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• Nur Adibah Hassan

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Tutorial Week 8: Filtration

1.

a)

Hindered flow is observed when large number of particles are present in a settling process” – Do you agree with statement? Justify your answer. [4 marks]

b)

Calculate the flow rate of filtrate (m3 filtrate/s) if a rotary-drum is used to filter a slurry where concentration of solid in slurry is 0.191 kg solids/ kg slurry and density of water is 996.6 kg/m 3. The filter cake is such that the ratio of weight of wet cake to dry cake is 2.0. The area of the filter is 2.20 m2 and 28% of the drum is submerged in the feed. The filter-cycle time is 300 s and pressure drop is 62.0 kN/m2. Assume that the specific cake resistance is 1.1971011 m/kg and the filter medium resistance can be neglected. You may use the equation given below. 𝑉 2𝑓 (−∆𝑃) 1/2 =[ ] 𝐴𝑡 𝑡𝛼𝜇𝑐𝑠

Where, V

=

Filtrate volume, m3

t

=

Filtration cycle, s

A

=

Filter area, m2

f

=

fraction of drum used for cake formation

α

=

cake resistance, m/kg

-Δp

=

pressure drop, N/m2

µ

=

viscosity, 0.8937 x 10-3 Pa.s

cs

=

Solid concentration in filtrate, kg solids/ m3 filtrate

[6 marks]

Internal

2.

a.

Explain in term of specific cake the difference between the compressible and incompressible cake. [2 marks]

b)

Filtration for separating CaCO3 from water by plate and frame filter press under constant pressure the following equation is used:

dt  K pV  B ; dV Where t = time of filtration, V= total volume of filtrate collected, Kp and B are filtration constants At the end of the filtration cycle, a total filtrate volume of 3.37 m 3 is collected in total time of 269.7 s. The cake is to be washed by thorough washing in the plate-and-frame press using a volume of wash water equal to 10% of the filtrate volume. The values of the constants are given as the following: Kp = 37.93s / m6 ; B = 16.10 s/m3 Cleaning the filter takes 20 min. Calculate: i.

The time of washing [4 marks]

ii.

Total filter cycle time [4 marks]

Internal

3.

a)

Filtration using filter press is usually operated at constant pressure. The filtration rate of slurry is depending on several important factors. Give ONE (1) most important factor that control the filtration rate and explain how this factor influence the rate of cake formation in the frame. [2 marks]

b)

An experimental filter press having an area of 0.0414 m 2 is used to filter aqueous BaCO3 slurry at a constant pressure of 267 kPa. The filtration equation obtained was

t  10.2510 6 V  3.4 10 3 V Where: t V

Internal

= filtration time (s) = filtrate volume (m3)

i.

If the same slurry and conditions are used in a leaf press having an area of 6.97 m2, how long will it take to obtain 1.00 m3 of filtrate? [4 marks]

ii.

After filtration, the cake is to be washed with 0.100 m3 of water. Calculate the time of washing. Assume that the wash water rate is equivalent to the filtration rate. [4 marks]