New granulators are more demanding regarding input materials. New organic fertilizer granulators utilize a wet agglomeration process, where materials roll into spheres on the pan surface using their own moisture content. They operate within a narrower window for moisture content and particle fineness compared to older equipment—requiring stable moisture levels of 25%–35% and fineness exceeding 60 mesh. If the upstream semi-wet material crusher fails to achieve sufficient fineness, or if moisture levels fluctuate significantly after fermentation and turning, the new granulator struggles to "feed" properly or form round granules. Consequently, the granulation rate plummets, the volume of recycled material surges, and actual output inevitably declines. Older equipment often relied on high water input and high rotation speeds to force granulation; while granule quality was poor, the output figures looked impressive. In contrast, new equipment prioritizes high quality, thereby imposing stricter requirements on pre-processing.

Bio-organic fertilizer granulation involves an additional constraint: a temperature limit. When producing bio-organic fertilizer, the new granulator must operate below 55°C; otherwise, the functional bacteria will die in large numbers. This means fermented material must be thoroughly cooled before entering the granulator—a process that takes time. If the production pace of the old line is maintained—feeding hot material directly into the machine—the granulation temperature will exceed limits, killing the bacteria and forcing the product to be downgraded from bio-organic to standard organic fertilizer. Without integrating a cooling step into the upgrade, both output and quality will suffer.

The double-roller extrusion process, meanwhile, faces challenges regarding "fineness matching." If a production line switches from the wet disc granulation process to dry extrusion—installing a double-roller press granulator and associated roller press machinery—it is essential to ensure that the feedstock is pulverized to a fineness of ≤0.6 mm and has a moisture content of 8%–15%. Roller extrusion granulation relies on high-pressure forming; consequently, the roll gap and pressure settings must be recalibrated based on the specific material properties. If the coarse pulverization and natural moisture levels of the old line are retained, issues such as roll slippage and loose material cakes arise. The granulation rate plummets from 80% to 50%, and the overall capacity of the roller press granulation line is crippled by the burden of recirculating material.

In contrast, a BB (Bulk Blend) fertilizer line should not be retrofitted with a granulator at all. BB fertilizer lines utilize finished granules as raw materials and perform only physical blending. BB fertilizer mixers employ a twin-shaft paddle design for gentle mixing, achieving homogeneity (CV ≤5%) within 2 to 5 minutes. Installing a modern granulator on a blending line would actually damage the granule structure, generate fines, and exacerbate material segregation.

Upgrading a production line is not merely a matter of swapping out individual machines; it requires systemic compatibility. Modern granulators demand finer material pre-treatment, stricter temperature control, and a well-matched material recirculation design. Installing new equipment into an old system is akin to using standard engine oil in a sports car—no matter how excellent the machine is, it cannot achieve its intended performance.