Moisture laboratory testing

Technical brochure information rarely reports the baas of cake moisture. Laboratory tests on the latter [Bosley, 1986] involve carefid sampling of the wet cake weired quantities of the latter are dried at 105°C to constant dry weight. The amount of hquor evaporated is then ejqrressed as a percentage of the wet (or dry) cake. In the table below, a wet baas is assumed. 

The influence of moisture is fundamental, as it is with other forms of corrosion. Long-term contact tests with ponderosa pine, some treated with zinc chloride, in atmospheres at 30, 65 and 95% r.h. showed that at 30 and 65% r.h. plain wire nails were not very severely corroded even in zinc chloride-impregnated wood. At 95% r.h. plain wire nails were severely corroded, though galvanised nails were attacked only by impregnated wood. Brass and aluminium were also attacked to some extent at 95% r.h. Some concurrent outdoor tests at Madison, Wisconsin, showed that the outdoor climate there was somewhat more severe than a 65% r.h. laboratory test. 

The minimum bed diameter is a function of the operating velocity, the particle characteristics and the humidity of the drying gas. The hot gas at the inlet rapidly loses heat and gains moisture as it passes through the bed which it eventually leaves at the bed temperature Tb and with a relative humidity which is approximately equal to the relative humidity which would be in equilibrium with the dried product at the bed temperature. The operating velocity may be taken as twice the minimum fluidising velocity, obtained from the equations in Section 6.1.3, by laboratory tests, or more conveniently from Figure 16.26. 

The absorption capacity of the litter determines the amount used, and also affects the functioning of hydraulic manure presses. The absorption capacity of litter depends on its initial moisture content. In the laboratory tests, peat had a much greater absorption capacity than other litters. 

For assessment of the potential to predict granule moisture content, a large 1032-object data set recorded dnring 5 months of urea production was used. The first 900 objects were used for calibration and the last 132 as a validation test set [2]. The data matrix was resampled to allow acoustic data to be calibrated against laboratory tests of moisture content, which were only available with a relatively low sampling rate however, plenty of results were at hand to allow a full assessment of the multivariate prediction performance for granule moisture. The validated prediction results can be seen in Figure 9.11. 

Figure 11.3. Laboratory test data with a vacuum leaf filter, (a) Rates of formation of dry cake and filtrate, (b) Washing efficiency, (c) Air flow rate vs. drying time, (d) Correlation of moisture content with the air rate, pressure difference AP, cake amount W Ib/sqft, drying time 6d min and viscosity of liquid Dahlstrom and Silverblatt, 1977).

Laboratory tests must be taken only as a general guide. In practice, surface cleanliness and lubrication by dust, moisture and oil traces will greatly affect the actual friction properties. 

The nature of moisture content determinations is perhaps best exemplified by the fact that the Handbook of Pharmaceutical Excipients lists 31 separate versions of laboratory tests to determine moisture content and one to determine equilibrium moisture content. These methods were used to assess the moisture content in the compilation of 148 monographs, many of which do not deal with solids. 

The desirable properties for the final pavement are determined by moisture-density, freeze-thaw, wet-dry, and strength tests in the laboratory, using the unmodified in-situ soil. Generally, the freeze-thaw and wet-dry tests are done first, to determine the amount of cement to be used. This value is then used for the moisture-density tests. Cement contents can vary... 

Laboratory test tube centrifuges can determine if there is a sufficient density difference between the two phases to consider sedimentation as an alternative. If there is a sharp separation, one can anticipate the same in the field. One can also answer the following questions. Do the solids settle or float Is the solid phase granular or amorphous What is the moisture content The characteristics of the solids indicate the solids discharge design required, i.e., scroll in decanters, or in disk centrifuges, flow-through nozzles or wall valves. 

The above has to be established by laboratory testing prior to a formal stability programme. As with all pack selections, detailed knowledge of the product, the packaging materials and the process to be employed is an essential requirement. Blister packs are unlikely to give sufficient protection to products severely affected by moisture, oxygen, carbon dioxide, as all known plastic materials are to some degree permeable to these factors. 

Laboratory testing is more economical where environmental conditions are not complicated by coupling (such as high moisture and temperature accompanying mechanical stress) in the application. 

Table 33.5 presents a summary of the various types of dryers, together with examples of pharmaceutical products for which they are used commercially. It should be noted that in most cases alternate dryers are used in practice to dry the same product. Typical operating data for drying of selected pharmaceuticals are given in Table 33.6. The information contained in Table 33.6 is derived from operating dryer performance data as well as from laboratory-scale experiments. Laboratory and often pilot-scale tests are necessary before a commercial-scale dryer may be designed with confidence. For pharmaceutical products, laboratory tests are performed to provide data on the thermal sensitivity, oxidizability, stability, and final product moisture content. This forms the basis for the selection of a dryer and process parameters. If the product is produced in small quantities, a batch dryer may be selected. In large-scale production, energy losses, losses due to deterioration of the product quality, and other losses can be quite substantial if the dryer type and operating parameters are not optimally...

The pilot plant experiments were carried out with various pigments (Table 10.1) dried in a spray dryer with the shock-wave atomizer designed according to the aforementioned procedure (Figure 10.7). Each test was run for 8 hours to obtain a representative sample of about 2000 kg of dry product. The filter cake at an initial moisture content from 50% to 60% wb was dried under optimum conditions determined from laboratory tests, that is, at an inlet air temperature of 170°C and a feed rate of about 120 kg/h. An average evaporation rate for all tests was about 28 kg H20/(m h), which is markedly higher than for currently used spray dryers for which the volumetric evaporation capacity is about 10 kg/(m h). 

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