Mixtank/Batch type slakers are best suited to applications in which the lime slaking rate is relatively low and the quicklime and water sources do not change. They are by far the least expensive to install, but come at a cost of efficiency and quality of lime slurry produced. This type of slaker can produce a carefully metered batch often using load cells to weigh the inputs, however they are not able to react to changes in quicklime quality, water temperature or other changes to process conditions.
A typical batch slaker consists simply of an agitated tank. Water and lime are fed into the tank, agitated for a set period of time then discharged to a storage tank. Most batch slakers will pass the discharge through grit removal system (vibratory screen or inclined screw) before discharging into the process or storage tank. Some will use a dish bottom tank in an effort to prevent grit from building up in the slaker, while others may be designed to only run on powdered quicklime where grit is not required to be screened.
Mixtank/batch slakers are available in a wide range of slaking capacities, but are generally only practical up to 500 kg/hr. They operate at water to lime ratios between 3.5:1 to 6.0:1. The water to lime ratio is controlled by carefully monitoring the lime and water feed into the tank. Slaking temperature is monitored but not controlled, and because of the batch process the temperature does not reach a steady state as is the case with the other slaker types. Combined with a mixing that is not necessarily homogenous, this type of slaker is very difficult to optimize for maximum reactivity.
Because lime slurry quality is not a primary focus for mixtank/batch slakers, they are frequently run without preheating the water. This simplicity in operation comes at a cost of increased chemical consumption. Resulting slurry concentration can be set at any point below the point at which the slurry transitions from a “milk of lime” to a “paste” (between 25% and 35% for most lime/water combinations).