1 Overview of coal preparation plant
Xinjiang Coal preparation plant is a mine type steam coal preparation plant. After several renovations and expansions, the current processing capacity has reached 2.4Mt/a
In July 2018, the flotation system was reformed to realize the jig-flotation combined process. Washing process: raw coal is graded by vibrating screen, and less than 13mm grain grade is not washed, and it is directly sold as final raw coal products. The grain grade greater than 13mm enters the washing system, and the products such as washing medium block (38~80mm), washing small block (18~38mm) washing granular coal (13~18mm) and final cleaned coal (-13mm) are produced after washing.
2. Adjust the screening process before washing
In recent years, washed grain coal gradually in the eastern Henan coal market selling price continues to rise. In order to expand the economy by increasing the yield of washed grain coal
For economic benefit, Xinjiang coal preparation plant has adjusted the structure of some commercial coal and reduced the upper grain size of the final raw coal from 13mm to 8mm
The lower limit of grain size of washed coal is reduced from 13mm to 8mm, and the upper limit of final cleaned coal is reduced from 13mm to 8mm. The adjusted commercial coal products are mainly final raw coal (-8mm), final cleaned coal (-8mm), washing block (38~80mm), washing small block (18~38)mm), granulated coal (8~18mm), etc. According to the product requirements, the process flow of the raw coal system in the coal preparation plant has been adjusted (Figure 1). The final raw coal products in the coal preparation plant mainly come from the bottom of the raw coal grading screen, while the final clean coal (-8mm) and washing block (38~80)
mm), washing small pieces (18~38mm), washing grain coal (8~18mm) are produced by the subsequent washing system. It can be seen that the key to improve the yield of washed grain coal is the effective screening of fine grain grade less than 8mm in the raw coal system. In order to further improve the screening effect, Xinjiang Coal Preparation Plant has replaced the screening equipment in two sets of raw coal classification systems A and B in recent years, in which the sag screen in system A and the coal banana screen in system B are replaced, and the two equipment are from the same manufacturer. At present, coal banana screen and relaxation screen are used together in coal preparation plants. According to the actual use of the two screening equipment in Xinjiang Coal preparation plant, the characteristics and technological effects of the two vibrating screens were compared.
3 Comparison of working principles
3.1banana screen
banana screen is optimized by the principle of equal thickness screening, using ZDQ09AFC box exciter, through the disc coupling and spline drive shaft connected with the drive mechanism to transmit power and linear vibration power. At the operating frequency, the exciter drives the sieve box to vibrate, so that the material is excited to layer through the sieve forward, from the feeding end to the discharge end, all the material is screened through the screen surface.
banana screen is mounted on the same screen frame with 7 different angles of the screen surface, each segment decreases at 4 Angle intervals. in
Under the same vibration strength, the material can obtain different shifting strength and movement speed on each section of the screen surface, and the material layer thickness on the screen surface is decreased from the feeding end to the discharging end, so that the thickness of the material layer on the screen surface is basically unchanged from the feeding end to the discharging end, so as to achieve equal thickness screening.
3.2 Relax the screen
The relaxation screen vibrates on the principle of two-body subresonance, using one basic circular vibration to drive the other one
The vibration amplitude of the floating bed is much greater than that of the traditional vibration equipment, and according to the regularity of the movement of the material group itself, the simple harmonic excitation force generated by the box exciter drives the material layer to achieve loose, layered and sifting.
4 Structure Comparison
4.1banana screen
coal banana screen is an efficient vibrating screen composed of 7 screen surfaces of different angles. Its main structural features are as follows: The screen surface is divided into 7 segments, decreasing segment by segment at 4° inclination interval; Box type vibration exciter, high strength, light weight; Modular component design, high degree of universality, easy to install, maintenance, according to user needs to use different structure of the screen surface; adopt
The steel helical spring can reduce the dynamic load of the screening machine to the foundation to the maximum extent and ensure the stable operation of the equipment.
4.2 Relax the screen
Relaxation screen is the use of special elastic sieve surface relaxation motion for material screening equipment, its main structural characteristics are as follows
Sub-resonance principle to achieve vibration, equipment needs less power; Although the relaxation screen has two exciters, only one drive motor is required; The box exciter moves in a linear manner and adopts steel helical spring to reduce vibration. The side part of the screen machine is sealed with a "U" shape design, which can effectively prevent the above screen from entering the below screen.
In order to meet the market demand, the thermal coal preparation plant has put forward more and more requirements for the screening of fine grade coal. Through the comparative analysis of two vibrating screens in use at the same time in Xinjiang coal preparation plant, it can be seen that compared with coal banana screen, the relaxation screen has the advantages of large processing capacity and high screening efficiency. Therefore, in the fine grade screening, the relaxation screen should be preferred under the same conditions. However, from the actual application of the relaxation screen in Xinjiang coal preparation plant, there is still a certain gap between the application effect of the relaxation screen in the fine grade screening process and the actual demand, and the equipment performance of the relaxation screen still needs to continue to improve in order to continuously meet the production demand.
