Section 7 common
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This document discusses rules and examples for constant pressure and constant rate filtration. It provides the equations to calculate specific cake resistance, filter medium resistance, and filter area needed based on given slurry characteristics and operating parameters. It also presents sample calculations for these values using data from constant pressure filtration experiments and relates specific cake resistance to operating pressure for a given material. Finally, it poses a follow up problem calculating total filtration time under changing operating conditions.
Section 7 common
- 1. Common Mechanical Operation Section 7 Eng. Kareem H. Mokhtar
- 2. Rules • Constant pressure filtration • Plot t/v versus v to get (Kp/2) as a slope and B as the intercept
- 3. • Constant rate • Draw delta P against time, at time=zero get delta Pm • Plot log t versus log delta Pc to get (1-S) as a slope • Get Kr • Get alpha
- 4. Q1 • It is required to evaluate the characteristics of the cake obtained on filtering a slurry containing 120 kg/m3 water using canvas filter medium. To this effect, a one plate filter of dimensions 300×300 mm2 was used under a positive pressure of 0.8 atmg. The following data were obtained for the variation of volume of filtrate with time. • Estimate the specific cake resistance and the filter medium resistance
- 5. Q1- Answer • Const. P V 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 T/v 840000 1140000 1400000 1590000 1824000 2040000 2245714.29 2445000 y = 5E+08x + 677148 0 500000 1000000 1500000 2000000 2500000 3000000 0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045
- 6. • Kp = 109 s/m6 and B = 677148 s/m3 • Alpha = 5.4 x 1012 m/kg • Rm = 4.87x 1012 m-1
- 7. Q4 • The following relation has been determined between specific cake resistance and pressure drop for light P.E. • A slurry of this material containing 50 kg of cake per cubic meter filtrate is to be filtered under a constant pressure of 70 psig. Taking the filter medium resistance as 4x 1010 m-1 , how many square meters of filter surface are needed to yield 7 m3 of filtrate in one hour filtration? • Where, ∆p is in psi and α in ft/lb.
- 8. Q4 - answer • 3600/7 = Kp * (7/2) +B • From relation: alpha= 8.9x 1010 ft/lb = 5.43 x 1010 m/kg • Kp = 0.001∗5.43∗1010∗50 𝐴2∗4.76∗105 • B = 0.001∗4∗1010 𝐴∗4.76∗105 • A= 6.31 m2
- 9. Assignment Next time • 5)The filter in problem (2) is operated at constant rate = 15 lit.m-2 .min-1. from the start of the run until the pressure reaches 70 psig. Then a constant pressure is applied until 40 lit of filtrate are collected. Calculate the total time required for filtration