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This post was last edited by jxkelley on 2017-4-21 at 11:22. The selection of chemical packing involves determining the type, specifications, and material of the packing. The selected filler must meet the requirements of the production process while minimizing equipment investment and operating costs. I. Selection of types of chemical industry packing: When choosing the type of chemical industry packing, it is necessary to take into account the requirements of the separation process. Generally, the following aspects are considered: 1. High mass transfer efficiency – Typically, structured packing has a higher mass transfer efficiency than random packing. 2. High flux – While ensuring high mass transfer efficiency, packing with a high gas velocity or gas kinetic energy factor should be selected. 3. Low pressure drop across the packing layer. 4. The packing should have good resistance to fouling, and it should be easy to install, remove, and maintain. II. Selection of specifications for chemical industry packing: The specifications of packing refer to its nominal dimensions or specific surface area. (1) Selection of bulk packing specifications. The common bulk packing materials used in industrial towers include specifications such as DN16, DN25, DN38, DN50, and DN76. For similar packing materials, the smaller the size, the higher the separation efficiency; however, this leads to increased resistance, reduced flux, and a significantly higher cost for the packing. The use of large-sized packing in small-diameter columns leads to poor liquid distribution and severe wall flow, thereby reducing the separation efficiency of the column. Therefore, a specification must be set for the ratio of the tower diameter to the packing size; generally, the ratio D/d of the tower diameter to the nominal diameter of the packing should be greater than 8. (2) Selection of the specifications for structured packing. There are many ways to denote the models and specifications of structured packing commonly used in industry. In China, the specific surface area is the standard parameter used for this purpose; the main specifications include 125, 150, 250, 350, 500, 700, etc. For structured packing of the same type, the greater the specific surface area, the higher the mass transfer efficiency. However, this leads to increased resistance, reduced flux, and a significant rise in the cost of the packing. When selecting, a comprehensive consideration should be given to factors such as separation requirements, throughput requirements, site conditions, material properties, as well as equipment investment and operating costs, so that the selected packing can meet the technical requirements while also being economically viable. It should be noted that a packing tower can use packing of the same type and specification, or it can also use packing of the same type but different specifications ； The same type of filler can be used, or a different type of filler can also be chosen ； Some tower sections can use structured packing, while others can use random packing. Flexibility should be exercised during design, and the specifications of the filler should be selected in accordance with the principle of integrating technology and economics. III. Selection of materials for chemical industry packing: The materials for packing fall into three main categories: ceramics, metals, and plastics. (1) Ceramic fillers: Ceramic fillers possess excellent corrosion and heat resistance. They are inexpensive and have good surface wetting properties; however, their greatest drawback is that they are brittle and easy to break. It is widely used in processes such as gas absorption, gas washing, and liquid extraction. (2) Metal fillers: Metal fillers can be made from various materials, and corrosion is the main factor to consider when selecting them. Carbon steel packing is inexpensive and has good surface wetting properties; it should be given priority for use in systems with no corrosion or low corrosion potential ； Stainless steel packing has strong corrosion resistance and can generally withstand corrosion from common substances other than Cl–. However, it is more expensive, and its surface wettability is poor; in certain special applications (such as vacuum distillation processes with extremely low spray densities), its surface must be treated to achieve good performance ； Packers made of materials such as titanium and special alloy steels are very expensive, and are generally used only in environments with extremely high corrosivity. Generally, metal fillers can be made into thin-walled structures; they have a high flow rate, low gas resistance, and excellent impact resistance, allowing them to be used under conditions of high temperature, high pressure, and high impact stress, which makes them the most widely used type. (3) Plastic fillers: The materials used for plastic fillers mainly include polypropylene (PP), polyethylene (PE), and polyvinyl chloride (PVC); in China, polypropylene is generally the most commonly used material. Plastic fillers have good corrosion resistance and can withstand the corrosion of common inorganic acids, bases, and organic solvents. It has good heat resistance and can be used for a long time at temperatures below 100°C. Plastic fillers are lightweight and inexpensive, possess good toughness, are impact-resistant and not easy to break, allowing them to be used in thin-walled structures. It features high throughput and low pressure, and is widely used in devices for absorption, desorption, extraction, dust removal, etc. The disadvantage of plastic fillers is their poor surface wettability, but this can be improved through appropriate surface treatment.