Application of KERUN Inverter in Energy-Saving Retrofit of Ball Mills
-- ACD500-10 Series Ball Mill Specialized Inverter
Abstract: Based on the actual operating conditions and working principle of ball mills, this paper introduces and analyzes the practical application characteristics and energy-saving effects of KERUN inverters on ball mills.
1. Overview
For a long time, ball mills have been widely used in ceramics, floor tile, cement, and chemical plants for grinding raw materials. The power consumption of ball mills accounts for a major portion of a company's electricity usage. They typically employ outdated and complex multi-speed control, which easily leads to high speed with low material load, low grinding efficiency, high power consumption per unit time, large starting current, significant impact on equipment and the power grid, increased production, maintenance, and wear of mechanical equipment, and considerable electrical energy waste. This inevitably hinders production scale-up. The drawbacks of direct online control of ball mills are fully exposed and severely impede the rapid development of industrial enterprises. This drives the development of solutions offering smooth starting, higher grinding efficiency, and lower energy consumption-such as inverter control.
2. Main Structure
The ball mill in the cement industry mainly consists of a transmission device, cylinder device, feeding device, discharge device, and electrical control device.
3. Transmission Device
Cement ball mills operate with circulating feed, requiring substantial power consumption. Therefore, cement plant ball mills typically use one high-power motor (several hundred kilowatts) to drive a hard-geared cylindrical gear reducer, which then drives the cylinder to rotate via a pair of gears or pulleys, achieving the grinding of materials.
Industrial Principle: The ball mill is mainly composed of the feeding section, discharge section, rotary section, and transmission section (reducer, pinion gear, motor, electrical control).
Cement plants generally have a horizontally placed cylinder. The cylinder is divided into 3~4 grinding chambers by partition plates (plates drilled with many small holes-screen plates). Each grinding chamber is filled with grinding media of specific shapes and sizes. When the cylinder rotates, materials and grinding media are lifted to a certain height by the cylinder under the action of friction and centrifugal force. Then, under gravity, they fall along an approximate parabolic trajectory to impact and grind another part of the material at the bottom of the cylinder, also generating some axial movement to promote uniform grinding and mixing of the material.
4. Requirements
Based on the problems existing in the original working conditions and combined with production process requirements, the ball mill system after applying the ACD500-10 series should meet the following requirements:
(1) The retrofitted equipment must have sufficient starting torque to meet the requirement of high ball mill loading capacity. It must also ensure smooth motor operation under inverter control and maintain constant power characteristics for the motor.
(2) Utilize the variable frequency speed control system to retrofit the original ball mill drive system, enabling normal low-speed operation of the ball mill, ensuring normal process control quality, extending the service life of the ball mill and motor, and reducing maintenance.
(3) The retrofitted equipment should be capable of automatic control, manual/line frequency operation, and automatic fault switching, etc. It should also overcome the back electromotive force caused by the large inertia of the ball mill, effectively ensuring normal equipment operation.
Based on the above principles, our company's ACD500-10 series specialized ball mill inverter is selected, as the system can meet the aforementioned working condition requirements.
(1) The ACD500-10 series inverter adopts Flux Vector Control technology, achieving 150% rated torque output capability even at low speed (0.5 Hz). It features multiple control and operation modes and comprehensive protection functions.
(2) The ACD500-10 series inverter offers high frequency accuracy: digital setting ±0.01%, analog setting ±0.2%. The output frequency resolution can reach 0.01 Hz, ensuring smooth operation to meet design requirements.
(3) The overvoltage and overcurrent stall prevention functions of the ACD500-10 series inverter allow it to hold the frequency during acceleration/deceleration if overvoltage or overcurrent occurs, automatically resuming acceleration/deceleration only after the condition is cleared.
(4) Reliable torque control function: The product controls output torque through a torque limiting function, suitable for high-inertia impact loads like starting machinery and conveying machinery.
(5) Independent air duct fully enclosed design, dust-proof, gas-proof, corrosion-resistant, with strong environmental adaptability and longer service life.
5. Basic Electrical Control Device
Cement ball mills are low-speed, heavy-duty equipment with high loading capacity and large starting torque. Therefore, cement industry ball mills typically use additional devices like liquid resistance starters or soft starters for startup, causing significant impact on the power grid. Furthermore, the required torque decreases after startup during normal operation, leaving substantial room for energy saving.
6. Retrofit Solution (Case Introduction)
Based on the problems existing in the original working conditions and combined with production process requirements, the retrofitted ball mill system should meet the following requirements:
Requirements:
(1) The retrofitted equipment must have sufficient starting torque to meet the requirement of high ball mill loading capacity. It must also ensure smooth motor operation under inverter control and maintain constant power characteristics for the motor.
(2) Utilize the variable frequency speed control system to retrofit the original ball mill drive system, enabling normal low-speed operation of the ball mill, ensuring normal process control quality, extending the service life of the ball mill and motor, and reducing maintenance.
(3) The retrofitted equipment should be capable of automatic control, manual/line frequency operation, and automatic fault switching, etc. It should also overcome the back electromotive force caused by the large inertia of the ball mill, effectively ensuring normal equipment operation.
(4) Motor specifications: Power 350KW, Voltage 380V, Current 680A, Speed 740 rpm, Frequency 50Hz, Rotor Voltage 540V, Rotor Current 425A, Delta connection.
(5) On-site Test Data (Test data for a 350KW motor on-site)
| Test Item | Max Value | Average Value | Min Value | |
|---|---|---|---|---|
| Starting Current | 740 A | |||
| Running Current | Yellow: 658A Green: 623A Red: 624A |
Yellow: 589A Green: 570A Red: 560A |
||
| Mill Body Speed (rpm) | 23.5 /min | 23.5 /min | ||
| Rotor Running Current | 257 A | 154 A | ||
| Stator Winding Insulation | >500 MΩ | >500 MΩ | >500 MΩ | |
| Stator Winding Resistance | 0.4 Ω | 0.4 Ω | 0.4 Ω | |
| Grid Voltage Range | 375 V | 375 V | 374 V | |
| Ambient Temp. (Motor) | +30°C | -30°C |
7. Equipment Operation Test & Energy-Saving Benefit Calculation
Since its establishment, the company has successively implemented energy-saving retrofits for projects including Jiangxi Fengcheng Dongpeng Ceramics Factory, Qingdao Cement Plant, several ore plants and cement plants in Houma, Shanxi, Henan Ceramics Factory, and Jining Dayu Cement Plant. Application results show an average energy saving of 5% to 15%.
8. Advantages After Equipment Retrofit
The superior performance after applying the KERUN ACD500-10 series inverter:
• Using variable frequency speed control technology to retrofit the ball mill drive system meets the characteristics of low-speed operation and high starting torque, achieving continuously adjustable operating speed for the ball mill.
• No inrush current during motor starting, sufficient starting torque, and comprehensive protection functions. Ensures process control quality and saves maintenance costs.
• The retrofitted equipment is capable of automatic control, manual/line frequency operation, automatic fault switching, etc., and can overcome the back electromotive force caused by the large inertia of the ball mill, effectively ensuring normal equipment operation.
9. Conclusion:
Using inverter speed control technology to retrofit the ball mill drive system meets the characteristics of low-speed operation and high starting torque, achieving continuously adjustable operating speed for the ball mill. Energy can be saved by reducing the frequency as much as possible within the allowable speed range. Motor starting involves no inrush current, avoiding grid pollution, with complete protection functions. This ensures process control quality and can save significant electrical energy during 24-hour continuous operation, conserving energy and reducing costs.