Coarse Screening System for Paper Mills – Process, Advantages & Limitations

 

“First Line of Defence for Cleaner Pulp and Safer Downstream Equipment”

 

Coarse screening is a stage in the pulp stock preparation line where large contaminants and undesired particles are removed from the pulp before refining and forming on the board machine.

This is especially important in recycled fiber and multilayer board production where waste paper streams may contain plastics, metals, adhesives, coatings and other large impurities.

 

Coarse screen

 

The purpose:
 Improve stock cleanliness
Protect refiners, screens, and head box
 Improve paperboard quality and machine run ability.

 Working Principle

In a stock preparation coarse screening system (pressure screens or rotating/basket screens) work flow are as:

Typical Workflow

                    

1. 1. Feed Entry: Pulp stock from the dump chest (usually ~2–4% consistency) enters the coarse screen.

1. 1. Screen Basket Separation: The stock is forced through a perforated or slotted screen basket. Fibers and fine material pass through the screen accept side, and larger contaminants are retained reject side.

1. 1. Rotor/Screen Action: A rotor located inside or around the basket creates centrifugal and hydraulic forces — helping stock pass through and keeping contaminants from blocking the screen.

1. 1. Reject Discharge: Large trash, plastics, knots, etc. are removed continuously (or periodically) through a reject outlet and sent to reject handling (reject separator).

                                                             Types of Coarse Screen

Advantages Coarse Screen

1. Protection of Downstream Equipment: Removes heavy contaminants (plastics, metals, stones) so that refiners, fractionators and forming sections aren’t damaged.

2. Low Fiber Loss: Well-designed coarse screens physically separate contaminants while allowing fibers to pass with minimal fiber loss.

3. High Screening Capacity & Efficiency: Modern screens handle high throughput in low to medium consistency stock, improving overall productivity.

4. Gentle Action on Fibers: Rotating basket and optimized rotor designs avoid excessive fiber degradation or cutting of contaminants into fines.

5. Lower Operating & Maintenance Costs: Compared to complex fine screens or cleaners, coarse screens are simpler, and operate at lower energy.

Limitations Coarse Screen

1. Limited Removal of Small Impurities: Coarse screens don’t remove very fine particles, stickies, or dissolved contaminants, so further fine screening or cleaning stages are essential.

2. Possible Basket Blinding: Strong accumulation of sticky materials or poorly designed rotors can lead to screen basket blinding, reducing efficiency if not cleaned well.

3. Reject Handling Required: Proper reject handling system is required. Without proper reject handling system, stock preparation flow is disrupted.

4. Higher Energy Use (at High Consistencies): Handling higher consistency stock requires greater power and robust motors.

 Manufacturers and Suppliers

Here are common suppliers and systems used for coarse screening in board machine stock preparation (international & relevant specialist vendors):

 International Suppliers & Their Specialization

• • Valmet – Coarse screening systems optimized for recycled fiber and stock prep (vertical rotating basket technology).

• • Toscotec – Offers Super screen and Vorti screen series for coarse screening in board and recycled stock lines.

• • Andritz – ModuScreen CR for Recycle fiber and ModuScreen C&F for combined (recycle and Virgin fiber) can be used for coarse screening.

Regional / Other Suppliers

• • Samarth Paper Machinery – Offers up flow and pressure screens used in coarse stock screening.

• • JST Machinery – Supplies screening systems (up flow coarse screens) for paper machines and stock preparation.

• • Leizhan Paper Equipment – Supplies coarse/pressure screening equipment often used in stock preparation.

• • Parasons Machineries – Manufacture pressure screens and cleaners for pulp screening stages.

Summary (At a Glance)

Aspect	Detail
Purpose	Remove large contaminants from pulp stock in multilayer board machine preparation.
Working Principle	Stock forced through a basket/slot screen; rotors help screen and repel contaminants; accepts pass through, rejects discharged.
Merits	Protects equipment, high capacity, low fiber loss, simpler & efficient.
Demerits	Doesn’t remove small particles, requires reject handling, needs good cleaning design.
Suppliers	Valmet, Toscotec, JST Machinery, Samarth, Leizhan, Indian OEMs like Mohseen.