Lime: The moisture and carbon dioxide are removed from the limestone by the process of calcination and the product which is remained after removing the moisture and carbon dioxide is termed as lime. The chemical composition of lime is CaO i.e. Calcium oxide
Manufacturing of Lime by Continuous Kiln: These kilns are used when lime is to be manufactured on large scale. The is kiln is a vertical structure line with fireclay bricks. It is usually built on a slope to facilitate continuous removal of lime. Alternate layers of limestone and coal (sometimes wood) are charged from the top and lime is removed from an opening at the ground level. Limestone free from earth or impurities are broken into small pieces to about 5 cm gauge. Alternate layers of 75 mm stone and 6mm coal dust are fed into the kiln. Fire is lighted in the kiln and as the calcination progresses lime is continuously withdrawn and fresh change is fed from the top. Air is required for combustion enters the same opening through which lime is removed; thus it gets heated while the lime is cooled. Burnt material is drawn out daily and fresh charge of limestone and fuel is added from the top. Over burnt pieces are discarded whereas the under burnt ones reloaded into the kiln. Lime obtained from such kiln is not of high purity as it gets mixed with as of fuel. Its thermal efficiency is however higher than of other furnaces.