Coal Mine Energy Company – Inner Mongolia, Asia
Project Background:
The open-pit coal mine of an energy company we cooperate with is located in Inner Mongolia. It has a continental subarctic climate, with long and cold winters, short and hot summers, large temperature differences between day and night, large coal dust on site, and large sandstorms in spring. The seasonal freezing depth is 2.41 meters, and the thickness of frozen soil is 2-4 meters. Coal mine crushing equipment needs to maintain normal operation under severe weather conditions such as wind, snow, rain and sand in an environment of -50~+40℃.
The energy company can produce 35 million tons of high-quality lignite annually. The storage center is a comprehensive ground production system of tens of millions of tons that integrates crushing, screening, coal storage, and rapid quantitative loading. It is mainly responsible for the secondary crushing of the company’s coal production and rapid loading of railway coal. It provides screening blocks and finished coal of different coal qualities for the company’s winter heating, surrounding civil heating, power generation and heating in the northern region, and other production and living areas. At the same time, it stores and transports coal of different particle sizes and coal quality requirements for local coal-to-oil, coal chemical industry, quality-improving shaped coal and other industrial and mining enterprises.
The working area is mainly composed of two parts: the first phase open-pit mine tens of millions of tons of ground production system and the second phase open-pit mine tens of millions of tons of ground production system. In the past, the motor and reducer of the crushing station of the tens of millions of tons production system used hydraulic couplings as soft start equipment. Since the hydraulic coupling runs at full load for a long time, it needs to be refueled and maintained during use, and the oil seal also needs to be replaced frequently to keep the coupling working properly. Once the hydraulic coupling fails, it must be shut down for maintenance. Its disassembly and assembly is very inconvenient. It takes about 5 hours to replace the entire hydraulic coupling, which will inevitably bring economic losses and many other adverse effects to the production department.
Crushing material characteristics:
- Loose sand layer, soft clay layer: shear strength value is 25, C value is 0.015MPa.
- Crushing rock mass: rock mass in the strong weathering zone of coal series, with a compressive strength of 1.56MPa.
- Layered block fracture rock section: all coal series strata below the weathering zone, composed of mudstone, sandstone, and coal seam. Among them, mudstone accounts for 70%, with a large thickness and a compressive strength between 1.56 and 9.60 MPa.
- The feed is lump coal, and the compressive strength of the coal seam is between 5.48 and 16.8 MPa (F3 to F5), with an average of 10.18 MPa; the average shear strength is 0.88 MPa.
- Coal bulk density: 1.28 to 1.41 t/m3.
- Coal body loose coefficient: 0.7.
- Rock body bulk density: average bulk density ≤ 2.14 t/m3.
- Rock loose coefficient: 1.3.
- Coal rock moisture content: The moisture content of the raw coal in the coal seam is between 3.59% and 19.87%, and the average moisture content of each rock layer is ≤ 23.4%.
Problem Points:
The problems that existed when using hydraulic couplings before were:
- The No. 3 secondary crusher is a parallel double unit, and the crushing capacity of each unit is 2000t/h (400kw/unit, feed particle size is less than 300mm, and discharge particle size is less than 50mm). Designed and installed by a certain engineering machinery company, the impact load of the dual-motor driven crusher is very large, and the coupling uses imported hydraulic couplings. However, due to the influence of foreign iron objects (iron objects left in the open-pit mine), the crusher gear roller often gets stuck, causing the coupling, reducer and even the gear roller to be damaged to varying degrees, or even deformed and unusable, causing the entire production system to be unable to operate, bringing many hidden dangers to safe production work, and seriously restricting production.
- While considering its own strength, due to environmental factors, crusher equipment manufacturers often vigorously increase the output power of the crusher. Therefore, the hydraulic coupling as a connecting part will instantly bear a very large impact force, and due to its structural characteristics, it is inevitable to be damaged. For example, the pin coupling is often damaged. The normal operation of the hydraulic coupling requires hydraulic oil to complete the transmission of torque. Hydraulic oil often leaks due to overload or poor sealing, polluting the environment and affecting the normal torque transmission. Therefore, in order to ensure the normal operation of the hydraulic coupling, it is necessary to frequently maintain and inspect the workroom and seal, and regularly add or replace the hydraulic oil. These maintenance work will inevitably cause the equipment to start and stop many times, increase the workload of the staff, and more importantly, the output, efficiency, and equipment utilization of the coal mine will also decrease, while the maintenance costs and other expenses are rising.
Solution:
A high-power torque-limiting magnetic coupling is customized according to the power required by the daily crusher. This coupling is mainly composed of two parts, one is a conductor of special material connected to the end of the motor shaft, and the other is a permanent magnet connected to the load end. When working, the relative movement of the two parts generates a magnetic field, which generates eddy currents in the disc conductor. The magnetic field generated by the eddy current interacts with the permanent magnet, so that the rotor and the conductor transmit torque through the air gap.
After installation and commissioning, it is basically not disturbed and affected by the use environment, and the operation is stable and reliable. Since there is no power, there is no electromagnetic interference problem. Since the shaft connection between the crushing magnetic coupling motor and the load is non-contact, the vibration of the load will not be transmitted to the motor. It is precisely because the shaft connection is non-contact that it brings two benefits:
- The requirements for alignment during installation are low;
- There will be no bearing and seal damage caused by direct shaft connection, thereby ensuring the service life of the equipment. The design theoretical life of the crushing magnetic coupling is 30 years, showing excellent long-term operation stability.
On December 9, 2013, the operator detected that the crusher was overloaded during operation. The crushing magnetic coupling responded instantly, and the disc was effectively disengaged to protect the motor. After investigation, it was found that a piece of iron was stuck between the roller teeth, causing the overload. From that case, it can be seen that the disc of the magnetic coupling can be instantly decoupled in an emergency state, accurately and effectively avoiding the wear of the entire crusher system.
Result Summary:
According to the feedback from customers during the use of the magnetic coupling after installation, the performance characteristics of the crushing magnetic coupling are compared with the previous hydraulic coupling transmission equipment. The crushing magnetic coupling has a compact structure and does not require the installation of other auxiliary equipment. Since the torque is transmitted through the air gap, there is no contact between the two parts, so there are no wear parts, and the vibration can be reduced by more than 80%, extending the life of equipment parts and bearings. Large eccentricity is allowed; no lubrication is required; the specified allowable pulsating load can be provided, and the impact load can be absorbed and buffered. Soft start, load start, and overload protection can be achieved without damaging the motor or load. It is easy to install and maintenance-free.
Advantages of magnetic motor coupling
- Reduce energy consumption by 25% to 66%.
- This product has a small maintenance workload, small product maintenance, and low maintenance cost.
- The installation centering error can be controlled within 5mm, which greatly simplifies the installation and debugging process.
- It has an overload protection function, which improves the reliability of the entire system and prevents the system from being damaged due to overload.
- When multiple machines are driven, it can reduce impact vibration, coordinate load distribution, and improve the starting ability of the motor.
- The speed regulation type can realize continuous adjustment of the output speed without changing the motor speed.
- Long service life, with a design life of 30 years, and the service life of system components can be further extended.
- It can realize long-distance and automatic control, and has high process control accuracy.
- It has a simple structure and is suitable for harsh environments. It is free of pollutants, harmonics, small in size, and easy to install.
- When the active magnetic pole moves at a speed V, the components of the forces P1 and P2 generated by the active magnetic pole and the driven magnetic pole in the direction of movement are superimposed, while the components perpendicular to the direction of movement are opposite and basically offset.
Economic analysis of magnetic motor coupling
- Initial investment: The initial investment of magnetic coupling is currently roughly the same as that of frequency converter.
- Maintenance cost: Since magnetic coupling is basically maintenance-free, the maintenance cost is almost zero.
- Economic losses caused by failures: Although the inverter is also an energy-saving device, it cannot really let users see the benefits of energy saving because its average failure-free time is too short, occurring once a year on average. The load reduction and increased fuel consumption caused by the failure will not be worth the loss.
To sum up, whether considering single performance or overall performance, individual energy efficiency or overall system energy efficiency, Magnetic motor couplings are the best choice. The advantages of Magnetic motor couplings become even more pronounced when all costs over the life of the device are considered. The magnetic motor coupling operates reliably on the coal mine crusher.
