For effective burden distribution in a blast furnace, correct prediction of material trajectory is very important. A mathematical model based on single particle approach has been developed to estimate the material trajectory in a blast furnace fitted with a compact bell-less top. The model has been validated with in-furnace measurements of Tata Steel's 'F' blast furnace. Results obtained regarding the applicability of the model are promising.

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The burden material in a blast furnace is essentially a collection of particles having wide range of size and shape. It is discharged from the hopper and distributed on the stock level. The mass distribution of the falling stream determines the shape of the stock profile. The stock profile dictates the radial variation of ore/coke ratio, size segregation, gas distribution and burden descent, which in turn influence the formation and shape of the cohesive zone. Knowledge of the stock profile is therefore essential for understanding these phenomena. The complex nature of the flow has made a first-principle prediction of the mass distribution in the falling stream extremely difficult. Kondoh et al. 1) have reported mass fraction distribution in the falling stream at different elevation but the complete description as a function of chute angle is not reported. The present work attempts to predict the mass fraction distribution in the falling stream for three burden materials, viz. iron ore, coke and sinter. ExperimentationThe experiments were conducted using actual bell less top charging equipment of the furnace in a trial rig. Figure 1 shows a schematic diagram of the experimental setup. The rig was comprised of the complete material charging system including receiving hopper, common hopper, upper seal valve, lower seal valve, flow control gate and rotation chute. A brick-walled cylindrical tank of 5 m diameter and 1.5 m height was built for simulating the furnace throat. A small section of the cylindrical wall was kept open for removal of the charged materials. Proper electrical and mechanical arrangements were made for the rotational motion of the distributing chute. Tilting angle of the chute was changed manually and the chute was set to rotate at a constant speed. To feed the material in the receiving hopper, a special charging hopper of volume 1.43 m 3 was fabricated with a discharge gate at the bottom.For the purpose of collecting the materials from the falling particle stream, a semi-cylindrical pipe was inserted along the throat diameter at 1.6 m below the chute tip (design stock level). The pipe was divided into 25 compartments of 20 cm width each. In the experiment, rotating chute distributed the material along the peripheral direction and completed full rings. When the falling stream crossed the inserted pipe, material was collected in the different compartments, as shown in Fig. 2. For each full ring rotation of the chute, material was collected in two different locations, one on either side of the throat centre-line. Materials from individual compartments were weighed and mass fraction distribution was calculated. Results and DiscussionThe striking position of the falling stream of sinter for different chute inclination angle is shown in Fig. 3. The stream moves toward furnace wall with the increase in chute angle. In the figure, the filled points are the striking positions of the outer stream and the void points are the striking points of the inner stream. The stream width, defined as the distance...

Estimation and prediction of the stock profile in the radial direction of the furnace is essential for controlling ore and coke distribution and permeability distribution. In this paper, based on experiments carried out in different scaled model of blast furnace with different material, a general purpose methodology to estimate the stock profile in blast furnace burden distribution is proposed.KEY WORDS: burden distribution; heap formation; stock level; bell less top.

Burden distribution control in a blast furnace has a close relationship with wind acceptance and gas utilisation. Quantification of radial distribution of ore and coke is important for proper control of blast furnace operation. Charging of metallic burden over a layer of coke causes a portion of the coke layer to get dislodged from its original position, similar to the situation observed when a heavy material is dropped on a bed of lighter particles. This phenomenon, designated 'coke collapse', significantly changes the ore/coke distribution in the radial direction and thus affects the permeability of the furnace shaft. In the present work a mathematical model for quantifying the amount of coke collapse has been proposed on the basis of 'stability of slope theory'. The calculation from this model has been compared with the results from experiments in simplified physical models. Predictions of the mathematical model are in good agreement with experimental results. List of symbolsE M formation energy of mixed bed F s factor of safety F v external force g acceleration due to gravity H vertical distance between falling point of ore and the burden surface at the furnace centre DL c increase of coke layer thickness in the centre M charged mass of ore in one dump N r normal component of the reaction to gravity P n normal force, act on the side of the nth slice r radius of potential failure surface R reaction to gravity T r tangential component of the reaction to gravity T n shearing force, act on the side of the nth slice V component of ore velocity in the direction of coke surface W n weight of a slice a n Angle between the normal component of reaction to gravity and vertical direction s normal stress t f shear strength of the soil t d shear stress developed along the potential failure surface w angle of internal friction