The Energy Challenge in Corrugated Medium Production

Corrugated medium—the fluted layer sandwiched between linerboards—operates on thin margins. Raw material (almost exclusively recycled fiber—OCC and mixed waste) and energy are the two largest variable costs. In a typical medium mill, stock preparation accounts for 30–40% of total electrical consumption, with pulping and refining as the dominant loads.

A 300 TPD medium mill consuming 320 kWh/ton in stock prep spends approximately $660,000 annually on stock preparation electricity alone (at $0.07/kWh). Reducing this by just 10%—an achievable target with proper equipment selection and operation—saves $66,000 per year. Over the 15–20 year life of the equipment, that single efficiency gain pays for the machinery several times over.

Pulping: High Consistency = Lower Energy

The most impactful decision in medium stock preparation is pulping consistency. Low-consistency pulping (4–6%) requires significantly more water pumping and heating, and the shear mechanism relies on rotor turbulence that wastes energy as heat rather than fiber separation. High-consistency pulping (15–18%) uses inter-fiber friction as the primary separation mechanism:

• Specific energy (OCC to 80% defibering): HC drum pulper: 30–40 kWh/ton; LC batch pulper: 55–70 kWh/ton
• Annual savings (300 TPD mill, 330 days/year): (65 – 35) × 300 × 330 × $0.07 = ~$208,000
• Additional benefit: HC pulping preserves contaminant size, making downstream screening more effective

Leizhan’s HC drum pulper features a wear-resistant screen plate section (8–12 mm perforations in the first zone, 6–8 mm in the second) with a hardened steel construction. The drum’s internal lifters are arranged in a helical pattern that advances the stock at 1.5–2.5 meters per drum revolution while providing the tumbling action that separates fibers.

Refining Strategy for Medium: Don’t Over-Refine

Medium paper has different strength requirements than linerboard. The Concora Medium Test (CMT) measures the flat crush resistance of the fluted medium, which depends more on fiber bonding in the thickness direction than on tensile strength. Over-refining medium stock is a common waste of energy:

• Target freeness: 35–45°SR for 100% OCC medium furnish
• Refining energy budget: 30–60 kWh/ton maximum—beyond this, CMT gains level off while energy costs continue climbing linearly
• No-load power check: A refiner that draws more than 8–10% of motor nameplate at zero gap has bearing or alignment issues consuming power without treating fiber

Leizhan’s medium-consistency conical refiner (Model ZDJ series, 3–5% feed consistency) is designed specifically for OCC-based medium production. The fillings use a medium-coarse bar pattern (3.5–4.5 mm bar width, 5–6 mm groove width) that develops fiber bonding without excessive cutting. The tapered rotor geometry provides a longer treatment zone than disc refiners, achieving the target freeness reduction in fewer passes with lower specific energy.

Consistency Control: The Overlooked Efficiency Lever

Refining efficiency depends heavily on feed consistency. At 2.5% rather than the design 4%, the same refiner must process 60% more water volume, reducing fiber-fiber contact and wasting energy on water pumping. The relationship is approximately:

Refining efficiency at 2.5% ≈ 65–70% of efficiency at 4.0% consistency

Leizhan recommends a disc thickener or screw press ahead of the refiner to boost consistency to 3.5–4.5%, achieving consistent treatment regardless of upstream process variations. A disc thickener with 0.25 mm slot screen and 3–5 m disc diameter can raise consistency from 0.8% to 4.0% at throughputs of 100–250 TPD per unit. The filtrate (typically 0.01–0.03% consistency with PEO or equivalent polymer dosing) is reused as dilution water, closing the water loop and reducing fresh water demand.

Screening System Efficiency

Medium stock screening typically uses 0.25–0.35 mm slots at feed consistencies of 2.0–3.5%. The key metric is debris removal efficiency (DRE)—the percentage of incoming contaminants removed. At 0.25 mm slots with 2.0 m/s slot velocity, expect DRE values:

• Stickies >100 μm: 75–85% removal
• Shives (Somerville >0.15 mm): 85–95% removal
• Plastic flakes: 60–75% (flat plastics orient to pass slots)

Leizhan’s pressure screen series achieves these targets with wedge-wire baskets (wedge angle 8–12°) in a cylinder configuration. For medium grades, a multi-stage screening cascade (primary → secondary → tertiary) limits total fiber loss to below 0.5% of incoming fiber mass.

Energy Audit Checklist

For medium mill operators evaluating their current energy consumption, these quick checks often reveal improvement opportunities:

• Refiner no-load power: Measure motor kW with refiner plates fully open. If no-load exceeds 10% of motor rating, inspect bearings and alignment.
• Pulping consistency: Measure with a microwave consistency meter at the pulper discharge. Below 12% in HC pulping? Add a thickener upstream or reduce dilution water.
• Screening pressure drop: Delta-P across fine screen rising more than 20% above clean-basket baseline? Basket blinding—schedule chemical or mechanical cleaning.
• Pump sizing: A stock pump operating below 60% of BEP (best efficiency point) wastes 15–25% of input power as turbulence and heat. Right-size or add a VFD.
• System pressure losses: Walk the pipe gallery with an ultrasonic flow meter and pressure gauge. Each unnecessary 90° elbow costs roughly 0.5 meters of head loss at 2.5 m/s stock velocity.

For a detailed energy audit of your corrugated medium stock preparation line or to discuss Leizhan’s range of pulpers, refiners, and thickening equipment, get in touch with our process team.

Contact Leizhan for Your Paper Machinery Needs

Zhengzhou Leizhan Technology Paper Machinery Co., Ltd. supplies complete stock preparation systems and paper machine equipment for tissue, kraft liner, coating board, and corrugated medium production worldwide. For technical consultation or equipment inquiries, reach our team at:

📧 leizhanzhang@gmail.com