Granulation of fertilizer products provides some of the most viable ways to blend minerals to create a multi-nutrient fertilizer, allow for bulk storage and packaging, as well as provide ease of handling and application. One piece of equipment that has become known for its consistency and versatility in fertilizer manufacturing is the rotary granulation drum. This rotary processing equipment and the variety of products it is able to manufacture is an ideal fit for the fertilizer industry’s broad and ever-changing demands.
Granulation Drum Design
A rotary granulation drum is relatively simple in design – raw material is fed into a large rotating cylinder, liquid binder is added, and the material tumbles to create solid, spherical pellets. However, extensive design and engineering is needed in order to build a quality piece of equipment capable of creating a consistent product at high capacities.
Several questions must first be addressed before design can begin. Some of these questions include:
- Is the material(s) organic vs. inorganic?
- What is the nutrient content?
- What binders will work the best for the desired time release, while still preventing degradation from storage and shipping?
These, along with many other factors, will affect the overall design of a granulation drum.
After the multitude of material questions have been answered, efforts move to the sizing aspects of the drum, which will control the desired output (usually measured in tons per hour {tph}). Finally, rotational speed and drum slope need to be taken into account. To get a consistent granule, the granulation drum has to run at a speed that allows the material to cascade off the side of the drum; too slow, and the material will shuffle back and forth at the bottom of the drum, too fast and the material will cling to the drum walls due to centrifugal force.
A perfect balance must be achieved. This balance point is usually obtained through research and development at FEECO’s on-site Innovation Center, or through our years of experience and knowledge of the fertilizer industry and its many material compositions.
Advances in Granulation Drum Design
Nearly all industries have seen tremendous advancements due to modern technology. Some of the common advancements in granulation drum design include:
Integrated Pipe Reactor: Completely mixes and reacts ammonia with phosphoric and/or sulfuric acid, creating a neutralized liquid or hot melt that is then sprayed into the drum. This eliminates the need for pre-neutralization tanks and also increases efficiency.
Flexible and Corrosion-Resistant Drum Liners: Can be used to reduce or eliminate material build-up on the drum walls, as well as decrease the damage caused by corrosive materials/binders.
Tumbler flights: Used to increase the material agitation to perfect the cascading effect and create the desired granule properties.
How the Granulation Drum Produces a Superior Fertilizer Product
The definition of a granule, as it relates to this piece of equipment, is a solid, spherical pellet, in the size range of approximately 1-6 mm. These granules can vary in properties and chemical makeup, depending on what is desired for the application. An inorganic fertilizer such as NPK, which is considered a multi-nutrient fertilizer, consists of nitrogen (N), phosphate (P), and potassium (K), and is a commonly pelletized product. A granulation drum is frequently used to agglomerate these minerals, which typically start as a fine powder. The minerals can be blended into one granule, providing an all-in-one product, or the individual granules can be blended with others later in packaging. Without this technology, the fine powdery materials would be dusty and hard to handle; the denser particles would settle to the bottom of the bag or barrel, creating an inconsistent blend and causing significant application challenges.
In addition to developing a durable and consistent granule, a granulation drum can also create a more dynamic granule. Different liquid binders can be used to create an encapsulated granule that has different time release properties, or a multi-layered pellet can be created by adding different minerals at varying stages of the granulation process.
In the granulation of inorganic fertilizers, for example, the production of diammonium phosphate (DAP) or monoammonium phosphate (MAP), the granulation drum is utilized for a continued chemical reaction in correlation with the formation of a solid granule. The reaction, traditionally initiated in a pre-neutralizer tank, neutralizes the phosphoric acid slurry with ammonia, while simultaneously creating a granule that contains both phosphate and nitrogen, two vital nutrients needed in a multi-nutrient fertilizer. However, as previously mentioned, another option that can increase efficiency in some settings is the addition of a pipe reactor, which pre-mixes the liquids and forms DAP or MAP hot melt. The hot melt is then fed into the granulation drum; the heat from the chemical reaction along with a specific amount of dry, seed material creates a pellet containing both nitrogen and phosphate.
The granulation drum’s versatility does not end at DAP or MAP creation; potash powder can also be introduced into this process to create a complete NPK. The cascading effect of the drum rotation works well with almost any combination of wet and dry inorganic minerals.
The fertilizer industry has been utilizing rotary granulation drums for many years with no signs of stopping. This versatile piece of equipment has helped bring numerous fertilizer products to the consumer market by creating a durable granule that is easy to package, ship and apply. FEECO has been manufacturing equipment for the fertilizer industry since 1951. We take pride in the quality of our equipment and strive for new and innovative solutions to all of our customer’s needs.
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