Disc Pelletizers

Not all materials respond favorably to agitation agglomeration, so disc pelletizers are not always an option. Further, depending on the end product goals, a different type of equipment might suit the process or product better.

Determining whether or not a disc pelletizer is the best fit for an intended agglomeration process is typically based around expertise, testing, or in many cases, both. Pelletizer feasibility tests can be used to assess whether or not a disc pelletizer is a good fit for a new material or novel application.

Oftentimes, past experience can inform the manufacturer on whether or not a disc pelletizer is the best fit for a given material, though it’s important to note that even the same material from different sources can respond differently to agglomeration based on its unique physical and chemical composition, making testing a valuable tool.

Disc pelletizers are capable of producing a wide range of pellet sizes, typically anywhere from 40 mesh to ¾” (400μm to 20mm).

Yes. Pelletizing relies on a liquid binder, along with agitation, to join fines together and continue layering material onto them. The liquid binder is what allows the fines and pellets to become tacky so they can continue to coalesce.

With that said, in some cases, the material may naturally exhibit a binding agent. This is rare, and an additional binder (or simply water) may be needed to bring the material to the required moisture range needed for pellet formation, but it can happen.

Like other agitation agglomeration equipment, disc pelletizers employ agitation and a liquid binder (in most cases) to encourage granule formation and growth. The disc pelletizer is a continuous device.

Fines or premade seed pellets are continuously fed to the disc pelletizer, along with the liquid binder. The disc rotates at a predetermined speed and angle. As fines or seed pellets pass under the binder spray, they become tacky, which allows them to pick up additional fines, layering and growing larger. The centrifugal force of the rotating disc carries pellets of varying sizes up the side of the pelletizer and causes the different sizes to self segregate upon cascading down the face of the pan. Once pellets reach the desired size, they discharge from the pelletizer.

Several variables can be adjusted during processing in order to respond to changes in feedstock or refine pellet formation and growth.

Disc pelletizers are available in a wide range of sizes to accommodate various capacities. Pelletizer capacities typically range from 100-500 pounds per hour (lb/hr) (depending on the size) to 100 tons per hour (TPH).

Disc pelletizer size is dependent on many factors, but is typically a function of pellet size, desired capacity, the material’s bulk density, and whether or not a preconditioning step (typically a pin mixer) is utilized. Equipment engineers often use a testing program such as those available in the FEECO Innovation Center to inform on sizing and design decisions.

It is a common setup to precede the disc pelletizer with a pin mixer as a preconditioning step in a pelletizing operation. A pin mixer typically always adds benefits to the process and material, but is not essential in all cases.

If the pellet must be made up of a homogeneous mixture of multiple feedstocks, a pin mixer (or pugmill mixer) will be required, because the disc pelletizer is not intended to homogeneously mix multiple components.

Likewise, if the operation requires a certain capacity that the disc pelletizer alone cannot meet, the addition of a pin mixer will speed up production and allow the system to reach a higher capacity.

Operations with strict dust control standards may also require a pin mixer (in this setting, the pin mixer provides an enclosed vessel in which to mix the liquid binder and fines, providing a mixed and de-dusted feedstock to the disc pelletizer.

Because a liquid binder is used to aid in granule formation, pellets typically require drying.

However, some pellets may “self cure” with time, while other downstream processes may not require dry pellets, making the drying requirement situation-dependent.

Pre-grinding may or may not be necessary depending on the particle size distribution of the feedstock in its natural state.

The particle size distribution at which optimal pellet formation can occur is different for each material, but in general, falls below 60 mesh, or 250 micron. Material that falls beyond this will require grinding.

Additionally, particle shape can also impact the pelletizing process, so pellets that are oblong or rectangular are likely to require grinding as well.

While pelletizers are capable of producing pellets alone, they are typically not used in isolation; instead, they are part of a larger system that helps to prepare pellets, process recycle, and dry the pellets. A typical pelletizer plant utilizes the following:

• Pin mixer (for preconditioning feed and binder for the pelletizer – NOTE – as mentioned above, pin mixers offer many benefits but are not necessary in all cases.)
• Disc Pelletizer
• Liquid Introduction System (for binder incorporation)
• Rotary Dryer
• Screen
• Hammer/Chain Mill (for crushing oversize product to use as recycle)

Yes. In addition to the various sizing options, pelletizers can be customized in a number of different ways. This includes the use of different materials of construction (such as stainless steel), a full or partial hood/cover, use of a variable frequency drive (VFD), or inclusion of a reciprocating scraper.

While not all aspects of pelletizer operation allow for automation capabilities at this time, it is possible to gather pellet moisture content at discharge, as well as material feed rate and the amount of liquid being sprayed onto the product.

Typical retention time on a disc pelletizer ranges from one to three minutes, though this depends on several factors. The retention time required to reach the desired pellet size and quality is also dependent on whether or not a pin mixer precedes the disc pelletizer.

Retention time on the disc can be reduced if a pin mixer is utilized prior to the disc, because the pin mixer uses motion to densify the product and create seed pellets (as opposed to additional binder which must be added gradually on the pelletizer).

An operator can supervise more than one disc pelletizer at a time. However, because there are variables in the pelletizing process and operators must be able to respond to changes in production or feedstock, if the operator is inexperienced, fewer may be better.

Pelletizer training programs are a valuable option for helping operators to understand the process and equipment.