The main sources of thermal energy of the earth. Geothermal energy and methods of its production

Doctor of technical sciences ON THE. I swear, professor,
academician Russian Academy Technological Sciences, Moscow

AT recent decades in the world is considered the direction of more effective use energy of the deep heat of the Earth with the aim of partial replacement of natural gas, oil, coal. This will become possible not only in areas with high geothermal parameters, but also in any areas. the globe when drilling injection and production wells and creating circulation systems between them.

The interest in alternative energy sources that has grown in recent decades in the world is caused by the depletion of hydrocarbon fuel reserves and the need to solve a number of problems. environmental issues. Objective factors (reserves of fossil fuels and uranium, as well as changes in the environment caused by traditional fire and nuclear energy) allow us to assert that the transition to new methods and forms of energy production is inevitable.

The world economy is currently heading towards the transition to a rational combination of traditional and new energy sources. The heat of the Earth occupies one of the first places among them.

Geothermal energy resources are divided into hydrogeological and petrogeothermal. The first of them are represented by heat carriers (comprising only 1% of the total geothermal energy resources) - groundwater, steam and steam-water mixtures. The latter are geothermal energy contained in incandescent rocks Oh.

The fountain technology (self-discharge) used in our country and abroad for the extraction of natural steam and geo thermal waters simple but inefficient. With a low flow rate of self-flowing wells, their heat production can recoup the cost of drilling only at a shallow depth of geothermal reservoirs with high temperatures in areas of thermal anomalies. The service life of such wells in many countries does not even reach 10 years.

At the same time, experience confirms that in the presence of shallow collectors of natural steam, the construction of a Geothermal power plant is the most profitable option for using geothermal energy. The operation of such GeoTPPs has shown their competitiveness in comparison with other types of power plants. Therefore, the use of reserves of geothermal waters and steam hydrotherms in our country on the Kamchatka Peninsula and on the islands of the Kuril chain, in the regions of the North Caucasus, and also possibly in other areas, is expedient and timely. But steam deposits are a rarity, its known and predicted reserves are small. Much more common deposits of heat and power water are not always located close enough to the consumer - the heat supply object. This excludes the possibility of large scales of their effective use.

Often in difficult problem outgrow the issues of combating salinity. The use of geothermal, as a rule, mineralized sources as a heat carrier leads to overgrowth of borehole zones with iron oxide, calcium carbonate and silicate formations. In addition, the problems of erosion-corrosion and scaling adversely affect the operation of the equipment. The problem, also, is the discharge of mineralized and wastewater containing toxic impurities. Therefore, the simplest fountain technology cannot serve as the basis for the widespread development of geothermal resources.

By preliminary estimates within the territory of Russian Federation predicted reserves of thermal waters with a temperature of 40-250 °C, salinity of 35-200 g/l and a depth of up to 3000 m are 21-22 million m3/day, which is equivalent to burning 30-40 million tons of equivalent fuel. in year.

The predicted reserves of the steam-air mixture with a temperature of 150-250 °C in the Kamchatka Peninsula and the Kuril Islands are 500 thousand m3/day. and reserves of thermal waters with a temperature of 40-100 ° C - 150 thousand m3 / day.

The reserves of thermal waters with a flow rate of about 8 million m3/day, with a salinity of up to 10 g/l and a temperature above 50 °C are considered top priority for development.

Of much greater importance for the energy of the future is the extraction of thermal energy, practically inexhaustible petrogeothermal resources. This geothermal energy, enclosed in solid hot rocks, is 99% of the total resources of underground thermal energy. At a depth of up to 4-6 km, massifs with a temperature of 300-400 °C can be found only near the intermediate chambers of some volcanoes, but hot rocks with a temperature of 100-150 °C are distributed almost everywhere at these depths, and with a temperature of 180-200 °C in a fairly significant part territory of Russia.

For billions of years, nuclear, gravitational and other processes inside the Earth have generated and continue to generate thermal energy. Some of it is radiated into outer space, and heat is accumulated in the depths, i.e. heat content of solid, liquid and gaseous phases terrestrial matter and is called geothermal energy.

The continuous generation of intra-terrestrial heat compensates for it external losses, serves as a source of accumulation of geothermal energy and determines the renewable part of its resources. The total heat removal of the subsoil to earth's surface three times the current capacity of power plants in the world and is estimated at 30 TW.

However, it is clear that renewability matters only for limited natural resources, a overall potential geothermal energy is practically inexhaustible, since it should be defined as total heat available to the earth.

It is no coincidence that in recent decades, the world has been considering the direction of more efficient use of the energy of the deep heat of the Earth in order to partially replace natural gas, oil, and coal. This will become possible not only in areas with high geothermal parameters, but also in any area of the globe when drilling injection and production wells and creating circulation systems between them.

Of course, with low thermal conductivity of rocks, for the effective operation of circulation systems, it is necessary to have or create a sufficiently developed heat exchange surface in the heat extraction zone. Such a surface is often found in porous formations and zones of natural fracture resistance, which are often found at the above depths, the permeability of which makes it possible to organize forced filtration of the coolant with efficient extraction of rock energy, as well as the artificial creation of an extensive heat exchange surface in low-permeable porous massifs by hydraulic fracturing (see figure).

At present, hydraulic fracturing is used in oil and gas industry as a way to increase reservoir permeability to enhance oil recovery in the development of oil fields. Modern technology makes it possible to create a narrow but long crack, or a short but wide one. Examples of hydraulic fractures with fractures up to 2-3 km long are known.

The domestic idea of extracting the main geothermal resources contained in solid rocks was expressed as early as 1914 by K.E. Obruchev.

In 1963, the first GCC was created in Paris to extract heat from porous formation rocks for heating and air conditioning in the premises of the Broadcasting Chaos complex. In 1985, 64 GCCs were already operating in France with a total thermal capacity of 450 MW, with an annual saving of approximately 150,000 tons of oil. In the same year, the first such GCC was created in the USSR in the Khankala valley near the city of Grozny.

In 1977, according to the project of the Los Alamos National Laboratory of the USA, tests of an experimental GCC with hydraulic fracturing of an almost impermeable massif began at the Fenton Hill site in the state of New Mexico. Cold fresh water injected through the well (injection) was heated due to heat exchange with a rock mass (185 OC) in a vertical fracture with an area of 8000 m2, formed by hydraulic fracturing at a depth of 2.7 km. In another well (production), also crossing this crack, superheated water came to the surface in the form of a steam jet. When circulating in a closed circuit under pressure, the temperature of superheated water on the surface reached 160-180 °C, and the thermal power of the system - 4-5 MW. Coolant leaks into the surrounding massif amounted to about 1% of the total flow. The concentration of mechanical and chemical impurities (up to 0.2 g/l) corresponded to the conditions of fresh water drinking water. The hydraulic fracture did not require fixing and was kept open by the hydrostatic pressure of the fluid. The free convection developing in it ensured effective participation in the heat exchange of almost the entire surface of the outcrop of the hot rock mass.

The extraction of underground thermal energy from hot impermeable rocks, based on the methods of inclined drilling and hydraulic fracturing that have been mastered and practiced in the oil and gas industry for a long time, did not cause seismic activity, nor any other harmful effects on the environment.

In 1983, British scientists repeated the American experience by creating an experimental GCC with hydraulic fracturing of granites in Carnwell. Similar works were held in Germany, Sweden. More than 224 geothermal heating projects have been implemented in the USA. It is assumed, however, that geothermal resources can provide the bulk of the US's future non-electric thermal energy needs. In Japan, the capacity of GeoTPP in 2000 reached approximately 50 GW.

Currently, research and exploration of geothermal resources is carried out in 65 countries. In the world, based on geothermal energy, stations with a total capacity of about 10 GW have been created. The United Nations is actively supporting the development of geothermal energy.

The experience accumulated in many countries of the world in the use of geothermal coolants shows that in favorable conditions they turn out to be 2-5 times more profitable than thermal and nuclear power plants. Calculations show that one geothermal well can replace 158 thousand tons of coal per year.

Thus, the Earth's heat is perhaps the only major renewable energy resource, the rational development of which promises to reduce the cost of energy compared to modern fuel energy. With an equally inexhaustible energy potential, solar and thermonuclear installations, unfortunately, will be more expensive than existing fuel.

Despite the very long history of the development of the Earth's heat, today geothermal technology has not yet reached its high development. The development of the thermal energy of the Earth is experiencing great difficulties in construction deep wells, which are a channel for bringing the coolant to the surface. Due to the high temperature at the bottomhole (200-250 °C), traditional rock cutting tools are unsuitable for working in such conditions, there are special requirements for the choice of drill and casing pipes, cement slurries, drilling technology, well casing and completion. Domestic measuring equipment, serial operational fittings and equipment are produced in a design that allows temperatures not higher than 150-200 ° C. Traditional deep mechanical drilling of wells is sometimes delayed for years and requires significant financial costs. In the main production assets, the cost of wells is from 70 to 90%. This problem can and should be solved only by creating a progressive technology for the development of the main part of geothermal resources, i.e. extraction of energy from hot rocks.

Our group of Russian scientists and specialists has been dealing with the problem of extracting and using the inexhaustible, renewable deep thermal energy of the Earth's hot rocks on the territory of the Russian Federation for more than one year. The purpose of the work is to create on the basis of domestic, high technologies technical means for deep penetration into the bowels of the earth's crust. Currently, several variants of drilling tools (BS) have been developed, which have no analogues in world practice.

The work of the first version of the BS is linked to the current traditional technology well drilling. Hard rock drilling speed ( average density 2500-3300 kg/m3) up to 30 m/h, well diameter 200-500 mm. The second variant of the BS performs drilling of wells in an autonomous and automatic mode. The launch is carried out from a special launch and acceptance platform, from which its movement is controlled. One thousand meters of BS in hard rocks will be able to pass within a few hours. Well diameter from 500 to 1000 mm. Reusable BS variants have great cost-effectiveness and huge potential value. The introduction of BS into production will open new stage in the construction of wells and provide access to inexhaustible sources of thermal energy of the Earth.

For the needs of heat supply, the required depth of wells throughout the country lies in the range of up to 3-4.5 thousand meters and does not exceed 5-6 thousand meters. The temperature of the heat carrier for housing and communal heat supply does not go beyond 150 °C. For industrial facilities, the temperature, as a rule, does not exceed 180-200 °C.

The purpose of creating the GCC is to provide constant, affordable, cheap heat to remote, hard-to-reach and undeveloped regions of the Russian Federation. The duration of operation of the GCS is 25-30 years or more. The payback period of the stations (taking into account the latest drilling technologies) is 3-4 years.

The creation in the Russian Federation in the coming years of appropriate capacities for the use of geothermal energy for non-electric needs will replace about 600 million tons of equivalent fuel. Savings can be up to 2 trillion rubles.

Until 2030, it becomes possible to create energy capacities to replace fire energy by up to 30%, and until 2040 to almost completely eliminate organic raw materials as fuel from the energy balance of the Russian Federation.

Literature

1. Goncharov S.A. Thermodynamics. Moscow: MGTUim. N.E. Bauman, 2002. 440 p.

2. Dyadkin Yu.D. etc. Geothermal thermal physics. St. Petersburg: Nauka, 1993. 255 p.

3. Mineral resource base fuel and energy complex of Russia. Status and prognosis / V.K. Branchhugov, E.A. Gavrilov, V.S. Litvinenko and others. Ed. V.Z. Garipova, E.A. Kozlovsky. M. 2004. 548 p.

4. Novikov G. P. et al. Drilling wells for thermal waters. M.: Nedra, 1986. 229 p.

With the development and formation of society, mankind began to look for more and more modern and at the same time economical ways to obtain energy. For this, various stations are being built today, but at the same time, the energy contained in the bowels of the earth is widely used. What is she like? Let's try to figure it out.

geothermal energy

Already from the name it is clear that it represents the heat of the earth's interior. Under the earth's crust is a layer of magma, which is a fiery-liquid silicate melt. According to research data, the energy potential of this heat is much higher than the energy of the world's natural gas reserves, as well as oil. Magma comes to the surface - lava. And most active observed in those layers of the earth on which the boundaries are located tectonic plates, and also where the earth's crust is characterized by thinness. geothermal energy Earth is obtained as follows: the lava and water resources of the planet are in contact, as a result of which the water begins to heat up sharply. This leads to the eruption of the geyser, the formation of the so-called hot lakes and undercurrents. That is, precisely those phenomena of nature, the properties of which are actively used as energies.

Artificial geothermal sources

The energy contained in the bowels of the earth must be used wisely. For example, there is an idea to create underground boilers. To do this, you need to drill two wells of sufficient depth, which will be connected at the bottom. That is, it turns out that in almost any corner of the land it is possible to obtain geothermal energy in an industrial way: cold water will be pumped into the reservoir through one well, and hot water or steam will be extracted through the second. Artificial heat sources will be beneficial and rational if the resulting heat will provide more energy. The steam can be sent to turbine generators that will generate electricity.

Of course, the extracted heat is only a fraction of what is available in the total reserves. But it should be remembered that the deep heat will be constantly replenished due to the processes of compression of rocks, stratification of the bowels. According to experts, the earth's crust accumulates heat, the total amount of which is 5,000 times greater calorific value all the fossil resources of the earth as a whole. It turns out that the operating time of such artificially created geothermal stations can be unlimited.

Source Features

The sources that make it possible to obtain geothermal energy are almost impossible to fully use. They exist in more than 60 countries of the world, with the largest number of terrestrial volcanoes on the territory of the Pacific volcanic ring of fire. But in practice, it turns out that geothermal sources in different regions worlds are completely different in their properties, namely, average temperature, salinity, gas composition, acidity, and so on.

Geysers are sources of energy on Earth, the features of which are that they certain intervals spew boiling water. After the eruption, the pool becomes free of water, at its bottom you can see a channel that goes deep into the ground. Geysers are used as energy sources in such regions as Kamchatka, Iceland, New Zealand and North America, and single geysers are also found in some other areas.

Where does energy come from?

Uncooled magma is located very close to the earth's surface. Gases and vapors are released from it, which rise and pass through the cracks. Mixing with groundwater, they cause them to heat up, they themselves turn into hot water, in which many substances are dissolved. This water is released to the earth's surface in the form of geothermal sources: hot springs, mineral springs, geysers and so on. According to scientists, the hot bowels of the earth are caves or chambers connected by passages, cracks and channels. They are just filled with groundwater, and very close to them are magma chambers. In this natural way, the thermal energy of the earth is formed.

Earth's electric field

There is another alternative energy source in nature, which is renewable, environmentally friendly, and easy to use. True, so far this source has only been studied and not applied in practice. So, the potential energy of the Earth lies in its electric field. You can get energy in this way based on the study of the basic laws of electrostatics and features electric field Earth. In fact, our planet from an electrical point of view is a spherical capacitor charged up to 300,000 volts. Its inner sphere has a negative charge, and the outer one - the ionosphere - is positive. is an insulator. Through it there is a constant flow of ionic and convective currents, which reach strengths of many thousands of amperes. However, the potential difference between the plates does not decrease in this case.

This suggests that in nature there is a generator, the role of which is to constantly replenish the leakage of charges from the capacitor plates. The magnetic field of the Earth acts as such a generator, rotating together with our planet in a stream solar wind. The energy of the Earth's magnetic field can be obtained just by connecting an energy consumer to this generator. To do this, you need to install a reliable ground.

Renewable sources

As the population of our planet is steadily growing, we need more and more energy to provide for the population. The energy contained in the bowels of the earth can be very different. For example, there are renewable sources: wind, solar and water energy. They are environmentally friendly, and therefore you can use them without fear of harming the environment.

water energy

This method has been used for many centuries. Today, a huge number of dams and reservoirs have been built, in which water is used to generate electrical energy. The essence of this mechanism is simple: under the influence of the flow of the river, the wheels of the turbines rotate, respectively, the energy of the water is converted into electrical energy.

Today there is a large number of hydroelectric power plants that convert the energy of the flow of water into electricity. The peculiarity of this method is that it is renewable, respectively, such designs have a low cost. That is why, despite the fact that the construction of hydroelectric power plants takes quite a long time, and the process itself is very costly, nevertheless, these facilities significantly outperform electric-intensive industries.

Solar energy: modern and promising

Solar energy is obtained using solar panels, but modern technologies allow the use of new methods for this. The largest system in the world is built in the California desert. It fully provides energy for 2,000 homes. The design works as follows: mirrors reflect Sun rays, which are sent to the central water boiler. It boils and turns into steam, which turns the turbine. It, in turn, is connected to an electric generator. The wind can also be used as the energy that the Earth gives us. The wind blows the sails, turns the windmills. And now with its help you can create devices that will generate electrical energy. By rotating the blades of the windmill, it drives the turbine shaft, which, in turn, is connected to an electric generator.

Internal energy of the Earth

It appeared as a result of several processes, the main of which are accretion and radioactivity. According to scientists, the formation of the Earth and its mass took place over several million years, and this happened due to the formation of planetesimals. They stuck together, respectively, the mass of the Earth became more and more. After our planet began to have a modern mass, but was still devoid of an atmosphere, meteoric and asteroid bodies fell on it without hindrance. This process is just called accretion, and it led to the fact that significant gravitational energy was released. And the larger bodies hit the planet, the more released the energy contained in the bowels of the Earth.

This gravitational differentiation led to the fact that substances began to separate: heavy substances simply sank, while light and volatile substances floated up. Differentiation also affected the additional release of gravitational energy.

Atomic Energy

The use of earth energy can occur in different ways. For example, with the help of the construction of nuclear power plants, when thermal energy is released due to the decay smallest particles matter of atoms. The main fuel is uranium, which is contained in the earth's crust. Many believe that this method of obtaining energy is the most promising, but its use is associated with a number of problems. First, uranium emits radiation that kills all living organisms. In addition, if this substance enters the soil or atmosphere, then a real man-made disaster will occur. Sad consequences we are experiencing the accident at the Chernobyl nuclear power plant to this day. The danger lies in the fact that radioactive waste can threaten all living things very, very much. for a long time for millennia.

New time - new ideas

Of course, people do not stop there, and every year more and more attempts are made to find new ways to get energy. If the energy of the earth's heat is obtained quite simply, then some methods are not so simple. For example, as an energy source, it is quite possible to use biological gas, which is obtained during the decay of waste. It can be used for heating houses and heating water.

Increasingly, they are being built when dams and turbines are installed across the mouths of reservoirs, which are driven by ebbs and flows, respectively, electricity is obtained.

Burning garbage, we get energy

Another method that is already being used in Japan is to create waste incinerators. Today they are built in England, Italy, Denmark, Germany, France, the Netherlands and the USA, but only in Japan these enterprises began to be used not only for their intended purpose, but also for generating electricity. At local factories, 2/3 of all garbage is burned, while the factories are equipped with steam turbines. Accordingly, they supply heat and electricity to nearby areas. At the same time, in terms of costs, building such an enterprise is much more profitable than building a thermal power plant.

More tempting is the prospect of using the Earth's heat where volcanoes are concentrated. In this case, it will not be necessary to drill the Earth too deeply, since already at a depth of 300-500 meters the temperature will be at least twice as high as the boiling point of water.

There is also such a way to generate electricity, as Hydrogen - the simplest and lightest chemical element - can be considered an ideal fuel, because it is where there is water. If you burn hydrogen, you can get water, which decomposes into oxygen and hydrogen. The hydrogen flame itself is harmless, that is, there will be no harm to the environment. The peculiarity of this element is that it has a high calorific value.

What's in the future?

Of course, the energy of the Earth's magnetic field or that which is obtained at nuclear power plants cannot fully satisfy all the needs of mankind, which are growing every year. However, experts say that there is no reason to worry, since the planet's fuel resources are still enough. Moreover, more and more new sources are being used, environmentally friendly and renewable.

The problem of pollution remains environment, and it is growing exponentially fast. The amount of harmful emissions goes off scale, respectively, the air we breathe is harmful, the water has dangerous impurities, and the soil is gradually depleted. That is why it is so important to start studying such a phenomenon as energy in the bowels of the Earth in a timely manner in order to look for ways to reduce the need for fossil fuels and make more active use of non-traditional energy sources.

In our country, rich in hydrocarbons, geothermal energy is a kind of exotic resource that, in the current state of affairs, is unlikely to compete with oil and gas. However, this alternative view energy can be used almost everywhere and quite efficiently.

Geothermal energy is the heat of the earth's interior. It is produced in the depths and comes to the surface of the Earth in different forms and with different intensity.

The temperature of the upper layers of the soil depends mainly on external (exogenous) factors - sunlight and air temperature. In summer and during the day, the soil warms up to certain depths, and in winter and at night it cools down following the change in air temperature and with some delay, increasing with depth. The influence of daily fluctuations in air temperature ends at depths from a few to several tens of centimeters. Seasonal fluctuations capture deeper layers of soil - up to tens of meters.

At a certain depth - from tens to hundreds of meters - the temperature of the soil is kept constant, equal to the average annual air temperature near the Earth's surface. This is easy to verify by going down into a fairly deep cave.

When the average annual air temperature in a given area is below zero, this manifests itself as permafrost (more precisely, permafrost). AT Eastern Siberia The thickness, that is, the thickness, of year-round frozen soils reaches 200–300 m in places.

From a certain depth (its own for each point on the map), the effect of the Sun and the atmosphere weakens so much that endogenous (internal) factors come first and the earth's interior is heated from the inside, so that the temperature begins to rise with depth.

The heating of the deep layers of the Earth is associated mainly with the decay of the radioactive elements located there, although other sources of heat are also named, for example, physicochemical, tectonic processes in the deep layers of the earth's crust and mantle. But whatever the cause, the temperature of rocks and associated liquid and gaseous substances increases with depth. Miners face this phenomenon - it is always hot in deep mines. At a depth of 1 km, thirty-degree heat is normal, and deeper the temperature is even higher.

The heat flow of the earth's interior, reaching the surface of the Earth, is small - on average, its power is 0.03–0.05 W / m 2, or approximately 350 W h / m 2 per year. Against the background of the heat flow from the Sun and the air heated by it, this is an imperceptible value: the Sun gives everyone square meter the earth's surface is about 4,000 kWh annually, that is, 10,000 times more (of course, this is on average, with a huge spread between polar and equatorial latitudes and depending on other climatic and weather factors).

The insignificance of the heat flow from the depths to the surface in most of the planet is associated with the low thermal conductivity of rocks and the peculiarities of the geological structure. But there are exceptions - places where the heat flow is high. These are, first of all, zones of tectonic faults, increased seismic activity and volcanism, where the energy of the earth's interior finds a way out. Such zones are characterized by thermal anomalies of the lithosphere, here the heat flow reaching the Earth's surface can be many times and even orders of magnitude more powerful than the "usual" one. A huge amount of heat is brought to the surface in these zones by volcanic eruptions and hot springs of water.

It is these areas that are most favorable for the development of geothermal energy. On the territory of Russia, these are, first of all, Kamchatka, the Kuril Islands and the Caucasus.

At the same time, the development of geothermal energy is possible almost everywhere, since the increase in temperature with depth is a ubiquitous phenomenon, and the task is to “extract” heat from the bowels, just as mineral raw materials are extracted from there.

On average, the temperature increases with depth by 2.5–3°C for every 100 m. The ratio of the temperature difference between two points lying at different depths to the difference in depth between them is called the geothermal gradient.

The reciprocal is the geothermal step, or the depth interval at which the temperature rises by 1°C.

The higher the gradient and, accordingly, the lower the step, the closer warmth depths of the Earth approaches the surface and the area is more promising for the development of geothermal energy.

AT different areas, depending on the geological structure and other regional and local conditions, the rate of temperature increase with depth can differ sharply. On the scale of the Earth, fluctuations in the values of geothermal gradients and steps reach 25 times. For example, in the state of Oregon (USA) the gradient is 150°C per 1 km, and in South Africa it is 6°C per 1 km.

The question is, what is the temperature at great depths - 5, 10 km or more? If the trend continues, temperatures at a depth of 10 km should average around 250–300°C. This is more or less confirmed by direct observations in ultradeep wells, although the picture is much more complicated than the linear increase in temperature.

For example, in the Kola superdeep well drilled in the Baltic crystal shield, the temperature to a depth of 3 km changes at a rate of 10°C/1 km, and then the geothermal gradient becomes 2–2.5 times greater. At a depth of 7 km, a temperature of 120°C has already been recorded, at 10 km - 180°C, and at 12 km - 220°C.

Another example is a well laid in the Northern Caspian, where at a depth of 500 m a temperature of 42°C was recorded, at 1.5 km - 70°C, at 2 km - 80°C, at 3 km - 108°C.

It is assumed that the geothermal gradient decreases starting from a depth of 20–30 km: at a depth of 100 km, the estimated temperatures are about 1300–1500°C, at a depth of 400 km - 1600°C, in the Earth's core (depths of more than 6000 km) - 4000–5000° C.

At depths up to 10–12 km, temperature is measured through drilled wells; where they do not exist, it is determined by indirect signs in the same way as at greater depths. Such indirect signs may be the nature of the passage seismic waves or the temperature of the erupting lava.

However, for the purposes of geothermal energy, data on temperatures at depths of more than 10 km are not yet of practical interest.

There is a lot of heat at depths of several kilometers, but how to raise it? Sometimes nature itself solves this problem for us with the help of a natural coolant - heated thermal waters that come to the surface or lie at a depth accessible to us. In some cases, the water in the depths is heated to the state of steam.

There is no strict definition of the concept of "thermal waters". As a rule, they mean hot groundwater in a liquid state or in the form of steam, including those that come to the Earth's surface with a temperature above 20 ° C, that is, as a rule, higher than the air temperature.

The heat of groundwater, steam, steam-water mixtures is hydrothermal energy. Accordingly, energy based on its use is called hydrothermal.

The situation is more complicated with the production of heat directly from dry rocks - petrothermal energy, especially since sufficiently high temperatures, as a rule, begin from depths of several kilometers.

On the territory of Russia, the potential of petrothermal energy is a hundred times higher than that of hydrothermal energy - 3,500 and 35 trillion tons of standard fuel, respectively. This is quite natural - the warmth of the Earth's depths is everywhere, and thermal waters are found locally. However, due to obvious technical difficulties, most of the thermal waters are currently used to generate heat and electricity.

Water temperatures from 20-30 to 100°C are suitable for heating, temperatures from 150°C and above - and for the generation of electricity in geothermal power plants.

In general, geothermal resources on the territory of Russia, in terms of tons of reference fuel or any other unit of energy measurement, are approximately 10 times higher than fossil fuel reserves.

Theoretically, only geothermal energy could fully meet the energy needs of the country. Practically on this moment in most of its territory, this is not feasible for technical and economic reasons.

In the world, the use of geothermal energy is most often associated with Iceland - a country located at the northern end of the Mid-Atlantic Ridge, in an extremely active tectonic and volcanic zone. Probably everyone remembers the powerful eruption of the volcano Eyyafyatlayokudl ( Eyjafjallajokull) in 2010 year.

It is thanks to this geological specificity that Iceland has huge reserves of geothermal energy, including hot springs that come to the surface of the Earth and even gushing in the form of geysers.

In Iceland, more than 60% of all energy consumed is currently taken from the Earth. Including due to geothermal sources, 90% of heating and 30% of electricity generation are provided. We add that the rest of the electricity in the country is produced by hydroelectric power plants, that is, also using a renewable energy source, thanks to which Iceland looks like a kind of global environmental standard.

The "taming" of geothermal energy in the 20th century helped Iceland significantly economically. Until the middle of the last century, it was very poor country, now ranks first in the world in terms of installed capacity and production of geothermal energy per capita and is in the top ten in terms of absolute value installed capacity of geothermal power plants. However, its population is only 300 thousand people, which simplifies the task of switching to environmentally friendly clean sources energy: the need for it is generally small.

In addition to Iceland, a high share of geothermal energy in general balance sheet electricity generation provided in New Zealand and the island nations South-East Asia(Philippines and Indonesia), the countries of Central America and East Africa, whose territory is also characterized by high seismic and volcanic activity. For these countries, at their current level of development and needs, geothermal energy makes a significant contribution to socio-economic development.

The use of geothermal energy has a very long history. One of the first famous examples- Italy, a place in the province of Tuscany, now called Larderello, where, at the beginning of the 19th century, local hot thermal waters, flowing naturally or extracted from shallow wells, were used for energy purposes.

Water from underground sources, rich in boron, was used here to obtain boric acid. Initially, this acid was obtained by evaporation in iron boilers, and ordinary firewood was taken as fuel from nearby forests, but in 1827 Francesco Larderel created a system that worked on the heat of the waters themselves. At the same time, the energy of natural water vapor began to be used for the operation of drilling rigs, and at the beginning of the 20th century, for heating local houses and greenhouses. In the same place, in Larderello, in 1904, thermal water vapor became energy source to get electricity.

The example of Italy at the end of the 19th and beginning of the 20th century was followed by some other countries. For example, in 1892, thermal waters were first used for local heating in the United States (Boise, Idaho), in 1919 - in Japan, in 1928 - in Iceland.

In the United States, the first hydrothermal power plant appeared in California in the early 1930s, in New Zealand - in 1958, in Mexico - in 1959, in Russia (the world's first binary GeoPP) - in 1965 .

An old principle at a new source

Electricity generation requires a higher water source temperature than heating, over 150°C. The principle of operation of a geothermal power plant (GeoES) is similar to the principle of operation of a conventional thermal power plant (TPP). In fact, a geothermal power plant is a type of thermal power plant.

At thermal power plants, as a rule, coal, gas or fuel oil act as the primary source of energy, and water vapor serves as the working fluid. The fuel, burning, heats the water to a state of steam, which rotates the steam turbine, and it generates electricity.

The difference between the GeoPP is that the primary source of energy here is the heat of the earth's interior and working body in the form of steam enters the turbine blades of the electric generator in a "ready" form directly from the production well.

There are three main schemes of GeoPP operation: direct, using dry (geothermal) steam; indirect, based on hydrothermal water, and mixed, or binary.

The use of one or another scheme depends on the state of aggregation and the temperature of the energy carrier.

The simplest and therefore the first of the mastered schemes is the direct one, in which the steam coming from the well is passed directly through the turbine. The world's first GeoPP in Larderello in 1904 also operated on dry steam.

GeoPP with indirect scheme jobs are the most common these days. They use hot underground water, which is injected under high pressure into the evaporator, where part of it is evaporated, and the resulting steam rotates the turbine. In some cases, additional devices and circuits are required to purify geothermal water and steam from aggressive compounds.

The exhaust steam enters the injection well or is used for space heating - in this case, the principle is the same as during the operation of a CHP.

At binary GeoPPs, hot thermal water interacts with another liquid that acts as a working fluid with a lower boiling point. Both liquids are passed through a heat exchanger, where thermal water evaporates the working liquid, the vapors of which rotate the turbine.

This system is closed, which solves the problem of emissions into the atmosphere. In addition, working fluids with a relatively low boiling point make it possible to use not very hot thermal waters as a primary source of energy.

All three schemes use a hydrothermal source, but petrothermal energy can also be used to generate electricity.

The circuit diagram in this case is also quite simple. It is necessary to drill two interconnected wells - injection and production. Water is pumped into the injection well. At depth, it heats up, then heated water or steam formed as a result of strong heating is supplied to the surface through a production well. Further, it all depends on how the petrothermal energy is used - for heating or for the production of electricity. A closed cycle is possible with the pumping of exhaust steam and water back into the injection well or another method of disposal.

The disadvantage of such a system is obvious: in order to obtain a sufficiently high temperature of the working fluid, it is necessary to drill wells to a great depth. And this is a serious cost and the risk of significant heat loss when the fluid moves up. Therefore, petrothermal systems are still less common than hydrothermal ones, although the potential of petrothermal energy is orders of magnitude higher.

Currently, the leader in the creation of the so-called petrothermal circulating systems (PCS) is Australia. In addition, this direction of geothermal energy is actively developing in the USA, Switzerland, Great Britain, and Japan.

Gift from Lord Kelvin

The invention of the heat pump in 1852 by physicist William Thompson (aka Lord Kelvin) provided humanity with a real opportunity to use low-grade heat upper layers of soil. The heat pump system, or heat multiplier as Thompson called it, is based on the physical process of transferring heat from the environment to the refrigerant. In fact, it uses the same principle as in petrothermal systems. The difference is in the source of heat, in connection with which a terminological question may arise: to what extent can a heat pump be considered a geothermal system? The fact is that in the upper layers, to depths of tens or hundreds of meters, the rocks and the fluids contained in them are heated not by the deep heat of the earth, but by the sun. Thus, it is the sun in this case that is the primary source of heat, although it is taken, as in geothermal systems, from the earth.

The operation of a heat pump is based on the delay in the heating and cooling of the soil compared to the atmosphere, as a result of which a temperature gradient is formed between the surface and deeper layers, which retain heat even in winter, similar to how it happens in reservoirs. The main purpose of heat pumps is space heating. In fact, it is a “refrigerator in reverse”. Both the heat pump and the refrigerator interact with three components: the internal environment (in the first case - a heated room, in the second - a cooled refrigerator chamber), the external environment - an energy source and a refrigerant (refrigerant), which is also a coolant that provides heat transfer or cold.

A substance with a low boiling point acts as a refrigerant, which allows it to take heat from a source that has even a relatively low temperature.

In the refrigerator, the liquid refrigerant enters the evaporator through a throttle (pressure regulator), where, due to a sharp decrease in pressure, the liquid evaporates. Evaporation is an endothermic process requiring heat to be absorbed from outside. As a result, heat is taken from the inner walls of the evaporator, which provides a cooling effect in the refrigerator chamber. Further from the evaporator, the refrigerant is sucked into the compressor, where it returns to the liquid state of aggregation. This is the reverse process, leading to the release of the extracted heat during external environment. As a rule, it is thrown into the room, and the back wall of the refrigerator is relatively warm.

The heat pump works in almost the same way, with the difference that heat is taken from the external environment and enters the internal environment through the evaporator - the room heating system.

In a real heat pump, water is heated, passing through an external circuit laid in the ground or a reservoir, then enters the evaporator.

In the evaporator, heat is transferred to an internal circuit filled with a refrigerant with a low boiling point, which, passing through the evaporator, changes from a liquid state to a gaseous state, taking heat.

Next, the gaseous refrigerant enters the compressor, where it is compressed to high pressure and temperature, and enters the condenser, where heat exchange takes place between the hot gas and the coolant from the heating system.

The compressor requires electricity to operate, however, the transformation ratio (the ratio of consumed and generated energy) in modern systems high enough to be effective.

Currently, heat pumps are widely used for space heating, mainly in economically developed countries.

Eco-correct energy

Geothermal energy is considered environmentally friendly, which is generally true. First of all, it uses a renewable and practically inexhaustible resource. Geothermal energy does not require large areas, Unlike large hydroelectric power plants or wind farms, and does not pollute the atmosphere, unlike hydrocarbon energy. On average, GeoPP occupies 400 m 2 in terms of 1 GW of electricity generated. The same figure for a coal-fired thermal power plant, for example, is 3600 m 2. The environmental benefits of GeoPPs also include low water consumption - 20 liters of fresh water per 1 kW, while thermal power plants and nuclear power plants require about 1000 liters. Note that these are the environmental indicators of the "average" GeoPP.

But there are still negative side effects. Among them, noise is most often distinguished, thermal pollution atmosphere and chemical - water and soil, as well as the formation of solid waste.

The main source of chemical pollution of the environment is thermal water itself (with high temperature and salinity), which often contains large amounts of toxic compounds, and therefore there is a problem of waste water and hazardous substances disposal.

The negative effects of geothermal energy can be traced at several stages, starting with drilling wells. Here, the same dangers arise as when drilling any well: destruction of the soil and vegetation cover, pollution of the soil and groundwater.

At the stage of operation of the GeoPP, the problems of environmental pollution persist. Thermal fluids - water and steam - typically contain carbon dioxide (CO 2), sulfur sulfide (H 2 S), ammonia (NH 3), methane (CH 4), table salt(NaCl), boron (B), arsenic (As), mercury (Hg). When released into the environment, they become sources of pollution. In addition, an aggressive chemical environment can cause corrosion damage to GeoTPP structures.

At the same time, pollutant emissions at GeoPPs are on average lower than at TPPs. For example, carbon dioxide emissions per kilowatt-hour of electricity generated are up to 380 g at GeoPPs, 1042 g at coal-fired thermal power plants, 906 g at fuel oil and 453 g at gas-fired thermal power plants.

The question arises: what to do with waste water? With low salinity, after cooling, it can be discharged into surface waters. The other way is to pump it back into the aquifer through an injection well, which is the preferred and predominant practice at present.

The extraction of thermal water from aquifers (as well as pumping out ordinary water) can cause subsidence and ground movements, other deformations of geological layers, and micro-earthquakes. The probability of such phenomena is usually low, although individual cases have been recorded (for example, at the GeoPP in Staufen im Breisgau in Germany).

It should be emphasized that most of GeoPP is located in relatively sparsely populated areas and in third world countries, where environmental requirements are less stringent than in developed countries. In addition, at the moment the number of GeoPPs and their capacities are relatively small. With a larger development of geothermal energy environmental risks can grow and multiply.

How much is the energy of the Earth?

Investment costs for the construction of geothermal systems vary greatly. wide range- from 200 to 5000 dollars per 1 kW of installed capacity, that is, the cheapest options are comparable to the cost of building a thermal power plant. They depend, first of all, on the conditions of occurrence of thermal waters, their composition, and the design of the system. Drilling to great depths, creating a closed system with two wells, the need for water treatment can multiply the cost.

For example, investments in the creation of a petrothermal circulation system (PTS) are estimated at 1.6–4 thousand dollars per 1 kW of installed capacity, which exceeds the costs of building a nuclear power plant and is comparable to the costs of building wind and solar power plants.

The obvious economic advantage of GeoTPP is a free energy carrier. For comparison, in the cost structure of an operating thermal power plant or nuclear power plant, fuel accounts for 50–80% or even more, depending on current energy prices. Hence, another advantage of the geothermal system: operating costs are more stable and predictable, since they do not depend on the external conjuncture of energy prices. In general, the operating costs of the GeoTPP are estimated at 2–10 cents (60 kopecks–3 rubles) per 1 kWh of generated capacity.

The second largest (and very significant) item of expenditure after the energy carrier is, as a rule, the salary of the station staff, which can vary dramatically by country and region.

On average, the cost of 1 kWh of geothermal energy is comparable to that for thermal power plants (in Russian conditions - about 1 ruble / 1 kWh) and ten times higher than the cost of electricity generation at hydroelectric power plants (5–10 kopecks / 1 kWh ).

Part of the reason for the high cost is that, unlike thermal and hydraulic power plants, GeoTPP has a relatively small capacity. In addition, it is necessary to compare systems located in the same region and in similar conditions. So, for example, in Kamchatka, according to experts, 1 kWh of geothermal electricity costs 2-3 times cheaper than electricity produced at local thermal power plants.

Indicators economic efficiency The work of a geothermal system depends, for example, on whether it is necessary to dispose of the waste water and in what ways this is done, whether the combined use of the resource is possible. So, chemical elements and compounds extracted from thermal water can give additional income. Let us recall the example of Larderello: the primary chemical production, and the use of geothermal energy was originally of an auxiliary nature.

Geothermal Energy Forwards

Geothermal energy is developing somewhat differently than wind and solar. At present, it largely depends on the nature of the resource itself, which differs sharply by region, and the highest concentrations are tied to narrow zones of geothermal anomalies, usually associated with areas of tectonic faults and volcanism.

In addition, geothermal energy is less technologically capacious compared to wind and even more so with solar energy: the systems of geothermal stations are quite simple.

In the overall structure of world electricity production, the geothermal component accounts for less than 1%, but in some regions and countries its share reaches 25–30%. Due to the linkage to geological conditions, a significant part of the geothermal energy capacities is concentrated in third world countries, where three clusters are distinguished greatest development industries - the islands of Southeast Asia, Central America and East Africa. The first two regions are part of the Pacific "Fire Belt of the Earth", the third is tied to the East African Rift. With the greatest probability, geothermal energy will continue to develop in these belts. A more distant prospect is the development of petrothermal energy, using the heat of the earth's layers lying at a depth of several kilometers. This is an almost ubiquitous resource, but its extraction requires high costs, so petrothermal energy is developing primarily in the most economically and technologically powerful countries.

In general, given the ubiquity of geothermal resources and an acceptable level of environmental safety, there is reason to believe that geothermal energy has good prospects development. Especially with the growing threat of a shortage of traditional energy carriers and rising prices for them.

From Kamchatka to the Caucasus

In Russia, the development of geothermal energy has a fairly long history, and in a number of positions we are among the world leaders, although the share of geothermal energy in the overall energy balance of a huge country is still negligible.

The pioneers and centers for the development of geothermal energy in Russia were two regions - Kamchatka and the North Caucasus, and if in the first case we are talking primarily about the electric power industry, then in the second - about the use of thermal energy of thermal water.

In the North Caucasus, in Krasnodar Territory, Chechnya, Dagestan - the heat of thermal waters for energy purposes was used even before the Great Patriotic War. In the 1980s–1990s, the development of geothermal energy in the region, for obvious reasons, stalled and has not yet recovered from the state of stagnation. Nevertheless, geothermal water supply in the North Caucasus provides heat for about 500 thousand people, and, for example, the city of Labinsk in the Krasnodar Territory with a population of 60 thousand people is completely heated by geothermal waters.

In Kamchatka, the history of geothermal energy is associated primarily with the construction of the GeoPP. The first of them, still operating Pauzhetskaya and Paratunskaya stations, were built back in 1965–1967, while the Paratunskaya GeoPP with a capacity of 600 kW became the first station in the world with a binary cycle. It was the development of Soviet scientists S. S. Kutateladze and A. M. Rosenfeld from the Institute of Thermal Physics of the Siberian Branch of the Russian Academy of Sciences, who received in 1965 a copyright certificate for extracting electricity from water with a temperature of 70 ° C. This technology subsequently became the prototype for more than 400 binary GeoPPs in the world.

The capacity of the Pauzhetskaya GeoPP, commissioned in 1966, was initially 5 MW and subsequently increased to 12 MW. Currently, the station is under construction of a binary block, which will increase its capacity by another 2.5 MW.

The development of geothermal energy in the USSR and Russia was hindered by the availability of traditional energy sources - oil, gas, coal, but never stopped. The largest geothermal power facilities at the moment are the Verkhne-Mutnovskaya GeoPP with a total capacity of 12 MW power units, commissioned in 1999, and the Mutnovskaya GeoPP with a capacity of 50 MW (2002).

Mutnovskaya and Verkhne-Mutnovskaya GeoPP are unique objects not only for Russia, but also on a global scale. The stations are located at the foot of the Mutnovsky volcano, at an altitude of 800 meters above sea level, and operate in extreme climatic conditions, where it is winter for 9-10 months a year. The equipment of the Mutnovsky GeoPPs, currently one of the most modern in the world, was completely created at domestic enterprises of power engineering.

At present, the share of Mutnovsky stations in the overall structure of energy consumption of the Central Kamchatka energy hub is 40%. An increase in capacity is planned in the coming years.

Separately, it should be said about Russian petrothermal developments. We do not yet have large PCSs, but there are Hi-tech drilling to a great depth (about 10 km), which also have no analogues in the world. Their further development will make it possible to drastically reduce the costs of creating petrothermal systems. The developers of these technologies and projects are N. A. Gnatus, M. D. Khutorskoy (Geological Institute of the Russian Academy of Sciences), A. S. Nekrasov (Institute of Economic Forecasting of the Russian Academy of Sciences) and specialists from the Kaluga Turbine Plant. Currently, the petrothermal circulation system project in Russia is at the pilot stage.

There are prospects for geothermal energy in Russia, although they are relatively distant: at the moment, the potential is quite large and the position of traditional energy is strong. At the same time, in a number of remote regions of the country, the use of geothermal energy is economically profitable and is in demand even now. These are territories with high geoenergy potential (Chukotka, Kamchatka, Kuriles - Russian part the Pacific “Fiery Belt of the Earth”, the mountains of Southern Siberia and the Caucasus) and at the same time remote and cut off from the centralized energy supply.

It is likely that in the coming decades, geothermal energy in our country will develop precisely in such regions.

For Russia, the energy of the Earth's heat can become a constant, reliable source of providing cheap and affordable electricity and heat using new high, environmentally friendly technologies for its extraction and supply to the consumer. This is especially true at the moment

Limited resources of fossil energy raw materials

The demand for organic energy raw materials is high in industrialized and developing countries(USA, Japan, states of united Europe, China, India, etc.). At the same time, their own hydrocarbon resources in these countries are either insufficient or reserved, and a country, such as the United States, buys energy raw materials abroad or develops deposits in other countries.

In Russia, one of the richest countries in terms of energy resources, the economic needs for energy are still satisfied by the possibilities of using natural resources. However, the extraction of fossil hydrocarbons from the subsoil occurs at a very fast pace. If in the 1940s-1960s. the main oil-producing regions were the “Second Baku” in the Volga and Cis-Urals, then, starting from the 1970s, and to the present, such an area is Western Siberia. But even here there is a significant decline in the production of fossil hydrocarbons. The era of "dry" Cenomanian gas is passing away. The previous stage of extensive development of natural gas production has come to an end. Its extraction from such giant deposits as Medvezhye, Urengoyskoye and Yamburgskoye amounted to 84, 65 and 50%, respectively. Specific gravity oil reserves favorable for development are also declining over time.

Due to the active consumption of hydrocarbon fuels, onshore reserves of oil and natural gas have been significantly reduced. Now their main reserves are concentrated on the continental shelf. And although the raw material base of the oil and gas industry is still sufficient for the production of oil and gas in Russia in the required volumes, in the near future it will be provided to an increasing extent through the development of fields with complex mining and geological conditions. At the same time, the cost of hydrocarbon production will grow.

Most of the non-renewable resources extracted from the subsoil are used as fuel for power plants. First of all, this is the share of which in the fuel structure is 64%.

In Russia, 70% of electricity is generated at thermal power plants. Energy enterprises of the country annually burn about 500 million tons of c.e. tons for the purpose of generating electricity and heat, while the production of heat consumes 3-4 times more hydrocarbon fuel than the generation of electricity.

The amount of heat obtained from the combustion of these volumes of hydrocarbon raw materials is equivalent to the use of hundreds of tons of nuclear fuel - the difference is huge. However nuclear energy requires ensuring environmental safety (to prevent a repeat of Chernobyl) and protecting it from possible terrorist attacks, as well as the safe and costly decommissioning of obsolete and outdated nuclear power units. The proven recoverable reserves of uranium in the world are about 3 million 400 thousand tons. For the entire previous period (until 2007), about 2 million tons were mined.

RES as the future of global energy

The increased interest in the world in recent decades in alternative renewable energy sources (RES) is caused not only by the depletion of hydrocarbon fuel reserves, but also by the need to solve environmental problems. Objective factors (fossil fuel and uranium reserves, as well as environmental changes associated with the use of traditional fire and nuclear energy) and energy development trends suggest that the transition to new methods and forms of energy generation is inevitable. Already in the first half of the XXI century. there will be a complete or almost complete transition to non-traditional energy sources.

The sooner a breakthrough is made in this direction, the less painful it will be for the whole society and more beneficial for the country where decisive steps in the indicated direction.

The world economy has already set a course for the transition to a rational combination of traditional and new energy sources. Energy consumption in the world by 2000 amounted to more than 18 billion tons of fuel equivalent. tons, and energy consumption by 2025 may increase to 30–38 billion tons of fuel equivalent. tons, according to forecast data, by 2050 consumption at the level of 60 billion tons of fuel equivalent is possible. t. A characteristic trend in the development of the world economy in the period under review is a systematic decrease in the consumption of fossil fuels and a corresponding increase in the use of non-traditional energy resources. The thermal energy of the Earth occupies one of the first places among them.

At present, the Ministry of Energy of the Russian Federation has adopted a development program non-traditional energy, including 30 major projects the use of heat pump installations (HPU), the principle of operation of which is based on the consumption of low-potential thermal energy of the Earth.

Low-potential energy of the Earth's heat and heat pumps

The sources of low-potential heat energy of the Earth are solar radiation and thermal radiation heated bowels of our planet. At present, the use of such energy is one of the most dynamically developing areas of energy based on renewable energy sources.

The heat of the earth can be used in various types buildings and structures for heating, hot water supply, air conditioning (cooling), as well as for heating tracks in the winter season, preventing icing, heating fields in outdoor stadiums, etc. technical literature systems that utilize the earth's heat in heating and air conditioning systems are referred to as GHP - "geothermal heat pumps" (geothermal heat pumps). Climate characteristics the countries of Central and Northern Europe, which, together with the United States and Canada, are the main areas for the use of low-grade heat of the Earth, determine this mainly for heating purposes; air cooling even in summer period relatively rarely required. Therefore, unlike in the USA, heat pumps in European countries operate mainly in heating mode. In the US, they are more often used in air heating systems combined with ventilation, which allows both heating and cooling of the outside air. In European countries, heat pumps are usually used in water heating systems. Since their efficiency increases as the temperature difference between the evaporator and condenser decreases, underfloor heating systems are often used for heating buildings, in which a coolant of a relatively low temperature (35–40 ° C) circulates.

Types of systems for the use of low-potential energy of the Earth's heat

AT general case There are two types of systems for using the low-potential energy of the Earth's heat:

- open systems: as a source of low-grade thermal energy, groundwater is used, which is supplied directly to heat pumps;

- closed systems: heat exchangers are located in the soil massif; when a coolant with a temperature lower than the ground circulates through them, thermal energy is “taken off” from the ground and transferred to the heat pump evaporator (or when a coolant with a higher temperature relative to the ground is used, it is cooled).

The disadvantages of open systems are that wells require maintenance. In addition, the use of such systems is not possible in all areas. The main requirements for soil and groundwater are as follows:

- sufficient water permeability of the soil, allowing replenishment of water reserves;

- good chemical composition groundwater (e.g. low iron content) to avoid pipe scale and corrosion problems.

Closed systems for the use of low-potential energy of the Earth's heat

Closed systems are horizontal and vertical (Figure 1).

Rice. 1. Scheme of a geothermal heat pump installation with: a - horizontal

and b - vertical ground heat exchangers.

Horizontal ground heat exchanger

In the countries of Western and Central Europe, horizontal ground heat exchangers are usually separate pipes laid relatively tightly and connected to each other in series or in parallel (Fig. 2).

Rice. 2. Horizontal ground heat exchangers with: a - sequential and

b - parallel connection.

To save the area of the site where the heat is removed, improved types of heat exchangers have been developed, for example, heat exchangers in the form of a spiral (Fig. 3), located horizontally or vertically. This form of heat exchangers is common in the USA.

In our country, rich in hydrocarbons, geothermal energy is a kind of exotic resource that, in the current state of affairs, is unlikely to compete with oil and gas. Nevertheless, this alternative form of energy can be used almost everywhere and quite efficiently.

Geothermal energy is the heat of the earth's interior. It is produced in the depths and comes to the surface of the Earth in different forms and with different intensity.

When the average annual air temperature in a given area is below zero, this manifests itself as permafrost (more precisely, permafrost). In Eastern Siberia, the thickness, that is, the thickness, of year-round frozen soils reaches 200–300 m in places.

The heat flow of the earth's interior, reaching the surface of the Earth, is small - on average, its power is 0.03–0.05 W / m 2, or approximately 350 W h / m 2 per year. Against the background of the heat flow from the Sun and the air heated by it, this is an imperceptible value: the Sun gives each square meter of the earth's surface about 4000 kWh annually, that is, 10,000 times more (of course, this is on average, with a huge spread between polar and equatorial latitudes and depending on other climatic and weather factors).

It is these areas that are most favorable for the development of geothermal energy. On the territory of Russia, these are, first of all, Kamchatka, the Kuril Islands and the Caucasus.

The reciprocal is the geothermal step, or the depth interval at which the temperature rises by 1°C.

The higher the gradient and, accordingly, the lower the step, the closer the heat of the Earth's depths approaches the surface and the more promising this area is for the development of geothermal energy.

In different areas, depending on the geological structure and other regional and local conditions, the rate of temperature increase with depth can vary dramatically. On the scale of the Earth, fluctuations in the values of geothermal gradients and steps reach 25 times. For example, in the state of Oregon (USA) the gradient is 150°C per 1 km, and in South Africa it is 6°C per 1 km.

For example, in the Kola superdeep well drilled in the Baltic Crystalline Shield, the temperature changes at a rate of 10°C/1 km to a depth of 3 km, and then the geothermal gradient becomes 2–2.5 times greater. At a depth of 7 km, a temperature of 120°C has already been recorded, at 10 km - 180°C, and at 12 km - 220°C.

Another example is a well laid in the Northern Caspian, where at a depth of 500 m a temperature of 42°C was recorded, at 1.5 km - 70°C, at 2 km - 80°C, at 3 km - 108°C.

At depths up to 10–12 km, temperature is measured through drilled wells; where they do not exist, it is determined by indirect signs in the same way as at greater depths. Such indirect signs may be the nature of the passage of seismic waves or the temperature of the erupting lava.

However, for the purposes of geothermal energy, data on temperatures at depths of more than 10 km are not yet of practical interest.

The heat of groundwater, steam, steam-water mixtures is hydrothermal energy. Accordingly, energy based on its use is called hydrothermal.

Water temperatures from 20-30 to 100°C are suitable for heating, temperatures from 150°C and above - and for the generation of electricity in geothermal power plants.

In general, geothermal resources on the territory of Russia, in terms of tons of reference fuel or any other unit of energy measurement, are approximately 10 times higher than fossil fuel reserves.

Theoretically, only geothermal energy could fully meet the energy needs of the country. In practice, at the moment, in most of its territory, this is not feasible for technical and economic reasons.

It is thanks to this geological specificity that Iceland has huge reserves of geothermal energy, including hot springs that come to the surface of the Earth and even gushing in the form of geysers.

The "taming" of geothermal energy in the 20th century helped Iceland significantly economically. Until the middle of the last century, it was a very poor country, now it ranks first in the world in terms of installed capacity and production of geothermal energy per capita, and is in the top ten in terms of absolute installed capacity of geothermal power plants. However, its population is only 300 thousand people, which simplifies the task of switching to environmentally friendly energy sources: the need for it is generally small.

In addition to Iceland, a high share of geothermal energy in the total balance of electricity production is provided in New Zealand and the island states of Southeast Asia (Philippines and Indonesia), the countries of Central America and East Africa, whose territory is also characterized by high seismic and volcanic activity. For these countries, at their current level of development and needs, geothermal energy makes a significant contribution to socio-economic development.

The use of geothermal energy has a very long history. One of the first known examples is Italy, a place in the province of Tuscany, now called Larderello, where, as early as the beginning of the 19th century, local hot thermal waters, flowing naturally or extracted from shallow wells, were used for energy purposes.