A Innovative Solution to the Problem of Mill Rejects in Thermal Power Plants

Abstract

The present paper discusses an innovative means for solving the problem of accumulation of waste coal in some pulverized coal fired plants. A major waste in a pulverized coal fired power plant is the reject produced from pulverizing mills. When coal is ground in a bowl mill heavy mineral matters are separated, but they still contain a small amount of coal mixed. However, the heating value of the rejects is generally too low for combustion in conventional boilers. As a result they find limited commercial use and are dumped in the plant adding to the fugitive dust, leaching problem and most importantly devastating damage to the landscape. The amount of mill reject is significant in older operating plant. In India for example, it is about 0.5–1.0% of coal throughput into the boiler. In this paper, an exercise is undertaken to show how these rejects could be burnt to produce low pressure process steam, which could save the bleeding of main steam of the power plant and thereby augment power generation. A subcompact novel circulating fluidized bed boiler has been designed, built and commissioned for this purpose. The present paper discusses the finding of above exercise.