A Method for Reduction in the Start-Up Time of a Bubbling Bed Boiler Combustor

A study on the heating of inert bed solids in a bubbling fluidized bed by means of an over-bed start-up oil burner is presented in this paper. Experiments carried out in a 160 mm diameter bed shows that the bed heats up nonlinearly with time. The rate of heating and the peak temperature reached by the bed solids depend on the bed depth, the mean particle size, and the superficial velocity through the bed. It was further noted that premixing a certain amount of biomass with the inert bed solids accelerates the rate of heating, as well as increase the peak temperature attained. The internal heat generation in the biomass is found to start at temperatures as low as $200°C$⁠. Thus, premixing some biomass with inert bed materials could reduce the combustion start-up time of a fluidized bed boiler, reducing at the same time the start-up cost by saving on consumption of expensive fuel oil in the burner. Experimental data in the present laboratory-scale unit shows good agreement with those obtained earlier in an industrial fluidized bed tested with waste-coal.