Modelling of limestone calcination for optimisation of prallel flow regenerative shaft kiln (PFR), case study: Iran Alumina Plant

To produce the lime required for the Bayer process, two parallel flow regenerative shaft kilns (PFR) were used in the Iran Alumina plant located in Jajarm, North Khorasan Province, Iran. In this study, the calcination conditions of limestone were modelled in a laboratory furnace by considering three factors of limestone size, temperature and calcination time using the Box-Behnken method. The calcination model of limestone was obtained using a quadratic equation. Due to the importance of limestone dust in the performance of industrial kilns, conditions of calcification and its reactivity with water were examined at three temperature ranges of 800, 1000, and 1200°C, by two methods of titration and standard ASTM C110. The results indicated a decrease in reactivity of lime relative to the increased temperature of calcination and the lack of forming the burnt lime particles that stick together (blocking). Finally, the ratio of input limestone (kg) to fuel (m3) was reduced from 16.4 to 15.3 to increase the average temperature of the burning zone to 1000°C. Also, excess air was reduced from 40 to 20%. In this condition, the lime quality was increased by about 6% in the kilns