Cloth selection

The fiber cloth is the deciding ctor in the success or failure of all press operations. In view of the wide range of process variables involved in the filtration process, it is virtually in ossible to select a filter medium that will satisfy all process requirements and the usual limited time scale available for cloth selection is used to find an acceptable medium, i.e. one that will satisfy most, if not all of the requirements. In this reject, one particular requirement (e.g. filtrate clarity) may have to be relaxed, if other specifications (e.g. filtrate rate, absence of blinding) are to be maximised. Thus the more open weave Mcs will be superior in nonblinding characteristics, but may have poor particle retention. The latter will in rove in the order monofilament muldfilament staple fibre. Tabulated information is presented in Tables 4.2,4.3 and 4.4 below on the effect of yam properties, weave patterns, etc. on the processes of cake release, productivity, resistance to blinding, etc.. 

Fmther information of this type,on the effects of fibre materials and weave pattern, is provided in the literature [Purchas, 1981]. 

Cloth selection fi om tabulated information is unpossible without reference to the durry being processed. The tables give general guidelines to the behaviour of media interaction of the latter with particles can only be determined by practical trials. The best test method, of course, is the installation of potential media in an operation unit. This type of study will produce relevant information on wear characteristics, cloth life expectancy and other ctors (which are difficult to predict with certainty fi om other test m ods). 

The next-best option is the use of a pilot-scale model of the fiber. Here the fluid flow patterns at the sur ce of the medium will, at least, be similar to the large-scale luut. The pilot fiber cannot produce information on wear properties, e.g. produced by the effect of movement of large, heavy plates. Cloth behaviour must at least be studied e q)erimentally using laboratory Buchner fibers. The latter low-pressure test units will provide information on the resistance of the used medium, tendency to blind, etc. However, the fibration process conducted downwards on the sur ce of the medium, imder a pressure differential of 0.5 bar, cannot be expected to simulate exactly the processes occurring inside large recessed-p te or plate and fi ame fibers where particle movement is a complex mixture in vertical and horizontal directions. 

Fibre Form Spun staple Monofilament Monofilament Monofilament Spun staple Monofilam t 

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For orientation in cloth selection for a given process, the following information is... 

In selecting cloths made from synthetic materials, one must account for the fact that staple cloths provide a good retentivity of solid particles due to the short hairs on their surface. However, cake removal is often difficult from these cloths - more than from cloths of polyfilament and, especially, monofilament fibers. The type of fiber weave and pore size determine the degree of retentivity and permeability. The objective of the process, and the properties of particles, suspension and cake should be accounted for. The cloth selected in this maimer should be confirmed or corrected by laboratory tests. Such tests can be performed on a single filter. These tests, however, provide no information on progressive pore plugging and cloth wear. However, they do provide indications of expected filtrate pureness, capacity and final cake wetness. 

From the perspective of protective clothing selection and chemical resistance, the pesticide formulation types may be more generally categorized as ... 

As discussed earlier, the washed oxide produced is very sticky, making it hard to handle in ordinary equipment. We are working at different levels to solve this problem. Present efforts address the filter operation, including the filter cycle, cloth selection, process parameters and blending equipment. 

The critical in 5)ortance of filter cloth selection in filter press systems has been stressed in the literature [Regan, 1977], As discussed above, methods of filter cloth selection have been based on selection factors [Purchas, 1967, 1981]. These factors include textile fibre type, yam type, fabric geometry and weave pattern. Other factors include cloth shrinkage and stretching, filter cake release, cloth sur ce characteristics and cleaning. These added factors are considered below. 

The following is a recommended sequence of tests that can assist in cloth selection for continuous vacuum filters. 

When the cycle consists of filtration, washing and dewatering, the tests are considered principally in the same manner. The economic aspects of cloth selection should be considered after complete determination of cloth characteristics. 

A wide variety of filter media are available to suit most applications. Selection of a medium must take into account many factors and requires testwork to be undertaken to evaluate the suitability of a medium for any application. Bearing in mind the critical role played by the medium in a filtration process insofar as an incorrect selection may prevent correct functioning of the filter or lead to high running costs, or it may cause too frequent downtimes, or lead to a liquid product of low quality or to overly wet cakes selection of an appropriate medium becomes self-evident. An investment in cloth selection can prevent avoidable costs after installation of the filtration system. 

From the above, it is clear that the operator has many cloth selection factors to consider in order to obtain optimum performance. Often the only way is by trial and error, guided by broad general principles. Once the optimum cloth is found, the following benefits are obtained a clean filtrate with no loss of solids by bleeding, an economic filtration time (production rate), an easily discharged filter cake, no deterioration of the medium by sudden or gradual blinding and an adequate cloth life. 

If special clothing is required, then the type of clothing selected depends upon the nature of the hazard. 

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