Page 334 - Chemical process engineering design and economics

Separator Design 313

10
T>
/n
a = 1.604x10'" (P 0-P0 -vO.2664
where P 0 - Pj is in bars and a in m/kg. The pressure at the interface of the filter
cake and filter medium, Pj, is assumed to be equal to the pressure downstream of
4
the filter medium, P v. Therefore, P 0 - P v = 0.658 bar or 6.58xl0 Pa according to
Walas [6.6] for filtering a CaCO 3 slurry. Therefore,
0 2664
10
10
10
a = 1.604xl0 (0.658) ' = 1.435xl0 m/kg (2.14xl0 Mb)
McCabe and Smith [23] state that the cycle time for filtering CaCO 3 is 5
min. According to Table 6.20, 37.5 % of the drum is submerged during filtration.
Because the drum is only partially submerged, the filtering time,
tf= 0.375 (5) (60)= 112.5s

The volume of filtrate collected,

3
3
V F = V 2 t F = [(18.86 / 3600)] (112.5) = 0.5894 m (20.8 ft )
From Equation 6.18.8, the concentration of solids in the entering stream,

3
3
c u = 0.15 (1255) = 188.3 kg/m (11.76 lb/ft )
Finally, the filter area can now be calculated from Equation 6.18.5.

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(1-0.2664) 1.435xl0 m 0.001 Pa-s 188.3kg (0.5894) 2 m 6
2 _
2 (115.5) s 1 kg 6.58xl0 4 Pa 1m 3 1
2
2
A F = 6.731m (72.4 ft )
According to Equation 6.18.6, the drum area,

2
A T = 6.731 / 0.375 = 17.95 m 2 ( 193 ft )
From Table 6.20, a standard filter has 250 ft2 (23.2 m2) of surface area. This
choice will result in a safety factor of 29.5%. The final decision on the filter size,
will require laboratory or pilot plant tests. In most cases, the filter manufacturer
will provide this service.

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