Refiner selection has a direct impact on fiber quality, energy consumption, and final paper properties. Yet many mills continue operating with a single refiner type without evaluating whether a conical refiner vs disc refiner would better serve their furnish and grade requirements. Both types operate at low consistency (3-6%) and share the same specific edge load (SEL) range. The difference lies in geometry — and geometry shapes everything from fiber development to operating cost.
This article compares working principles, energy efficiency, fiber quality, maintenance, and application suitability to help mill engineers make an informed refiner selection.
What Refiners Do in the Papermaking Process
Refining is the mechanical treatment of pulp fibers to develop bonding potential. As fibers pass between rotating bar surfaces, they undergo fibrillation, internal delamination, and controlled cutting. These actions increase fiber flexibility, surface area, and inter-fiber bonding strength.
Refining intensity is controlled by two parameters, as defined by TAPPI standards:
- Specific edge load (SEL): 0.5-3.0 J/m
- Specific surface load (SSL): 0.1-1.0 J/m²
The degree of refining is measured by freeness — Canadian Standard Freeness (CSF) ranges from 200-700 mL, with lower values indicating more refined stock. Both conical and disc refiners perform this function. The distinction is in how each geometry applies mechanical energy to the fiber.
How Does a Conical Refiner Work Compared to a Disc Refiner?
Disc Refiners
Disc refiners use two parallel discs — one or both rotating — with stock entering at the center and moving radially outward through the bar pattern. The flat refining zone provides uniform bar contact across the entire plate surface. Centrifugal force drives stock flow from the center toward the periphery.
Conical Refiners
Conical refiners use a tapered rotor inside a conical stator shell. Stock flows axially along the length of the cone. The geometry creates a progressive refining zone: a wider gap at the inlet narrowing toward the outlet. This gradual narrowing produces a gentler, more staged fiber treatment compared to the uniform action of a flat disc.
The conical flow path also reduces hydraulic turbulence because stock moves axially rather than fighting centrifugal forces. Disc refiners, by contrast, deliver more intense and uniform refining action across the full plate face.
Which Refiner Produces Better Fiber Quality?
The geometry difference translates directly into fiber treatment. Conical refiners favor fibrillation over cutting. The progressive narrowing of the refining zone applies increasing pressure gradually, which preserves fiber length and reduces fines generation. This makes conical refiners particularly effective for hardwood (short-fiber) furnish where maintaining fiber integrity is critical.
Disc refiners provide a stronger cutting action at equivalent SEL values. The uniform gap and centrifugal flow produce more aggressive fiber shortening, which is effective for breaking down fiber bundles and shives. For softwood (long-fiber) furnish, disc refiners handle high-intensity refining well.
Both disc refiners used in pulp processing use the same plate patterns: fine (1.0-2.0 mm bar width), medium (2.0-3.5 mm), and coarse (3.5-5.0 mm).
Which Refiner Is More Energy Efficient?
Energy consumption is often the deciding factor in refiner selection. Conical refiners operate at 50-150 kWh/t net specific energy, while disc refiners require 80-200 kWh/t for comparable refining targets. Both types share the same SEL range of 0.5-3.0 J/m and SSL range of 0.1-1.0 J/m².
The energy advantage of conical refiners stems from their axial flow path. Stock moves through the refining zone with less hydraulic resistance compared to the centrifugal flow in disc refiners. This reduces no-load power consumption and improves net energy transfer to the fiber.
In post-refining applications, mills have reported energy savings of 15-30% when switching from disc to conical units.
For mills focused on energy solutions for the paper industry, the conical design offers a measurable advantage — particularly in applications where target freeness can be reached at lower total energy input.
Which Refiner Is Best for Your Paper Grade?
Each refiner type has applications where it performs at its strongest.
Conical Refiners Excel In
- Post-refining stages
- Hardwood furnish processing
- Printing and writing papers (60-120 g/m², tensile index 40-70 Nm/g)
- Tissue grades where softness depends on intact fibers
Disc Refiners Excel In
- General-purpose refining
- Softwood-heavy furnish
- Packaging grades (kraftliner at 125-440 g/m², fluting at 90-200 g/m²)
- Recycled fiber processing
Mills processing waste paper grades such as OCC and mixed waste typically prefer disc refiners because they handle variable furnish quality and contaminant loads with greater tolerance.
For multi-grade mills running diverse furnish types, disc refiners offer the flexibility to adapt across different production campaigns.
Maintenance and Plate Life
Disc refiners have a practical advantage in maintenance. The housing design allows direct access to plates without removing the rotor assembly. Plate changes are faster, and disc plates are available in a wider range of patterns from multiple suppliers. Mills can also run different plate patterns on each disc side for targeted refining effects.
For guidance on pattern selection, see our guide on choosing the right refiner plate.
Conical refiner plate changes require removing the rotor assembly, which increases downtime per change. However, conical plates may last longer per set in some applications because the progressive refining action distributes wear more evenly across the plate surface. Both types use stainless steel or Ni-Hard alloy plates with comparable wear characteristics.
Process Control and Operational Flexibility
Disc refiners allow a wider gap adjustment range, making them more responsive to grade changes. They can operate in single-disc or double-disc configurations, adding further flexibility. For mills with frequent grade transitions, disc refiners adapt faster to new operating targets.
Conical refiners provide smoother, more predictable responses to load changes. The simpler axial flow path produces more stable operation at constant load — an advantage for mills running a narrow grade range over extended periods. The progressive refining zone also reduces the risk of sudden fiber damage from gap disturbances.
Process stability after refining also depends on downstream equipment. Proper thickening after refining ensures consistent stock delivery to the paper machine.
How to Choose Between a Conical and Disc Refiner
No single refiner type is universally superior. The right choice depends on furnish type, target grade, energy cost sensitivity, and operational needs. Many mills use both types in sequence — disc refiners for primary refining and conical refiners for post-refining — to combine the strengths of each geometry.
Key Takeaways
- Conical refiners consume 50-150 kWh/t compared to 80-200 kWh/t for disc refiners, providing an energy advantage in many applications
- Conical geometry favors fibrillation and fiber length preservation, making it well-suited for hardwood and quality-sensitive grades
- Disc refiners offer greater versatility, easier plate changes, and better handling of variable and recycled furnish
- Both refiner types use the same SEL range (0.5-3.0 J/m) — the difference is in how energy transfers to fibers
- The right choice depends on furnish type, target grade, energy costs, and operational flexibility requirements
- Many mills benefit from using both types in sequence — disc for primary refining, conical for post-refining
- Neither refiner is universally superior — match the tool to the application
Conclusion
Conical and disc refiners each bring distinct advantages to the stock preparation line. Conical refiners deliver lower energy consumption and gentler fiber development — advantages that matter most in post-refining, hardwood processing, and quality-sensitive grades. Disc refiners provide operational flexibility, easier maintenance, and reliable performance across a wide range of furnish types and paper grades.
The decision is not about which refiner is better overall. It is about which refiner fits the specific application. Mills that match refiner geometry to their furnish, grade requirements, and energy priorities will achieve the strongest results in both fiber quality and operating efficiency.
Explore refining equipment options suited to your furnish and grade requirements.
