Optimum filtration

If ah of the nonfiltration operations are grouped together into a downtime, assumed to be fixed and known, an optimum filtration time in relation to p can be derived by optimizing the average dry cake production obtained from the cycle. Eor constant pressure filtration and where the medium resistance R and the specific cake resistance are constant, the fohowing equation appHes ... 

When the medium resistance R is smah compared with the specific cake resistance (, the second term in the above equation becomes negligible and the optimum filtration time becomes equal to downtime p. For any other case, p is always greater than p. It fohows, therefore, that the filtration time... 

The results of simulation have been confirmed by determination of Fe traces in quai tz sand, Cu and Mo in flotation tails and Ag in waste fixing waters on BRA-17-02 analyzer based on X-ray gas-filled electroluminescent detector and on BRA-18 analyzer based on Si-drift detector. The results of the simulation conform satisfactory with the experimental data in the mentioned cases the optimum filtration results in 2 to 5 times lowering of the detection limit. 

If the operating cost during filtration is 10/ks and the cost of a shutdown is 100, what is the optimum filtration time for minimum cost ... 

Powders vary dramatically in particle size on the basis of their origin. It is common for catalyst manufacturers to classify powders in order to assure users of consistency from batch to batch since suspension, settling rates, filtration, and performance in slurry-phase reactions are all dependent on particle size. The effect on suspension, settling rates, and filtration is obvious. However, factors that favor these are unfavorable for kinetics. For reactions controlled by transport rates from the bulk fluid to the surface of the catalyst, the overall reaction rate is a strong function of geometric surface area and thus is favored by small particles. Pore diffusion resistance is also minimized by smaller particles since reaction paths to active sites are smaller. The only mode of reaction control not influenced by particle size is for those reactions in which rate is controlled by reaction at active sites. Therefore, a compromise for optimum filtration and maximum reaction rates must be made. 

The differential pressure is initially low and increases gradually, depending on adjustments to the accretion process. Optimum filtration conditions require a pressure increase of 0.1-1 bar per hour throughout the cycle. 

It may be noted, as a consequence of these relationships, that the filtration time for a given quantity of filtrate is proportional to the square of the thickness of the cake at the end of the filtration. Maximum filter productivity WIA(6 + 6 under batchwise constant-pressure filtration, with the medium resistance neglected, is obtained when the filtration time 6 is equal to the downtime 0, which is the sum of the time required to remove the product cake and to prepare the medium for the next cycle. The greater the resistance of the filter medium and the longer the preparation downtime, the longer is the optimum filtration time and the thicker is the optimum cake. 

In the case of nonwoven fabrics, a reduction in pore size is achieved by compressing the fibres into a more dense structure (loads up to 300decaNm" may be necessary) and, by selection of the appropriate conditions, a more durable (Fig. 3.31) surface can also be obtained through partial fusion of the surface fibres. With woven fabrics, on the other hand, some deformation of the yams may be necessary to achieve the optimum filtration properties. This is particularly graphic in the case of fabrics woven from monofilament yams, as shown in Fig. 3.32 and Fig. 3.33. 

As a general rule, a suitable filter aid should be capable of creating a thin layer structure with a maximum pore size over the medium s external surface and producing a prespecified filtrate clarity at an optimum filtration rate. 

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