This set of Separation Processes Multiple Choice Questions & Answers (MCQs) focuses on “Solid-liquid Cascades”.

1. 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}

View Answer

Explanation: 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. 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}

View Answer

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

3. 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}

View Answer

Explanation: 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. 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 )

View Answer

Explanation: 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. 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} )

View Answer

Explanation: (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. 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}

View Answer

Explanation: The cascade for any given S, maximizes Y

_{1}, the amount of B dissolved in a solvent nleaving stage 1.

7. 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

View Answer

Explanation: S

_{min}=RF

_{A}, thus S

_{min}= 2ooo*0.5=1oookg/hr.

8. 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

View Answer

Explanation: Since W= S/RF

_{A}, W= 3000/2000*0.5=3.

9. 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

View Answer

Explanation: S

_{min}=RF

_{A}, thus S

_{min}= 2oo*0.3=600kg/hr.

10. 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

View Answer

Explanation: Since W= S/RF

_{A}, W= 2500/500*0.3=16.66.

11. 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

View Answer

Explanation: Since W= S/RF

_{A}, W= 2500/1000*0.5=2.5.

12. 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

View Answer

Explanation: Since W= S/RF

_{A}, W= 2800/2000*0.7=2.

13. 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

View Answer

Explanation: Since W= S/RF

_{A}, W= 3000/10000*0.2=1.5.

14. 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

View Answer

Explanation: Since W= S/RF

_{A}, W= 1000/10000*0.1=1.

15. 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

View Answer

Explanation: Since W= S/RF

_{A}, W= 2300/2000*0.3=3.83.

**Sanfoundry Global Education & Learning Series – Separation Processes.**

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