Ring Granulator Type Coal Crusher - Working Principle,Parts

Ring granulator type crushers are widely used in coal handling plants for crushing coal to the required size before it is sent to the coal bunker of a thermal power plant.

Crushing Principle Of Ring Granulator Type Coal Crusher

A ring granulator crusher uses a combination of impact and rolling compression to reduce the size of coal.

Coal enters the crusher through the feed opening and falls into the crushing zone. As the rotor rotates, the suspended crushing rings move with it. The rings strike the incoming coal and force it against the breaker plate and cage assembly.

When the rotor reaches operating speed, centrifugal force causes the rings to move outward from the rotor centre. As coal enters the crushing chamber, the rings move inward and outward according to the resistance offered by the material.

The combination of impact from the rotating rings and rolling/compressive action against the cage breaks the coal into smaller particles.

The crushed coal then passes through the openings in the cage bars or screen plates. The final product size is primarily influenced by the screen opening size and the clearance between the crushing rings and cage assembly.

How the Crushing Rings Work

The crushing rings are mounted on suspension bars attached to the rotor assembly. This allows the rings to move relative to the rotor instead of being rigidly fixed.

When a ring encounters coal, it moves and exerts a crushing force on the material. The rolling action of the rings helps maintain continuous contact with the coal bed and produces a relatively uniform granular product.

This arrangement also allows the rings to respond to variations in the material being crushed.

Different ring configurations, including single-tooth, plain and double-tooth rings, can be selected depending on the coal characteristics and required crushing conditions.

Ring Granulator Type Coal Crusher Consist Of Following Parts:

1. Crusher Frame

The crusher frame is fabricated from heavy steel plates and forms the main structural body of the machine. Large inspection doors are provided at the front and rear for inspection and maintenance. The doors are generally provided with dust-tight sealing arrangements. Top access is provided for maintenance activities, while side doors may facilitate rotor removal without completely dismantling the crusher.

A hydraulic door-opening arrangement may also be provided depending on the crusher design.

2. Rotor Assembly

The rotor is one of the most important assemblies of the ring granulator. It is generally dynamically balanced to minimize vibration during operation.

The rotor assembly consists of:

Rotor shaft
End discs
Rotor arms
Suspension bars
Crushing rings
Bearings and bearing housings

Rotor Shaft

The rotor shaft is manufactured from forged and heat-treated alloy steel to withstand the mechanical loads generated during crushing.

Ring Hammer / Crushing Ring

The crushing rings are generally manufactured from wear-resistant cast alloy steel, depending on the application. Tooth configuration and ring material are selected according to coal characteristics, required product size and expected wear.

For more information, see:

Ring Hammer Replacement Process

Bearings

Heavy-duty spherical roller bearings are commonly used to support the rotor shaft. The bearings are housed in robust bearing housings with suitable sealing arrangements to protect against coal dust ingress.

3. Cage Frame

The cage frame forms the lower crushing and sizing section of the crusher. It is fabricated from heavy steel plates and is supported through the cage shaft and associated adjustment mechanism. The cage works together with the crushing rings to provide the required crushing clearance and product-size control.

4. Cage Adjustment

The cage adjustment mechanism is used to control the clearance between the cage/screen assembly and the path of the crushing rings. Changing this clearance influences the crushing action and product size within the limits specified by the crusher manufacturer. The cage assembly can be moved using the provided adjustment mechanism, such as a worm gear and ratchet arrangement, depending on the crusher design.

Important: Cage adjustment should be carried out only according to the manufacturer’s operating and maintenance procedure. If adjustment during operation is specifically permitted by the equipment design, the prescribed procedure and safety precautions must be followed.

5. Cage Bars / Screen Plates

The cage bars or screen plates control the size of coal leaving the crushing chamber. The screen opening is selected according to the required coal size downstream of the crusher. Because these components are continuously exposed to abrasive coal, they are normally manufactured from wear-resistant material. Excessive wear can increase the product size and affect crusher performance.

6. Breaker Plate

The breaker plate provides a surface against which the incoming coal is crushed by the rotating rings. It also protects the crusher casing from direct impact and wear. The breaker plate is normally made from replaceable abrasion-resistant material.

7. Tramp Iron Pocket

The tramp iron pocket provides a collection area for tramp iron and other uncrushable foreign material. The arrangement prevents such material from continuously circulating through the crushing zone. The collected material should be removed periodically according to the plant’s maintenance procedure.

Work Involved During Preventive Maintenance Of Ring Granulator Type Coal Crusher

During preventive maintenance of ring granulator type crusher following equipments/parts are checked and detected problems are corrected.

1. Rotor Assembly

The granulator rotor assembly generally require minimum maintenance with the exception of hammer and suspension bar replacement. Frequency of hammer and suspension bar replacement will depend upon the material crushed and the rate it is fed. Preventive maintenance of rotor assembly include the following:

Check wear on hammers and suspension bars.
Check disc clamp nuts for tightness. If not tight, suspension arms will loosen and cause wear on the rotor key, rotor shaft and suspension arm bore. In addition, vibration may occur.
Check suspension bar holes in suspension arms for any elongation. After a long period of service, this is likely to occur.
Check The suspension bar ends for wear which may also occur during the wearing period of set of hammers.
Check End disc proper tightness & should not be any wear & tear.
Check any erosion on blade arm and hard facing condition.

2. Kick off plates – Check proper tightness, any wear & tear.

3. Liners – Check proper tightness, any wear & tear.

4. Breaker Plate– Check for proper tightness & any wear & tear.

5. Screen Plate – Check proper tightness, any wear & tear.

6. Hydraulic System – Check for oil leakages, oil level, oil condition, cleanness.

7. Casing Bolt – Check bolts tightness with washer.

8. Receiving chute sealing (Bellow) – Check during operation no dust leakage from the discharge chute. Bellow all bolts should be proper tight.

9. Discharge Chute – Check inside condition of chute. Cleaning should be done if required.

10. NDE and DE Bearing

Bearing greasing in regular interval of time.
Check bearing clearance, grease quality & labyrinth seal condition.

11. Coupling – Check condition of all coupling.

12. Gear Box – Check for oil leakages, oil level, oil condition and cleanness.

13. Bolts – Check proper tightening of all bolts.

Common Issues and Remedies of Ring Granulator Type Crusher

Issue 1: Excessive Vibration

Probable Cause:

Uneven or fluctuating coal feed.
Worn-out or unbalanced ring hammers.
Loose foundation bolts or coupling bolts.
Improper cage alignment or damaged screen plates.

Remedy:

Ensure uniform coal feeding to the crusher.
Inspect hammers for wear; replace in balanced pairs.
Tighten all foundation and coupling bolts to specified torque.
Realign or replace cage and screen plates if required.

Issue 2: Oversized Output or Poor Crushing

Probable Cause:

Excessive clearance between cage and hammer path.
Worn or broken screen plates.
Ring hammers worn beyond allowable limit.
Rotor speed too low or feed rate too high.

Remedy:

Adjust cage clearance as per standard setting.
Replace worn or damaged screen plates.
Replace worn hammers; maintain uniform weight balance.
Maintain correct rotor speed and feed rate.

Issue 3: High Bearing Temperature

Probable Cause:

Over-greasing or insufficient lubrication.
Misalignment of rotor shaft.
Dust or moisture ingress into bearing housings.
Bearing wear or damage.

Remedy:

Follow correct greasing schedule and quantity (use MOBIL XHP 222 or equivalent).
Check and correct alignment between rotor and motor.
Clean seals and replace if leakage is found.
Replace damaged bearings and refill with fresh grease.

Issue 4: Overload

Probable Cause:

Tramp iron or uncrushable material inside chamber.
Excessive feed rate or wet, sticky coal.
Blocked discharge path or cage choking.
Electrical overload or jammed rotor.

Remedy:

Clean tramp iron pocket regularly to remove metallic pieces.
Regulate coal feed and avoid overloading.
Inspect and clean cage openings to prevent choking.
Check motor protection settings and free rotation of rotor.

Issue 5: Abnormal Noise During Operation

Probable Cause:

Loose ring hammers or suspension bars.
Hammer tips touching the cage or breaker plate.
Damaged liners, screen plates, or rotor components.
Excessive wear in bearing housings.

Remedy:

Tighten hammer suspension pins and bolts.
Adjust cage clearance properly.
Replace damaged liners, screens, or hammers.
Inspect bearing housing; replace worn components.

Issue 6: Dust Leakage Around Crusher

Probable Cause:

Worn or missing gland seals.
Gaps between housing joints.
Damaged flexible connection to feed or discharge chutes.

Remedy:

Replace worn seals and gaskets.
Apply sealing compound on housing joints.
Refit flexible chute covers tightly.