How to choose fillers?

The selection of fillers includes determining the type, specification, and material of the filler. The selected filler should not only meet the requirements of the production process, but also have low equipment investment and operating costs.

1. Selection of filler types

Considering the requirements of the separation process, the following aspects are usually considered:

Generally speaking, the mass transfer efficiency of regular fillers is higher than that of bulk fillers.

The flux should be large. On the premise of ensuring high mass transfer efficiency, fillers with higher flooding point gas velocity or gas phase kinetic energy factor should be selected.

The pressure drop of the packing layer should be low.

The filler has strong anti fouling and blocking performance, and is easy to disassemble and repair.

2. Selection of filler specifications

Filler specifications refer to the nominal size or specific surface area of the filler.

Selection of bulk filler specifications

The commonly used bulk fillers for industrial towers include several specifications such as DN16, DN25, DN38, DN50, and DN76.

The smaller the size of similar fillers, the higher the separation efficiency, but the resistance increases, the flux decreases, and the cost of fillers also increases significantly. However, the application of large-sized fillers in small diameter towers can result in poor liquid distribution and severe wall flow, which reduces the separation efficiency of the tower.

Therefore, there should be a regulation on the ratio of tower diameter to packing size, and the ratio D/d of tower diameter to nominal packing diameter should generally be greater than 8.

Selection of regular filler specifications

There are many ways to represent the types and specifications of regular fillers commonly used in industry. In China, specific surface area is commonly used, mainly including 125, 150, 250, 350, 500, 700, and other specifications.

The larger the specific surface area of the same type of structured packing, the higher the mass transfer efficiency, but the resistance increases, the flux decreases, and the packing cost also significantly increases.

When selecting, comprehensive consideration should be given to separation requirements, flux requirements, site conditions, material properties, equipment investment, operating costs, etc., so that the selected filler can not only meet technical requirements but also have economic rationality.

3. Selection of filler material

The materials of fillers are divided into three categories: ceramic, metal, and plastic.

Ceramic filler

Ceramic fillers have excellent corrosion resistance and heat resistance. Ceramic fillers are inexpensive and have good surface wetting properties, but their brittleness and fragility are their drawbacks. It is widely used in processes such as gas absorption, gas washing, and liquid extraction.

Plastic filler

The materials of plastic fillers mainly include polypropylene (PP), polyethylene (PE), and polyvinyl chloride (PVC), among which polypropylene is commonly used in China. Plastic fillers have good corrosion resistance and can withstand the corrosion of general inorganic acids, alkalis, and organic solvents. It has good temperature resistance and can be used for a long time below 100 ℃.

Plastic fillers are lightweight, inexpensive, and have good toughness, impact resistance, and are not fragile, making them suitable for thin-walled structures. Its high flux and low pressure are commonly used in absorption, desorption, extraction, dust removal and other devices.

The disadvantage of plastic fillers is poor surface wettability, but their surface wettability can be improved through appropriate surface treatment.

Metal filler

Metal fillers can be made of various materials, and corrosion is the main consideration when selecting them.

Carbon steel fillers have low cost and good surface wettability, and should be prioritized for use in non corrosive or low corrosive systems.

Stainless steel fillers have strong corrosion resistance and are generally resistant to corrosion from common systems other than Cl -. However, their cost is high and their surface wettability is poor. In some special occasions (such as vacuum distillation processes at extremely low spray densities), their surface needs to be treated to achieve good results.

Fillers made of materials such as titanium and special alloy steel have a high cost and are generally only used in certain highly corrosive systems.

Generally speaking, metal fillers can be made into thin-walled structures with high flux, low gas resistance, and high impact resistance. They can be used under high temperature, high pressure, and high impact strength, and have a wide range of applications.

Summary:

When selecting fillers, for a specific application, the standards for fillers are based on the expected performance of the composite material, and the following basic principles must be considered.

1. The filler must maintain its original structure during processing, and maintain inertness, insolubility, thermal stability, non volatility, no catalytic activity, and low adsorption.

2. The filler must be compatible with the substrate and non corrosive.

3. Easy to handle, high stacking density, low moisture content, low dust, and non-toxic.

4. It must be easy to obtain, with sufficient supply, moderate price, and stable quality.