which forces manufacturers to find solutions. with improved sorption capacity.
    In this perspective, the composition and process of WO 97/14650 should be improved in terms of efficiency, so as to comply with the new specifications, but also in terms of implementation.
    There is therefore a need to find a way to produce highly porous slaked lime, with improved sorption capabilities, which is industrially feasible, which means that does not require too much human intervention to control the process and which is reproducible to be able to maintain the properties of the slaked lime in time.
    The present invention aims to provide a solution to this need by specifying and improving the conditions of manufacture of slaked lime with high porosity properties, the latter being reproducible and durable over time. To this end, it is provided according to the present invention, a method, as mentioned at the beginning, characterized in that said lime feed step and said water supply step are performed so as to obtain a ratio in weight water / quicklime between 0.8 and 1.3, preferably between 0.9 and 1.2 and more preferably close to 1 (the extreme values being included), the method further comprising a step of withdrawal of steam generated during said quenching step, said vapor stripping step being carried out substantially along said quenching zone to form a high porosity raw slaked lime, namely slaked lime with a high specific surface area and a high pore volume.
    It has indeed been shown according to the invention that the combination of controlling the ratio of water to quicklime, together with the elimination of the steam (steam) generated, makes it possible to achieve a determined and reproducible quality of the slaked lime. with characteristics of high porosity, and with a high production yield avoiding clogging during the extinguishing process.
    The water / lime ratio must be adapted to obtain a raw lime whose moisture content is between 15 and 30% by weight, preferably between 20 and 25% by weight relative to the weight of the slaked lime. This water / lime ratio must also be adapted to the nature (water reactivity, granulometry, etc.) of the quicklime to be extinguished and the specific surface area and pore volume parameters desired for the slaked lime.
    By eliminating the steam generated substantially along said quenching zone, the contact between the steam and the lime, at this stage, which is detrimental to the porosity properties of the slaked lime, is avoided. This also helps to keep the moisture content under control, avoiding the condensation of water vapor in the cooler parts of the hydrator, which would otherwise have caused the hydrator to become clogged by the formation of water. a paste of lime.
    By the term "removal of steam generated substantially along said quench zone", it is understood that the vapor removal is carried out over 80% to 300% of the length of the extinguishing zone, preferably over 90% or more of the length of the extinction zone, more preferably 100% or more of the length of the extinction zone.
    According to the present invention, it has been found that the removal of water vapor along the quench zone, which essentially means along the entire length of the quenching zone of the hydrator (being a multi -floor or single-storey) is a key success factor for achieving slaked lime with controlled and homogeneous porosity characteristics.
    Furthermore, because of the lime / water ratio used in the process according to the present invention, said high porosity slaked lime obtained by the process has a high BET specific surface area which is very homogeneous, reproducible and stable from one production season to the next. other and which is between 30 m 2 / g and 50 m 2 / g, preferably greater than or equal to 32 m 2 / g, more preferably greater than or equal to 35 m 2 / g, more particularly greater than or equal to 38 m 2 / g g such that, for example greater than or equal to 40 m 2 / g and typically less than or equal to 48 m 2 / g.
    Similarly, said high porosity slaked lime obtained by the process according to the present invention has a very reproducible and stable total pore volume BJH from one production season to another, composed of pores with a diameter of less than 1000 Å, greater than or equal to 0.15 cm 3 / g, preferably greater than or equal to 0.17 cm 3 / g, advantageously greater than or equal to 0.18 cm 3 / g, in particular greater than or equal to 0.20 cm 3 / g and typically lower at 0.3 cm3 / g, in particular less than 0.28 cm3 / g.
    Alternatively, the high-porosity slaked lime obtained by the process according to the present invention has a very reproducible and stable partial pore volume BJH from one production season to another, constituted by pores having a diameter ranging from 100 angstroms to 300. angstroms, greater than or equal to 0.07 cm3 / g, preferably greater than or equal to 0.10 cm3 / g, advantageously greater than or equal to 0.11 cm3 / g, in particular greater than or equal to 0.12 cm3 / g and typically less than 0.15 cm3 / g, especially less than 0.14 cm3 / g.
    For the purposes of the present description, the term BET specific surface area is understood to mean the specific surface area measured by nitrogen adsorption manometry after degassing under vacuum at a temperature of between 150 and 250 ° C., in particular at 190 ° C. for minus 2 hours and calculated according to the multipoint BET method as described in ISO 9277: 2010E.
    The terms porous volume BJH according to the present invention means the pore volume, as measured by nitrogen adsorption manometry and calculated according to the BJH method, using the desorption curve.
    In a particular embodiment, the process of the present invention further comprises a step of drying said raw slaked lime to form a powdered dry dry lime with a high specific surface area and a high pore volume.
    Preferably, according to the present invention, said step of quenching said quicklime is carried out in a single-stage hydrator, which means that the hydrator used for the production process is a single-stage hydrator.
    It is indeed preferable according to the method of the present invention, against all odds to use a single-stage hydrator, although nowadays, the multi-stage moisturizers are generally preferred for their longer residence time, thus making it possible to use less reactive and / or coarser fractions of quicklime, while being more flexible in terms of water injection point and allowing greater tolerance of water / lime ratio adjustment to produce slaked lime standard with a desired humidity range.
    According to the present invention, the use of a single-stage hydrator makes the step of removing steam easier, said step being crucial for the present invention. Indeed, in the present invention, the contact between the vapor and the hydrate must be avoided or at least limited to a time as short as possible in order to maintain the high specific surface and the high pore volume of the slaked lime thus formed.
    For this reason, the mono-stage hydrator is preferred according to the present invention, because, contrary to what one might have thought, it is more convenient and perfectly suited to the manufacture of very porous slaked lime with a large specific surface area BET and a high pore volume BJH.
    Indeed, even though the multi-stage moisturizers are advantageously used nowadays to produce standard hydrated lime because of their greater flexibility, it has been found that the single-stage hydrator is specifically more suited to a process such as of the present invention where the humidity can reach 30% since, as already mentioned, the mono-stage hydrator facilitates the extraction of steam and will also not be confronted with the clogging problems encountered between the different stages of a multi hydrator -stories, due to the high moisture content of the hydrate.
    As a general rule, the steam removal in a hydrator can be carried out either by wet technology or by dry technology using a wet scrubber or a fabric filter, usually a bag filter, respectively.
    Advantageously, in the process according to the present invention, said vapor removal step is carried out through a fabric filter, in particular a bag filter.
    Indeed, the fabric filter makes it possible to separate the dust produced during the quenching step from the vapor while at the same time independently injecting the extinguishing water at a controlled and relatively low temperature, preferably at a controlled temperature. beginning of the hydrator, which allows to better control the hydration temperature. This leads to a more stable quenching reaction process and improved porosity of slaked lime.
    In addition, the fabric filter should extend as far as possible over the entire length of the extinguishing area to ensure the removal of water vapor close to its production by the exothermic quenching reaction and thus minimizing the contact time between the steam and the hydrate, which could be detrimental to the porosity of the slaked lime. The objective of having a filter extending the entire length (or maximum possible length) of the extinction zone is to shorten as much as possible the trajectory of the water vapor from the point where it is produced. to where it is released into the atmosphere.
    For the removal of water vapor, a specific pressure must be used to extract the vapor effectively while reducing as much as possible the aspiration of the fine particles because otherwise the filter bags will be quickly plugged and will require too high costs of maintenance.
    In a preferred embodiment, the pressure pulses are applied to the filter sleeves to inflate and vibrate and drop the particles down into the hydrator again. The pulses can be generated by blowing pressurized air into the filter handles at regular intervals to prevent clogging and excessive pressure drop.
    In a particular embodiment, there is an envelope in the sleeves and, optionally, a heating and tracing system for heating the sleeves, thereby reducing the condensation of water on the sleeves and the falling of the liquid water of the filter in the hydrator, just like the clogging of the sleeves.
    Preferably, the sleeves are made from a hydrophobic material and adapted to the steam, the temperature and the elemental nature of the material to be filtered.
    In a variant of the method according to the present invention, said step of feeding the quicklime is carried out by a weighing device, such as a conveyor belt, allowing the quicklime to fall into the hydrator.
    Preferably, the quicklime is determined by gravimetry (weighing hopper) and the amount of water introduced into the hydrator is determined by a mass flow meter.
    Before the quicklime falls into the hydrator, it may be advantageous to subject the flow of lime to a magnetic field (permanent magnet) to prevent any metal parts from entering the hydrator.
    Advantageously, the water supply is performed at a single point at the inlet of the hydrator, preferably on the drop of quicklime.
    It has been observed that water supply at several locations along the length of the hydrator will lead to warmer areas, increased steam production and increase the risk of clogging.
    According to a particular embodiment of the process according to the present invention, said quicklime has a reactivity with water t60, measured in accordance with the European standard EN 459-2, equal to or greater than 15 seconds and equal to or less than 10 minutes, preferably equal to or less than 5 minutes, more preferably equal to or less than 3 minutes, and most preferably equal to or less than 2 minutes.
    Advantageously, said quicklime has a particle size of d98 between 90 pm and 10 mm, preferably equal to or less than 5 mm, more preferably equal to or less than 2 mm. The notation d98 represents the diameter, expressed in mm, relative to which 98% by weight of the particles measured are smaller.
    According to the present invention, the particle size should be as small as possible for the homogeneity of the lime and the reaction, as long as the fineness of the lime does not influence its flowability and does not lead to problems of inaccuracy of dosage. Particles with a particle size of d98 greater than 5 mm can also be used, provided that they have a high water reactivity (t60 of less than 2 minutes measured according to the European standard EN 459-2), in order to ensure complete hydration of the quicklime during its residence time in the hydrator.
    Preferably, according to the present invention, said water has a temperature equal to or lower than 60 ° C, preferably equal to or lower than 40 ° C, preferably equal to or lower than 20 ° C.
    The temperature of the water is preferably as low as possible. The water may also contain certain impurities such as chlorides, nitrates, sulphates and / or phosphates. The total amount of chlorides and nitrates is preferably less than 1 g / dm3, more preferably less than or equal to 0.5 g / dm3 and most preferably equal to or less than 0.1 g / dm3. The total amount of the sulfates and phosphates is preferably less than 1 g / dm 3, more preferably less than or equal to 0.5 g / dm 3 and most preferably equal to or less than 0.1 g / dm 3.
    In a preferred embodiment of the method according to the present invention, during said extinction step, the lime is mixed and transported by a horizontal shaft equipped with mixing blades. The mixing blades can be specifically designed to ensure the proper mixing necessary to achieve a reproducible reaction, but also to ensure lifting and lifting and lime, as well as its downstream movement in the direction of extinction .
    The rotation speed of the shaft equipped with mixing blades must remain less than 30 revolutions per minute in order to avoid agglomeration of the hydrates, preferably it is between 10 and 20 revolutions per minute.
    The filling level of the hydrator can be adjusted to the reactivity of the quicklime and the residence time required in the hydrator.
    In a preferred embodiment, the fill rate of the hydrator must be adjusted using for example a wear plate at the exit of the hydrator and must be adjusted between 30 and 60% of the volume of the hydrator. the hydrator (height), preferably close to 50% of the volume (tree level).
    In a particular embodiment of the process according to the present invention, the residence time of the lime in the hydrator is between 20 and 40 minutes, preferably about 30 minutes.
    In a particularly preferred embodiment according to the present invention, the temperature in the hydrator is kept below 100 ° C, preferably between 85 and 99 ° C, more preferably between 95 and 98 ° C.
    Indeed, as mentioned above, the temperature in the hydrator should not be too high to avoid as much as possible the extinction by the water vapor of the quicklime which is detrimental to the porosity characteristics, but not too low either to avoid the condensation of water and the formation of a paste in the hydrator, the latter being detrimental to the homogeneity of the lime thus produced and the installation itself.
    In an advantageous embodiment of the process according to the present invention, the method of manufacturing very sluggable slaked lime is controlled by measuring the moisture of the raw slaked lime (slaked lime at the exit of the hydrator, before the drying stage) or by the motor intensity of the shaft equipped with mixing blades.
    The manufacturing process can also be controlled by measuring the temperature, but controlling the temperature in the hydrator is difficult to achieve accurately due to the hydrate crust that forms around the probes.
    In the method according to the present invention, the measurement of the moisture of the raw slaked lime or engine intensity of the shaft equipped with mixing blades have been chosen as measures to control the quenching reaction. Indeed, based on the measurement of the humidity or the intensity of the motor, the flow of water is adjusted. The motor intensity also provides information regarding the water content of the raw slaked lime because the higher the water content, the harder it is for the mixing shaft to rotate, the higher the engine intensity. is high. These two parameters can be tracked online and allow a quick response and better control of the quenching reaction.
    An increase in motor intensity corresponds to an increase in moisture of the hydrate and indicates that the flow of water must be decreased.
    In another particular embodiment according to the present invention, the step of supplying water is a step of supplying water containing additives such as, but not limited to, di-ethylene glycol, a alkali metal compound selected from the group consisting of alkali metal hydroxides, carbonates, hydrogenocarbonates and mixtures thereof, for example to promote the development of porosity or capture properties of slaked lime.
    According to a specific embodiment of the present invention, in the case of a mono-stage hydrator, the extinction zone extends over at least 30%, preferably 40%, in particular 50%, more preferably 60% of the length of the hydrator. Other embodiments of the method according to the present invention are mentioned in the appended claims.
    The subject of the present invention is also a lime composition obtained by the process according to the present invention, having a reproducible partial porous BJH volume constituted by pores having a diameter ranging from 100 angstroms to 300 angstroms, greater than or equal to 0.07 cm3. / g, preferably greater than or equal to 0.10 cm3 / g, advantageously greater than or equal to 0.11 cm3 / g, in particular greater than or equal to 0.12 cm3 / g and typically less than 0.15 cm3 / g , in particular less than 0.14 cm3 / g. Other embodiments of the lime composition according to the present invention are mentioned in the appended claims. Other features and advantages of the present invention may be derived from the following non-limiting description and with reference to the drawings and examples.
    Figure 1 is a CFD simulation illustrating a hydrator with a small section extraction hood located at the end of the hydrator extinction zone.
    Figure 2 is a CFD simulation illustrating a hydrator with a small section extraction hood located in the center of the hydrator's extinction zone.
    Figure 3 is a CFD simulation illustrating a hydrator with a long extraction hood covering the length of the hydrator's extinguishing zone.
    Figure 4 is a schematic illustration of the length and position of the extraction hood on a hydrator for carrying out the method according to the present invention.
    In the drawings, the same reference numerals have been assigned to identical or similar elements.
    The present invention therefore aims to eliminate as quickly as possible the steam generated by the extinction reaction of the quicklime so as to avoid contact between said steam and the hydrated lime thus formed, said contact being detrimental to the porosity of the lime off. Steam is produced mainly in the hydrator's quench zone. Therefore, in order to optimize the step of removing the vapor according to the method of the present invention, the hydrator (single-stage or multistage) must be equipped with an extraction hood which preferably extends over 100 % of the length of the hydrator.
    Alternatively, said extraction hood must extend over a portion of the length of the hydrator, which starts from 0%, preferably to at least 10%, preferably 20%, more preferably 30%, in particular 35% the length of said hydrator, upstream of the extinction direction, until at least 65%, preferably 70%, in particular 80%, more preferably 90%, especially 100% of the length of the hydrator (see Figure 4).
    EXAMPLES
    Example 1
    CFD simulations were carried out to show the flow path of the water vapor generated during a quicklime quenching reaction with a water / lime ratio between 0.8 and 1.3. depending on the size / section and position of the baghouse on the hydrator (extinguishing unit).
    In these simulations, illustrated in Figures 1 to 3, the half cylinder represents the upper half of the hydrator, namely the portion of the hydrator located above the bed of lime.
    Such an upper half of the hydrator is connected to a suction hood which will evacuate water vapor to the bag filter (not shown).
    The bag filter has the same section as the suction hood to which it is connected.
    Three situations were considered. 1: small section extraction hood located at the end of the hydrator (Figure 1). 2: small section extraction hood located in the center of the hydrator (Figure 2). 3: extraction hood covering the length of the hydrator's extinction zone (Figure 3).
    The results show that in situation 1 (Figure 1), the water vapor has a very long flow path that forces the water vapor to stay in the hydrator in close contact with the lime bed for a long time. a significant period of time before being evacuated by the bag filter. During this period of time, the water vapor will interfere with the extinction of quicklime, thus preventing precise control of the hydration process.
    Situation 2 (Figure 2) performs better than Situation 1 because it reduces the flow path of the water vapor. However, the steam produced, even if it is less in contact with the lime undergoing the quenching reaction, is still in contact with it.
    Situation 3 (Figure 3) is the best situation since the steam produced is directly extracted before coming into contact with lime in the quench zone.
    In conclusion, it is preferable to have a bag filter along the major section of the hydrator so as to evacuate the water vapor through a shortest and most vertical flow path possible, thus avoiding the presence of cross currents that would lead to undesirable hydration.
    Example 2.-
    Highly porous slaked lime is manufactured industrially according to the present invention in a mono-stage hydrator measuring approximately 5.5 m in length and 2.1 m in diameter (only the hydration reservoir), producing about 6 t / h of slaked lime and equipped with a bag filter. For this process, a quicklime (d98 of 3 mm) with a reactivity t60 of less than 1 min is extinguished with water in a water / lime ratio equal to 1.05 by weight, the water being brought to ambient temperature. . The average moisture content of the raw hydrate, which means the moisture content of the raw slaked lime before the drying step, is equal to 21.3% by weight. The filter extraction hood (contact zone between the hydrator and the filter) is located along the extinction zone, namely in a central position relative to the length of the hydrator.
    With this hydrator, a dry hydrated lime having a mean annual BET surface area equal to 42.6 m 2 / g and an average annual total pore volume BJH (pore up to 1000 Å) equal to 0.255 cm 3 / g is produced.
    Example 3.-
    A very porous slaked lime is manufactured industrially according to the present invention in another mono-stage hydrator, much larger than that of Example 2 as it produces 9 to 10 t / h of slaked lime. This hydrator is also equipped with a bag filter, whose extraction hood is also located along the extinction zone, namely in a central position relative to the length of the hydrator. For this process, a quicklime (d98 of 3 mm) with a reactivity t60 of 1.3 min is extinguished with water in a ratio water / lime equal to 1.0 by weight. The average moisture content of the raw hydrate, which means the moisture content of the raw slaked lime before the drying step, is equal to 24.2% by weight.
    With this hydrator, a dry hydrated lime having an average annual BET surface area equal to 41.4 m 2 / g and a mean annual total pore volume BJH (pore up to 1000 Å) equal to 0.203 cm 3 / g is produced.
    Example 4.-
    A very porous slaked lime is manufactured industrially according to the present invention in a multi-stage hydrator measuring approximately 5 m in length, producing about 3 t / h of slaked lime and equipped with a bag filter. The hydrator itself consists of three superimposed floors that are all the same length. Quicklime and water are both fed at the beginning of the first stage of the hydrator. Diethylene glycol is added to the extinguishing water in an amount of 0.3% by weight based on the total amount of quicklime. The extraction hood of the baghouse is located along the entire length of the hydrator. For this process, a quicklime having a reactivity t60 of 1.1 min is extinguished with water in a water / quicklime ratio equal to 1.0 by weight, the water being brought to ambient temperature. The average moisture content of the raw hydrate, which means the water content of the raw slaked lime before the drying step is equal to 25% by weight.
    With this hydrator, a dry hydrated lime having an average annual BET surface area equal to 39.7 m 2 / g and an average annual total pore volume BJH (pores up to 1000 Å) equal to 0.195 cm 3 / g is produced.
    Comparative Example 1.-
    Quicklime hydration tests are carried out at the laboratory scale on a small scale with a mono-stage hydrator measuring about 80 cm in length, having a diameter of about 25 cm and producing about 20 kg / h of slaked lime. In this hydrator, quicklime and extinguishing water are introduced upstream of the hydrator and driven along the direction of extinction until the end of the hydrator by a shaft provided with mixing blades.
    A first test consists in producing a very porous slaked lime according to the present invention by extinguishing a quicklime with water in a water / lime ratio of 1.1% by weight, and extracting the steam generated during the extinguishing reaction along the extinction zone using an extraction duct. The experiment proceeded very well and a dry hydrated lime having a BET specific surface area equal to 40.6 m 2 / g and a total BJH (pore up to 1000 Å) pore volume equal to 0.179 cm 3 / g is produced.
    Then the steam extraction is moved towards the end of the hydrator, all other conditions being kept constant. This experiment must be stopped due to almost continuous blockages of the lime supply line and the extraction line. Indeed, under these conditions, the water vapor, which is mainly generated in the central part of the hydrator must travel a long way to reach the extraction pipe. Therefore, a part of the water vapor does not go in this way, but rather in the other direction and leaves the reactor by the point of feed of the quicklime, which leads to a regular plugging of the point d feeding of lime. In addition, in order to better draw steam through the extraction duct, the applied vacuum must be increased, which also leads to the extraction of more dust (indeed, there is not only steam in the hydrator, but steam in which a significant amount of dusts of slaked lime is in suspension), and thus to the closure of the extraction duct, at regular intervals (every 2 minutes approximately). Due to these difficult conditions, it was not possible to continue the extinguishing process.
    It should be understood that the present invention is not limited to the embodiments described and that modifications may be applied without departing from the scope of the appended claims.
    权利要求:
    Claims (16)
    [1]
    1. A process for producing high porosity slaked lime comprising a step of feeding a quicklime, a step of supplying water to a feed zone of a hydrator, a step of extinguishing said lime live in an extinction zone of said hydrator and a maturation step in a maturation zone of the hydrator to form a slaked lime, characterized in that the step of feeding the quicklime and said feeding step of water are produced in such a way as to obtain a ratio by weight of water / quicklime between 0.8 and 1.3 and preferably between 0.9 and 1.2 and more preferably of approximately 1, the process also comprising a step vapor withdrawal process generated during the quenching step said vapor stripping step being performed along the quenching zone to form a high porosity raw slaked lime, which slaked lime has a high surface area and a high volume porous.
    [2]
    A method for producing high porosity slaked lime according to claim 1, comprising a step of drying said raw slaked lime to form a dry pulverized dry lime with a high surface area and a high pore volume.
    [3]
    A method for producing high porosity slaked lime according to claim 1 or claim 2, wherein said step of quenching said quicklime is performed in a single-stage hydrator.
    [4]
    A method of producing high porosity slaked lime according to any one of claims 1 to 3, wherein said vapor withdrawal step is performed by means of a bag filter.
    [5]
    A method for producing high porosity slaked lime according to any one of claims 1 to 4, wherein said vapor withdrawal step is performed along the entire hydrator.
    [6]
    6. A process for producing high porosity slaked lime according to any one of claims 1 to 5, wherein said step of feeding quicklime is carried out by means of a weighing device, in particular a conveyor belt, allowing quicklime to fall into the hydrator.
    [7]
    A method for producing high porosity slaked lime according to claim 6, wherein the water supply is carried out at a single point at the inlet of the hydrator, preferably on the quicklime falling into the water. hydrator.
    [8]
    8. A process for producing high porosity slaked lime according to any one of claims 1 to 7, wherein said quicklime has a reactivity to water t60, measured according to the European standard EN 459-2, equal to or greater than 15 seconds, and equal to or less than 10 minutes, preferably equal to or less than 5 minutes, more preferably equal to or less than 3 minutes, and most preferably equal to or less than 2 minutes.
    [9]
    9. A method for producing high porosity slaked lime according to any one of claims 1 to 8, wherein said quicklime has a particle size of d98 between 90 pm and 10 mm, preferably equal to or less than 5 mm, more preferably equal to or less than 2 mm.
    [10]
    10. A process for producing high porosity slaked lime according to any one of claims 1 to 9, wherein said water has a temperature equal to or less than 60 ° C, preferably equal to or less than 40 ° C, more preferably equal to or below 20 ° C.
    [11]
    11. A method for producing high porosity slaked lime according to any one of claims 1 to 10, wherein during the extinction step, the lime is mixed and transported by a horizontal shaft equipped with mixing blades.
    [12]
    12. A process for producing high porosity slaked lime according to any one of claims 1 to 11, wherein the temperature in the hydrator is maintained below 100 ° C, preferably between 85 and 99 ° C, more preferably between 95 and 98 ° C.
    [13]
    A process for producing high porosity slaked lime according to any one of claims 11 to 12, wherein the high porosity slaked lime manufacturing process is controlled by measuring the moisture of the raw slaked lime or the intensity engine shaft equipped with mixing blades.
    [14]
    A process for producing high porosity slaked lime according to any one of claims 1 to 13, wherein the moisture of the raw slaked lime is in the range of from 15 to 30% by weight, preferably from 20 to 25% by weight, based on the total weight of slaked lime.
    [15]
    The high porosity slaked lime manufacturing method according to any one of claims 1 to 14, wherein said water supplying step is a water supply step comprising additives, such as ethylene glycol, an alkali metal compound selected from the group of alkali metal hydroxides, alkali metal carbonates, alkali metal hydrogencarbonates and mixtures thereof.
    [16]
    A lime composition obtained by the process according to any one of claims 1 to 15 having a reproducible partial porous BJH volume composed of pores having a diameter in the range of from 100 Angstroms to 300 Angstroms, greater than or equal to at 0.07 cm3 / g, preferably greater than or equal to 0.10 cm3 / g, preferably greater than or equal to 0.11 cm3 / g, in particular greater than or equal to 0.12 cm3 / g and typically less than 0.15 cm3 / g, in particular less than 0.14 cm3 / g.
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    EP15181104.9|2015-08-14|
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