Heat balance of the rotary kiln for the limestone burning and its analysis

Comparative analysis of the known methods of calculation of material and heat balances of the rotary kilns with heat exchangers for limestone burning has been done. It is shown that the methods of calculations, proposed by the authors, have restrictions and inaccuracies, associated with both the assumptions made by authors for their conditions and the design of the units. Based on the made analysis the main provisions of the generalized method of calculation of the material and heat balances, that best describes the process of limestone burning in the rotary kiln with heat exchangers, have been developed. As can be seen it is impossible to perform analytical calculation of material and heat balances of the existing rotary kiln without balance test results. Thus, in the material balance calculation, besides of the content of carbonates, hydrated moisture and impurities in the feedstock, the influence of the physical humidity, which may vary depending on season and storage conditions, should be taken into account. The amount and chemical composition of burnt dust carried away from the kiln, may differ significantly from the literature data. The value of the cold air inflow can reach 15% of the total amount of air entering the kiln, it has a significant impact on fuel consumption for lime burning. When calculating the heat balance needs to know the actual temperature of the heated air and burnt lime, temperature and flue gas composition at the outlet of the heater, the temperature of the flue dust. Determining of the heat loss to the environment through the kiln body is not possible without measuring the temperature of its surface. The accuracy of determining the heat transfer coefficient, depending on the temperature of the surface of the kiln can also have a significant impact on the calculation results