Interpretation of dynamics of pressure measurements

Paper i proceeding, 2006

This work investigates how wall-sampled pressure measurements are to be interpreted with respect to dynamics of industrial fluidized bed units. Such units have large cross sections with many bubbles passing the bed more or less simultaneously and, consequently, wall measurements will reflect superimposed dynamics from these bubbles and interpretation of pressure signals is therefore not straight forward. In addition, variations in release of volatiles may also cause pressure fluctuations. The work applies pressure measurements in a cold fluidized bed unit (over the cross section of the riser) as well as in a 12 MW CFB boiler (in the bottom bed, the freeboard and the air feed system). The dynamics of the release of volatiles were studied by means of zirconia-cell probes. The results show that the coupling between in-bed and wall pressure fluctuations in the dense bottom bed depends strongly on fluidization regime and that variations in release of volatiles can give rise to large pressure fluctuations, however, on a different time scale than that of the in-bed fluid dynamics. In the freeboard there was, as expected, a strong coupling between in-bed and wall pressure fluctuations.