Separation Processes Questions and Answers – Stage Efficiency and Column Height for Trayed Columns

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This set of Separation Processes test focuses on “Stage Efficiency and Column Height for Trayed Columns”.

1. When it is not assumed that the vapor and liquid leaving a stage are not at same temperature?
a) When pressure changes from stage to stage
b) When temperature changes from stage to stage
c) When concentration of solute changes from stage to stage
d) When concentration of vapor changes from stage to stage
View Answer

Answer: b
Explanation: When temperature changes from stage to stage it cannot be assumed that the vapor and liquid leaving a stage are not at same temperature.
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2. To determine the actual number of required plates for a trayed column, what must be used?
a) K values
b) Process efficiency
c) Stage efficiency
d) Equilibrium between vapor and liquid
View Answer

Answer: c
Explanation: To determine the actual number of required plates for a trayed column, stage effieiency or tray efficiency must be used.

3. What is the formula for overall stage efficiency given by lewis?
a) E o = Nt /N a
b) Eo = Nt N a
c) Eo = Nt -N a
d) Eo = Nt +N a
View Answer

Answer: a
Explanation: The formula for overall stage efficiency given by Lewis is E o = Nt /N a , where Eo is the fractional stage efficiency, N t is the calculated equilibrium stages and N a is the actual number of required plates.

4. The overall stage efficiency is not a complex function of which of the following?
a) Geometry and design of contacting trays
b) Flow rates and flow paths for liquid and vapor phases
c) Compositions and properties of vapor and liquid phases
d) Material of the tray used
View Answer

Answer: d
Explanation: The overall stage efficiency is not dependent on the material of the plates used.

5. What is the height added above the top tray to remove the entrained liquid?
a) 2ft
b) 4ft
c) 6ft
d) 8ft
View Answer

Answer: b
Explanation: 4ft is added above the top tray to remove the entrained liquid.
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6. What is the height added below the bottom tray for bottom surge capacity?
a) 4ft
b) 6ft
c) 8ft
d) 10ft
View Answer

Answer: d
Explanation: The height of 10ft is added below the bottom tray for bottom surge capacity.

7. When are the columns in series preferred?
a) If the estimated height is above 100ft
b) If the estimated height Is above 150ft
c) If the estimated height is above 250ft
d) If the number of trays are less
View Answer

Answer: c
Explanation: If the estimated height is above 250ft, columns in series are preferred.

8. What is the tallest column in the world?
a) 240ft
b) 248ft
c) 300ft
d) 338ft
View Answer

Answer: d
Explanation: The tallest column in the world located at Shell Company, texas is 338ft.

9. What are the actual numbers of required plates when the overall stage efficiency is 0.8 and the calculated equilibrium stages are 4?
a) 2
b) 3
c) 5
d) 7
View Answer

Answer: c
Explanation: By E o = Nt /N a , N a = 4/0.8=5.
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10. What are the actual numbers of required plates when the overall stage efficiency is 0.9 and the calculated equilibrium stages are 9?
a) 12
b) 11
c) 5
d) 10
View Answer

Answer: d
Explanation: By E o = Nt /N a , N a = 9/0.9=10.

11. What are the actual numbers of required plates when the overall stage efficiency is 0.7 and the calculated equilibrium stages are 2.8?
a) 2
b) 4
c) 5
d) 7
View Answer

Answer: b
Explanation: By E o = Nt /N a , N a = 2.8/0.7=4.

12. What are the actual numbers of required plates when the overall stage efficiency is 0.6 and the calculated equilibrium stages are 4.8?
a) 8
b) 3
c) 5
d) 7
View Answer

Answer: a
Explanation: By E o = Nt /N a , N a= 4.8/0.6=8.

13. What is the overall stage efficiency if the calculated equilibrium stages are 8 and the actual plates required are 12?
a) 0.75
b) 0.6
c) 0.56
d) 0.12
View Answer

Answer: a
Explanation: By E o = Nt /N a , E o = 8/12 = 0.75.
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14. What is the overall stage efficiency if the calculated equilibrium stages are 9 and the actual plates required are 11?
a) 0.75
b) 0.82
c) 0.56
d) 0.12
View Answer

Answer: b
Explanation: By E o = Nt /N a , E o = 9/1 = 0.82.

15. What is the overall stage efficiency if the calculated equilibrium stages are 7 and the actual plates required are 13?
a) 0.75
b) 0.6
c) 0.54
d) 0.12
View Answer

Answer: c
Explanation: By E o = Nt /N a , E o = 7/13 = 0.54.

Sanfoundry Global Education & Learning Series – Separation Processes.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn