By Shane Le Capitaine | Process Sales Engineer, FEECO International
Potash’s unique qualities, combined with the high capacities at which it is processed, can present significant challenges to producers if equipment is not adequately designed.
In selecting a manufacturer, be sure to find one that is familiar with the specific challenges potash presents, and can design and manufacture equipment suited to its needs.
Common potash processing challenges
Clumping & caking
Potash’s ability to absorb moisture from the environment poses several challenges during production. This hygroscopic quality can lead to clumping, sticking, buildup, and caking issues during pelletizing, drying, handling, and storage. Ultimately this translates into product loss, increased downtime and maintenance expenses, and in some cases, safety risks.
While facility and product moisture management to abate these risks must be a primary focus at potash operations, equipment should also be designed to minimize any potential clumping or caking. Designing around this hygroscopic nature can be broken down into three primary categories:
Materials of construction: Materials of construction, as well as surface treatments and coatings, play an important role in mitigating the potential for clumping and caking in equipment. Smooth finishes, such as the use of polished stainless steel, discourage material from catching and accumulating in equipment.
Managing buildup: Despite careful selection of materials of construction and surface treatments for equipment, some buildup is still possible, requiring further preventative measures.
Potash’s sticky nature makes conveyors particularly prone to carryback, or the sticking of material onto the underside of the belt after discharge. This allows material to migrate to idlers and other mechanical components, potentially clogging up equipment and causing corrosion over time. Dual-belt cleaners are recommended to manage carryback and prevent fugitive material from navigating to unprotected components.
Clumping and buildup is also common during the drying stages of processing, where moisture content is generally higher. The use of knockers on rotary dryers and flexible liners in granulation drums is useful in this effort, dislodging any clumped material from the drum’s interior.
Product coating equipment selection: Caking of finished potash products is also a serious concern and is widely addressed through coating granules with anti-caking agents.
Producers employing this technique must consider that the coating is only as good as its application; a granule must be completely coated to prevent moisture from infiltrating the granule and beginning the formation of crystal bridges (the origin of caking).
This need for maximum coating uniformity makes the selection of proper coating equipment essential. In this case, a coating drum can offer more uniform coating compared to alternatives, as a result of the rolling action that occurs in the material bed, which helps to evenly distribute the coating.
Because coatings and granule properties vary widely, producers should conduct testing in a process development facility such as the FEECO Innovation Center to establish process criteria and ensure consistent results.
Corrosive properties
Potash is notoriously corrosive and can quickly degrade equipment if not properly addressed through initial design and construction.
Because increased moisture accelerates corrosive action, corrosion is especially problematic when working with potash in a high-moisture state; any surfaces or components in contact with the wet material should be fully seal-welded and welds ground down to a smooth surface to prevent areas where material could potentially catch and accumulate.
One effective approach to preventing corrosion during the drying process (where moisture content is high) is to construct the inlet area of the rotary dryer with an alloy or stainless steel. This provides protection from corrosion until further down the drum where the material’s moisture content has been sufficiently reduced so as not to be destructive to carbon steel.
Heat sensitivity (discoloration)
Potash can also exhibit sensitivity to heat, particularly as a finished product. If not careful, overheating potash could result in product degradation (increased attrition) and discoloration.
To avoid the risk of overheating potash, FEECO recommends a co-current flow rotary dryer. The co-current configuration puts the hottest combustion gases in contact with the material during its wettest state. This promotes an initial reduction of moisture and then a more gradual, gentle drying action as the material moves down the length of the dryer.
In contrast, a counter-current dryer would expose the product to the hottest combustion gases at the outlet, where the material is in its driest state, increasing the potential for discoloration and product breakdown due to high heat exposure.
The incorporation of a combustion chamber is also useful in maintaining product integrity when drying potash, as it prevents direct contact between the material and burner flame.
Attrition
Attrition, or the breakdown of product into dust and fines, is a concern with any potash product, but it is especially troubling with granules produced via compaction granulation. This is due to the jagged, irregular edges that rub together and break down.
While glazing (spraying the hot potash with a mist of water to cause crystallization of the granule surface) offers an effective approach to reducing attrition, the effect can be enhanced by conducting the glazing process either within the rotary dryer (at the outlet), or in a separate polishing drum.
In both cases, the rolling and tumbling action of the bed imparted by the rotating drum helps to polish granules, breaking away any loose edges.
Attrition is less of a concern with granules produced via wet granulation methods, but the use of a rotary dryer for the finished product can still offer some benefit, further polishing the rounded granules.
High processing capacities
The large-scale production common in potash processing settings requires equipment that can handle substantial volumes while maintaining efficiency and reliability. Equipment must be robust enough to manage the high throughput, without compromising on performance.
Equipment must be backed by incredibly robust engineering and fabrication, and underpinned by strict quality control practices.
In addition to selecting proper materials of construction, this translates to following tight tolerances, as well as ensuring precision welding and expert fitting.
In selecting a manufacturer, request quality control documentation and look for proven reliability through case studies, project profiles, or customer references.
Maintaining potash equipment
As important as it is to choose the right equipment, it is equally important to select an OEM that can support the equipment after the sale; even the most well-designed equipment must be properly maintained to ensure continued reliable operation.
The demanding conditions potash equipment operates within make regular maintenance and routine monitoring even more vital in minimizing unnecessary downtime and prolonging equipment life.
Conclusion
While potash can be tough on production and handling equipment, designing equipment around potash’s unique characteristics and high throughput, as well as following maintenance recommendations, is the best way to ensure reliable, long-lasting equipment. Always work with a manufacturer with proven experience that can tailor equipment to potash production conditions and continue to support their equipment after the sale.
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