Why Your Potash Granulation Loop Fails - and How to Fix It

23.07.2026, Remscheid

Sigurd Schütz, RHEWUM GmbH

In potash compaction, nothing is trivial: a single weak point can destabilize the entire granulation circuit - because small influences have big and costly effects. From pressing force to roller wear to the screening machine as the true "value-adding machine" - we have summarized the 10 most critical points that really matter.

The granulation loop in potash compaction is not a linear process - it is a closed system in which every stage affects every other. Roller press, impact mill, and screening machine are so tightly interconnected that a single weak point can destabilize the entire operation. As experts in precision screening classification, we accompany this loop time and again at its most critical interface - and know exactly what throws it off balance. A compaction-screening loop that "runs out of control" leads to an overload of the roller press, which then - as the most expensive single machine in the system - becomes the bottleneck that limits overall output. The rule is simple: small influences have large - and costly - effects.

01 | Flake Quality: Pressure Makes the Difference

The roller press compacts fine salt under pressure into a solid flake - if that compaction pressure is too low, the flake disintegrates in the downstream impact mill into fines rather than granules. These fines travel back into the fine salt loop after screening and worsen the ratio of fines to fresh salt, further weakening the next compaction run. The result is a self-reinforcing vicious cycle that can push mass yield below 20% and lead to an overload of the roller press.

02 | Compaction Pressure: Hard to Believe - Too Little and Too Much Both Kill Performance

The optimal operating pressure of a roller press depends on material temperature, particle size distribution, and moisture content - and typically falls in the range of 30 to 50 kN/cm for potash. Too little pressure produces fragile flakes with a high fines content; too much pressure accelerates roller wear and drives up energy consumption unnecessarily. The hydraulic system, which simultaneously acts as a safety valve against foreign objects, must therefore be continuously monitored and regularly adjusted to match process conditions.

03 | Roller Wear: A Concave Roll Profile - The Silent Process Enemy

Under the continuous abrasion of potash salt, the rolls develop a concave profile - compaction pressure then distributes unevenly across the roll width, producing weak flakes at the wider nip. Some manufacturers address this with specially hardened roll shells, but even optimized surfaces are subject to wear and shaft deflection. A worn profile often goes undetected until the loop has already been destabilized.

04 | Impact Mill Breaker Bars: Sharp - or Useless?

Sharp-edged breaker bars strike the pre-broken flake centrally and produce controlled size reduction into the target particle range of 2 to 4 mm through impact stress. When the bars are worn, uncontrolled edge impacts replace clean fractures - fines content rises, granule yield drops. Both hurt plant performance. The wear itself is gradual - but its effect on the loop is exponential: more fines means more recirculation, lower throughput, weaker flakes.

05 | Fine Salt Loop Ratio After Screening: The Invisible Control Variable

The ratio of recirculated fines to fresh fine salt from the dryer largely determines the compactability of the blend in the roller press. Too much fines degrades pressability; too little leads to air entrapment and unstable flakes that generate unnecessary undersize in the downstream flake crusher. Operators who continuously monitor this ratio and actively control it via dosing equipment have one of the most powerful levers for product quality and mass yield at their disposal.

06 | Loop Overflow: When the System Collapses

When the loop generates more material than can be discharged - for example due to excessive fines formation, blinded screen panels, weak flakes, or over-milling of flakes - the loop can run in overflow for hours, overloading every piece of equipment in the circuit. Positive feedback is the real problem: once out of balance, the disturbance amplifies itself, and restoring normal operation requires significant intervention. Continuous monitoring with automatic control of material flows is the only reliable preventive measure - alongside correct sizing of the screening machine as the only discharging component in the loop.

07 | Aperture Size: What You Don't Know Will Cost You

Choosing the right aperture size is not a minor detail: at a typical flake throughput, a deviation of just 0.35 mm in the bottom screen deck can cause enormous quantities of recoverable granules to be incorrectly discharged into the fine salt loop - a measurable financial loss that adds up fast. Do you know the right aperture shape? Square apertures tend to blind with granular potash; slotted apertures deliver significantly more stable results at the same separation sharpness. RHEWUM tests different screen media types on the actual product in advance to minimize good-product loss and blinding tendency.

08 | Near-Size Particles: Open Screen Media Is Everything

Particles whose size closely matches the aperture opening get stuck and block the effective screening area - with hygroscopic potash salt, these near-size particles also swell slightly and cause the screen mesh to blind, amplifying the effect further. RHEWUM screening machines of the REHEduo® and RHEduox® series address this through adequate screen area and integrated screen media cleaning. The screen cloth stays open even with difficult, hygroscopic products - without production downtime. A blinded screen cloth easily leads to product overflow that overloads downstream equipment.

09 | Damaged Screen Panels: The Defect That Eats Quality

Tears, broken apertures, or enlarged mesh openings cause misclassification: oversized particles enter the fines stream, undersized particles enter the product - both contaminate the loop, degrade the specification, and impair circulation volume. Damaged screen panels must be replaced immediately, as a single defective panel overloads adjacent screen surfaces and systematically extends the damage. Keeping replacement screen cloth in stock protects against unplanned production stoppages that can easily last several hours after a mesh failure - with delivery lead times that can stretch to several weeks.

10 | Screen Machine Sizing: The Discharge Point Creates the Value

The screening machine is the only piece of equipment in the loop that discharges product - and therefore the only one that creates value. The roller press and impact mill prepare; the screening machine decides. It is not a downstream sorting tool but the quality filter of the entire system. It also corrects what compaction cannot deliver perfectly: fluctuating compaction pressure, early-stage roller wear, and varying moisture all result in a broader particle size distribution - precise, stable screening prevents these process variations from passing directly through to product quality. Operators who size the screening machine for normal operation rather than the worst case create exactly the bottleneck that triggers loop overflow - and then amplifies itself. Screen area, machine technology, and cleaning systems must be designed for the most difficult material and the highest loop load. Because here, and only here, fine salt becomes a marketable granule - not a cost center, but the value-creation machine of a functioning process.

The potash compaction loop tolerates no half-measures. Each of the ten points can destabilize operations on its own - in combination, their effects multiply. RHEWUM develops screening solutions that do not start at the end of the chain but keep the entire loop in view: from the right aperture geometry and reliable self-cleaning to integrated material distribution and screening solutions with the necessary performance reserves.