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Lime Slaking, Slaking Systems, Lime Slaker

The term lime slaking applies to the combination of varying proportions of water and quicklime in order to produce milk-of-lime, a lime slurry or a viscous lime paste. Chemically, the slaking process is an exothermic reaction that releases appreciable heat and forms hydroxides.
There are a number of variables affecting lime slaking these include:
  • reactivity of the quicklime - whether the quicklime is hard, soft, or medium burned, which influences speed of slaking and temperature attainment
  • purity of the quicklime - whether or not the lime contains a large quantity of “non-lime”  impurities
  • particle size and gradation of the quicklime - whether the quicklime is lump, ground, pulverised or run-of-kiln gradation, the finer sizes of the same quality slake most rapidly
  • optimum water amount - whether too much or too little water is used
  • temperature of the water - whether slaking water is too cold or possibly too hot (steam) for the particular slaking conditions. Slow reacting limes need heated water, reactive limes do not
  • distribution of the water - whether water is introduced into the slaking chamber unevenly as surges. An even flow is desired
  • quality of the water - whether the water is of potable quality or contains salts
  • agitation - whether too vigorous or insufficient agitation of quicklime and water is employed. Some agitation is necessary.
The design of the Bulk Technik lime slakers takes into account all of these factors resulting in a slaking system that is compact, self-contained and produces milk-of-lime with consistent quality and minimal unslaked grit (lime quality dependant).
Low maintenance has been designed into the machine e.g. the mixer impellers and grit removal screw are the only moving parts subject to wear. The main housing is protected by wear plates in every slaking compartment. There are no packing or packed bearings below liquid level.
The slaking process is one, in which an optimum balance between viscosity in the slaking compartment and temperature is required. The viscosity in the slaking compartment must be high enough to maintain the grit in suspension for carry-over into the separating chamber while maintaining as high a temperature as possible to produce a fine hydroxide particle.
In general, South African lime falls in the medium to high calcium oxide content range with the lime in the normal to over burned range. The lime will thus generally slake in less than twenty minutes, and the Bulk Technik slaker performance has been based on these grades of lime. 
The Bulk Technik slurry type lime slaker consists of a welded steel tank assembly with a mixing and slaking compartments of a size and shape which achieves thorough blending and slaking of the lime. A propeller type mechanical agitator, vee belt driven is fitted to the slaking compartments. The slaked lime slurry flows into an integral grit chamber which permits suspended grit to settle out. The design of the grit chamber permits automatic grit removal without interruption of slaker operation. After grit separation and final dilution, the lime slurry is discharged by gravity flow to process.
The lime slaker is insulated on exterior walls in order to maintain slaking temperature with lower grades of lime. Plate-coil type heat exchangers are available as optional equipment to pre-heat the water for less reactive grades of lime.
The slaker material inlet is equipped with an electro-pneumatically operated butterfly valve and a feed chute with purge air connection fitted with a solenoid valve. Lime dropping in from the screw feeder creates dust. A high operating temperature in the slaker causes vapours and the combination of these two could cause excessive lime build-ups and subsequent blockages of both the chute and screw feeder.
Each lime slaker is shipped fully assembled, complete with grit chamber, agitator(s) and integral piping and is fitted with suitable lifting lugs for ease of installation.

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