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The warmth of the earth. Thermal state of the inner parts of the globe Soil temperature at different depths in winter
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 intensities.
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). In 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 action 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 earth's surface about 4,000 kWh annually, that is, 10,000 times more (of course, this is an 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 features 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 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.
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 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.
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 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.
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 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 standard fuel or any other unit of energy measurement, are about 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 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), 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.
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 an energy source for generating 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 the working fluid 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.
GeoPPs with an indirect scheme of operation are the most common in our time. They use hot underground water, which is pumped under high pressure into an evaporator, where part of it is evaporated, and the resulting steam rotates a 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 the physicist William Thompson (aka Lord Kelvin) provided mankind with a real opportunity to use the low-grade heat of the upper layers of the 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 this case- the primary source of heat, although it is taken, as in geothermal systems, from the ground.
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 what 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 taken heat into the 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 liquid to gaseous state, taking heat.
Further, 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 heat carrier 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 quite 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 GeoPP also include low water consumption - 20 liters 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 negative side effects yet there are. Among them, noise, thermal pollution of the atmosphere and chemical pollution of water and soil, as well as the formation of solid waste are most often distinguished.
The main source of chemical pollution of the environment is thermal water itself (with high temperature and mineralization), 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 the drilling of 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), common 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 the GeoPPs are 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 increase and multiply.
How much is the energy of the Earth?
Investment costs for the construction of geothermal systems vary in a very 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, wage plant personnel, which can vary dramatically across countries and regions.
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 HPPs (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.
The indicators of economic efficiency of the geothermal system depend, for example, on whether it is necessary to dispose of 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 provide additional income. Recall the example of Larderello: it was chemical production that was primary there, and the use of geothermal energy was initially 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.
AT overall structure The geothermal component accounts for less than 1% of global electricity production, 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. FROM most likely 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 development prospects. 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.
Two regions, Kamchatka and 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 PDS, however, there are advanced technologies for drilling to great depths (about 10 km), which also have no analogues in the world. Them further development will drastically reduce the cost 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 a high geo-energy potential (Chukotka, Kamchatka, the Kuriles - the Russian part of the Pacific "Fire Belt of the Earth", the mountains of Southern Siberia and the Caucasus) and at the same time remote and cut off from centralized energy supply.
It is likely that in the coming decades, geothermal energy in our country will develop precisely in such regions.
In vertical collectors, energy is taken from the earth using geothermal earth probes. These are closed systems with wells with a diameter of 145-150mm and a depth of 50 to 150m, through which pipes are laid. A return U elbow is installed at the end of the pipeline. Usually installation is done with a single loop probe with 2x d40 pipes (Swedish system) or a double loop probe with 4x d32 pipes. Double-loop probes should achieve 10-15% more heat extraction. For wells deeper than 150 m, 4xd40 pipes should be used (to reduce pressure loss).
Currently, most of the wells for extracting ground heat are 150 m deep. At greater depths, more heat can be obtained, but the costs of such wells will be very high. Therefore, it is important to calculate in advance the cost of installing a vertical collector in comparison with the expected savings in the future. In the case of installing an active-passive cooling system, deeper wells are not made due to the higher temperature in the soil and the lower potential at the time of heat transfer from the solution environment. An anti-freeze mixture (alcohol, glycerin, glycol) circulates in the system, diluted with water to the desired anti-freeze consistency. In a heat pump, it transfers the heat taken from the ground to the refrigerant. The temperature of the earth at a depth of 20 m is approximately 10°C, and rises every 30m by 1°C. It is not affected by climatic conditions, and therefore you can count on high-quality energy extraction both in winter and in summer. It should be added that the temperature in the ground is slightly different at the beginning of the season (September-October) from the temperature at the end of the season (March-April). Therefore, when calculating the depth of vertical collectors, it is necessary to take into account the length of the heating season at the installation site.
When extracting heat with geothermal vertical probes, the correct calculations and design of the collectors are very important. To carry out competent calculations, it is necessary to know whether it is possible to drill at the installation site to the desired depth.
For a heat pump with a power of 10kW, approximately 120-180 m of wells are needed. Wells should be placed at least 8m apart. The number and depth of wells depends on geological conditions, the presence of groundwater, the ability of the soil to retain heat and drilling technology. When drilling multiple wells, the total desired length of the well is divided by the number of wells.
The advantage of a vertical collector over a horizontal collector is a smaller area of land to use, a more stable heat source, and independence of the heat source on weather conditions. The downside of vertical collectors is the high cost of earthworks and the gradual cooling of the earth near the collector (competent calculations of the required power are required during design).
Calculation of the required well depth
Information required for the preliminary calculation of the depth and number of wells:
Heat pump power
Selected type of heating - "warm floors", radiators, combined
Estimated number of hours of operation of the heat pump per year, covering the energy demand
Place of installation
Use of a geothermal well - heating, DHW heating, seasonal pool heating, year-round pool heating
Using the passive (active) cooling function in the facility
Total annual heat consumption for heating (MWh)
The chart is at the bottom of the article.
Dacha (on the border of New Moscow and the Kaluga region) winter, periodic visits (2-4 times a month for a couple of days).
The blind area and the basement of the house are not insulated, since autumn they have been closed with heat-insulating plugs (10 cm of foam). The heat loss of the veranda where the riser goes in January has changed. See Note 10.
Measurements at a depth of 130 cm are made by the Xital GSM system (), discrete - 0.5 * C, add. the error is about 0.3 * C.
The sensor is installed in a 20mm HDPE pipe welded from below near the riser, (on the outside of the riser thermal insulation, but inside the 110mm pipe).
The abscissa shows dates, the ordinate shows temperatures.
Note 1:
I will also monitor the temperature of the water in the well, as well as at the ground level under the house, right on the riser without water, but only upon arrival. The error is about + -0.6 * C.
Note 2:
Temperature at ground level under the house, at the water supply riser, in the absence of people and water, it already dropped to minus 5 * C. This suggests that I did not make the system in vain - By the way, the thermostat that showed -5 * C is just from this system (RT-12-16).
Note 3:
The temperature of the water "in the well" is measured by the same sensor (it is also in Note 2) as "at ground level" - it stands right on the riser under the thermal insulation, close to the riser at ground level. These two measurements are made at different times. "At ground level" - before pumping water into the riser and "in the well" - after pumping about 50 liters for half an hour with interruptions.
Note 4:
The temperature of the water in the well can be somewhat underestimated, because. I can't look for this fucking asymptote, endlessly pumping water (mine)... I play as best I can.
Note 5: Not relevant, deleted.
Note 6:
The error of fixing the street temperature is approximately + - (3-7) * С.
Note 7:
The rate of cooling of water at ground level (without turning on the pump) is very approximately 1-2 * C per hour (this is at minus 5 * C at ground level).
Note 8:
I forgot to describe how my underground riser is arranged and insulated. Two stockings of insulation are put on PND-32 in total - 2 cm. thickness (apparently, foamed polyethylene), all this is inserted into a 110mm sewer pipe and foamed there to a depth of 130cm. True, since PND-32 did not go in the center of the 110th pipe, and also the fact that in its middle the mass of ordinary foam may not harden for a long time, which means it does not turn into a heater, I strongly doubt the quality of such additional insulation .. It would probably be better to use a two-component foam, the existence of which I only found out later...
Note 9:
I want to draw the attention of readers to the temperature measurement "At ground level" dated 01/12/2013. and dated January 18, 2013. Here, in my opinion, the value of +0.3 * C is much higher than expected. I think that this is a consequence of the operation "Filling the basement at the riser with snow", carried out on 12/31/2012.
Note 10:
From January 12 to February 3, he made additional insulation of the veranda, where the underground riser goes.
As a result, according to approximate estimates, the heat loss of the veranda was reduced from 100 W / sq.m. floor to about 50 (this is at minus 20 * C on the street).
This is also reflected in the charts. See the temperature at ground level on February 9: +1.4*C and on February 16: +1.1 - there have not been such high temperatures since the beginning of real winter.
And one more thing: from February 4 to February 16, for the first time in two winters, from Sunday to Friday, the boiler did not turn on to maintain the set minimum temperature because it did not reach this minimum ...
Note 11:
As promised (for "order" and to complete the annual cycle), I will periodically publish temperatures in the summer. But - not in the schedule, so as not to "obscure" the winter, but here, in Note-11.
May 11, 2013
After 3 weeks of ventilation, the vents were closed until autumn to avoid condensation.
May 13, 2013(on the street for a week + 25-30 * C):
- under the house at ground level + 10.5 * C,
- under the house at a depth of 130cm. +6*С,
June 12, 2013:
- under the house at ground level + 14.5 * C,
- under the house at a depth of 130cm. +10*С.
- water in the well from a depth of 25 m not higher than + 8 * C.
June 26, 2013:
- under the house at ground level + 16 * C,
- under the house at a depth of 130 cm. +11*С.
- water in the well from a depth of 25m is not higher than +9.3*C.
August 19, 2013:
- under the house at ground level + 15.5 * C,
- under the house at a depth of 130cm. +13.5*С.
- water in the well from a depth of 25m not higher than +9.0*C.
September 28, 2013:
- under the house at ground level + 10.3 * C,
- under the house at a depth of 130cm. +12*С.
- water in the well from a depth of 25m = + 8.0 * C.
October 26, 2013:
- under the house at ground level + 8.5 * C,
- under the house at a depth of 130cm. +9.5*С.
- water in the well from a depth of 25 m not higher than + 7.5 * C.
November 16, 2013:
- under the house at ground level + 7.5 * C,
- under the house at a depth of 130cm. +9.0*С.
- water in the well from a depth of 25m + 7.5 * C.
February 20, 2014:
This is probably the last entry in this article.
All winter we live in the house all the time, the point in repeating last year's measurements is small, so only two significant figures:
- the minimum temperature under the house at ground level in the very frosts (-20 - -30 * C) a week after they began, repeatedly fell below + 0.5 * C. At these moments, I worked
Kirill Degtyarev, Researcher, Moscow State University them. M. V. Lomonosov.
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.
Photo by Igor Konstantinov.
Change in soil temperature with depth.
Temperature increase of thermal waters and dry rocks containing them with depth.
Change in temperature with depth in different regions.
The eruption of the Icelandic volcano Eyjafjallajökull is an illustration of violent volcanic processes occurring in active tectonic and volcanic zones with a powerful heat flow from the earth's interior.
Installed capacities of geothermal power plants by countries of the world, MW.
Distribution of geothermal resources on the territory of Russia. The reserves of geothermal energy, according to experts, are several times higher than the energy reserves of organic fossil fuels. According to the Geothermal Energy Society Association.
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). In 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 action 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 about 350 Wh/m 2 per year. Against the background of the heat flux 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).
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 o 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 o 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 o C per 1 km, and in South Africa - 6 o C per 1 km.
The question is, what is the temperature at great depths - 5, 10 km or more? If the trend continues, the temperature at a depth of 10 km should average about 250-300 o C. This is more or less confirmed by direct observations in ultra-deep wells, although the picture is much more complicated than a linear increase in temperature.
For example, in the Kola superdeep well drilled in the Baltic crystalline shield, the temperature changes at a rate of 10 o 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 o C was already recorded, at 10 km - 180 o C, and at 12 km - 220 o C.
Another example is a well laid in the Northern Caspian, where at a depth of 500 m a temperature of 42 o C was recorded, at 1.5 km - 70 o C, at 2 km - 80 o C, at 3 km - 108 o 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 o C, at a depth of 400 km - 1600 o C, in the Earth's core (depths of more than 6000 km) - 4000-5000 o FROM.
At depths up to 10-12 km, the 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.
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 underground waters in a liquid state or in the form of steam, including those that come to the surface of the Earth 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.
Waters with temperatures from 20-30 to 100 o C are suitable for heating, temperatures from 150 o C and above - and for generating electricity at geothermal power plants.
In general, geothermal resources on the territory of Russia, in terms of tons of standard fuel or any other unit of energy measurement, are about 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.
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 Eyjafjallajökull volcano in 2010.
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 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.
(Ending follows.)
