PAM for Paper Making

Four PAM duties in one mill

A paper mill is unusual among PAM buyers because a single site runs four separate polymer duties at once, and they pull in different directions. The wet end wants cationic charge to hold fines and filler on the sheet. The sludge press wants much higher charge to release water from biological solids. The effluent clarifier usually wants anionic polymer working behind alum or PAC. Broke recovery wants something mild enough not to over-flocculate recovered stock. Mills that try to cover all four with one drum of general-purpose flocculant end up over-dosing three of them.

That is the practical reason mill enquiries take a little longer to quote than a single-duty water treatment enquiry. Furnish type, machine speed, dewatering equipment, and discharge limit each point to a different grade, and the right answer is usually two or three grades rather than one. The sections below cover the duties in the order they consume volume.

Retention and drainage on the wet end

Cationic PAM in the 20-40% charge density range is the standard wet-end retention aid. The positive charge attaches fines and fillers to the anionically charged cellulose network, and first-pass retention typically moves from the 60-70% range into 85-95%. The benefit shows up in three places at once: less fibre and filler lost to the white water loop, better sheet formation, and faster drainage that can let the machine run harder.

Molecular weight decides how much of that effect comes from bridging rather than from charge neutralisation, which is why two grades at the same charge density can behave differently on two machines. Addition point matters as much as grade — the same polymer dosed before a pressure screen instead of after it can lose much of its effect to shear. Our CPAM retention aid guide covers grade selection, jar testing, anionic trash, and the cost arithmetic in full detail.

Sludge dewatering

Sludge is where a mill spends the most polymer per tonne. High-charge-density cationic PAM, generally 40-60% CD, conditions primary and secondary sludge ahead of a belt press or centrifuge, taking cake from 95-97% moisture into the 75-80% range. Because disposal is billed by weight, most of the water removed is money that never leaves the site.

Primary fibre sludge and secondary biological sludge do not respond to the same polymer. Biological solids are more hydrated and carry more surface charge, so they need higher charge density than fibre sludge at the same solids loading. Mills running both streams into one press often find that a single compromise grade under-performs on both, and that two grades dosed to each stream costs less in total polymer. Equipment matters too: a centrifuge shears floc harder than a belt press, so the grade that works on one is not automatically right for the other.

Effluent treatment and discharge compliance

Mill effluent carries fine fibres, filler, ink particles from recycled furnish, and dissolved organics. Anionic PAM in the 8-12 million MW range works as a coagulant aid behind alum or PAC, bridging the destabilised solids into flocs heavy enough to settle in a clarifier or lift cleanly in a DAF unit. Clarified water is normally recycled back into the process rather than discharged, which is what makes the polymer cost defensible even where discharge limits are loose.

Recycled-fibre mills carry the heaviest effluent load, because every cycle adds more dissolved and colloidal material that the wet end could not hold. Where COD or colour limits are tight, polymer alone will not close the gap and the programme has to be designed alongside the coagulant. See paper mill wastewater treatment for the full treatment train.

Broke recovery

Broke pulping systems use lower-charge CPAM, around 20-30% CD, to recover fine fibre from broke water and keep white water clear enough to reuse. Dosage here is the lowest of the four duties, and over-dosing is the common error: too much polymer flocculates recovered stock into lumps that cause formation defects when the broke returns to the furnish. Mills on recycled fibre lean on this stage more heavily, since their fibre is shorter and more of it escapes the wire.

Broke is also the duty most often left un-optimised, because it does not show up as a discharge number or a disposal invoice. The loss hides inside fibre yield instead. A mill that has never measured broke water clarity is usually leaving recoverable fibre in the loop, and the polymer needed to recover it costs a fraction of the pulp it saves.

Dosage by Application

Why furnish changes the polymer bill

Two mills producing the same grade at the same tonnage can differ by a wide margin in polymer consumption, and furnish is usually the reason. Recycled fibre carries dissolved and colloidal anionic material — sizing residues, dispersants, coating binders, and fines accumulated over repeated cycles. This anionic trash consumes cationic charge before the polymer ever reaches the fibre, so the effective dose at the wire is lower than the dose added at the pump.

Raising dosage is the instinctive response and the expensive one. The more reliable sequence is to measure cationic demand on the actual white water, then decide between three options: raise charge density, add a low-molecular-weight fixative ahead of the retention aid to mop up the trash first, or move the addition point closer to the headbox so less charge is consumed in transit. A mill that has measured its cationic demand can hold retention while spending less polymer than one that keeps increasing dose blindly. Seasonal swings in recovered paper quality mean that measurement is worth repeating rather than doing once.

Buying PAM for a paper mill

Mill procurement differs from single-duty buying in two ways. First, a trial has to cover more than one grade, because the wet end and the sludge press will not accept the same product. Second, consumption is steady rather than seasonal, so mills usually move to a monthly schedule after the trial rather than reordering ad hoc. Our public supply baseline is MOQ 500 kg per grade for trials, free samples before bulk confirmation, 7-10 day lead time for common grades, T/T or L/C payment, and 25 kg export bags — kraft paper with plastic liner, or PE.

A useful trial sequence is to jar-test the effluent and sludge grades first, since those give a clear numeric result on the bench, and run the wet-end grade on the machine afterwards where the only honest measurement is on-machine retention. Sending furnish type, paper grade, machine speed, application points, white water pH and conductivity, dewatering equipment, and estimated monthly volume with your enquiry is enough for us to propose starting grades and a test plan rather than a price list. Factory background is on our China PAM supplier profile, and cationic PAM grades lists the charge density options for the wet-end and sludge duties.

Paper Making PAM FAQs