1. Introduction
With the sustained and rapid development of my country's economy, the steel industry has also grown rapidly. The demand for iron ore from domestic steel companies has increased dramatically, and domestic mining production can no longer meet the demand, forcing reliance on high-quality iron ore resources from abroad. Statistics show that my country's iron ore imports have increased year by year since 1985. In 2013, the Beijing International Mining Rights Exchange (BIME) released its annual research report on the Chinese iron ore spot market, showing that China imported 819 million tons of iron ore in 2013, setting a new historical record.
2. Background and Process Introduction of the Modification
Alashan League Desheng Metallurgical Furnace Materials Co., Ltd. is a wholly-owned subsidiary of Inner Mongolia Desheng Industrial Group. Located in the Huhehada mining area of Alashan Right Banner, Inner Mongolia, the company started construction in early May 2013, with a planned investment of 1.35 billion yuan to build a mining and beneficiation plant to improve the company's ore self-sufficiency rate and alleviate the pressure of imported iron ore. The project is expected to be completed and put into operation by the end of October. The group has now formed two industrial chains: raw coal mining, beneficiation, coking coal chemical industry, iron ore mining, beneficiation, smelting, metal products and waste heat power generation from coal gas, and slag cement. With the high attention of party committees and governments at all levels and relevant departments, and with the support of Dali, the group is achieving the goal of developing a circular economy.
Research and exploration indicate that my country's iron ore deposits are diverse in type, with complex storage conditions and varied ore types. They contain high levels of harmful components such as sulfur, phosphorus, and silica, and multi-component symbiotic iron ores constitute a significant proportion. Furthermore, the useful components are finely distributed, resulting in challenging mining and beneficiation processes, low efficiency, and poor product quality. To efficiently develop and utilize limited resources, Desheng Metallurgical Furnace Materials Co., Ltd. has boldly adopted new technologies and innovated and optimized its beneficiation processes, using technological means to increase concentrate production.
The mineral processing flow chart of the plant is shown below.
Most ore processing plants in my country typically employ a three-stage crushing process—coarse crushing, medium crushing, and fine crushing—to crush iron ore. However, in order to increase production capacity and efficiency, Desheng Metallurgical Materials Co., Ltd. has added a roller mill process after the three-stage crushing operation. After the roller mill, the ore enters the air classifier workshop for air classification.
The air classification workshop has two main units. One is a multi-stage series dispersing air classifier, which is a new type of classification equipment that integrates material cake dispersing and particle classification. Its dispersing method adopts the principle of centrifugal impact crushing. The material after being squeezed by the roller mill is in the form of a relatively dense cake, which is continuously and evenly fed in through symmetrically arranged feed inlets and falls onto the dispersing disc with hammer-shaped convex ribs. The main shaft drives the dispersing disc to rotate at high speed, so that the material cake falling on the dispersing disc is accelerated and detached from the dispersing disc under the action of the hammer-shaped convex parts of the liner. The material cake is thrown out at high speed along the tangential direction of the dispersing disc and then impacts the impact liner and is crushed.
Another system fan has a flow rate of 2,000,000 m³/h, a total pressure of 5900 Pa, and a power of 5000 kW. Our Senlan high-voltage frequency converter is used to upgrade this system fan; the frequency converter model is SBH-100-5600. After being broken down and pulverized, the material is guided by the baffle cone and enters the wind-driven sorting zone, distributed along the impeller, through the annular channel surrounding the baffle cone. Due to their high inertia, coarse particles in the material classification experience minimal change in motion during settling in the wind-driven sorting zone and fall into the inner cone, where they are collected and discharged from the coarse powder discharge port. They then return to the weighing bin above the roller mill along with the fresh material from the batching system. Fine powder, due to its low inertia, experiences greater change in motion during settling in the wind-driven sorting zone and falls between the inner and outer cones, where it is collected.
After passing through the air separation workshop, the ore is evenly separated into coarse, medium, and fine forms. This demonstrates the importance of the air separation system's blowers in the entire mineral processing procedure. The ore then proceeds to the magnetic separation workshop and the wet separation workshop, ultimately producing a high-grade concentrate.
3. Retrofitting Scheme for Senlan High Voltage Frequency Converter
Considering the importance of the equipment, and after repeated demonstrations, the user ultimately adopted Senlan's third-generation SBH series high-voltage frequency converter to retrofit the system's fans. The specific retrofit plan is described below. The system's primary schematic diagram is shown below:
Considering the limited grid capacity and high motor power at the user's site, a charging resistor is added to the main circuit to avoid inrush current during power transmission. This is used to reduce inrush current and control bus voltage drop. The main circuit uses a vacuum contactor and automatically switches on and off after charging is complete. A field control box and a DCS system are used to control and monitor the high-voltage frequency converter.
Senlan SBH-100-5600 high-voltage frequency converter undergoes factory testing.
Senlan SBH-100-5600 high-voltage frequency converter at the user's site
After a year of use, users unanimously agree that Senlan high-voltage frequency converters have the following advantages:
1. The frequency conversion system operates stably and reliably, and has a significant energy-saving effect, greatly reducing power consumption by about 30%.
2. It enables soft starting of the motor, extending the service life of the machinery and reducing maintenance workload and costs.
3. Wide speed range, high precision, and air volume can be adjusted according to process requirements.
4. Senlan high-voltage frequency converters have multiple protection functions such as overcurrent, short circuit, overvoltage, undervoltage, phase loss, and temperature rise protection, which are very comprehensive and better protect the motor.
5. Improve operating conditions and reduce the labor intensity of workers.
