When choosing random packing media, you must consider several selection factors. Understanding the reasons for using random packing instead of structured or stacked tower packing also plays an important role when servicing a tower. Use this guide to choosing random packing media to aid your selection process.
What Are Types of Packing in a Packed Column and What Are Their Uses?
When considering how to choose tower packing, you have options for random and structured packing. These differ significantly in how contact occurs between fluids. For the purposes of this guide for the selection of tower packing, the focus will remain on random packing.
Towers allow for mass transfer or chemical separation in one of two ways, depending on whether they have trays or packing media. For trayed towers, vapor moves up through liquid to enable mass transfer by increasing the surface area. Packed towers use gravity’s force and the shape of the packed media to enable mass transfer. Ideally, there should not be anything left once the liquid passes through the packed material portion of the tower.
An optimal packing media will effectively spread out fluids that flow through them, increasing the surface area.
What Is Random Tower Packing?
Random tower packing simply pours the filtration media into the tower. The uneven distribution and orientation of the parts increase the surface area and enhances the transfer of mass between two fluids. The benefits of random packing media only come from narrow towers without ready access. In some instances, random packing material may augment existing material to increase a tower’s capacity.
The media used for this type of packing have a variety of shapes. The shapes determine the total surface area, uniformity of distribution, wetting area and more. You can use these selection criteria of packings to find the best media for a specific application.
What Are the Uses of Random Tower Packing?
Random tower packing is used in several sectors. Most often, industries that handle the following may use random packing:
- Acid gas scrubbing
- Mist elimination
- Particulate removal
- Corrosive component
When Is Random Packing Used?
Several factors determine how to use packing in a tower. Random packing is suitable for any size tower, and the size of the tower will determine how much packing is needed. Packed columns have a lower pressure drop because the packing has a greater open area compared to trays. However, structured packings, such as corrugated sheets, have an even lower pressure drop than random packing. Also, packing works as a better alternative to trays in situations that require the media to come into contact with corrosive materials.
How Is Random Packing Used?
To use random packing, individuals pour the selected media into the tower. Selecting the correct media matters more than the pieces’ arrangement.
Both dry and wet packing methods exist based on the media used. Dry packing works best for durable materials, such as plastics and metals. Filling the tower requires either a rope and bucket method or a chute and sock method, both of which are variations of dropping the media into the column.
For delicate media like ceramic or carbon, it’s best to use a wet packing method. Filling the space with water before adding the media prevents breakage as the water cushions the pieces’ fall into the tower. Because wet packing allows for more randomness in the media arrangement, it reduces pressure drop in the column and increases capacity. Before using the tower, however, you must drain the packing water and allow the media to dry thoroughly. The extra steps required for wet packing are some of its only disadvantages.
Both methods of packing a tower make random media a preferred option for any towers that need a solution for increasing capacity.
Applications of Random Packing Media
Packing towers offer filtration benefits that multiple industries take advantage of. The material flowing through the tower often dictates the type of packing media required.
Industries That Use Random Packing Media and Wet Scrubbers
Multiple industries use random tower packing. The applications of tower packing within these sectors include the following:
- Water treatment
- Treating greenhouse gases in acid or catalytic gas scrubber
- Biological filtering
- Particulate removal
Where Is Random Packing Used?
Random packing works best in some types of towers or when operation towers require certain characteristics of mass transfer, including:
- Low residence time: Packed towers offer low liquid holdup compared to trayed structures, which can have a holdup volume of 20% to 30%. Higher percentages of liquid holdup volume indicate slower-moving gases. In situations where slower-moving gas can cause damage, the low residence time offered by random packing materials provides a solution.
- Higher capacity for a tower size: Compared to trayed towers, packed towers can have a higher capacity. Changing the type of media used in the packing will affect the efficiency and capacity of the tower.
- Corrosive systems: You can use the corrosive nature of the system as a criterion among other packing factors for the selection of media. As with other tower packing selection criteria, always consider the properties of the packing media both in shape and material for use in a corrosive system.
- Vacuums or low-pressure situations: Random packing outperforms structured packing when working with vacuums or low pressure. Random packing causes a lower change in pressure compared to structured packing.
- Reduced foaming: Problems caused by foaming include flooding, reduced capacity, solvent loss and liquid carry-over. Foaming can happen when using solvents that have high molecular weights. The continuous liquid phase in trayed towers may cause the material to froth. When foaming starts in a trayed tower, it can worsen quickly as the gas moves liquid between trays to create more foaming. Foam will also move vapors down through the trays. Packed towers have a lower chance of foaming
Types of Random Packing Media
To understand how to select random packing, you must know about the options available. These various shapes also have different materials in their construction. Both the shape and makeup of the media will affect the best applications for it. These eight options reflect a small number of the random packing media available. With customization options and proprietary designs from MACH like our MACH Bio-Media rings for wastewater treatment, you have many options for media in a random packing tower.
1. Raschig Rings
Raschig rings are one of the oldest packing media. These were a first-generation media, introduced between 1907 and 1950. Due to their simple design of a basic ceramic ring, Raschig rings are rarely used in towers today. The pall ring evolved from this media’s structure, improving upon the original design.
2. Pall Rings
The Pall ring’s design features a more open variation of the closed Raschig ring to introduce openings on the sides. The updated design allowed for a greater surface area compared to its predecessor. Pall rings are among the second-generation designs, which came into use between the later half of the 1950s and the 1970s.
Pall rings come in plastic, metal and ceramic compositions. Customization of the polymers used and the sizes of the plastic rings allow for adaptation to multiple uses. Metal Pall rings made from aluminum, carbon steel or stainless steel can better resist corrosion and high temperatures than their plastic counterparts. Ceramic pall rings provide an increased absorbency because they are thicker than plastic rings.
3. Hi-Flow Ring
We call this design the MACH Hi-Ring. The Hi-Ring features a large void space, low specific gravity and high physical strength. These rings work best in environmental applications, oil and gas industries, chemical sectors and alkaline chloride use.
The original saddle, the Berl saddle, was another first-generation fill product introduced between 1907 and 1950. Over time, engineers have improved upon the simple original saddle design. Modern metal saddle rings, also known as IMTP, offer better performance in high-capacity situations. The metal saddle rings used today are a third-generation design, introduced after the 1970s.
5. Super Saddle
Super saddles are a third-generation design that has a wider shape than other saddle products. Made from ceramic or plastic, the larger saddle shape offers a greater surface area for more mass transfer compared to smaller products.
6. Metal Intalox Saddle
As a second-generation product, the metal Intalox saddle came into use between the 1950s and 1970s. Many designs today have improved on this saddle design. Like most older models, modern variations of Intalox saddles have replaced them.
Tri-Packs have an innovative design that works best in degasifiers, strippers and scrubbers. The industry introduced these plastic fill pieces in the late 1970s. Each piece has a shape like an open sphere with ribs evenly spaced along the sides and on the interior. These ribs permit even liquid distribution to allow for unimpeded contact between gases and liquids.
8. Raschig Super Ring
We call these MACH Super Rings. As a third-generation design, our MACH Super Rings offer many benefits of later models. Made from stainless steel, the MACH Super Rings come in sizes varying from 0.1 inches up to 4 inches. The open weave design maximizes contact, reduces pressure changes, creates more stability and resists fouling.
Many applications use this ring, including the treatment of liquid natural gas, production of butadiene, separating methane from heavy hydrocarbons and removing carbon dioxide and hydrogen sulfide from biogas and natural gas.
Random Packing Selection Criteria
When choosing random packing materials, several factors will narrow down the options available for your application. Ask yourself the following questions:
- Is the material a direct replacement of the existing packing you use?
- Do you know the type of packing and performance you require?
- Does the media work with your process?
To help decide if a media works with your process, consider its surface area, wetting area, friction and other performance factors to find the ideal option to use in your tower.
1. Surface Area
Increase efficiency by choosing random packings with a greater surface area. The more surface area per volume of the packing, the higher the vapor liquid contact. On average, the latest random packing media have a surface area of 300 square meters per cubic meter. The surface area you get from your media depends on multiple other factors, including the size and shape of the pieces.
2. Wetting Rate
Each material has an inherent wetting rate. If the liquid load drops below the wetting rate, the surfaces of the packings will dry out. The effects of liquids dropping below the wetting rate for the given material include decreased efficiency.
3. Uniformity of Distribution
The benefit of random packing is the lack of structure the material creates. When pieces interlock, they can create paths for fluid flow. When fluids have the chance to move along channels, the system loses efficiency.
4. Uniform Spreading Surface
How the surfaces of the media spread fluids determines their efficiency. While surface area plays an important part in how efficiently the system operates, when pieces have a uniform spreading surface to allow more vapor liquid contact, the packing works better.
5. Package Voidage
Increasing the amount of void space as much as possible reduces the chances the media will slow down the upward movement of vapor through the system. Due to more void space inside the parts, the capacity of a tower will rise when using larger random packing pieces.
Lower friction for packing media opens spaces between the pieces and inside them. With more space, the tower has a greater capacity and operates more efficiently.
7. Packing Strength
The mechanical strength of the material should withstand compression and other damage from typical use in a tower. Resisting corrosion and thermal damage also contributes to the overall strength of a packing media.
8. Packing Material
The materials available include plastics, ceramics and metals. Within each of these categories, you have more options for the types of polymers or metals used:
- Metals: Media made from metals have a wider range of designs, extra durability, compression resistance and higher capacity compared to other materials.
- Plastics: Plastics work best in low-temperature applications below 250 degrees Fahrenheit. They offer the most cost-effective option.
- Ceramics: Ceramics require gentle handling and wet packing to avoid breakage. Though delicate, they resist damage from high temperatures and corrosion. Their surfaces also do not react with other materials. Sulfuric acid absorption and treatment of similarly corrosive materials is best completed with ceramic media.
Advantages of Random Packing Media
Random tower packing is suitable for any size tower and provides numerous benefits. The advantages of random packing media include the following:
- Relatively inexpensive: Compared to structured packing, random packings provide a more cost-effective method of filling a tower. The design, material and amount you choose will ultimately determine the final cost.
- High strength-to-weight ratio: The individual pieces, especially those made from more durable materials, have a high ratio of strength-to-weight. Overall, the random packing media can physically endure mechanical stress well, especially in relation to their lightweight construction.
- Ease of use in difficult-to-access sites: Random packing materials have an easy to install method that does not require frequent servicing as trays do. For narrow towers with hard-to-reach openings, using random packing material will provide a better option.
Find a Selection of Random Packing Media From MACH Engineering
To correctly calculate the type of packing your application requires, let MACH Engineering run the numbers for you. In addition to educating you about how to choose random packing, we offer a variety of media for your tower. For more information about our products or services, contact us today at MACH Engineering.