Measurement elutriation

Special attention has to be paid to a definition of attrition rates in the case of continuous processes where fresh solid material is continuously added. This is particularly the case in heterogeneously catalyzed fluidized bed processes where fresh make-up catalyst must be added to compensate for attrition losses. The fresh catalyst may contain elutriable fines which add to the measurable elutriation rate thus leading to an apparently higher attrition rate. 

Consequently, it is very difficult to evaluate the cyclone attrition rate from the measured elutriation rate. In order to study the cyclone attrition mechanism in detail it is necessary to study the cyclone in isolation. This can be achieved by feeding a cyclone batch-wise and directly without any additional equipment that could contribute to attrition. 

The terminal velocity in the case of fine particles is approached so quickly that in practical engineering calculations the settling is taken as a constant velocity motion and the acceleration period is neglected. Equation 7 can also be appHed to nonspherical particles if the particle size x is the equivalent Stokes diameter as deterrnined by sedimentation or elutriation methods of particle-size measurement. 

Various methods are used for evaluatiag the quaflty, ie, physical strength and ensyme dust formation, of the granulate. In the elutriation process, a sample of product is fluidised ia a glass tube with a perforated bottom plate for 40 miautes. Dust from the sample is collected oa a filter and the ensyme activity measured. An acceptable dust level is when less than 5—10 ppm of the activity of the sample has been collected. In the so-called Heubach method, 20 g of granulate is elutriated. During the elutriation, four steel balls are rotated ia the bed ia order to evaluate the impact of attritioa oa the dust release of the ensyme. The dust is collected oa a filter and measured. The acceptable dust level is very low. 

As measured by the vertical elutriator cotton-dust samples. 

Lint-free dust as measured by the vertical elutriator cotton-dust sampler described in the Transactions of the National Conference on Cotton Dust, p. 33, J.R. Lynch (May 2, 1970). 

The simulated FBAC consists of an acrylic main reactor (0.5m-H x 0.5m-W x l.Om-L), an air distributor system, particles feeding system including a feed hopper, a discharging sampler, a bag filter for capture of the elutriated fine particles and, pressure and flow rate measurement systems (Fig. 1). The air distributor system has ten air headers. An individual air header is connected with 5 air nozzles and can regulate the airflow rate. The opening ratio of the distributor is 2.1% and each nozzle has four holes for uniform air supply. To measure the pressure fluctuation at an individual air header, high frequency pressure transmitters were mounted at the approach and the exit headers of the FBAC. 

The dynamic methods involve the placement of particles to be measured in an environment which is subsequently disturbed. The members belonging to the particle set react differently to these imposed environmental impulses. These different reactions are observed and therefrom deductions are made as regards the size characteristics. As examples of dynamic methods mention may be made of sieving, streaming, elutriation, and sedimentation. 

In fluidized bed experiments, most authors assume that all attrition products are elutriated. Consequently, they measure either the decrease in bed mass and use Eq. (2) (e.g.,Kono, 1981 Kokkoris etal., 1991, 1995) or the elutriated mass (e.g., Seville et al., 1992, Werther and Xi, 1993). It should be noted that all these authors used a certain particle size as a threshold below which all particles are assigned to be attrition products provided that all initial particles are clearly larger. Breakage events, which lead to particle sizes above the threshold level are, therefore, not considered. The choice of this threshold is very arbitrary and differs between the various research groups. 

Catalyst manufacturing processes usually make particles in a distribution of sizes, although special shapes such as Raschig rings or cylinders made by extrusion and other shapes made by stamping may be quite uniform. Size distribution is measured by sieving or elutriation. A mean diameter is a convenient quantity. The kind of mean value that is applicable when surface is the main property of interest is the volume-surface mean that is applied in P7.01.09. 

The prototype cotton-dust analyzer used in the initial study was designed to measure dust smaller than 100 pm, whereas a vertical elutriator in a card room measures only the dust that is smaller than about 15 pm. Differences in particle size distributions of dust from various types of cotton would likely affect the relationship between the two dust measurements. Therefore, we deemed it necessary to investigate the use of sizing screens with smaller openings i.e., openings whose size approximated the maximum size of particles collected by a vertical elutriator. The purpose of this report is to describe additional modifications to the cotton-dust analyzer and to present data on the performance of the machine when 17-, 50-, and 100-pm sizing screens were used. 

The alternative Instrument used was a Portable Continuous Aerosol Monitor (PCAM) manufactured by ppm, Inc., and dust concentrations measured with the PCAM were 5-15% lower than values obtained with standard vertical elutriators. Calculations and examples for TWA exposures, equivalency tests, and vertical elutriator coefficients of variation are included. 

After all data has been compiled to show TWA values this information is then shared with employees using a computerized employee exposure form. This concludes the task of dust measurement by means of the standardized vertical elutriator method. 

The algebraic calculations of the distribution parameters included all cells of the histogram while those obtained from the cumulative plots were sometimes based on only a part of the cells. When the distribution was multimodal, the latter calculations included only the values from the distribution with the smaller diameter, and no attempt was made to adjust the percentage count for the number of points in the larger dicuneter distribution(s). Other factors reported are the number of particles per 0.1 ft, the dust concentration measured with the Vertical Elutriator Cotton Dust Samplers (VE), the nature of the cumulative plots, and for multimodal distributions, the percent of particles in the distribution with the smaller dieuneter. 

In the other study. X-ray fluorescence spectroscopy was used to analyze trace element concentrations by observing dusts on 37 ram diameter cellulose acetate filters (20). Twenty-three elutriator and twenty-three area samples from 10 different bales of cotton were analyzed. The average fraction of total dust accounted for by the elements analyzed was 14.4% amd 7.6% for vertical elutriator and area samples, respectively. Although the variation in absolute quantity of atn element was high, the relative abundance of an element was consistent for measurements within a bale. Averaged over all the samples analyzed, calcium was the most abundant element detected (3.6%), followed by silicon (2.9%), potassium (2.7%), iron (1.1%), aluminum (1.1%), sulfur (1.0%), chlorine (0.8%) and phosphorous (0.6%). Other elements detected in smaller aunounts included titanium, manganese, nickel, copper, zinc, bromine, rubidium, strontium, barium, mercury amd lead. 

Recent reports suggest that a significant portion of the dust measured by a vertical elutriator in a card room may be due to solids in humidifier water (23,25,43). Undoubtedly, much of the inorganic matter found in the model card room dusts arises from this source. 

A Typical Profile of Elements Measured by X-Ray Fluorescence in Cotton Dust Collected by a Vertical Elutriator on a Cellulose-Ester Filter (20)... 

Similar phenomena has been observed by others (43). Thus, much of the dust measured in total or elutriated s2unples of cotton dusts arises from the spray drying of the humidifier water. 

Dust Concentrations Measured in a Textile Mill with Vertical Elutriator Samplers as a Function of Variation in Water in Humidifier System. (25)... 

Separation of mixtures of particulate solids according to size may be accomplished with a series of screens with openings of standard sizes. Table 12.1 compares several such sets of standards. Sizes smaller than the 38 pm in these tables are determined by elutriation, microscopic examination, pressure drop measurements, and other indirect means. The distribution of sizes of a given mixture often is of importance. Some ways of recording such data are illustrated in Figure 16.4 and discussed in Section 16.2. 

Measurements of binary vapor-liquid equilibria can be expressed in terms of activity coefficients, and then correlated by the Wilson or other suitable equation. Data on all possible pairs of components can be combined to represent the vapor-liquid behavior of the complete mixture. For exploratory purposes, several rapid experimental techniques are applicable. For example, differential ebulliometry can obtain data for several systems in one laboratory day, from which infinite dilution activity coefficients can be calculated and then used to evaluate the parameters of correlating equations. Chromatography also is a well-developed rapid technique for vapor-liquid equilibrium measurement of extractive distillation systems. The low-boiling solvent is deposited on an inert carrier to serve as the adsorbent. The mathematics is known from which the relative volatility of a pair of substances can be calculated from the effluent trace of the elutriated stream. Some of the literature of these two techniques is cited by Walas (1985, pp. 216-217). 

Bioassay using a biological system which measures toxic effects of the liquid/aquatic phase of a test material (e.g., porewater, elutriate, leachate) and determines a response (e.g., acute and/or chronic toxicity). See also Solid-phase (toxicity) test. Volume 1(2), Volume 2(9). 

Determination of the effect of a material or substance on a group of selected organisms (e.g., Vibrio fischeri), under defined conditions. An aquatic toxicity test usually measures either (a) the proportions of organisms affected (quantal) or (b) the degree of effect shown (quantitative or graded), after exposure to specific concentrations of test material or complex mixture (e.g., chemical, effluent, elutriate, leachate, or receiving water). Volume 1(2,10). 

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