Dryers fluid-bed

Continuous fluid bed dryers can be used for drying materials which have a consistency whereby the initial material is friable. This is an important consideration, especially in continuous processing, since the cake must continue to move along the path of the bed at a fairly constant rate. Otherwise 

The constant rate part of the drying process in a fluid bed occurs at the porous plate or screen where the heaviest (and usually the wettest) material rests. This part of the process is the most critical as the material needs to become fluidized here to continue through the bed in stages, over weirs or simply down the deck of the bed. The air flow here needs to be at the highest velocity to compensate for the denser (wetter) material. 

Fines removal is achieved by placing a recycle fan/duct loop at a peak above the front-center of the top of the chamber. By lifting the fines up into this area they can be sent off to a bag house or cyclone where they can be collected for removal from the batch or for recycling. 

When agglomeration is desired, a spray bar can be incorporated to introduce a mist to a point near the inlet throat of the fluid bed unit where the wet material can be mixed with fines which are recycled as described above. This process is used mainly after a product has been spray dried or if the initial material to the fluid bed is not too wet. 

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Process Va.ria.tlons. The conventional techniques for tea manufacture have been replaced in part by newer processing methods adopted for a greater degree of automation and control. These newer methods include withering modification (78), different types of maceration equipment (79), closed systems for fermentation (80), and fluid-bed dryers (81). A thermal process has been described which utilizes decreased time periods for enzymatic reactions but depends on heat treatment at 50—65°C to develop black tea character (82). It is claimed that tannin—protein complex formation is decreased and, therefore, greater tannin extractabiUty is achieved. Tea value is beheved to be increased through use of this process. 

Fig. 12. Material residence time profiles in A, a pneumatic conveyor, B, a spray, and C, a rotary or fluid-bed dryer.

Fig. 15. A two-stage fluid bed dryer (a) gas and material temperature profiles (b) bed arrangements.

Fig. 21. Iadirect-heat, two-stage, back mixed, and plug flow fluid-bed dryer.

Several other processes that are aimed at the manufacture of gasoline from coal have been applied over the years. The main reactor in these processes uses three phase fluidization in which solid coal particles, gases, and liquids are all contacted at very high temperatures and pressures. Fluid bed dryers and fluid cokers are also used in synthetic fuels manufacmre. 

Since it was known that theophylline monohydrate can be thermally dehydrated to form either the stable Form I or the metastable Form I, the effect of different drying methods on the phase composition was studied [89], Using either a multichamber microscale fluid bed dryer or the hot stage of a variable-temperature XRPD diffractometer, Form I was produced when the drying was conducted at 40-50°C. Drying at 60°C in the VT-XRPD unit yielded only Form I, while mixtures of products were produced in the microscale fluid bed dryer even at temperatures as high as 90 °C. 

A chemical valued at 0.94/lb is currently being dried in a fluid-bed dryer that allows 0.1 percent of the 4-million lb/year throughput to be carried out in the exhaust. An engineer is considering installing a 10,000 cyclone that would recover the fines extra... 

See also Fluidized-bed entries Fluid-bed direct oxidation process, 10 656 Fluid-bed dryers, 9 122-123, 130-131 two-stage, 9 125 Fluid-bed roasters, 16 141 Fluid catalytic cracking (FCC), 11 678-699, 700-734 18 651, 653 20 777 24 257, 271. See also FCC entries Fluidized-bed catalytic cracking (FCC) clean fuels production and, 11 686-689 defined, 11 700... 

Butcher, C. Chem. Engr. London No 450 (July 1988) 16. Fluid bed dryers. 

Given that the introduction of solvent obviously produces wet granules, the wet granulation process includes a drying step. Drying typically occurs in a fluid bed dryer. But there are other options, such as microwave vacuum dryers. In 1994, White applied on-line NIRS to monitor moisture content and predict drying end point in two TK Fielder microwave dryers. The NIR spectral data were correlated to off-line Karl Fischer measurements which resulted in a standard error of prediction equal to 0.6% when the samples... 

R.L. Green, G. Thurau, N.C. Pixley, A. Mateos, R.A. Reed and J.P. Higgins, In-line monitoring of moisture content in fluid bed dryers using near-IR spectroscopy with consideration of sampling effects on method accuracy. Anal. Chem., 77(40), 4515 522 (2005). 

Reay, D. and Allen, R.W.K., Predicting the performance of a continuous well-mixed fluid bed dryer from batch tests, in Ashworth, J., (ed.). Proceedings of the Third International Drying Symposium, volume 2, Birmingham, 1982, 130-140. 

The quality of air at or near the points of supply of large volume forced air supplied coming into direct contact with products (e.g., fluid bed dryers, tablet coating machines, etc.) must comply with the following standards ... 

Figure 15 Fluid bed dryer with integrated high-shear granulator and mills.

All products require a volume and velocity of air to break the cohesive bonds between particles, wet, or dry, and to permit the batch to become fully fluidized. Laboratory trials will yield values for process air volume for the various stages of the process. Using this volume and the dimensions of the product container, a face velocity through the distributor plate can be estimated (permeability of the plate is not considered). It is reasonable to assume that approximately the same velocity will be needed in scale-up. In Table 4, estimates for process air volume are derived from the cross-sectional areas of the base of the product container for various sizes of fluid bed dryers. 

Rotary granulator subclasses primarily are distinguished by their structural architecture. They have either open top architecture, such as a vertical centrifugal spheronizer, or closed top architecture, such as a closed top fluid bed dryer. 

Direct Heating, Fluidized Solids Bed (Fluid Bed Dryer)... 

Although fluid bed dryers may differ from one another in geometry, operating pressures, and other conditions, no fluidized solids bed dryer subclasses have been identified. 

Step 3—In a separate step, styrene-acrylonitrile (SAN) resin is prepared by emulsion, suspension, or mass polymerization by free-radical techniques. The operation is carried out in stainless-steel reactors operated at about 75°C (167°F) and moderate pressure for about 7 hours. Tlie final chemical operation is the blending of the ABS graft phase with the SAN resin, plus adding various antioxidants, lubricants, stabilizers, and pigments. Final operations involve preparation of a slurry of fine resin particles (via chemical flocculation), filtering, and drying in a standard fluid-bed dryer at 121-132°C (250-270°F) inlet air temperature. 

Mean drying time for the oven tray process is 19.2 hr. All 15 batches were dried within the specified time of 16 to 20 hr. No seasonal influence was apparent. The average moisture content of these batches is 1.2% the standard deviation is 0.3%. The 15 batches dried using the fluid bed dryer had a residual moisture of 0.8% (SD = 0.1%). Drying time is mechanically controlled and not recorded. The statistics favor the fluid bed process it is more efficient and uniform. There is nothing in these data to disqualify the oven tray dryer from further use, however. 

Table 2 Drug A Comparison of Oven Tray Dryer and Fluid Bed Dryer Processes...

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