The Benefits of Using rotary drying machine

Rotary dryers are a cornerstone of modern industrial processing, offering efficient, high-capacity drying for a wide range of materials. From traditional techniques to novel processes, rotary dryers are a diverse and reliable option for any facility looking to dry bulk solids.

Zoneding machine are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.

The following covers the many benefits these industrial drying systems can offer as well as applications and limitations. The article also explains how these dryers work and discusses considerations in design. 

Why choose a rotary dryer?

While a number of industrial dryer types are available, rotary dryers have remained a preferred choice for decades thanks to several key advantages: 

Customization. Rotary dryers are extremely customizable, allowing producers to tailor a system to their precise material and process goals. 

Reliability and longevity. Thanks to a robust build and simple mechanical operation, rotary dryers are recognized for their reliability and longevity. When properly maintained, a rotary dryer can operate for decades without issue. 

Tolerance to feedstock variation. One key advantage particularly suited to many bulk solids processing operations is the rotary dryer's tolerance to variation in feedstock and processing conditions. Unlike with some other dryer types, slight changes in particle size distribution, moisture content, and even throughput do not cause process upsets. 

Added polishing of granules. Producers looking to dry a granular product also favor the rotary dryer for the 'polishing' it can offer. The dryer's rolling action helps to break off particle edges and further round granules, creating a premium product. 

High throughput. Rotary dryers are also favored for their high-capacity processing, which ranges from 1 tph to over 200 tph. This makes them an ideal fit for working with bulk solids. 

Rotary dryer operation

Rotary dryers consist of a large rotating cylinder (called the 'drum') set horizontally but at a slight angle. Material passes through the drum and is heated by a heating medium according to a predetermined temperature profile and retention (or residence) time to achieve a target moisture content. 

A burner is mounted at one end of the drum, and exhaust gas handling equipment is mounted at the other end. Flexible seals connect the rotating drum to stationary inlet and outlet breechings. 

Riding rings, or tires, support the drum and facilitate smooth rotation of the unit on trunnion roller assemblies. A drive assembly, most commonly a gear and pinion type, provides the power to rotate the drum. 

Material is fed into the drum at one end and discharged at the other end, with gravity and the rotation of the drum shell helping to convey material along the slight downward slope through the unit.

The material and products of combustion may be fed into the same end of the unit (parallel or co-current flow) or into opposing ends (counter-current flow). The choice between co-current or counter-current flow depends on the characteristics of the material to be dried. 

Co-current dryers are often chosen for materials that carry the bulk of their moisture as surface moisture, as this configuration puts the hottest air in contact with the material at its wettest point. The co-current configuration is also ideal for controlling material temperature, minimizing the potential for overheating the material, diminishing the potential for discoloring the material, and reducing the generation of fines (attrition). 

In contrast, a counter-current dryer puts the material in contact with the hottest air at its driest point. This provides increased thermal efficiency for materials that must be heated to higher temperatures. The counter-current configuration is also beneficial when drying materials that have internal moisture and therefore require higher heat and an extended drying cycle to draw out the moisture.

Indirect rotary dryers

With the indirect configuration, the rotating drum is enclosed in a furnace or heat shroud, which is externally heated to prevent contact between the material and any process gasses, and the material is heated via conduction. While flights on the drum interior are ineffective in this configuration, bed disturbers are typically employed to ensure that the material bed is in constant rotation. 

Indirect rotary dryers are used in settings where the material must not come into contact with process gasses or when the particle size distribution is very small, such that direct drying would risk the material becoming entrained in the airflow. As such, indirect dryers are typically employed in processing specialty products such as catalysts and adsorbents. 

Rotary dryer applications and limitations

Few applications exist that are not a fit for rotary dryers. Their extreme versatility has them in use in nearly every industry. They are widely used to process: 

• Aggregates, minerals, and ores
• Fertilizers and soil amendments
• Limestone and gypsum
• Organic and inorganic chemicals
• Paper pulp and sludge
• Potash
• Recycled manure solids (RMS) bedding
• Roofing granules
• Salts and sugars
• Sand 

While rotary dryers are extremely universal in application, there are a few cases in which another dryer type, such as a fluid bed, may provide a better option. 

Since rotary dryers pick up and drop the material during processing, some particle degradation can occur if the material is fragile. When fragility is a concern, a fluid bed dryer may be more suitable. 

Some sludge-like materials can also be challenging for rotary dryers, though several options are available for managing a non-flowable material in the dryer, including the incorporation of a back-mix circuit.

Design considerations

While standardized designs are available on the market, rotary dryers offer the greatest efficiency, performance and reliability when designed according to the characteristics of the material to be dried, facility considerations and process goals. The following points are essential aspects of rotary dryer design. 

Material

Rotary dryer manufacturers must consider a number of material characteristics when designing a rotary dryer. Characteristics such as particle size distribution, bulk density, raw material moisture content, specific heat, heat transfer properties, fragility, chemical composition and additional physical qualities, all influence how a material will respond to the drying process. A rotary dryer must be designed around these characteristics to optimize dryer performance and longevity. 

For this reason, many producers can benefit from testing their material in a facility such as the FEECO Innovation Center. In this setting, a pilot-scale dryer is used for testing trials to gather critical process data and aid in the design of a commercial-scale unit. 

It is important to recognize that material use can have ramifications on dryer design as well, particularly on whether the dryer must be direct or indirect depending on whether or not the material can be exposed to combustion gasses. 

Facility

Operating facility factors can also influence dryer performance and must be considered during the design process. This includes elevation, whether the dryer will be operating indoors or outdoors, and climate, particularly humidity and ambient air temperature.

Exhaust gas handling

To meet regulatory emissions requirements, direct rotary dryers must be equipped with exhaust gas handling equipment. While indirect dryers must also meet local, state and federal regulations, their exhaust gas management requirements are minimal since the material does not come into contact with the products of combustion. For this reason, indirect dryers also hold greater potential for capturing and reusing waste heat in other applications in the plant. 

The level of exhaust gas handling required in a given setting can vary significantly, depending on the specific emissions produced by the system and where the facility is located. 

The most common configuration consists of an induced draft (ID) fan paired with a baghouse. This combination is ideal in settings where excessive carryover is not an issue and there is no need to treat the exhaust gas for chemical pollutants such as VOCs or fluorine. Other options include cyclones and scrubbers. 

Automation and controls

Automation and control systems are powerful tools in optimizing dryer efficiency, minimizing maintenance requirements and avoiding process upsets. Not long ago, these systems were considered a luxury, but as technology has advanced, they have quickly become a necessity in efforts to improve efficiency and maintenance planning. 

Systems range in complexity, from those that simply assist in startup and shutdown, to more advanced systems that can allow control from a remote location, alert operators when key parameters fall out of spec, and even provide trends and reporting around performance and operating data. This type of information is extremely powerful in predictive maintenance planning, as well as in optimizing overall efficiency. 

Conclusion

Due to their versatility and benefits such as high throughput and long-term reliability, rotary dryers have become the preferred option for drying a range of bulk solids, from ores to chemicals and everything in between. 

Are you interested in learning more about rotary drying machine? Contact us today to secure an expert consultation!

For optimal performance and longevity, rotary dryers should be designed around the unique characteristics of the material to be processed, as well as the process goals. This makes testing a significant advantage in developing a commercial-scale unit. 

Facility considerations also influence the design process, while local, state, and federal regulatory requirements, along with the dryer's unique emissions, dictate exhaust gas handling needs. Automation and control systems can help to maximize performance and longevity. 

For these reasons, it is important to work with an expert supplier for the design and fabrication of a commercial-scale system.

Shane Le Capitaine is process sales engineer at FEECO International. 

FEECO International

www.feeco.com

Rotary dryers are used to remove moisture from bulk materials through heating. This is done either directly or indirectly with heated air and/or gasses. They can consist of several drums (also called shells) or a single drum, with multi-drum rotary dryers enabling equipment to produce greater throughput in the same size space. Heating of rotary dryers with multiple drums is usually done directly via gas or oil burners. Some rotary dryers also have a combustion chamber positioned at the end of the feed, optimizing fuel usage to keep air temperatures the same throughout the drum. While their primary task is drying materials, some rotary dryers combine this process with shredding, separating, cooling, cleaning, or other processes.

Versatility of Rotary Dryers

Though rotary dryers are used primarily for chemical processing and mineral extraction, they are extraordinarily versatile machines. They're also widely used in agriculture, ceramics, dairy, food, lumber, paper, rubber, and other industries.

Rotary dryers can be used for applications that include:

• Dehydrating corn gluten meal after wet milling.
• Drying rice directly from the paddy.
• Eliminating contaminants in soil.
• Extracting vegetable oils.
• Processing citrus peels and pulp for animal feed.
• Removing moisture during the processing of chemicals and minerals.
• Roasting cocoa beans, nuts, and sesame seeds.
• Mineral processing and lithium mining.

A rotary dryer's job is essentially to dry out a variety of materials before, during, and after processing, including biosolids, concentrates, copper, fly ash, gypsum, limestone, manure, metal shavings and chips, plastics, potash, rubber, salts, sugars, and various ores.

How a Rotary Dryer Works

Rotary dryers are often used to process bulk materials and powders, fed continuously into the dryer's drum, along with hot air. A rotary dryer's drum rotates, using lifting flights to carry particles upwards. Near the drum's top, particles come off the lifting flight and fall through a heated air stream.

The rotary dryer's drum is at a slight incline, fed from the higher end of the drum and discharging from the bottom part. Hot air or another heated gas blows counter currently or concurrently, and as the drum rotates, material is pulled in the direction in which the drum is revolving. Once it reaches a certain angle, material falls back to the bottom of the drum, with most drying action happening as it falls through the heated air or gas.

Rotary Dryers: Direct vs. Indirect Heating

Heating in rotary dryers occurs either directly or indirectly. Direct drying happens when material comes into contact with heated air or gasses, whereas indirect drying happens due to contact with a drum that's externally heated. Normally, a combustion chamber is found in directly heated rotary dryer designs, in order to stop material from coming into direct contact with the burner's flame. Indirect drying is the less efficient means for removing moisture from material during processing, though this method is used for certain niche applications for which it performs better than direct rotary dryers.

A wide range of applications use rotary dryers that heat directly for processing bulk solids like minerals, mined ores, fertilizers and chemicals. In this direct configuration, material is heated via convection. For applications where materials must not make contact with heated gases, rotary dryers that utilize indirect heating should be used. Additionally, if a very narrow particle size distribution is necessary, directly drying the material would cause it to get trapped within the airflow. For this reason, adsorbents, catalysts and other specialty materials require rotary dryers that employ indirect drying methods.

Chemical Processing Applications for Rotary Dryers

Dry slurries and pastes use rotary dryers in mining activities to help chemically remove the ores from the rock they're found, their robust nature and large capacities make them particularly useful for handling abrasive materials. They're also used to dry and mix the chemicals used in making pharmaceuticals. Along with manure drying, rotary dryers can also be used to process fertilizers like DAP (di-ammonium phosphate) and NPK (nitrogen, phosphorus, and potassium) fertilizers of various ratios.

In chemical processing operations, rotary dryers help with:

• Augmenting handling, as dried chemical ingredients, are easier to convey.
• Forming material into specific textures, such as achieving maximal particle surface area in catalysts.
• Lowering transportation costs by removing liquids from materials.
• Meeting necessary requirements for post-processing of materials.
• Producing agglomerated chemical arrangements.
• Removing toxins in the material being processed
• Stabilizing and conserving solid materials.

Rotary drums play an essential role in chemical processing, where they serve not only as dryers but as coating drums, coolers, granulators, kilns, and other purposes. In fact, they play such an important part in many chemical processing plants that on the very rare occasions when they require maintenance, the whole plant needs to shut down. Because of their important role, rotary dryers for the industry require special designs that enable them to deal with factors common in chemical processing, such as abrasion, corrosion, and materials building up.

Abrasion

While chemical processing often involves handling abrasive materials, abrasion is further heightened by the rotary dryer's drum continuous revolutions. For this reason, rotary dryers for the chemical processing industry often use abrasive-resistant materials, along with liners. Additionally, many equipment manufacturers suggest reinforcing areas that experience more wear, like discharge and feed chutes.

Corrosion

The most common issue when working with chemical compounds involves corrosion. Many chemicals corrode materials relentlessly, while others do so under certain conditions. Minimizing the effects of corrosion is a requirement for most rotary dryers designed for the chemical processing industry. Depending on the type of drum used, special alloys or superior grades of steel are often used within a rotary dryer's construction. In cases where the material only becomes corrosive at when it has a high moisture content, stainless steel or similar corrosion-resistant alloys are used for the rotary dryer's inlet section, while the remainder is built from carbon steel. Sometimes protective coatings made from acrylics, epoxy polymers, latex or urethane are used instead, or in addition to these other strategies. Non-heating drums for coating or granulating will generally use various types of liners to resist corrosion.

Material Buildup

Regardless of the purpose for which it's used, buildup of materials in a rotary dryer's drum is often a concern, especially when working with hygroscopic or high-moisture materials. Material buildup can lead to serious issues during processing, depending on the application for which a dryer is used. This may increase the risk of fire, reduce the machine's efficiency, impede material flow or even damage the drum internally as larger chunks break away.

There are, however, ways in which rotary dryer design can discourage this buildup. For non-heating drums, linings that also protect against abrasion and corrosion are effective, while cast iron plating is also sometimes utilized. Rotary dryers can also incorporate internal knockers into the drum design, which work to dislodge buildup as it rotates. In certain cases, rotary dryer construction may include polished stainless steel to help prevent sticking.

Another way to limit buildup involves reconfiguring airflow, especially for rotary dryers used as kilns. For material that tends to clump, fitting a trommel screen to the lower end of the drum where material discharges will help break up clumps as material exits. Flight design that expends less force can also mitigate material buildup while placing advancing flights close to the inlet allows the material to quickly leave the area where the material is discharged to discourage buildup.

Advantages of Using a Rotary Dryer

Though other types of dryers have been used to dry bulk materials ' including fluid bed dryers and flash dryers ' rotary dryers are still largely preferred for industrial processing. Advantages of rotary dryers include: 

Versatility: Feedstock often varies when processing bulk solids, and the rotary dryer can tolerate variations in both feedstock and the conditions under which it's processed; this makes it more capable of dealing with changes in moisture content, particle size distribution, and throughput.

Customization: The wide range of designs, sizes, and materials from which rotary dryers can be made allows them to be easily customized to suit the material and processing objectives.

Longevity: Due to their simple yet robust design, they can operate for decades without trouble when properly maintained.

Polishing: When working with granulated materials, the rotary dryer's rolling action helps round off edges on the particles, making them more 'polished.'

Reliability: With fewer moving parts and hardy construction, rotary dryers are known to be incredibly dependable machines.

Throughput: The high capacity to process bulk solids makes them ideal for many industries, with output ranging from 1 to over 200 tons per hour.

Rotary Dryers by Heyl Patterson

Heyl Patterson Thermal Processing makes rotary dryers that are among the most versatile on the market. Used as workhorses in processing bulk and powdered solids, our rotary dryers can handle a wide range of materials, from liquid sludges to fine powders. Additionally, Heyl Patterson rotary dryers can be set for starting and finishing moisture content, retention time, air velocity, and temperatures for the product and the air used in drying.

Our rotary dryers are ideal for processing: 

Want more information on Heavy Duty Mining Equipment? Feel free to contact us.

• Biomass
• Carbon fibers
• Fertilizers
• Hemp 
• Inorganic Chemicals
• Minerals
• Pulp for paper