Pall Rings as Efficient Packing Solutions for Wet Scrubbers

Author: Michael Klepik, Chief Executive Officer

Unlike Raschig rings, Pall rings have a more complex structure due to additional struts, walls, and lamellae. These design elements significantly increase the contact area between the two phases (liquid and gas), leading to improved efficiency.

Their more open structure allows for increased liquid irrigation and reduced gas flow resistance through the mass transfer layer. This positively impacts reaction speed and energy consumption.

Pall rings are effective for removing the following contaminants:

• Sulfur compounds (SO₂, H₂S)
• Carbon dioxide (CO₂)
• Ammonia (NH₃)
• Nitrogen oxides (NOₓ)
• Acid gases (HCl, HF)
• Organic compounds (VOCs)
• Heavy metals (mercury, lead)

Pall rings are continuously tested in both laboratory and field trials across various projects. This extensive experience has resulted in a robust mathematical and chemical framework that enables accurate project calculations and ensures the desired efficiency.

Reaction Rate
Thanks to their complex branched structure and increased phase contact area, Pall rings allow for greater flexibility in regulating the reaction rate inside the scrubber. This makes it possible to reduce the packing layer thickness while maintaining high process efficiency.
Bulk Density
The optimized shape of Pall rings allows for a reduction in the height of the packing layer and the column diameter compared to Raschig rings. This decreases the overall amount of material used and enhances mass transfer efficiency.
Aerodynamic Resistance
The more open structure of Pall rings provides significantly lower aerodynamic resistance compared to Raschig rings. This improves gas circulation and reduces energy consumption within the system.

Plastic Rings:
✔ Have low density, which reduces the load on equipment.
✔ Resistant to corrosion and aggressive chemical environments, including acids and alkalis.
✔ Have low hydraulic resistance and good throughput capacity.
✔ Limited in application due to temperature constraints (usually up to 150°C).

It is also important to consider that commercial efficiency depends on the resistance of the scrubber column, which directly affects your electricity costs. The higher the aerodynamic resistance of the column, the more powerful a fan is required, increasing the overall cost of processed material.
The size of the column is a crucial factor. Compared to Raschig rings, Pall rings allow for a narrower yet taller column while maintaining comparable resistance. This means that the overall efficiency of the scrubber is higher. As a result, we can reduce pressure drop while increasing throughput.
Pall ring sizes range from 14-16 mm to 150-200 mm. This flexibility allows us to design scrubbers of virtually any size and air handling capacity, offering a wide range of applications for Pall rings. Smaller sizes are used in columns with high packing density, while larger sizes are suitable for columns with low density.
Additionally, we can model the efficiency of columns with Pall rings, leveraging over a century of accumulated knowledge.
The packing effect inside the column is also significant. Due to their open structure and optimized surface distribution across the scrubber’s cross-section, Pall rings provide greater phase contact, directly improving the scrubber’s speed and efficiency.
Since liquids can more easily flow through the packing, fluid replacement on the packing surface occurs rapidly, enhancing mass transfer.
The ability of Pall rings to retain liquid on their surface increases the absorption effect. This feature allows engineers to design scrubbers that either slow down or accelerate reaction rates depending on process requirements.
The support strut structure of Pall rings ensures high mechanical strength, enabling the use of taller packing layers.
Finally, flow turbulence in the packing mass plays a crucial role. Due to the random arrangement of the packing inside the scrubber, Pall rings create a natural barrier between the liquid and gas phases. This interaction generates turbulent effects, further improving scrubbing efficiency.

In the chemical industry, Pall rings are widely used in ammonia, carbon dioxide, and other gas absorption processes, where their superior performance significantly reduces waste. Recent studies show that using Pall rings in these processes increases mass transfer coefficients and reduces energy consumption by 10-15%.
In large manufacturing facilities such as chemical plants or petrochemical complexes, there is often a need to clean emissions from harmful gases such as ammonia, sulfur compounds, nitrogen oxides, and other toxic substances.
Studies show that their use in such installations significantly improves the absorption of pollutants. As gas passes through a column with Pall rings, it effectively interacts with the liquid phase, which helps to reduce the concentration of harmful substances in emissions to levels that meet strict environmental standards. This approach ensures a higher cleaning speed and reduces the load on equipment, lowering operational and maintenance costs.

Maintaining a packing element, such as Pall rings, requires regular inspection and care to ensure their effective operation in mass transfer systems, especially in devices like scrubbers. Here are some key aspects related to the maintenance and care of these rings:
1. Inspection of Packing Condition
The packing can undergo mechanical wear and degradation due to aggressive chemicals and elevated temperatures. Check for cracks, fractures, or deformations that could reduce the efficiency of the absorption or filtration process.
2. Cleaning from Contaminants
Over time, the elements may become covered with deposits or contaminants such as salts, oils, chemicals, or organic materials. Their accumulation reduces mass transfer efficiency and can lead to blockages, which in turn increases aerodynamic resistance and reduces gas flow speed. Regular cleaning using appropriate solvents or cleaning agents helps restore their operating performance.
3. Monitoring Liquid Condition
In wet scrubbers with Pall rings, an important element is maintaining the quality and level of the liquid. It is necessary to ensure that the liquid used in the absorption process is not contaminated and does not lose its cleaning properties. Periodic replacement of the liquid or addition of necessary chemicals can significantly extend the lifespan of the packing and improve the efficiency of the entire system.
4. Maintenance of Columns and Containers
In addition to the rings themselves, the columns or containers in which they are placed are an important part of the system. These structures should be regularly inspected for cracks, corrosion, or other damages. Leaks of gas or liquid can significantly reduce system performance. It is also essential to ensure that the ventilation and pumping systems are correctly set up to maintain the required gas and liquid flow parameters.
5. Corrosion Resistance
For metallic elements, it is important to regularly check the protective coatings for signs of corrosion. This is crucial for extending the lifespan in aggressive chemical environments. Anti-corrosion coatings or replaceable inserts can be used in areas with a significant risk of corrosion exposure.