Pulp & Paper: Retention Aids and Drainage

Contents

• How to use this guide
• Where it fits in the process
• What good looks like (KPIs)
• Common retention system architectures
• Selection decision factors
• Polymer make-down & dosing best practices
• Injection points & mixing (critical)
• White water closure, pitch/stickies, and deposits
• Troubleshooting patterns
• Specification & acceptance checks
• RFQ notes
• FAQ

How to use this guide

This is a practical decision aid for pulp & paper teams. Use it to align procurement, EHS, and operations on retention system selection, acceptance checks, monitoring signals, and field trial discipline. If you share furnish details, wet-end chemistry, and current KPIs, we can propose supply-ready chemical options with documentation and logistics aligned to your site.

Where it fits in the process

• Wet end: stock prep → fan pump → headbox → forming section → white-water loop.
• Primary objectives: retain fines & fillers in the sheet, improve drainage, reduce load to saveall/DAF, stabilize formation.
• Secondary effects: strength (via fines retention), opticals (filler distribution), press dryness, felt life, steam consumption.
• Constraints: machine speed, closure level, recycled content, additive package (ASA/AKD, dyes, starch), discharge limitations.

What good looks like (KPIs you can manage)

Choose 3–5 KPIs and keep them consistent during trials. Typical metrics include:

• First-pass retention (FPR): fines and ash retention (often tracked via white-water solids/ash).
• Drainage / dewatering: vacuum demand, couch solids, press solids, or lab drainage tests.
• Formation / sheet uniformity: visual/online scanner formation index; reduced two-sidedness.
• Runnability: breaks per day, wet-end stability, foaming issues, slime/deposit frequency.
• White-water load: turbidity, TSS, COD load to saveall/DAF; clarified water quality.
• Chemical efficiency: kg additive per ton (retention aid, filler, starch), and total cost per ton.

Common retention system architectures

Most mills use one of these proven “building blocks,” sometimes combined:

1) Single polymer retention (often CPAM)

• What it is: a cationic polyacrylamide (CPAM) provides flocculation/bridging to retain fines and fillers.
• Where it fits: simpler furnishes, lower closure, moderate filler loads.
• Watch-outs: overdosing can create large flocs → poor formation, higher breaks, and uneven filler distribution.

2) Dual-polymer (coagulant + CPAM or CPAM + APAM)

• What it is: a coagulant (e.g., polyDADMAC/PEI) neutralizes anionic trash, then CPAM builds flocs; or CPAM + anionic PAM (APAM) creates microflocs.
• Where it fits: recycled fiber, high anionic demand, closed loops, high filler, variable furnish.
• Benefit: better robustness under variability; often improves drainage without sacrificing formation (if tuned).

3) Microparticle systems (CPAM + colloidal silica or bentonite)

• What it is: CPAM forms initial flocs; microparticles “restructure” flocs into stronger microflocs that drain well and retain ash/fines.
• Where it fits: high-speed machines, high filler, demanding drainage/formation balance, high closure.
• Watch-outs: injection sequence and shear conditions are critical; wrong placement can collapse benefits.

4) Specialty programs (furnish- and grade-dependent)

• Strength + retention: cationic starch + retention aid coordination.
• Pitch/stickies management: fixatives, talc, detackifiers integrated with retention strategy.
• Wet strength / sizing interactions: ASA/AKD performance can be influenced by charge balance and retention approach.

Selection decision factors

Retention systems are not “one size fits all.” Use these factors to shortlist candidates before trials:

• Furnish: virgin vs recycled, fines content, presence of stickies/ink, and variability.
• Filler strategy: ash target (PCC/GCC/clay), particle size distribution, and desired opacity/brightness.
• Wet-end charge: charge demand / zeta potential; anionic trash from dispersants, lignin, DCS, and recycled contaminants.
• Closure level: conductivity, calcium, dissolved organics; higher closure often increases demand for coagulant + robust retention design.
• Shear profile: fan pump, pressure screens, cleaners; determines polymer MW and injection strategy.
• Grade sensitivity: formation-critical grades (printing/writing) vs board/packaging (often higher tolerance for floc size).
• Downstream: saveall/DAF load and clarified water re-use constraints.
• Deposit risk: pitch/stickies, scaling, biofilm; retention changes can shift deposition patterns.

Polymer make-down & dosing best practices

Many mills lose performance because polymers are not prepared correctly. Procurement should specify not only the polymer, but also the make-down requirements and equipment capability.

Emulsion polymers (common for CPAM/APAM)

• Activation/inversion: requires proper inversion water quality and mixing energy.
• Make-down concentration: keep within supplier guidance to avoid fisheyes and viscosity issues.
• Aging time: allow time for full activation; under-aged solutions can appear “weak.”
• Water quality: avoid high hardness/iron or contaminated water that can destabilize solution.

Solution polymers

• Simpler handling: no inversion step, but viscosity can be high; heating/insulated lines may be needed.
• Metering: confirm pump can handle viscosity and provide stable low-flow control.

Common dosing discipline

• Start low and step up in small increments; define a “stop point” to protect formation.
• Change one variable at a time (coagulant first for charge, then polymer, then microparticle).
• Log additions and KPIs every shift; retention systems drift with furnish and closure changes.

Injection points & mixing (critical)

The same chemical can perform brilliantly or fail completely based on where it’s added. As a general concept: add charge-control upstream, add retention polymers where mixing is adequate but before excessive shear, and add microparticles after polymer floc formation with controlled shear.

• Coagulant/fixative: often in machine chest or fan pump suction (depends on system design).
• CPAM: commonly before screens/headbox but after points that cause extreme shear; ensure good mixing.
• Microparticle: typically downstream of CPAM after initial flocs form, sometimes after pressure screen (system dependent).

Site geometry matters—use trials and observation. Incorrect placement is a top cause of “it didn’t work.”

White water closure, pitch/stickies, and deposits

Retention optimization changes where fines, fillers, and dissolved organics end up. In higher-closure systems, you may need integrated control:

• Anionic trash control: coagulants/fixatives to reduce charge demand swings.
• Pitch/stickies control: detackifiers, talc, or targeted fixatives to prevent felt and roll deposition.
• Deposit prevention: scale inhibitors and dispersants where scaling occurs; biocide programs for slime control.
• Felt conditioning: manage surfactants/defoamers so they don’t disrupt retention performance.

Troubleshooting patterns

Symptom: sheet breaks increased after retention change

• Over-flocculation hurting formation
• Wrong injection point (too much shear or insufficient mixing)
• Charge imbalance (coagulant under/overdosed)

Symptom: high white-water turbidity / poor FPR

• Insufficient polymer activation/make-down issues
• Anionic trash consuming polymer (need coagulant step)
• Microparticle sequence incorrect

Symptom: deposit buildup on felts / increased felt plugging

• Shift in fines/stickies retention pattern; review pitch/stickies program
• Overdosing creating dense flocs and poor drainage distribution
• Biofilm/slime contribution—check microbiological control

Symptom: odor / slime, unstable wet end

• Microbial growth in white-water loop (closure increases risk)
• Organic load up (COD) → demand for biocide/oxidant program review
• Dead zones and poor housekeeping

Specification & acceptance checks

When comparing retention and drainage aids, ask for data you can verify on receipt:

• Identity: product name, form (emulsion/solution/powder), manufacturer, batch/lot traceability.
• Quality (COA): active content, viscosity (as supplied), density, pH (if applicable), appearance.
• Functional descriptors: charge type (cationic/anionic), charge density, molecular weight class, recommended dilution range.
• Make-down requirements: inversion needs, aging time, mixing energy, and recommended water quality.
• Packaging: drum/IBC/bulk, liner type, closures, cold-weather handling if relevant.
• Safety: up-to-date SDS, handling precautions, and required PPE.
• Logistics: lead time, Incoterms, shelf life, storage temperature window.

Handling & storage

• Store in original sealed packaging; protect emulsions from freezing and excessive heat.
• Use secondary containment and clear labeling in the chemical area.
• For transfers: verify hose compatibility; keep containers clean to avoid contamination.
• Manage slips/spills—many polymers create extreme slip hazards.

RFQ notes (what to include)

• Machine & grade: tissue/board/printing paper; speed; ash target.
• Furnish: recycled %, filler type, fines level, problematic contaminants (stickies, ink, DCS).
• Wet-end conditions: pH, temperature, conductivity/closure level, calcium level if relevant.
• Current program: sizing (ASA/AKD), starch, dyes, defoamers, biocides, pitch/stickies agents.
• Current KPIs: FPR/white-water turbidity, drainage metrics, breaks, deposit frequency.
• Constraints: food-contact or regulatory requirements (grade-dependent), discharge constraints, storage limitations.
• Volumes & packaging: monthly tonnage, drum/IBC/bulk preference, delivery location.

FAQ

Why did retention improve but formation got worse?

You likely moved into over-flocculation. Back off polymer dose, review injection/mixing, and consider a microparticle system to create smaller, more resilient flocs.

Can we solve retention just by increasing CPAM dose?

Often not. If anionic trash is high, extra CPAM can get “consumed” without building effective flocs. Add a coagulant/fixative step and stabilize charge first.

Do microparticle systems always improve drainage?

They often do when properly implemented, but sequence and shear are critical. Incorrect placement can reduce benefits or cause deposits.

Educational content only. Always follow site EHS rules and the supplier SDS for safe use. Final chemical selection and dosing strategy must be validated for your furnish, machine conditions, and compliance requirements.