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.
- Over-lime excursion.
- 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.
- Dregs Excursion?
a) What is the color of the cake? It should be white not green.
- Soap, Black Liquor, foul condensate in the process?
- Feed to drum vat should be 25% solids.
- 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.
- Continuous pre-coat shower bar operating correctly, full travel and correct pressure.
- Temperature of the lime mud storage should be above 135° F.
- Shower temp should be between 165° F and 185° F – low enough not to flash.
- Is the filtrate receiver tank shaking? Is filtrate leaving?
- What is the vacuum? 20 inches of Hg is optimum.
- Has a new cloth been installed?
- Drum speed – should be 3 rpm
- Solids to filter – 25%
- How many shower bars are there and how much water, and how are they aimed? Do not use shower water 35 degrees above horizontal.
- Dull Doctor Blades can drop solids by 6-8%.
- Temperature of shower water? 165° F to 185° F.
- Lime quality? See above