This research deals with the start up process, an important aspect of the operation of both bubbling and circulating fluidized bed boilers. Though there are various start-up methods, over-bed oil firing is most commonly used for boiler start-ups. In view of the escalating price of oil the need for optimization of this aspect of the boiler operation is more important than ever before.; The experimental study was carried out in a 3.2 MWth industrial scale research circulating fluidized bed boiler at Kolaghat Thermal Power Station, West Bengal, India. Waste product (mill rejects) from the coal pulverizing mills of the pulverized coal fired boilers of this plant, is used as the design fuel in this unit.; This work is based on the hypothesis that solid fuels when mixed with inert solids can contribute heat to the start up process at temperatures well below their ignition temperature and, therefore premixing of such fuels with bed materials is a viable option for minimization of the start up oil consumption.; An oil burner placed above the furnace grid is used to heat up the bed solids to a temperature at which sustained combustion of mill rejects can begin. Temperature of the bed and other parts of the freeboard is measured during the oil heating of the bed. Studies were done on the influence of a number of parameters such as initial particle size distribution, static depth of bed solids and fluidizing air velocity on the heating profile of the bed. Experiments were also conducted to determine the effect of premixing of good grade coal and design fuel with the bed solids. Studies were done to establish the optimum percentage of fuel mix in the bed which could reduce the consumption of fuel oil.
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