Rotary drum granulators, also known as agglomeration or granulation drums, are pivotal to a wide array of industrial processes, helping producers working with bulk solids to condition and agglomerate their materials for downstream processing, easier handling, and improved performance.
In selecting agglomeration/granulation equipment and evaluating the fit of a drum granulator for a given process, many questions may arise. What follows are some of the most frequently asked questions we field in the process of helping our customers bring their granulation processes to life.
How does a rotary drum granulator work?
A drum granulator works by tumbling material in the presence of a liquid binder to encourage granule formation and growth. Feed material and binder are constantly fed through the rotating drum. The rolling action, combined with the stickiness from the binder, causes fines to collect together into particles. These particles continue to pick up additional fines and binder as they tumble in the bed, causing them to densify and pick up additional layers in a phenomenon known as coalescence. Tumbling flights can be incorporated into the unit to increase agitation of the material bed.
This way of forming agglomerates is a type of agitation agglomeration also known as wet granulation, balling, or pelletizing.
What types of materials can a rotary drum granulator process?
Generally speaking, drum granulators can process any bulk solid in the form of a dry, fine powder. This flexibility lends well to a host of industries, processing materials ranging from specialty chemicals and fertilizers, to minerals and ores, and everything in between.
In some cases, the feedstock may require pretreatment in the form of crushing, grinding, or drying to be a suitable feed for the granulator and produce the characteristics desired in the end product.
What’s the advantage of a rotary drum granulator over a disc pelletizer?
In choosing between a drum granulator and a disc pelletizer, the drum is often chosen because it offers a higher throughput than the disc pelletizer. The rotary drum also has the advantage of being a “closed” system, meaning that granulation occurs inside a contained environment, so fugitive material is limited.
What capacities can a granulation drum accommodate?
Granulation drums can be customized to nearly any size, accommodating capacities ranging from 500 lb/hr – 3500 TPH+.
Are drum granulators batch or continuous?
Rotary drum granulators are typically employed in a continuous setting, though they may function as a batch device in some R&D environments, such as the FEECO Innovation Center.
What is the retention time of a rotary drum granulator?
Retention time is one process parameter used to control the characteristics and quality of the material exiting the drum, so it can vary significantly depending on the process and product goals. In general, retention time in a granulator may fall anywhere between 30 seconds and 60 minutes.
What are the typical wear items?
Rotary drum granulators are generally low maintenance, but some items can become worn, depending on the operating conditions, and particularly if the drum falls out of alignment. The most common wear items for a drum granulator typically include the liner (where applicable), tumbling flights (where applicable), and potentially trunnion wheels, tires, and thrust rollers.
Rotary drum alignment is an important aspect of drum maintenance to prevent wear of the tires and trunnion wheels. When a drum falls out of alignment, it puts added stress on all components, encouraging undue wear.
Does the product exiting the granulator require drying?
Since the granulation process relies on a liquid binder to form and layer granules, the product exiting the granulator is wet and must be dried unless it is moving immediately to a downstream process that does not require drying (such as in the case of iron ore balling, where pellets go to a grate kiln).
Drying is typically carried out in a rotary dryer, which further rounds and “polishes” the granules as a result of the tumbling action that occurs as the drum rotates.
How do I know if a rotary drum granulator is right for my application?
Whether or not a rotary drum granulator is the right fit for a given project depends on specific process and product goals, such as capacity, level of control over particle characteristics, product parameters, and more.
When it is not clear if a drum granulator will be able to meet the project objectives, testing can be carried out in the FEECO Innovation Center to evaluate the process and identify the most suitable equipment configuration.
Is any other equipment required to support a rotary drum granulator?
Drum granulators require a feeding and offtake system to convey material into and away from the drum. They also typically require screens and a recycle circuit to recover overs and unders and recycle them back into the process
Drum granulators are also typically followed by a rotary dryer and in some cases, may be preceded by a mixer for providing a homogeneous feedstock to the unit.
What does the design process look like?
Rotary drum granulator design typically begins with testing to assess the feasibility of granulating the intended material and to gather key process data such as percent fill, retention time, drum speed and slope, spray system design, and more.
Once the data has been gathered, engineers work off of this to size the drum and incorporate any necessary features or modifications needed to produce the desired product at the intended capacity.
What data is needed to design a rotary drum granulator?
A variety of data points are necessary to design the granulator. Along with a process description, the follow data is typically required:
Raw Feed Data
- Material and chemical composition
- Moisture content
- Temperature
- Bulk density and true density
- Material consistency (sticky, plastic, etc.)
- Material qualities (abrasive, heat sensitive, hazardous, etc.)
Product Data
- Desired particle size distribution (PSD – minimum and maximum)
- Expected bulk density
- Binder use and restrictions
Process/Equipment Data
- Preferred materials of construction
- Electrical controls (volts, hertz, phases)
- Temperature of ambient air in processing environemnt – minimum and maximum
- Humidity of ambient air in processing environment – minimum and maximum
- Elevation of plant
- Retention time (if known)
Depending on how much is known about the material, much of this data is often gathered through testing.
What materials of construction are available?
Rotary drum granulators can be constructed from nearly any form of steel desired. Carbon steel is typical, as is stainless steel and abrasion-resistant steel.
Depending on the application, various liners are also available for protecting against corrosion and helping to reduce buildup in the drum.
Can the granulator be automated?
Yes. Rotary drum granulators can be fitted with programmable logic controllers (PLCs) and motor control centers (MCCs) for automating the unit, adjusting the process from a human-machine interface (HMI), as well as collecting and trending valuable process data.
Are drum granulators customizable?
Yes. Rotary drum granulators offer ample opportunity for customization. FEECO tailors the mechanical components, internals, materials of construction, size, and more to optimize how the unit works with the material to produce the desired results efficiently.
A variety of add-ons and customizations are available as well, including knockers, liners, spray systems, and more.
Will the process require a recycle circuit?
While some processes don’t necessarily require a recycle circuit, the addition of one is always recommended, as it helps to make the process more efficient.
In other cases, a recycle circuit is necessary for the operation to function on a continuous basis, relying on recycled fines to bring down the moisture content of the feedstock entering the process (a processing technique known as back mixing).
Conclusion
Rotary drum granulators provide a reliable, high-capacity processing device for conditioning and granulating bulk solids in a range of settings.
FEECO granulators are expertly engineered to suit the specific processing objectives at hand, and can be provided as a standalone unit or as part of a complete granulation line. In addition to the world’s most reputable granulators, FEECO also provides feasibility and process development services, as well as parts and service support. For more information on our granulation drums, contact us today!