Soil temperature at depth during the winter months. Use of land as a heat-cold accumulator. Cooling in summer
It might seem like a fantasy if it weren't true. It turns out that in the harsh Siberian conditions, you can get heat directly from the ground. The first objects with geothermal heating systems appeared in the Tomsk region last year, and although they allow to reduce the cost of heat in comparison with traditional sources by about four times, there is no mass circulation "underground" yet. But the trend is noticeable and, most importantly, it is gaining momentum. In fact, this is the most affordable alternative energy source for Siberia, where solar panels or wind generators, for example, cannot always show their effectiveness. Geothermal energy is, in fact, just under our feet.
“The depth of soil freezing is 2–2.5 meters. The temperature of the earth below this mark remains the same both in winter and in summer in the range from plus one to plus five degrees Celsius. The work of the heat pump is based on this property, - says the power engineer of the Education Department of the Tomsk District Administration. Roman Alekseenko... - Communicating pipes are buried into the earthen contour to a depth of 2.5 meters, at a distance of about one and a half meters from each other. The coolant circulates in the pipe system - ethylene glycol. An external horizontal earthen circuit communicates with a refrigeration unit, in which a refrigerant circulates - freon, a gas with a low boiling point. At plus three degrees Celsius, this gas begins to boil, and when the compressor abruptly compresses the boiling gas, the temperature of the latter rises to plus 50 degrees Celsius. The heated gas is directed to a heat exchanger in which ordinary distilled water is circulated. The liquid heats up and carries heat throughout the floor heating system. "
Pure physics and no miracles
A kindergarten equipped with a modern Danish geothermal heating system opened in the village of Turuntaevo near Tomsk last summer. According to the director of the Tomsk company "Ecoclimate" George Granin, the energy efficient system made it possible to reduce the payment for heat supply by several times. For eight years this Tomsk enterprise has already equipped about two hundred objects in different regions of Russia with geothermal heating systems and continues to do this in the Tomsk region. So there is no doubt about the words of Granin. A year before the opening of the kindergarten in Turuntaevo, "Ecoclimate" equipped a geothermal heating system, which cost 13 million rubles, another kindergarten "Sunny Bunny" in the Tomsk microdistrict "Zelenye Gorki". In fact, this was the first experience of this kind. And he turned out to be quite successful.
Back in 2012, during a visit to Denmark organized under the Euro Info program of the Correspondence Center (EICC-Tomsk region), the company managed to agree on cooperation with the Danish company Danfoss. And today Danish equipment helps to extract heat from the Tomsk subsoil, and, as experts say without undue modesty, it turns out quite efficiently. The main indicator of efficiency is economy. “The heating system of a 250 square meter kindergarten building in Turuntaevo cost 1.9 million rubles,” Granin says. “And the heating fee is 20-25 thousand rubles a year.” This amount is incomparable with what a kindergarten would pay for heat using traditional sources.
The system worked without any problems in the conditions of the Siberian winter. A calculation was made for the compliance of heating equipment with the SanPiN standards, according to which it must maintain a temperature in the kindergarten building not lower than + 19 ° C at an outside air temperature of -40 ° C. In total, about four million rubles were spent on redevelopment, repair and re-equipment of the building. Together with the heat pump, the amount was just under six million. Thanks to heat pumps, kindergarten heating is now a completely insulated and independent system. There are no traditional radiators in the building now, and the heating of the premises is realized with the help of the "warm floor" system.
Turuntaevsky kindergarten is insulated, as they say, "from" and "to" - the building is equipped with additional thermal insulation: on top of the existing wall (three bricks thick), a 10-centimeter layer of insulation is installed, equivalent to two or three bricks. There is an air gap behind the insulation, followed by metal siding. The roof is insulated in the same way. The main focus of the builders was on the "warm floor" - the building's heating system. Several layers turned out: a concrete floor, a layer of foam plastic 50 mm thick, a system of pipes in which hot water and linoleum circulate. Although the water temperature in the heat exchanger can reach + 50 ° C, the maximum heating of the actual floor covering does not exceed + 30 ° C. The actual temperature of each room can be adjusted manually - automatic sensors allow you to set the floor temperature in such a way that the kindergarten room warms up to the required sanitary standards.
The pump power in the Turuntaevsky kindergarten is 40 kW of generated heat energy, for the production of which the heat pump requires 10 kW of electrical power. Thus, out of 1 kW of consumed electrical energy, the heat pump produces 4 kW of heat. “We were a little afraid of winter - we didn't know how the heat pumps would behave. But even in severe frosts, the kindergarten was steadily warm - from plus 18 to 23 degrees Celsius, - says the director of the Turuntaevskaya secondary school Evgeny Belonogov... - Of course, here it is worth considering that the building itself was well insulated. The equipment is unpretentious in maintenance, and despite the fact that this is a western development, in our harsh Siberian conditions it has shown itself to be quite effective. "
A comprehensive project for the exchange of experience in the field of resource conservation was implemented by the EICC-Tomsk Region of the Tomsk Chamber of Commerce and Industry. It was attended by small and medium-sized enterprises developing and implementing resource-saving technologies. In May last year, within the framework of the Russian-Danish project, Danish experts visited Tomsk, and the result was, as they say, obvious.
Innovation comes to school
New school in the village of Vershinino, Tomsk region, built by a farmer Mikhail Kolpakov, is the third object in the region that uses the heat of the earth as a source of heat for heating and hot water supply. The school is also unique because it has the highest energy efficiency category - "A". The heating system was designed and launched by the same company "Ecoclimate".
“When we were deciding what kind of heating to do in the school, we had several options - a coal-fired boiler house and heat pumps,” says Mikhail Kolpakov. - We studied the experience of an energy-efficient kindergarten in Zelenye Gorki and calculated that heating the old-fashioned way, using coal, would cost us more than 1.2 million rubles per winter, and we also need hot water. And with heat pumps, the costs will be about 170 thousand for the whole year, together with hot water. "
The system only needs electricity to generate heat. Consuming 1 kW of electricity, heat pumps in the school generate about 7 kW of thermal energy. In addition, unlike coal and gas, the heat of the earth is a self-renewable source of energy. The installation of a modern heating system for the school cost about 10 million rubles. For this, 28 wells were drilled on the school grounds.
“The arithmetic is simple here. We calculated that the maintenance of a coal-fired boiler house, taking into account the salary of the stoker and the cost of fuel, would cost more than a million rubles a year, - said the head of the education department. Sergey Efimov... - When using heat pumps, you will have to pay about fifteen thousand rubles a month for all resources. The undoubted advantages of using heat pumps are their efficiency and environmental friendliness. The heat supply system allows you to regulate the supply of heat depending on the weather outside, which excludes the so-called "underflooding" or "overheating" of the room. "
According to preliminary calculations, expensive Danish equipment will pay for itself in four to five years. The service life of Danfoss heat pumps with which Ecoclimate LLC works is 50 years. Receiving information about the air temperature outside, the computer determines when to warm up the school, and when it can not be done. Therefore, the question of the date of turning on and off the heating disappears altogether. Regardless of the weather outside the windows inside the school, climate control will always work for children.
“When the Ambassador Extraordinary and Plenipotentiary of the Kingdom of Denmark came to the All-Russian meeting last year and visited our kindergarten in Zelenye Gorki, he was pleasantly surprised that the technologies that are considered innovative even in Copenhagen have been applied and are working in the Tomsk Region, - says the commercial director of the company "Ecoclimate" Alexander Granin.
In general, the use of local renewable energy sources in various sectors of the economy, in this case in the social sphere, which includes schools and kindergartens, is one of the main directions being implemented in the region as part of the energy saving and energy efficiency program. The development of renewable energy is actively supported by the Governor of the region Sergey Zhvachkin... And three budgetary institutions with a geothermal heating system are just the first steps towards the implementation of a large and promising project.
The kindergarten in Zelenye Gorki was recognized as the best energy efficient facility in Russia at the Skolkovo competition. Then the Vershininskaya school appeared with geothermal heating, also of the highest energy efficiency category. The next object, no less significant for the Tomsk region, is a kindergarten in Turuntaevo. This year, Gazkhimstroyinvest and Stroygarant have already started building kindergartens for 80 and 60 children in the villages of the Tomsk region, Kopylovo and Kandinka, respectively. Both new facilities will be heated by geothermal heating systems - from heat pumps. In total, this year the regional administration intends to spend almost 205 million rubles on the construction of new kindergartens and the repair of existing ones. Reconstruction and re-equipment of a building for a kindergarten in the village of Takhtamyshevo is to be done. In this building, heating will also be realized by means of heat pumps, since the system has managed to prove itself well.
The temperature inside the earth is most often a rather subjective indicator, since the exact temperature can be called only in accessible places, for example, in the Kola well (depth 12 km). But this place belongs to the outer part of the earth's crust.
Temperatures at different depths of the Earth
As scientists have found out, the temperature rises by 3 degrees every 100 meters deep into the Earth. This figure is constant for all continents and parts of the globe. Such an increase in temperature occurs in the upper part of the earth's crust, approximately for the first 20 kilometers, then the temperature increase slows down.
The largest increase was recorded in the United States, where temperatures rose by 150 degrees per 1,000 meters inland. The slowest growth was recorded in South Africa, with the thermometer rising by only 6 degrees Celsius.
At a depth of about 35-40 kilometers, the temperature fluctuates around 1400 degrees. The boundary between the mantle and the outer core at a depth of 25 to 3000 km is heated from 2000 to 3000 degrees. The inner core is heated to 4000 degrees. The temperature in the very center of the Earth, according to the latest information obtained as a result of complex experiments, is about 6,000 degrees. The Sun can boast of the same temperature on its surface.
Minimum and maximum temperatures of the depths of the Earth
When calculating the minimum and maximum temperature inside the Earth, the data of the constant temperature belt are not taken into account. In this belt, the temperature is constant throughout the year. The belt is located at a depth of 5 meters (tropics) and up to 30 meters (high latitudes).
The maximum temperature was measured and recorded at a depth of about 6,000 meters and was 274 degrees Celsius. The minimum temperature inside the earth is recorded mainly in the northern regions of our planet, where even at a depth of more than 100 meters the thermometer shows sub-zero temperatures.
Where does heat come from and how is it distributed in the bowels of the planet
The heat inside the earth comes from several sources:
1) Decay of radioactive elements;
2) The gravitational differentiation of matter heated in the Earth's core;
3) Tidal friction (the impact of the Moon on the Earth, accompanied by a slowing down of the latter).
These are some options for the occurrence of heat in the bowels of the earth, but the question of the complete list and the correctness of the existing one is still open.
The heat flow emanating from the bowels of our planet varies depending on the structural zones. Therefore, the distribution of heat in a place where the ocean, mountains or plains are located has completely different indicators.
Kirill Degtyarev, Research Fellow, Moscow State University. M.V. Lomonosov.
In our country rich in hydrocarbons, geothermal energy is an exotic resource that, given 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 is quite efficient.
Photo by Igor Konstantinov.
Change in soil temperature with depth.
Temperature rise of thermal waters and their host dry rocks with depth.
Temperature change with depth in different regions.
The eruption of the Icelandic volcano Eyjafjallajokull 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 over the territory of Russia. The reserves of geothermal energy, according to experts, are several times higher than those of organic fossil fuels. According to the Association "Geothermal Energy Society".
Geothermal energy is the warmth 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 a 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 cover deeper layers of soil - up to tens of meters.
At a certain depth - from tens to hundreds of meters - the soil temperature is kept constant, equal to the average annual air temperature at the Earth's surface. It is easy to be convinced of this by going down into a sufficiently 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 out on top and the earth's interior heats up from the inside, so that the temperature begins to rise with depth.
The heating of the deep layers of the Earth is mainly associated with the decay of the radioactive elements located there, although other sources of heat are also called, for example, physicochemical, tectonic processes in the deep layers of the earth's crust and mantle. But whatever the reason, the temperature of rocks and associated liquid and gaseous substances grows with depth. Miners are faced with 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 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).
The insignificance of the heat flow from the depths to the surface on 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 an outlet. Such zones are characterized by thermal anomalies of the lithosphere, here the heat flux reaching the Earth's surface can be several times and even orders of magnitude more powerful than the "usual" one. Volcanic eruptions and hot water springs carry a huge amount of heat to the surface in these zones.
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 an 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 rises 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 o C.
The higher the gradient and, accordingly, the lower the step, the closer the warmth of the depths of the Earth comes to 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 rise with depth can vary dramatically. On the Earth's scale, fluctuations in the magnitudes 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 superdeep 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 to a depth of 3 km changes at a rate of 10 о С / 1 km, and then the geothermal gradient becomes 2-2.5 times higher. 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 region, 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 assumed temperatures are about 1300-1500 o С, at a depth of 400 km - 1600 o С, in the Earth's core (depths over 6000 km) - 4000-5000 o WITH.
At depths of up to 10-12 km, the temperature is measured through drilled wells; where they are absent, 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 outflowing 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 this problem is solved for us by nature itself with the help of a natural heat carrier - 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 term "thermal waters". As a rule, they mean hot groundwater in a liquid state or in the form of steam, including those coming out 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, the 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 rather high temperatures, as a rule, start 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 - 3500 and 35 trillion tons of fuel equivalent, respectively. This is quite natural - the warmth of the depths of the Earth is everywhere, and thermal waters are found locally. However, due to obvious technical difficulties for generating heat and electricity, thermal waters are currently used mostly.
Waters with temperatures ranging from 20-30 to 100 o C are suitable for heating, temperatures ranging 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 equivalent fuel or any other unit of energy measurement are about 10 times higher than the reserves of fossil fuel.
Theoretically, only geothermal energy could fully satisfy the country's energy needs. 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 enormous reserves of geothermal energy, including hot springs that come out to the surface of the Earth and even gush out in the form of geysers.
In Iceland, more than 60% of all energy consumed is currently taken from the Earth. Including geothermal sources provide 90% of heating and 30% of electricity generation. We add that the rest of the country's electricity is produced at hydroelectric power plants, that is, also using a renewable energy source, thanks to which Iceland looks like a kind of global environmental standard.
The domestication of geothermal energy in the 20th century helped Iceland noticeably 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 value of 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 needs for it are 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 (the Philippines and Indonesia), countries of Central America and East Africa, the territory of which is also characterized by high seismic and volcanic activity. For these countries, given their current level of development and needs, geothermal energy makes a significant contribution to socio-economic development.
(The ending follows.)
Description:
In contrast to the “direct” use of high-potential geothermal heat (hydrothermal resources), the use of the soil of the surface layers of the Earth as a source of low-potential thermal energy for geothermal heat pump heat supply systems (GTST) is possible almost everywhere. At present, it is one of the most dynamically developing areas of the use of non-traditional renewable energy sources in the world.
Geothermal heat pump heat supply systems and the efficiency of their application in the climatic conditions of Russia
G. P. Vasiliev, Scientific Supervisor of OJSC "INSOLAR-INVEST"
In contrast to the “direct” use of high-potential geothermal heat (hydrothermal resources), the use of the soil of the surface layers of the Earth as a source of low-potential thermal energy for geothermal heat pump heat supply systems (GTST) is possible almost everywhere. At present, it is one of the most dynamically developing areas of the use of non-traditional renewable energy sources in the world.
The soil of the surface layers of the Earth is actually a heat accumulator of unlimited power. The thermal regime of the soil is formed under the influence of two main factors - the solar radiation falling on the surface and the flux of radiogenic heat from the earth's interior. Seasonal and daily changes in the intensity of solar radiation and the temperature of the outside air cause fluctuations in the temperature of the upper layers of the soil. The penetration depth of daily fluctuations in the outside air temperature and the intensity of the incident solar radiation, depending on specific soil and climatic conditions, ranges from several tens of centimeters to one and a half meters. The penetration depth of seasonal fluctuations in the outside air temperature and the intensity of the incident solar radiation does not exceed, as a rule, 15–20 m.
The thermal regime of soil layers located below this depth ("neutral zone") is formed under the influence of thermal energy coming from the bowels of the Earth and practically does not depend on seasonal, and even more so daily, changes in the parameters of the external climate (Fig. 1). With increasing depth, the temperature of the ground also increases in accordance with the geothermal gradient (about 3 ° C for every 100 m). The magnitude of the flux of radiogenic heat coming from the earth's interior differs for different areas. As a rule, this value is 0.05–0.12 W / m 2.
Picture 1. |
During the operation of the GTST, the soil mass, located within the zone of thermal influence of the register of pipes of the soil heat exchanger of the system for collecting low-potential soil heat (heat collection system), due to seasonal changes in the parameters of the external climate, as well as under the influence of operational loads on the heat collection system, as a rule, is subjected to repeated freezing and thawing. In this case, naturally, there is a change in the state of aggregation of moisture contained in the pores of the soil and in the general case both in the liquid and in the solid and gaseous phases simultaneously. At the same time, in capillary-porous systems, which is the soil mass of the heat collection system, the presence of moisture in the pore space has a noticeable effect on the heat propagation process. The correct accounting of this influence today is associated with significant difficulties, which are primarily associated with the lack of clear ideas about the nature of the distribution of solid, liquid and gaseous phases of moisture in a particular structure of the system. In the presence of a temperature gradient in the thickness of the soil massif, water vapor molecules move to places with a reduced temperature potential, but at the same time, under the action of gravitational forces, an oppositely directed flow of moisture occurs in the liquid phase. In addition, the temperature regime of the upper layers of the soil is influenced by the moisture of atmospheric precipitation, as well as groundwater.
The characteristic features of the thermal regime of soil heat collection systems as a design object should also include the so-called "informative uncertainty" of mathematical models describing such processes, or, in other words, the lack of reliable information about the impact on the environment system (atmosphere and soil mass located outside the zone of thermal influence of the soil heat exchanger of the heat collection system) and the extreme complexity of their approximation. Indeed, if the approximation of the impacts on the external climate system, although complex, can still be realized with a certain expenditure of "computer time" and the use of existing models (for example, a "typical climatic year"), then the problem of taking into account in the model the impact on the system of atmospheric impacts (dew, fog, rain, snow, etc.), as well as the approximation of the thermal effect on the soil mass of the system of heat collection of the underlying and surrounding soil layers is practically not solvable today and could be the subject of separate studies. So, for example, the lack of knowledge of the processes of formation of filtration flows of groundwater, their speed regime, as well as the impossibility of obtaining reliable information about the heat and moisture regime of soil layers located below the zone of thermal influence of a ground heat exchanger, significantly complicates the task of constructing a correct mathematical model of the thermal regime of a system for collecting low-potential heat. soil.
To overcome the described difficulties arising in the design of the GTST, the created and tested in practice method of mathematical modeling of the thermal regime of soil heat collection systems and the method of accounting for the phase transitions of moisture in the pore space of the soil massif of heat collection systems can be recommended.
The essence of the method is to consider the difference between two problems when constructing a mathematical model: the “basic” problem describing the thermal regime of the soil in its natural state (without the influence of the soil heat exchanger of the heat collection system), and the problem being solved, describing the thermal regime of the soil mass with heat sinks (sources). As a result, the method makes it possible to obtain a solution regarding a certain new function, which is a function of the effect of heat sinks on the natural thermal regime of the soil and the equal temperature difference between the soil massif in its natural state and the soil massif with drains (heat sources) - with the soil heat storage system of the heat collection system. The use of this method in the construction of mathematical models of the thermal regime of systems for collecting low-potential soil heat made it possible not only to bypass the difficulties associated with the approximation of external influences on the heat collection system, but also to use in the models the information about the natural thermal regime of the soil, experimentally obtained by meteorological stations. This makes it possible to partially take into account the whole complex of factors (such as the presence of groundwater, their velocity and thermal regimes, the structure and location of soil layers, the "thermal" background of the Earth, atmospheric precipitation, phase transformations of moisture in the pore space, and much more), which significantly affect the formation of the thermal regime of the heat collection system and the joint accounting of which in the strict formulation of the problem is practically impossible.
The method of accounting for the phase transitions of moisture in the pore space of the soil massif in the design of the GTST is based on the new concept of the “equivalent” thermal conductivity of the soil, which is determined by replacing the problem of the thermal regime of the soil cylinder frozen around the pipes of the soil heat exchanger with an “equivalent” quasi-stationary problem with a close temperature field and the same boundary conditions, but with a different "equivalent" thermal conductivity.
The most important task solved in the design of geothermal heating systems for buildings is a detailed assessment of the energy capabilities of the climate in the construction area and, on this basis, drawing up a conclusion on the effectiveness and feasibility of using one or another circuit design of the GTST. The calculated values of climatic parameters given in the current regulatory documents do not give a complete characteristic of the outdoor climate, its variability by months, as well as in certain periods of the year - the heating season, the overheating period, etc. Therefore, when deciding on the temperature potential of geothermal heat, assessing its possibility combination with other natural sources of heat of low potential, assessment of their (sources) temperature level in the annual cycle, it is necessary to attract more complete climatic data, cited, for example, in the Handbook on the climate of the USSR (Leningrad: Gidromethioizdat. Issues 1–34).
Among such climatic information, in our case, it should be highlighted, first of all:
- data on the average monthly soil temperature at different depths;
- data on the arrival of solar radiation on variously oriented surfaces.
Table Figures 1–5 show data on average monthly ground temperatures at different depths for some cities of Russia. Table 1 shows the average monthly soil temperatures in 23 cities of the Russian Federation at a depth of 1.6 m, which seems to be the most rational from the point of view of the temperature potential of the soil and the possibilities of mechanizing the production of works on laying horizontal ground heat exchangers.
| Table 1 Average soil temperatures by months at a depth of 1.6 m for some cities of Russia |
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| table 2 Soil temperature in Stavropol (soil - black soil) |
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| Table 3 Soil temperatures in Yakutsk (silty-sandy soil with an admixture of humus, below - sand) |
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| Table 4 Soil temperatures in Pskov (bottom, loamy soil, subsoil - clay) |
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| Table 5 Soil temperature in Vladivostok (brown stony soil, bulk) |
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The information presented in the tables on the natural course of soil temperatures at a depth of 3.2 m (ie, in the "working" soil layer for a GTST with a horizontal arrangement of a ground heat exchanger) clearly illustrates the possibilities of using soil as a low-potential heat source. The relatively small interval of variation in the temperature of layers located at the same depth on the territory of Russia is obvious. For example, the minimum soil temperature at a depth of 3.2 m from the surface in Stavropol is 7.4 ° C, and in Yakutsk - (–4.4 ° C); accordingly, the interval of soil temperature change at a given depth is 11.8 degrees. This fact makes it possible to count on the creation of a sufficiently unified heat pump equipment suitable for operation practically throughout the entire territory of Russia.
As can be seen from the tables presented, a characteristic feature of the natural temperature regime of the soil is the lag of the minimum soil temperatures relative to the time of arrival of the minimum outside air temperatures. The minimum outside air temperatures are observed everywhere in January, the minimum temperatures in the ground at a depth of 1.6 m in Stavropol are observed in March, in Yakutsk - in March, in Sochi - in March, in Vladivostok - in April. ... Thus, it is obvious that by the time the minimum temperatures in the ground occur, the load on the heat pump heat supply system (heat loss of the building) decreases. This moment opens up quite serious opportunities for reducing the installed capacity of the GTST (saving capital costs) and must be taken into account when designing.
To assess the effectiveness of the use of geothermal heat pump systems for heat supply in the climatic conditions of Russia, zoning of the territory of the Russian Federation was carried out according to the efficiency of using geothermal heat of low potential for heat supply purposes. The zoning was carried out on the basis of the results of numerical experiments on modeling the operating modes of the GTST in the climatic conditions of various regions of the territory of the Russian Federation. Numerical experiments were carried out on the example of a hypothetical two-story cottage with a heated area of 200 m2, equipped with a geothermal heat pump system for heat supply. The external enclosing structures of the house in question have the following reduced heat transfer resistances:
- external walls - 3.2 m 2 h ° C / W;
- windows and doors - 0.6 m 2 h ° C / W;
- coverings and floors - 4.2 m 2 h ° C / W.
When carrying out numerical experiments, the following were considered:
- a system for collecting soil heat with a low density of geothermal energy consumption;
- horizontal heat collection system made of polyethylene pipes with a diameter of 0.05 m and a length of 400 m;
- a system for collecting soil heat with a high density of geothermal energy consumption;
- vertical heat collection system from one thermal well with a diameter of 0.16 m and a length of 40 m.
The studies have shown that the consumption of thermal energy from the soil mass by the end of the heating season causes a decrease in the soil temperature near the register of pipes of the heat collection system, which in the soil and climatic conditions of most of the territory of the Russian Federation does not have time to compensate in the summer period of the year, and by the beginning of the next heating season, the soil comes out with a reduced temperature potential. The consumption of thermal energy during the next heating season causes a further decrease in soil temperature, and by the beginning of the third heating season, its temperature potential is even more different from the natural one. And so on. operation, long-term consumption of thermal energy from the soil massif of the heat collection system is accompanied by periodic changes in its temperature. Thus, when carrying out zoning of the territory of the Russian Federation, it was necessary to take into account the drop in the temperatures of the soil massif caused by the long-term operation of the heat collection system, and use the soil temperatures expected for the 5th year of operation of the GTST as the calculated parameters of the temperatures of the soil massif. Considering this circumstance, when carrying out zoning of the territory of the Russian Federation according to the efficiency of the GTST application, the average heat transformation coefficient K p tr was chosen as a criterion for the efficiency of the geothermal heat pump heat supply system for the 5th year of operation, which is the ratio of the useful thermal energy generated by the GTST to the energy spent on its drive, and determined for the ideal thermodynamic Carnot cycle as follows:
K tr = T about / (T about - T u), (1)
where T about - the temperature potential of the heat removed to the heating or heat supply system, K;
T and is the temperature potential of the heat source, K.
The transformation ratio of the heat pump heat supply system Ktr is the ratio of the useful heat removed to the consumer's heat supply system to the energy spent on the operation of the GTST, and is numerically equal to the amount of useful heat obtained at temperatures T o and T and per unit of energy spent on the drive of the GTST ... The real transformation ratio differs from the ideal one described by formula (1) by the value of the coefficient h, which takes into account the degree of thermodynamic perfection of the GTST and irreversible energy losses during the cycle.
Numerical experiments were carried out using the program created at INSOLAR-INVEST OJSC, which ensures the determination of the optimal parameters of the heat collection system depending on the climatic conditions of the construction area, the heat-shielding qualities of the building, the performance characteristics of the heat pump equipment, circulation pumps, heating devices of the heating system, as well as their modes. exploitation. The program is based on the previously described method for constructing mathematical models of the thermal regime of systems for collecting low-potential soil heat, which made it possible to circumvent the difficulties associated with the informative uncertainty of models and the approximation of external influences, due to the use of experimentally obtained information about the natural thermal regime of the soil in the program, which allows partially taking into account the whole complex of factors (such as the presence of groundwater, their speed and thermal regimes, the structure and location of soil layers, the "thermal" background of the Earth, precipitation, phase transformations of moisture in the pore space, and much more) that significantly affect the formation of the thermal regime of the system heat collection, and the joint accounting of which in a strict formulation of the problem is practically impossible today. As a solution to the "basic" problem, we used the data of the USSR Climate Handbook (Leningrad: Gidromethioizdat. Issue 1–34).
The program actually makes it possible to solve the problem of multi-parameter optimization of the GTST configuration for a specific building and construction area. In this case, the target function of the optimization problem is the minimum annual energy costs for the operation of the GTST, and the optimization criteria are the radius of the pipes of the ground heat exchanger, its (heat exchanger) length and depth.
The results of numerical experiments and zoning of the territory of Russia in terms of the efficiency of using low-potential geothermal heat for heat supply to buildings are presented graphically in Fig. 2-9.
In fig. 2 shows the values and isolines of the transformation ratio of geothermal heat pump heat supply systems with horizontal heat collection systems, and in Fig. 3 - for GTST with vertical heat collection systems. As can be seen from the figures, the maximum values of Kp tr 4.24 for horizontal heat collection systems and 4.14 for vertical systems can be expected in the south of the territory of Russia, and the minimum values, respectively, are 2.87 and 2.73 in the north, in Uelen. For central Russia, the values of K ptr for horizontal heat collection systems are in the range of 3.4–3.6, and for vertical systems, in the range of 3.2–3.4. Sufficiently high values of Кррт (3.2–3.5) for the regions of the Far East, regions with traditionally difficult conditions of fuel supply attract themselves. Apparently, the Far East is the region of the priority implementation of the GTST.
In fig. 4 shows the values and isolines of specific annual energy consumption for the drive of "horizontal" GTST + PD (peak closer), including energy consumption for heating, ventilation and hot water supply, reduced to 1 m 2 of the heated area, and in Fig. 5 - for GTST with vertical heat collection systems. As can be seen from the figures, the annual specific energy consumption for the drive of horizontal GTST, reduced to 1 m2 of heated building area, varies from 28.8 kWh / (year m2) in the south of Russia to 241 kWh / (year m2) in St. Yakutsk, and for vertical GTST, respectively, from 28.7 kWh / / (year m2) in the south and up to 248 kWh / / (year m2) in Yakutsk. If we multiply the value of the annual specific energy consumption for the drive of the GTST presented in the figures for a particular area by the value for this area K r tr, reduced by 1, then we get the amount of energy saved by the GTST from 1 m 2 of the heated area per year. For example, for Moscow for a vertical GTST, this value will be 189.2 kWh from 1 m 2 per year. For comparison, we can cite the values of the specific energy consumption established by the Moscow standards for energy conservation MGSN 2.01–99 for low-rise buildings at 130, and for multi-storey buildings at 95 kWh / (year m 2). At the same time, the standardized MGSN 2.01–99 energy costs include only energy costs for heating and ventilation, in our case, energy costs for hot water supply are also included in energy costs. The fact is that the approach to the assessment of energy costs for the operation of a building existing in the current standards allocates energy costs for heating and ventilation of a building and energy costs for its hot water supply in separate items. At the same time, energy consumption for hot water supply is not standardized. This approach does not seem correct, since the energy consumption for hot water supply is often commensurate with the energy consumption for heating and ventilation.
In fig. 6 shows the values and isolines of the rational ratio of the thermal power of the peak closer (PD) and the installed electrical power of horizontal GTSS in fractions of a unit, and in Fig. 7 - for GTST with vertical heat collection systems. The criterion for the rational ratio of the thermal power of the peak closer and the installed electrical power of the GTST (excluding PD) was the minimum annual electricity consumption for the GTST + PD drive. As can be seen from the figures, the rational ratio of the capacities of the thermal DP and electric GTST (without DP) varies from 0 in the south of Russia, to 2.88 - for horizontal GTST and 2.92 for vertical systems in Yakutsk. In the central zone of the territory of the Russian Federation, the rational ratio of the thermal power of the closer and the installed electrical power of the GTST + PD is in the range of 1.1–1.3 for both horizontal and vertical GTST. At this point, you need to dwell in more detail. The fact is that when replacing, for example, electric heating in the Central zone of Russia, we actually have the opportunity to reduce the capacity of the electrical equipment installed in the heated building by 35-40% and, accordingly, reduce the electric power requested from RAO UES, which today “costs »About 50 thousand rubles. for 1 kW of electric power installed in the house. So, for example, for a cottage with an estimated heat loss in the coldest five-day period equal to 15 kW, we will save 6 kW of installed electrical power and, accordingly, about 300 thousand rubles. or ≈ 11.5 thousand US dollars. This figure is practically equal to the cost of a GTST of such heat capacity.
Thus, if we correctly take into account all the costs associated with connecting a building to a centralized power supply, it turns out that with the current tariffs for electricity and connecting to centralized power supply networks in the central zone of the Russian Federation, even at a one-time cost, the GTST turns out to be more profitable than electric heating, not to mention 60 % energy saving.
In fig. 8 shows the values and isolines of the specific weight of thermal energy generated during the year by the peak closer (PD) in the total annual energy consumption of the horizontal GTST + PD system in percent, and in Fig. 9 - for GTST with vertical heat collection systems. As can be seen from the figures, the specific weight of thermal energy generated during the year by the peak closer (PD) in the total annual energy consumption of the horizontal GTST + PD system varies from 0% in southern Russia to 38–40% in Yakutsk and Tura, and for vertical GTST + PD - respectively, from 0% in the south and up to 48.5% in Yakutsk. In the Central zone of Russia, these values are about 5–7% for both vertical and horizontal GTST. This is a small energy consumption, and in this regard, you need to be careful when choosing a peak closer. The most rational from the point of view of both the specific capital investment in 1 kW of power, and automation are peak electrodes. The use of pellet boilers deserves attention.
In conclusion, I would like to dwell on a very important issue: the problem of choosing a rational level of thermal protection of buildings. This problem is today a very serious task, for the solution of which a serious numerical analysis is required, taking into account both the specifics of our climate, and the features of the engineering equipment used, the infrastructure of centralized networks, as well as the ecological situation in cities, which is literally deteriorating before our eyes, and much more. It is obvious that today it is already incorrect to formulate any requirements for the shell of a building without taking into account its (building) relationships with the climate and the energy supply system, utilities, etc. As a result, in the very near future, the solution to the problem of choosing a rational level of thermal protection will be possible only on the basis of considering the complex building + energy supply system + climate + environment as a single eco-energy system, and with this approach, the competitive advantages of the GTST in the domestic market can hardly be overestimated.
Literature
1. Sanner B. Ground Heat Sources for Heat Pumps (classification, characteristics, advantages). Course on geothermal heat pumps, 2002.
2. Vasiliev GP Economically reasonable level of thermal protection of buildings. Energosberezhenie. - 2002. - No. 5.
3. Vasiliev GP Heat and cold supply of buildings and structures with the use of low-potential thermal energy of the surface layers of the Earth: Monograph. Publishing house "Granitsa". - M.: Krasnaya Zvezda, 2006.
In our country rich in hydrocarbons, geothermal energy is an exotic resource that, given 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 is quite efficient.
Geothermal energy is the warmth 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 a 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 cover deeper layers of soil - up to tens of meters.
At a certain depth - from tens to hundreds of meters - the soil temperature is kept constant, equal to the average annual air temperature at the Earth's surface. It is easy to be convinced of this by going down into a sufficiently 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 out on top and the earth's interior heats up from the inside, so that the temperature begins to rise with depth.
The heating of the deep layers of the Earth is mainly associated with the decay of the radioactive elements located there, although other sources of heat are also called, for example, physicochemical, tectonic processes in the deep layers of the earth's crust and mantle. But whatever the reason, the temperature of rocks and associated liquid and gaseous substances grows with depth. Miners are faced with 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 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).
The insignificance of the heat flow from the depths to the surface on 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 an outlet. Such zones are characterized by thermal anomalies of the lithosphere, here the heat flux reaching the Earth's surface can be several times and even orders of magnitude more powerful than the "usual" one. Volcanic eruptions and hot water springs carry a huge amount of heat to the surface in these zones.
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 an 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 at different depths to the difference in depth between them is called the geothermal gradient.
The reciprocal is the geothermal step, or depth interval, at which the temperature rises by 1 ° C.
The higher the gradient and, accordingly, the lower the step, the closer the warmth of the depths of the Earth comes to 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 rise with depth can vary dramatically. On the Earth's scale, fluctuations in the magnitudes of geothermal gradients and steps reach 25 times. For example, in Oregon (USA) the gradient is 150 ° C per km, and in South Africa it is 6 ° C per km.
The question is, what is the temperature at great depths - 5, 10 km or more? If the trend continues, temperatures at 10 km depth should average around 250–300 ° C. This is more or less confirmed by direct observations in superdeep 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 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 was already recorded, at a depth of 10 km - 180 ° C, and at 12 km - 220 ° C.
Another example is a well drilled in the Northern Caspian region, where a temperature of 42 ° C was recorded at a depth of 500 m, 70 ° C at 1.5 km, 80 ° C at 2 km, and 108 ° C at 3 km.
It is assumed that the geothermal gradient decreases starting from a depth of 20-30 km: at a depth of 100 km, the assumed temperatures are about 1300-1500 ° C, at a depth of 400 km - 1600 ° C, in the Earth's core (depths over 6000 km) - 4000-5000 ° C.
At depths of up to 10–12 km, the temperature is measured through drilled wells; where they are absent, 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 outflowing 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 this problem is solved for us by nature itself with the help of a natural heat carrier - 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 term "thermal waters". As a rule, they mean hot groundwater in a liquid state or in the form of steam, including those coming out 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, the 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 rather high temperatures, as a rule, start 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 - 3500 and 35 trillion tons of fuel equivalent, respectively. This is quite natural - the warmth of the depths of the Earth is everywhere, and thermal waters are found locally. However, due to obvious technical difficulties for generating heat and electricity, thermal waters are currently used mostly.
Waters with temperatures between 20-30 ° C and 100 ° C are suitable for heating, temperatures between 150 ° C and above - and for generating electricity in geothermal power plants.
In general, geothermal resources on the territory of Russia in terms of tons of equivalent fuel or any other unit of energy measurement are about 10 times higher than the reserves of fossil fuel.
Theoretically, only geothermal energy could fully satisfy the country's energy needs. 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 Eyjafjallajokull volcano ( Eyjafjallajökull) in 2010 year.
It is thanks to this geological specificity that Iceland has enormous reserves of geothermal energy, including hot springs that come out to the surface of the Earth and even gush out in the form of geysers.
In Iceland, more than 60% of all energy consumed is currently taken from the Earth. Including geothermal sources provide 90% of heating and 30% of electricity generation. We add that the rest of the country's electricity is produced at hydroelectric power plants, that is, also using a renewable energy source, thanks to which Iceland looks like a kind of global environmental standard.
The domestication of geothermal energy in the 20th century helped Iceland noticeably 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 value of 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 needs for it are 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 (the Philippines and Indonesia), countries of Central America and East Africa, the territory of which is also characterized by high seismic and volcanic activity. For these countries, given 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, the local hot thermal waters, poured out naturally or extracted from shallow wells, were used for energy purposes.
Boron-rich underground water was used here to obtain boric acid. Initially, this acid was obtained by evaporation in iron boilers, and ordinary firewood from the nearby forests was taken as fuel, 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.
Some other countries followed the example of Italy in the late 19th and early 20th centuries. For example, in 1892, thermal waters were first used for local heating in the United States (Boise, Idaho), in 1919 in Japan, and 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 geothermal power plant) in 1965 ...
Old principle on a new source
Electricity generation requires a higher temperature of the hydro source than for heating - more than 150 ° C. The principle of operation of a geothermal power plant (GeoPP) is similar to the principle of operation of a conventional thermal power plant (TPP). In fact, a geothermal power plant is a kind of thermal power plant.
At TPPs, as a rule, coal, gas or fuel oil act as the primary source of energy, and water vapor serves as the working fluid. Fuel, burning, heats water to the state of steam, which rotates the steam turbine, and it generates electricity.
The difference between GeoPPs 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 is supplied to the turbine blades of an electric generator in a "ready-made" 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 application of this or that 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 straight line, in which the steam coming from the well is passed directly through the turbine. The world's first GeoPP in Larderello also operated on dry steam in 1904.
GeoPPs with an indirect scheme of work are the most common in our time. They use hot underground water, which is pumped into an evaporator under high pressure, 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.
Waste steam enters the injection well or is used for space heating - in this case, the principle is the same as in 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 fluids are passed through a heat exchanger, where thermal water evaporates the working fluid, the vapor of which rotates 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 schematic diagram in this case is also quite simple. It is necessary to drill two interconnected wells - injection and production wells. 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 the production well. Further, it all depends on how petrothermal energy is used - for heating or for generating electricity. A closed cycle is possible with the injection of waste steam and water back into the injection well or another way of disposal.
The disadvantage of such a system is obvious: to obtain a sufficiently high temperature of the working fluid, it is necessary to drill wells to a great depth. And these are serious costs and the risk of significant heat loss when the fluid moves upward. Therefore, petrothermal systems are still less widespread than hydrothermal ones, although the potential of petrothermal energy is orders of magnitude higher.
Currently, Australia is the leader in the creation of the so-called petrothermal circulation systems (PCS). In addition, this direction of geothermal energy is actively developing in the USA, Switzerland, Great Britain, and Japan.
Lord Kelvin's gift
The invention of a heat pump by physicist William Thompson (aka Lord Kelvin) in 1852 provided mankind with a real opportunity to use the low-potential heat of the upper soil layers. The heat pump system, or, as Thompson called it, the heat multiplier, 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 heat source, 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 to 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 work of a heat pump is based on a 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 water bodies. The main purpose of heat pumps is space heating. In fact, it is a “reverse refrigerator”. Both the heat pump and the refrigerator interact with three components: the internal environment (in the first case - the heated room, in the second - the refrigerated chamber of the refrigerator), the external environment - the energy source and the refrigerant (coolant), it is also the heat carrier 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 that requires external heat absorption. 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 a reverse process leading to the release of the removed heat into the external environment. As a rule, it is thrown into the room and the back of the refrigerator is relatively warm.
A heat pump works in much the same way, with the difference that heat is taken from the external environment and through the evaporator enters the internal environment - the room heating system.
In a real heat pump, water is heated, passing along an external circuit, laid in the ground or in a reservoir, and 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 to a gaseous state, taking heat away.
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 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 is high enough to ensure their efficiency.
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, a GeoPP occupies 400 m 2 in terms of 1 GW of generated electricity. The same indicator for a coal-fired power plant, for example, is 3600 m 2. The ecological advantages of GeoPPs also include low water consumption - 20 liters of fresh water per 1 kW, while TPPs and NPPs require about 1000 liters. Note that these are environmental indicators of the "average" GeoPP.
But there are still negative side effects. Among them, noise, thermal pollution of the atmosphere and chemical pollution - 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 the actual thermal water (with high temperature and mineralization), which often contains large amounts of toxic compounds, in connection with which there is a problem of disposal of waste water and hazardous substances.
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 soil and vegetation cover, soil and groundwater pollution.
At the stage of operation of the GeoPP, the problems of environmental pollution persist. Thermal fluids - water and steam - usually 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 its pollution. In addition, an aggressive chemical environment can cause corrosion damage to the structures of the GeoTPP.
At the same time, emissions of pollutants at GeoPPs are on average lower than at TPPs. For example, carbon dioxide emissions for each kilowatt-hour of generated electricity are up to 380 g at GeoPPs, 1,042 g - at coal-fired TPPs, 906 g - at fuel oil and 453 g - at gas-fired TPPs.
The question arises: what to do with the waste water? With low salinity, it can be discharged into surface waters after cooling. Another way is to pump it back into the aquifer through an injection well, which is preferred and predominantly used today.
Extraction of thermal water from aquifers (as well as pumping out ordinary water) can cause subsidence and movement of the soil, other deformations of geological layers, and micro-earthquakes. The likelihood of such phenomena, as a rule, is small, 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 more extensive 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 $ 5,000 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 purification can multiply the cost.
For example, investments in the creation of a petrothermal circulation system (PCS) are estimated at 1.6–4 thousand dollars per 1 kW of installed capacity, which exceeds the cost of building a nuclear power plant and is comparable to the cost 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 TPP or NPP, 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 produced capacity.
The second largest (after energy carrier) (and very significant) item of expenditure is, as a rule, the salaries of plant personnel, which can radically differ 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 generating electricity at hydroelectric power plants (5-10 kopecks / 1 kWh ).
Part of the reason for the high cost lies in the fact 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. For example, in Kamchatka, according to experts, 1 kWh of geothermal electricity costs 2-3 times less than electricity produced at local thermal power plants.
The indicators of the economic efficiency of a geothermal system depend, for example, on whether it is necessary to dispose of waste water and in what ways it is done, whether a combined use of the resource is possible. Thus, chemical elements and compounds extracted from thermal water can provide additional income. Let us recall the example of Larderello: it was chemical production that was primary there, and the use of geothermal energy was initially auxiliary.
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, associated, as a rule, with areas of tectonic faults and volcanism.
In addition, geothermal energy is less technologically capacious in comparison with wind, and even more so with solar energy: the systems of geothermal plants are quite simple.
In the total 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 the third world countries, where there are three clusters of the industry's greatest development - the islands of Southeast Asia, Central America and East Africa. The first two regions are included in the Pacific "Earth's fire belt", the third is tied to the East African Rift. 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 layers of the earth, lying at a depth of several kilometers. This is an almost ubiquitous resource, but its extraction requires high costs; therefore, petrothermal energy is developing primarily in the most economically and technologically powerful countries.
In general, given the ubiquitous distribution 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 sources 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 total energy balance of a huge country is still negligible.
Two regions - Kamchatka and the North Caucasus - have become pioneers and centers for the development of geothermal energy in Russia, 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 the Krasnodar Territory, Chechnya, Dagestan - the heat of thermal waters for energy purposes was used even before the Great Patriotic War. In the 1980s and 1990s, the development of geothermal energy in the region for obvious reasons stalled and has not yet emerged from a state of stagnation. Nevertheless, geothermal water supply in the North Caucasus provides heat to 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 GeoPPs. 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 Thermophysics of the SB RAS, who in 1965 received an author's certificate for the extraction of electricity from water with a temperature of 70 ° C. This technology later became a 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, a binary block is under construction at the station, which will increase its capacity by another 2.5 MW.
The development of geothermal energy in the USSR and Russia was hampered by the availability of traditional energy sources - oil, gas, coal, but never stopped. The largest geothermal energy 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 GeoPPs 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 9-10 months a year. The equipment of the Mutnovsky GeoPPs, currently one of the most modern in the world, is completely created at domestic enterprises of power engineering.
At present, the share of Mutnovskie plants in the total 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 have large DSPs yet, but there are advanced technologies for drilling to great depths (about 10 km), which also have no analogues in the world. Their further development will make it possible to drastically reduce the cost of creating petrothermal systems. The developers of these technologies and projects are N. A. Gnatus, M. D. Khutorskoy (Geological Institute, RAS), A. S. Nekrasov (Institute of Economic Forecasting, RAS) and specialists from the Kaluga Turbine Works. The project for a petrothermal circulation system in Russia is currently at an experimental stage.
There are prospects for geothermal energy in Russia, albeit relatively distant: at the moment, the potential is quite large and the positions of traditional energy are 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 now. These are territories with high geoenergetic potential (Chukotka, Kamchatka, Kuriles - the Russian part of the Pacific "Earth's fire belt", the mountains of South Siberia and the Caucasus) and at the same time remote and cut off from the centralized energy supply.
Probably, in the coming decades, geothermal energy in our country will develop precisely in such regions.