Limestone 10 to 33 mm in size are fed into the annular space between the fixed drum and the kiln lid, forming a solid bed on the rotary hearth. The height of the solid bed is maintained to be practically uniform by the rotation of the hearth. The hot gas from the rotary kiln percolates through the solid bed, 25 to 30% of the limestone being calcined to quick lime. The rotary hearth is intermittently rotated one turn in approx. 2 hours by the pushing force of the hydraulic cylinder. A number of pushers force the limestone toward the central area of the rotary hearth, and limestone are dropped into the chute made of refractory, and then transferred to the rotary kiln.The operation of the pushers assures uniform movement of the limestone. The hot gas from the rotary kiln supplies the necessary heat to the bed of limestone.It is cooled (to 250℃ for 500 tons of product per day), and is induced into the dust collector (bag filter) for cleaning. Static pressure of flowing gas is -0.2 kPa (-20mm H2O) at the inlet of the solid bed and then -3kPa (-300mm H2O) at its outlet.The induction blower is operated under low load, because pressure drop is low across the bed.

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