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Annular Shaft Kiln

Annular Shaft Kiln
Main characteristics The main features of the annular shaft kiln are the adjustability of the product quality from soft burnt to medium burnt and the continuous stream of exhaust gas with a high CO2 content. These are the characteristics which have made this type of kiln the preferred choice for PCC production. As the kiln is not sensitive to finematerial adhering to the feed, it is, in many cases, not necessary to wash the raw material before feeding it to the kiln. This makes the annular shaft kiln the most economic unit in desert areas or cold climatic zones in which the obtaining or handling of water poses problems. Because the annular shaft kiln is operated under negative pressure conditions, it is possible to perform maintenance work whilethe kiln is working. Working Principle of the Annular Shaft Kiln
exhaust gas to filter / stack upper inner cylinder bridge of refractory material above the upper combustion chamber recirculating gas duct upper combustion chamber lower combustion chamber
Fig. 1: Gas Flow in the Annular Shaft Kiln

While being drawn downwards in a co-current flow, the gas is constantly cooled due to the heattransfer of the material being decarbonated. At the end of the co-current flow zone the gas is then sucked into the inner cylinder together with the lime-cooling air by the combined action of the injectors and the process fan. This co-current flow gas, together with the limecooling air from the cooling zone, is drawn by the

stone charging unit

heat-exchanger

rotating chute

injectorburner bridge of refractory material above the lower combustion chamber lower inner cylinder recirculating gas inlets

The annular shaft kiln operates with negative pressure, i.e. the exhaust gas is constantly sucked out of the kiln’s top by the process fan. The screened and weighed limestone is conveyed from the batch weigher by the skip bucket to the kiln top. From the feeding chute thelimestone to be burned is distributed to the feeding sluice. The limestone is then charged from the rotating chute into the top of the annular shaft kiln. The limestone entering the preheating zone via the feeding system is dried by the exhaust gas in countercurrent flow and preheated to decarbonation temperature. The exhaust gas emerging via a collecting chamber mingles with the exhaust gas stream fromthe heat-exchanger before being delivered by the process fan to a dedusting system. 2

lime-discharge table

lime hopper lime cooling air duct
Fig. 2: Annular Shaft Kiln

fers its heat in countercurrent to the lime-cooling air drawn in by the process fan. At the end of the cooling zone the quick lime is discharged from the discharge table by a hydraulically operated pushing ram system andfalls into a hopper under the kiln shaft. A vibrating trough empties the hopper discontinuously. In the burning zone the kiln has two burner levels. Depending on the capacity of the kiln, each burner level has three or more combustion chambers symmetrically distributed around the kiln periphery. These radially mounted cylindrical burning chambers divide this kiln segment into 2 burning zonesworking in countercurrent and 1 working in co-current flow. The arrangement of the upper and lower combustion chambers, as well as the recirculating gas inlets in the inner cylinder between the co-current flow zone and the cooling zone, ensure a uniform gas distribution over the entire cross section of the annular shaft. Above each combustion chamber outlet there is a bridge of refractory materialbetween the outer shell and the inner cylinder. The gases flowing out of the combustion chambers pass through cavities between the slope of the heated bed and the bottom of the bridges and uniformly penetrate the material bed over the entire width of the annular shaft. Principal layout and performance data Production Capacity: 200 – 600 tpd burned lime Raw limestone: Hard Crystalline Limestone No...