Fluidized bed with a rotating distributor operated under defluidization conditions

Abstract

h i g h l i g h t sThe capability of a rotating distributor to recover a defluidized bed was analyzed. Defluidization was reached by injecting a punctual volume of water on the bed surface. Fluidization and recovery processes were analyzed in the time and frequency domain. An excellent agreement was found for the time and frequency domain results. The rotating distributor improves the fluidization quality of a defluidized bed. Keywords: Fluidized bed Liquid injection Defluidization Rotating distributor a b s t r a c tThe fluidization conditions of a rotating distributor applied to a 3-D bubbling fluidized bed was studied to assess its potential use as a counteracting measure of defluidization phenomena. The performance of the fluidized bed operating under nominal conditions was characterized for the rotating and the static distributor configuration. Different methods of analysis in the time and frequency domain were applied to establish the performance of the fluidized bed. The frequency domain analysis suggests some kind of local structuring of fluidized bed dynamics imposed by the distributor motion. The punctual injection of water over the surface of the bed lead to a high cohesive wet region that tend to settle down on top of the distributor giving rise to defluidization. The water-induced defluidization tests reflect an improvement of the fluidization quality with the distributor rotation.

Wide band energy analysis of fluidized bed pressure fluctuation signals using a frequency division method

“…The dynamic features of the fluidized bed were then modified by varying the bed aspect ratio, h b /D ¼0.75, 1.5 and 2. In these tests, the relative fluidization velocity was constant at U r ¼1.6, where the bed was shown to be well-fluidized (Gómez-Hernández et al, 2012). The effect of the pressure probe location and the influence of the pressure sensor type were also analyzed.…”

“…In these tests, the aspect ratio was fixed at h b /D¼ 0.75, and the fluidization velocity was U r ¼1.6. According to Gómez-Hernández et al (2012), the tests started with the bed working without the presence of agglomerates, i.e., nominal conditions. Then, 150 ml of water was injected on the surface of the bed, at a distance of 1 m perpendicular to the distributor, causing defluidization of the bed.…”

“…According to Johnsson et al (2000), this variable, the wide band energy, reflects the change in operational regimes and can be used to characterize the structure of a fluidized bed. More recently, the wide band energy has been used to detect defluidization phenomena (Gómez-Hernández et al, 2012).…”

“…The easy and fast computation of the wide band energy provides a reliable view of the dynamic behavior of the system once the power spectrum is properly divided into a set of frequency regions (Briongos and Guardiola, 2003;Gómez-Hernández et al, 2012;van der Schaaf et al, 2002van der Schaaf et al, , 2004. Traditionally, this type of frequency division has been conducted using visual selection of the cut-off frequencies between the different spectral regions.…”

“…Traditionally, this type of frequency division has been conducted using visual selection of the cut-off frequencies between the different spectral regions. In this procedure, the observer visually identifies the frequency limits by studying the behavior of the frequency domain either in the power spectrum (Johnsson et al, 2000;van der Schaaf et al, 1999;Vander Stappen, 1996) or as the cumulative energy distribution (Gómez-Hernández et al, 2012). However, the visual inspection approach has at least two major drawbacks, as follows: (i) the cut-off frequencies obtained through the visual inspection depend on the observer and (ii) the power spectrum fall-off is unavoidably affected by the quality of the measured signal, i.e., the transducer type and the signal conditioning.…”