In short
- Structured packing gives lower pressure drop and a shorter bed for the same separation.
- Random packing is cheaper per cubic metre and far more tolerant of fouling and poor distribution.
- For most acid and chemical gas scrubbing, plastic random packing is the sensible default.
Packing is the heart of a packed tower. It creates the wetted surface where gas and liquid meet, and it largely sets how tall the tower is, how hard the fan works and how often the scrubber needs cleaning. This article compares the two main families, random and structured, for scrubbing duties.
The two families
Random packing consists of individual shaped pieces, such as rings and saddles, poured into the tower. Structured packing consists of corrugated sheets or gauze assembled into blocks with fixed flow channels.
How they compare
The figures below come from a packing manufacturer and are indicative only. Real performance depends on the specific product, size and duty.
| Parameter | Random packing | Structured packing |
|---|---|---|
| Wet pressure drop | 3 to 10 mbar/m | 0.3 to 3 mbar/m |
| Bed height for same separation | Baseline | 30 to 50% shorter |
| Packing cost per m³ | 30 to 60% lower | 30 to 60% higher |
| Turndown | 5:1 to 10:1 | 3:1 to 5:1 |
| Fouling and solids tolerance | Good | Fixed channels can clog |
| Liquid distribution | Tolerant | Needs high-quality distributors |
Height-limited, or worried about fouling?
Send us the duty and the site constraints. We will recommend the packing.
Why random packing suits most acid gas scrubbing
The same manufacturer lists simple acid gas absorption, including HCl, ammonia and SO2, as a typical random packing duty, and reserves structured packing for services such as vacuum distillation where pressure drop is critical.
Scrubbing liquors carry salts that can crystallise, and some extracts carry dust or mist. Random packing tolerates that much better, and plastic random packing is easy to remove and clean. The higher pressure drop is usually a modest cost in fan power at scrubber scales.
When structured packing earns its place
- Where height is fixed, such as inside a building, and a shorter bed is the only way to fit.
- Where fan power is a major running cost and the gas is clean.
- Where very high efficiency is needed in a limited space and liquid distribution can be engineered to suit.
Engineer's note
When a packed tower loses performance, we look at the pressure drop trend first. A steady rise usually points to scale or fouling in the packing; a sudden fall can mean channelling or a disturbed support.
Material matters as much as shape
For acid and chemical duties, packing is normally polypropylene, with PVDF for higher temperatures or aggressive fluorine duties. Published chemical resistance tables rate polypropylene to around 80°C and PVDF to around 100°C in chemical service. For HF, glass or silica-based packing must never be used.
Want to see how we build our towers? Our packed tower scrubbers page covers packing, distribution and mist elimination.
See packed tower scrubbersEvery packed tower scrubber we quote states the packing type, depth and predicted pressure drop on its datasheet.
Common questions
Can I change packing in an existing scrubber?
Often yes, but distributors, supports and fan duty need checking. Switching to structured packing in particular usually needs a better liquid distributor.
How often should packing be cleaned?
It depends on the duty. Rising pressure drop across the bed is the best indicator, which is why a differential pressure gauge across the bed is worth fitting.
Does deeper packing always mean better performance?
Up to a point. Beyond the depth the duty needs, extra packing adds pressure drop and cost without meaningful benefit.