Abstract
A selective crushing unit was installed at the Durgapur Steel Plant (DSP) of the Steel Authority of India Ltd (SAIL) in March 1997 for better coal preparation and improvement in coke quality with respect to M10, coke reactivity index (CRI) and coke strength after reaction (CSR). However, the selective crushing performance deteriorated especially during the monsoon period, because of poor fluidisation of coal due to a high moisture level in the coal charge. In the selective crushing unit at DSP, coal is fed from silos to primary crusher units through two conveyors, namely C14-A and C14-B. The system is designed for a maximum moisture level of 8·5% in the coal charge. During the monsoon period, the moisture level of the coal increases beyond 8·5%, leading to problems such as jamming of chutes and classifiers. Sometimes the classifiers are bypassed in order to supply coal to service bunkers continuously. This causes deterioration of coal crushing and in turn coke quality. Addition of an oil-water emulsion to the coal blend reduces the angle of repose and improves the bulk density of coal charge improving its flowability. It also allows more coal to be charged per oven leading to an increase in oven throughput. The Research and Development Centre for Iron and Steel (RDCIS), SAIL has designed and installed a system for oil-water emulsion spraying over coal blend for the first time in DSP. The system has been commissioned and is in continuous operation. Trials were conducted with varying proportions of oil and water mixture in the emulsion. High speed diesel oil and water were varied in the ratio of 1:5 to 1:6 so that the oil addition to the coal blend was around 0·02 to 0·03% of the coal charge. Spraying of oil-water emulsion has also given rise to benefits in respect of crushing levels (through 3 mm) and coke quality (M10) improvement etc.
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