In tissue manufacturing, the drying section is the single largest energy consumer — typically accounting for 50-65% of total steam usage in a tissue paper machine. For mills running at 1,800-2,200 m/min, even a 3% reduction in specific steam consumption translates to significant annual savings. The challenge has always been maintaining the bulk and softness that end-users demand while driving down energy costs.

Understanding the Drying Profile

A modern crescent former tissue machine typically operates with Yankee cylinder steam pressure between 0.6 and 0.9 MPa, with shell surface temperatures reaching 140-170°C depending on the grade. The critical parameter is the specific steam consumption, which for premium tissue grades should ideally fall between 1.25 and 1.45 tonnes of steam per tonne of paper. Mills operating above 1.6 t/t should investigate their drying profile immediately.

Key factors affecting steam efficiency include hood temperature balancing (wet-end vs. dry-end hoods), proper siphon design for condensate removal, and the Yankee coating chemistry. A well-balanced hood system should maintain wet-end temperatures around 320-380°C and dry-end temperatures of 180-240°C, with the precise values depending on the creping doctor setup and the target sheet properties.

Stock Preparation’s Overlooked Role

What many operators miss is how upstream stock preparation directly impacts drying efficiency. Fibre fibrillation during refining influences water retention in the sheet entering the press section. Over-refined stock holds more water, forcing the drying section to work harder. For tissue grades, freeness targets between 450-550 mL CSF with fibre length distribution optimized for the specific furnish blend (virgin kraft, deinked pulp, or mixed furnish) can reduce post-press moisture by 1-2%, directly lowering Yankee steam demand.

Press Section Optimization

The suction press roll on a crescent former should achieve 38-42% dryness after pressing. Every 1% increase in post-press dryness reduces Yankee steam consumption by approximately 4-5%. Regular inspection of press roll covers, maintaining correct nip loading (typically 80-120 kN/m for tissue), and ensuring suction box vacuum levels are within specification are low-cost measures that deliver rapid payback.

Practical Maintenance Tips for Sustained Efficiency

• Yankee Coating Inspection: Check the coating layer uniformity every shift. Uneven coating causes localized overheating and reduces heat transfer efficiency by up to 15%.
• Condensate Removal: Verify siphon clearance to the shell inner surface quarterly. A gap exceeding 0.8-1.0 mm can cause condensate pooling that reduces heat transfer and risks shell damage.
• Hood Air Balance: Monitor exhaust humidity levels — optimal range is 0.16-0.22 kg H₂O/kg dry air. Recirculation dampers should be inspected monthly.
• Doctor Blade Management: Creping doctor angle and blade bevel directly impact sheet adhesion to the Yankee. Poor adhesion = lower heat transfer = higher steam consumption.

Energy optimization for tissue machines is a systems challenge, not a single-variable problem. Mills that take an integrated approach — linking stock preparation, press section, drying, and hood balance — consistently achieve the lowest specific energy consumption figures in their peer groups.

If you are evaluating ways to improve your tissue machine’s energy performance or considering upgrading your stock preparation line, contact us for a technical discussion.

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