2. 2
Packed Columns
• Processes using packed columns:
• Distillation
• Gas Absorption
• Liquid-liquid extraction
• Continuous gas liquid contact
• No stages involved
• Good gas and liquid distribution throughout the column
• Large interfacial area for diffusion
• Vapors flow upward and reflux steadily goes down, giving perfect counter
current flow arrangement
10. 10
Types of Packing
• Principal requirements of packings are:
• Provide a large surface area: a high interfacial
area between liquid and gas
• Have an open structure: low resistance to gas
flow
• Promote uniform liquid distribution on the
packing surface
• Promote uniform vapor gas flow
11. 11
Types of Packing
Random Packings
Dumped into the column and
take up random arrangement
Such as: Rings, saddles and
proprietary shapes
Structured Packings
With a regular geometry
Such as: stacked rings, grids and
proprietary structured packings
17. 17
• Applications include:
• For difficult separations requiring many stages such as the separation
of isotopes
• High vacuum distillation
• For column revamps: to increase capacity and reduce reflux ratio
requirements
Structured Packing
18. 18
Calculation of Enrichment in Packed Columns
• In a plate column, vapor leaving the plate will be richer in more
volatile component than the vapor entering the plate, by one
equilibrium step.
• The same enrichment of vapor will occur in a certain height of
packing, suggested by Peter and known as HETP, height equivalent of
a theoretical plate.
• All sections of packing will be same physically, so:
• One equilibrium stage=height of packing
• Required height of packing=HETP*(no. of ideal stages required)
19. 19
Murch relationship
• Column diameter = 50-70 mm
• Packing height = 0.9-3 m
• Most of conditions of total reflux
• Vapor rate = 0.18-2.5 kg/m2
s which correspond to 25-80% flooding
• C1, C2 and C3 are constants, vary with packing type given in table 11.4
𝐻𝐸𝑇𝑃 =𝐶1 𝐺
′ 𝐶 2
𝑑𝑐
𝐶3
𝑍
1 / 3
(𝛼 𝜇𝐿
𝜌 𝐿
)
20. 20
Ellis relationship
• Equation for HETP (Zt) of packed column using 25 and 50 mm Raschig
rings:
• dr= the diameter of the rings
• m= average slope of equilibrium curve
• G’=vapor flow rate
• L’=liquid flow rate
𝑍 𝑡 = 18 𝑑𝑟 +12 𝑚
[ 𝐺
′
𝐿
′
− 1
]
21. 21
• HETP concept is used to convert empirically the number of theoretical
stages to packing height.
• most data is for small scale operations, do not provide a good guide
for full-scale plant.
![20
Ellis relationship
• Equation for HETP (Zt) of packed column using 25 and 50 mm Raschig
rings:
• dr= the diameter of the rings
• m= average slope of equilibrium curve
• G’=vapor flow rate
• L’=liquid flow rate
𝑍 𝑡 = 18 𝑑𝑟 +12 𝑚
[ 𝐺
′
𝐿
′
− 1
]](https://image.slidesharecdn.com/packedcolumn1-250218184406-305a10e9/85/Packed-Column-1-design-basics-lecture-pptx-20-320.jpg)
