Circular MAERZ® Kiln
Main characteristics
The burning of limestone and dolomite, based on the principle of parallel flow of material and combustion gases in the burning zone and the regenerative preheating of combustion air, is described in detail in „pfr1.pdf“.

Fig. 2:
Two Circular MAERZ® Kilns
Type R2 (400 tpd)

Fig. 1: Gas Flow in the Circular MAERZ® Kiln

For larger capacities, e.g. from 300 to 800 tons per day, kilns of circular cross section are recommended. These kilns have circular ring channels collecting the combustion gases before they enter the nonburning shaft via the crossover channel, as illustrated in Fig. 1. The gases exit the burning shaft and enter the non-burning shaft radially around the complete shaft perimeter thereby guaranteeing an absolute even heat distribution. This is a major key factor in ensuring the high quality of the burned lime or dolomite.
The charging system has to ensure perfectly symmetrical charging of the shafts. A bucket positioned vertically above each shaft is used for charging raw stone into the kiln shafts. Stone distribution is further improved by rotating the bucket during charging from the conveyor belts or vibrating feeders.
As described above, the circular shaft design facilitates uniform stone and fuel distribution during charging and calcination throughout the complete shaft cross section. As a result this kiln type produces the best product quality of all PFR-Kiln types.
In addition to the classic design of the refractory kiln lining, as shown in Fig. 2 and 3, an air cooled “suspended inner cylinder” can be installed instead of supporting pillars.
Principal layout and performance data
The present range of circular MAERZ® Kilns comprises the following standard types:
Kiln type:
R1 to R5
Daily output (tons):
290 to 850
Stone grain size (mm):
30-160
Fuels: gaseous, liquid and pulverised solid fuels
Heat consumption (kJ/kg of product): approx. 3520
(kcal/kg of product): approx. 840
Reactivity of lime: very high to medium
References
Since 1966 more than 180 circular MAERZ® Kilns (see Fig. 2) operating with gaseous, liquid and pulverised solid fuels or a combination of these, have been built world-wide.

Fig. 3:
The Circular MAERZ® Kiln