Principles of lime burning

The lime-burning process requires sufficient heat to be transferred to the limestone to preheat it to the dissociation temperature and to decompose the calcium and magnesium carbonates. 

The heat requirement for the former process is 442kcal/kg of CaO [mass x specific heat X temperature difference = 1.79 x 0.279 x (900-15)] while the heat of calcination is 733kcal/kg CaO (section 15.2.1). It might naively be assumed that the minimum heat requirement for lime burning is (442 + 733) = 1175 kcal/kg CaO. 

In practice, however, the achieved heat requirement can be much lower than the above value and modern lime kilns achieve net heat usages (see section 14.3.6) below 900 kcal/kg CaO. The above calculation makes two major omissions. 

Part of the skill of the lime kiln designer is to minimise heat requirements by integrating efficient heat transfer with controlled combustion. This maximises both heat recovery and the amount of high grade heat available for calcination. 

Heat transfer in lime burning can be divided into three stages. To simplify the presentation, the following relates to high-calcium limestone, but the principles also apply to other types of limestone. 

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