Assuming that the actual rate of washing is 85 percent of the theoretical rate, how long will it take to wash the cake in the press of Prob. 29.4 with a volume of wash water equal to that of the filtrate?

Prob. 29.4

The slurry of Prob. 29.3 is to be filtered in a press having a total area of 8 m² and operated at a constant pressure drop of 2 atm. The frames are 36 mm thick. Assume that the filter medium resistance in the large press is the same as that in the laboratory filter. Calculate the filtration time required and the volume of filtrate obtained in one cycle.

Prob. 29.3

The data in Table 29.6 were taken in a constant-pressure filtration of a slurry of CaCO₃ in H₂O. The filter was a 6-in. filter press with an area of 1.0 ft². The mass fraction of solids in the feed to the press was 0.139. Calculate the values of α, R_m, and cake thickness for each of the experiments. The temperature is 70°F.

Table 29.6

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TABLE 29.6 Data from constant-pressure filtration 5-lb,/in.³ pressure drop (1) Filtrate, Time, lb S 0 2 4 6 8 10 12 14 16 18 0 24 71 15-lb/in. pressure drop (2) Filtrate, Time, lb 5 ongnan 0 5 10 146 15 244 372 524 690 888 1.188 20 25 30 35 0 50 181 385 660 1,009 1,443 2.117 30-lb,/in.² pressure drop (3) Filtrate, lb 0 5 10 15 20 25 30 35 Time, S 0 26 98 211 361 555 788 1,083 50-tby/in. pressure drop (4) Filtrate, Th 10 Time, S 19 68 142 368 524 702