Controlling Buildup in a Rotary Drum

Buildup is caused by material sticking to itself, or to the interior of the drum, and is almost always the result of a sticky material. Dealing with buildup in a rotary drum is a common factor faced in many industries, from fertilizer to mineral processing. Depending on the material, and the process, there are several ways to control buildup.

One option for controlling buildup in a rotary drum is to use a liner on the interior of the drum. There are many types of liners, from rubber liners, to stainless steel liners, all the way to ceramic tiles, the choice of which is dependent upon the material and the purpose of the liner.

Adding a liner is mainly used as an option in the case of granulators, coolers, and agglomerators, when heat is not involved in the process. Heat does not work well with most types of liners. Even a stainless steel liner can run into troubles when in a heated operation, because the heat causes liner and base materials to expand at different rates. A stainless steel liner inside a carbon steel shell could have a potential for cracking. When heat is involved, such as in the case of a rotary dryer or rotary kiln, external means can be taken to help prevent buildup, as opposed to using any sort of liner.

Another option for controlling buildup in a rotary drum is to “knock” off buildup through external means. The use of external means is typically employed in the case of rotary dryers, because, liners can pose problems in heat applications.

There are three basic knocker designs,: the ball and tube knocker, hammers, and pneumatic hammers.

Ball and tube knockers consist of tubes attached to the drum that hold heavy balls (think shot put)that drop on the drum by gravity as the drum rotates. A wear plate protects the shell, while still allowing for enough force to knock material off of the interior of the drum.

Ball and Tube Knocker

Hammer knockers are a similar set-up, using gravity as the delivery mechanism. A hammer is set up on a pivot, so as the rotary drum turns, gravity causes the hammer to fall, knocking the drum, and causing buildup to fall off. A wear band around the drum protects the shell, while still allowing for enough force to knock material off of the interior of the drum.

Hammer Knocker

Pneumatic hammers – . A “hammer,” set up on a hydraulic system, is mounted to the ceiling or support structure above the rotary drum. This hammer can be programmed to knock the drum at set time intervals. A wear band around the drum protects the shell, while still allowing for enough force to knock material off of the interior of the drum.

Pneumatic Hammer Knocker

In the fertilizer industry for rotary granulators, the liner of choice is often a flexible rubber liner. Flexible rubber liners work by having strips of rubber fixed to the interior, running parallel to the drum. As the drum rotates, gravity causes the rubber to flex down, sloughing off any material that was caked on. Historically, the fertilizer industry typically used scrapers on the interior of the drum to control buildup. However, the potential for the drum to “jump,” or jar, due to the scraper coming in contact with a large, heavy, built-up mass of material.. The move from scrapers to flexible liners was two-fold for fertilizer manufacturers, because not only did these liners help control buildup, but they also offered some corrosion protection.

Flexible Rubber Liner

Although there are many ways to keep buildup under control, the best way to control buildup is to prevent it from the start. There are a couple of ways to approach this.

One way to prevent buildup is to adjust the feedstock through what is called back mixing. Back mixing takes place when dry material is added to the wet, raw material in order to make the material less sticky. However, this is not always an option, as some materials remain sticky for a wide range of moisture levels. In cases such as this, a heated screw could be a more efficient choice over a rotary dryer.

Another way to prevent buildup is to design a less aggressive internal flight or lifter. Because buildup tends to occur in sharp corners, a less aggressive flight can lessen the propensity for buildup to occur. In this situation, some efficiency is lost, but the decline in buildup can be a compensating factor. Additionally, adding a bald section in the beginning of the drum allows the feedstock to dry a little before it hits the flights, also lessening the chances for buildup to occur.

While buildup is a common challenge faced by those utilizing a rotary drum in their process, there are many methods to combat buildup, or prevent it from occurring. Next we will look at corrosion and abrasion problems in rotary drums.

FEECO has been an industry leader in custom-engineering rotary dryers, coolers, kilns, and agglomerators, for over 60 years. Our equipment is robust, and built for longevity. With process design and optimization services, our equipment and systems are built to suit material needs, so you get the best process for your material. Contact us today to learn more about our rotary equipment capabilities.

Check back soon for the second half of this two-part series on the challenges faced in the use of a rotary drum.

Left: Pelletizing Disc, or Pelletizer | Right: Rotary Drum Agglomerator

When it comes to agglomerating a material, people are often faced with the decision of choosing between a rotary drum agglomerator and a disc pelletizer. Though the choice may seem overwhelming at first, there are many things to take into account that will help you make the right decision for your material.

Material Specific Considerations

Many times the choice between a rotary drum or a pan pelletizer is dependent upon historical preference. Throughout various industries, one or the other has been used for generations, and there is no need for change. Taking a look at the pros and cons of each can help to make an informed decision, whether you’re a start-up company, or a plant looking to optimize your process.

There are many differences between a drum and a disc, but whether they are an advantage or a disadvantage is often dependent upon the material. This is clear when looking at the amount of recycle in a process.

Overall, a pelletizer results in far lower recycle than a rotary drum does. This is ideal in situations where the material goes from a pelletizer to a dryer, because the less recycle that has to be dried, the more efficient the process will be (ie. the more recycle that needs to be dried, the more energy spent on drying there will be).

While rotary drums may result in a higher amount of recycle, this recycle can also be beneficial to a process. For example, when utilizing a rotary drum agglomerator, the higher amount of recycle acts as a buffer in the process. If there is any upset in conditions, there is enough recycle in the process to help even things out. However, with a pelletizer, there is such little recycle, that when there is an upset in conditions, the output is almost immediately effected.

Additionally, some material processes require a certain amount of recycle to function efficiently, and whether using a drum or pan, extra recycle is a advantageous. Such is often the case when a pin mixer is introduced into the process. Some materials require a certain amount of recycle to be mixed in with the dry feedstock going into the pin mixer, in order for the feedstock to mix efficiently before going into the pelletizer. For this reason, it is often a requirement to have a little more recycle on hand.

Customization and System Considerations

Another aspect to consider when choosing between a rotary drum agglomerator or a disc pelletizer, is the throughput. When it comes to running a very high capacity, rotary drums are often the equipment of choice. Typically, rotary drums can handle a much higher throughput than a pan pelletizer can. Where it might take a few pelletizers to get to the desired capacity, it may only take a single drum. While rotary drums allow for a higher throughput, pelletizers are the equipment of choice when a tight window of size range is desired for the output product.

Creating pellets on a pelletizer has been likened to a form of art, allowing for extreme customization and fine-tuning of product. Pan speed, pan angle, pan depth, feed location, and binder location, are all things that can be adjusted to zero-in on the size range (among other qualities) of the pellets that you’re looking for. However, this also means a pelletizer requires a much more watchful eye than a rotary drum agglomerator. Where one operator would be capable of watching several drums, one operator should only watch a few pan pelletizers. In terms of rotary drums, they are far more “limited” in terms of customization, offering fewer variables for adjusting end product, but subsequently, they require less monitoring.

Another side to consider in the choice between a rotary drum or a pelletizer, is whether or not a closed system is desired. Rotary drums are considered a “closed system,” because the agglomerating happens within the drum, meaning the vessel can be sealed to help control dust and odor. Whereas a pelletizer is a more open system, meaning the operation happens in a less sealed atmosphere than a drum.

Maintenance

In terms of maintenance, pelletizers take the cake, requiring somewhat less maintenance than a rotary drum. Though pelletizers do need to be maintenance properly in order to function efficiently, there are few parts to be replaced, typically only scrapers and spray nozzles. With rotary drums, there are many parts that not only require regular maintenance, also need replacing now and then. Although the performance of either piece of equipment is severely hindered if not maintenanced regularly.

Conclusion

While material characteristics (such as how quickly it pelletizes, particle size distribution, binder reaction time, etc.) can play a role in the choice between a pelletizer or a rotary drum agglomerator, ultimately, the choice comes down to what works best for the process and material to be pelletized.

FEECO has been a leader in the agglomeration industry for over 60 years, manufacturing rotary drum agglomerators, and disc pelletizers to suit the needs of your material. We can run agglomeration feasibility tests in our state-of-the-art testing facility to help you decide what is right for your process, and your material.

The world’s foremost event for the processing industry, the Powder Show is a gathering of professionals from various industries, in areas such as handling, packaging, transport, testing, processing, and storage of bulk solids.

With a long history in the bulk solids processing and handling industry, FEECO will be an exhibitor at this year’s Powder Show. For over 60 years, FEECO has been involved in providing thermal processing, material handling, and agglomeration solutions for a variety of materials.

At this year’s event, FEECO will not only be featuring several on-site equipment models, including a rotary dryer, but will be giving away three exciting prizes: a Kindle^TM, a Kindle Touch^TM, and a Kindle Fire^TM. Be sure to stop by the FEECO booth (#1400) to check out the equipment models, and to enter for your chance to win one of the three prizes!

If you haven’t yet, it’s not too late to register for a free pass! Use the promo code in the picture below to register for a free pass to Powder Show 2012.

Amazon, Kindle, Kindle Fire, the Amazon Kindle logo and the Kindle Fire logo are trademarks of Amazon.com, Inc. or its affiliates.

Export Import Bank, better known as Ex Im Bank, is the official export credit agency of the U.S. government, and helps finance the purchase of U.S. goods and services in international markets. Ultimately, their contribution to businesses both large and small, helps create and maintain jobs in the U.S., and also helps contribute to a stronger economy.

In order to be eligible, exporters must be located in the United States, have at least a one year operating history, and have a positive net worth. In order for exports to be eligible, exports must be shipped from the U.S., have at least 50% U.S. content, and services must be performed by U.S.-based personnel.

FEECO has been working with Ex Im Bank for around a decade, exporting equipment and services to locations around the world. “As a U.S. company doing business internationally, it has been very helpful for our customers to be able to work flexibly on financing,” said Lee Hoffman, General Manager and Vice President of Sales at FEECO. “At the end of the day, we’re helping create jobs here by exporting our American-made goods around the world.”

FEECO grew its roots in the fertilizer industry over 60 years ago, and has since grown to provide thermal processing, agglomeration, and material handling solutions to a variety of industries worldwide.

When it comes to buying an industrial dryer, people are often faced with the decision to choose between a rotary dryer, and a fluid bed dryer. Though the choice between the two can be material specific, ultimately, each dryer has its advantages and disadvantages, and the decision often comes down to customer preference.

Historically, rotary dryers have been used for more industrial applications, such as minerals, fertilizers, sand, etc., while fluid bed dryers have been used in the pharmaceutical and food industries, although, there can be a lot of overlap in applications for the two dryers.

Rotary dryers have been called the “workhorse” of the industry, due to their heavy-duty construction, their high capacity capabilities, and their ability to accept a wide variability in feedstock. Because of this, rotary dryers are better suited for heavy duty materials where a lot of variety in feedstock is a given, such as in the case of various minerals. Rotary dryers are known for their ability to take what is given, big or small, wet or dry, and churn out a quality product.

Conversely, fluid bed dryers have a very tight window when it comes to variability in feedstock. Whereas a rotary dryer will just keep running, variability in feedstock with a fluid bed dryer can cause process problems and the potential to leave an operation at a standstill.

Fluid bed dryers have the advantage of being modular. Though they are smaller in size than a rotary dryer, fluid bed dryers can be added on to, making them ideal for operation growth. Though not always an issue, rotary dryers require more space than a fluid bed dryer. Rotary dryers are often reliant on the ability of a material to tumble through the first few feet of the drum, where fluid bed dryers have no such need.

While a rotary dryer is robust, it does require more maintenance, because it is made up of so many moving parts. Although, rotary dryers do live a long productive life, when maintained well. Additionally, though it is material-specific, rotary dryers typically have slightly more attrition than fluid bed dryers, because they are picking up and showering the material. However, the rotational movement of a rotary dryer is an advantage in many cases, because it is ideal for rounding and polishing the product, something the fluid bed dryer does not accomplish.

The choice between a rotary dryer or fluid bed dryer is also a matter of energy. Fluid bed dryers work by fluidizing the material, which requires a high magnitude of air. Fluid bed dryers can be slightly more thermally efficient, but subsequently, can require much more electricity to run because of the need to “fluidize” and lift the material with air. Because the material is fluidized, it is not always practical to run high volume, heavy materials through a fluid bed dryer, because of the extra energy required to fluidize the material.

While the choice between a rotary dryer and a fluid bed dryer may seem complex, ultimately, it comes down to material characteristics, capitol costs, energy costs, and space.

FEECO custom engineers robust rotary dryers to handle the specific needs of your material. For more information on rotary dryers, contact us today!

You might also enjoy…
Rotary Kilns vs. Rotary Dryers: What’s the Difference
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FEECO Rotary Dryers for Frac Sand

Heap leaching, a process by which base metals such as gold, silver, nickel, uranium, and copper are recovered from ore, has been in long been the method of choice for ore beneficiation. While this process has proven to be an efficient process, often chosen for its cost-effectiveness, the efficiency of the heap leaching process relies heavily on the process of agglomeration.

Upon removal from the ground, ore is sent through a crusher to break the ore down into fines. The ore fines are then “heaped,” or piled, into a large pile. This mound is irrigated with a special solution that is dependent upon the type of ore being extracted. In the case of copper, sulfuric acid is used, because it reacts with the copper to create Copper Sulfate, a by-product that has many potential reuse applications. The irrigated solution is allowed to sit for several days, permeating through the ore, and draining to the bottom of the heap. The ore pile sits over a permeable layer, such as plastic, that collects the leached material as it drains through. Once the solution is collected, it can be purified to extract the valuable copper material.

While this process is efficient on its own, efficiency is greatly improved by adding an agglomeration drum to the process. Heap leaching relies on the ability of the leaching solution to penetrate through the mound, around particles.

When the ore is not properly agglomerated, fines can vary in size, severely reducing the ability for the solution to penetrate through the heap. Using a rotary drum agglomerator to agglomerate the ore fines will ensure crushed ore particles are uniform in size, making it easier for the leaching solution to travel through the channels between particles (See Figure 1). In addition to the benefit of increased percolation, adding a rotary drum agglomerator into the process also allows for an added opportunity to mix the leaching solution with the ore fines. As the ore fines are agglomerated, the solution can be sprayed throughout the drum and mixed thoroughly with the ore fines. This creates further increased efficiency benefits, as the solution can begin to concentrate around the ore fine agglomerates, furthering the efficiency of the leach.

Figure 1
Left: Ore fines pre-agglomeration, Right: Agglomerated ore fines

FEECO has been a leader in the agglomeration industry for over 60 years, and provides rotary ore agglomerators to heap leaching operations around the world. Our custom built, superior quality rotary drum agglomerators are robust, and built for longevity.

Earth Day is again upon us, and FEECO International will be celebrating Earth Day as it does every year: the same way they do every day. Though the “official” Earth Day comes but once a year, at FEECO, every day is Earth Day.

Earth Day was established 42 years ago by Senator Gaylord Nelson, who wanted to set aside April 22 each year not only to honor and raise environmental awareness, but also to aid in the effort to put regulations on toxins going into the environment.

While FEECO manufactures equipment for a variety of industries, an area of expertise is in developing processes and manufacturing equipment that takes aggregated waste and process by-products and turns them into value-added products. FEECO has helped companies all over the world to divert process by-products and “waste” materials from landfills. “A lot of our waste to value customers have by-products that they had been throwing away, and eventually, the question arises, ‘can we do something of value with this?’” stated Ron Eichorn, FEECO Lab Engineer. “Things like sulfur stack emissions, fly ash, and steel sludge, can all be processed and either utilized accordingly, or recovered for valuable material that they may contain.” {See more waste transformations here}

In order to keep track of all this waste, FEECO recently introduced their waste counter: a running count on the number of tons of waste that FEECO has helped divert from landfills to date. “It’s one thing to say you’ve diverted a lot of waste from landfills, but it’s pretty staggering to see the actual numbers,” said Nick Reckinger, Process and Bioresource Sales Engineer at FEECO. The waste counter can be seen on the homepage of their website.

This past year, FEECO also received the title of “Green Professional” from the Wisconsin Sustainable Business Council’s Green Masters Program. Recognition as a Green Professional is the second highest tier in the Green Masters Program. Candidates are judged on a comprehensive range of sustainability issues from energy and natural resource use to education outreach and purchasing.

It has been a “green” year for FEECO International, and we are proud to do our part in acting as a sustainable business, and helping to divert wastes from landfills, contributing to a better tomorrow. Happy Earth Day!

For more information on FEECO’s waste transformation capabilities, or for information on the FEECO lab, contact us today!

The Powder Show is the world’s foremost event for those in the processing industry, gathering professionals from areas such as handling, packaging, transport, testing, storage, and processing of bulk solids, from across various industries. This show showcases everything from accessories and services, to dryers, mixers, and screening. The show is a must for processing and production engineers, to plant and operations managers. The show is sponsored by Powder Bulk Solids, and the Process Equipment Manufacturer’s Association (PEMA).

FEECO International will be among those exhibiting at this year’s event. With a long history in the bulk solids handling industry, providing thermal processing, material handling, and agglomeration solutions to various types of materials, FEECO has a lot of process knowledge and experience to contribute. This year, the FEECO booth will be featuring several on-site detailed models of their equipment, including a pin mixer, a pan pelletizer, a compactor, and a rotary dryer.

FEECO will be giving away three exciting prizes this year: a Kindle^TM, a Kindle Touch^TM, and a Kindle Fire^TM. Make sure to put the FEECO booth, #1400, at the top of your list of places to stop at Powder Show 2012, and enter for your chance to win one of three prizes!

Didn’t register? No problem! Follow the link below and register for a free pass using the promo code in the picture. See you there!

Amazon, Kindle, Kindle Fire, the Amazon Kindle logo and the Kindle Fire logo are trademarks of Amazon.com, Inc. or its affiliates.

Even though we might not notice it, we think about heat transfer all the time – From cooking, to global warming – heat transfer is constantly at work around us. There are a couple basic rules to remember when thinking about heat transfer. First, heat ALWAYS transfers from a hotter object to a cooler one; the opposite of this is just not possible. Second, some materials can transfer heat better than others.

Materials are categorized into two basic groups, depending on their ability to transfer heat. Conductors are materials that transfer heat very well. Some of the best conductors are the non-ferous metals, such as copper and aluminum. Ferrous metals such as steel and stainless steel are also good conductors. The opposite of a conductor, is an insulator. Wood, rubber, ceramic, and brick, are all examples of insulators, or items that do not transfer heat well.

Conduction

There are three types of heat transfer: conduction, convection, and radiation. Conduction is the transfer of heat between two materials through direct contact. Think of touching your hand to the stove – this is a prime example of how conduction works. The heat of the burner, a physical object, is transferring heat to your hand, through means of touch. Other examples of conduction include curling irons, and cooking an egg on the sidewalk.

Convection

With convection, which is the primary mode of heat transfer for gases and liquids, heat transfers from a heat source, be it a liquid or gas, to a physical object. For example, a pizza cooks in the oven by means of convection: the heat from the oven is transferring from the heat source to the colder object, ie. the pizza. Convection works by the moving of the liquid or gas atoms in response to the heat. Once moving, the atoms can move around, in a sense, to surround an object, therefore heating it. Other examples of convection include hot air balloons, and boiling water.

Radiation

The third type of heat is radiation. Radiation is the transfer of heat through a direct path.This is different from conduction and convection, because it does not require physical contact (conduction), and because it is a direct path, it cannot surround an object (convection). Radiation works similar to light. An easy way to understand radiation is by thinking of getting a tan. If you are sitting on a beach, the sun, in direct contact you’re your skin, will tan your skin. But if you put an umbrella over yourself, you are blocking the sun rays. The sun rays don’t go around the umbrella, like convection, they are just simply blocked. Other examples of radiation include the sun heating the planets, and a fireplace heating a house. However, because heat rises in a fireplace, most of the heat from conduction is lost through the chimney, leaving the primary mode of heat transfer to your house as radiation.

All of these principles apply to the operation of rotary dryers, rotary coolers, and rotary kilns. Depending on the type of system in use, heat transfers to or from a material differently. In the case of a rotary dryer, the material is being heated directly by the gases, ie. convection. However, the material is also getting heat from the shell of the rotary dryer through means of conduction. In an indirect fired rotary kiln, conduction is the only source of heat transfer. The refractory is heated and transmits the heat from the refractory to the material by direct contact. Radiation is also present in all of these scenarios, because heat is being transferred through the atmosphere.

In the case of a rotary cooler, material is transferring heat from itself to the atmosphere (remember, heat can only transfer from a hotter object to a cooler one).

Heat transfer is an important component to consider in the operation of rotary dryers, rotary kilns, or rotary coolers. Knowing how heat transfer works can help in sizing a rotary drum, and being able to anticipate how heat will be lost throughout the system.

FEECO has been custom engineering rotary dryers, kilns, and coolers for over 60 years. For more information, see our thermal processing page, or contact us today!

“Like” our page to stay up to date on our latest blog posts, photos, and events. You can view photos of our equipment lines, from rotary dryers, to pan pelletizers, and even pin mixers. We even have pictures of FEECO through the years, since its founding in 1951.

We will be taking advantage of the timeline, and helping to share FEECO’s rich history. So what are you waiting for? Head on over to the FEECO Facebook page!

Hope to see you soon!