Filtration equipment application and performance

Particulate filtration removes suspended liquid or solid materials whose size, shape, and mass allow them to remain airborne at the air velocity conditions present. Filters are available in a range of efficiencies, with higher efficiency indicating removal of a greater proportion of particles and of smaller particles. Moving to medium efficiency pleated filters is advisable to improve lAQ and increase protection for equipment. However, the higher the efficiency of the filter, the more it will increase the pressure drop within the air distribution system and reduce total airflow (unless other adjustments are made to compensate). It is important to select an appropriate filter for the specific application and to make sure that the HVAC system will continue to perform as designed. Filters are rated by different standards which measure different aspects of performance. 

Data of commercially available sizes of filtration equipment, their typical applications, and specific performances are available only to a limited extent in the general literature, but more completely in... 

Data of commercially available sizes of filtration equipment, typical applications, and specific performances are available only to a hmited extent in the general literature, but more complete in manufacturers hterature. Representative data are collected in this section and summarized in tabular form. One of the reasons why more performance data have not been published is the difficulty of describing each system concisely in adequate detail. Nevertheless, the limited hstings here should afford some perspective of the nature and magnitude of some actual and possibly potential applications. 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Over the years the performance standards of hydraulic equipment have risen. Whereas a pressure of about 1000 psi used to be adequate for industrial hydraulic systems, nowadays systems operating with pressures of 2000-3500psi are common. Pressures above 5000psi are to be found in applications such as large presses for which suitable high-pressure pumps have been developed. Additionally, systems have to provide increased power densities, more accurate response, better reliability and increased safety. Their use in numerically controlled machine tools and other advanced control systems creates the need for enhanced filtration. Full flow filters as fine as 1-10 micron retention capabilities are now to be found in many hydraulic systems. 

Various small scale test units and procedures are available to determine slurry characteristics and suitability for a particular application. Buchner funnel, and vacuum leaf test units can be purchased or rented fi om vendors to perform in-house tests, or one can have tests conducted at the vendor s facility. Pilot testing on the actual equipment would be the optimum with a rental unit in the plant. In either case, slurry integrity must be maintained to ensure accurate filtration data. 

Processes for adenovirus purification typically end with concentration, formulation, and sterile filtration operations [40, 80,106]. Concentration and formulation are usually carried out in ultra-filtration units equipped with 100-300-kDA membranes [40,106]. The exact composition of the formulation buffer will depend on the intended application, mode of administration (injectable, aerosol), and required short-term and shelf stability [104,123]. A typical liquid formulation may include an aqueous buffer supplemented with cryoprotectants (e.g., sucrose) and stabilizers such as the nonionic-surfactant polysorbate-80, the chelating agent EDTA, and the oxidation inhibitors ethanol and histidine [123]. Filtration under sterile conditions is typically performed with 0.22-pm membranes [103,106]. 

Hydrocyclones are also used as classifiers simply to improve the performance of other filtration or separation equipment. A good example is in applications where the cyclone separates the feed into coarse and fine particles, and the coarse material is fed onto the horizontal belt filter first, as a precoat, with fines to follow (see Figure 6.25). This will, if the cut point of the cyclone is set correctly, give good filtrate clarity and extend the usefulness of vacuum filters to finer feeds without necessarily adversely affecting the moisture content of the cake. 

Formulation as Sprays. Virus formulations have usually been for application as sprays using conventional application equipment. Most viruses tested by researchers in field trials have been aqueous suspensions of filtrates or precipitates from macerated virus-killed cadavers. These are stable for long periods under refrigeration or when frozen and usually are easily tank-mixed with water and other adjuvants (12, 13). Performance of these simple formulations in field trials usually is equal or superior to more elaborate formulations. They are seldom practical for commercialization, however. Commercial formulations are concentrated precipitates because stable and concentrated product is needed for storage and shipping. 

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