Sunday, September 16, 2012

Kiln burning continued..

When lime of high purity is required continuous separate feed kilns are used. The kiln is similar to the kiln described above except that two or four fireplaces are provided by the side of the kiln near the bottom. In the fireplaces coal or wood are burnt and the hot gases of combustion move up the shaft of the kiln. The advantage of using wood as a fuel is that the long flames are produced and the temperature of the limestone is not raised too much. When coal is burnt same steam is introduced which maintains a low temperature and forms water gas. The water gas so produced burns and heats the kiln up to a greater height. Lime stone is supplied to the kiln from the top and the lime removed from the bottom.
The Rotary kiln used for the burning lime is similar to that used for cement manufacturing but is much smaller in size and is worked at a lower temperature. It consists of an inclined steel cylinder 1.5 to 2.5m in diameter and 15m to 45m long, lined with refractory bricks. Limestone crushed to much smaller pieces is charged at the upper end. Kiln is fired with coal, oil or producer gas and daily out turn is nearly 70 to 80 tonnes if lime. Due to better control on the operation product obtained is of superior quality. Rotary kilns are widely used in highly industrialized countries and for making lime for chemical industries.
1. The quantity of fuel to be used should be carefully worked out.
2. Before burning the limestone they should be broken into suitable sizes.
3. Quick heating of limestone may blow the limestone due to quick release of moisture and carbon dioxide so the burning should be gradual.
5. Over burning and under burning of the lime should be avoided as the over burnt or under burnt lime does not slake and is known as the dead lime.

Note: This content is prepared with the help of some books written on the topic, if you want the reference names please leave a comment. 

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