# Distillation Design Questions and Answers – Theoretical Stages

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This set of Distillation Design Multiple Choice Questions & Answers (MCQs) focuses on “Theoretical Stages”.

1. An ideal distillation stage is the one that
a) Operates at steady state
b) Operates at High temperature
c) Operates at Low pressure
d) Operates at high pressure

Explanation: An ideal distillation stage operates at steady state has liquid product and vapor product, i.e. Liquid rate equals the gas flow rate.

2. When heat is supplied to bottom of liquid stage to vaporize a portion it is called
a) Condensing
b) Boil up
c) Cooling
d) Desalting

Explanation: Such operations used in stripping section called as Boil up, the boiler is used as a heat exchanger to reheat the condensed liquid.

3. When Cooling is applied to condense a part of overhead product it is called
a) Reflux
b) Dew point
c) Boil Up
d) Relative BP

Explanation: Such operations is called as Rectifying stages and called Reflux, It is also called the ratio of distillate and liquid flow rate.
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4. When rectifying and stripping both are combined in single stage process this is
a) Differentiation
b) Fractionation
c) Recycle
d) Purging

Explanation: Such is an operation is also called Fractional Distillation, The moles of the components reduce with respect to time in this operation.

5. Minimum number of trays can be calculated using
a) Bernoulli’s Eon
b) Henry’s Law
c) Fenske’s Equation
d) Homotomy Equation

Explanation: Minimum number of trays can be easily calculated using Fenske’s equation with use of relative volatility.

6. The external reflux ratio can be defined as
a) L0/D
b) D/L
c) D0/L
d) V/L

Explanation: The reflux ratio is defined as the ratio of liquid flow rate and distilled flow rate, also this is called as the slope of rectifying line.

7. The boil up ratio can be defined as ratio of
a) V/L
b) D/V
c) V/W
d) L/W

Explanation: Boil up ratio is the ratio of vapor leaving the rebuilder to liquid at bottom product, also it is defined as the slope of stripping line.

8. Optimum reflux ratio ranges between
a) 2 to 5
b) 2 to 3
c) 1.0 to 1 .5
d) 1.0 to 2.5

Explanation: Best optimum reflux is between ranges. 1.0<R<1.5, as it is very close to unity the optimum conditions are best condition to operate.

9. If stages are fixed, then Reflux ratio
a) Decreases
b) Increases
c) Equates to 0
d) Approaches infinity.

Explanation: The stages and the reflux ratio are directly proportional, while when it approaches to 0 the distillate is not withdrawn and if infinite all feed is withdrawn.

10. If reflux increases, then the cost of operation
a) First increases then decreases
b) Goes on increasing
c) Approaches infinity
d) First decreases then increases