Tissue paper production demands a delicate balance between softness, strength, and runnability. Every piece of equipment in the stock preparation line directly influences the final sheet quality and the overall efficiency of the tissue machine. Making the wrong equipment choice can lead to excessive fines generation, poor formation, and costly downtime.

Why Stock Preparation Defines Tissue Quality

In tissue manufacturing, the stock preparation system performs three critical functions: fiber separation, contaminant removal, and fiber treatment through refining. The pulping system must achieve complete fiberization at the lowest possible energy input while preserving fiber length. For virgin pulp applications, a medium-consistency pulper operating at 8–12% consistency typically achieves the best balance. When processing recycled fiber for tissue grades, a drum pulper with gentle mechanical action helps maintain fiber integrity while removing lightweight contaminants.

Screening Precision for Tissue Grades

Tissue grades require exceptionally clean stock. Even microscopic contaminants can cause web breaks at the low basis weights common in tissue production (typically 13–25 g/m²). A two-stage screening system is the minimum standard:

• Primary screen: 0.15–0.25 mm slot size, pressure screen design
• Secondary screen: 0.20–0.30 mm slot size, handling primary rejects

The pressure screen basket configuration matters significantly. Slotted baskets with wedge-wire profiles deliver superior stickies removal compared to drilled hole baskets, which is essential when running recycled fiber content in tissue furnish. A well-designed screening system should achieve >95% stickies removal efficiency while keeping fiber loss below 1.5% at the secondary stage.

Refining Strategy for Tissue Softness and Strength

Refining is where the tissue maker earns their stripes. The goal is to develop bonding capacity through fibrillation without cutting fibers excessively. For tissue grades, low-intensity refining with disc refiners operating at 1.0–1.5 W.s/m specific edge load is the preferred approach. Key parameters:

• Target freeness drop: 50–100 mL CSF per pass (moderate treatment)
• Specific energy consumption: 40–80 kWh/t for virgin softwood, 20–40 kWh/t for hardwood
• Refiner plate pattern: Fine bar width (1.5–2.0 mm) with shallow groove depth

A double-disc refiner configuration allows the operator to optimize both long-fiber and short-fiber fractions independently, giving superior control over the strength-softness balance that defines premium tissue products.

Energy Efficiency Considerations

Tissue mills operating 24/7 can see substantial cost differences from equipment choices. A high-efficiency pressure screen consumes approximately 15–20 kWh per ton of pulp processed. By comparison, older open-type screens can draw 25–35 kWh/t. Over a year of continuous operation producing 50,000 tons, this 10 kWh/t difference translates to approximately 500,000 kWh saved — a significant operational cost reduction.

Similarly, modern low-consistency refiners with energy-efficient motors and optimized plate geometries can operate at 0.8–1.2 kWh per ton per °SR increase, compared to 1.5–2.0 kWh/t/°SR for older designs.

Maintenance Practices That Protect Uptime

Tissue machines run at high speeds, often exceeding 1,800 m/min on modern lines. Any stock preparation downtime cascades quickly. Recommended preventive maintenance intervals:

• Pressure screen baskets: Inspect every 3–4 months for slot wear; replace when slots widen beyond 10% of original dimension
• Refiner plates: Check bar edge sharpness monthly; typical plate life is 1,500–2,500 operating hours depending on furnish abrasiveness
• Pulper extraction plates: Inspect hole condition quarterly; replace when hole edges show rounding beyond 0.5 mm

Stock preparation equipment selection is a long-term decision that affects tissue quality, energy costs, and machine availability for years. Working with experienced equipment suppliers who understand the specific demands of tissue production helps mills avoid the most common pitfalls.

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