Detention type slakers are best suited to applications in which the lime quality is medium to high and the lime feed rate changes infrequently. They are relatively inexpensive to install and are well suited for operations where lime quality is reliable. These slakers are the easiest to tune to maximize lime reactivity and reduce overall chemical consumption.
A typical detention slaker consists of two or three slaking compartments, each continuously agitated. Water and lime are fed into the first compartment and then overflow a weir from one compartment to the next. The product then discharges into the grit removal system (vibratory screen or inclined screw) before discharging into the process or storage tank.
Detention type slakers are available in a variety of quicklime slaking capacities up to 26,000 kg/hr. They operate at water to lime ratios (in the slaking compartment) between 3.5:1 to 6.0:1. The water to lime ratio is adjusted automatically to maintain a constant slaking temperature based on a temperature probe directly in the reaction chamber. Detention slakers typically operate between 75 oC and 85oC, however with good water temperature control and a stable lime supply, these slakers can be run at temperatures in excess of 90 oC producing an extremely reactive hydrate (see case study on effects of slaking temperature).
Typical operating temperature rise at a 4:1 water to lime ratio is approximately 55 o
C (this varies with each quicklime source) above the temperature of the incoming water. With slakers of this type, it is important to incorporate heating of the slaking water for efficient operation in cold weather locations. Steady state operation is usually reached within 15 minutes of start-up. Resulting lime slurry discharge is typically 18-25% solids at the slaker’s rated maximum capacity.