Coal preparation aims to remove impurities from raw coal and improve the quality of coal to meet the coal demand in different industrial fields.

I. Raw coal preparation

1. Receiving coal

The coal preparation process starts with the receiving coal link. When the raw coal is gathered at the coal preparation plant by means of transportation such as trains and cars, it must be accurately unloaded into the receiving coal pit first. During train transportation, the dumper works in conjunction with the receiving coal pit to efficiently dump the raw coal of the entire train into the pit at one time; the unloading of coal by car is often done through an automatic unloading platform, assisted by manual cleaning of scattered coal blocks to ensure the complete collection of raw coal. The capacity design of the receiving coal pit is quite particular. It must be able to accommodate the amount of coal during peak hours and avoid coal flow overflow, and it must also consider the processing rhythm of subsequent equipment, play a buffering role, stabilize the coal supply rate, and prevent subsequent processes from being stuck due to uneven raw coal supply.

2. Screening

After receiving the coal, the raw coal is sent to the vibrating screen for screening. The mesh size of the vibrating screen is varied, and the common sizes are 50mm, 25mm, 15mm, 10mm, etc. After the particle size is screened to meet the requirements of the sorting equipment, it can flow directly into the subsequent process, reducing unnecessary crushing steps and reducing energy consumption.

The screening efficiency depends on the amplitude, frequency, screen material and inclination angle of the vibrating screen. Accurate control can significantly improve the overall screening effect.

3. Crushing

The large-size raw coal on the screen enters the crusher. The jaw crusher relies on the extrusion movement of the two jaw plates to bite the large pieces of coal like a huge "tiger's mouth"; the hammer crusher relies on the high-speed rotating hammer head to violently impact the coal blocks, causing them to break into smaller particles. During the crushing process, the crushing ratio must be strictly controlled to avoid excessive crushing to generate too much fine coal powder, which will increase the difficulty of subsequent coal slurry water treatment. At the same time, the adaptability of the size of the crusher's inlet and outlet is very critical. It is necessary to accurately match the particle size of the previous screening material and the subsequent sorting requirements to maintain a uniform and stable material particle size.

II. Sorting process

MINGDER X-ray dry coal separation is a modern coal separation method based on X-ray imaging technology and automatic control. It is mainly used to achieve efficient separation of raw coal under water-free conditions (removing gangue and improving the quality of clean coal). The following are its core points:

1. Technical principle

- Density difference identification: Utilize the difference in attenuation when X-rays penetrate coal and gangue (the density of coal and gangue usually differs by 0.2-0.5 g/cm³), capture images through detectors and generate gray value data.

- Real-time analysis: Combined with AI image recognition algorithm, automatically determine the boundary between coal blocks and gangue, and control actuators (such as pneumatic nozzles) for sorting.

- Non-contact separation: No physical contact with coal blocks is required, reducing equipment wear and energy consumption.

2. Core advantages

- Environmental protection and water saving: Completely replace the water resource consumption of traditional wet coal separation and reduce wastewater discharge (suitable for water-scarce areas).

- High-precision sorting: The sorting efficiency of low-density gangue (such as pyrite and shale) can reach more than 90%, and the ash content of clean coal can be reduced by 2-3 percentage points.

- Flexible and adaptable: It can process raw coal with a particle size of -50mm to +50mm, and is compatible with different types of coal (thermal coal, coking coal, etc.).

- Low maintenance cost: water-free medium, equipment corrosion problems are significantly reduced.

3. Typical application scenarios

- Coal mine raw coal pre-selection: directly sort gangue at the mining end to reduce subsequent transportation and washing costs.

- Lignite quality improvement: improve the calorific value of lignite by removing moisture and impurities.

- Renewable resource recovery: recover metal minerals (such as rare earth elements) from coal gangue.

4. Development trend

- Intelligent upgrade: combine deep learning (such as Yolov series models) to optimize gangue identification accuracy.

- Compact design: develop modular small equipment to meet the needs of small and medium-sized coal mines.

- Multimodal fusion: Combined with infrared, laser and other technologies, it improves the ability to sort complex minerals.

- Policy-driven: Global investment in low-carbon mining technologies has increased (such as the EU's "Green New Deal").

5. Actual Cases

- Inner Mongolia piloted the application of X-ray dry coal preparation system, with an annual processing capacity of 3 million tons per production line.

- Australia successfully sorted coal gangue in copper mine tailings, with a recovery rate of 92%.