Deep in the earth, 25 ~ 50 kilometers from the ground, the temperature is 200℃ ~1000℃; If the depth reaches 6370 kilometers from the ground, that is, the depth of the earth's center, the temperature can be as high as 4500℃.
It is estimated that if only underground heat energy is consumed according to the current speed of electricity consumption in the world, even if it is used for 4 1 10,000 years, the temperature of the earth will only drop by 1℃. This shows that there is so much heat energy on the earth. The temperature distribution of the earth is very regular. Generally, within the range of more than ten kilometers in the uppermost part of the earth's crust, the formation temperature will increase by about 65438 0℃ for every 30 meters increase in formation depth. Between underground15 ~ 25km, the temperature rises1.5℃ with the increase of depth100m; In the area below 25 kilometers, the temperature will only rise by 0.8℃ for every increase in depth of 100 meters; Later, when we go deeper to a certain depth, the temperature will remain the same.
Why is there so much heat energy stored in the depths of the earth? Where did they come from? For this problem, it is still in the exploration stage. However, most scholars believe that this is due to the natural transformation of radioactive materials in the earth. In the process of nuclear reaction, a large amount of heat energy was released, which gradually accumulated in closed and isolated strata over time, forming the present geothermal energy. It is worth pointing out that geothermal resources are a kind of renewable energy, which can be supplemented and regenerated as long as it does not exceed the development intensity of geothermal resources.
Usually, people divide geothermal resources into four categories:
(1) hydrothermal resources. This is a large number of geothermal resources stored in underground aquifers, including geothermal steam and geothermal water. Geothermal steam is easy to develop and utilize, but its reserves are very small, accounting for only 0.5% of the total proven geothermal resources. Geothermal water reserves are large, accounting for about 10% of the proven geothermal resources, and its temperature ranges from near room temperature to as high as 390℃.
(2) Ground pressure resources. This is high salinity hot water containing methane in sedimentary rocks deep in the stratum. Because the thermal energy is sealed by the upper rock cover, the pressure of hot water exceeds the static pressure of water, the temperature is about 150℃~260℃, and its reserves are about 20% of the total proven geothermal resources.
(3) dry and hot rocks. This is a hot rock stratum with the deep temperature of 150℃~650℃, and its stored heat energy accounts for about 30% of the total proven geothermal resources.
④ Lava. This is a completely melted hot lava with the deepest burial place, and the temperature is as high as 650℃~ 1200℃. Lava stores more heat energy than other kinds, accounting for about 40% of the total proven geothermal resources.
Up to now, the utilization of geothermal resources is mainly the development of hydrothermal resources. In recent years, some countries have begun to carry out research and experiments on the development of dry-hot rocks, and excavating artificial hot springs is one of the specific applications of dry-hot rocks. However, the utilization of ground pressure resources and lava resources is still in the exploration stage.
China is an early country in the world to develop and utilize geothermal resources, and it is also developing rapidly. Beijing is one of the six capitals with good geothermal development and utilization in the world (the other five are Paris in France, Budapest in Hungary, Sofia in Bulgaria, Reykjavik in Iceland and Addis Ababa in Ethiopia).
The geothermal water temperature in Beijing is mostly between 25℃ and 70℃. Because geothermal water contains special mineral components such as fluorine, hydrogen, cadmium and soluble silicon dioxide, it can be made into drinking mineral water after treatment. In some areas, geothermal water also contains hydrogen sulfide, so it is very suitable for bath therapy and physical therapy.
At present, geothermal resources in Beijing have been widely used. For example, the area used for heating reaches more than 320,000 square meters, which can save more than 3 million yuan in boiler room construction investment, save 6.5438+0.8 million tons of coal every year, and reduce 7.6 tons of dust pollution caused by coal-fired heating every year. Geothermal hot springs have more than 50 baths, with more than 60,000 baths every day; African crucian carp raised in geothermal water grows fast and tastes delicious. Some printing and dyeing factories in Beijing also use geothermal water for printing and desizing, which can save thousands of tons of coal every year.
In addition to Beijing, there are geothermal resources in many areas of China, and there are more than 3,500 natural geothermal springs with temperatures below 100℃. In Tibet, Yunnan and Taiwan Province provinces, there are many geothermal fields with high temperature exceeding 150℃. A hot spring in Pingtung County, Taiwan, temperature140℃; The largest geothermal power station in China was built in Yangbajing, Tibet. The average geothermal wellhead temperature of this power station is 140℃, and the installed power generation capacity is 10000 kW. A bigger geothermal power station will be built here in the future.
From the distribution of hot springs, China's geothermal resources are mainly concentrated in the southeast coastal provinces and Tibet, Yunnan, western Sichuan and other places. There are two tropical zones with a large number of hot springs, high temperature and shallow burial, which are called coastal Pacific tropical zone and Tibet-Yunnan tropical zone respectively. There are more than 600 hot springs in the pre-tropical area, accounting for about 1/3 of the total number of hot springs in China, of which dozens of hot springs exceed 90℃, and some even exceed 100℃. The latter tropical area is the most active area of hydrothermal activity in Chinese mainland, with a large number of fountains and steam springs. There are more than 700 hot springs in this area, of which nearly 100 is a hydrothermal active area above the local boiling point, which is a high temperature water vapor distribution zone. In addition, some basins in eastern China are rich in underground hot water, covering a wide range, starting from Songliao Plain and North China Plain in the north and Jianghan Plain and Beibu Gulf in the south. For example, there is a geothermal zone with a total area of nearly 700 square kilometers near the urban area and suburbs of Tianjin, in which there are more than 380 hot water wells with a depth of more than 500 meters, the water temperature is above 30℃, the highest water temperature is 94℃, the annual total output is nearly 50 million tons, and the available heat is equivalent to more than 300,000 tons of standard coal.
Geothermal energy is also widely distributed all over the world. Wanyan Valley in Alaska, USA, is a world-famous geothermal concentration area. There are tens of thousands of natural steam hot water spray holes within 24 square kilometers. The minimum temperature of hot water and steam is 97℃, and the high temperature steam reaches 645℃. 23 million liters of hot water and steam are ejected every second, and the heat energy brought to the ground from the interior of the earth is equivalent to 6 million tons of standard coal every year. There are nearly 70 geothermal fields and 1000 hot springs in New Zealand. There are many kinds of hot springs, including high-temperature hot springs with temperatures ranging from 200℃ to 300℃. Intermittent geysers; And boiling mud. The Mediterranean-Himalayan tropics across Eurasia, from Italy and Hungary on the northern shore of the Mediterranean, pass through Turkey, Russian Caucasus, Iran, Pakistan and China, northern India, Tibet, Myanmar and Malaysia, and finally connect with the tropical Pacific Rim in Indonesia.
It has been calculated that if the energy released by volcanic eruptions and earthquakes around the world and the energy stored in hot rocks are excluded, the total heat energy stored by underground hot water and geothermal steam alone is 65.438+0.7 billion times of all coal reserves on the earth. The geothermal energy currently available for mining within 3 kilometers underground is equivalent to all the heat released when 2900 billion tons of coal are burned. It can be seen. The development and utilization of geothermal energy has broad prospects.
For the development and utilization of geothermal energy, it has been nearly 100 years since Italy built the world's first geothermal power station in 1904. However, it was not until the last two or three decades that the development and utilization of geothermal energy gradually attracted universal attention and attention from all countries in the world.
According to statistics, more than 7,500 geothermal springs and wells have been discovered or drilled in more than 20 countries and regions in the world, which has continuously expanded the utilization of geothermal energy. At present, the utilization of geothermal energy is mainly in heating, power generation, breeding, greenhouse cultivation, bathing and so on. An American university has three geothermal wells with a depth of 600 meters and a water temperature of 89℃, which can heat a teaching building with a total area of more than 46,000 square meters, saving heating costs of 250,000 US dollars every year. Although Iceland is located in the cold zone, it is rich in geothermal resources. At present, more than 70% of the population in China has used geothermal heating.
Using geothermal energy to generate electricity has many unique advantages: the investment in building power stations is less, usually lower than that of hydropower stations; The cost of power generation is lower than that of hydropower, thermal power and nuclear power plants; The utilization time of power generation equipment is long; Geothermal energy is clean and does not pollute the environment; Steam and hot water used for power generation can also be used for heating or other aspects.
At present, the United States, Japan, Russia, Italy, Iceland and many other countries have built thermal power stations of different scales, totaling about 150, with a total installed capacity of 3.2 million kilowatts.
The principle of geothermal power generation is similar to that of general thermal power generation, that is, using geothermal energy to generate steam to promote steam turbine generator set to generate electricity. At present, about 3/4 geothermal power stations in the world use high-temperature steam as energy to generate electricity. This kind of power station leads geothermal steam out of the ground, then purifies and removes all kinds of impurities contained in it, and then it can drive turbine generators to generate electricity. Geothermal power stations with high-temperature steam as energy mostly use steam-water separation to generate electricity; For power stations with underground hot water as energy source, it is common to use underground hot water as heat source to generate steam in a certain way, and then use the steam to drive the steam turbine generator set to generate electricity.
In addition, geothermal energy can also be used for heating, drying, refrigeration and cold storage, dehydration processing, seawater desalination and extraction of chemical elements in industry. In medical care, hot spring water can treat diseases such as skin and joints, and many countries have hot springs.
Because there are few natural hot springs, and they are not everywhere, in some areas where there are no natural hot springs, people use the geothermal energy of the widely distributed dry-hot rocks to artificially create underground hot springs. Artificial hot springs are dug in hot rocks of dry-hot rock type. The earliest artificial hot spring in the world was dug in the northern part of New Mexico, USA, with a depth of 3000 meters and a temperature of 200℃.
An artificial hot spring thermal power plant was built in the United States, with a power generation capacity of 50,000 kilowatts. In addition, Los Alamos National Laboratory also drilled two geothermal wells with a depth of 4,389 meters. First, water was pumped into the well and pumped out after 65,438+02 hours. At this time, the water temperature is as high as 375℃. France has successively dug six artificial hot springs, each with a depth of 6000m, and can obtain hot water at 200℃ 100t per hour.
At present, the installed capacity of geothermal power stations in the United States has reached 9.3 million kilowatts, and will increase to 310.8 million kilowatts by 2020.
Now with the development of science and technology, people begin to build artificial thermal energy storage layer around the heat source of magma, and use heat source steam to generate electricity to develop high-temperature rock mass. It is predicted that by the end of 2 1 century, the global geothermal power generation capacity will reach 1 100 million kilowatts.