A Look at Micro Pelletizing

This article was co-authored by:

Chris Kozicki
Agglomeration Expert

Carrie Carlson
Technical Writer

What is Micro Pelletizing?

Micro pelletizing is the process of agglomerating material fines into small pellets. Unlike traditional pelletizing, where slightly larger pellets are produced, micro pelletizing produces pellets around 20-60 mesh.

Micro pelletizing can be carried out either in a stand-alone pin mixer (this process is sometimes referred to as “conditioning”), or with a pin mixer/disc pelletizer combination. When a full-scale pelletizing operation is not necessary, or when only smaller pellets or material conditioning is needed, the use of a pin mixer to micro pelletize material offers a cost-effective alternative to a full-scale pelletizing operation and can provide sufficient results.

Why Micro Pelletize?

Micro pelletizing is used to process fine materials in order to make them easier to handle, transport, and use. There are several reasons why this may be desirable: to improve how a product performs, to reduce product lost to dust, to condition a material prior to landfill, and to reduce other issues associated with dust.

Benefits of Micro Pelletizing

Like all agglomeration techniques, micro pelletizing a fine material ultimately reduces or eliminates dust, which offers a variety of benefits:

Significant Dust Suppression/Elimination

Dust reduction or elimination is beneficial for many reasons. Sometimes, materials are micro pelletized prior to being landfilled, to avoid excessive amounts of wind-blown material. This is commonly seen with fly ash, a by-product of burning fossil fuels that comes in the form of an ultra-fine powder. While some fly ash can be recycled into other products, other fly ash is not usable, and is therefore micro pelletized, or conditioned, before it is brought to a landfill, to avoid it being carried away by the wind upon deposit.

Dust suppression is also beneficial during processing. If not well managed, fugitive dust can easily escape into the air, which can not only damage equipment if left unchecked, but can also be a health and safety hazard. An extreme example of this can be found at coal-fired power plants, where coal fines are generated. Here, coal fines are micro pelletized because fugitive coal dust can be combustible if sufficiently aerated.

Dust reduction or elimination is also valuable because it reduces the amount of product or raw material lost to waste as dust, a common problem among dusty materials. This results in more usable material/product, and a reduction in material waste.

Improved Handling and Transport

As one can imagine, a fine, dusty material can be difficult to move around or haul without losing a significant amount of material. Micro pelletizing allows the material to be much more easily handled and transported, because micro-pellets offer significantly less dust, and won’t be easily picked up by the wind.

Improved Application and Use

While micro pelletizing generally focuses on making a material less dusty and easier to handle, it also allows for improved application and performance in many instances. A good example of this can be found in the agriculture industry, where soil amendments are sometimes micro pelletized, offering significant benefits, including:

  • More accurate application – micro pellets can move through spreading equipment much more efficiently than powdered materials, making application more precise and reliable.
  • More predictable results – Because micro pellets won’t blow away like a powdered material might, applications stay where they are applied, delivering nutrients where they are needed, and nowhere else.
  • Faster product breakdown – smaller pellets are more quickly broken down than larger ones and thus, in the case of soil amendments, nutrients reach the soil sooner.
  • Reduced visibility – micro pellets sink between the grass blades quickly. This is beneficial because the application does not detract from the beauty of the turf, a valuable characteristic for applications such as golf courses and lawns. This is a common reason for choosing micro pellets over larger particle sizes.
  • Micro pellets also offer the opportunity to serve as a “core” for applications that require the pellets to be coated, but still need the pellets to remain in the desired size range.

Materials that are Commonly Processed Using Micro Pelletizing

Because micro pelletizing can benefit nearly any material that comes in the form of a powder, the applications for micro pelletizing are innumerable (and growing!). Some of the most commonly micro pelletized materials include:

  • Pigments and Dyestuffs
  • Carbon Black
  • Coal Dust
  • Fly Ash
  • Specialty Powders
  • Filter Media
  • Catalysts

Micro Pelletizing in a Pin Mixer

While micro pelletizing can be done in a pugmill mixer, it is best carried out in a pin mixer. Pin mixers are the industry standard for micro pelletizing, offering an ideal solution for agglomerating material fines into small pellets. For this reason, pin mixers have been used extensively for decades in both the coal and carbon black industries.

Pin mixers utilize a high-speed spinning action that not only thoroughly mixes liquid and solid feeds, but also begins to agglomerate material fines as well, resulting in small, dense pellets. Pin mixers can act as a continuous, stand-alone unit to quickly and reliably produce micro-pellets in a process setting.

A Typical Micro Pelletizing Setup Looks like This:

Raw feed material is fed into the pin mixer at a continuous rate. Simultaneously, a binder spray system sprays binder into the pin mixer at a continuous, specified rate.

The material feedstock and binder are thoroughly mixed, and begin to agglomerate, forming micro pellets as the mixture moves through the length of the pin mixer.

At this stage, a disc pelletizer could be utilized to further grow and/or round the pellets if desired. In this scenario, the pin mixer prepares the material for optimal pellet formation on the disc. It also allows the target moisture level to be reached prior to the disc pelletizer, which can increase production and decrease the amount of binder required, because densification is being carried out in the pin mixer through motion, instead of on the disc pelletizer with additional binder.

After pellet formation is complete, micro-pellets are then typically discharged from the pin mixer, and carried via a conveyor to a rotary dryer, in order to reduce the moisture content of the pellets down to the desired level. Here, pellets tumble through the rotating drum, while flights pick up the material and drop it through the stream of process gas, maximizing heat transfer efficiency. A fluid bed dryer is also an industrial drying option in this setting.

Pellets are then discharged from the dryer, and taken by conveyor to their next processing stop (screening), or to storage or bagging. In some instances, it may also be desirable to cool the material prior to bagging or storage. Similar to drying, this can be carried out in a rotary cooler or fluid bed cooler.

Micro pelletizing offers a host of benefits, including reduced dust, improved handling, and enhanced application. Furthermore, when only rough agglomeration is desired, micro pelletizing in a pin mixer alone offers a cost-effective alternative to a full-scale disc pelletizing or drum operation.

FEECO has been a leader in agglomeration technology and equipment since 1951. We have the material experience and process knowledge to bring you the best agglomeration solution for your processing needs. Plus we offer extensive testing capabilities in our Innovation Center. For more information on our agglomeration systems, contact us today!

About the Authors . . .

Chris Kozicki is a Process Sales Engineer and agglomeration expert.

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Carrie Carlson is a technical writer and visual designer.

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