FR2788513A1 - Limewash preparation for injecting in a stream of fumes, comprises mixing water and quicklime in order to obtain a limewash with specified amount of dry material and grinding the limewash - Google Patents

Abstract

Process for preparing a limewash, comprises mixing water and quicklime in order to obtain a limewash with 100-600 g of dry material per liter and grinding the limewash.

Description

The present invention relates to a process for preparing a milk.

of

  lime for injection into a smoke stream.

  Products and methods are already known for treating fumes such as those described in document WO-97/14650-A, in which is described in particular a method for obtaining pre-dried calcium hydroxide particles.

  feeling in particular a moisture content of less than 2% by weight.

  According to this process of the prior art, quicklime particles are quenched

  (CaO) with sufficient water to obtain a cal-

  cium [Ca (OH) 2 having a residual humidity of between 15 and 30% by weight; then this hydroxide is dried by means of a gas having a temperature of less than 500 ° C. and a carbon dioxide (CO2) content of less than 500 mg / Nm3 in order to reduce its residual humidity to less than 2% and the dried product is ground to obtaining a first fraction of particles having a particle size less than 32 μm and a second fraction of particles having a particle size greater than 32 μm, the percentage by weight of refusal at 32 μm being between 10 and 90. Such a ground product can be used to deal with

  smoke by injecting particles into the smoke stream.

  Such a process leads to a pulverulent product which has the disadvantages

  nents inherent in powders and is a large consumer of energy in particular

during the drying phase.

  One of the aims of the present invention is therefore to provide a process for preparing a whitewash which overcomes the drawbacks of the prior art.

such as those cited above.

  Another object of the present invention is to provide such a method which can

be implemented in situ.

  These aims, as well as others which will appear subsequently, are achieved by a process for preparing a milk of lime which is characterized, according to the present invention, by the fact that a milk of lime having a content of lime from to 600 g of dry matter per liter of milk of lime by mixing water and

  quicklime (CaO) and grind this milk of lime.

  Preferably, the lime content of milk of lime is between 100 and

  250 g of dry matter per liter of lime milk.

  Advantageously, water or lime is added to a reaction retarder.

  activity such as ethylene glycol, mono-, bi- or tri-ethanolamine, at a rate of at most

  2% by weight thereof relative to the weight of lime.

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  Preferably, the quicklime is screened beforehand to remove the fines.

  particle size less than 2 mm.

  Advantageously, the slaked lime particles [Ca (OH) 2J in the milk of lime have a particle size less than 200 μm and preferably less than 20 μm. According to the process of the present invention, quicklime (CaO) is screened in order to remove the fine particles which have been induced and / or overcooked, that is to say those made up of lime carbonate (CaCO3), which do not may be eliminated by the

  continued: these particles generally have a large particle size of less than 2 mm.

  Then, water is added which can be added with a reactivity retarder at a concentration of at most 2% by weight relative to the weight of lime, such as for example ethylene glycol, the mono- , bi- or tri-ethanolamine without this list being limiting. The additive is added to the water of hydration or even to quicklime. The concentration of the additive may be less than 1% and

  preferably 0.5% by weight relative to the weight of quicklime.

  In the milk of lime thus obtained, the total pore volume of the slaked lime

  [Ca (OH) j is greater than 0.15 cm3 / g and even more than 0.25 cm3 / g.

  The mixture thus obtained, or milk of lime, comprises from 100 to 600 g of dry matter per liter of milk of lime, and preferably from 150 to 250 g of dry matter per liter of milk of lime. The whole is stirred for at least 10 min, and,

if necessary, for 20 minutes.

  Then this milk of lime is ground so that the slaked lime particles [Ca (OH) 2] have a particle size less than 200 μm; in fact 80% of the particles have a particle size less than 20 μm and even less than

  10 pm depending on the intensity of the grinding carried out in a grinder of the neck mill type

for example.

  The ground lime milk can be directly injected into a smoke stream

  in order to neutralize the acidic particles in suspension.

  The method according to the present invention makes it possible to use quicklime having a particle size greater than 2 mm, which, as will be appreciated by those skilled in the art, has an important economic advantage. Indeed, the use of such lime allows elimination by screening at 500 pum or 200 pm of the incised or overcooked particles. Thus, it is possible to obtain an excellent quality lime milk having a high content of slaked lime [Ca (OH) J, that is to say at least 95% by weight relative to the dry matter, and a low content in calcium carbonate

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  (CaC03) that is to say at most 1% by weight relative to the dry matter, from

  of a more strongly carbonated quicklime.

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Claims (4)

  1 - Process for preparing a milk of lime, characterized in that one prepares a milk of lime having a lime content of 100 to 600 g of dry matter per liter of milk of lime by mixing water and quicklime and that we grind this milk of lime.   2 - Process according to claim 1, characterized in that the quicklime content of the milk of lime is between 150 and 250 g of dry matter per liter of lime milk.   3 - Method according to claim 1, characterized in that one addi-   uses water with a reactivity retarder such as ethylene glycol, mono-, bi- or tri-ethanolamine.   4 - A method according to claim 1, characterized in that the quicklime is sieved to remove the incised and / or overcooked particles, which   have a particle size less than 2mm.   - Method according to claim 1, characterized in that the particles   slaked lime [Ca (OH) 2] has a particle size of less than 200 µm and preferably mainly less than 20 pm.