Control of Hydrating Plant

It is particularly important to limit the level of excess moisture in the plant, as the handling characteristics of hydrated lime deteriorate rapidly when the moisture content rises above 1.5 or 2 %. Excessive levels of moisture result in blockages within the plant and hold-ups in bunkers. 

Various techniques are used for determining the moisture content of the raw hydrate. They include visual inspection, a rapid carbide test method, infra-red moisture meters and conductivity probes. The latter can be built into the wall of the finishing stage vessel [20.5]. 

The grading of the fines streams may be determined by air-jet sieving and adjusted by varying either the speed or the settings of the air classifiers. Some customers require other properties to be controlled such as the specific surface area (measured by air permeability [20.6]) and the settling rate of milks of lime produced from the hydrate. 

6 Production of High Surface Area Hydrated Limes 

In the 1980 s the opportunity for using hydrated lime to remove acid gases from processes such as incinerators and small boilers was recognised. However, trials showed that relatively large excess of commercially available hydrate had to be added to reduce the acid gas concentrations to the required levels. It was postulated that increasing the effective surface area would increase absorption efficiencies. The challenge was how to produce a hydrate with significantly improved properties. 

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