Packed towers are widely used in chemical plants for gas absorption, scrubbing, and degassing. Their purpose is to maximize gas–liquid contact, which makes the design of internal structures and sizing very important.
For batch operations, packed towers are often the go-to choice, even though they may not be as visually iconic as tray towers. Understanding the design flow helps beginners read specifications, review drawings, and communicate with equipment vendors.
This guide explains the basic structure and step-by-step design process of packed towers in simple terms.
Overall Structure
A packed tower is a vertical column where gas flows upward and liquid flows downward (counter-current flow). Internal components ensure even distribution and efficient contact.
Packing
The heart of the tower. Packing promotes dispersion of liquid and gas, preventing channeling.
- Random packing: small pieces like Pall rings or saddles; easier maintenance, suited for batch plants.
- Structured packing: arranged blocks; higher efficiency, widely used in continuous plants.
Support Grid
A grid or grating that holds the weight of packing and liquid. Proper open area must be maintained to avoid pressure drop and flooding.
Feed Pipe / Distributor
Introduces liquid evenly across the cross-section.
- Pipe distributors: common for small diameters.
- Trough distributors: used when pressure drop is critical or for larger diameters.
Always design them for removal and cleaning access.
Redistributors
For tall towers, intermediate collectors and redistributors ensure liquid remains evenly spread throughout the column height.
Tower Diameter
A balance:
- Too small → high gas velocity → flooding, pressure drop.
- Too large → increased cost and higher liquid circulation needs.
Diameter selection is a trade-off between hydraulics and economics.
Packing Height
Typically based on past plant experience or empirical data. Theoretical stage concepts from distillation can be applied, but not directly.
Materials of Construction
- Stainless steel: common choice, consistent for shell, packing, and distributors.
- Glass-lined steel: requires resin or ceramic internals; extra care for abrasion.
Material selection must consider chemical compatibility, pressure, and maintenance.
Pressure and Operating Range
Packed towers often operate from vacuum to near-atmospheric conditions. Ensure the top and bottom heads are designed to withstand external pressure under vacuum.
Applications
- Distillation (in batch processes)
- Gas absorption and scrubbing systems
Maintenance is key in fouling or salt deposition services.
Conclusion
Packed towers look simple but require careful design of packing, distributors, supports, and sizing. For beginners, following a logical design flow—from process conditions to materials—makes the task much clearer.
By mastering these basics, you’ll gain confidence in reviewing drawings and specifications, and in discussing designs with vendors or senior engineers.
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