Successful mining! Feel the temperature 4,200 meters underground

As a resource, hot dry rock has always been regarded by the scientific community as one of the future energy sources with great potential. What exactly is hot dry rock? How can we use it?

What is hot dry rock?

From space, the Earth is a blue planet. However, if you enter the Earth from the surface, you will find that it is a fireball filled with high temperatures.

The core of the Earth has a temperature similar to that of the surface of the Sun, 6000 degrees Celsius, and the decay of a large amount of radioactive substances continues to release heat. From the core to the surface, the temperature of the Earth gradually decreases, and eventually it is low enough for humans to survive.

About 3 to 10 kilometers below human feet, there are some huge rocks with a lot of heat energy inside. Scientists call it hot dry rock. From the moment it was discovered, humans have always wanted to develop and utilize it. However, it was not until 1974 that this dream was realized.

How to mine hot dry rocks?

Hot dry rocks, like hot springs, are a type of geothermal resource. However, their location and high temperatures make their mining extremely difficult. Hot dry rocks are buried 3-10 kilometers underground, with temperatures above 200 degrees Celsius and up to nearly 1,000 degrees Celsius. The high temperature and high pressure underground prevent humans from entering the interior of the earth.

At present, the deepest that humans can drill underground is only 12.2 kilometers, but it took 22 years. Ordinary oil wells for oil extraction need to be about 3 kilometers deep. Drilling below 3 kilometers underground, or even 10 kilometers, is very difficult.

How to find shallower hot dry rocks and extract their heat has become a technical challenge that scientific researchers need to overcome.

A well is drilled to the location of the hot dry rock, and water is injected under pressure, while the hot dry rock is fractured to create cracks. After passing through these cracks, the water turns into high-temperature water or steam and comes out of another well. This is the process of traditional hot dry rock mining.

my country's innovative gravity heat pipe technology is to insert a heat pipe deep into the dry hot rock layer. The wall of the heat pipe is a material with extremely fast heat conduction speed. The heat pipe is filled with ammonia water with a very low boiling point. After contacting the hot well wall, the ammonia water quickly turns into ammonia vapor and returns to the ground under the action of gravity. Gravity heat pipe technology only requires drilling a well, without fracturing rocks or consuming other energy. It is a safer and more energy-saving technology.

After more than a decade of hard work, Chinese researchers have made new innovations in hot dry rock mining. In January 2022, the 4,200-meter gravity heat pipe heat extraction test device developed by China was successfully put into trial operation, realizing the long-distance transportation of hot dry rock heat energy for the first time in China, and also laying a technical foundation for the mining and utilization of hot dry rocks in China.

Hot dry rock prospects

Over the past 200 years, fossil fuels such as oil and coal have driven the rapid development of human society. However, as time goes by, the reserves of non-renewable fossil fuels are running out. At the same time, the pollution caused by the burning of fossil fuels is becoming increasingly serious.

Therefore, in recent years, the development and utilization of green new energy has become a goal of the whole world. Hot dry rock has a large storage capacity and is clean, making it a highly anticipated new energy source.

According to the assessment of the China Geological Survey, the reserves of hot dry rocks within 3 to 10 kilometers in my country are equivalent to 856 trillion tons of standard coal. In 2021, my country's total annual energy consumption is 5.24 billion tons of standard coal. If hot dry rocks can be mined on a large scale, it will be an important supplement to my country's energy.

Over the past decade, Chinese scientists have conducted many innovative research and developments in the mining of hot dry rocks. Currently, the drilling depth of hot dry rocks in China has exceeded 4 kilometers, and the exploration is moving towards deeper levels.

Source: CCTV Science and Education

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