Modelling of feed distributor at coal washeries

The biased subdivision of slurry feed to a number of unit operations in parallel results in each unit operating under different density volumetric flow rate, feed concentration. Consequently some of the units may operate under sub-optimal conditions leading to reduced operating efficiencies of sizing and cleaning units. The objective of this work was to identify the reasons for biased slurry subdivision in the feed distributor of Washery-II, West Bokaro, Tata Steel, Jamshedpur, India. A lab model of the feed distributor was set up at R&D using the principles of geometric similarity and dynamic similarity. A number of experimental investigations were carried out based on Design Of Experiments and the results analysed using ANOVA. The variation of feed rate of coal and its size distribution through different outlet ports were quantified through two terms, the coal split ratio and the variation index. The design of the insert, the number of water inlets, and the feeding position of coal in the distributor were the most important factors affecting the variation index. In case of coal split ratio, apart from the first two variables, none of the others had a significant effect. Four water inlets with symmetrically arranged outlets, equal water flow rate in the inlets and the material being fed in an annular ring into the distributor was found to reduce both the coal split ratio and the variation index.Upon implementation of the recommendations the bias in distribution was reduced and the efficiency of the cyclones improved and hence the coarse clean coal yield increased.