Lime Burning

Like chalk, limestone is largely calcium carbonate and dissociates reversibly to lime and carbon dioxide at sufficiently high temperatures (calcination)  

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Theory of Calcination. The reversible reaction involved in the calcination and recarbonation of lime—limestone is one of the simplest and most fundamental of all chemical reactions. In practice, lime burning can be quite complex, however, and many empirical modifications are often necessary for efficient performance. 

Limestone and marble have been mined as building materials and the oxide of calcium, lime [1305-78-8], has been used ia the manufacture of mortar for centuries (see Building materials, survey Lime and limestone). Lime-burning was one of the first iadustries ia the American colonies, where calcining of limestone was accompHshed ia kilns dug out of the sides of hills. 

FIG. 23-43 Reactors for solids, (a) Temperature profiles in a rotary cement lain, (h) A multiple hearth reactor, (c) Vertical lain for lime burning, 55 ton/d. (d) Five-stage fluidized bed lime burner, 4 by 14 m, 100 ton/d. (e) A fluidized bed for roasting iron sulfides. (/) Conditions in a vertical moving bed (blast furnace) for reduction of iron oxides, (g) A mechanical salt cake furnace. To convert ton/d to kg/h, multiply by 907. 

Here are some standard thermo chemical data relevant to lime burning (limestone can be taken to be pure, solid CaCC>3 in its calcite form) ... 

The chief examples are smelting for the recovery of metals from ores, cement manufacture, and lime burning. The converters, roasters, and kilns for these purposes are huge special devices, not usually adaptable to other chemical applications. Shale oil is recovered from crushed rock in a vertical kiln on a batch or continuous basis—moving bed in the latter case—sometimes in a hydrogen-rich atmosphere for simultaneous denitrification and desulfurization. The capacity of ore roasters is of the order of 300-700 tons/(day)(m3 of reactor volume). Rotary kilns for cement have capacities of 0.4-1.ltons/(day)(m3) for other purposes the range is 0.1-2. 

Fuller s earth, dry gruular Lime, burned or quick lump or pebble ... 

Lime burning formerly took place in holes in the ground and kilns with wood, coal or peat as fuel, in which the limestone covered the fuel. These developed into the so-called shaft kilns . Limestone is ground into coarse particles (0 = ca. 60 to 120 mm) and loaded layer-wise with coal in the shaft kiln. The burning of the mixed-in coal produces a temperature of 900 to 1100°C, whereupon carbon dioxide is liberated. 

In addition to the different shaft kiln types, rotary kilns are often used for lime burning. This enables good quality quicklime to be obtained with cheap fuels. Smaller limestone particles (10 to 60 mm) are utilized. 

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