Acoustic fluidized beds

Dense-phase fluidization can also be conducted in the presence of force fields other than a gravitational field. Such force fields include vibrational, acoustic, centrifugal, and magnetic fields. Operations with applications of these fields are known, respectively, as vibrofluidized beds [Mori et al., 1992], acoustic fluidized beds [Montz et al., 1988 Chirone et al., 1992],... 

The acoustic chemometric approach can also be used to monitor industrial production processes involving particles and powders and to provide a complementary tool for process operators for more efficient process control, or to monitor particle movement in a fluidized bed [7] for example. Below we illustrate the application potential by focusing on two applications process monitoring of a granulation process and monitoring of ammonia concentration. 

Figure 9.14 shows that the score T1 for the acoustic model and T1 for the process data have similar trend lines for the start-up procedure on the 20 February 2001, however the acoustic T1 has a significantly faster response than T1 for the process data when the fluidized bed is filled with granules. 

The plot in Figure 9.17 shows clearly that the acoustic data have a faster response to sudden changes in the airflow rate to the fluidized bed reactor. This means that monitoring the start-up sequence with acoustic chemometrics could indeed be an added value to the operators. 

One major objective of this feasibility was to assess the potential of acoustic chemometrics to monitor the general process state of the granulation reactor in order to give reliable early warning if a critical situation occurs in the bed. Critical situations in the fluidized bed are often a result of lump formation and/or layering on the perforated bottom plate of the reactor (see Figure 9.5). 

A comparison of Figures 9.18 and 9.19 shows that the acoustic chemometric approach is much more sensitive to changes in the process state(s) of the fluidized bed than the traditional process data alone. Of course an industrial implementation of this process monitoring facility would include both acoustic data and process data, together with relevant chemometric data analysis (PCA, PLS) and the resulting appropriate plots. 

In the hot gas clean-up system of a coal-burning fluidized bed power plant, acoustic agglomeration could be installed after the first cleaning cyclones and followed by a high efficiency cyclone. The power required to operate the acoustic agglomerator is about 0.02-0.5<7o of the power plant output. This means that for a 250 MW power plant several hundred kilowatts of acoustic power are needed. Compared with the acoustic power output of a four-engine jet aircraft... 

Colver, G. M., Electric Suspensions Above Fixed, Fluidized and Acoustically Excited Beds , J. Powder Bulk Solids Tech., 4, 1980, pp. 21-31. 

Valverde JM (2013) Acoustic streaming in gas-fluidized beds of small particle. Soft Matter... 

Since the 1990s, there have been significant developments in the application of acoustic emission to monitoring processes including fluidized beds, high-shear granulation, crystallization, entrainment of solid particulates, and liquid droplets in gas streams. All of these are dynamic processes involving at least two phases. 

Powder transport lines can be considered as very lean fluidized beds. These are encountered in many industries for instance, conveying powder-laden gases to cyclone separators. Here, acoustic emission proves to be a sensitive indicator for the presence of powders or liquid droplets, the detection of blockages, and as a semiquantitative indicator of the particulate mass flow. 

Texas) in 1964 and 1965. Toyo also will provide the acoustic vibration unit. In prilling, the urea melt is concentrated via vacuum evaporation to 99.8% and fed as quickly as possible into the bucket to minimize biuret formation. The liquid forms drops that then fall down a cylindrical concrete tower that has either induced, forced, or natural draft air flow. The prills solidify and are removed at the bottom by belt conveying to storage. Some plants have a fluidized-bed cooler in the prill tower bottom and others use an in-line cooler before storage. If low biuret product is to be produced, the urea melt from the last decomposition stage of the synthesis plant is first crystallized and the crystals are then melted just before prilling. 

Of course the spectrum of quantities, which need to be measured in a fluidized bed, is much wider. These include, for example, local solids volume concentrations, solids velocities and solids mass flows, the vertical and the horizontal distribution of solids inside the system or the lateral distribution of the fluidizing gas. In response to these needs a number of more sophisticated measurement techniques were proposed. For example, suction probes were developed to measure local solids and mass flow, heat transfer probes were proposed for detection of de-fluidized zones and solids flow inside fluidized-bed reactors. Other techniques include capacitance probes, optical probes, or y-ray densitometry - a detailed review was given recently by Werther [1]. Cody et al. 2 reported the use of an acoustic probe to measure particle velocity at the wall of fluidized beds. 

---