Pressure fluctuations as a diagnostic tool for fluidized beds. [Quarterly] technical progress report, January 1, 1995--March 31, 1995

A series of preliminary experiments were conducted at the Iowa State University power plant circulating fluidized bed boiler (CFB). Pressure fluctuation measurements were recorded from a pressure transducer located immediately above the primary air distributor at the base of the CFB boiler under normal operating conditions. The purpose of these initial experiments was to examine the general pressure fluctuation structure of the fluidized bed boiler in order to assess what further signal processing techniques may be necessary for valid pressure fluctuation analysis and analytical characterization. These initial results show that the CFB boiler pressure fluctuations obtained are highly periodic. Due to the dominance of this periodic component (and its subsequent harmonics), the Bode plots of these pressure fluctuation signals are difficult to interpret. While an overall system roll-off is apparent, neither the overall system order nor the system time constants can be adequately estimated from this initial data. Further data recorded from other locations in the CFB boiler should provide a more complete explanation of the nature of boiler pressure fluctuations. This initial experimentation suggests that a better description of pressure fluctuations could be attained using signal filtering techniques. Numerous experiments were also completed using the 2.0 inch diameter cold-model CFB, completing the first stage of a comprehensive set of similitude experiments. This bed was pressurized, and fluidized with 0.15 and 0.2 mm steel shot. A variety of operating conditions were selected such that similitude parameters could be matched in a 4.0 inch diameter CFB model exactly twice the scale of this small CFB. Currently, the final similitude tests in the small CFB with 0.1 mm steel shot are being performed