Acoustic Monitor for Particle Size and Bed Friction in a Carbonate Fluidized Bed at High Temperature - 18014
Previous work has shown that acoustic spectra of fluidized bed pressure fluctuations show many useful bed properties [1-3]. This current work further explores the use of acoustic monitors for an 18' diameter, 66-74'' height fluidized bed at >640 deg. C. This process denitrates and agglomerates an injected sodium/aluminum nitrate aqueous simulant and produces at steady-state a denitrated product of 200-300 micron sodium carbonate/aluminate particles. The fluidized bed shows characteristic acoustic resonances around 1-2 Hz in the FFT (Fast Fourier Transform) of pressure fluctuations for each of three taps at fluidized bed heights of 12'', 39'', and 58''. The acoustic resonance spectra depend on a bed friction that once calibrated, monitors the HMPD (harmonic mass mean particle diameter or Sauter mean diameter) along with other important bed properties. This fluidized bed operates at high temperature with an evolving HMPD that can be steady state with an appropriate superficial spatial velocity (SSV). The acoustic FFT integrated power spectrum, IPS, of pressure fluctuations represents the bed-friction damped RMS (root mean square) pressure fluctuations at each tap. The transition from a static to fluidized bed at each bed height occurs when the damped bed RMS pressure fluctuations are greater than the static head (the FFT zero Hz designated zero Hz proportional to FFT zero Hz) at that bed height. A bed will de-fluidize and become static at a bed height when bed friction completely dampens the RMS pressure fluctuations, which occurs for decreasing particle size among other factors. The ratio IPS/zero Hz then provides a continuous monitor of bed friction damping as well as particle size as the HMPD. Since HMPD and bed friction damping are both very important parameters for fluidized particle beds, the acoustic HMPD and bed friction damping both provide very useful monitors for fluidized bed operation. Such acoustic monitors have shown that they are especially sensitive to the presence of very fine particles in the bed of less than 50 microns diameter. Acoustic monitors for particle size and bed friction damping will be very useful in any fluidized bed, especially fluidized beds where particle size changes. The fluidized bed friction damping depends on many other bed properties besides particle size such as bed height, density, SSV, void fraction, gas viscosity, and fluidization scheme and so acoustic bed friction should also be useful for monitoring other bed properties besides particle size. In fact, the change in the static bed friction slope with SSV upon fluidization follows the Ergun function and reveals a minimum fluidization velocity for each HMPD. (authors)