Method for producing a highly porous fine powdered slaked lime composition, and product obtained therefrom

Abstract

The present invention relates to a method for producing a highly porous fine powdery slaked lime composition, comprising a fluidification step for forming said highly porous fine powdery slaked lime composition having an Alpine fluidity greater than 50% and which is carried out in a dryer/grinder chosen from the group consisting of a pin-type dryer/grinder, a cage-type dryer/grinder, an instantaneous dryer/disagglomerator and a combination of these until the powdery slaked lime composition has a non-solid residual-phase content of less than or equal to 3.5% by weight and greater than or equal to 0.3% by weight, as well as the product obtained therefrom.

Claims

1. Method for producing a highly porous fine powdery slaked lime composition, comprising the steps consisting of: introducing quicklime into a feeding zone of a hydrator, introducing water into the feeding zone of the hydrator; slaking said quicklime in a slaking zone of the hydrator by means of a quantity of water that is sufficient to obtain a slaked lime having a non-solid residual-phase content of between 15% and 55% by weight; drying and grinding said slaked lime in order to form the powdery slaked lime composition, characterised in that said drying and grinding steps are performed simultaneously and are a single step of fluidification of the slaked lime in order to form said fine and highly porous fine powdery slaked lime composition having an Alpine fluidity greater than 50%, the Alpine fluidity AF being defined by the equation $\mathrm{AF}=\frac{m_i-m_{R_{90}\left(T_{15};P_{100}\right)}}{m_i-m_{R_{90}\left(T_{120};P_{150}\right)}}.Math.100$ where: m.sub.1 is the is the initial mass of 50 g of powder distributed over a 90 m sieve; m.sub.R90(T15; P100) is the mass of residues of material on the sieve after 15 seconds with a negative pressure at 100 mm of manometric liquid of density 0.88; m.sub.R90(T120; P150) is the mass of residues of material on the sieve after 15 seconds with a negative pressure at 100 mm of manometric liquid of density 0.88 and after 120 seconds with a negative pressure at 150 mm of manometric liquid of density 0.88; said drying and grinding steps being carried out in a drier/grinder selected from the group consisting of a pin-type dryer/grinder, a cage-type dryer/grinder, an instantaneous dryer/disagglomerator and a combination of these until the highly porous fine powdery slaked lime composition has a residual non-solid phase content, measured by a loss-on-ignition test at 180 C., less than or equal to 3.5% by weight and greater than or equal to 0.3% by weight with respect to the total weight of the powdery slaked lime composition; and characterised in that the drying/grinding steps are performed until the powdery slaked lime composition has a first fraction of particles having a size less than 32 m and a second fraction of particles having a size greater than 32 m, provided that the second fraction is less than or equal to 50% by weight with respect to the total weight of the powdery slaked lime composition.

2. Method according to claim 1, characterised in that it further comprises, before, during and/or after the step of slaking the lime and/or before, during and/or after the drying and grinding steps, a step consisting of adding an additive to the quicklime, the slaking water and/or the slaked lime.

3. Method according to claim 1, characterised in that the drying/grinding steps are performed until the powdery slaked lime composition has a mean particular size d.sub.50 of less than or equal to 10 m.

4. Method according to claim 1, in which the hot air is supplied during the drying/grinding step, at a temperature between 250 C. and 500 C.

5. Method according to claim 1, in which the drying/grinding step has a duration of between a few seconds and a few minutes.

Description

(1) Other features and advantages of the invention will emerge more dearly in the light of the following description of a particular non-limitative embodiment of the invention, while referring to the FIGURES.

(2) FIG. 1 shows a schematic diagram of an installation intended for preparing a highly porous powdery slaked lime composition according to the present invention.

(3) The device shown in FIG. 1 comprises a slaking unit, also referred to as the hydrator 1. This hydrator 1 is supplied with quicklime by means of a feed conduit 2 and with water by means of a feed conduit 3. If an additive is used in the preparation of the absorbent, said additive is supplied by means of at least one feed conduit 4.

(4) In one embodiment, said additive is first of all dissolved in a reservoir (not shown), from which it is pumped by means of a pump (not shown) and added to the slaking-water feed conduit 3 before entering the hydrator 1. In a variant, if necessary, the additive may also be added directly in the hydrator 1.

(5) In another variant, the additive may also be added to the quicklime before slaking.

(6) The additive may also be added after the hydrator, namely before the dryer/grinder, but also in the dryer/grinder or after the dryer/grinder.

(7) At the discharge from the hydrator, the non-solid residual-phase content of the product is measured continuously by an infrared appliance 5. This non-solid residual-phase content is generally greater than 20% by weight. The product, wet slaked lime, is transferred into a dryer/grinder 6, which is supplied with hot air at approximately 400 C., by means of the feed conduit 7, which makes it possible to disagglomerate and dry the product. The final product is next separated from the drying airflow in a bag filter 8, and then directed to a storage silo 9.

(8) The production installation according to the present invention is characterised in that the dryer/grinder 6 is chosen from the group consisting of a pin-type dryer/grinder, a cage-type dryer/grinder and an instantaneous dryer/disagglomerator.

(9) The invention will now be described in more detail by means of non-limitative examples.

EXAMPLES

(10) In the following examples, as in all the cases mentioned in the present document, the BET specific surface area is determined by manometry with adsorption of nitrogen at 77 K after degassing under vacuum at a temperature of between 150 and 250 C., in particular at 190 C. for at least 2 hours and calculated according to the multipoint BET method described in ISO 9277:2010E.

(11) The BJH pore volume is measured by manometry with adsorption of nitrogen at 77 K after degassing under vacuum at a temperature between 150 and 250 C., in particular at 190 C. or at least 2 hours and calculated according to the BJH method, using the desorption curve for pores having a diameter of less than 1000 .

(12) The total pore volume corresponds to the BJH pore volume composed of pores having a diameter of less than 1000 Angstroms.

(13) The notation d.sub.x represents a diameter expressed in m, measured by laser granulometry in methanol after sonication, with respect to which X % by volume of the particles measured have a size less than or equal to.

(14) The loss-on-ignition test is carried out according to the operating method described previously.

(15) The Alpine fluidity is measured on approximately 50 g of the powder sample, in accordance with the operating mode described previously.

Example 1

(16) A highly porous powdery hydrated lime with high fluidity according to the invention is produced industrially by mixing water and quicklime in a hydrator (4.5 tonnes/hour of quicklime), in quantities such that the product emerges from the hydrator with a non-solid residual-phase content, measured by a loss-on-ignition test at 180 C., of 23% to 24% by weight. This wet hydrated lime is next transported and arrives in a pin-type dryer/grinder (Atritor Dryer-Pulverizer marketed by Atritor Limited) in which hot air is injected (approximately 20,000 Nm.sup.3/hour, 370 C.). In this pin-type dryer/grinder, the product is disagglomerated and dried simultaneously, because of the high temperature of the drying air and the rotation speed (850 rev/min) of the pin-type grinder, only a very short residence time of a few minutes is necessary in the pin-type grinder to achieve the target in terms of particle size and non-solid residual-phase content. The drying can therefore be considered to be instantaneous. Once dried and disagglomerated, the slaked lime product is separated from the air by a bag filter. During the transport of the dry slaked lime product from the pin-type dryer/grinder to the bag filter, a 100% solution of DEG is atomised by an atomisation nozzle in the pipe so as to create a DEG mist through which the slaked lime particles must pass. In this way, good contact between the particles and the DEG droplets is ensured, which produces a homogeneous product. The quantity of DEG corresponds to 0.3% by weight of the powdery slaked lime composition. This resulting powdery slaked lime composition has an Alpine fluidity of 57% and a non-solid residual-phase content of 0.5% by weight when measured by a loss-on-ignition test at 180 C., and 0.3% by weight when measured by a loss-on-ignition test at 110 C. The powdery slaked lime composition has a d.sub.50 of 5 m and a fraction of particles with a size greater than 32 m of 10% by weight. Its BET specific surface area and its total pore volume are respectively 44.1 m.sup.2/g and 0.240 cm.sup.3/g.

Example 2

(17) A highly porous powdery slaked lime composition with a high fluidity according to the invention is produced industrially by mixing water and quicklime in a hydrator (6 tonnes/hour of quicklime), in quantities such that the product emerges from the hydrator with a non-solid residual-phase content, measured by a loss-on-ignition test at 180 C., of between 17.4% and 21% by weight. This wet hydrated lime is next transported and arrives in a cage-type dryer/grinder (marketed by PSP Engineering) in which hot air is injected (12,500 Nm.sup.3/hour, 370 to 400 C.). The drying can therefore once again be considered to be instantaneous and the product emerges from the cage-type dryer/grinder at a temperature of around 120 C. to 125 C. The cage-type grinder is composed of five concentric wheels, two static wheels and the other three are rotating (rotation speed ranging up to 900 rev/min). As in example 1, once dried and disagglomerated, the slaked lime product is separated from the air by a bag filter. In this case, there is no addition of DEG after the drying, but a very small quantity (<0.1% by weight, expressed as a percentage by weight of quicklime) is added in the slaking water before hydration. The resulting powdery slaked lime composition has an Alpine fluidity of 60% and a non-solid residual-phase content, when measured by a loss-on-ignition test at 180 C., of 0.5% by weight. The powdery slaked lime composition has d.sub.50 of 5 m and a particle fraction with a size greater than 32 m of 46% by weight. Its specific surface area and its total pore volume are respectively 42.0 m.sup.2/g and 0.225 cm.sup.3/g.

Example 3

(18) A highly porous powdery slaked lime composition with a high fluidity according to the invention is produced industrially by mixing water and quicklime in a hydrator (6.8 tonnes/hour of quicklime), in quantities such that the product emerges from the hydrator with a non-solid residual-phase content, measured by a loss-on-ignition test at 186 C., of between 23% and 25% by weight. This wet hydrated lime is next transported and arrives in a cage-type dryer/grinder (marketed by Stedman) in which hot air is injected (23,600 Nm.sup.3/hour, 260 to 290 C.). The cage-type grinder is composed of three concentric wheels (rotation speed of around 520 rev/min under standard conditions). Once again, once dried and disagglomerated, the slaked lime product is separated from the air by a bag filter. In this case, as in example 2, there is no addition of DEG after drying but 0.4% of DEG (expressed as a percentage by weight of quicklime) is added in the slaking water before hydration. The resulting powdery slaked lime composition has an Alpine fluidity of 52.3% and a non-solid residual-phase content of 0.7% by weight when measured by a loss-on-ignition test at 180 C., and 0.4% by weight when measured by a loss-on-ignition test at 110 C. The powdery slaked lime composition has a d.sub.50 of 9.3 m and a particle fraction with a size greater than 32 m of 34.3% by weight. Its specific surface area and its total pore volume are respectively 41.1 m.sup.2/g and 0.209 cm.sup.3/g.

Example 4

(19) A highly porous powdery slaked lime composition is produced industrially by mixing water and quicklime (2.7 tonnes/hour of quicklime) in a hydrator, in quantities such that the product emerges from the hydrator with a non-solid residual-phase content, measured by a loss-on-ignition (LOI) test at 180 C., of between 22% and 24% by weight. 0.2% of DEG (expressed as a percentage of the weight of quicklime) is added in the slaking water before hydration. The wet slaked lime that emerges from the hydrator is next transported to a pin-type dryer/grinder (Atritor Dryer-Pulverizer marketed by Atritor Limited) in which hot air is injected in order to instantaneously dry the wet slaked lime and to produce the highly porous powdery slaked lime composition before storing it in a storage area.

(20) A representative sample of approximately 20 kg of this industrial powdery slaked lime composition is taken and analysed (BET specific surface area=41.1 m.sup.2/g, total pore volume=0.214 cm.sup.3/g, d.sub.50=4.2 m, R.sub.32=6.2%).

(21) Next a subsample of approximately 1 kg is dried further on a laboratory scale in an oven at 180 C. in order to obtain a fully dried slaked lime (non-solid residual phase measured by LOI at 180 C.=0.03% by weight). After this complete drying, the resulting completely dried slaked lime is mixed with various given quantities of water and/or diethylene glycol (DEG). The mixing is carried out by adding water and/or DEG drop by drop on the completely dried slaked lime, which is being stirred in an intensive laboratory mixer (Eirich ELI). When DEG and water are used together, the DEG is added to the water before the addition of this liquid solution to the completely dried slaked lime. The resulting mixture is stirred for 5 minutes and then subjected to a loss-on-ignition (LOI) test at 180 C. The results are presented in table 1 below, in which the percentages by weight are expressed with respect to the total weight of the powdery slaked lime composition.

(22) The purpose of this methodology is to assess whether the non-solid residual-phase content, measured by LOI at 180 C., is representative of the sum of the quantity of water and of DEG present in the powdery slaked lime composition.

(23) TABLE-US-00001 TABLE 1 Quantity of water Quantity Total water LOI measured added of DEG and DEG at 180 C. Variation (% by added (% by (% by (% by weight) (% by weight) weight) weight) weight) 0.3 0.2 0.5 0.4 0.10 0.8 0.2 1.0 1.1 0.14 1.3 0.2 1.5 1.5 0.01 1.8 0.2 2.0 2.0 0.04 0.5 0.5 1.0 0.8 0.18 1.0 0.5 1.5 1.5 0.04 1.5 0.5 2.0 1.9 0.06

(24) As can be seen in table 1, the non-solid residual phase, measured by LOI at 180 C. in accordance with the operating method described previously, constitutes a good indicator of the sum of the water and DEG added in the laboratory to the completely dried slaked lime since the variation, which is the difference between the theoretical value and the measured value, is less than 0.20%, most of the time less than 0.10%.

Example 5

(25) The following example is implemented in order to assess the influence of the non-solid residual-phase content, in particular of the water and/or DEG content of the powdery slaked lime composition, on its fluidity, all the other parameters being fixed, such as the particle size, the particle shape, the chemical composition, the specific surface area and the pore volume of the slaked lime composition.

(26) In this regard, various samples of powdery slaked lime compositions are prepared from the completely dried slaked lime prepared in example 4 and to which various quantities of water and/or DEG are added by mixing. The Alpine fluidity of these powdery slaked lime compositions is measured in accordance with the procedure described previously. The results are presented in tables 2 and 3, in which the percentages by weight are expressed with respect to the total weight of the powdery slaked lime composition.

(27) In this table, on the basis of the conclusion of example 4, we have considered that the sum of the quantity of water and DEG added to the completely dried slaked lime corresponds to the non-solid residual-phase content that we would have obtained if it had been measured by a loss-on-ignition test at 180 C. (theoretical LOI at 180 C.).

(28) Likewise, we have considered that the quantity of water added to the completely dried slaked lime corresponds to the non-solid residual-phase content that we would have obtained if it had been measured by a loss of ignition test at 110 C. (theoretical LOI at 110 C.).

(29) TABLE-US-00002 TABLE 2 Quantity of water added, ie theoretical LOI Quantity of Theoretical Alpine at 110 C. DEG added LOI at 180 C. fluidity (% by weight) (% by weight) (% by weight) (%) EXAMPLE 0.7 0.0 0.7 59 5.1 EXAMPLE 1.0 0.0 1.0 65 5.2 EXAMPLE 1.4 0.0 1.4 60 5.3

(30) It can be seen from table 2 that the powdery slaked lime compositions having a water content greater than or equal to 0.7% by weight and less than or equal to 1.4% by weight have good fluidity (Alpine fluidity greater than 50%), even without the addition of DEG.

(31) TABLE-US-00003 TABLE 3 Quantity of water added, ie theoretical LOI Quantity of Theoretical Alpine at 110 C. DEG added LOI at 180 C. fluidity (% by weight) (% by weight) (% by weight) (%) EXAMPLE 0.3 0.2 0.5 87 5.4 EXAMPLE 0.8 0.2 1.0 83 5.5 EXAMPLE 1.3 0.2 1.5 83 5.6 EXAMPLE 1.8 0.2 2.0 68 5.7 EXAMPLE 0.5 0.5 1.0 86 5.8 EXAMPLE 1.0 0.5 1.5 88 5.9 EXAMPLE 1.5 0.5 2.0 88 5.10

(32) It can be seen from table 3 that the fluidity of the powdery slaked lime compositions having a water content greater than or equal to 0.3% by weight and less than 2% by weight can also be improved by the presence of diethylene glycol (DEG).

Comparative Example 1

(33) The same procedure as in example 5 is followed, except that the water content is modified. The results are illustrated in tables 4 and 5.

(34) TABLE-US-00004 TABLE 4 Quantity of water added, ie theoretical LOI Quantity of Theoretical Alpine at 110 C. DEG added LOI at 180 C. fluidity (% by weight) (% by weight) (% by weight) (%) Comparative 0.0 0.0 0.0 36 example 1.1 Comparative 0.0 0.2 0.2 45 example 1.2

(35) It can be seen from table 4 that the powdery slaked lime compositions to which no water has been added after the complete drying on a laboratory scale have an Alpine fluidity of less than 50%. When diethylene glycol (DEG) is added in a quantity of 0.2% by weight with respect to the total weight of the powdery slaked lime composition, the fluidity is improved but remains less than 50%.

(36) TABLE-US-00005 TABLE 5 Quantity of water added, ie theoretical LOI Quantity of Theoretical Alpine at 110 C. DEG added LOI at 180 C. fluidity (% by weight) (% by weight) (% by weight) (%) Comparative 2.0 0.0 2.0 40 example 1.3 Comparative 2.8 0.2 3.0 43 example 1.4 Comparative 3.0 0.0 3.0 27 example 1.5

(37) It can be seen from table 5 that the powdery slaked lime compositions having a water content greater than or equal to 2% by weight have an Alpine fluidity of less than 50% and this fluidity decreases when the water content increases. For a water content of 2.8%, adding 0.2% DEG improves the fluidity, but not sufficiently to obtain an Alpine fluidity of greater than 50%.

(38) The fluidity obtained with these samples is not sufficient to give a power suitable for an industrial application.

Example 6

(39) The same procedure as in example 5 is followed except that various quantities of water and DEG are added to the completely dried slaked lime with the same method as that described in example 4. The results are mentioned in table 8.

(40) TABLE-US-00006 TABLE 6 Quantity of water added, ie theoretical LOI Quantity of Theoretical Alpine at 110 C. DEG added LOI at 180 C. fluidity (% by weight) (% by weight) (% by weight) (%) Comparative 0.01 0.5 0.5 72 example 6.1

(41) It can be seen from table 6 that it is possible to obtain powdery slaked lime compositions having a water content close to 0 (since no water was added to the completely dried sample in this case), however having good fluidity (Alpine fluidity greater than 50%) by adding diethylene glycol (DEG) so as to obtain a non-solid residual-phase content measured by a loss-on-ignition test at 180 C. of formula;
LOI 180 C.LOI 110 C.+0.3%

(42) TABLE-US-00007 TABLE 7 Quantity of water added, ie theoretical LOI Quantity of Theoretical Alpine at 110 C. DEG added LOI at 180 C. fluidity (% by weight) (% by weight) (% by weight) (%) Comparative 2.5 0.5 3.0 60 example 6.2

(43) It can be seen from table 7 that it is possible to obtain powdery slaked lime compositions having a water content of greater than or equal to 2% by weight and less than or equal to 2.5% by weight, however having good fluidity (Alpine fluidity greater than 50%) by adding diethylene glycol (DEG) so as to obtain a non-solid residual-phase content measured by a loss-on-ignition test at 180 C. of formula:
LOI 180 C.LOI 110 C.+0.2%

Example 7

(44) In this example, five industrial samples of powdery slaked lime produced according to the present invention, satisfying Alpine fluidity >50%, but with different Alpine fluidity values, are selected. The cohesion index is measured with a Granudrum apparatus (model Aptis from GranuTOOLS) using a rotation speed of 2 rev/min and a data analysis with Aptis Granudrum software. The results are presented in table 8 below.

(45) TABLE-US-00008 TABLE 8 Alpine fluidity Granudrum cohesion index 50% 0.43 53% 0.51 57% 0.4 60% 0.31 70% 0.35

(46) It can be seen from table 8 that, in general, an increase in the Alpine fluidity, referring to an improved flow behaviour of the powdery slaked lime, corresponds to a reduction in the cohesion index measured with the Granudrum.

(47) Although the preferred embodiments of the invention have been described by way of illustration, a person skilled in the art knows that various modifications, additions or substitutions are possible, without departing from the scope and spirit of the invention as described in the accompanying claims.