Document oM7b0MDM4XvzVmZRBqJNawLQo

Having defined the 'ca tio n el filtration anu decided on th e ^^ filter type requires to fulfill that function the next step is to: Design the m osteconomicalsystem w hich w ill fulfill the function The most economical filtration system usually combines depth filters and screen fil ters. The graphs shown below illustrate the effects of various combinations in a typical process. Fig. 22 shows what happens when the 0 45 /tm screen filter is protected by a rela tively coarse depth filter. (Pressure drop as a function of volume is shown for each filter by the broken line.) Flere, because there is little pressure build-up across the depth filter, it evidently is not providing enough retention efficiency to protect the final filter. As a result, the final filter plugs quite rapidly, and maxi mum pressure is exceeded, with most of the batch still to be processed. In Fig. 23 a much tighter depth filter has been used. The depth filter has more than adequate retention efficiency, but insufficient dirt-holding capacity. This time, it is the depth filter that clogs prematurely. Fig. 24 shows what happens when the depth filter has just the right retention effi ciency and dirt-holding capacity. The proper ties of the two filters are perfectly matched, and overall pressure drop has just reached the pressure limits of the system as the last of the batch has been processed. Note that at the end of the run, both filters have exhausted almost all their dirt-holding capacity. For contrast, Fig. 25 shows what would have happened if the final filter had been used alone, with no depth filter. In some cases, the most economical combination might be a final filter protected by a highly efficient depth filter which is in turn protected by another depth filter which is low in efficiency, but high in dirt-holding capacity. Fig. 22 Screen filter protected by relatively coarse depth 'Iters inadequate prfiltration has resulted in premature cioggmg of screen filter 0 1,000 Liters Volume Filtered Fig 24. Properly matched depth filter and screen filter, resulting in full use of both filter capacities and complete filtration of batch. 4 f , P' Fere tv ic- . 'e< J I y d rn tn f.ner vv th too little 1 r' ' '! ' . cur } ' C . I r.w ' o r c m t i j u < 1 j png of dcDth 0 .000 t iters Volumi 1Itevd : : ; Witlu i,t i m i ii t u t i P n 'h e s e v e n * uer a.. . > , clog s, r<-. " m i : " ' i l : thrr : ` u '