Phosphorus is a versatile component to life on Earth, aiding in a multitude of biological processes that create strong plants, animals, and even humans.
As such a vital building block to life, it’s no wonder that ore-bearing phosphate rock is processed into all sorts of products, from fertilizers to animal feeds, and even consumer products. Despite such variation in end use, however, one industrial tool helps to make all of these products possible: the rotary dryer.
From the initial beneficiation, all the way through to the end product, rotary dryers remain a key tool in producing the many phosphate products our growing world requires.
This article will look at three key areas where products would not be possible without the help of a rotary dryer.
Drying Phosphate Rock
Beneficiation of phosphate rock differs greatly from one deposit to the next, with common methods including screening, grinding, flotation, classification, filtration, and more. In general, however, they are all processed via a wet process, resulting in a wet phosphate rock, which must be dried before it can move on to subsequent processing.
Benefits of Drying Phosphate Rock
The drying of phosphate rock is an essential step in transforming ore-bearing phosphate rock into usable products, offering significant benefits to the process as a whole, and to any subsequent processing that will need to occur. This includes:
Improved Product Handling:
Drying phosphate rock reduces moisture content, so handling issues associated with wet or sticky phosphate rock are avoided.
Reduced Potential for Buildup:
Dried phosphate rock offers reduced opportunity for buildup in equipment. This decreases the potential for equipment to clog, ultimately improving process flow and efficiency.
Drying Phosphatic Fertilizers
While a variety of phosphatic fertilizer products exist, they are nearly all produced by granulation. Here, raw ingredients are reacted and fed to a rotary granulator, where the reacted material simultaneously solidifies and granulates as it tumbles through the rotating drum. Upon granulation, the resulting material must be dried.
Drying plays a critical role in the success of fertilizer products. Since many fertilizer products will move on to bagging, storage, or shipping, the moisture content must be reduced to help prevent caking issues and to maintain product integrity.
Drying Animal Feeds
Similar to fertilizer production, phosphate rock that is processed into animal feed also requires a drying step. Here again, phosphate materials are granulated into agglomerates that must then be dried.
Benefits to Drying Granular Phosphate Products
Enhanced Product Quality:
For both phosphatic animal feeds and fertilizer products, drying can offer an added benefit when dried in a rotary dryer; granule characteristics are improved, because the tumbling action imparted by the dryer wears down rough edges, reducing the opportunity for attrition later, and essentially polishing the granules to create a premium granular product.
Hardened Granule Surface:
Drying cures granular phosphate products into their final form, yielding a hardened product that is capable of withstanding handling, transportation, and even application. As mentioned, this hardened surface also reduces the potential for caking issues during storage.
How Phosphate Dryers Work
Rotary dryers are the ideal choice in processing any type of phosphate product. Rotary dryers are robust in design and construction, allowing them to withstand the rigors of drying phosphate products. Additionally, their high throughput is ideal for the high capacity requirements of phosphate processing.
These industrial drying systems are also valued for their ability to accept variance in feedstock, which is often a given in processing phosphates, particularly at phosphate mining and beneficiation sites where ore can vary in makeup and moisture content.
Phosphate rotary dryers work by tumbling the material to be dried in a rotating drum in the presence of a drying air. These dryers are typically of the co-current air-flow configuration, meaning that the material and drying air flow in the same direction. When drying an animal feed or fertilizer product that has been granulated by reaction, this helps prevent the driest material from becoming too hot, which would result in the creation of fines and attrition. When drying phosphate rock, the co-current configuration helps to “flash off” initial surface moisture, and allow the rock to be dried through to the core as it moves down the length of the drum.
Flights, or material lifters, pick up the material and drop it through the stream of drying hot gases as the drum rotates in order to maximize heat transfer efficiency.
Material Considerations in Phosphate Drying
Phosphates can be a challenging material to work with, presenting a number of characteristics that affect the drying process. Some of the most common characteristics to take into consideration during design and development stages include:
Buildup
Because phosphate materials can tend to clump, knocking systems are typically required on rotary dryers, with the ball and tube type knocker being the most common choice. A knocking system serves to dislodge potential buildup inside the drum by “knocking” the exterior of the drum as it rotates.
A screw conveyor may also be an option in combatting buildup; screw conveyors “fling” material into the dryer, helping to break up potential clumps as they enter the dryer.
In addition, various materials of construction such as stainless steel with a 2B finish can aid in the prevention of buildup.
Abrasion
Phosphates can be abrasive. Because of this, materials of construction must be carefully chosen. Additional modifications may be required for high-wear areas, such as the material inlet of the dryer.
Dusting
Phosphates can also be a dusty material to work with. This is particularly problematic when drying phosphate rock. Here, particulate matter in the form of phosphate rock dust is collected in a baghouse as part of the emissions control system.
While this dust is difficult to handle, opportunity does lie in agglomerating the phosphate rock dust for subsequent processing, reducing the need for waste disposal of the collected dust.
Conclusion
Rotary dryers continue to provide an ideal drying medium for all types of phosphate processing operations. From animal feeds and fertilizers, to phosphate rock, rotary dryers play a critical role in helping phosphoric products get to market while offering many benefits along the way. And although phosphates can present challenges in processing, custom rotary dryers can be designed to work around these difficult characteristics, producing an end product of quality, and prolonging equipment life.
FEECO has been providing phosphate dryers and complete process systems since 1951. Our heavy-duty, custom rotary dryers are an ideal fit for the demanding conditions of a phosphate processing operation, whether you’re processing fertilizers, animal feeds, or drying phosphate rock. For more information on our phosphate dryers and other phosphate capabilities, contact us today!