# Distillation Design Questions and Answers – Reflux Stage Relationships

This set of Distillation Design Multiple Choice Questions & Answers (MCQs) focuses on “Reflux Stage Relationships”.

1. Fenske’s Equation can be written as
a) Nmin = S/ ln α
b) Nmin = ln S/ ln α
c) Nmin – 1 = ln S/ ln α
d) Nmin + 1 = ln S/ ln α

Explanation: The Fenske’s equation is given by this equation Nmin = ln S/ ln α, where N is the number of trays and alpha is the relative volatility.

2. The term S in the Fenske’s equation, is given as
a) (xLKxHK)D(xLKxHK)B
b) (xLKxHK)D(xLKxHK)L(xLKxHK)R
c) (xLKxHK)L(xLKxHK)V
d) (xLKxHK)HK(xLKxHK)LK

Explanation: The term S in the Fenske’s equation is given as (xLKxHK)D(xLKxHK)B, representing High and Low keys of the gas and liquid phases.

3. N√αN this equation is called as
a) Sorel’s Method
b) Polson Equation
c) Fenske’s Equation
d) Gilliland Equation

Explanation: Fenske’s Equation that is rigorous, Gilliland Equation are used and based on the trial and error basis.

4. Calculate ln S? If XLK=0.41 and XHK = 0.005 and XL= 0.417 and XH= 0.01, then
a) 9.45
b) 8.90
c) 8.137
d) 7.98

Explanation: As ln (0.41/0.005) (0.417/0.01) = 8.137.

5. A non-key component may be distributed if
a) Close to that of one key
b) The Specified separation is sloppy
c) Intermediate between keys
d) Intermediate one key

Explanation: For distributed systems the Specified separation is sloppy, while for the distributed system it is close to that of one key.
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6. In a distillation operation, the reflux ratio may vary between
a) Zero and one
b) Zero and infinity
c) Minimum and infinity
d) One and two

Explanation: L0/D Varies from zero to one, as the ratio cannot be more than one because that will cause the failure of the column.

7. Most distillation columns are designed for reflux ratio between
a) 3 to 5 Rmin
b) 1.2 and 1 .7 Rmin
c) 2 to 10 Rmin
d) 0.2 to 0.7 Rmin

Explanation: This is the most suitable for 1.2 and 1.7 Rmin times reflux ratio, this also reduces the operating and the final cost of the system.

8. If Component is non-distributed, then
a) DR >1
b) DR<1
c) DR=0
d) DR=∞

Explanation: If component is non-distributed then DR >1 contained entirely distillate, while if components are distributed they are entirely withdrawn.

9. If Component is distributed, then
a) 0< DR> 1
b) 0< DR< 1
c) DR= 0
d) DR < 0

Explanation: If Component is distributed then 0< DR< 1, DR is recovery component, if DR = 0 then there exists no distributed components in the systems.

10. Underwood’s equation can be used to find
a) Distributed components
b) Non distributed components
c) Reflux for components
d) Non reflux components

Explanation: Underwood’s equation can be used to find Distributed components (n) including key.

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