Minor issue with filler installation

This post was last edited by zjiris on 2009-9-2 at 13:55. Bulk packing materials are granular substances with specific geometric shapes and sizes, which are generally piled up in the tower in a random manner; they are also known as randomly packed packing or granular packing. Depending on their structural characteristics, bulk packing materials can be further divided into ring packing, saddle packing, ring-saddle packing, and spherical packing, etc. Regular packing materials are those that are arranged in a specific geometric pattern and stacked neatly. There are many types of structured packing, which can be classified into grid packing, corrugated packing, etc., based on their geometric structure. Since bulk packing and structured packing are classified according to their installation method, it is the type of packing you install that determines whether it will be installed in a structured manner or as bulk packing.

This is all theoretical knowledge. The actual installation of the packing should be based on practical operations. Pre-installation treatments for the packing: ① Oil removal from the packing – There is a thin layer of oil on the surface of new packing; this layer may have formed as a result of the use of lubricants during the processing of metal packing, or it may be rust preventive 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 oil layers, it is better to use water-soluble lubricants in filler processing. Carbon steel packing should be stored in a dry and sealed place, and should not be removed in advance to prevent rust. ② Removal of 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. 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 – just pour the packing into the tower. However, 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. This leads to an uneven distribution of gas and liquid, thereby reducing the separation efficiency. Ceramic fillers and non-carbon steel metal fillers should be filled by wet method if conditions permit. Wet filling is used: after installing the support plate, water is poured into the tower, and the packing is gently poured into the water from above; the packing floats down 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; the amount of filler used is reduced by about 5%, the filler flux increases, and the pressure drop decreases. 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 used as much as possible in situations where flux is limited. When using dry packing, the filler should always be poured from a certain height above the packing layer; for towers with large diameters, dry packing is employed, and sometimes it is necessary for a person to stand on the packing layer to carry out the filling. 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 using wet packing or dry packing, the filling should proceed from the tower walls toward the center to prevent bridging of the packing at those walls. The packing should not be compressed too tightly to avoid deformation and uneven density. 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 taking into account the dimensions and shape of the tower, as well as the requirements regarding the tower’s ellipticity mentioned in the previous section. When upgrading old towers with structured packing, the ellipticity of such packing often fails to meet the required standards; therefore, it is necessary to address this issue through proper manufacturing and installation of the packing to ensure that it is suitable for the tower structure. For small towers with a diameter of less than 800 mm, the structured packing is usually made in the form of complete disks that are fitted using flange holes. For towers with a diameter greater than 800 mm, the structured packing is usually divided into several pieces, which are inserted into the tower through manholes and arranged in a circular shape inside the tower. Whether arranged as a single circle or in separate pieces, their diameter must be smaller than that of the tower; otherwise, they 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; 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 one ring serves two purposes, acting both as an anti-wall-flow ring and as part of the **packing itself. The anti-washout 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. In the figure, several common types of anti-wall-flow coils allow the gas-liquid mixture to flow in a baffled manner through the gaps in the tower wall; this prevents wall flow while also utilizing those gaps for mass transfer. C. Installation of small-diameter circular structured packing: When installing small-diameter circular structured packing, first turn up and align the anti-wall-flow rings; then place the corrugated sheets of adjacent packing discs at 90-degree angles inside the tower, pressing them down firmly with a disc. For towers with a high packing layer height and a slightly larger diameter, to prevent the situation shown in the diagram from occurring, a push plate can be used to guide the packing trays to the desired position; this requires personnel with installation experience to carry out the operation. It is also possible to thread several packing trays together before inserting them into the tower, or two people can use steel bars to hold the packing trays and lower them to the intended 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 between 100 and 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, metal wires or packing tape are simply used instead. To prevent the mesh packing from deforming during transportation, metal corners are used to protect it. If the anti-wall-flow ring is integrated with the packing, it must be opened as required before each piece of packing is installed; if the anti-wall-flow ring is separate from the packing, it needs to be placed in position as required during installation. Typically, the installation proceeds from one end to the other, with the corrugations of adjacent packing rings forming a 90-degree angle. Every four packing discs constitute one cycle; by rotating the packing discs in a clockwise (or counterclockwise) direction in this manner, the horizontal error at 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 \"bottom of a pot\" effect with higher levels on the sides and a lower level in the middle. The installation of the final piece of packing for each disc requires the use of a sliding plate, as shown in Figure 9. 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 structure. Over-tightening the packing can cause the packing pieces to deform, increasing the overall height of the packing and resulting in an uneven upper surface, which in turn reduces the efficiency and flow rate. 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: Discrepancies between installation and design often lead to problems; the earlier errors are detected, the easier it is to correct them. Therefore, inspections should be carried out simultaneously with installation. Inspections should preferably be carried out by on-site technical service engineers or designers. These professionals generally have a good understanding of the fluid flow and mass transfer conditions within the tower, which makes it easy for them to identify errors. Moreover, on-site inspections serve as an excellent opportunity for training, helping to 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 of the liquid by the distributor and the collection of liquid by the 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.

In the case of a packing system for a polysilicon off-gas recovery system, the bulk packing used is mainly Pall ring packs; at the upper part of the stripping tower, regular packing is typically used, with corrugated packing being the most common type. The height of the packing needs to be determined based on the physical and chemical properties of the material, as well as the operating pressure and temperature. Generally, design firms provide the necessary parameters for this purpose. There are specialized manufacturers for installing fillers, so I won’t go into details on that