Determination of Aspect Ratio and Excess Air Coefficient to Shorten Start-up Time at Small Size Fluidized Bed Boiler

Energy production from clean and renewable sources has gained prominence in recent years. The use of fluidized bed boilers in industrial applications is increasing due to their high combustion efficiency and low NOx emission. Fluidized beds are suitable for coal and biomass combustion and other gasification applications. Therefore, these systems are expected to become more widespread. Although they are widely used in industry, fluidized bed combustion systems start-up processes are generally based on experience. Start-up is an essential process in the operation of small size fluidized beds. Shorter start-up times are desired, especially in systems requiring frequent start-ups. This study investigated the effect of the height of static bed material and the coefficient of burner excess air on start-up time. Therefore, a bench-scale experimental setup was established. CFD analysis was verified with temperature data measured by the testing apparatus. Then, CFD analyses were carried out for different bed aspect ratios (0.55, 0.65, and 0.90) and different coefficients of burner excess air (1.2, 1.4, and 1.6). The analysis results show start-up time decreases (up to 32%) as the bed aspect ratio decreases. On the other hand, as the excess air coefficient increases, the start-up time increases (up to 44%). In addition, in the start-up process, EAC 1.4 and then 1.2 were proposed for a shorter start-up time with an aspect ratio of 0.9.