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

Abstract

A process is shown for manufacturing a milk of lime of great fineness which includes at least the steps of providing one lime compound chosen in the group consisting of prehydrated lime, a paste of lime obtained by addition of water to quicklime instead of addition of quicklime to water and their mixture, and forming a milk of slaked lime of great fineness with the chosen lime compound. The paste of lime is obtained by progressive addition of water to quicklime under agitation conditions.

Claims

1. Process for manufacturing a milk of lime of great fineness wherein said milk of lime comprises slaked lime particles in suspension into an aqueous phase, the slaked lime particles having a d.sub.50 greater than or equal to 2 m and lower than or equal to 6 m, measured by means of a laser granulometer in methanol, comprising at least the steps of: (a) adding water to quicklime instead of addition of quicklime to water to obtain a paste of lime and (b) forming a milk of slaked lime of great fineness with said paste of lime.

2. Process for manufacturing a milk of lime of great fineness according to claim 1, wherein said paste of lime is obtained by progressive addition of water to quicklime under agitation conditions.

3. Process for manufacturing a milk of lime of great fineness according to claim 2, wherein said progressive addition of water to quicklime comprises presenting a pattern of addition of water for controlling water uptake by the quicklime when forming the paste of lime.

4. Process for manufacturing a milk of slaked lime of great fineness according to claim 2, wherein said progressive addition to form the paste of lime is a continuous process during which progressive hydration of quicklime is performed by adjusting quicklime feeding rate into a hydrator wherein a predetermined atmosphere is fed containing a limited amount of water for addition of water to quicklime.

5. Process for manufacturing milk of slaked lime of great fineness according to claim 2, wherein progressive addition to form the paste of lime is performed by spraying a mist of water into a hydrator.

6. Process for manufacturing milk of slaked lime of great fineness according to claim 5, wherein said mist of water is a controlled size of droplets of addition of water.

7. Process for manufacturing a milk of lime of great fineness according to claim 1, wherein water added to form said paste of lime comprises an additive selected from the group consisting of carbohydrates, sugars, alcohol sugars, sorbitol, phosphates, sulfates, bicarbonates, silicates, phosphonates, polyacrylates, polycarboxylic acids, low molecular weight organic acids, mixtures and derivatives thereof.

8. Process for manufacturing a milk of lime of great fineness according to claim 1, wherein the slaked lime particles have a d.sub.50 greater than or equal to 2.5 m and lower than or equal to 5.5 m, measured by means of a laser granulometer in methanol.

9. Process for manufacturing a milk of lime of great fineness according to claim 1, wherein the step of forming a milk of slaked lime of great fineness with said paste of lime is a step of adding water to the paste of lime.

10. Process for manufacturing a milk of lime of great fineness according to claim 1, wherein the step of forming a milk of slaked lime of great fineness with said paste of lime is a step of adding paste of lime to water.

11. Process for manufacturing milk of lime of great fineness according to claim 1, wherein said step of forming a milk of slaked lime of great fineness is a batch step by addition of a predetermined amount of said paste of lime into a predetermined amount of water or by addition of a predetermined amount of water into a predetermined amount of said paste of lime to produce said milk of slaked lime of great fineness.

12. Process for manufacturing milk of lime of great fineness according to claim 1, wherein said step of forming a milk of slaked lime of great fineness is a continuous step comprising the steps of feeding said paste of lime into a vessel provided with an exit of milk of slaked lime of great fineness and containing an aqueous suspension of lime and feeding said vessel with water and is followed by an exit of said milk of slaked lime of great fineness thereby obtained.

13. Process for manufacturing a milk of slaked lime of great fineness according to claim 1, wherein the paste of lime is made by a progressive addition of water to quicklime, said progressive addition of water being pursued during the step of forming said milk of slaked lime of great fineness until said milk of slaked lime of great fineness is reached.

14. Process for manufacturing milk of lime of great fineness according to claim 13, wherein said progressive addition of water is carried out by increasing the amount of water added until said predetermined amount of water of the step of forming said milk of slaked lime of great fineness has been added.

Description

(1) FIG. 1 shows the lag time and the to temperature rise reactivity value of a prehydrated lime compared to initial quicklime.

(2) FIG. 2 is a graph showing the temperature evolution during slaking reaction of either quicklime or prehydrated lime for manufacturing milks of slaked lime according to example 2.

(3) FIG. 3 is a graph showing the temperature evolution during slaking reaction of quicklime for manufacturing milk of lime at different solid matter concentrations according to example 3.

(4) FIG. 4 is a graph showing the temperature evolution during slaking reaction of prehydrated lime for manufacturing milk of slaked lime of the present invention at different solid matter concentrations according to example 3.

(5) FIG. 5 is a graph showing the temperature rise reactivity curves of the lime samples according to example 4 during wet slaking, measured according to EN 459-2 depending on the amount of water present in the prehydrated lime.

(6) FIG. 6 is a graph showing the temperature evolution during the wet slaking of the samples according to example 6.

(7) FIG. 7 is a graph showing the temperature evolution during the wet slaking of the samples according to example 9.

(8) FIG. 8 is a graph showing the particle size distribution of a milk of slaked lime made according to the principles of the present invention.

(9) FIG. 9 is a graph illustrating the viscosity change over time for a milk of slaked lime of the invention.

(10) FIG. 10 is a graph illustrating the temperature profile obtained during the manufacturing of milk of slaked lime according to one embodiment of the invention, showing the maximum temperature of reaction achieved.

(11) FIG. 11 is a graph comparing the temperature profile obtained during the manufacturing of milk of slaked lime according to one embodiment of the invention, with the temperature profile obtained during the manufacturing of milk of slaked lime according to the prior art.

(12) FIG. 12 is a graph which compares the particle size distribution of two milks of slaked lime made according to one embodiment of the invention with two prior art milks of slaked lime.

(13) FIG. 13 is a graph comparing the viscosity change over time for two milks of slaked lime made according to one embodiment of the invention versus a prior art milk of slaked lime.

(14) The present invention relates to a process for manufacturing a milk of slaked lime of great fineness comprising a step of providing a lime compound chosen in the group consisting of prehydrated lime or a paste of lime obtained by the addition of water to quicklime to a step of forming a milk of slaked lime of great fineness by adding water to lime compound or lime compound to water.

(15) As briefly discussed in the Background section, the term lime can encompass quicklime (calcium oxideCaO), hydrated lime (calcium hydroxideCa(OH).sub.2) or milk of lime. Quicklime is manufactured by chemically converting limestone (calcium carbonateCaCO.sub.3) into calcium oxide in a high temperature kiln. Hydrated lime is created when quicklime chemically reacts with water and is generally in a powdered form.

(16) Milk of slaked lime is a suspension of hydrated lime in water and can be formed from either hydrated lime or quicklime; however, preferred milk of slaked lime used herein is produced from prehydrated quicklime or paste of lime obtained by the addition of water to lime rather than lime to water. The quicklime used for the purposes discussed herein may be high calcium lime, which contains no more than about 5 percent magnesium oxide or hydroxide.

(17) The preferred milk of slaked lime used herein will contain about 20-55% by weight of solids, preferably about 40-50% by weight of solids, and most preferably about 45% by weight of solids, based upon the total weight of the milk of slaked lime.

(18) This invention's goal is to produce milk of slaked lime with fine particle size distribution. This property is achieved by the batch or continuous process according to the invention comprising a first step of providing a lime compound chosen in the restricted group consisting of prehydrated lime and a paste of lime obtained by the addition of water to quicklime, followed by a step of forming said milk of slaked lime of great fineness which in its preferred form presents a particle size distribution d.sub.50 comprised between 2-5 m or even between 2.5-3.5 m, showing a slaked lime content of 42-45% by weight of solids.

(19) In the discussion which follows, the particle sizes distributions (also called granulometries) are measured by means of a laser granulometer in methanol; these distributions are characterized in terms of, for example, d.sub.50, d.sub.90 and d.sub.98, interpolated values of the particle size distribution curves. The dimensions d.sub.50, d.sub.90 and d.sub.98 correspond to the dimensions for which respectively 50%, 90% and 98% of the particles are less than a given value.

(20) The viscosity of these milks of lime is measured according to standard industry practice, as by the use of a Brookfield DV III Rheometer viscometer, with spindle N 3 at 100 rpm. The measurement was taken on the 30th second, once the viscometer motor was turned on.

(21) The milk of slaked lime of great fineness according to the present invention can be obtained either from prehydrated lime or from a paste of lime obtained by addition of water to quicklime instead of addition of quicklime to water.

(22) Indeed, it has been found that the selection of specific lime compound chosen in the group consisting of prehydrated lime or a paste of lime obtained by addition of water to quicklime instead of addition of quicklime to water shares the concept that milk of slaked lime of great fineness is obtained due to the existence of prehydrated lime compounds.

(23) If the milk of slaked lime of great fineness is formed from prehydrated lime, the particles of prehydrated lime introduced during the step of forming the milk of slaked lime are prehydrated particles and are further slaked with a predetermined volume of water for forming the milk of slaked lime. In this latter case, the volume of water can be added to the prehydrated lime particles or in the contrary, prehydrated lime can be added to the volume of water.

(24) If the milk of slaked lime of great fineness is formed from a paste of lime obtained by addition of water to quicklime instead of addition of quicklime to water, prehydrated lime is formed as intermediate product during the addition of water, which intermediate product progressively disappears more or less along water addition until the paste of lime is formed.

(25) First Preferred Way for Embodying the Invention: Forming a Milk of Slaked Lime of Great Fineness from Prehydrated Lime.

(26) In one embodiment according to the present invention, the milk of slaked lime of great fineness is obtained from prehydrated lime which may be freshly produced or commercially available. The prehydrated lime is then fed to the step of forming the milk of slaked lime of great fineness for adding water to the prehydrated lime or prehydrated lime to water. In both cases, the step of forming the milk of slaked lime of great fineness is a slaking step which may be a batch step or a continuous or progressive step.

(27) This alternatives show, besides the advantageous high reactivity of the resulting milk of lime due to its great fineness, another advantageous effect residing in the fact that the process according to the present invention also allows, when needed, to flatten existing quality variations whether they are due to quicklime parameter variations or to slaking conditions. The process according to the present invention therefore allows also to upgrade milk of lime qualities from a given quicklime by forming a coating on prehydrated lime particles which renders the quicklime suitable for applications where finer milk of slaked lime is needed.

(28) In this preferred embodiment of the process according to the invention, if the amount of water added to quicklime during partial hydration step is low (4-8 w % of Ca(OH).sub.2 with respect to prehydrated lime), the partial hydration step can be done in an existing equipment such as a screw conveying the quicklime to storage tank.

(29) Otherwise, prehydration step is done in an appropriate equipment such as an hydrator, hydrator-like vessel, blugers, or pug-mill.

(30) In a preferred embodiment of prehydration, when a control of the temperature is performed as controlled condition, in particular when such control is done by limiting, during or after the manufacturing of prehydrated lime, the heat generated by such process step, a cooling can be done within the screw of the hydrator or separately after the partial hydration step in a paddle cooler.

(31) In this case, the prehydrated lime is added into the front of the hydrator. The trough is oriented at a small angle of inclination. The paddles do not have a transport function; they are designed for maximum heat transfer, in this case for cooling without requiring introduction of cooling air. This equipment as well as the embodiment of the process according to the invention has shown to be optimized since due to the slowly-turning paddle shaft, the dust generation is limited. The temperature control by cooling down the prehydrated lime before slaking allows avoiding formation of agglomerates.

(32) It has to be understood that in this preferred embodiment of the process according to the invention, the prehydration step has to be carefully controlled so that quicklime will effectively be coated by a regular layer of hydrated lime around the quicklime core. In a variant of the process according to the present invention, the prehydrated lime can be obtained by submitting quicklime under gas containing steam, eventually CO.sub.2 at various temperatures in order to better control the thickness of the coating by agitating quicklime in a stream of gas.

(33) The coating of the quicklime core is not restricted to Ca(OH).sub.2 eventually comprising further CaCO.sub.3 but to any kind of chemicals that would delay temperature rise reactivity and show steeper temperature rise reactivity curve after a lag period, such as soluble phosphates, sulfates, bicarbonates, silicates or organic molecules adsorbed on lime particles such as sugars, phosphonates, polyacrylates, polycarboxylic acids, low molecular weight organic acids.

(34) The prehydrated lime may be obtained by a partial hydration step which is pursued continuously until the milk of slaked lime is produced, with the addition of at least water (water with or without additives) pursued under the same condition or increased in terms of flow rate. In this embodiment of the present invention, the fine particle size distribution and high percent solids properties of the milk of slaked lime are achieved by slaking quicklime to, for example, a 45 w % solids slurry, by utilizing a continuous hydration process, with water being added continuously in a controlled manner to the quicklime, rather than adding quicklime to a body of water in a vessel or container and agitating the mixture, as was done in the batch processes of the past.

(35) Alternatively, the prehydrated lime may be obtained by a continuous process where a fine spray mist of at least water can be provided initially, which step is followed by a stage in which at least water is added as a steady flow of water. However, in the preferred form of the invention, there is an initial stage which comprises a continuous controlled spray of a fine mist of at least water which is achieved, for example, with a full cone spray nozzle. A viscosity reducer or viscosity stabilizer can also be utilized. The controlled addition of at least water within the scope of the present invention can be achieved by utilizing a fine spray mist of at least water onto the quicklime or even on prehydrated lime.

(36) In alternative embodiment according to the present invention, prehydrated lime may be obtained by a steady addition of water on quicklime in a hydrator under high agitation conditions. The prehydrated lime thereby obtained is then fed to a slaking step into which water is added to prehydrated lime or prehydrated lime is added to water in a batch or continuous step to form the milk of lime of great fineness.

(37) Second Preferred Way for Embodying the Invention: Forming a Milk of Slaked Lime of Great Fineness from a Paste of Lime.

(38) According to this preferred embodiment, a paste of lime is obtained from quicklime before being diluted with water to form the milk of slaked lime of great fineness.

(39) For forming the paste of lime, water is added to quicklime in a progressive way, preferably in the form of a mist of at least water (with or without additives) in order to reach a high hydration temperature for reaching fine particles of lime. During this progressive hydration, prehydrated lime is formed as an intermediate product and undergoes hydration until a paste of lime is reached by pursuing the hydration process. The addition of water is controlled in such a way that lime is progressively hydrated and does not undergo directly full slaking, but merely with a ratio of hydration increasing along water addition and therefore along time. This may be done in a continuous process or in a batch process. In both case, the hydration is controlled to reach a progressive hydration of the quicklime. This is done by opposition of lime added to water yielding to full slaked lime particles and sometimes to a non homogeneous mixture of slaked lime and quicklime if no water remains for the further quicklime added.

(40) The paste of lime thereby obtained is further used to form the milk of slaked lime particles by adding water to the paste of lime or the paste of lime to water.

(41) In one embodiment, the paste of lime is obtained by a controlled hydration step which is pursued continuously until a milk of lime is produced, with the addition of at least water (water with or without additives) pursued under the same condition or increased in terms of flow rate. In this embodiment of the present invention, the fine particle size distribution and high percent solids properties of the milk of slaked lime are achieved by slaking quicklime to, for example, a 45 w % solids slurry, by utilizing a continuous hydration process, with water being added continuously in a controlled manner to the quicklime, rather than adding quicklime to a body of water in a vessel or container and agitating the mixture, as was done in the batch processes of the past.

(42) Alternatively, the paste of lime may be obtained by a continuous process where a fine spray mist of at least water can be provided initially, which step is followed by a stage in which at least water is added as a steady flow of water. However, in the preferred form of the invention, there is an initial stage which comprises a continuous controlled spray of a fine mist of at least water which is achieved, for example, with a full cone spray nozzle. A viscosity reducer or viscosity stabilizer can also be utilized.

(43) The controlled addition of at least water within the scope of the present invention can be achieved by utilizing a fine spray mist of at least water onto the quicklime.

(44) In alternative embodiment according to the present invention, a paste of lime may be obtained by a steady addition of water on quicklime in a hydrator under high agitation conditions. The paste of lime thereby obtained is then fed to a dilution step into which water is added to paste of lime or the paste of lime is added to water in a batch or continuous step to form the milk of lime of great fineness.

(45) Thus, in its most preferred form of this embodiment of the present invention, the new process is a continuous or progressive process in which quicklime is slaked, by exposing the quicklime to a fine mist of at least water in a continuous or progressive process. Particle size and viscosity of the slurry are best controlled if the water which is used for the misting operation also contains sugar or a sucrose material, such as, sorbitol, a sugar alcohol. The slaking temperature of the quicklime is preferably monitored, and is preferably maintained in the range from about 200 C. (about 400 F.) to about 350 C. (about 650 F.), before cooling down as water continues to be added to form the final milk of lime of great fineness.

(46) An important aspect of this embodiment is the fact that water is being continuously added to dry quicklime, preferably in the form of a fine mist, forming the paste of lime by passing via a prehydrated lime under controlled conditions; rather than dry quicklime being introduced into a body of water in a mixing tank. Also, there is no necessity for the intermediary steps of producing the final milk of lime of great fineness.

(47) The product which results from the practice of the method of the present invention is a milk of lime which is high in solids, for example 40 to 45 w % solids, which has a particle size, or granulometric dimension, d.sub.50, in the 2 to-5 micron size range, with a viscosity less than 400 mPa.Math.s, preferably even less than 250 mPa.Math.s, all very desirable characteristics from an industrial viewpoint.

EXAMPLES

Example 1: Impact of the Prehydration on the Prehydrated Lime Granulometry

(48) Three batches of quicklime (crushed to reach d.sub.90<90 m) are submitted to a batch prehydration in a conveying screw by spraying 4 w % water (based on the quicklime weight) in order to determine the influence of quicklime prehydration on prehydrated lime granulometry.

(49) The granulometry curves of quicklime and prehydrated quicklime are measured with a laser granulometer Beckman Coulter LS 13320. The results of the granulometry measurements are shown in Table 1.

(50) In the obtained prehydrated lime product, Ca(OH).sub.2 and CaCO.sub.3 contents are measured by weight losses at respectively 550 C. (1022 F.) and 950 C. (1742 F.) which are assumed to be water and CO.sub.2 respectively. These values are used to calculate the Ca(OH).sub.2 and CaCO.sub.3 contents in the prehydrated lime according to the invention. The results are shown in Table 1.

(51) There is almost no evaporation of water during the partial hydration step as almost all added water reacts with the CaO to form Ca(OH).sub.2. The amount of Ca(OH).sub.2 formed in the prehydrated lime is around 17 w %.

(52) As shown in Table 1, prehydrated lime results in coarser particle size distribution compared to the starting quicklime. This is notably explained by an agglomeration of the Ca(OH).sub.2 particles during prehydration.

(53) TABLE-US-00001 TABLE 1 Granulometry Weight loss at Batch d100 d98 d95 d90 d50 d25 550 C. 950 C. Ca(OH).sub.2 CaCO.sub.3 no m m m m m m % % % % Quicklime 1 282 170 144 113 12.9 6.1 0.504 2.573 2.07 5.85 2 310 187 158 127 14.2 6.4 0.237 0.3 0.97 0.68 3 310 176 150 119 12.7 6.0 0.388 0.423 1.60 0.96 Prehydrated 1 373 193 158 122 20.6 10.8 4.203 2.415 17.28 5.49 lime 2 595 210 164 123 18.5 9.4 4.218 0.453 17.34 1.03 3 653 201 154 113 20.7 11.9 3.961 0.501 16.28 1.14

Example 2: Forming a Milk of Lime of Great Fineness from Prehydrated Lime in Batch

(54) The samples of quicklime and prehydrated lime obtained from Example 1 have been respectively slaked on laboratory scale to obtain a milk of slaked lime with a solid content of slaked lime of 30 w % with respect to the total weight of the milk of lime.

(55) The granulometry of the milk of slaked lime obtained according to the present invention, from prehydrated lime provided under controlled condition, is compared to the granulometry of milk of lime slaked under similar condition, but from quicklime, meaning without prehydration.

(56) Granulometry measurements are made as in Example 1. The dry content of slaked lime in the milk of slaked lime is measured by drying a sample of around 10 g of milk of lime at 150 C. (300 F.) on a thermobalance (accuracy 0.01% dry content) until reaching a constant weight. The results of those measures are given in Table 2.

(57) TABLE-US-00002 TABLE 2 Granulometry Dry Batch d100 d98 d95 d90 d50 d25 content no m m m m m m % Milk from 1 213 86 49 31 9.7 5.0 30.1 quicklime 2 194 79 47 30 8.7 4.6 30.2 (prior art) 3 257 140 103 63 13.0 6.5 30.7 Milk from 1 53 32 27 21 7.1 3.9 28.4 prehydrated 2 53 32 27 20 7.0 3.9 29.0 lime 3 101 39 30 24 7.3 4.0 28.9

(58) As it can be seen from Table 2, the prehydration of quicklime according to the invention results in a milk of slaked lime in which the d.sub.50 is reduced from 9-13 m to about 7 m and agglomerates of slaked lime particles are nearly absent as the d.sub.95, d.sub.98 and d.sub.100 values are dramatically reduced.

(59) The viscosity of the samples was also measured at 20 C. (68 F.) with a Brookfield DV III Ultra rheometer while using LV mobiles n61, 62 and 63 turning at 100 rpm over a period of 3 weeks. The viscosity of the milk of slaked lime from the prehydrated quicklime have a higher viscosity value than the milk of slaked lime from fresh quicklime. This is a reflection of particle size reduction.

(60) Mobile n61 is used for a viscosity up to 60 mPa.Math.s; the mobile n62 for viscosities between 60 and 300 mPa.Math.s; the mobile n63 for viscosities up to 1200 mPa.Math.s. The results of the measures are given in table 3 (in mPa.Math.s).

(61) The conductivity reactivity of the so-formed milks of slaked lime was also determined through the measurement of the dissolution kinetic in water of the milk of slaked lime samples, following the teaching the European Standard EN 12485

(62) The following conditions were used. 5 ml of milk of slaked lime diluted to 2 w % dry content were added in 700 g of demineralized water at 25 C. (77 F.) under agitation while continuously measuring the conductivity. The time necessary to reach respectively 63, 90 and 100% of the total conductivity are compared and given in Table 3. The lower are the values of 100, 90 and 63, the more reactive is the milk of slaked lime.

(63) TABLE-US-00003 TABLE 3 Viscosity after Solubility Index Batch 1 day 1 week 2 weeks 3 weeks T100 T90 T63 no mPa .Math. s mPa .Math. s mPa .Math. s mPa .Math. s s s s Milk from 1 105 125 125 120 159.0 16.5 4.0 quicklime 2 130 135 235 235 207.0 23.0 4.5 (prior art) 3 80 105 105 115 183.0 26.5 6.0 Milk from 1 170 200 205 205 56.5 8.0 3.0 prehydrated 2 250 315 315 330 60.5 5.5 2.5 lime 3 210 250 280 290 79.5 9.0 4.0

(64) As it can be seen from Table 3, the following conclusions can be made. The fine granulometry of the slaked lime particles of the milk of slaked lime is reflected in the viscosity and solubility index measurements. Prehydrated lime produces more viscous and more reactive milk of slaked lime due to its increased fineness which can be related to enhanced dissolution kinetic.

(65) The temperature evolution during the slaking reaction of the prehydrated lime for manufacturing milk of slaked lime according to the invention was also monitored and compared to the temperature evolution measured during the slaking reaction of quicklime for manufacturing milk of slaked lime of the prior art. In both cases, the measurements were performed by using the same protocol as the one given into EN 459-2 except that quicklime/water ratio or prehydrated lime/water ratio were adapted to obtain 30 w % of Ca(OH).sub.2 in the resulting milk of lime. The results are given in FIG. 2.

(66) As it can be seen from FIG. 2, partial hydration of quicklime increases the time necessary to reach 30 C., generating therefore a lag time. The time necessary to reach 60 C. is also slightly increased.

Example 3.Forming a Milk of Lime of Great Fineness from Prehydrated Lime in Batch

(67) Another batch of quicklime (crushed to reach d.sub.90<90 m) has been submitted to a partial hydration step leading to a prehydrated lime as explained in Example 1.

(68) Granulometry curves of both quicklime and prehydrated lime are measured in the same way as disclosed in Example 1. The results are shown in Table 4.

(69) TABLE-US-00004 TABLE 4 Ca(OH).sub.2 Granulometry content d100 d98 d95 d90 d50 d25 % m m m m m m Quicklime 4.1 282 170 144 113 12.9 6.1 Prehydrated lime 15.6 373 193 158 122 20.6 10.8

(70) Both quicklime and prehydrated lime have been wet slaked with demineralized water in order to produce various milks of lime with different solid matter concentrations (5, 10, 15, 20 and 30 w % based on the total weight of the milk of slaked lime). The evolution of the temperature during manufacturing of said aforementioned milks of lime was monitored using the same protocol as the one given into EN 459-2. The results are illustrated in FIGS. 3 (milks of slaked lime at different concentrations produced from quicklime according to prior art) and 4 (milks of slaked lime at different concentrations produced from prehydrated lime according to the invention).

(71) As shown in FIGS. 3 and 4, the evolution of the temperature during wet slaking for manufacturing milk of slaked lime, either from quicklime or from prehydrated lime, shows different profiles depending on the milk of lime concentration. More precisely, higher concentrations of solid matter in the milk of lime lead to higher temperatures reached during its manufacturing. For example, when milk of lime is produced from prehydrated lime, the maximum temperature reached for a 30 w % Ca(OH).sub.2 milk of slaked lime is 75 C. (167 F.) while it is only 27 C. (80.6 F.) for a 5 w % Ca(OH).sub.2 milk of slaked lime.

(72) As it can be further seen from FIG. 4, prehydrated lime requires longer time to reach 30 C. (86 F.) compared to quicklime at a same solid matter concentration. Moreover, prehydrated lime further exhibits steeper curves for all concentrations of milk of slaked lime compared to quicklime.

(73) The granulometry of the aforementioned milks of slaked lime have been measured in the same way as in Example 1. They have been compared with the granulometry of milks of lime produced from fully hydrated lime at various solid matter contents. The results are shown in Tables 5 and 6.

(74) As it can be seen from Table 5, when producing milk of lime from either quicklime or fully hydrated lime according to prior art, it is not possible to control the granulometry of the so-formed milk of lime by adjusting the solid matter concentration since no correlation can be observed between these two parameters.

(75) However, as it can be seen from Table 6, when producing milk of slaked lime from prehydrated lime, according to the invention, increasing the solid matter concentration leads to finer granulometry of the slaked lime particle in the so-formed milk of slaked lime. For example, raising the milk of lime concentration from 5 to 30 w % reduces the d.sub.50 value from 9.6 to 6.3 m.

(76) TABLE-US-00005 TABLE 5 Milk Of Lime Granulometry Dry content d100 d98 d95 d90 d50 d25 % m m m m m m Fully 100 282 158 116 53 5.7 3.2 hydrated (dry lime) Lime 20.4 410 174 114 38 6.7 3.6 (prior art) 30.2 373 177 123 56 6.1 3.3 Quicklime 6.4 101 40 32 27 11.4 6.3 (prior art) 11.3 177 39 31 26 10.1 5.5 16.3 111 41 32 26 9.5 5.0 21.1 213 73 41 29 9.7 5.1 30.2 234 82 43 28 8.5 4.4

(77) TABLE-US-00006 TABLE 6 Milk Of Lime Granulometry Dry content d100 d98 d95 d90 d50 d25 % m m m m m m Prehydrated 5.3 53 32 27 22 9.6 5.5 lime 10.2 53 31 26 21 8.5 4.9 14.7 48 30 25 19 8.1 4.6 19.4 48 30 25 19 7.8 4.5 29.4 48 29 23 15 6.3 3.5

(78) As a conclusion, prehydrated lime not only reduces the granulometry of a milk of slaked lime at 30 w % Ca(OH).sub.2 with respect to the total weight of the milk of slaked lime but also at far lower concentration such as 5 w % Ca(OH).sub.2 with respect to the total weight of the milk of slaked lime. Indeed, the mean value of d.sub.50 is 2 m smaller all through the concentration range and the d.sub.100 is also rather low: around 50 m all through the concentration range for the milk of slaked lime obtained from prehydrated lime. This shows the less tendency of this process to produce agglomerates.

(79) The temperature rise is so marginal at 5% dry content that the slaking facility will not face dust as well as reagglomeration problems that are commonly experienced with standard quicklime during manufacturing of a fine milk of slaked lime.

(80) The conductivity reactivity of the aforementioned milks of slaked lime was also determined through the measurement of their solubility index. The results are given in Table 7.

(81) TABLE-US-00007 TABLE 7 Milk of Lime Solubility index Dry content 100 90 63 % s s s Fully hydrated lime 100 104 5.0 2.0 (prior art) (dry lime) Quicklime 6.4 122 15.5 4.0 (prior art) 11.3 132 15.0 3.0 16.3 155 16.5 3.5 21.1 151 17.0 4.0 30.2 161 15.0 3.5 Prehydrated lime 5.3 35 6.0 2.5 10.2 47 6.0 2.5 14.7 34 7.0 3.5 19.4 34 5.0 2.0 29.4 23 6.0 3.0

Example 4.Forming a Milk of Lime of Great Fineness from Prehydrated Lime in Batch

(82) Quicklime has been prehydrated with different amounts of water from 0 to 16 w % with respect to the amount of quicklime in order to reach prehydrated lime with different amounts of Ca(OH).sub.2 in the coating around the quicklime core. The different samples of prehydrated lime thereby obtained were further slaked to produce milks of slaked lime.

(83) One kg of quicklime is placed in a 4 L laboratory mixer consisting of a fixed bowl fitted with a single paddle-like mixing blade. A plastic film is covering the bowl after filling the quicklime. Small holes are made in the film in order to spray the water. The water is sprayed quickly on the quicklime. Mixing is done during the time necessary for the partial hydration reaction to be completed.

(84) The prehydrated lime is taken out from the mixer and let cooled down until room temperature is reached in a confined container before slaking to milk of slaked lime. Slaking can be done either quickly after partial hydration, in continuation of such step or days after partial hydration.

(85) The impact of quicklime prehydration level on the granulometry of slaked lime particles in the resulting milk of slaked lime was studied, the latter being measured as explained in Example 1.

(86) The solubility index of the resulting milk of slaked lime was also measured, according to the procedure disclosed in Example 3. The results are given in Table 8.

(87) The temperature evolution during wet slaking of said aforementioned samples was also measured according to EN 459-2. The results are illustrated in FIG. 5.

(88) TABLE-US-00008 TABLE 8 Max. Prehydration Ca(OH).sub.2 Ca(OH).sub.2 Granulometry Dry temp. Solubility index by adding H.sub.2O expected measured CaCO.sub.3 d100 d98 d95 d90 d50 d25 content reached 100 90 63 % % % % m m m m m m % C. s s s 0 0 0.6 2.1 194 79 48 29 7.8 4.2 30.0 77.2 286 12.5 3.5 2 8 6.6 2.4 44 27 21 14 6.1 3.5 30.0 82.4 29 4 2 4 16 13.9 2.3 44 15 13 11 5.7 3.4 30.0 80.0 28.5 3 2 8 30 26.3 2.4 44 27 17 13 6.4 3.7 30.0 75.7 15.5 2 1 12 44 37.7 4.1 17 12 10 9 4.6 2.7 40.0 87.8 14 50 47.0 3.8 17 11 10 9 4.6 2.7 40.0 79.3 16 57 55.52 4.0 16 11 10 8 4.1 2.4 45.0 88.5

(89) As it can be seen from Table 8, it was possible to produce high solid content milk of slaked lime, and reduce the granulometry of the milk of slaked lime by increasing the amount of water added onto the quicklime during prehydration, thereby producing prehydrated lime with increasing level of Ca(OH).sub.2 in the coating around the quicklime core.

(90) Milk of slaked lime is finer when the amount of water added during the prehydration is higher than the minimum amount of water necessary to build a coating of slaked lime.

(91) It is shown that spraying 16 w % water onto quicklime (16 g water on 100 g quicklime) increases the amount of Ca(OH).sub.2 to a similar amount than the one expected in theory (in theory meaning such as if no water losses would occur). It was indeed possible to reach prehydrated lime containing 55.5 w % Ca(OH).sub.2 compared to 56.7 w % Ca(OH).sub.2 (theoretical calculated value), despite the higher temperature that was reached.

(92) The partial hydration of quicklime with 16 w % water while reaching 55 w % Ca(OH).sub.2 as mentioned further allows to produce, after slaking, a milk of slaked lime containing 45 w % solid particles of slaked lime with a slaking temperature reaching max. 88 C. (190 F.). The process used in this example not only increases milk of slaked lime concentration but reduces the d.sub.50 from 7.8 m to 4.1 m and d.sub.100 from 194 m to 16 m.

(93) As it can be seen from FIG. 5, increasing the water content during partial hydration increases as well the lag time which support the coating theory.

Example 5.Forming a Milk of Lime of Great Fineness from Prehydrated Lime in a Batch

(94) Four different quicklimes, showing different reactivities have been prehydrated with 4 w % water.

(95) The first quicklime (A) is the quicklime used in Batch Process Example 1, crushed to reach d.sub.90<90 m and showing a t.sub.60 of 192 sec according to EN 459-2. The second quicklime (B) has a temperature rise reactivity t.sub.60 of 133 sec according to the same standard and has a mean particle size between 0-2 mm, sieved to reach a maximum particle size of 500 m while the latter (C) also crushed to reach d.sub.90<90 m shows a temperature rise reactivity t.sub.60 of 58 sec.

(96) After spraying 4 w % water for partial hydration, slaking was performed and the granulometry of the particles in the resulting milks of slaked lime was measured as explained in Example 1.

(97) The granulometry of the quicklime samples used for the prehydration is shown in Table 9 while the granulometry of the slaked lime particles in the resulting milks of slaked lime is shown in Table 10.

(98) The efficiency of the partial hydration appears to be correlated with quicklime temperature rise reactivity. Indeed, fineness of the particles in milk of slaked lime is increasing with the increasing starting quicklime reactivity, e.g. lower t.sub.60 value, (higher temperature rise reactivity meaning less time to reach 60 C. in water).

(99) It must be noted however that the impact of the partial hydration is less relevant for highly reactive quicklime since such compound is already known to produce fine milk of lime. For less reactive quicklime, on the other hand, the impact of partial hydration is particularly surprising, since it allows reaching fine milk of slaked lime, even if the initial quicklime has a limited temperature rise reactivity t.sub.60.

(100) TABLE-US-00009 TABLE 9 Reactivity Granulometry t60 d100 d98 d95 d90 d50 d25 Sample s m m m m m m Quick- A 192 234 82 43 28 8.5 4.4 lime B 133 410 158 68 34 6.3 3.1 C 58 44 25 10 8 3.7 2.1

(101) TABLE-US-00010 TABLE 10 Granulometry d100 d98 d95 d90 d50 d25 Sample m m m m m m Milk of lime A 49 29 23 15 6.3 3.5 B 48 30 24 14 6.1 3.3 C 48 28 22 13 5.0 2.3

Example 6.Forming a Milk of Lime of Great Fineness from Prehydrated Lime in a Batch Process

(102) Quicklime sample as in Example 1 was prehydrated with respectively 12 and 16 w % water. The resulting prehydrated limes were both slaked to produce milks of slaked lime containing respectively 40 and 34 w % solid particles of slaked lime. The procedure has been reproduced but this time 1 and 2 w % of saccharose with respect to the weight of quicklime, were respectively added into the predetermined amount of water added for slaking. The granulometry of the slaked lime particles in the milks of slaked lime has been measured as explained in Example 1. The results are given in Table 11.

(103) TABLE-US-00011 TABLE 11 Granulometry d100 d98 d95 d90 d50 d25 Prehydration (m) (m) (m) (m) (m) (m) 12% H.sub.2O 17 12 10 9 4.6 2.7 12% H.sub.2O + 1% saccharose 14 9 8 8 4 2.4 12% H.sub.2O + 2% saccharose 14 9 8 7 4 2.4 16% H.sub.2O 16 11 10 8 4.1 2.4 16% H.sub.2O + 2% saccharose 14 9 8 7 3.8 2.3 16% H.sub.2O + 4% saccharose 13 9 8 7 3.7 2.2

(104) The temperature evolution during the wet slaking was also measured and the results are shown in FIG. 6.

(105) As it can be seen, saccharose is dramatically increasing the lag time together with decreasing the granulometry of the slaked lime particles in the milk of slaked lime.

Example 7.Forming a Milk of Lime of Great Fineness from Prehydrated Lime in a Batch

(106) Quicklime samples have been taken every week during 3 weeks out of the same plant.

(107) A first portion of each sample was commonly wet slaked to produce milk of slaked lime containing 30 w % solid particles of slaked lime according to the prior art.

(108) A second portion of each sample was prehydrated in a conveying screw with 4 w % water with respect to the quicklime weight. After partial hydration, the prehydrated lime was subjected to wet slaking for producing milk of slaked lime according to the invention.

(109) The granulometry of the milks of slaked lime was measured as in Example 1. The results are given in Table 12.

(110) TABLE-US-00012 TABLE 12 Granulometry Dry Batch Ca(OH).sub.2 d100 d98 d95 d90 d50 d25 content no % m m m m m m % Milk from 1 2.1 213 86 49 31 9.7 5.0 30.1 quicklime 2 1.0 194 79 47 30 8.7 4.6 30.2 (prior art) 3 1.6 257 140 103 53 13.0 6.5 30.7 Milk from 1 17.3 53 32 27 21 7.1 3.9 28.4 prehydrated 2 17.3 53 32 27 20 7.0 3.9 29.0 lime 3 16.3 101 39 30 24 7.3 4.0 28.9

(111) As it can be seen, when directly slaking quicklime as conventionally done, d.sub.50 is varying from 8.7 m to 13.0 m. When a partial hydration step is performed under controlled condition before wet slaking, d.sub.50 variation is reduced to 7.0-7.3 m.

Comparative Example 8.Forming a Milk of Lime of Great Fineness from Naturally Aged Prehydrated Lime

(112) Quicklime samples have been stored at room atmosphere on a bench, allowing to pick-up water at different levels to reach max. 9 w % Ca(OH).sub.2 in the layer surrounding the quicklime core. Milks of slaked lime containing 30 w % solid particles of slaked lime were then produced by slaking with water such naturally aged lime. For each sample, a post addition of 2 w % water with respect to the weight of the naturally aged lime (naturally prehydrated limenot controlled prehydrated lime) was also performed. The temperature evolution was measured during the wet slaking of the samples and the granulometry of the slaked lime particles in the milk of slaked lime was measured as explained in Example 1. The results are shown in Table 13.

(113) TABLE-US-00013 TABLE 13 Granulometry t60 Ca(OH).sub.2 d100 d98 d95 d90 d50 d25 Aging with min. % m m m m m m low water uptake 1.8 2.9 101 55 31 23 5.1 2.8 further prehydration with 2% H.sub.2O 5.0 84 39 30 24 5.9 2.9 medium water uptake 5.3 5.8 194 109 85 63 13.1 5.4 further prehydration with 2% H.sub.2O 11.1 234 128 93 66 15.6 6.0 high water uptake 9.5 9.0 213 133 113 89 19.8 6.9 further prehydration with 2% H.sub.2O 14.8 257 134 103 71 16.0 6.5

(114) As it can be seen, this natural partial hydration does not produce fine milk of lime with no agglomerates. Moreover, a controlled post addition of 2 w % water by spraying (i.e a controlled prehydration) does not produce the beneficial effect observed when starting from quicklime.

Example 9.Forming a Milk of Lime of Great Fineness from Prehydrated Lime in Batch

(115) The same quicklime as the one used in Example 1 is submitted during 1 hour to a gas stream containing 10% V/V water steam at 150 C. (302 F.) until around 4% weight gain is obtained. Same is done with a gas at 200 C. (392 F.) containing 10% V/V water steam and 15% V/V CO.sub.2.

(116) Milk of slaked lime containing 30 w % solid particles was then produced by slaking with water the prehydrated lime sample thereby obtained. The temperature evolution was measured during the slaking of the samples and the granulometry of the slaked lime particles in the milk of slaked lime was measured as explained in Example 1. The results are shown in Table 14 and FIG. 7.

(117) TABLE-US-00014 TABLE 14 Granulometry d100 d98 d95 d90 d50 d25 Aging with m m m m m m Prehydrated 150 C. 10% steam 194 117 90 63 9.2 5.2 lime 200 C. 10% steam + 15% CO.sub.2 257 148 120 81 9.9 5.5 30% 150 C. 10% steam 44 28 21 13 5.7 3.2 milk of lime 200 C. 10% steam + 15% CO.sub.2 44 28 22 14 5.9 3.2

(118) As it can be seen, both treatments allow producing fine 30% solid particles milk of lime of same granulometry as obtained by pulverizing water as in Example 2. As it can be seen from FIG. 7, both treatments generate a lag time in the temperature evolution.

Example 10.Forming a Milk of Lime of Great Fineness from Paste of Lime: Batch Process

(119) Twenty-one hundred grams of Quicklime fines (<6 mm) are introduced into a 4 L laboratory mixer. Although the initial experiments used quicklime fines, pebble product or other size lime could also be used. The mixer's motor should be powerful enough to turn the dry quicklime as well as the moistened prehydrated/quicklime clumps that form during the process. The total slaking time from quicklime to slurry was set for 15 minutes.

(120) The flow rate of water mixture (water with or without additives) for the examples which follow was set to 4.79 cm.sup.3/s (0.076 gpm) which was theoretically calculated for a batch that would slake 2100 grams of quicklime in order to form subsequently a prehydrated lime, a paste of lime and the milk of lime of great fineness along addition of water mixture under the form of a mist. The water and a viscosity reducer mixture were introduced from the top of the mixer, enabling all the quicklime in the mixer to equally interact with water, thereby forming the intermediate prehydrated lime before paste of lime and finally said milk of slaked lime of great fineness.

(121) Towels were placed about the mixer bowl opening to control dust and steam emission. The water and viscosity reducer mixture should be in fine mist form which can also be referred as cone shaped mist. This condition is achieved by installing nozzles to mist the liquid mixture over the quicklime. A thermocouple with a data logger was installed on the mixer literally touching the quicklime, the paste of lime and milk of slaked lime in the mixing bowl in order to track the temperature rise during the slaking process. The slaking should start simultaneously and is continuous/progressive. The water mixture initially reacts with the quicklime, thereby forming intermediate prehydrated lime. After prehydrated lime forms, due to the excess water in the mix, particles will start clumping together. The prehydrated lime particles then form a mud that dissolutes rapidly with the continued addition of at least water mixture forming firstly a paste of slaked lime and finally, upon addition of water mixture, diluting until a slaked milk of lime of a 45 w % solid content is reached.

Example 11.Forming a Milk of Lime of Great Fineness from a Paste of Lime; Continuous Process

(122) Three hundred and forty four pounds (156 kg) of crushed high calcium quicklime less than or 1.27 cm) was placed in a 20 cubic foot (566 dm.sup.3) paddle mixer. A spray bar with six conical spray nozzles was placed on the mixer to deliver the 654 pounds (296.7 kg) of water containing 4.91 pounds (2.23 kg) of sorbitol at a rate of 4.75 gallons per minute (18 dm.sup.3/min.). The mixer was set for 37.5 rotations per minute and the batch was completed at 16.5 minutes. By delivering a mist of water continuously over the quicklime, the reaction temperature reached 435 F. (224 C.) creating very fine hydrate particles. The resulting slurry had the characteristics shown in Table 15.

(123) TABLE-US-00015 TABLE 15 % Solids 45.9 Initial Viscosity cP (mPa .Math. s) 511 Viscosity after 30 days cP (mPa .Math. s) 617 PSD d.sub.50 m 2.65

Example 12.Forming a Lime of Great Fineness from Past of Lime: Continuous Process

(124) Two hundred and twenty nine pounds (103.9 kg) of crushed high calcium quicklime (less than or 1.27 cm) was placed in a 20 cubic foot (566 dm.sup.3) paddle mixer. A spray bar with eight conical spray nozzles was placed on the mixer to deliver the 403 pounds (182.8 kg) of water containing 3.27 pounds (1.48 kg) of sorbitol at a rate of 3.8 gpm (14.4 dm.sup.3/min.). After 8 minutes the water flow rate was increased to 4.6 gpm (17.4 dm.sup.3/min.). After 12 minutes, 1.16 pounds (0.53 kg) of dispersant (Neomere Tech 646) were added directly to the slurry and the mixer speed was increased from 37.5 to 125 rpm. The slurry was screened to 150 m to remove coarser agglomerations. The results are shown in Table 16.

(125) TABLE-US-00016 TABLE 16 % Solids 46.3 Initial Viscosity cP (mPa .Math. s) 127 Viscosity after 30 days cP (mPa .Math. s) 243 PSD d.sub.10 m 0.871 PSD d.sub.50 m 2.55 PSD d.sub.90 m 29.0 PSD d.sub.98 m 82.4

(126) An alternative to screening the slurry could be to run through a high shear disagglomeration machine. Two portions of the unscreened slurry at 46.3% solids was submitted to two different high speed conditions at 1330 rpm and 1770 rpm and produced the particle size distribution as shown in Table 17.

(127) TABLE-US-00017 TABLE 17 d.sub.10 m d.sub.50 m d.sub.90 m d.sub.98 m d.sub.100 m % solids 1330 rpm 0.830 2.23 22.6 71.3 143 49.4 1775 rpm 0.831 2.24 20.8 63.4 130 48.5

Example 13.Forming a Milk of Lime of Great Fineness from a Paste of Lime: Continuous Process

(128) The procedure according to example 10 has been followed. The amount and ratios of material used for Example 13 are shown in Table 18.

(129) TABLE-US-00018 TABLE 18 Material Amount Unit Quicklime (CaO) 2100 g Water (H.sub.2O) 4281 g Viscosity reducer 36 g Total milk of lime 4317 (liquid) g

(130) Approximately 12 grams of sorbitol (viscosity reducer) were equally distributed in all three of the water portions, with the first two portions being applied by fine mist and the last (third) portion being dumped into the mixer. The temperature of reaction was achieved 260 to 315 C. (500 to 600 F.). Grit fell out of suspension which is related to the low viscosity values of <100 cP and the product was observed to have a stable viscosity for one month.

(131) Table 19 is a comparison of various milk of lime products produced by the invention as compared to commercial slurries of the prior art.

(132) The rate of settlement was measured in a 100 cm.sup.3 graduated cylinder according to the standard ASTM C110-11.14. In this method, we measure the height (expressed in cm.sup.3) of supernatant present in the cylinder. Since the cylinder have a capacity of 100 cm.sup.3, those heights correspond also to a volumetric percentage.

(133) TABLE-US-00019 TABLE 19 325 Mesh Settling rate (vol %) Initial 30 days Percent (45 m) After After After d.sub.50 Viscosity viscosity Solids % 24 48 28 Sample m cP cP % retained hours hours days Plant A 3.02 57 188 43.5 2.60 1.0 3.0 6 milk of lime 44% Plant B 2.56 63 99 42.2 3.36 2.6 3.4 9.5 milk of lime 42% Neutralac 2.77 140 153 44.7 0.30 <1 4.0 14 SLS45 (prior art- reference) Plant A 12.0 1948 3084 44.7 6.48 7.9 7.9 3 Commercial Slurry 44% (prior art)

(134) The resulting milk of lime met the general criteria set for the project. Specifically, the Plant A and the Plant B quicklimes were slaked according to the method steps previously described in Example 13 with respect to the method of the invention. In Table 16, they are compared to the existing Neutralac SLS45 commercial product and to a Plant A Commercial which was a Portabatch type batch slaking operation where quicklime is added to water without prehydration step.

(135) For the milks of slaked lime according to the invention (Plant A and Plant B), their initial viscosities are lower than the one of the prior art of reference (Neutralac SLS45) while after 30 days, their viscosities have increased but to a limited extent such as to be similar to the one of the prior art reference.

(136) The milk of slaked lime from Plant A quicklime and the Plant B quicklime, prepared according to the invention, exhibited the desired characteristics of:

(137) d.sub.50 in range of 2.5-3.5 m;

(138) slurries which were viscosity stable below 200 mPa.Math.s after one month of testing;

(139) % solids range from 42-44% by weight, based upon the weight of slurry;

(140) Grit dropped out of suspension at low initial viscosities;

(141) Settling rate slower than the commercial Neutralac SLS45 product;

(142) FIGS. 8 and 9 show the particle size distribution and viscosity change with time for a slurry made according to the method of the invention described in Example 13. These parameters are both within acceptable limits for the purpose of the experiments outlined above.

(143) The most critical points in examples 10-13 are the introduction of the fine mist over the quicklime, maintaining an equal distribution of water mixture through the use of the fine spray mist, and the achievement of targeted temperatures through exothermic reaction of the quicklime with the water, i.e., a maximum temperature of reaction in the range from about 260 C.-350 C. (about 500-600 F.), as compared to a Portabatch slaking system where the quicklime is added to the water once and maximum temperature of about 100 C. (212 F.) is reached.

(144) FIG. 10 shows the slaking temperature profile for a milk of slaked lime prepared according to the principles of the invention as illustrated in Example 13, showing the maximum temperature of reaction in the desired range from about 260 C.-350 C. (about 500-600 F.), before rapidly cooling down with the continued addition of water. A dramatic difference can be seen in FIG. 11 between the slaking temperature profile of a milk of slaked lime made according to the invention as illustrated in example 13, as compared to the prior art milk of lime produced from regularly slaked quicklime. The prior art milk of slaked lime, made for example in a Portabatch apparatus, peaks out at about 100 C. (212 F.).

(145) FIG. 12 is a graph showing a comparison of the particle size distribution for two milks of slaked lime made according to the principles of the invention as disclosed in example 13, as compared to two milks of slaked lime made by prior art methods. The milks of slaked lime of the invention are designated as the Plant A Quicklime slurry and Plant B Quicklime slurry. These are compared to the Neutralac SLS45 milk of lime and the Plant A Commercial Slurry which is a batch slaking operation where quicklime is added to water, as previously described. The results show more fine particles in the milks of slaked lime of the invention, but also a larger coarse fraction, which latter may be left in for a high quality regular slurry or screened out.

(146) FIG. 13 is a graph of viscosity over time for two slurries of the invention as illustrated in example 13, designated as the Plant A Quicklime Slurry and the Plant B Quicklime Slurry, as compared to a prior art Neutralac SLS45 slurry. The milks of slaked lime made according to the principles of the invention illustrated in Example 13 exhibit a viscosity below 200 mPa.Math.s after one month.

(147) An invention has been provided with several advantages. The product made according to the continuous/progressive hydration process of the invention as illustrated in Example 13 has a relatively high solids content, high reactivity, fine particle size distribution and relatively lower viscosity, as compared to lime slurries made by the prior art processes. The method of the invention would also be less expensive than certain of the existing commercial processes to practice.

(148) 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.