The Application of Roller Screen in the Coal Conveying System of Thermal Power Plants

The Roller screen is a screening equipment used in the coal conveying system of thermal power plants. The Roller screen is widely applied in various fields such as thermal power plants, coal mines, and mines that require material screening. Its application is particularly common in thermal power plants. The Roller screen is mainly composed of a screen shaft, screen plates (the screen shaft and screen plates are collectively referred to as the roller), driving structure, and housing, etc. The distribution structure of the screen shaft and screen plates, with the inclination angle of each section of the screen surface along the material flow direction of the screen gradually decreasing from large to small, forms a segmented inclined screen surface. The materials entering the Roller screen first complete rapid separation on the section with a large inclination angle, then flow to the sections with smaller and smaller inclination angles, and undergo thorough separation here. Materials smaller than the screen holes are screened off, and large pieces are discharged to the discharge outlet.

The working principle of the roller screen

Since the screen shafts are arranged at different working angles, the speed of the material is faster when it runs at a higher working angle; and it is slower when it runs at a lower working angle. When the materials run at these two different speeds and converge at a certain position on the screen surface, they start to move axially. This causes the materials to be evenly distributed on the screen surface, achieving the purpose of improving the screening efficiency.

Roller screen structure

The Roller screen is composed of six major parts: the body, the cover, the screen shaft, the coal inlet hopper, the outlet housing and the control cabinet.

Body part

The body is a welded component. All the screen shaft assemblies are fixed to the body with connecting bolts. The side of the body is equipped with a liner plate.

Cover part

The cover is a welded component. The cover serves as a seal. An inspection door is provided on the cover. The front and rear coal inlet hoppers and the outlet housing shell are connected to the cover.

Screen shaft assembly

It consists of a roller screen motor (including a reducer), the screen shaft, the screen plate, flat keys, locking nuts, coupling, bearing housing and bearing housing accessories. The motor (including a reducer is directly connected to the screen shaft through a coupling.

Coal inlet hopper

It is a welded component. An inner baffle is provided inside. The baffle is driven by an electric pusher actuator and rotates in a limit position. The inlet hopper is equipped with a liner plate.

Outlet housing shell part

The outlet housing shell is a welded component. The outlet housing shell serves as a seal. An inspection door is provided on the outlet housing shell.

Control cabinet part

It is suitable for the coal conveying system of coal-fired power plants and the coal selection system of coal mines for screening the particle size of coal.

Performance characteristics of Roller Screen

Single drive

Each sieve shaft is driven separately by a motor reducer, meaning that each group of sieve shafts has a set of drive devices.

No jamming

Each sieve shaft rotates in the same direction at the same speed and has overload capacity. All rotating components rotate flexibly and there is no jamming phenomenon.

Multi-angle sieve shafts

The sieve shafts are reasonably arranged at multiple angles. At the inlet section of the roller screen, the angle between the sieve shaft and the horizontal plane is 15°, and at the outlet section, it is 5°. This enables the coal to enter the equipment first through a preliminary coarse screening and then undergo a secondary fine screening, thereby improving the screening efficiency and preventing coal blockage.

Coupling connection

The coupling between the reducer and the Roller Screen uses an elastic pin coupling; if any one of the sieve shafts fails, the coal can be pushed by the previous sieve shaft to continue moving, and the roller screen can still operate normally.

Mushroom-shaped sieve plates

The wear-prone components such as the sieve shafts and sieve plates are easy to replace; the sieve plates adopt a mushroom-shaped design and are arranged alternately. This not only facilitates the transportation of coal but also reduces the dead angles formed by adjacent sieve shafts, avoiding blockages.

Advantages of the roller screen

Screen plate shape

The screen plate shape is designed based on the characteristics of different materials and coal conveying flow. The common shapes of the screen plate include heart-shaped, parabolic, elliptical, and tooth-shaped. The selection of the screen plate mainly considers disturbing the materials and better separating the materials by loosening them, transporting the materials forward along the screen surface, and ensuring that the process is not prone to blockage.

The parabolic-shaped screen plate has a rotation deflection of the screen plate that is generally greater than that of other types of screen plates, causing the materials to be thrown forward at approximately 45°along the screen surface. The elliptical screen plate, when performing circular motion, generates a sinusoidal trajectory to disturb the materials, dispersing and stratifying the materials on the screen surface, and transporting the materials forward along a certain incline while achieving efficient screening.

Self-cleaning device

During the operation of the screen plate, impurities mixed in the coal are thrown to the tip of the parabolic-shaped screen plate by the rotation of the screen plate. A small amount of soft debris attached to the working surface of the screen plate can be removed by the coal flow during the rotation of the screen plate. The self-cleaning device of the screen shaft is made of wear-resistant steel in the form of comb teeth and has a cutting edge, and is inclinedly installed at the lower part of the screen shaft. When some fibrous debris is wound around the screen plate and the cleaning device, the cutting edge of the cleaning device can cut it off. When the moisture on the coal surface is too high, some fine coal attached to the screen plate will be automatically removed by the cleaning device, thereby solving the blockage of the screen surface.

Conclusion

Compared with traditional vibrating screens, the Roller screen is less prone to clogging when grading wet and sticky coal. It can ensure the processing capacity and screening effect. Moreover, the Roller screen has the advantages of simple structure, no vibrating components, good sealing performance, no dust spillage, and low noise. When choosing screening equipment in thermal power plants, Roller screen can be given priority consideration.