Rotary kiln with preheater: hot gas flows
Rotary kilns started to be used for lime manufacture at the start of the 20th century and now account for a large proportion of new installations if energy costs are less important. Old fashioned 'long' rotary kilns operate at 7 to 10 MJ/t. Modern installations partially overcome this disadvantage by adding a preheater, which has the same good solids/gas contact as a shaft kiln, but fuel consumption is still somewhat higher, typically in range of 4,5 to 6 MJ/t. In the design shown, a circle of shafts (typically 8-15) is arranged around the kiln riser duct. Hot limestone is discharged from the shafts in sequence, by the action of a hydraulic 'pusher plate'. Kilns of 1000 tonnes per day output are typical. The rotary kiln is the most flexible of any lime kilns able to produce soft, medium, or hard burned as well as dead-burned lime or dolime.
Early lime kiln
A lime kiln is used to produce quicklime through the calcination of limestone (calcium carbonate). The chemical equation for this reaction is
CaCO3 + heat → CaO + CO2
This reaction takes place at 900°C (at which temperature the partial pressure of CO2 is 1 atmosphere), but a temperature around 1000°C (at which temperature the partial pressure of CO2 is 3.8 atmospheres[1]) is usually used to make the reaction proceed quickly.[2] Excessive temperature is avoided because it produces unreactive, 'dead-burned' lime.
rotary kiln: http://www.hxjq-mill.com/products/rotary_kiln.html
preheater: http://www.hx-crusher.com/n267.html
lime kiln:
http://www.hxjq-mill.com/news/kiln_dryer.html