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The development and manufacturing of fillers are generally carried out by filler manufacturers, who also provide the performance data for these fillers; it goes without saying that they are responsible for ensuring their quality as well. 1. Treatment prior to filler installation (1) Degreasing of the filler: There is a thin layer of oil on the surface of new fillers; this layer may have been formed due to the use of lubricating oil during the processing of metal fillers ； It may also be an anti-rust oil added to prevent carbon steel packing from corroding during transportation and storage. The presence of this layer of oil is absolutely unacceptable in certain systems; for example, in air separation systems, when the oil layer is washed away and comes into contact with liquid oxygen, it can cause an explosion. In aqueous solution systems, this layer of oil can prevent the formation of a liquid film; in some alkaline systems, it can also cause the solution to foam. Therefore, it is necessary to understand the physical properties of this oil and remove it before starting up the system. To facilitate the removal of the oil layer, it is better to use water-soluble lubricants in filler processing. Carbon steel packing should be stored in a dry, enclosed place and should not be removed in advance to prevent rust. (2) Removing fragments from ceramic fillers: New ceramic fillers as well as those that have been refilled should have any fragments removed from them; sometimes this requires manual removal of each fragment one by one. It is inevitable that bulk ceramic fillers get damaged during transportation, but larger pieces of broken filler can still be used. Their flow rate will decrease and the pressure drop will increase, but the separation efficiency will not decline. (3) Removal of the tower support rings: When converting a tray tower into a packed tower, it is necessary to remove the original tray plates, downcomers, and support rings. The horizontal support ring should be cut as clean as possible. The horizontal support rings are retained; they interfere with the gas-liquid distribution inside the tower, reduce its effective cross-sectional area, thereby increasing resistance and reducing flux, which in turn lowers efficiency. When converting a plate tower using bulk packing, there is no need to remove the support rings as long as their area is less than 10% of the tower’s cross-sectional area. Plate towers are modified using structured packing; before installation, the support rings must be removed and polished clean, with the remaining amount generally should be less than 5 mm, or the advice of the packing manufacturer can also be followed. 2. For the installation of packing and internal tower components, those that require welding, such as packing supports, liquid collectors, and gas-liquid distributors, it is best to complete them before installing the packing, in order to prevent welding slag from entering the packing and causing a fire. The oil layer on the surface of metal fillers can easily catch fire under the high temperatures generated by welding slag, while plastic fillers are even more likely to cause fires. The slag remaining in the tower can also cause blockages in the liquid distributor, affecting the tower’s efficiency. If certain components must be installed during or after the packing installation, asbestos cloth, asbestos sheets, etc. should be placed beneath the welds to isolate the welds from the packing. Installation steps for the packing and internal components: (1) Install the packing support ； (2) Install the packing ； (3) Install the packing fixing or compressing device, and level it ； (4) Install the liquid distributor or redistributor, fix it, and adjust its level ； (5) After installation, perform a check. 3. Installation of the packing: The installation of the packing is crucial for ensuring the separation efficiency of the tower, and it must be carried out under the guidance of technicians from the packing manufacturer. Improper installation can lead to poor distribution of gas and liquid, resulting in reduced separation efficiency and processing capacity as well as increased pressure drop. (1) Installation of bulk packing: The installation of bulk packing seems simple – simply pouring the packing into the tower – but this is not the case. Such a straightforward installation can, in mild cases, result in uneven packing density, while in more severe cases it can cause the metal packing to deform or the ceramic packing to break, leading to uneven distribution of gas and liquid and thereby reducing the separation efficiency. Ceramic fillers and non-carbon steel metal fillers should be filled by wet method if conditions permit. Using wet filling, after installing the support plate, water is filled into the tower; the packing is then gently poured into the water from above the water surface. The packing floats and descends in the water, with the water level being at least 1 meter above the packing. Wet filling can reduce filler damage and deformation. Wet filling also improves the uniformity of the bulk filler, reduces the filler usage by about 5%, increases the filler flux, and decreases the pressure drop. Billet conducted comparative experiments using Dg38 Pall rings for wet and dry filling in a 500mm diameter tower; the results showed that wet filling required 5% less filler than dry filling, the pressure drop was reduced by 10%, and the efficiency was almost identical. Therefore, wet filling should be preferred as much as possible in situations where flux is limited. When using dry packing, the packing material should always be poured from a certain height above the packing layer. For large-diameter towers, dry packing sometimes requires personnel to stand on the packing layer in order to carry out the packing process. It should be noted that people must not stand directly on the packing to prevent it from being compressed and deformed as well as from having uneven density; wooden planks can be placed on the packing to distribute the stress. Whether wet packing or dry packing is used, the packing should be filled from the tower wall towards the center to prevent bridging of the packing at the walls. The packing should not be compressed into place, so as to avoid uneven bulk density due to deformation. After the packing in each section has been installed, it is necessary to check whether the upper part of the packing is level; if there are any unevenities, they should be leveled out. (2) Installation of structured packing A. Dimensions of structured packing Structured packing cannot be installed in a tower arbitrarily, without considering the shape of the tower, as is the case with bulk packing. It must be manufactured and installed based on the dimensions and shape of the tower, as well as the requirements regarding the tower’s ellipticity mentioned in the previous section. When retrofitting old towers with structured packing, its ellipticity often fails to meet these requirements; therefore, it is necessary to address the issues related to the manufacturing and installation of the packing to ensure that it is suitable for the tower. For small towers with a diameter of less than 800 mm, structured packing is usually made in the form of complete disks that are installed through flange holes. For towers with a diameter greater than 800 mm, structured packing is usually divided into several sections, which are inserted into the tower through manholes and then assembled into a circle inside the tower. Whether assembled as a complete circle or from multiple sections, its diameter must be smaller than the tower diameter; otherwise, it cannot be installed. The gap between the packing and the tower wall should be determined based on the type of anti-wall-flow ring used, and each packing manufacturer typically has its own standards. B. Anti-wall-flow rings for structured packing: These are typically used to prevent gas-liquid wall flow that occurs due to the gap between the packing and the tower wall; anti-wall-flow rings are installed in this gap. This baffle flow ring can be integrated with the packing or assembled separately inside the tower. Typically, for small-diameter solid disk packing, the anti-wall-flow ring is integrated with the packing; sometimes a single ring serves two purposes, acting both as an anti-wall-flow ring and as a support for the packing. The flow barrier ring should not completely seal the gap between the packing and the tower wall in the vertical direction; this not only reduces the tower’s throughput and increases resistance, especially in towers with small diameters, but experiments have also shown that it leads to a decrease in separation efficiency. Common anti-wall flow coils allow the gas-liquid mixture to flow in a baffled manner through the gaps in the tower wall, thereby preventing wall flow while utilizing these gaps for mass transfer. C. Installation of small-diameter uniform packed beds: When installing small-diameter uniform packed beds, first turn up and align the anti-wall-flow rings; then place the corrugated sheets of adjacent packed bed layers at 90-degree angles inside the tower, pressing them down appropriately with disks. For towers with a relatively high packing layer and a somewhat larger diameter, to prevent the situation shown in the figure from occurring, packing trays can be tracked using pusher plates to deliver them to their designated positions. However, this must be carried out by personnel with installation experience. Alternatively, several packing trays can be strung together before being loaded into the tower; or two people can use steel bars to hook onto the packing and lower it to the desired position. D. Installation of large-diameter structured packing: Large-diameter structured packing must be installed in sections through the manhole into the tower; the height of each section is usually 100–300 mm. The length of each section can be equal to the span of the tower, or it can be divided into several sections. To facilitate manufacturing, packaging, transportation, and disassembly, the length of each piece should not exceed 1.8 meters. In each packing piece, the packing sheets are assembled using pins; sometimes they are simply tied together with wire or packing tape. To prevent the screen packing from deforming during transportation, metal corners are used to protect it. If the anti-wall-flow ring is integrated with the packing, the anti-wall-flow ring must be opened as required before each piece of packing is installed ； If the flow baffle ring and packing are separate, the flow baffle ring must be placed in position as required during installation. Typically, the installation proceeds from one end to the other, with the corrugations of adjacent packing discs forming a 90-degree angle. Every four packing discs constitute one cycle; by rotating the packing discs in a clockwise (or counterclockwise) direction, the horizontal error on the upper surface of the packing can be reduced. After each tray of screen packing is installed, remove the wrapping corners. Installers should not always stand in the middle of the tower cross-section, as this can lead to a \"bottomed-out\" shape with higher levels on the sides and a lower level in the middle. The final packing element in each pack must be installed using a slide board. Due to the non-circular shape of the tower and other reasons, it is sometimes necessary to add or remove packing pieces as appropriate in order to make the packing fit the tower. Over-tightening of the packing can cause the packing strips to deform, resulting in an increased overall height of the packing, an uneven upper surface, and a decrease in efficiency and throughput. Similarly, if the packing is installed too loosely, it will lead to uneven gas-liquid distribution and a decrease in separation efficiency. In certain special cases, due to lack of time or other reasons, it is not possible to remove the tray sections in a plate tower and replace them with structured packing; therefore, packing pieces with diameters matching those of the tray sections must be manufactured for installation at those locations. The design must take into account the resulting losses in efficiency and flow rate. 4. Inspection before sealing: Inconsistencies between installation and design often lead to problems; the earlier errors are detected, the easier it is to correct them. Therefore, inspection should be carried out simultaneously with installation. The inspection should preferably be carried out by on-site technical service engineers or designers. These professionals generally have a good understanding of the fluid flow patterns and mass transfer processes within the tower, which makes it easy for them to identify any errors ； Furthermore, on-site inspections are also a great form of training; they can improve design skills and lead to more refined designs in the future. It is best to prepare a checklist in advance and check each item against it to avoid omissions. For the modified tower, special attention should be paid to the parts that have been modified. After installation, it is advisable to conduct a cold test using water or another medium if possible, in order to check the distribution by the liquid distributor and the collection by the liquid collector. This task can be carried out simultaneously with cleaning the packing. Once the testing is complete, the impurities present in the liquid distributor and collector should be removed from the tower before it can be sealed.