Filters safety considerations

For a study of methods of assessment of thermal runaway risk from laboratory to industrial scales [2], A more detailed but eminently clear treatment of this and other needful safety considerations on scaling reactions up to production has since been published [3], So slight a scale-up as replacing two charcoal filters by one bigger one may cause a fire because heat loss was reduced [4], A journal largely devoted to scale-up of organic chemical processes has been launched [5]. 

Consider the internal and external environment, medium characteristics, compatibility of all the materials used in the process, and the conditions of operation when studying your choices for components. Then, put your goal through the filters that will separate fact from fiction. Those filters are consideration of the cost, safety, and performance of your designed system. 

Decoupling by installing parallel arrangements of equipment which is particularly susceptible. For example, filters and fittings that are susceptible to failure should be provided with a bypass if safety considerations permit (e.g., heat exchangers in the main flow in which severe fouling is to be expected). 

As with the polymers, a high polarity of the solvent improves the electrostatic process. Further a high electrical conductivity of the solvent is required for the production of nano-fibers. PVA and PEO are favorites for experiments as they can be processed from aqueous solutions and no special safety considerations have to be made regarding toxicity or explosivity. In addition, water is highly polar and most suitable for electrostatic spinning. (Their use for filters is limited, of course.) These are the main requirements on the solvents. In practice these ideal conditions will rarely be found. The use of chlorinated organic solvents is accepted when only small amounts are processed (e.g. for medical applications). It is difficult to obtain an operation permit for... 

Elutriation is important in most industrial fluidized beds and is generally thought of as a disadvantage. In addition to the small particles which may be present in the initial particle size distribution, fines may be created in the course of operation by the attrition of bed particles. Elutriated particles usually need to be collected and recovered either because they represent the loss of product particles of a given size, because they must be separated from the exhaust gas for environmental reasons, or because of safety concerns there is a considerable risk of a dust explosion with very fine particles and perhaps especially so with many food particulates. Therefore the fluidized bed plant will require ancillary gas cleaning equipment such as a cyclone, filter or electrostatic precipitator to separate the fines from the gas. The loss of a particular size fraction from the bed may change fluidized bed behaviour and it then becomes important to return the fines to the bed continuously. 

Filters are used for clarification, removal of small molecules, exchange of buffers, and concentration of product, as well as sterilization and virus removal. A recent review of validation of filtration describes the critical validation issues [29], Filter compatibility is tested with process conditions to avoid nonspecific binding of product to the filter or addition of extractables to the process stream. Extractables are defined and limits established based on final product safety studies. Special considerations apply for sterilizing filters and those that are designed for virus removal. These filters are single use, however, which simplifies the validation effort. 

To limit considerably the release of fission products beyond the containment, a permanent under-pressure is maintained in the inter-containment gap of the V-392 design. This safety function, one of the most important, is fulfilled by two systems (1) an exhaust ventilation system equipped with a filtering plant with suction from the inter-containment gap and outlet... 

Finally, the process filtration will probably be performed over a difiierait time fi om that of the laboratory test, so it is usu to calculate the flux obtained in the laboratory on the basis of volume per unit time and filter area and to check that this is considerably in excess of that required by the process after having applied safety ctors to the process filtration area calculation (typically 1.5 or more). 

In the past few years, the AEC has required solution excursion analyses for new construction as well as plants already in operation. These hypothetical excursions should be chosen to be representative of the most severe excursion that could be reasonably expected in the particular systems involved since the results of the analysis will, in turn, determine the size and types of the hot exhaust filtering system and shielding thickness, etc. An example of the "most severe excursion may be helpful. Consider a tank 3 ft in diameter by 4 ft high which is shown by a safety review to have solution. For the excursion parameter of maximum total fissions, the most severe condition is a tank that is critical when nearly full hence, the full tank volume is used for the total fission estimate. The specifications of the process systems are usually such that the excursions chosen are limited by practic design considerations to tanks of 2- to 5-ft diam with a height of 1 to 2 diam and a solution transfer rate of 7i gpm or less. 

Health and safety aspects Handling powdered media (e.g. filter aids) can pose health and safety problems, and disposal of contaminated media may require special considerations. 

The concerns for sterility can he addressed by installation of laminar flow sterile air filters that provide a constant source of clean air to the work area. Mechanically, room air is channeled through a prefilter and then a sterile high-efficiency particulate air (HEPA) filter prior to flowing across the work surface at uniform velocity (Fig. 18.2). Fully equipped laminar flow safety cabinets are very expensive (> 8000) and may not be justified in the winery microbiology laboratory. However, tabletop workstations that incorporate HEPA-filtered air are available at considerably less cost ( 3000) and serve as good alternatives. 

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