By Staff Reporters

In China, thin coal seams account for 20 percent of the total reserves, but their output only makes up about 10 percent of the total coal production, due to the extreme mining difficulties. However, the industrial fine powder contained within the seams — coking coal, known as the "rare earth" of coal, is an indispensable and important raw material for steel enterprises.

To conquer the challenge of mining coal seams with a thickness of less than 1.3 meters, an R&D team led by Heilongjiang University of Science and Technology (USTH) has developed an intelligent mining system of extremely thin coal seams at a depth of over a kilometer underground.

This has led to the remote control and real-time monitoring of the mining of extremely thin coal seams.

Smaller machine

In thin coal seam mining, the major challenge is to integrate the small size and high power of the coal shearer machine, according to USTH Professor Wu Weidong.

Usually, the thinner the coal seam, the harder it is. To mine a coal seam over two meters thick usually requires a machine powered by 200 kilowatts. However, an installed power of 500 to 900 kilowatts is required for mining extremely thin coal seams.

The key is innovation in building the machine  material and structure. By using high-performance material, the rigidity, wear resistance, and load-bearing capacity increase. Through structural reconstruction, the equipment's lifespan is prolonged, and the overall height is also reduced.

To further reduce the size of the machine's motor, the team decided to increase the voltage from 1,140 volts to 3,300 volts, which meant that all electrical components had to be reconfigured. It took four months to adjust and testify parameters, finally reducing the height of the equipment from 630 mm to 588 mm, and even leaving 20 mm of extra space for the machine to pass through.

In October 2022, the sample machine was sent into the mine for testing, nimbly shuttling through the extremely thin coal seam. After its application, the mining efficiency of extremely thin coal seams was raised from 15,000 to 20,000 tonnes per month to 40,000 to 50,000 tonnes, while the number of workers has been reduced from around 20 to just five or six.

5G remote control

In extremely thin coal seams, the narrow space and strong electromagnetic interference make it impossible to deploy conventional 5G equipment.   

"Just like putting a base station in a matchbox, it needs to be both compact and have a full signal," said Yang Qingjiang, professor at USTH, who is in charge of communication technology.

After numerous failed attempts, the team came to a deadlock. USTH Professor Liu Fugang suggested using leaky-wave antennas, which can reduce the volume without affecting the signal.

The team integrated multiple previously used devices into a single unit, significantly reducing its volume and weight. They replaced traditional antennas with leaky-wave antennas and laid them along the gaps of the brackets to achieve uniform signal coverage in the operation area.

After three months of installation and commissioning, data showed that key technical indicators such as the uplink and downlink rates and latency of 5G signals in extremely thin coal seam working faces all meet the national standards. This is the first successful deployment of 5G in extremely thin coal seam working faces in China.

Real-time scenes and equipment status can all be transmitted to the surface without any delay, laying a solid foundation for remote intelligent control, said Yang.

Precise mining

The occurrence of extremely thin coal seams (referring to their existing state and distribution characteristics in the stratum) is unstable, so a slight mistake can lead to the shearer cutting into the rock, which not only easily damages the equipment but also may cause accidents.

Therefore, building a high-precision geological model is the prerequisite for intelligent mining, said USTH Professor Liu Yongli, who is in charge of geological modeling for this project.

Within a space of 0.7 to one meter high, technicians could only crawl forward. Every time they went down the mine, they had to carry over ten pounds of detection instruments, self-rescuers and miners' lamps.

During the crawling exploration, the team accumulated a vast amount of geological data and integrated drilling and geophysical exploration data to build a three-dimensional geological model of the extremely thin coal seam, with an accuracy of 0.1 meters. It was akin to giving the coal seam a "CT scan," which made all details clearly visible.

With the 3D built precise model, the coal shearer can plan the path in advance, automatically adjust the height and reduce risks, realizing precise mining in the thin coal seams.

To date, this technology has been promoted in Heilongjiang, Yunnan, Shaanxi and other provinces. The mining efficiency of extremely thin coal seams has increased by 200 percent, with an additional production capacity of over 1.5 million tonnes, and an additional revenue of over 600 million RMB.