Wet-Strength Broke Repulping in Kraft Liner Mills: High-Consistency Pulper Design

Wet-Strength Broke: The Hidden Capacity Drain in Kraft Liner Mills

Broke represents 8-15% of total production in a typical kraft liner mill, and wet-strength grades are the most difficult fraction to recover. Standard low-consistency pulping leaves undefibered flakes that overload downstream screens, increase reject rates, and force mills to landfill recoverable fiber. A dedicated high-consistency repulping stage closes this loop and returns wet-strength broke to the stock preparation line at usable quality.

High-Consistency Pulping Principle

Wet-strength broke contains cross-linked resins that resist water penetration at normal pulping conditions. Defibering requires a combination of elevated consistency, temperature, and mechanical shear:

• Consistency: 12-18% in the pulping zone concentrates fiber-to-fiber friction, which breaks resin bonds more effectively than rotor impact alone
• Temperature: 60-75°C softens wet-strength resins and accelerates fiber separation
• Retention time: 20-40 minutes batch cycle depending on resin content and sheet grammage
• Chemical assist: Optional alkali addition at pH 9-10.5 for heavily sized or resin-rich broke grades

Leizhan high-consistency hydrapulpers are configured with S-type rotors and hardened wear plates sized for batch broke handling from 5 to 40 t/day per unit, with motor ratings from 55 kW to 315 kW.

Energy and Fiber Recovery Data

Specific energy demand for wet-strength broke defibering runs 35-45 kWh/t, compared with 18-22 kWh/t for standard OCC pulping. The higher energy input is recovered through fiber yield: mills routinely convert 92-96% of wet-strength broke back into usable furnish, displacing virgin kraft pulp worth significantly more than the additional electricity. On a 300 TPD kraft liner line generating 30 t/day of wet-strength broke, effective repulping returns roughly 28 t/day of fiber to the machine — equivalent to more than 10,000 tonnes of recovered furnish per year.

System Integration

The repulped broke stream discharges at 4-6% consistency through an extraction plate with 8-16 mm holes, then passes a high-density cleaner and deflaker before blending into the main chest. Positioning the deflaker immediately after the pulper eliminates residual flakes before they can reach pressure screens, protecting screen baskets from overload and extending basket service life.

Maintenance Points

• Inspect rotor wear plates every 2,000 operating hours; rotate or replace when leading-edge wear exceeds 6 mm
• Check extraction plate hole enlargement monthly; replace when holes exceed nominal diameter by 2 mm
• Grease main bearings every 500 hours with lithium-based EP2 grease; monitor temperature below 75°C
• Verify gland packing compression weekly to prevent stock leakage without over-tightening the shaft sleeve

Effective broke handling directly improves machine efficiency and fiber cost per tonne. For wet-strength repulping system sizing, rotor selection, and complete broke line layout, contact the Leizhan engineering team.

Email: leizhanzhang@gmail.com