Dry Slaking of Quicklime

In dry slaking calcium hydroxide is obtained as a dry powder. Use is made of the fact that so much heat is produced by the reaction of calcium oxide with water that the amount of water bound is approximately equal to that which can be evaporated. The so-called reactivity of the quicklime influences the product quality. Highly reactive lime leads, upon slaking, to a granular material, which has to be ground again. 

Industrially, a continuously operating overflow tank is generally used. About twice the stoichiometric quantity of water is added to the calcium oxide in a premixer and the mixture transported to the reaction tank, in which the heat from the exothermic reaction heats up the reaction mixture to 100° C. The evaporating excess water entrains the very small lime hydrate particles and carries them upwards, where they are separated by an overflow from the coarse particles. The hydration process is then completed. The calcium hydroxide obtained contains less than 1 % water. 

In the case of difficult to slake lime, i.e. particularly highly calcined limes and limes with a high magnesium oxide-content, complete hydration can only be achieved under pressure. During the reaction a pressure of 2 to 8 bar is attained under which even the poorly soluble components are hydrated. The steam is separated from the dry calcium hydrate by rapid pressure release (Corson process). 

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