Filler selection issues

Material and temperature are also related, which is also very important, and there are many forms.

The selection of fillers must comprehensively consider factors such as production capacity, efficiency, operating flexibility, cost, and pressure drop. The corrosiveness of the material must also be considered. The following factors should be considered: Filling materials: It should first be determined based on the corrosiveness of the materials being processed and the operating temperature. Filler size: The appropriate ratio (diameter ratio) between the tower diameter and the outer diameter of the packing has a lower limit. When the diameter ratio is lower than this value, it is difficult to predict their performance and the throughput capacity of the packing.: The ultimate passing capacity of the packing is the efficiency of the packing at the empty tower gas velocity at the liquid flooding point.: The factors that affect performance are very complex. It is more reliable to design the pressure drop of the filler based on actual measured values.: The power consumption of the packed tower mainly depends on the total pressure drop of the entire tower in the gas phase.

The selection of filler includes determining the type, specification and material of filler. The selected filler must not only meet the requirements of the production process, but also minimize equipment investment and operating costs. 1. Selection of filler types: The selection of filler types should consider the requirements of the separation process, usually considering the following aspects:: (1) The mass transfer efficiency must be high. Generally speaking, the mass transfer efficiency of structured packing is higher than that of bulk packing. (2) The flux must be large. On the premise of ensuring higher mass transfer efficiency, packing with higher flood point gas velocity or gas phase kinetic energy factor should be selected. (3) The pressure drop of the packing layer should be low. (4) The packing has strong anti-fouling and plugging properties, and is easy to disassemble, install and repair. 2. Selection of filler specifications Filler specifications refer to the nominal size or specific surface area of ​​the filler. (1) Selection of bulk filler specifications Commonly used bulk fillers in industrial towers mainly include DN16, DN25, DN38, DN50, DN76 and other specifications. For similar packings, the smaller the size, the higher the separation efficiency, but the resistance increases, the flux decreases, and the packing cost also increases a lot. When large-size packing is used in small-diameter towers, poor liquid distribution and severe wall flow will occur, which will reduce the separation efficiency of the tower. Therefore, there must be a regulation on the ratio of tower diameter to packing size. Generally, the ratio D/d of tower diameter to nominal packing diameter should be greater than 8. (2) Selection of structured packing specifications. There are many ways to express the models and specifications of structured packings commonly used in industry. Domestic * The conventional specific surface area is expressed in several specifications such as 125, 150, 250, 350, 500, 700, etc. For the same type of structured packing, the larger the specific surface area, the higher the mass transfer efficiency, but the resistance increases, the flux decreases, and the packing cost also increases significantly. 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 the technical requirements, but also be economically rational. It should be pointed out that a packed tower can use the same type and specification of packing, or the same type of packing with different specifications. ； You can use the same type of fillers or different types of fillers ； Some tower sections can use structured packing, while some tower sections can use bulk packing. The design should be flexible and the specifications of the filler should be selected based on the principle of technical and economic unity. 3. Selection of filler materials The filler materials are divided into three categories: ceramic, metal and plastic. (1) Ceramic filler Ceramic filler has good corrosion resistance and heat resistance. Ceramic filler is cheap and has good surface wetting properties. Its biggest shortcomings are brittleness and brittleness. It is widely used in gas absorption, gas scrubbing, liquid extraction and other processes. (2) Metal fillers Metal fillers can be made of a variety of materials, and corrosion issues are mainly considered when selecting. Carbon steel fillers are low cost and have good surface wetting properties. They should be given priority for non-corrosive or low-corrosive systems. ； Stainless steel packing has strong corrosion resistance and is generally resistant to corrosion by common substances except Cl–. However, its cost is high and its surface wetting performance is poor. In some special occasions (such as the vacuum distillation process under extremely low spray density), its surface needs to be treated to achieve good results. ； Fillers made of titanium, special alloy steel and other materials are very expensive and are generally only used in certain highly corrosive systems. Generally speaking, metal fillers can be made into thin-walled structures, which have large flux, small gas resistance, and high impact resistance. They can be used under high temperature, high pressure, and high impact strength, and have the widest range of applications. (3) Plastic filler The materials of plastic filler mainly include polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), etc. Polypropylene is generally used in China. Plastic fillers have good corrosion resistance and can withstand corrosion from general inorganic acids, alkalis and organic solvents. It has good temperature resistance and can be used below 100°C for a long time. Plastic fillers are lightweight, cheap, have good toughness, are impact-resistant and not brittle, and can be made into thin-walled structures. It has large flux and low pressure, and is mostly used in absorption, desorption, extraction, dust removal and other devices. The disadvantage of plastic fillers is poor surface wetting properties, but their surface wetting properties can be improved through appropriate surface treatment.