The selection of filler is to confirm the type of filler, specification, materials and so on. The selected filler should not only meet the requirements of production techniques, but also minimize the equipment investment and operating costs.

1. 1，Selection of filler type

The selection of filler type shall consider the requirements of separation technique. Generally speaking, there are following aspects to be considered:

(1) In general, the mass transfer efficiency of structured packing is higher than that of bulk packing.

(2) The flux should be large.

On the premise of ensuring high mass transfer efficiency, the filter with high flooding point gas velocity or gas phase kinetic energy factor shall be selected.

(3) The pressure drop of the filter layer should be low.

(4) The filter has strong anti fouling performance., which is easy to disassemble and repair.

1. 2，Selection of filler specifications

The filler specification refers to the nominal size or specific surface area of the filler.

(1) Selection of Bulk Filler Specifications

The commonly used bulk fillers for industrial tower mainly include DN16, DN25, DN38, DN50, DN76 and other specifications. The smaller the size of fillers is, the higher the separation efficiency will become. However, the resistance increases and the flux decreases, which will increase the cost of filler. When the large sized filler is used in packed tower with small diameter, it will cause poor liquid distribution and serious wall flow, which will reduce the separation efficiency of tower. Therefore, the ratio of tower diameter to filler size should be specified. Generally, the ratio D/d of tower diameter to nominal diameter of filler should be greater than 8.

(2) Selection of structured filler’s specification

There are many methods to express the model and specification of regular fillers commonly used in industry. It is customary to use specific surface area to express, such as 125, 150, 250, 350, 500, 700 and other specifications. Considering the regular packing of same type, the larger the specific surface area is, the higher the mass transfer efficiency will become. However, it will increase the resistance and decrease the flux, which will increase the filler cost significantly. During selection, it needs to make integrative consideration on separation requirements, flux requirements, site conditions, comprehensively properties, equipment investment, operating costs and other aspects. Thus, the selected filler can not only meet the technical requirements, but also be economically reasonable.

It should be pointed out that the same type and specification of filler can be selected for a packed tower, or the same type and different specifications of filler can be selected for the packed tower. In addition, it can also select the same type of filler can be selected, or different types of filler. Some tower sections can use regular filler, while some tower sections can use bulk filler. Thus, the design shall be flexible. The specification of filler shall be selected according to the principle of technical and economic unity.

1. 3,Selection of filler material

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

(1) Ceramic filler

Ceramic filler has good corrosion-resistant and heat-resistant performance. It has low level price and good surface wettability. However, the brittleness and fragility are its biggest shortcomings. It is commonly presented in gas absorption, gas washing, liquid extraction and other processes.

(2) Metal filler

Metal filler can be made of various materials. In selecting the metal fillers, the corrosion is the main consideration. Carbon steel filler has low cost and good surface wettability. Thus, it should be preferred for non corrosive or low corrosive materials. Stainless steel filler has strong corrosion resistance. In general, it can resist the corrosion of common systems other than C -. However, stainless steel filler has high cost and relatively poor  surface wettability. In some special occasions (such as vacuum distillation process under extremely low spray density), its surface needs to be treated to obtain good use effect. The fillers which are made of titanium materials, special alloy steel and other materials are usually very expensive. Generally, they are only used in some highly corrosive systems. Generally speaking, metal filler can be made into thin wall structure. It has large flux, small gas resistance, and high impact resistance. The steel filler can be used under high temperature, high pressure, and high impact strength. Their range of applications is large in the world.

(3) Plastic filler

The materials of plastic fillers mainly include polypropylene (PP), polyethylene (PE) and polyvinyl chloride (PVC). In China, the popular materials should be PP. The plastic filler has good corrosion resistance, which can resist the corrosion of ordinary inorganic acid, alkali and organic solvent. It has good temperature resistance. Thus, the plastic filler can be used under 100 degree for a long time. Plastic filler is light and cheap, while it has good toughness, good impact resistant performance. Especially, the plastic filler is not fragile, which can be made into thin-walled structures. It has large flux and low pressure, which is mainly used in absorption, desorption, extraction, dust removal and other devices. The disadvantage of plastic filler is its poor surface wettability. However, its surface wettability can be improved by proper surface treatment.