Dryer monitoring

Although this particular apphcation is well established, it only works if the probe is seeing a sample representative of the process. If plugging of wet sainile at the probe tip occurs, then fresh sample will not be seen. On such occasions, systems are available to insert/extract the probe between agitator rotations or air pressure can be used to blow the tip clean. Both should be avoided if at all possible. 

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For example, in rotary vacuum dryers it is possible to prevent the formation of explosible dust-air mixtures by setting and monitoring a certain partial vacuum (negative pressure). This pressure value must be determined by experiment for each type of dust. With pressures of less than O.I bar, in general, hazardous effects of dust explosions need not be anticipated. If the vacuum system malfunctions, the partial vacuum must be released by inert gas and the instaUation shut down. 

Commercial laundry dryers can not be easily vented to the outside in the same way that home laundry dryers are. Because of this fact, the moist air is passed through a condenser where the water will accumulate. If there is no direct water drain, the water is directed to a holding tank. The water level is monitored using a magnetic float. When the water rises to the full level, the reed sensor is activated and shuts down the dryer. Once the water is removed, the reed sensor is deactivated, enabling the dryer to operate. 

The hydration state of risedronate sodium was monitored continuously in a fluidized bed dryer and correlated to data on the physical stability of tablets made from the monitored material [275]. The final granulation moisture was found to affect the solid-state form, which in turn dictated the drug s physical stability over time. The process of freeze-drying mannitol was monitored continuously with in-line Raman and at-line NIR spectroscopies [276]. The thin polymer solvent coatings, such as poly(vinyl acetate) with toluene, methanol, benzene, and combinations of the solvents, were monitored as they dried to generate concentra-tion/time profiles [277]. 

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... 

C. Coffey, A. Predoehl, D.S. Walker, Dryer effluent monitoring in a chemical pilot plant via fiber-optic near-infrared spectroscopy, Appl. Spectrosc., 52(5), 717-724 (1998). 

S.C. Harris and D.S. Walker, Quantitative real-time monitoring of dryer effluent using fiber optic near-infrared spectroscopy, J. Pharm. Sci., 89(9), 1180-1186 (2000). 

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). 

C. Buschmilller, W. Wiedey, C. Doscher, J. Dressier and J. Breitkreutz, In-line monitoring of granule moisture in fluidized-bed dryers using microwave resonance technology, Eur. J. Pharm. Biopharm., 69, 380-387 (2008). 

Buschmuller et have demonstrated that microwave resonance can be used effectively as means to monitor the moisture levels in a fluidized-bed dryer during the granulation process. The penetration depth of microwave resonance may be limited to a few microns, and hence this technique may not have any real advantages over NIR which has also been used for monitoring moisture in dryers, and has the advantage of providing chemical information such as solvent levels in addition to water, and other important properties such as polymorphic form, and particle size. 

Around our home we are exposed to a variety of different types of radiation. Home appliances such as hair dryers emit electromagnetic radiation. Our TVs and computer monitors expose us to additional electromagnetic radiation, as do our cell phones and radios (Table 12.1). 

Notes Particulate monitoring during unloading freeze dryer area will be considered as level III locations not in use will be monitored during the complete area monitoring once per week R represents hypothetical room numbers. 

Therefore, product temperature should be monitored closely to control the fluidized bed drying process. During fluid-bed drying, the product passes through three distinct temperature phases (Fig. 21). At the beginning of the drying process, the material heats up from the ambient temperature to approximately the wet-bulb temperature of the air in the dryer. This temperature is maintained until the granule moisture content is reduced to the critical level. At this point, the material holds no free surface water, and the temperature starts to rise further. 

Once the cores are compressed, one to three sealing coats may be applied by the process operator. The third coat was never required, however. All 19 batches were completed with two coats of shellac. The volume of shellac applied was always 350 mL for both steps, as required by the batch record, and the record further indicates that the temperature of the air directed into the coating pan was always set at 40°C. There is no record of the temperature being monitored, however. The shellacked cores were dried overnight at 35°C. The dryer temperature was tracked and automatically recorded no variablity was encountered when the temperature chart was reviewed. 

In an extension of simply monitoring and controlling dryers, Morris and colleagues have demonstrated how in situ probes can provide real-time analysis that enables optimization of a drying process.61,62 In these articles, the authors demonstrate how evaporative cooling can be used to expedite drying in formulations where heat transfer... 

VOC concentration monitors which control air flow to each dryer stage to maintain the dryers at 25-40% of the LEL (lower explosive limit)... 

A typical Mazzoni fatty acid neutralization soap plant is illustrated in Fig. 36.5.6 The operation of this plant involves the pumping of the reactants through preheaters to a turbodisperser, or high-shear mixer, where the contact of the reactants with each other initiates the formation of neat soap. The soap mass, which is partially reacted at this stage, then proceeds to the mixer where it is recirculated until the neutralization is complete. The completion of the neutralization reaction is monitored continuously by an electric potential (millivolt, mV) measurement for alkalinity. The neat soap is then dried by vacuum spray-dryers, as described earlier, to produce soap pellets ready for finishing into soap bars. 

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