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# Separation Processes MCQ’s – Solid-liquid Cascades

1 - Question

A material balance for any soluble material B around any interior stage from n=2 to N-1 is:

a) Y n+1 S + X n-1 RF A =Y n S + X n RF A

b) Y n+1 S + X n-2 RF A =Y n S + X n RF A

c) Y n+1 S + X n+1 RF A =Y n S + X n RF A

d) Y n+1 + X n-2 RF A =Y n S + X n RF A

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Answer: aExplanation: Material balance for any soluble material B around any interior stage from n=2 to Y n+1 S + X n-1 RF A =Y n S + X n RF A Where Y j is the mass of solute per mass of solvent and F A is the mass flow rate of slurry and R is the constant ratio of mass of solvent to mass of insoluble solids.

2 - Question

Which equation holds true at equilibrium?

a) Y N+1 = Y N

b) X N = Y N

c) F B = F A

d) R 1 =R 2

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Answer: bExplanation: At equilibrium the concentration of B in each overflow equals the concentration of B in liquid part.

3 - Question

What is the formula for washing factor?

a) W= SRF A

b) W= RF A /S

c) W=SF A/R

d) W=S/RF A

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Answer: dExplanation: The formula for washing factor is W=S/RF A, where F A is the mass flow rate of slurry and R is the constant ratio of mass of solvent to mass of insoluble solids.

4 - Question

The concentration of solute is given by:

a) (F B /S)(1/W Nsub>n-1 )

b) (F B S)(1/W sub>n-1 )

c) (F B /S)(1/W sub>n-1 )

d) (F B S)(W sub>n-1 )

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Answer: cExplanation: The concentration of solute X N is given by (F B /S)(1/W sub>n-1 ) where S is the flow rate at stage N and F B is the mass flow rate of slurry and W is the washing factor.

5 - Question

What will be the concentration of solute in overflow doe N=2?

a) (F B /S)(1/W +1)

b) (F B /S)(1+W+W 2 /W 2 )

c) (F B /S)(1+W+W 2 /W)

d) (F B /S)(1+W/W 2 )

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Answer: aExplanation: (F B /S)(1/W +1) is the equation used. Now for N=2, (F B /S)(1/W +1)= (F B /S)(1/W +1)

6 - Question

Which of the following is true about cascades for a particular S?

a) Maximizes Y 1

b) Maximizes X N

c) Minimizes Y 1

d) Does not affect X N

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Answer: aExplanation: The cascade for any given S, maximizes Y 1 , the amount of B dissolved in a solvent nleaving stage 1.

7 - Question

The minimum amount of solvent required is underflow ratio is 0.5 and insoluble solids feed rate is 2000Kg/hr is:

a) 2000kg/hr

b) 1000kg/hr

c) 4000kg/hr

d) 500kg/hr

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Answer: bExplanation: S min =RF A , thus S min = 2ooo*0.5=1oookg/hr.

8 - Question

What is the washing factor if solvent feed rate is 3000kh/hr , underflow ratio is 0.5 and insoluble solids feed rate is 2000?

a) 2

b) 3

c) 4

d) 5

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Answer: bExplanation: Since W= S/RFA , W= 3000/2000*0.5=3.

9 - Question

The minimum amount of solvent required is underflow ratio is 0.3 and insoluble solids feed rate is 200Kg/hr is:

a) 50kg/hr

b) 600kg/hr

c) 666.66kg/hr

d) 60kg/hr

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Answer: dExplanation: S min =RF A , thus S min = 2oo*0.3=600kg/hr.

10 - Question

What is the washing factor if solvent feed rate is 2500kh/hr , underflow ratio is 0.3 and insoluble solids feed rate is 500?

a) 13.33

b) 166.66

c) 16.66

d) 133.33

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Answer: cExplanation: Since W= S/RFA , W= 2500/500*0.3=16.66.

11 - Question

What is the washing factor if solvent feed rate is 2500kh/hr , underflow ratio is 0.5 and insoluble solids feed rate is 2000?

a) 0.5

b) 1

c) 1.5

d) 2.5

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Answer: dExplanation: Since W= S/RFA , W= 2500/1000*0.5=2.5.

12 - Question

What is the washing factor if solvent feed rate is 2800kh/hr , underflow ratio is 0.7 and insoluble solids feed rate is 2000?

a) 1

b) 2

c) 3

d) 4

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Answer: bExplanation: Since W= S/RFA , W= 2800/2000*0.7=2.

13 - Question

What is the washing factor if solvent feed rate is 3000kh/hr , underflow ratio is 0.2 and insoluble solids feed rate is 10000?

a) 1

b) 2.5

c) 1.5

d) 4

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Answer:cExplanation: Since W= S/RFA , W= 3000/10000*0.2=1.5.

14 - Question

What is the washing factor if solvent feed rate is 1000kh/hr , underflow ratio is 0.1 and insoluble solids feed rate is 10000?

a) 1

b) 2

c) 3

d) 4

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Answer: aExplanation: Since W= S/RFA , W= 1000/10000*0.1=1.

15 - Question

What is the washing factor if solvent feed rate is 2300kh/hr , underflow ratio is 0.3 and insoluble solids feed rate is 2000?

a) 1.97

b) 2.33

c) 3.07

d) 3.83

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Answer: cExplanation: Since W= S/RFA , W= 2300/2000*0.3=3.83.