Particles capital cost

Particle Segregation Mechanisms. Segregation is the process by which an assembly of soHd particles separates as it is being handled. This often results in cosdy quaUty control problems due to the waste of raw or finished materials, lost production, increased maintenance, and capital costs required to retrofit existing faciUties. 

There are many techniques available for measuring the particle-size distribution of powders. The wide size range covered, from nanometers to millimeters, cannot be analyzed using a single measurement principle. Added to this are the usual constraints of capital costs versus running costs, speed of operation, degree of skill required, and, most important, the end-use requirement. 

Microfiltration and ultrafiltration have recently been introduced for the removal of particles down to any desired size. Their capital cost is relatively high. Experience with them is limited, and a short trial with a small-scale pilot element is advisable. Prediction of full-scale performance from such trials is normally quite reliable. 

Figure 5 represents a typical example of the variation of the number of polymer particles with mean residence time 0. The solid line shows the theoretical value predicted by the Nomura and Harada model with e= 1.28x 10 . The dotted line is that predicted by the Gershberg model(or the Nomura and Harada model with Case C for ), where Eq. (23) was used instead of Eq.(16) for Ap. The value of Nt produced at longer mean residence time differs, therefore, by a factor of T(5/3) between the solid and dotted lines in Figure 5. From the comparison between the experimental and theoretical results shown in Figure 5, it is confirmed that the steady state particle number can be maximized by operating the first stage reactor at a certain low value of mean residence time max which is considerably lower than that in the succeeding reactors. This is so-called "pre-reactor principle". It is, therefore, desirable to operate the first reactor at such mean residence time as producing something like a maximum number of polymer particles in order to increase the rate of polymerization in the succeeding reactors. This will result in a decrease in the number of necessary reactors and hence, in the capital cost.

The X-ray fluorescence method normally affords adequate sensitivity for most elements of interest. However, overlapping X-ray emission lines may limit the use of this method. For instance, a lead line seriously interferes in the analysis of arsenic, and some transition elements may have overlapping spectra. Because of difficulties in calibration for thick samples, particle deposits on filters must be kept to minimal values of mass per unit area. For urban atmospheres, sampling is limited to about a one to six-hour period by the combination of detection limit and sample loading requirements. The elimination of sample preparation makes this method attractive despite relatively high capital costs. Sample mass loading limitations are even more severe for X-ray methods using particle excitation, such as with protons, than with the photon excitation fluorescence technique. 

For CFB reactors further aspects have to be taken into account restricted range of admittable particle properties increased particle attrition decreased suspension-to-wall heat transfer coefficients more complexity in designing and operating the circulating loop higher capital costs. 

This indicates that a higher cross-flow velocity under turbulent conditions can result in more than proportional increase in the pressure drop requiring larger pump discharge pressure to maintain a specified recirculation rate. This limits the number of modules that may be placed in series to minimize capital costs. Typical range of cross-flow velocity values is 2 to 7 m/s. The choice of pump is critical to obtain efficient fluid recirculation. It is critical to understand the shear sensitivity of the fluid/particle to be processed to determine the optimal cross-flow velocity in situations where shear-sensitive materials are involved. 

Viscosity and physical properties of liquids Character of solid particles Capital and expected maintenance costs Expected precision and accuracy of readings Possible foam, boiling, and agitation... 

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