Contents
- How to use this guide
- Foam vs entrained air: what to control
- Where foam is created (and why it gets worse in closed water)
- What foam/air does to quality and runnability
- Key selection factors
- Defoamer families and typical roles
- Feed points & strategy
- Monitoring signals (KPIs)
- Compatibility & side effects
- Troubleshooting: symptom → likely causes → first checks
- Procurement specs & acceptance checks (COA/SDS)
- RFQ notes
- FAQ
How to use this guide
This is a practical decision aid for mill operations, EHS, and procurement. Use it to align on what you are optimizing (quality, runnability, yield, safety, or cost), how you will measure success (KPIs), and how you will specify supply (COA/SDS, packaging, lead time).
Safety-first: Always follow site procedures and the supplier SDS/label for safe handling, storage, and dosing. This guide describes program design principles—not product-specific dosing instructions.
Foam vs entrained air: what to control
Foam (surface)
Bubbles concentrated at the liquid surface.
- Visible froth in chests, trays, and saveall pits
- Often driven by surfactants, dispersants, and dissolved organics
- Creates level control issues and carryover
Entrained air (in the stock)
Microbubbles dispersed through the slurry.
- Harder to see; shows up as “spongy” flow and unstable pressure
- Impacts drainage, formation, and defects (e.g., pinholes)
- Often linked to shear, pumps, agitation, and closed water chemistry
Where foam is created (and why it gets worse in closed water)
Foam is rarely “one location.” It is a system behavior driven by chemistry (surfactants), hydrodynamics (shear), and water closure (build-up of organics).
| Common foam zones | Why foam forms there | What to check first |
|---|---|---|
| Mixing chests / machine chests | High agitation + surfactant load from broke, inks, dispersants, starch | Agitation intensity, stock consistency, temperature, recent chemical changes |
| White water trays / pits | Air entrainment from waterfalls, turbulence, and recirculation | Drop heights, broken seals, air leaks, pump suction conditions |
| Saveall systems | High fines/organics + shear, surfactants from recycled fiber | Fines loading, polymer carryover, closure trends, surfactant sources |
| Approach flow | Microbubble stability; pressure fluctuations; entrained air release | Air content if measured, pressure stability, deaeration performance |
What foam/air does to quality and runnability
Quality impacts
- Pinholes, spots, and coating/printing defects
- Formation variability and basis weight instability
- Strength loss due to poor bonding and drainage artifacts
Runnability impacts
- Sheet breaks and instability in approach/headbox
- Drainage loss and felt loading
- Level-control issues in chests and pits
Cost impacts
- Higher chemical consumption (retention, wet-end aids)
- More cleaning and downtime
- Yield loss (carryover, off-spec, trim waste)
Key selection factors
Defoamer selection is a balance: enough foam/air control without creating deposits, harming sizing/retention, or causing downstream quality issues.
| Selection factor | Why it matters | What to define |
|---|---|---|
| Foam type & severity | Surface foam vs entrained air may require different chemistries and feed points | Where foam appears, when it spikes, and what changes correlate |
| Operating window | Temperature, pH, shear, and residence time influence performance | Typical ranges + upset conditions (startups, grade changes) |
| Wet-end chemistry | Risk of interference with retention, sizing, charge balance, and strength | Retention aids, sizing system (ASA/AKD), starch, fillers, dispersants |
| Deposit sensitivity | Some defoamers can contribute to deposits or interact with pitch/stickies | Current deposit locations, pitch/stickies situation, cleaning frequency |
| Water closure level | Higher closure increases organics and surfactant load, raising foam propensity | Closure trends and COD/organics indicators (if available) |
| Compliance & EHS | Discharge rules, food-contact needs, VOC/site rules may restrict options | Site restrictions, approvals, documentation requirements |
Defoamer families and typical roles
Most mills trial multiple chemistries because “best” depends on your exact furnish, additives, and closure level. The table below is a practical mapping of typical roles.
| Family | Typical strengths | Common watch-outs | Where it often works best |
|---|---|---|---|
| Oil-based (mineral/vegetable) + hydrophobes | Good general foam knockdown; cost-effective | Deposit risk if overdosed or poorly dispersed; may affect sizing/printing in some grades | Chests, white water loops, recycled fiber systems |
| Silicone-based | Strong antifoam activity at low dose; fast surface foam control | Potential downstream defects (e.g., spots) in sensitive grades; deposit/compatibility checks critical | High-foaming zones where quick knockdown is required |
| EO/PO polymer defoamers | Good balance for entrained air release and stability in some systems | Performance varies with water chemistry; may require different feed strategy | Approach flow / systems where entrained air is the main issue |
| Water-based emulsions/blends | Easier handling; adaptable blends for system needs | Freeze/thaw and storage stability; compatibility with dosing equipment | Sites prioritizing handling simplicity and consistent metering |
Trial design tip: compare candidates on a defined KPI set (e.g., breaks + defect rate + drainage stability) and include a deposit/cleanliness check. “Looks less foamy” is not enough if sheet quality or deposits worsen.
Feed points & strategy
Correct feed strategy is often the difference between success and chasing foam with increasing dosage. Your goal is to treat where foam/air is generated and stabilize the loop.
Feed-point principles
- Upstream of foam generation: dose before high-shear or waterfall zones where possible
- Give contact time: ensure mixing and residence time for dispersion
- Target entrained air: some systems benefit from approach-flow dosing (with care)
- Avoid “over-correcting”: step changes can destabilize wet-end chemistry
Operational patterns
- Base feed + trim: stable base dose with small trims during upsets
- Grade-change logic: different base dose for high-starch or high-dispersant grades
- Startup spikes: temporary higher control during warm-up/closure transitions
- Equipment checks: verify pump calibration, injection quill position, and mixing quality
Monitoring signals (KPIs)
Choose a small KPI set you can measure consistently. Trend outcomes at fixed points and times.
| Signal | What it indicates | Practical notes |
|---|---|---|
| Foam observation score | Surface foam severity | Use a standard location list + a simple 0–5 scoring system |
| Defects trend (pinholes/spots) | Entrained air and surface contamination risk | Track by grade and correlate to water closure and dose changes |
| Drainage stability | Air impacts on dewatering and formation | Look for smoother vacuum/pressure behavior and more stable drainage |
| Sheet breaks / downtime | Business impact | Use as a primary KPI but pair with faster “early signals” above |
| Retention/sizing KPIs | Compatibility with wet-end | Watch for shifts in ash retention, sizing efficiency, or charge demand |
Minimum KPI set (practical)
Pick 3: foam score at fixed locations, defect rate (pinholes/spots), and sheet breaks. Add retention/sizing metrics if you are changing chemistry families.
Compatibility & side effects
Defoamers can interact with additives and deposits. Validate these areas during trials:
| Area | Potential issue | What to check |
|---|---|---|
| Sizing (ASA/AKD) | Efficiency loss, deposit risk changes | Sizing response trend, deposit locations near dosing points, emulsion stability indicators |
| Retention/drainage aids | Interference with flocculation or charge balance | Retention stability, formation, ash control, charge demand if monitored |
| Pitch/stickies | Deposit formation or release | Felt/roll cleanliness scoring; cleaning frequency; deposit appearance changes |
| Coating/printing sensitivity | Spots/defects in sensitive grades | QC feedback and defect mapping vs dose/chemistry changes |
| Effluent/compliance | Discharge constraints and approvals | Align with EHS on permitted chemistries and documentation needs |
Troubleshooting: symptom → likely causes → first checks
| Symptom | Likely causes | First checks |
|---|---|---|
| Foam spikes after grade change | Surfactant load shift (dispersants, broke), closure changes, temperature changes | Review additive changes; check closure trend; adjust base dose logic by grade |
| Foam is lower but defects increase | Entrained air not controlled; chemistry causing surface defects | Check approach flow stability; compare chemistry family; validate dose point for entrained air control |
| Need increasing dose over time | Organics build-up, dosing equipment drift, poor mixing, new surfactant source | Calibrate pumps; inspect injection/mixing; evaluate closure/organics trend; check broke quality |
| Deposits increase after defoamer change | Compatibility mismatch, overdosing, poor dispersion | Inspect deposit type/location; reduce dose stepwise; adjust feed point; trial alternate chemistry |
Procurement specs & acceptance checks (COA/SDS)
Defoamers are performance-sensitive to formulation and consistency. Define what you need and verify on receipt.
| Category | What to request | What to verify on receipt |
|---|---|---|
| Identity & traceability | Product name/grade, manufacturer, batch/lot, production date | Label matches PO; batch traceability retained |
| Quality (COA) | Appearance, active content (if applicable), density, pH (if applicable), viscosity range | COA within agreed limits; no phase separation; consistent viscosity for metering |
| Storage stability | Shelf life; temperature limits; freeze/thaw behavior (if relevant) | Storage conditions available; product remains homogeneous after storage |
| Packaging | Drum/IBC/bulk, liner/closure type, labeling language | Compatible with dosing equipment and secondary containment |
| EHS documentation | Current SDS; handling guidance; regulatory/compliance statements as required | EHS approval completed; PPE and handling procedures updated |
| Logistics | Lead time, Incoterms, reorder plan, storage requirements | Reorder point and safety stock defined; FEFO practiced |
Commercial note: request pricing with delivered terms and confirm consistent formulation. A cheaper defoamer that increases defects or deposits usually costs more overall.
RFQ notes (what to include)
- System: grade/furnish, closure level, key chests/loops, known foam zones.
- Operating window: temperature and pH ranges, consistency at key points, shear conditions.
- Current symptoms: foam locations/timing, pinholes/spots, breaks, drainage instability.
- Current chemistry: sizing (ASA/AKD), retention aids, dispersants, starch, pitch/stickies program.
- Constraints: effluent/discharge, food-contact needs, site rules, preferred chemistries.
- Volumes: monthly demand estimate, packaging preference, delivery destination and Incoterms.
- Documentation: SDS/COA, batch traceability, storage guidance.
FAQ
Do we need a different defoamer for foam vs entrained air?
Often yes. Some products mainly collapse surface foam, while others help release entrained air depending on chemistry and dose point. Many mills use one “base” defoamer plus a second option for specific zones or upsets.
What’s the most common non-chemical cause of foam?
Air leaks and poor hydraulics (waterfalls, turbulent returns, pump suction issues) can create persistent foam/air problems. Fixing these sometimes reduces chemical demand dramatically.
How long should a defoamer trial run?
Long enough to cover normal variability: grade changes, closure swings, and cleaning cycles. Trend KPIs and include at least one cleanliness/deposit check before deciding.
Educational content only. Always follow site EHS rules and the supplier SDS/label for safe use. Program effectiveness depends on system conditions, feed points, and consistent monitoring.