Production of Ground Quicklime

Generally, the best outlets for both primary and secondary fines are as a feed to ground lime and hydrating plants. They have also been used as a source of calcium oxide in dry process cement plants, where their use resulted in a significant reduction in heat requirements [17.1]. 

The demand for various grades and qualities of ground quicklime has grown rapidly ever since the 1950s. Particle size requirements vary from relatively coarse products used for soil stabilisation (e.g. 99 % less than 2 mm with 50 % less than 75 pm) to very finely divided products for specialist applications (e.g. more than 99 % less than 50 pm). 

The coarser products may be produced relatively cheaply in a single pass through a beater mill fitted with an integral basket, which acts as a screen. Finer products are generally produced in tube mills and vertical roller mills [17.2]. In the latter case, a variable speed classifier is fitted above the mill to control the grading of the product, and recycle over-sized particles. 

All grinding systems use air to convey the ground quicklime and, although part of the air is recycled, the remainder is purged via a bag filter to remove fines and heat. This inevitably leads to a limited amount of air slaking in addition to that which already occurs in the cooling zone of the lime kiln. Under typical conditions, the measured combined water may rise from 0.5 % in the feed to 0.7 % in the ground quicklime. 

While the combined water content does not cause problems for many users of ground hme, variations caused by changes in temperature and humidity can become an issue. For example, the saturated vapour pressure of water rises rapidly from 4.6 mm of mercury at 0 °C to 31.8 mm at 30 °C, which has been observed to cause a corresponding increase in the combined water content. 

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