Random packings suffer from liquid dewetting and maldistribution sensitivity at low liquid rates. 5) allows the size of the column to be reduced with a higher F-factor of ~2.3 Pa 0.5 . The term structured packing refers to a range of specially designed materials for use in absorption and distillation columns. (5) Structured packing, made from folded metal sheets or gauze, the latter being much the more expensive. "Cartridge" trays or an oversized diameter are often used. Better separation efficiency. The loss of capacity of structured packing is greatest in this range. This advantage disappears as the parameter approaches 0.1. Trays and random packings have about the same efficiency and capacity. There is much that can be done to alleviate plugging with random packing. Type of packing Material 4 Structured packings from Sulzer Chemtech Mellapak 64.X/64.Y Mellapak125.X/125.Y Mellapak170.X/170.Y Mellapak 2 X/2 Y … In packed towers, every complexity requires additional distribution and/or liquid collection equipment. Sieve trays. In the loaded sections of the tower, larger packings can overcome capacity bottlenecks at the expense of loss in separation. Our units are configured for easy onsite installation. Trays vs. packings Tower internals can be trays, random packing, or structured packing. The low gas and liquid velocities in packing suppress foam formation. Combining excellent capacity and efficiency char- Less trays will be required to achieve the same degree of separation. Zuiderweg and Nutter [IChemE Symp. However, it’s advantages counter this. When to Use Random vs. Materials of construction. For a service in which carbon steel is usually satisfactory with trays, stainless steel is usually required with structured packings. ... Table 3 and Fig. In a natural gas dehydration plant you want to avoid - or minimize - maintenance wherever possible - especially human entry into vessels. Structured packing towers offer more surface area and have a lower pressure drop than packed towers do. Low liquid holdup. Due to their sensitivity to maldistribution there is greater uncertainty in predicting packed column performance. special types of structured packing or on bubble cap trays to achieve the desired degree of dehydration. Eng. The large open area of the larger random packing promotes foam dispersal. Columns with diameter less than 1 m (3 ft) are difficult to access from inside to install and maintain the trays. When the gas is moved by a fan through the tower, or when the tower is in the suction of a compressor, the smaller packing pressure drop is often a controlling consideration. Mellapak is the most widely used structured packing worldwide. 3. Such large holes are readily applied with high liquid flow rates, but often not practical for small liquid flow rates. Tray towers usually weigh less than packed towers, saving on the cost of foundations, supports, and column shell. structured packing has been successfully utilized in a variety of high liquid rate,high pressure systems besides the usual applications in vacuum and atmospheric processes normally reserved for structured packing. These translate to less product degradation, greater capacity, and smaller energy consumption, giving packings a major advantage. Also, packing should not be used in treating gases containing H2S which are contaminated with oxygen because of the potential for plugging with elemental sulfur. Structured packed columns are shorter than trayed columns. The factors below represent economic pros and cons that favor each and may be overridden. Trays vs. Complex towers. Structured packing has the least capacity and efficiency. If high capacity and efficiency are lower priorities but cost is a restricting factor, random packing offers … 128, A481 (1992)] explain the loss of capacity/efficiency by a large degree of backmixing and vapor recycle at high flow parameters, promoted by the solid walls of the corrugated packing layers. Like the other 2 devices, the primary purpose of random packing is to create surface area for vapor/liquid contact so that Mother Nature (and Father Thermodynamics) can produce chemical separation. With respect to the Selexol process, I believe most - if not all of the absorbers - would be packed. The random packing appears to have the highest capacity and efficiency with conventional trays just slightly behind. Well sealed (often welded) bubble cap trays and random packing are the better options. While good distributor design, water testing, and inspection can eliminate most maldistribution issues, it only takes a few small details that fall through the cracks to turn success into failure. This is often advantageous for reducing polymerization, degradation, or the inventory of hazardous materials. equipped with trays or random packings, have been revamped with Mellapak in orderto improve yield or purity or to in-crease . Attendant benefits include less energy usage and lower construction costs. Packing fires. Structured Packing. Structured packing has about the same capacity as trays and random packings. 5. While the low gas and liquid velocities help, the solid walls restrict lateral movement of foams and give support to the foams. The capacity of structured packings tends to rapidly fall off at high liquid rates. Because of the smaller liquid holdup of packing, a higher percentage of the liquid can be recovered as top product. The thin sheets of structured packing (typically 0.1 mm) poorly dissipate heat away from hot spots. operations where trayed towers are used. Maldistribution. Solids. Trays can be manufactured in nonmetals, but packing is usually a cheaper and more desirable alternative. At low vapor rates, the decreased turbulence in structured packing can reduce efficiency. FLEXIPAC ® Structured Packing. Bubble-cap trays and raschig ring packings were once commonly used in amine plant absorbers and strippers, however, modern plants are generally designed to use more effective trays (e.g., sieve or valve types) and improved packing shapes (e.g. [Chem. 14-31, 14-55, and 14-56) and the following tentative conclusions could be drawn: 1. Large, open packing with minimal pockets offers good plugging resistance. Random packings are usually more troublesome than trays in services prone to process surges (e.g., those caused by slugs of water entering a hot oil tower, relief valve lifting, compressor surges, or instability of liquid seal loops). as gum formation can lead to plugging of the packing. (Page 1) When it comes to distillation trays and packing, chemical processors require the same criteria they seek from all equipment in this tight economy — technology that will reduce energy use and boost throughput without costly facility expansion. The valves are either moveable (con-ventional) or fixed. (The other 2 devices are structured packing and trays.) Corrosive systems. Small-diameter columns. Due to maldistribution, there are far more failures experienced with packing than in trays, and it takes more trials "to get it right" than with trays. One way of allowing for design uncertainties and feedstock variation is by installing alternate feed points. 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