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