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Abstract
At the West Bokaro Washery of Tata Steel, India, the coarse coal is dewatered in a vibrating basket centrifuge and fine clean coal is dewatered in a screen bowl centrifuge. Due to the higher amount of fine fraction (0.038 mm) treated in the flotation circuit of the washery (about 9% of ROM), the moisture content of the clean coal fines is high. A polyacrylate surfactant reduced the fine coal moisture content by 8% and it was found to be the best among the various reagents tested in the laboratory. The chemical was found very effective for dewatering the coarse clean coal. Laboratory and plant trials showed that through treating only the coarse clean coal by the surfactant, the moisture in the composite clean coal could be reduced from 12.0% to 9.8%. The optimum dosage of the reagent was 0.24 kg/t dry coal. Laboratory-scale filtration using coagulant and surfactant increased filtration rate of centrifuge centrate. Also, the final moisture content was found to be 10% less than that obtained without addition of any reagents. For improving the clarity of thickener overflow, anionic polyacrylate based flocculant was found better than present plant flocculant based on polyamide. The optimum dosage of the recommended flocculant was 0.012–0.016 kg/t of dry fine coal.
The authors are thankful to Mr. A. D. Baijal, Dr. O. N. Mohanty, and Mr. Om. Narayan for their keen interest and guidance in carrying out the studies. Thanks are also due to Mr. M. V. S. Rao, Mr. Surindra Prasad, Mr. S. C. Choudhary, and colleagues of Geological services and West Bokaro Washeries for their active involvement in carrying out the plant trials and the laboratory studies.
Notes
∗At this stage foaming problem in the plant was observed.
∗∗This centrifuge constantly showed high moisture.
∗Basket of centrifuge was damaged and hence sample could not be collected.