Interpretation of dynamics of pressure measurements
Paper in proceedings, 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.