Innovative means for reduction of oil consumption for over bed start-up of fluidised bed boilers

Abstract

Everyday, around the world thousands of fluidised bed boilers are started up. Thus, start-up is an important aspect of a fluidised bed boiler operation. Although there are various start-up methods, oil firing is the most popular and commonly used technique for the boiler start-up. The spiralling price rise of oil necessitates a deeper understanding of this process and thereby development of a means for reduction of the start-up oil consumption. Research work on the start-up process was carried out in a subcompact circulating fluidised bed boiler built jointly by Dalhousie University and Greenfield Research Inc. at Kolaghat Thermal Power Station, W. Bengal, India. This 3˙2 MWth unit is used for research and it also has the provision to supply auxiliary steam to the 210 MWe pulverised coal fired boiler. Waste product (Mill Rejects) from the coal pulverising mills of the utility boilers, is used as the design fuel in this unit. An oil burner placed above the furnace grid is used to heat up bed solids to a temperature at which the combustion of Mill Rejects can initiate. Temperature of the bed and other parts of the freeboard is measured during the heating up of the bed. Results showed that parameters such as initial particle size distribution, static depth of bed solids and fluidising air velocity influenced the heating profile of the bed. Based on this information, a method of reduction in oil consumption by premixing fuels with the bed solids was developed. This process accelerated the heating rate of the bed, thus reducing the oil consumption during the start-up. Studies were carried out to establish the optimum percentage of fuel mix in the bed. This paper presents preliminary results of a comprehensive study aimed at optimising consumption of fuel oil per start-up.