Eco-Friendly Retention & Drainage Aids: Why They Pay Off
A well-designed retention and drainage program is the most profitable chemical you can add to a paper machine – it saves fibre, steam, chemicals and effluent load at the same time.
If you could add one chemical program that lowered fibre loss, cut steam consumption, reduced other chemical dosages and eased the load on your effluent plant, you would call it a miracle. Paper makers simply call it a retention and drainage aid program – and many mills still run it on autopilot, leaving money on the table.
What the program does
- Retention keeps fines, fillers and functional chemicals (size, starch, dye, OBA) in the sheet instead of the backwater.
- Drainage removes water faster on the wire and in the press, so the sheet enters the dryers drier.
The two are linked: better retention of fines also opens up the sheet structure and improves drainage.
Where the savings come from
- Fibre and filler: raising first-pass retention from 70% to 85% on a 150 TPD machine keeps roughly 2-3 tonnes of solids per day out of the effluent.
- Steam: every 1% increase in dryness after the press saves about 4% dryer steam.
- Other chemicals: retained size, starch and dye mean lower dosages of AKD, DSR and dyes for the same result.
- Effluent: fewer suspended solids and lower BOD/COD going to the ETP, lower sludge handling cost.
- Runnability: cleaner white water means fewer deposits, fewer breaks and longer fabric life.
Building an eco-friendly program
Step 1 – Coagulant for charge control
Recycled furnish brings anionic trash that consumes cationic chemicals. A coagulant (low molecular weight, high charge) neutralises it and lets the flocculant work. Modern organic coagulants replace alum and PAC, reducing sludge and conductivity.
Step 2 – Flocculant for retention
A high-molecular-weight cationic flocculant (typically a cationic polyacrylamide) bridges fines and fillers to fibre. Dose it late – after the pressure screen – so flocs are not broken by shear.
Step 3 – Micro-particle or dual system for drainage
For high-speed or high-ash grades, a dual system (cationic polymer plus anionic micro-particle such as bentonite or colloidal silica) re-flocculates after shear and gives the best drainage with a uniform formation.
Step 4 – Optimise, do not maximise
Over-flocculation hurts formation and gives a two-sided sheet. Use a drainage tester and a formation index; target the dosage where retention gains flatten out.
What makes a program "eco-friendly"
- Organic coagulants instead of alum/PAC → less sludge and lower conductivity
- Low-dosage, high-efficiency flocculants → less polymer to the environment
- Higher retention → cleaner effluent and lower fresh-water demand
- Products free of APEO, formaldehyde and heavy metals
Typical payback
Most mills recover the cost of a properly tuned program within weeks through fibre savings alone; steam and chemical savings are a bonus. A 15% reduction in total wet-end chemical spend is common after optimisation.
VB Global supplies eco-friendly coagulants, flocculants, retention & drainage aids and ash retention chemicals, and provides wet-end surveys and on-machine trials to optimise your program.
