Modelling of Granulation/pelletisation-cum-iron ore sintering process

Figure 1: Granulation-cum-sintering process

Sintering of iron ore is an integral part of iron making to improve the performance of Blast Furnaces. The process of sintering is preceded by the preparation of sinter charge mix where the base mix material (iron ore, coke breeze, flux, return sinter and water) undergoes agglomeration in a rotating drum. The resulting granules are charged on to a moving strand where they are leveled off to form a uniform bed. The top of the bed is ignited with the help of burners to initiate combustion of coke. As the material is conveyed along the strand a heat wave progresses downwards with the combustion of coke and sintering of granules. The air required for combustion is sucked through the surface of the bed and the products of combustion are exhausted through wind boxes situated below the strand as shown in figure 1. The operating parameters of the sinter strand are controlled in such a way that the completion of sintering (known as burn-through point) takes place just before the last wind box. Here, the balling step is more critical. Sub-optimal balling is invariably compensated by slowing the strand speed, lowering the bed height, increasing the firing temperature, etc. Net result is lower productivity. Therefore, balling and sintering steps must be examined in tandem as two interlocking components of the same problem. Therefore, an integral  (combine) mathematical model of whole sintering cum pelletization/granulation process in order to obtain the optimum permeability of the bed (optimal balling conditions) and optimum sintering parameters for increasing the over all productivity of the sinter plant.

During the granulation process fines get deposited or layered itself onto coarse particles, as a result granulated product in turn is larger in size and narrower in size distribution than the original feed. Two models have been developed for granulation; one is based on Litster et al. approach (Model 1) and another is based on Kapur et al. approach (Model 2). Figure 2 shows the comparison of the results obtained from the above two models along with the published (Litster et al.) experimental data. A reasonable agreement is evident.

Figure 2. Comparison of experimental multicomponent published data against two model’s data

Sintering model is a complex model which considers all the major physico-chemical reactions over a large range of temperature which are taking place during the iron ore sintering such as evaporation/condensation of moisture ahead of the flame front, calcination of limestone near the flame front, coke combustion in the flame front and melting/solidification. This sintering model has been combined with the granulation/pelletisation model making it a full comprehensive model which is available today to take care of both granulation-cum-sintering process simultaneously. Result has been compared against published experimental data in figure 3 which shows a reasonable agreement between the two, lending a good support to the granulation-cum-sintering model.

Figure 3. Comparison of published experimental temperature in sinter bed at a distance of 100mm with computed data

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