Pre-coated filter

Filter aids are widely used in die fermentation industry to improve the efficiency of filtration. It is a pre-coated filter medium to prevent blockage or blinding of the filter by solids, which would otherwise wedge diemselves into the pores of the cloth. Filter aid can be added to the fermentation broth to increase the porosity of the cake as it formed. This is only recommended when fermentation product is extracellular. Filter aid adds to the cost of filtration. The minimum quantity needed to achieve the desired result must be established experimentally. Fermentation broths can be pretreated to improve filtration characteristics. Heating to denature proteins enhances the filterability of mycelial broths such as in penicillin production. Alternatively, electrolytes may be added to promote coagulation of colloids into larger, denser particles, which are easier to filter. The filtration process is affected by the viscosity and composition of the broth, and the cell cake.5... 

Oil and hydrocarbon leaks that return with the condensate coat heat-exchange surfaces and cause FW system fouling and deposit binding. These materials must be removed or they will reenter the boiler to produce nonwettable boiler surfaces, and create serious problems. Oil in condensate should be removed by the use of an inline pre-coat filter. The pre-coating should be either aluminum hydroxide ox ferric hydroxide becaue both these hydrous oxide gels have an affinity for oil. 

Precoat filters are widely used in the chemical process industry. In this operation, instead of mixing the filter aid with the sludge, the filter aid is placed onto the filter fabric before the sludge is introduced. This prevents rapid premature clogging of the smaller pores and allows for a greater filter yield. Diatomaceous earth is an effective but expensive filter aid for pre-coat filters. 

In the pre-coat mode, filter aids allow filtration of very fine or compressible solids from suspensions of 5% or higher solids concentration on a rotary drum pre-coat filter . This modification of the rotary drum vacuum filter uses an advancing knife to skim off the separated solids and the uppermost layer of the thick pre-coat continuously, until the whole of the pre-coat is removed and a new layer has to be applied. This makes it possible to discharge very thin cakes as well as that part of the pre-coat which has been penetrated into by the sohds and partially blinded. 

As the feed suspension enters the drum from the bottom (in the most common bottom feed version), fast settling slurries are not suitable for most rotary drum filters. Nor are very fine slurries because of the inevitable penetration problems. Note the unfavourable stratification of particle size within the cake discussed in section 13.10.2 and shown in Figure 13.15. In units designed to use a pre-coat filter aid (rotary drum pre-coat filters), the drum can be evacuated over the full 360 degrees and fitted with an advancing knife system that continuously shaves off the deposited solids together with a thin layer of the pre-coat. The pre-coat has to be renewed periodically. 

As can be seen from Figure 13.13, cake thicknesses below about 3 millimetres cannot be discharged with a knife or a scraper (area A). This area clearly represents a very difficult-to-filter slurry, which if fine and very dilute, may even require a rotary drum pre-coat filter (section 13.7). Areas B, C and D show the types of filters applicable to increasingly filterable slurries, with... 

If the supplier cannot meet the specified quality, contact an engineer of the sulphonation equipment supplier. Poor quality sulphur can be upgraded by a refining process. Molten sulphur is recycled over a pre-coated filter, where organic material, extraneous solids and inorganic salts (from acid sulphur, H2SO4 and HjS, neutralised with ammonium bicarbonate) are trapped in the filter. 

The pre-coated filter can operate for a period of two to four weeks, depending on the level of impurities in sulphur. The equipment supplier can help you either to find a sulphur refining operation in the region to do the job or supply a sulphur upgrading unit. 

The compact fdter is a skid type mobile apparatus in which the vacuum fdter already has ad the accessories connected and is thus ready to plug in for instant operation. There are versions available as single-cell filters or as cell filters having ad the usual discharge arrangements, in addition to pre-coat filters with hydrauli-cal lowering filter trough [15]. 

Solid radioactive waste results from the operation and maintenance of the nuclear power plant and its associated processing systems for gaseous and liquid radioactive waste. The nature of such waste varies considerably from plant to plant, as do the associated levels of activity. Sohd radioactive waste may consist of spent ion exchange resins (both bead and powder) cartridge filters and pre-coat filter cake particulate filters from ventilation systems charcoal beds tools contaminated metal scrap core components debris from fuel assemblies or in-reactor components and contaminated rags, clothing, paper and plastic. 

As previously indicated, most bag-type filters require a pre-coat of particulates before they can effectively remove airborne contaminates. However, particles can completely block air flow if the filter material becomes overloaded. Therefore, the primary operating criterion is to maintain the efficiency of the filter media by controlling the cleaning frequency. 

This type of filter can be used for removal of Penicillium and Streptomyces mycelia in the production of penicillin and streptomycin, respectively.5 In these processes the rotary drum filter is used with a pre-coated cloth filter with filter aid the filter cake is removed by a knife blade which scrapes the cake from the rotating drum. 

The soluble ions of iron and aluminium are usually reduced to a minimum by adjusting the electrolyte pH. For the removal of solid iron hydroxide and aluminium hydroxide Bayer decided to use a new pre-coat-free brine purification technology -back-pulse filtration using GORE-TEX membrane filter cloths. 

Instead of the manual valves used in pre-coat operation of the Kelly filters, new ones activated by pressurised air were installed. The new filter system is connected to... 

Extraction of Tobacco. Methoprene is used on tobacco against the cigarette beetle and the tobacco moth. Methoprene-treated tobacco samples were extracted following a procedure for the extraction of plant materials for determining methoprene residues by GC (21). Known amounts of methoprene in 1 mL methanol were added to 1 g portions of shredded tobacco, mixed well and allowed to thoroughly air dry. The spiked tobacco was then stirred with a 25 mL mixture of acetonitrile/water/Celite 45 (250 mL/30 mL/10 g). The mixture was filtered by suction and the filter cake was washed with acetonitrile/water. The filtrate was extracted with ether, distilled water, and sodium chloride. Ether extracts were combined and washed three times with distilled water, dried, filtered and the solvent removed. The residue was taken up into methanol (1 mL) and applied to the pre-coated microtiter plates (5 jxL methanol/well), followed by the anti-methoprene antibody as described above. 

Waste Minimization and Disposal. CFF systems minimize disposal costs (e.g., when ceramic filters are used) whereas in diatomaceous (DE) pre-coat filtration substantial waste disposal costs may be incurred, particularly if the DE is contaminated with toxic organics. Currently, in many applications, DE is disposed of in landfills. In future, however, this option may become less available forcing the industry to use cross-flow microfiltration technology or adopt other waste minimization measures. 

The oil is mixed with diatomaceous earth through an in-line mixing system and filtered through a pressure leaf filter pre-coated with diatomaceous earth. 

An integrated membrane process based on MF-UF-diafiltration is shown in Figure 3.13 a backwashable dead-end MF with a pore size of 5.0 pm to separate the green fraction at pH 8.0 followed by UF to recover the white fraction and purification of the white fraction using diafiltration (DF). MF with a pre-coat traps the chloroplastic fraction producing a chlorophyU-free brown liquor. The pre-coat material can be dia-tomaceous earth or com starch. The latter is preferred since the filter cake is useful as... 

Filter aids are qrplied in two ways (a) as a pre-coat, where a thin ( proximately 2 mm) layer of aid is depoated on the fitter medium, before the commencement of filtration, or (b) as a body feed where a certain quantity of aid is added to the feed shmy. The latter procedure is adopted in cases where the su ended solids have poor fitterabiUties and would ferm an inq>ervious layer on the surfece of the filter medium, or evoi the filter aid pre-coat. The combined deposit of filter aid and susp ided inq>urity possesses a mndi reduced filtration resistance. Usually an optimum dosage of body feed is sought, in ovoall cost tmn as discussed in Chapter S. 

The above equation indicates that in these operations, the pressure differential will rise with increase in filtration time, tf. Arrangements are made to tominate the sqparation whm the pressure differential reaches m uppa , safe limit. In some cases, the filter is pre-coated... 

Fully automatic operation is essential to take complete advantage of this mode of cake discharge. Design changes involving a reduction in vessel size, even for dry cake discharge, reduced overall costs. These units are also usefiil in liquor clarifications invoking the use of filter aids, as a pre-coat and/or as a body feed. 

Filter leaves are gaiera% of rigid constmction a metal finme covered with a metallic meih is common, hi some applications, the leaf will be covered by a suitable filter doth. Open-pore metalhc me ( 130 pm) can be used in pre-coating rqrphcations, in clarification processes. 

A pressure leaf filter is required for the clarification of a vegetable oil, operating at a constant flowrate of 3 m /h. Afler pre-coating the filter medium with a suitable filter aid, filtration ensues up to a maximum pressure difiEerential of 4.5 bar. 

Downtime includes filling, precoating and enqjtying the filter. In order to sinqjlify the problem, it may be assumed that tow = 0.3 4, irrespective of the size of the filter. Calculate the filter area requirements for cycle times of 1, 2, 7, and 14 h. If the pre-coating requirement involves the deposition of 2 mm of filter aid per cycle on the filter area A m, calculate the effect of cycle time on the sum of the purchase cost of the filter and the annual cost of filter aid. Assume an operating period of 14 h/d and 340 working days per annum. 

---