Pall ring or Raschig ring?

The published difference

Our published comparison, taken from the Pall ring product data, is stated against the Raschig ring as a baseline:

Gas throughput	More than 50 % higher
Mass transfer efficiency	About 30 % better
Capacity	More than 50 % higher
Pressure drop	50 % lower
Published surface area range	Metal 70–240 m²/m³, plastic 73–287 m²/m³, ceramic 110–260 m²/m³
Void space	70–95 % across the published range

Those four figures are the reason a Pall ring is the default in new absorption, scrubbing, stripping and degassing columns. The physical explanation is simple: the open wall lets gas and liquid meet on both faces of the same piece of material, instead of only on the outside of a closed cylinder, and the inward tongues redistribute liquid that would otherwise run down the wall.

When the Raschig ring is still the right answer

Dirty service. A closed cylinder has one continuous internal surface and no small windows to bridge. In a stream carrying solids or polymerising material, the Pall ring's windows are the first thing to block, and a blocked Pall ring performs worse than a clean Raschig ring.

Very high temperature or aggressive chemistry, with ceramic. Ceramic is available in both forms; where the specification is ceramic for temperature and chemical resistance, the geometry decision is made on the pressure-drop budget rather than on cost per cubic metre.

Small beds where the pressure drop does not matter. If the column has margin on both blower pressure and efficiency, the cheaper ring can be the honest choice. We will say so rather than upsell a bed that does not need it.

Sizing the ring: the trade that never goes away

Smaller nominal size means more surface per cubic metre and better separation, at the cost of pressure drop. In our published metal range the surface area falls from 240 m²/m³ at 16 mm to 70 m²/m³ at 76 mm while the dry packing factor falls from 300 to 80 m−1. Sizes run from 16 × 16 × 0.8 mm to 76 × 76 × 1.2 mm in metal and plastic, and 25 × 25 × 3 to 80 × 80 × 8 mm in ceramic.

Quantity is ordered by bed volume, and the packing count per cubic metre is published per size - from roughly 143,000 pcs/m³ at 16 mm down to 1,860 pcs/m³ at 76 mm - so the delivered quantity can be checked rather than assumed.

Product pages: Pall ring packing · Hacketten · Teller Rosette ring · guide: packing selection guide.

Frequently asked

Is a Pall ring always better than a Raschig ring?

In clean service, on capacity, efficiency and pressure drop, yes - our published comparison shows more than 50 percent higher gas throughput and capacity, about 30 percent better mass transfer and half the pressure drop. In dirty or fouling service the closed Raschig ring can outperform it because there are no windows to bridge.

What size Pall ring should I use?

The largest size that still meets the separation duty. Going one size down gains surface area but costs pressure drop: published metal surface area runs from 240 m2/m3 at 16 mm to 70 m2/m3 at 76 mm, with the dry packing factor falling from 300 to 80 per metre over the same range.

Metal, plastic or ceramic?

Plastic (polypropylene) for scrubbers and absorbers at moderate temperature with corrosive liquors; metal where the column runs hot or the solvent attacks polypropylene; ceramic where temperature and chemical resistance requirements rule out both. The published ranges differ, so the material choice changes the surface area figure you design against.

How is the quantity calculated?

Bed volume from the column cross-section and bed height, then checked against the published packing count per cubic metre for the size chosen. Every size in our table has its own count, so the delivered quantity can be verified against the volume ordered.