Application of high-pressure VFD (Variable-frequency Drive) in the transformation of tailings conveying system

0 Preface

With the rapid development of electronic industry science and technology, the application of VFD (Variable-frequency Drive) technology has entered a booming era. The application of low-voltage frequency conversion technology in China has developed from the early 1980s when several agency companies sold foreign products to the upper At the end of the 1990s, several companies possessed the research and development level and manufacturing capacity of low-voltage frequency conversion technology. While low-voltage frequency conversion technology has been widely used, the research and application of high-voltage frequency conversion technology has also begun to take shape. The "Direct High Technology" developed by Chengdu Sunwoele Company and the high-voltage VFD (Variable-frequency Drive) manufactured by Chengdu Sunwoele have brought China's domestic high-voltage frequency conversion technology to the forefront of the international level. Since 1995, Jinduicheng Molybdenum Industry Co., Ltd.’s Thirty Mudi Concentrator has conducted full market research and visits on the application of high-voltage frequency conversion technology in the primary pumping station for tailings transportation. , and expensive, forcing the project to shelve. After entering the 21st century, industrial electricity consumption has increased by leaps and bounds, and electricity prices have been rising all the way. It is imperative to apply high-voltage VFD (Variable-frequency Drive) technology to save electricity and reduce consumption in primary pumping stations in tailings transportation.

1 The change of tailings conveying process causes the reduction of electric energy efficiency

Tailings transportation is the very end of the production process of a concentrator. In the total cost of tailings transportation, electricity consumption occupies a relatively large share. The tailings conveying process of the concentrator described in this article requires that the conveying pump be equipped with a high-voltage motor in the primary pumping station of the tailings conveying system. The rated parameters of the high voltage motor are: P=3lOkW, U=6kV,=34A. Due to limited production conditions, the operating rate of the primary pumping station is almost 100%, the input current of the motor is generally about 22A when the motor is running, and the monthly power consumption is 16×104kw. more than h. In recent years, due to the change of the production process of the concentrator, there have been two ways for the tailings transportation process. One is the original 50m upward transportation, through the 300m pipeline to the secondary pumping station; the second is the newly established downward 5m output through the 1200m pipeline to the tailings collection station. According to the production setting requirements of the concentrator, the tailings downward conveying rate is ≥85%, and the tailings upward conveying rate is ≤15%. In this production system, there is a waste of electric energy in the tailings transportation of the primary pumping station. Although the monthly power consumption of the primary pumping station has dropped to 13×104kW h, the power efficiency has dropped significantly, that is, H2×W/P2 is much smaller than H×W/P1, where H represents the tailings conveying height, H2= -5m, H1=50m; P represents the output power of the motor, P2=200 kW, P1=230 kW; W represents the amount of tailings conveyed, which is basically a constant value. Such unreasonable power consumption makes it inevitable to transform the primary pumping station. However, through the demonstration, due to the limitation of funding conditions and geographical location, it is relatively difficult to completely transform the primary pumping station, and the investment cost is high. In the end, the only way to reduce the waste of electric energy in the primary pumping station is to reduce the power consumption of the motor as much as possible while ensuring the transportation of tailings.

2 Selecting high-voltage frequency conversion technology is the best transformation plan for the primary pumping station

In order to find the best solution for saving electric energy, the main equipment of the primary pumping station was modified and tested. Without changing the motor speed, replace the 3lOkW motor with a 210 kW motor. Under the test conditions, the motor output power of the primary pump operation was reduced to 135 kW, and the test was successful, which laid a theoretical foundation for the electrical transformation of the primary pump station. However, during the test, the start-up process of the primary pumping station became cumbersome, and valve control was needed to gradually realize the complete transportation of tailings. The start-up process took a long time and could not meet the requirements of the production process of the concentrator. The main reason for this phenomenon is that after the rated capacity of the motor is reduced, the starting torque of the motor also decreases, which cannot guarantee that the delivery pump can start as quickly as before.

If high-voltage frequency conversion technology is used to control the original motor, the maximum power efficiency can be achieved, and the start-up process can be simplified and the start-up time can be shortened. According to the relational expression of the relevant parameters of the delivery pump and the speed formula of the electric motor

In the formula: H represents the head of the pump;

qv represents the flow rate of the pump;

p represents the power of the motor;

n represents the synchronous speed of the motor.

The relationship between the power of the motor and the motor when the motor is running at different frequencies can be obtained

Equation (5) shows that when the motor runs at a lower frequency, its power consumption will be greatly reduced. However, as the input power frequency of the motor decreases, its speed also decreases. Can the process flow of the original system be guaranteed after the speed of the conveying pump decreases, that is to say, can it be ensured that the tailings can be transported smoothly under the condition of constant flow rate. Obtained from the above experiment that the output power of the electric motor falls in the range of 40-80kW when the system is stable. According to the calculation and comparison of formula (5), the change of input power frequency should be determined within the range of 30-45Hz. According to the calculation and comparison of formula (3), the synchronous speed of the motor should be determined within the range of 600-900 r/min. In order to ensure the application investment and income of high-pressure VFD (Variable-frequency Drive) technology in the primary pumping station