Why does my belt press cake stay too wet?

The symptom

Dry solids content drifts down over weeks while polymer consumption climbs. Operators compensate with slower belt speed, which cuts throughput; disposal costs rise with every extra percent of water hauled off site.

Root causes

1. 01 Blinded belt: fines, grease or polymer residue fill the fabric, so drainage capacity is gone even though the belt looks serviceable.
2. 02 Wrong belt permeability for the sludge: an open belt loses fines and stresses the filtrate side, a tight belt drains too slowly for the throughput.
3. 03 Polymer dosing mismatched to the belt: flocs sized for a different drainage profile shear apart in the wedge zone, releasing water the press has already separated.
4. 04 Worn or damaged seam and edges: local leak paths let sludge bypass the pressing zones entirely.

The mesh solution

• ▸ Match the belt type to the sludge, not to the previous order: strength, openness and retention (for example psb 15/50 versus 29/85) follow from the drainage profile.
• ▸ Restore drainage: professional cleaning where economical, on-site seam repair where the fabric is sound, replacement where it is not.
• ▸ Re-tune polymer dosing together with the new belt: belt and floc are one system, changing one without the other wastes both.
• ▸ Have the whole installation assessed: rollers, doctor blades, wash water and tracking decide belt life as much as the fabric itself.

Prevention

• ⊕ Trend dry-solids and polymer dose per tonne weekly: the ratio degrades long before the cake visibly changes.
• ⊕ Keep wash-water pressure and nozzle condition in the maintenance schedule; a blinded spray bar blinds the belt behind it.
• ⊕ Measure the belt before the shutdown, so the replacement waits for the window instead of the reverse.