In brown stock washing, SY-3000 is injected into the filtrate return line rather than directly into the blow tank. The fatty alcohol defoamer is selected for this position because black liquor at 70–90 °C and pH 12–13 generates foam stabilized by tall oil soap and residual kraft lignin, not by free air alone. Rotary vacuum drum washers and single or double-roll presses lose displacement efficiency when foam accumulates in the filtrate pan; the air fraction in the mat reduces hydraulic conductivity and increases sodium carryover to the bleach plant. A representative addition level for northern softwood kraft is 0.1–0.5 kg/t oven-dry pulp, with the lower third of the range used on hardwood furnish containing less resin acid soap. Addition is split between the washer shower water header and the filtrate tank inlet to control foam both on the drum surface and in the pump suction. The finished product is unbleached kraft pulp at 10–16 % consistency exiting the final press, with residual black liquor solids washed to less than 15 kg Na₂SO₄/t pulp in modern fibre lines. Drainage performance is measured according to ISO 5267-1, and filtrate solids are analysed against the mill mass balance. Black liquor foam control must be balanced against evaporator carryover: free fatty alcohol can alter black liquor viscosity and deposit on surface condenser tubes if the defoamer is overdosed for more than 72 h continuously. For food-contact kraft, the complete formulation must be checked against 21 CFR 176.210 since emulsifiers and preservatives in the commercial product require mill-specific clearance.

Injection is made with a diaphragm metering pump fitted with a pulsation dampener; the product is diluted with process water at 1:5 to 1:20 before a static mixer. Slug feeding is avoided because foam height in the filtrate tank responds within 20–30 min, and uneven addition creates washer mat defects. For hardwood lines with low resin acid soap concentrations, the lower end of the dosage range is often sufficient, whereas softwood lines carrying soap separation tank overflow may require the upper end during spring and early summer when extractives levels are elevated. Foam height is measured by capacitance probes, and the defoamer pump is interlocked with the washer shower water flow to avoid addition during shutdown flushing.

What Happens When Fatty Alcohol Defoamer Enters Alkaline Peroxide Bleach Towers?

Alkaline peroxide brightening of TMP and CTMP operates at 10–15 % consistency, 70–85 °C, initial pH 10.5–11.5, and retention times between 60 min and 120 min. Foam in the medium-consistency pump and tower is generated by peroxide decomposition oxygen, residual wood resin, and released anionic extractives. SY-3000 is added before the MC pump at 0.2–0.8 kg/t oven-dry pulp, usually split 70 % to the pump suction and 30 % to the tower discharge line. The defoamer collapses air pockets inside the pulp mat, allowing the alkaline peroxide liquor to contact the fibre uniformly and preventing brightening reversal caused by localised oxygen blanketing. The resulting furnish is bleached chemithermomechanical pulp with brightness targets of 70–80 % ISO depending on wood species; brightness is tested according to ISO 2470-1. Overdosing above 1.0 kg/t is not recommended because free fatty alcohol may precipitate with sodium silicate and form calcium soap deposits on the bleach tower outlet screw. Sodium silicate at 1.5–3.0 % on oven-dry pulp and DTPA at 0.1–0.2 % are compatible, but the mill must verify that residual defoamer does not reduce peroxide stabilisation; published peroxide residual data for SY-3000 in this exact configuration is limited.

The defoamer must remain stable in the alkaline peroxide liquor at high temperature. Phase separation in the dosing line is checked by turbidity meter; emulsion droplets larger than 10 µm can create localised darkening in the finished BCTMP bales due to carryover. The final pulp is dewatered through a twin-roll press and fluffer before baler; residual defoamer must not increase biological oxygen demand in the press filtrate beyond the mill discharge permit. COD increase is typically not measurable at 0.5 kg/t, but each mill must verify the effect against its own activated sludge kinetics and discharge permit limits.

Wet End White Water Loop Foam Suppression and First-Pass Retention

On alkaline fine paper machines, the wet end operates at pH 7.5–8.5, headbox consistency 0.6–1.2 %, and wire pit temperature 40–50 °C. Foam accumulates in the wire pit, tray water, and seal pit because cationic starch, AKD/ASA size, and anionic trash form surface-active complexes. SY-3000 is introduced at 0.05–0.15 kg/t dry fibre for woodfree fine paper and at 0.1–0.3 kg/t for recycled linerboard; addition is split between the wire pit return and the fan pump suction. Defoamer addition changes the air content in the headbox from 0.8–1.5 % by volume to below 0.4 %, which is monitored by an M-porosity sensor or by vacuum drainage testing with a Dynamic Drainage Analyzer at 10 kPa vacuum. Sheet formation is evaluated by beta formation index and by TAPPI T 205 handsheets. Overdosing beyond 0.5 kg/t on closed white water systems creates a competing hydrophobic surface that can reduce cationic retention aid efficiency and cause size reversion when ASA is used; the size test according to TAPPI T 530 Hercules size is used to confirm no loss. The split ratio between wire pit and fan pump suction must be changed when broke furnish increases. Broke from coated paper releases more surface-active coating binder; the defoamer demand can double within 30 min after a grade change. On high-speed tissue machines with crescent formers, the defoamer is added to the machine chest rather than the wire pit because the short circulation loop has a residence time of 5–10 min and foam can reach the headbox before chemical response. The target is to maintain headbox air content below 0.3 % by volume.

Post-flotation deinking lines using recovered office paper and old newsprint do not receive SY-3000 in the flotation cells. Residual defoamer in the flotation cell can reduce ink-laden foam overflow and decrease brightness gain by retaining hydrophobic ink particles in the accept stream. The application point is moved to the washer and thickener feed after the final flotation stage. Dosage on the washed recycled furnish is 0.05–0.2 kg/t dry fibre, adjusted to keep foam height in the wash filtrate tank below 30 cm; stock temperature is 40–50 °C and pH in the alkaline loop is 7.0–9.0. The defoamer controls fatty acid soap foam generated by saponified flexographic inks and coating binders. Residual ink is measured according to ISO 22754 or the ERIC method; effective residual ink concentration must remain below 250 mg/kg for deinked market pulp. Finished product includes recycled copy paper, tissue, and white-top linerboard. Overdosing above 0.3 kg/t can re-disperse ink into white water and increase dirt count; TAPPI T 213 dirt count is used for confirmation. A mill producing deinked market pulp from mixed office waste often sees defoamer demand peak after alkaline soak and dispersion, not after flotation. The dosage is then split between the disperser discharge and the post-bleaching washer. The use of SY-3000 after flotation must be validated by ERIC and brightness measurements because over-deaeration of wash filtrate can reduce the removal of microstickies; if ERIC increases by more than 50 mg/kg against the control, the dosage is reduced.

Surface Sizing Fails When Starch Foam Collapse Exceeds Pickup Stability Limits

At the size press, oxidised or enzyme-converted starch is held at 55–70 °C and pH 6.0–8.5. Foam in the starch circulation tank causes film splitting defects, rod lines, and starch pickup variation. SY-3000 is added to the cooked starch storage tank at 0.01–0.05 % on dry starch solids, or 0.05–0.20 L/t of surface size, before the supply pump. The defoamer reduces foam height without reducing surface tension to the point where the starch film dewets; pickup is measured on the size press by gravimetric difference and should remain within ±0.3 % absolute of the target. The finished sheets are converted into corrugated board, gypsum liner, or office paper. A compatibility issue arises when the defoamer is mixed with cationic starch at high pH after alum addition; cationic starch may precipitate with free fatty alcohol, creating white deposit on the drying cylinders. Foam collapse time is screened by ASTM E2407-04. Published mill-scale correlation for SY-3000 in enzyme-converted starch systems is limited; laboratory Ross-Miles foam height data should be confirmed in the circulating loop. Rod lines and starch foam are often confused with coater streak defects; the distinction is made by measuring foam rise in a graduated cylinder with recirculated starch at 60 °C. If static surface foam collapses within 15 s after SY-3000 addition but film splitting persists, the defect is rheological rather than foam-related. This diagnostic prevents unnecessary defoamer overdosing and reduces the risk of deposit on the first dryer cans. Converted sheet properties measured by ISO 2758 burst strength should not change outside mill variability.

When White Water Closure Raises Surface Foam in Dissolved Air Flotation

Closed white water circuits with save-alls or dissolved air flotation units process suspended solids loads from 500 mg/L to 5,000 mg/L at hydraulic loading rates of 5–15 m/h. Surface foam generated by residual sizing agents, starch, and anionic trash reduces clarifier efficiency and causes TSS carryover into clarified white water. SY-3000 is dosed into the DAF inlet line at 1–3 mg/L on total flow, upstream of the flocculation tube but downstream of dissolved air injection. The fatty alcohol defoamer collapses surface foam without producing mineral-oil sheen; clarified water TSS is verified by gravimetric analysis according to ISO 11923. Sludge solids from the DAF float are pressed to 25–40 % consistency and either returned to furnish or sent to disposal. Overdosing above 5 mg/L interferes with cationic polyacrylamide flocculation and can increase effluent COD due to unbound fatty alcohol; jar testing with the specific polymer lot is required before changing the ratio. The terminal stream is clarified white water reused for machine showers, with fibre recovery rates of 90–95 % on a mass balance basis.

The dosing point relative to dissolved air injection is critical. If SY-3000 is injected before the pressure release valve, the defoamer may depressurize partially and form an emulsion layer in the white water tank. If injected after the flocculation chamber, the surface foam collapses but the fine fibre flocs are not protected from air bubbles in the flotation zone. A split dose of 70 % upstream of the flocculator and 30 % onto the DAF surface is used when surface foam persists. The DAF float solids and clarified water quality are monitored by on-line turbidity and weekly gravimetric TSS; a turbidity value below 50 NTU is commonly required for shower water reuse.