Pre-Coat Drum Filter Operational Trouble Shooting

A 1% improvement in lime mud solids can save a mill $100,000 per year or more (basis 1,000 T of pulp/day).

Reliable and continual operation of the lime mud pre-coat filter is crucial for efficient lime kiln operations.  McFarlen Engineering has compiled a list of common issues to double check when troubleshooting the operation of the pre-coat drum filter.

Filter Blinding:

  1. Over-lime excursion.
  2. Purchased lime in the system:
    a) What is the carbonate test from the purchased truck
    b) What are the results of the 5-minute settling test? Solid liquid interface should be down 40% after 5 minutes.
  3. Dregs Excursion?
    a) What is the color of the cake? It should be white not green.
  4. Soap, Black Liquor, foul condensate in the process?
  5. Feed to drum vat should be 25% solids.
  6. Cake thickness 3/8”-1/2”:
    a) Make sure the doctor board clearance is reset after each cloth change.
    b) Set from high point of each end of the drum.
  7. Continuous pre-coat shower bar operating correctly, full travel and correct pressure.
  8. Temperature of the lime mud storage should be above 135° F.
  9. Shower temp should be between 165° F and 185° F – low enough not to flash.
  10. Is the filtrate receiver tank shaking? Is filtrate leaving?
  11. What is the vacuum? 20 inches of Hg is optimum.
  12. Has a new cloth been installed?

Low Solids:

  1. Drum speed – should be 3 rpm
  2. Solids to filter – 25%
  3. How many shower bars are there and how much water, and how are they aimed? Do not use shower water 35 degrees above horizontal.
  4. Dull Doctor Blades can drop solids by 6-8%.
  5. Temperature of shower water? 165° F to 185° F.
  6. Lime quality? See above


Trevor Van Bavel, E.I.T. at or (604) 818-5598

Jonn McFarlen, P.Eng. at or (604) 813-8616