Process for manufacturing a milk of slaked lime of great fineness and milk of lime of great fineness thereby obtained with process water

Abstract

Process for manufacturing a milk of lime of great fineness comprising at least the steps of providing one lime compound and forming said milk of lime with a process water and said lime compound.

Claims

1. A process for manufacturing a milk of lime of great fineness comprising at least the steps of a) providing a lime compound selected from the group consisting of quicklime, a first lime compound and their mixture said first lime compound being, selected front the group consisting of prehydrated lime obtained by the addition of a first water to quicklime, paste of lime obtained by the addition of a second water to quicklime, paste of lime obtained by the addition of a third water to prehydrated lime, paste of lime obtained by the addition of prehydrated lime to a third water and their mixture, and b) forming a milk of slaked lime of great fineness with, said lime compound by the addition of a fourth water to said lime compound or by the addition of the first lime compound to a fourth water, characterized in that at least one of the first, second, third or fourth water is process water selected from the group consisting of alkaline water, saline water, sulfate water comprising from 3 to 300 g solute/L and in that at least one of the first, second, third or fourth water is added to said lime compound, said milk of lime of great fineness having slaked lime particles presenting a d.sub.50 greater than or equal to 1 m and lower than or equal to 6 m, measured by laser diffraction using methanol as carrier solvent after screening of the milk of lime at 2 mm through a sieve for removing the grits.

2. Process for manufacturing a milk of lime of great fineness according to claim 1, wherein said at least one of the first, second, or fourth water is added to quicklime through a progressive addition of said at least one of the first, second, or fourth water to quicklime, under agitation conditions.

3. Process for manufacturing a milk of lime of great fineness according to claim 1, wherein said third water or said fourth water is added to prehydrated lime through a progressive addition of said third or fourth water to prehydrated lime under agitation conditions.

4. Process for manufacturing a milk of lime of great fineness according to claim 1, wherein said fourth water is added to paste of lime through a progressive addition of said fourth water to paste of lime under agitation conditions.

5. Process for manufacturing a milk of lime of great fineness according to claim 2, wherein said progressive addition of said at least one of the first, second, third or fourth water to said lime compound is presenting a pattern of addition of said at least one of the first, second, third or fourth water for controlling water uptake by the lime compound in a batch process or in a continuous process.

6. Process for manufacturing a milk of slaked lime of great fineness according to claim 2, wherein said progressive addition of said at least one of the first, second, third or fourth water is a continuous process during which progressive hydration of said lime compound is performed by adjusting lime compound feeding rate into a hydrator wherein a predetermined atmosphere is created containing a limited amount of said at least one of the first, second, third or fourth water for addition of said at least one of the first, second, third or fourth water to said lime compound.

7. Process for manufacturing milk of slaked lime of great fineness according to claim 2, wherein progressive addition of said at least one of the first, second, third or fourth water is performed by spraying a mist of said at least one of the first, second, third or fourth water into a hydrator.

8. Process for manufacturing milk of slaked lime of great fineness according to claim 2, wherein progressive addition of said at least one of the first, second, third or fourth water is a batch process during which progressive hydration of said lime compound is performed by placing a predetermined amount of lime compound into a hydrator wherein a predetermined atmosphere is created containing a limited amount of said at least one of the first, second, third or fourth water for addition of said at least one of the first, second, third or fourth water to said lime compound.

9. Process for manufacturing a milk of lime of great fineness according to claim 2, wherein said lime compound is quicklime onto which said fourth water being process water is progressively added until said milk of lime of great fineness is reached.

10. Process for manufacturing a milk of lime of great fineness according to claim 2, wherein said first lime compound is selected from the group consisting of prehydrated lime, paste of lime and their mixture obtained from quicklime onto which a first water or a second water being process water is progressively added for forming said first lime compound.

11. Process for manufacturing a milk of lime of great fineness according to claim 2, wherein said first lime compound is a paste of lime obtained from prehydratcd lime onto which said third water being process water is progressively added.

12. Process for manufacturing a milk of lime of great fineness according to claim 2, wherein said third and said fourth water are a same water and wherein said first lime compound is prehydrated lime onto which said third water, being said fourth water and being process water is progressively added until said milk of lime is reached.

13. Process for manufacturing a milk of lime of great fineness according to claim 1, further comprising an addition of at least one additive, said additive being added to or contained into said at least one of the first, second, third and fourth water or added to or contained into said lime compound.

14. Process for manufacturing a milk of lime of great fineness according to claim 13, wherein said additive is selected from the group consisting of carbohydrates, sugars, alcohol sugars, carbon dioxide, phosphates, sulfates, bicarbonates, silicates, phosphonates, polyacrylates, polycarboxylic acids, low molecular weight organic acids, mixtures and derivatives thereof.

15. Process for manufacturing a milk of lime of great fineness according to claim 1, wherein said at least one of the first, second, third and fourth water being process water is an aqueous phase selected from the group consisting of water comprising endogenous salt, industrial alkaline aqueous phase, industrial high sulfate water, saturated gypsum solutions, seawater, saline and hypersaline water, Brackish water and their mixture, whether recycled or not.

16. Process for manufacturing a milk of limo of great fineness according to claim 1, wherein said process water comprises at least 1 g/L mineral salt including mineral sulfate or sodium salt and their mixture.

17. Process for manufacturing a milk of time of great fineness according to claim 1, wherein the proportion of process water to the total amount of water used is higher than 40 w%.

18. Process for manufacturing a milk of lime of great fineness according to claim 1, further comprising a sieving or selection step to remove particles greater than 1 mm.

Description

EXAMPLES

(1) In the hereunder examples, the lime used is a lime from the Tapah plant, being typically a quicklime which produces under normal slaking conditions of adding quicklime to water a rather high viscosity milk of lime.

Example 1

(2) 2100 g of finely crushed quicklime as lime compound with a top size of 2 mm was placed in a 20 dm.sup.3 horizontally agitated laboratory paste mixer of the type Ldige M-20 MK. This mixer provides agitation by 2 plow shares and 2 wall scrapers, which were fixed to the agitator axis and allow to mix powder, paste and slurry products.

(3) The lid on top of the mixer was equipped with a water dosing system, i.e. a water line ending a nozzle, and a thermally and chemically resistant filter, which allowed any formed vapour to escape out of the mixer to an external ventilation system.

(4) An industrial process water (fourth water) was fed at a rate of 3.0 g/sec to the reactor and thus sprayed through the nozzle onto the lime. In total 4.2 kg of this process water were added in the course of ca. 25 min.

(5) The industrial process water contained ca. 2 g/dm.sup.3 of sodium hydroxide, 11 g/dm.sup.3 of sodium carbonate, ca. 7 g/dm.sup.3 of sodium aluminate, ca. 2 g/dm.sup.3 of sodium sulphate, ca. 0.5 g/dm.sup.3 sodium chloride and 5-15 g/dm.sup.3 of organic impurities, which were derived from humates.

(6) Additionally, ca. 10 g of sorbitol were added to the water.

(7) After completion of the dosing, the mixture is left under agitation in the mixer till cooled down to less than 50 C. Then it is removed from the mixer, screened at 2 mm through a sieve and analysed for solid content, viscosity and particle size distribution. The particle size distribution is measured with a Beckman-Coulter LS 13 320 Laser Diffraction Particle Sizer with an internal sonication cell in the recirculation circuit of the methanolic sample suspension. Sonication is applied in this cell for 30 sec at 50% of the maximum intensity prior to 2 measurement runs on the same sample. The results of these two runs are checked and compared, and if the 2 particle size distribution results match to a good level of confidence (based on the common standard deviation for these type of measurements with the equipment), the average of the 2 runs is taken as the final particle size distribution result. Otherwise, the measurement is repeated on the same sample, but without a second sonication.

(8) This experiment was repeated at the same conditions for a second time.

(9) Solid content was determined by residual weight after drying in an infra-red thermobalance at 110 C. Viscosity was measured with a Brookfield DV-3B Rheometer using the predetermined spindle at a rotational speed of 100 rpm.

(10) Particle size distribution was measured with a Beckman-Coulter LS 13 320 Laser Diffraction Particle Sizer using methanol as carrier solvent.

(11) The results are shown in Table 1

(12) TABLE-US-00002 TABLE 1 Viscosity Solid Content d.sub.50 d.sub.90 d.sub.97 Run [cPs] [wt. %] [m] [m] [m] 1 230 45.0 2.29 21.2 40.8 2 190 45.0 2.37 11.7 33.6

(13) The suspensions were then diluted by addition of demineralized water to the milk of lime to 23.0 wt. % solids content for easier comparison of the viscosity to the comparative examples. The results of the viscosity and solid content are shown in Table 2.-

(14) TABLE-US-00003 TABLE 2 Viscosity Solid Content Run [cPs] [wt. %] 1 22 23.0 2 18 23.0

Comparative Example 1

(15) The same experimental conditions as in Example 1.- were used, including the amount of quicklime, the amount of slaking water and sorbitol.

(16) Also the same finely crushed quicklime was used. But instead of the process water, demineralized water was employed. The results are shown in Table 3.-

(17) TABLE-US-00004 TABLE 3 Viscosity Solid Content d.sub.50 d.sub.90 d.sub.97 Run [cPs] [wt. %] [m] [m] [m] 3 240 39.1 2.76 32.1 54.8

(18) As it can be seen, the solids content of Comparative example 1 was reduced in comparison to Example 1, as a significant amount of pasty material was adhering to the agitator.

(19) Still, it can be observed that viscosity is similar despite the lower solid content and the particle size is less fine for this product obtained with clean water compared to the previous two obtained with the process water.

Comparative Example 2

(20) The same type of finely crushed quicklime as in Example 1 is slaked with the same industrial process water in a continuous pilot slaking installation, meaning that lime is added to water instead of according to the present invention where water is added to quicklime.

(21) This pilot installation consists of a 10 dm.sup.3 stirred tank reactor with double jacket, a screw feeder with hopper to continuously dose the quicklime, a dosing pump to continuously feed the slaking water and another dosing pump to continuously remove the slaked lime suspension from the reactor. The reactor is equipped with a thermostatic heating bath to control its temperature, a high capacity reflux cooler with attached ventilation system to withdraw any generated vapour and thermocouples at different positions to monitor reactor temperature.

(22) The agitation of the reactor has been designed and validated to provide agitation similar to industrial detention slakers. The reactor was fed continuously with 90 g/min of quicklime and 450 g/min of slaking water for an average residence time of ca. 20 min. Slaking temperature in the reactor was 80 C. The results of the milk-of-lime quality is shown in Table 4 and was obtained at steady state conditions (after ca. 7 residence times of operation).

(23) TABLE-US-00005 TABLE 4 Viscosity Solid Content d.sub.50 d.sub.90 d.sub.97 Run [cPs] [wt. %] [m] [m] [m] 1 40 25.6 8.33 52.6 75.7

Comparative Example 3

(24) Comparative example 2 was reproduced, but demineralized water was used instead of process water. The results are shown in table 5.-

(25) TABLE-US-00006 TABLE 5 Viscosity Solid Content d.sub.50 d.sub.90 Run [cPs] [wt. %] [m] [m] [m] 2 200 23.0 4.5 20 40

(26) As it can be seen, the effect of the industrial process water in classical, continuous slaking as practiced in industry is thus a significant coarsening of the milk-of-lime (Comparative example 2) in comparison to clean water (Comparative example 3).

Example 2

(27) The same experiment at the same conditions as according to Example 1 was conducted, but using a solution of sulphate salts, i.e. 10 g/dm.sup.3 of magnesium sulphate and 2 g/dm.sup.3 of sodium sulphate. Both salts were added in their anhydrous form as chemicals to demineralized water to produce this solution.

(28) After completion of the slaking experiment, the obtained milk-of-lime suspension was screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(29) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 6 were obtained.

(30) TABLE-US-00007 TABLE 6 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 215 43.7 3.74 29.3 51.8 15.7% 1.0%

(31) The suspensions were then diluted by addition of demineralized water to 26.6 wt. % solids content for easier comparison of the viscosity to the comparative examples. The results are shown in Table 7.-

(32) TABLE-US-00008 TABLE 7 Viscosity Solid Content Run [cPs] [wt. %] 1 8 26.6

Comparative Example 4

(33) The same lime as according to Example 1 was slaked in an experimental set-up as described in the norm EN 459-2, section 5.10: Reactivity. 150 g of finely crushed lime of a maximum particle size of 2 mm are added to 600 g of the same solution as in Example 2 with an initial solution temperature of 20 C. and slaked under agitation as described in the norm. The obtained suspension is then screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(34) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 8.- were obtained.

(35) TABLE-US-00009 TABLE 8 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 5 18 16.5 73 91 1.2% 2.8%

Example 3

(36) The same experiment at the same conditions according to Example 1 was conducted, but using another solution of sulphate salts, i.e. 30 g/dm.sup.3 of magnesium sulphate and 5 g/dm.sup.3 of sodium sulphate. Both salts were added in their anhydrous form as chemicals to demineralized water to produce this solution.

(37) After completion of the slaking experiment, the obtained milk-of-lime suspension was screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(38) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 9.- were obtained.

(39) TABLE-US-00010 TABLE 9 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 215 44.9 4.5 40.3 59.1 19.0% 1.4%

(40) The suspensions were then diluted by addition of demineralized water to 26.6 wt. % solids content for easier comparison of the viscosity to the comparative example. The results are shown in Table 10.-

(41) TABLE-US-00011 TABLE 10 Viscosity Solid Content Run [cPs] [wt. %] 1 8 26.6

Comparative Example 5

(42) The same lime as in Example 1 was slaked in an experimental set-up as described in the norm EN 459-2, section 5.10: Reactivity. 150 g of finely crushed lime of a max. size of 2 mm are added to 600 g of the same solution as in Example 3 with an initial solution temperature of 20 C. and slaked under agitation as described in the norm. The obtained suspension is then screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(43) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 11.- were obtained.

(44) TABLE-US-00012 TABLE 11 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 14 21.8 10.2 57.3 80.9 11.3% 3.4%

Example 4

(45) The same experiment at the same conditions according to Example 1 was conducted, but using a solution saturated in calcium sulphate, thus containing ca. 1.4 g/dm.sup.3 of dissolved calcium sulphate. Analytical grade gypsum was used to saturate the solution.

(46) After completion of the slaking experiment, the obtained milk-of-lime suspension was screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(47) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 12.- were obtained.

(48) TABLE-US-00013 TABLE 12 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 1300 40.1 2.81 24.8 43.3 9.6% 15.7%

(49) The suspensions were then diluted by addition of demineralized water to 22 wt. % solids content for easier comparison of the viscosity to the comparative examples. The results are shown in Table 13.-

(50) TABLE-US-00014 TABLE 13 Viscosity Solid Content Run [cPs] [wt. %] 1 63 22.0

Comparative Example 6

(51) The same lime as according to Example 1 was slaked in a test set-up described in the norm EN 459-2, section 5.10: Reactivity. 150 g of finely crushed lime of a max. size of 2 mm are added to 600 g of the same solution as in Example 4 with an initial solution temperature of 20 C. and slaked under agitation as described in the norm. The obtained suspension is then screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(52) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 14.- were obtained.

(53) TABLE-US-00015 TABLE 14 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 3 26.4 16.45 66.4 112.7 0.3% 1.8%

Example 5

(54) The same experiment at the same conditions according to Example 1 was conducted, but using a solution of sodium chloride, i.e. 10 g/dm.sup.3 of analytical grade sodium chloride were added to demineralized water to produce this solution.

(55) After completion of the slaking experiment, the obtained milk-of-lime suspension was screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(56) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 15.- were obtained

(57) TABLE-US-00016 TABLE 15 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 1480 37.8 2.80 31.3 64.6 4.8% 5.3%

(58) The suspensions were then diluted by addition of demineralized water to 20.4 wt. % solids content for easier comparison of the viscosity to the comparative examples. The results are shown in Table 16.-

(59) TABLE-US-00017 TABLE 16 Viscosity Solid Content Run [cPs] [wt. %] 1 43 20.4

Comparative Example 7

(60) The same lime as in Example 1 was slaked in a test set-up described in the norm EN 459-2, section 5.10: Reactivity. 150 g of finely crushed lime of a max. size of 2 mm are added to 600 g of the same solution as in Example 5 with an initial solution temperature of 20 C. and slaked under agitation as described in the norm. The obtained suspension is then screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(61) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 17.- were obtained.

(62) TABLE-US-00018 TABLE 17 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 21 28 6.22 31.9 52.5 8.0% 0.5%

Example 6

(63) The same experiment at the same conditions as according to Example 1 was conducted, but using another solution of sodium chloride, i.e. 40 g/dm.sup.3 of analytical grade sodium chloride were added to demineralized water to produce this solution.

(64) After completion of the slaking experiment, the obtained milk-of-lime suspension was screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(65) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results in Table 18.- were obtained.

(66) TABLE-US-00019 TABLE 18 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 2400 43.1 2.87 11.7 29.7 5.9% 12.4%

(67) The suspensions were then diluted by addition of demineralized water to 21.0 wt. % solids content for easier comparison of the viscosity to the comparative example. The results are shown in table 19.-

(68) TABLE-US-00020 TABLE 19 Viscosity Solid Content Run [cPs] [wt. %] 1 59 21.0

Comparative Example 8

(69) The same lime as according to Example 1 was slaked in a test set-up described in the norm EN 459-2, section 5.10: Reactivity. 150 g of finely crushed lime of a max. size of 2 mm are added to 600 g of the same solution as in Example 6 with an initial solution temperature of 20 C. and slaked under agitation as described in the norm. The obtained suspension is then screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(70) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results in Table 20.- were obtained.

(71) TABLE-US-00021 TABLE 20 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 17 29.6 7.86 45.9 67 7.6% 0.4%

Example 7

(72) The same experiment at the same conditions as Example 1 was conducted, but using another solution with the composition of seawater, i.e.:

(73) 27.4 g/dm.sup.3 NaCl

(74) 3.4 g/dm.sup.3 MgCl.sub.2

(75) 2.1 g/d MgSO.sub.4

(76) 1.4 g/dm.sup.3 CaSO.sub.4

(77) 0.7 g/d KCl

(78) This solution was produced from analytical grade anhydrous salts added to demineralized water.

(79) After completion of the slaking experiment, the obtained milk-of-lime suspension was screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(80) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 21.- were obtained.

(81) TABLE-US-00022 TABLE 21 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 2400 43.4 3.86 52.8 71.7 19.1% 8.4%

(82) The suspensions were then diluted by addition of demineralized water to 21.8 wt. % solids content for easier comparison of the viscosity to the comparative example. The results are shown in Table 22.-

(83) TABLE-US-00023 TABLE 22 Viscosity Solid Content Run [cPs] [wt. %] 1 27 21.8

Comparative Example 9

(84) The same lime as according to Example 1 was slaked in a test set-up described in the norm EN 459-2, section 5.10: Reactivity. 150 g of finely crushed lime of a max. size of 2 mm are added to 600 g of the same solution as in Example 7 with an initial solution temperature of 20 C. and slaked under agitation as described in the norm. The obtained suspension is then screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(85) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in table 23.- were obtained.

(86) TABLE-US-00024 TABLE 23 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 8 20.9 14.7 79.5 119 1.4% 3.6%

Example 8

(87) The same experiment at the same conditions as Example 1 was conducted, but using a solution with the following composition:

(88) 195 g/dm.sup.3 NaCl

(89) 15 g/dm.sup.3 MgSO.sub.4

(90) 7 g/dm.sup.3 Na.sub.2SO.sub.4

(91) 1.4 g/dm.sup.3 CaSO.sub.4

(92) 1.5 g/dm.sup.3 KCl

(93) This solution was produced from analytical grade anhydrous salts added to demineralized water.

(94) After completion of the slaking experiment, the obtained milk-of-lime suspension was screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(95) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 24.- were obtained.

(96) TABLE-US-00025 TABLE 24 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 147 49.6 5.49 61 85.9 8.8% 3.2%

(97) The suspensions were then diluted by addition of demineralized water to 28.1 wt. % solids content for easier comparison of the viscosity to the comparative examples. The results are shown in Table 25.-

(98) TABLE-US-00026 TABLE 25 Viscosity Solid Content Run [cPs] [wt. %] 1 9 28.1

Comparative Example 10

(99) The same lime as according to Example 1 was slaked in a test set-up described in the norm EN 459-2, section 5.10: Reactivity. 150 g of finely crushed lime of a max. size of 2 mm are added to 600 g of the same solution as in Example 8 with an initial solution temperature of 20 C. and slaked under agitation as described in the norm. The obtained suspension is then screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(100) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in Table 26.- were obtained.

(101) TABLE-US-00027 TABLE 26 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 18 35.7 15.1 70.2 91.8 14.1% 1.5%

Comparative Example 11

(102) The same lime as according to Example 1 was slaked in a test set-up described in the norm EN 459-2, section 5.10: Reactivity. 150 g of finely crushed lime of a max. size of 2 mm are added to 600 g of demineralized water with an initial solution temperature of 20 C. and slaked under agitation as described in the norm. The obtained suspension is then screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(103) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in table 27.- were obtained.

(104) TABLE-US-00028 TABLE 27 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 175 26.7 4.56 26.8 62.9 13.0% 0.2%

Comparative Example 12

(105) The same experimental conditions as in Comparative example 1 were used but with another starting quicklime.

(106) While the quicklime of Comparative example 1 was of t.sub.60 reactivity of 2.5 min (measured according to the procedure outlined in EN459-2), the quicklime sample used in this example is of low reactivity, i.e. a t.sub.60 of 4.2 min and additionally contains impurities, notably sulphate at a content of ca. 0.18 wt. % SO.sub.3, which would reduce the fineness of the obtained milk-of-lime.

(107) Demineralized water was fed at a rate of 3.0 g/sec to the reactor and thus sprayed through the nozzle onto the lime. About 10 g of sorbitol had been added to and dissolved in the water in advance. In total 4.2 kg of this water were added in the course of ca. 25 min.

(108) After completion of the dosing, the mixture is left under agitation in the mixer till cooled down to less than 50 C. Then it is removed from the mixer, screened first at 1 mm through a sieve and analysed for solid content and viscosity. Subsequently, it was screened at 200 m and its particle size distribution determined. The results shown in table 28.- were obtained.

(109) TABLE-US-00029 TABLE 28 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 52 44.2 2.72 9.33 27.7 0.2% 1.0%

(110) The suspensions were then diluted by addition of demineralized water to 21.2 wt. % solids content for easier comparison of viscosity to the comparative examples. The results are shown in Table 29.-

(111) TABLE-US-00030 TABLE 29 Viscosity Solid Content Run [cPs] [wt. %] 1 10 21.2

Comparative Example 13

(112) The same lime as in comparative example 12 was slaked in an experimental set-up as described in the norm EN 459-2, similarly as in comparative example 4.

(113) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in table 30.- were obtained.

(114) TABLE-US-00031 TABLE 30 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 123 26.7 4.96 11.61 27.5 0.0 0.0

(115) In comparison with comparative example 12, we observe that a significantly lower d.sub.50 and a lower viscosity were obtained in comparative example 12.

Comparative Example 14

(116) The same lime as in Example 1 was slaked in an experimental set-up as described in the norm EN 459-2, section 5.10: Reactivity. 150 g of finely crushed lime of a max. size of 2 mm are added to 600 g of the same process water as in example 9 with an initial solution temperature of 20 C. and slaked under agitation as described in the norm. The obtained suspension is then screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(117) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in table 31.- were obtained.

(118) TABLE-US-00032 TABLE 31 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 184 28.2 8.2 21.4 32.4 0.0% 0.0%

(119) Compared to the reactivity test with demineralized water, the slaking in the same test set-up with process water did not reach 60 C. even though the test was monitored for more than 15 min.

(120) Such a lack of heat generation was not noted on the slaking of Example 9, i.e. according to our invention, where again a milk of lime of lower d.sub.50 and lower viscosity was obtained compared to this example.

Example 9

(121) The same experiment at the same conditions as comparative example 12 was conducted, but using the industrial process water as described in Example 1 (i.e. method of the present invention with a low reactive quicklime). This industrial process water contained ca. 2 g/dm.sup.3 of sodium hydroxide, 11 g/dm.sup.3 of sodium carbonate, ca. 7 g/dm3 of sodium aluminate, ca. 2 g/dm.sup.3 of sodium sulphate, ca. 0.5 g/dm.sup.3 sodium chloride and 5-15 g/dm.sup.3 of organic impurities, which were derived from humates.

(122) As in the other Examples, ca. 10 g of sorbitol were added to the water.

(123) After completion of the slaking experiment, the obtained milk of lime suspension was screened on stainless steel sieves first of 1000 m and then of 200 m. The screen rejects were dried, weighed and the weight expressed as fraction of the total solids in the suspension.

(124) While solid content and viscosity were determined prior to the screening, the particle size distribution was measured after screening as described in Example 1. The results shown in table 32.- were obtained.

(125) TABLE-US-00033 TABLE 32 Reject Reject Solid >200 m >1 mm Viscosity Content d.sub.50 d.sub.90 d.sub.97 [wt. % [wt. % Run [cPs] [wt. %] [m] [m] [m] solids] solids] 1 976 46.7 2.3 9.6 36.9 0.5% 0.0%

(126) The suspensions were then diluted by addition of demineralized water to 23.7 wt. % solids content for easier comparison of the viscosity to the comparative examples. The results are shown in Table 33.-

(127) TABLE-US-00034 TABLE 33 Viscosity Solid Content Run [cPs] [wt. %] 1 80 23.7

(128) While the invention has been shown in several of its forms, it is not thus limited and is susceptible to various changes and modifications without departing from the spirit thereof and from the enclosed claims.