Pebble lime coolers

Pebble lime coolers

Extensive cooling and significant preheating

“Niems-style” packed bed cooler for pebble lime rotary kilns. In 1983 has acquired exclusive rights to the design and manufacture of the proven and world-renowned cooler technology of L.H. Niems & Associates. Today, the “Niems-style” cooler is the most efficient pebble lime cooler in the world.

Process overview

Pebble lime calcining is a process by which carbonates of calcium and magnesium (CaCO3 and MgCO3), or limestone, collectively, are heated to temperatures high enough to drive off CO2 and produce oxides of calcium and magnesium (CaO and MgO), lime product.  The process takes place within three major pieces of equipment—preheater, rotary kiln and stationary cooler.  The preheater, using hot process gases from the rotary kiln, preheats and begins to calcine the limestone feed material.  The material finishes calcining in the rotary kiln.  The kiln discharges into a stationary cooler where the lime product is cooled to temperatures low enough to be handled by typical rubber belt conveying equipment.

Pebble lime coolers (How it works)
How it works?

Ambient air is blown into the four quadrants of the cooler’s lower chamber through a common cooling air duct.  The cooling air enters the bed of hot pebble lime product, uniformly, through a collection of fixed stainless steel louvers.  The level of material in the cooler is controlled by how often the four vibratory feeders beneath the cooler are cycled between maximum and minimum speeds.  Thermocouples mounted in each of the four cooler discharge spouts monitor product temperatures, and material flow through each spout is automatically adjusted to provide uniform cooling of the lime product, and at the same time, maximize heat recovery.


Technical info

Standard cooler sizes of IV, VI, VIII and X are available for pebble lime production rates from 300 to 1200 tons per day.  Because cooler size is influenced by a number of factors other than the desired rate of production—the elevation of the installation site, the friability of the stone/lime being processed, and to a degree, the type of fuel(s) being used, each size cooler is able to accommodate a range of production capacities.  In addition, due to the variability of the sizing criteria, these production capacity ranges overlap from one cooler size to the next.

Metso Outotec supplies all of the spare and replacement parts that are integral to the design of its “Niems-style” pebble lime coolers, such as cooler grate castings and cooler grate support tubes.  Metso Outotec can also provide trained field service personnel to assist in the installation and maintenance of its coolers, as well as help trouble shoot and resolve any operational challenges that may arise.

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