Pelletizing

Experts in process design and material processing for over 60 years.

Limestone

Limestone is a sedimentary rock used frequently throughout the agricultural industry as a soil amendment for raising soil pH and unlocking nutrients for plant uptake.

While traditional products such as agricultural and powdered lime have served their purpose, both of these products present many problems.  

While traditionally products such as agricultural and powdered lime have served their purpose, both of these products present many problems.

Pelletized lime was created to resolve these issues. 

Ag Lime (Agricultural Lime)

Though effective, ag lime is inconsistently sized, and coarse in nature. This results in delayed product breakdown and nutrient delivery, sometimes taking years for results to be seen.  

Ag Lime (Agricultural Lime)

Though effective, ag lime is inconsistently sized, and coarse in nature. This results in delayed product breakdown and nutrient delivery, sometimes taking years for results to be seen.  Furthermore, because this product is inconsistently sized, results can bedifficult to predict.

Powdered Lime

Powdered lime negates the problems of ag lime, because it offers increased surface area and much faster nutrient delivery.

Powdered Lime

Powdered lime negates the problems of ag lime, because it offers increased surface area and much faster nutrient delivery.

However, because it is in a powder form, it is difficult to transport, apply, and handle. This can also result in windblown product reaching unintended areas.

Pelletized Lime

Pelletized lime is a limestone that has been finely ground, and then processed into a pellet form, mitigating any dust-related issues. This product offers many benefits:

• Dust-free product handling• Improved product formulations• Simplified transportation• More accurate and easier application• Mitigation of product lost as dust• Opportunity for including desirable additives

Limestone Pelletizing

Basics

Gypsum fines are fed into the pin mixer, with the addition of a binder.

Pelletizing limestone results in a durable pellet that can withstand handling, but still break down quickly under standard field conditions.

Pelletizing is carried out via tumble growth agglomeration, utilizing three main pieces of equipment: a pin mixer, disc pelletizer, and rotary dryer.

Pin Mixers Disc Pelletizers Rotary Dryers

Simplified Pelletizing Diagram1. Raw feed2. Pin/Paddle Mixer3. Binder Feed4. Spray Rate5. Disc Pelletizer6. Feed Onto Pelletizer7. Binder Feed8. Liquid Spray System9. Transfer Conveyor10. Rotary Dryer11. Vibrating Screen12. Oversize Mill13. Recycle14. Surge hopper

Pre-Conditioning

A pin mixer serves as a primary feed conditioner, mixing limestone powder with a binder. This produces densification and prepares the material for pellet formation on the disc pelletizer.

Note: not all operations utilize a pin mixer/pre-conditioning stage, but those that do often see many benefits, such as reduced binder costs, more uniform binder distribution resulting in more uniform pellets, higher throughput, and more on-size pellets.

Pelletization

Once limestone is fed onto the disc pelletizer, the rotating motion of the disc gradually rolls the tacky material to the desired size, with binder and feed being constantly added, making this a continuous process.

Drying

Once pellets have reached the desired size, they exit the disc pelletizer and are carried via conveyor to a limestone dryer.

A rotary dryer is commonly chosen when drying limestone, because of its high throughput capacity, heavy-duty construction, and ability to accept variance in feedstock.

In a rotary dryer, limestone pellets tumble through the drum, with flights picking up the material and showering it through a stream of hot air or combustion gas.   

In a rotary dryer, limestone pellets tumble through the drum, with flights picking up the material and showering it through a stream of hot air or combustion gas.  This efficiently dries and hardens the pellets into their final form. Fluid bed dryers are also an option here. 

It is sometimes desirable to cool limestone pellets prior to bagging or storage. In this case, a rotary cooler is often used, offering the same advantages as a rotary dryer. Again, fluid bed coolers are also an option.

While there are many things to consider in a limestone pelletizing operation, two of the most important factors are:

- Binder- Equipment

Binder

A binder aids in pellet formation and also helps to achieve the desired end product crush strength.  

A binder aids in pellet formation and also helps to achieve the desired end product crush strength.  Most commonly, lignosulfonate, or “lignin” is used in limestone pelletizing. If only water were to be used, the result would be a weak pellet.  

Different types of lignins are available, depending on the needs of the process. Some lignins may add extra nutrients, while others will be more cost-effective.

Consulting an agglomeration expert can help in deciding which binder will best suit your needs.

Equipment

Choosing quality equipment will go a long way in providing for an efficient, long-lasting operation that produces an optimum product. 

Choosing quality equipment will go a long way in providing for an efficient, long-lasting operation that produces an optimum product. Instead of a one-size-fits-all approach, equipment should be designed around limestone’s unique characteristics for best results.  

Limestone processing can be rigorous and demanding, so equipment should be heavy-duty and designed with such rigors in mind.

Limestone processing can be rigorous and demanding, so equipment should be heavy-duty and designed with such rigors in mind. Choosing quality equipment will not only aid in process efficiency, but will also typically require less maintenance and down time, and will often result in prolonged equipment life.

has been working with limestone for over 60 years, providing testing, process design and development, and manufacturing of custom limestone processing equipment.

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