The valves provide extra resistance to the rising The aggressive surface ... trays. 2. This advantage disappears as the parameter approaches 0.1. The factors below represent economic pros and cons that favor each and may be overridden. Tower packing is sometimes referred to as tower internals or structured packing, random packing or trays. Packing trays are generally used when a column is experiencing a bottleneck issue. The benefits of structured packing come at a price. For more information about our products , including components such as bubble caps, valve trays, and structure packing, please reach out to our team by calling 403-314-5422 or 1-800-993-9958 . 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. Consider a vacuum column with 10 theoretical stages, operating at 70-mbar top pressure. Structured packing. Trays are available in segmental or cartridge type construction to suit customer’s requirements. Our units are configured for easy onsite installation. 3. Small-diameter columns. One way of allowing for design uncertainties and feedstock variation is by installing alternate feed points. If high capacity and efficiency are lower priorities but cost is a restricting factor, random packing offers … With respect to the Selexol process, I believe most - if not all of the absorbers - would be packed. At a parameter of 0.02, the structured packing has a 1.3-1.4 capacity advantage over random packing and trays. Trays vs. packings Tower internals can be trays, random packing, or structured packing. The random packing appears to have the highest capacity and efficiency with conventional trays just slightly behind. Packing pressure drop is much lower than that of trays because the packing open area approaches the tower cross-sectional area, while the tray's open area is only 8 to 15 percent of the tower cross-sectional area. "Cartridge" trays or an oversized diameter are often used. High capacity 2. Weight. Structured packings are usually less troublesome than trays in such services. Very high-performance structured packing is seldom used for large commercial gas treating plants because of its high cost and sensitivity to plugging by small particles suspended in the solution. This packing consists of a set of corrugated sheets in the form of honeycombs. Structured packing towers offer more surface area and have a lower pressure drop than packed towers do. Inadequate removal of these fluids may be hazardous. Both attributes make random packing excellent for handling foams. 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. Due to their sensitivity to maldistribution there is greater uncertainty in predicting packed column performance. The bottom pressure will be 170 mbar with trays, but only 90 to 110 mbar with packings. Some information you will find in this text includes the following: Authored by Lili Lyddon - BR&E Technical Support / Help Author. In packed towers, every alternate feed point requires expensive distribution equipment. These translate to less product degradation, greater capacity, and smaller energy consumption, giving packings a major advantage. Attendant benefits include less energy usage and lower construction costs. Most separations can be performed either with trays or with packings. Because of the smaller liquid holdup of packing, a higher percentage of the liquid can be recovered as top product. Very high-performance structured packing is seldom used for large commercial gas treating plants because of its high cost and sensitivity to plugging by small particles suspended in the solution. Not all trays are fouling-resistant. Tray towers usually weigh less than packed towers, saving on the cost of foundations, supports, and column shell. as gum formation can lead to plugging of the packing. Floats on moving valve trays tend to "stick" to deposits on the tray deck. Trays and random packings have much the same efficiency and capacity. is a platform for academics to share research papers. Eng., p. 86 (April 2006)]. Random packing is one of the 3 primary devices used in mass and heat transfer applications. Capacity and Efficiency Comparison Kister et al. Performance prediction. Packing is normally a cheaper and more desirable alternative. The loss of capacity of structured packing is greatest in this range. (The other 2 devices are structured packing and trays.) Experience indicates that use of structured packings has capacity/ efficiency disadvantages in the higher-pressure (higher-flow-parameter) region. Corrosive systems. Trays requires separate are for the liquid flow (DC) while with packing liquid and vapor are flowing through whole cross section of the column. The choice between trays and packing is somewhat arbitrary because either can usually be designed to do an adequate job, and the overall economics are seldom decisively in favor of one or the other. Plugging in liquid distributors has been a common trouble spot. And with new technology, probably structured packing is now making inroads. However, if you're not running a continuous still there is a good deal of waste left behind in the column....hold-up volume. [Chem. Trays and random packings have about the same efficiency and capacity. In many cases recurrent foaming was alleviated by replacing trays by random packing, especially when tray downcomers were poorly designed. Structured Packings The following factors generally favor trays compared to structured packings, but not compared to random packings. 14-31, 14-55, and 14-56) and the following tentative conclusions could be drawn: 1. Low liquid rates. Columns with diameter less than 1 m (3 ft) are difficult to access from inside to install and maintain the trays. Structured packing efficiency is about 1.5 times that of trays or random packing. Vacuum systems. In a natural gas dehydration plant you want to avoid - or minimize - maintenance wherever possible - especially human entry into vessels. Kohl (1997) contains excellent information concerning trayed vs. packed columns for gas treating applications. Structured packing is generally more prone to maldistribution than random packing. The valves are either moveable (con-ventional) or fixed. Packing is also preferred for columns where pressure drop and possible foam formation are important considerations. Tower internals are arguably the most important piece of process equipment, since they cannot easily be accessed after startup. Typically, one needs 22 separations steps after a stripping run to adequately rectify upto 95%. When to Use Random vs. The capacity of structured packings tends to rapidly fall off at high liquid rates. Distributors that resist plugging have large holes (> 13-mm diameter). Solids. 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. special types of structured packing or on bubble cap trays to achieve the desired degree of dehydration. Support plate: Support plates for random packing units are often multi-beam units, set on a continuous ring. (4) Random packing, the traditional type of packing. (5) Structured packing, made from folded metal sheets or gauze, the latter being much the more expensive. The performance of the Column in relation to the process requirements (dew point) is determined by carefully selecting the following parameters: (a) Height of packing (or # of trays) (b) Packing or Tray Design (c) Glycol Concentration The term structured packing refers to a range of specially designed materials for use in absorption and distillation columns. While the low gas and liquid velocities help, the solid walls restrict lateral movement of foams and give support to the foams. The original packed towers used Raschig rings, hollow ceramic cylinders, typically 1 in outer diameter (OD), 0.75 in inner diameter (ID), and 1 in long.A state-of-the-art packing is called structured packing.This material is made of thin sheets of crimped or corrugated metal, with small holes, fastened together with thin bars. Well sealed (often welded) bubble cap trays and random packing are the better options. Structured Packing Versus Trays. Switching from trays to structured packing can aggravate foaming. FLEXIPAC ® Structured Packing. Washing and purging. However, packing distributors are limited to fairly narrow liquid-rate ranges for effective performance. Packed Column for Chemical Engineering Applications 28. Packing Tower Anatomy b) 2) Structured packing Structured packing … Trays require internal access for scheduled maintenance. For a service in which carbon steel is usually satisfactory with trays, stainless steel is usually required with structured packings. Low liquid holdup. 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. Figs. The thin sheets of structured packing (typically 0.1 mm) poorly dissipate heat away from hot spots. The low gas and liquid velocities in packing suppress foam formation. Process surges. Structured packed columns are shorter than trayed columns. Random packing advantages include high cost-effectiveness. For instance, column complexity is a factor favoring trays, but gas plant demethanizers that often use one or more interreboilers are traditionally packed. Large, open packing with minimal pockets offers good plugging resistance. Column wall inspection. Progr., 90(2), 23 (1994)] reported a study of the relative capacity and efficiency of conventional trays, modern random packings, and conventional structured packings. FLEXERAMIC® Ceramic Structured Packing Our geometrically arranged corrugated sheets provide greater resistance to fouling than random packing, while our design provides high capacity, higher efficiency and lower pressure drop than any random packing and most trays that are available today. 2. Structured packing compared to random packing has 1. 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. MellapakPlus™ is the latest generation of structured packing. Typically, tray pressure drop is of the order of 10 mbar per theoretical stage, compared to 3 to 4 mbar per theoretical stage with random packings and about one-half of that with structured packings. There is much that can be done to alleviate plugging with random packing. Ser. 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). Multipass trays effectively lower the liquid load "seen" by each part of the tray. Solids tend to accumulate in packing voids. Packing Tower Anatomy Random Packing Tray vs. Packings also offer an easy tradeoff between capacity and separation. Packing is often specified for CO2 removal columns, where a high degree of CO2 removal is desired and the low efficiency of trays may result in objectionably tall columns. Cartridge trays also run into problems with sealing to the tower wall and matching tower to tray hardware [Sands, Chem. Feed composition variation. Here the much higher liquid holdup on trays provides greater residence time for absorption or chemical reaction than does packing. Mellapak is the most widely used structured packing worldwide. Structured Packing. 1. Trays handle solids much more easily than packing. (3) Bubble cap tray, the traditional type of tray, extremely expensive, but it has its applications. Either option is expensive. Fouling-resistant trays have large sieve holes or large fixed valves, and these should be used when plugging and fouling are the primary considerations. © 2020 - Bryan Research & Engineering, LLC All Rights Reserved. If liquid load is not high then structured packing will requires smaller column ID (fixed cost) compared to trays hence structured packings are preferred. 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. operations where trayed towers are used. If the tower internals malfunction, the distillation tower will follow suit and the entire chemical process will suffer. The pressure drop advantage is invaluable in vacuum column revamps, can be translated to a capacity gain, an energy gain, a separation improvement, or various combinations of these benefits. Tray columns are particularly applicable for high pressure columns, where pressure drop is not an important consideration and gas purity specifications can readily be attained with about 20 trays. The efficiency advantage of structured packing over random packings and trays decreases from 1.5 to 1.2 as the parameter increases from 0.1 to 0.3. Cost high 4. Here excessive pressure drop in the tower increases the size of the fan or compressor (new plant), bottlenecks them (existing plant), and largely increases power consumption. Trays vs. Better separation efficiency. In the loaded sections of the tower, larger packings can overcome capacity bottlenecks at the expense of loss in separation. Low pressure drop(high open area and used for vaccume distillation) 3. However, it’s advantages counter this. Packing fires. Interreboilers, intercondensers, cooling coils, and side drawoffs are more easily incorporated in trays than in packed towers. The sensitivity of packing to liquid and gas maldistribution has been a common cause of failures in packed towers. Packing should not be used in absorbers treating unsaturated gases that can readily polymerize (propadiene, butadiene, butylene, etc.) Depending on the type and supplier, structured packing may not be cheaper than trays. Also, cleaning, cooling, and washing can be difficult, especially when distributors or packing plug up. 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. 5) allows the size of the column to be reduced with a higher F-factor of ~2.3 Pa 0.5 . FLEXIPAC ® structured packing is used for large crimp sizes where the addition of high-capacity features has little effect and for the replacement of standard structured packings where an exact duplicate is required. 2. In general, packing can handle wide vapor-rate ranges. They found that, for each device optimally designed for the design requirements, a rough guide could be developed on the basis of flow parameter L/G (pc/pL)0'5 (abcissa in. Less trays will be required to achieve the same degree of separation. This makes it difficult to inspect the column wall (e.g., for corrosion). Sieve trays. Structured packings are usually less troublesome than trays in such services. Unless very expensive distributors are used, packed tower turndown is usually limited by distributor turndown. Trays can be manufactured in nonmetals, but packing is usually a cheaper and more desirable alternative. Complex towers. The trays are orifice-type devices designed to disperse the gas uniformly on the tray and through the liquid on the tray. Due to the thin sheets of structured packings, their materials of construction need to have better resistance to oxidation or corrosion. Moving valve and bubble-cap trays normally give better turndown than packings. Revamps. Foaming (and emulsion). ... Table 3 and Fig. The separation loss can often be regained by retrofitting with smaller packings in sections of the tower that are not highly loaded. Three trays are very cheep ones and their maintenance is easy. Structured Packings The following factors generally favor trays compared to structured packings, but not compared to random packings. This is particularly true for towers operating close to atmospheric pressure. With the aid of serrated weirs, splash baffles, reverse-flow trays, and bubble-cap trays, low liquid rates can be handled better in trays. Eng. Packing Lili Lyddon December 12, 2006. The packing allows for a greater surface area with a low bulk density for gas and liquid to make contact, which can also allow for contact in different phases. The sieve trays have been developed when the hydrocarbon industry and the oil and gas industry have extended. Trays vs. Random Packings The following factors generally favor trays compared to random packings, but not compared to structured packings. Due to the compression ratio, pressure drop at the compressor discharge is far less important and seldom a controlling consideration. Such large holes are readily applied with high liquid flow rates, but often not practical for small liquid flow rates. Maldistribution issues are most severe in large-diameter towers, long beds, small liquid flow rates, and smaller packing. The thin sheets of structured packing (typically 0.1 mm) poorly dissipate heat away from hot spots. The packed tower will have a much better relative volatility in the lower parts, thus reducing reflux and reboil requirements and bottom temperature. These stages can be physical trays or theoretical trays (structured packing). Distillation towers are essential to the chemical process industries (CPI), so it is imperative that they are properly designed and operated. In packed towers, every complexity requires additional distribution and/or liquid collection equipment. Structured packing has about the same capacity as trays and random packings. And these are now becoming very rare in view of the results obtained with structured packing. The large open area of the larger random packing promotes foam dispersal. Packing fires. Batch distillation. Structured packing can be manufactured from corrugated sheets of perforated embossed metal, plastic (including PTFE), or wire gauze. Pall rings or high-performance proprietary designs). We have a variety of glycol contactors with valve trays, bubble cap trays, or structured packing. Maldistribution. Most of these fires were initiated by pyrophoric deposits, hot work (e.g., welding) above the packing, opening the tower while hot organics were still present, and packing metallurgy that was not fire-resistant. Structured packing has the least capacity and efficiency. Many incidents of packing fires during turnarounds (while towers with structured packings were open to atmosphere) have been reported. Packings have lower liquid holdup than do trays. This makes trays more robust. Flexibility. There are fewer locations on trays where solids can be deposited. Option 1: Until the 1980s, TEG contactors were designed with bubble cap trays. Zuiderweg and Nutter [IChemE Symp. 5. Thorough removal of residual liquid, wash water, air, or process gas trapped in structured packings at startup and shutdown is more difficult than with trays. Ceramic and plastic packings are cheap and effective. The practical range of packing materials is wider. The valve trays are typically with the covers provided to the per-forations of the sieve trays. Generally speaking, trays are used in applications with liquid rates of 30 m3/m2-h and above, and/or those where solids are present or fouling is a con-cern. 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. equipped with trays or random packings, have been revamped with Mellapak in orderto improve yield or purity or to in-crease . Cleaning trays is much easier than cleaning packings. Trays, structured packing, or random packing in the column are used to effect an intimate contact between the vapor and liquid phases, permitting the transfer of mass and heat from one phase to the other. Combining excellent capacity and efficiency char- Trays vs. Option 2: Sulzer Mellapak TM structured packing (Fig. Materials of construction. Random packings suffer from liquid dewetting and maldistribution sensitivity at low liquid rates. Turndown. Due to their snug fit, structured packings are easily damaged during removal. Detailed discussion can be found in Fractionation Research Inc. (FRI) Design Practices Committee, "Causes and Prevention of Packing Fires," Chem. How does it work? With the enhancement of the geometric structure of conventional Mellapak™, the pressure drop is much lower and the maximum capacity can … A similar trick cannot be applied with packings. 9 provide a detailed comparison of trayed vs. structured packing contactors in the same service. 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 … Single pass sieve tray DN 1600 in stainless steel . Structured Packing. Lower-pressure-drop applications. These trays are replaced with structured packing for three reasons: They provide extra inter-facial area for contact between vapor and liquid. Eng., July 2007. Likewise, for towers in the suction of compressors, replacing trays by packings reduces the compression ratio and helps debottleneck the compressor. The term structured packing refers to a range of specially designed materials for use in absorption and distillation columns and chemical reactors.Structured packings typically consist of thin corrugated metal plates or gauzes arranged in a way that force fluids to take complicated paths through the column, thereby creating a large surface area for contact between different phases. Trays vs. They are designed with a low F-factor of ~1.8 Pa 0.5 , resulting in large column sizes. This is often advantageous for reducing polymerization, degradation, or the inventory of hazardous materials. (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. Both gas and liquid velocities on trays are often an order of magnitude higher than through packing, providing a sweeping action that keeps tray openings clear. Chemical reaction, absorption. Best DIY Hacks for Saving Money on Electricity, System Limit The Ultimate Capacity Of Fractionators, Hengstebeck Diagrams - Structured Packings. Traditionally, the glycol absorber contains 6-12 trays to absorb water. High liquid rates. Structured packings are typically used in lower-liquid- Also, the tray liquid head, which incurs substantial pressure drop (typically about 50 mm of the liquid per tray), is absent in packing. 3. Structured packing is a type of packing proposed by Labbe known for its efficiency and low pressure drop.It allows to decrease the size of columns compared to other distillation column internals. In tray towers, changing tray spacing gives similar results, but is more difficult to do. 1. At this time, sieve tray columns are probably the most popular for both absorbers and strippers in conventional, large commercial amine plants; while packed columns are often used for revamps to increase capacity or efficiency and for special applications. 10.1 How Packed Towers Work. (2) Valve tray, the other common type, but marginally more expensive. At low vapor rates, the decreased turbulence in structured packing can reduce efficiency.