Week 3 Challenge

Task – 3: Distillation

1. Determine the total number of possible different column configuration for separating each of the individual component in the below mentioned composition. Explain at least 4 possible configuration

• Ethane- 0.3 mol%
• n-Pentane-0.2 mol%
• n-Hexane – 0.2 mol%
• n-Heptane-0.3 mol %

Column configuration: 1

In configuration: 1,

• Light key component is Ethane.
• Heavy key component is n-Pentane.

From T-100 ethane was separated as a distillate 1 (99.0% pure) and the rest of the components as Bottoms 1 are sent to the second column named as T-101 where n-pentane (99.9% pure) was separated as a distillate 1.1 and remaining components are in bottom product 1.1.

For T-100,

Minimum Reflux ratio = 0.185 and External Reflux ratio = 0.28.

The performance of the column is shown in below.

For T-101,

Minimum Reflux ratio = 1.907 and External Reflux ratio = 2.7.

The performance of the column is shown in below.

Column configuration: 2

In configuration: 2,

• Light key component is n-Pentane.
• Heavy key component is n-Hexane.

From T-102 Ethane & n-Pentane was separated as a distillate 2 and the rest of the components as Bottom products 2. Then distillate 2 is again fed to column T-104 where Ethen is taken out from top and n-Pentane is separated from bottom (only 40.9% pure). Then the bottom product 2 is fed to the column T-103 where we obtained n-Hexane (99.9% pure) as distillate and rest at bottom.

For T-102,

Minimum Reflux ratio = 0.405 and External Reflux ratio = 1.0.

The performance of the column is shown in below.

For T-104,

Minimum Reflux ratio = 0.002 and External Reflux ratio = 1.2

The performance of the column is shown in below.

For T-103,

Minimum Reflux ratio = 2.631 and External Reflux ratio = 3.2

The performance of the column is shown in below.

Column configuration: 3

In configuration: 3,

• Light key component is n-Hexane.
• Heavy key component is n-Heptane.

From T-105 n-Heptane was separated as Bottom product 3 (99.9% pure) and the rest of the components as distillate 3 which are sent to the second column named as T-106 where n-Hexane (99.7% pure) was separated as bottom product 3.1 and remaining components are in the distillate 3.1.

For T-105,

Minimum Reflux ratio = 0.339 and External Reflux ratio = 0.51

The performance of the column is shown in below.

For T-106,

Minimum Reflux ratio = 0.182 and External Reflux ratio = 0.32

The performance of the column is shown in below.

Column configuration: 4

In configuration: 4, n-Pentane was separated from the mixture. As shown in the below flowsheet, n-Pentane is taken out from bottom product 4 of the column T-107 and the rest of the light key components are separated from the distillate 4.

For T-107,

Minimum Reflux ratio = 0.329 and External Reflux ratio = 0.5

The performance of the column is shown in below.

Task -2,

2. Based on the composition provided in s.no-1 and feed condition of 45°C and 2 barg pressure, determine

• number of stages,
• Optimum feed stage location
• condenser duty,
• reboiler duty,
• vapor loading at each stage,
• liquid loading at each stage

to separate out 99.5 mol% of ethane and 98.5 mol % of n-pentane using distillation column with column operating pressure of 2 barg.

Answer: The short-cut column profile for this task is shown below.

The feed containing all the four components is fed to the column T-108 where ethane is separated (99.5% pure) from the distillate section and the remaining components are in the bottom product. Later the bottom product of T-108 is fed to T-109 to separate n-Pentane. The n-Pentane in distillate-1 is further fed to column T-110 as it still contains Ethane. From T-110, it achieved 99.5% pure Ethane in distillate-2 and 99.5% n-Pentane in bottom product-2. The reflux ratios and performance of all three columns is given below.

Column T-108,

Minimum Reflux ratio = 0.199 and External Reflux ratio = 0.28

The performance of the column is shown in below.

Column T-109,

Minimum Reflux ratio = 1.899 and External Reflux ratio = 2.7

The performance of the column is shown in below.

Column T-109,

Minimum Reflux ratio = 0.5 and External Reflux ratio = 0.75

The performance of the column is shown in below.

Actual distillation,

At column T-111,

• number of stages - 10
• Optimum feed stage location - 4
• condenser duty – 5.067e+005 KJ/h
• reboiler duty – 6.386e+005 KJ/h

The vapour and liquid loading at each stage of the column is given below

At T-112,

• number of stages - 31
• Optimum feed stage location - 17
• condenser duty – 1.38e+006 KJ/h
• reboiler duty – 1.53e+006 KJ/h

The vapour and liquid loading at each stage of the column is given below,

At T-113,

• number of stages - 8
• Optimum feed stage location - 5
• condenser duty – 15231 KJ/h
• reboiler duty – 43173 KJ/h

The vapour and liquid loading at each stage of the column is given below,