“Efficient removal of light contaminants for cleaner stock and stable machine operation”
What is a Low Density Cleaner?
A Low Density Cleaner (LDC) commonly called a Centri-cleaner is a hydraulic centrifugal cleaning device designed to remove lightweight contaminants from pulp stock,
Such as:
- Plastics (LDPE, HDPE, films)
- Wax particles
- Hot-melt & pressure-sensitive stickies
- Foams
- Lightweight shives and flakes
- Air-entrained contaminants
In multi-layer board machines, LDC are critical for:
- Surface quality (especially top layer)
- Runnability
- Forming fabric and headbox cleanliness
“They are especially important when using recycled fiber (OCC, MWP, mixed waste).”
Working Principle
Basic Principle: Reverse Centrifugal Separation: Unlike high density cleaners, Centri-cleaner are designed so that lighter contaminants move toward the center vortex, while fibers move outward.
Step-by-Step Operation
- Stock Feed
- Pulp enters tangentially at 0.4–1.0% consistency
- Creates a high-velocity rotating vortex inside the cleaner cone
- Centrifugal & Hydraulic Forces
- Heavier fibers move outward toward the cone wall
- Lighter contaminants (lower specific gravity than fiber) migrate toward the center vortex
- Separation
- Accept (clean fiber) exits through the bottom outlet
- Reject (light contaminants) exits through the top outlet
- Reject Handling
- Rejects go to secondary or tertiary cleaner stages for fiber recovery
Key Difference from HDC:
- HDC removes heavy dirt
- LDC removes light contaminants
Typical Position in Stock Preparation Line
Pulper → Coarse Screening → High Density Cleaner → Fine Screening → Low Density Cleaners (Multi-stage) → Approach Flow → Head box (Layer-wise)
“In multilayer board machines: Top layer → highest LDC efficiency required, Middle / back layers → fewer stages acceptable depending on furnish quality”
Advantages of Centri-cleaner
1. Excellent Removal of Light Contaminants
- Efficiently removes plastics, wax, stickies, foam
- Reduces sheet defects like: Holes, Spots, Pitch marks, Dirt specks.
2. Improves Paperboard Quality
- Better surface appearance
- Improved printability (critical for FBB, duplex, coated boards)
3. Protects Head box & Forming Section
- Reduces Headbox clogging
- Reduces Wire contamination
- Reduces Sheet breaks
4. No Moving Parts
- Simple design
- Very high operational reliability
- Low maintenance cost
5. Scalable & Modular
- Cleaner banks can be easily expanded
- Multi-stage systems improve fiber recovery
Disadvantages of Centri-cleaner
1. Fiber Loss in Rejects
- Light contaminants often carry good fibers
- Requires secondary and tertiary stages for fiber saving
2. Ineffective for Heavy Contaminants
- Cannot remove sand, metal, stones→ Needs High Density Cleaners upstream
3. Sensitive to Operating Conditions: Performance drops if –
- Consistency fluctuates
- Inlet pressure is unstable
- Air entrapment is high
4. Higher System Complexity
- Multiple stages
- More piping, valves, manifolds
- Needs good balancing and control
Typical Operating Parameters
| Parameter | Typical Range |
| Feed Consistency | 0.4 – 1.0% |
| Inlet Pressure | 2.0 – 3.5 bar |
| Reject Rate | 5 – 15% |
| No. of Stages | 2 – 4 |
| Contaminants Removed | SG < 1.0–1.1 |
Suppliers / Manufacturers
International Suppliers
- Valmet – Low density cleaner systems for board & recycled fiber lines
- ANDRITZ – Multi-stage LDC banks with reject recovery
- Voith – CLEANER LT series for lightweight contaminant removal
- Toscotec – Complete cleaning systems for multi-layer board machines
Indian & Asian Suppliers
- Parason Machinery – Centri-cleaners & complete stock prep systems
- JST Machinery – Low & high density cleaners
- Samarth Paper Machinery – LDC for OCC and mixed waste furnishes
- Leizhan Paper Equipment – Cost-effective cleaner banks
- Shree Vishwakarma / Mohsen Engineering – Indian centrifugal cleaner manufacturers
Comparison: High vs Low Density Cleaner (Quick View)
| Aspect | High Density Cleaner | Low Density Cleaner |
| Removes | Sand, metal, stones | Plastics, wax, stickies |
| Density Basis | Heavier than fiber | Lighter than fiber |
| Reject Outlet | Bottom | Top |
| Position | Before fine screening | After fine screening |
| Fiber Loss Risk | Low–Medium | Medium–High |
Conclusion
Low Density Cleaners are vital for maintaining multi-layer board quality, especially for the top layer. Centri-cleaner ensuring cleaner stock, better surface quality, and reliable machine performance.
Their effectiveness depends on stable consistency, efficient multi-stage reject recovery, and proper upstream screening and HDC operation,