Filtration Operation

This can be substituted for in the basic filtration equation 4, which can then be solved for the filtration operation in question. 

The VaHez filter, originally developed in the United States for the sugar industry, rotates the leaves at about 1 rpm during the filtration operation to keep the soHds in suspension and acliieve a more uniform cake. 

The cost of the filter station includes not only the installed cost of the filter itself but also that of all the accessories dedicated to the filtration operation. Examples are feed pumps and storage facihties, precoat tanks, vacuum systems (often a major cost factor for a vacuum filter station), and compressed-air systems. The dehvered cost of the accessories plus the cost of installation of filter and accessories generally is of the same order of magnitude as the dehvered filter cost and commonly is several times as large. Installation costs, of course, must be estimated with reference to local labor costs and site-specific considerations. 

Filtration operations are capable of handling suspensions of varying characteristics ranging from granular, incompressible, free-filtering materials to slime-like compositions, as well as finely divided colloidal suspensions in which the cakes are incompressible. These latter materials tend to contaminate or foul the filter medium. The interaction between the particles in suspension and the filter medium determines to a large extent the specific mechanisms responsible for filtration. 

For a 50,000 GPD filtration operation with an average loading 50 mg/L TSS (Total Suspended Solids) determine the optimum flocculant to use in order to achieve at least an 85 % reduction in solids. Assume that a rotary drum filter unit is used. 

The most favorable filtration operation with cake formation is process whereby no clogging of the filter medium occurs. Such a process is observed at sufficiently high concentrations of solid particles in suspension. From a practical standpoint this concentration may conditionally be assumed to be in excess of 1% by volume. Filtration is frequently accompanied by hindered or free gravitational settling of solid particles. The relative directions of action between gravity force and filtrate... 

Another method, which is even more successful in preventing binding of the septum, is the use of a precoat.53 Before filtration is begun a coating of 2-6 in (5-15 cm) of diatomaceous earth or perlite filter aid is deposited on the surface of the septum. During filtration operations the scraper is set so that it slowly removes the precoat and, of course, with it the materials that would have plugged the filter. Since the precoat causes a considerable pressure drop, the rate of filtration is slowed down. Flow rates may vary from 2 to 50 gal/hr/ft2 (0.025-0.60 m/hr). The precoat material costs around 3 or 40/lb and is used at the rate of 10- 15 lb/1,000 gal of feed (1,200 to 1,800 kg/m3). 

Improved Filtration Rate Filterability is an important powder catalyst physical property. Sometimes, it can become more important than the catalyst activity depending on the chemical process. When a simple reaction requires less reaction time, a slow filtration operation can slow down the whole process. From a practical point of view, an ideal catalyst not only should have good activity, but also it should have good filtration. From catalyst development point of view, one should consider the relationship between catalyst particle size and its distribution with its catalytic activity and filterability. Smaller catalyst particle size will have better activity but will generally result in slower filtration rate. A narrower particle size distribution with proper particle size will provide a better filtration rate and maintain good activity. 

E. Particle size effects on sedimentation and filtration operations... 

The dramatic changes in haze particle size seen with alterations in protein-to-polyphenol ratio in a model system, would, if this also occurs in real beverages, have profound effects on both sedimentation (e.g., cold maturation in a tank or centrifugation) and filtration operations. 

In a 1991 study by van Reis et al. (5), a filtration operation as applied to harvest of animal cells was optimized by the use of dimensional analysis. The fluid dynamic variables used in the scale-up work were the length of the fibers (L, per stage), the fiber diameter (D), the number of fibers per cartridge (k), the density of the culture (p), and the viscosity of the culture (p). From these variables, scale-up parameters such as wall shear rate (y ) and its effect on flux (L/m /h) were derived. Based on these calculations, an optimum wall shear rate for membrane utilization, operating time, and flux was found. However, because there is no single mathematical expression relating all of these parameters simultaneously, the optimal solution required additional experimental research. 

A practical consideration in working with ethanethiol is the pervasive stench of this and other volatile thiols, especially as such thiols are used in minute concentration as odor markers for natural gas. It is not easy to perform the standard preparative procedures, during which transfer and filtration operations are performed, in a closed system, and vapors carried through a venting system are detectable at considerable distances, hr small-scale operations, it may be possible to employ a sodium hypochlorite trap to convert the thiols into nonvolatile, oxidized products. 

E. Separations. The basic filtration operation has been previously illustrated. Low-temperature filtrations for the collection of thermally sensitive compounds or products which arc soluble al higher temperatures may be performed with an H-type Schlenk tube. Fig. 1.30, in a large low-temperature bath. The jacketed, fritted funnel illustrated in Fig. 1.25 also permits low-temperature filtration. 

The complexity of the sterile filtration operation and the CGMP regulations require the validation of sterilizing filter systems. The validation of a sterile filtration operation can be complex, with many operational parameters and their interactions needing to be identified, controlled, and predicted for each end product to demonstrate that sterility is adequately achieved by the filtration process. In the commonly used steam sterilization process, the heat parameters are identified and in-process controls specified such that a level of sterility assurance can be reproducibly obtained. In steam sterilization, the important parameter of heat, measured by temperature, can be accurately measured and continuously monitored to ensure the operational integrity of the autoclave however, unlike steam sterilization, filtration sterilization cannot be monitored on a continuous basis throughout the process. 

Figure 7.13 Typical in-line filtration operation using two cartridge filters in series. The prefilter removes all of the large particles and some of the smaller ones. The final polishing filter removes the remaining small particles...

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