Methods of electrical heating. Direct conversion of nuclear heat into electricity

Among the many devices that allow you to receive electricity, a special place is occupied by devices that allow you to convert thermal energy into electrical energy. Their main task is the direct conversion of one type of energy into another with a minimum number of different intermediate links. At the same time, the problem of increasing the efficiency of this process is being solved.

Converter device

The converter device consists of heated elements and electrical energy. For the manufacture of heated elements, a soft magnetic material is used, the Curie point of which is lowered. It loses its magnetic qualities when heated and exhibits a phase transition.

These elements are included in the magnetic circuit in the shape of the letter F. It has one middle and two side rods. The side rods consist of two elements, between which there are air gaps. They are adjacent to the middle rod and relative to it are located symmetrically on both sides.

The connection of the heated elements is carried out using a rigid bar. It is mounted on a hinge located at the edge of the middle rod along the axis of symmetry. When the bar changes its position, the heated elements in turn bridge the air gaps of the side rods. A heat pipe is located in the air gaps, with the help of which heat is supplied from the heater. In the absence of bridging of air gaps, the heated elements come into contact with the cooler. In the middle rod there is an excitation winding powered by direct current, the generating windings of the generator are located on the side rods.

Practical operation of the converter

The conversion of thermal energy into electrical energy is carried out according to a certain scheme. When power is applied to the winding, a magnetic flux is generated, which diverges along the side rods. The movable element is attracted to the side rod and closes the required air gap. There is an increase in the magnetic flux, while the heated element falls under the influence of the heat conductor. It is heated to a certain temperature at which the loss of magnetic properties occurs.

The movable element is attracted to the gap and the magnetic circuit of the side rod is closed. Thus, in one of the side rods the magnetic field increases, and in the other it falls. This process is repeated many times. The end result of all these actions is . Its quantity and power completely depend on the rate at which heat and cooling are supplied. From the same envy and efficiency of the entire system.

Physical current sources

Thermogenerators: how to "weld" electricity on gas stove

On one of the electrical forums, the following question was asked: How can I get electricity using ordinary household gas? This was motivated by the fact that this comrade's gas, and in fact, like many others, is paid simply according to the standards without a meter.

No matter how much you use it, you still pay a fixed amount, and why not turn already paid, but not used gas into free electricity? So a new topic appeared on the forum, which was picked up by the rest of the participants: a heart-to-heart conversation helps not only shorten the working day, but also kill free time.

Many options have been proposed. Just buy gasoline generator, and fill it with gasoline obtained by distillation of domestic gas, or convert the generator to work immediately on gas, like a car.

Instead of an internal combustion engine, a Stirling engine, also known as an external combustion engine, was proposed. Here are just a topikstarter (the one who created a new topic) claimed a generator power of at least 1 kilowatt, but he was reasoned with, they say, such a stirling would not fit even in the kitchen of a small dining room. In addition, it is important that the generator is silent, otherwise, well, you know what.

After many suggestions, someone remembered seeing a drawing in some book showing a kerosene lamp with a device in the form of a multi-beam star for powering a transistor receiver. But this will be discussed a little further, but for now

Thermogenerators. History and theory

In order to get electricity directly from a gas burner or other heat source, thermogenerators are used. Just like a thermocouple, their principle of operation is based on the Seebeck effect. opened in 1821.

The effect mentioned is that an emf appears in a closed circuit of two dissimilar conductors. if the junctions of the conductors are at different temperatures. For example, a hot junction is in a vessel of boiling water, and the other is in a cup of melting ice.

The effect arises from the fact that the energy of free electrons depends on temperature. In this case, the electrons begin to move from the conductor, where they have a higher energy to the conductor, where the energy of the charges is less. If one of the junctions is heated more than the other, then the difference in the energies of the charges on it is greater than on the cold one. Therefore, if the circuit is closed, a current appears in it, exactly the same thermoelectric power.

Approximately, the thermoelectric power can be determined by a simple formula:

E = &alpha * (T1 - T2). Here α is the thermoelectric coefficient, which depends only on the metals from which the thermocouple or thermoelement is composed. Its value is usually expressed in microvolts per degree.

The temperature difference of the junctions in this formula is (T1 - T2): T1 is the temperature of the hot junction, and T2, respectively, of the cold junction. The above formula is quite clearly illustrated in Figure 1.

Figure 1. The principle of operation of a thermocouple

This drawing is classic, it can be found in any physics textbook. The figure shows a ring made up of two conductors A and B. The junctions of the conductors are called junctions. As shown in the figure, in the hot junction T1, the thermoelectric power has a direction from metal B to metal A. And in the cold junction T2, from metal A to metal B. The direction of thermoelectric power indicated in the figure is valid for the case when the thermoelectric power of metal A is positive with respect to metal B .

How to determine the thermopower of a metal

The thermoelectric power of the metal is determined with respect to platinum. To do this, a thermocouple, one of the electrodes of which is platinum (Pt), and the other is the metal under test, is heated to 100 degrees Celsius. The resulting value in millivolts for some metals is shown below. Moreover, attention should be paid to the fact that not only the thermopower value changes, but also its sign with respect to platinum.

Platinum in this case plays the same role as 0 degrees on the temperature scale, and the entire scale of thermopower values ​​looks like in the following way:

Antimony +4.7, iron +1.6, cadmium +0.9, zinc +0.75, copper +0.74, gold +0.73, silver +0.71, tin +0.41, aluminum + 0.38, mercury 0, platinum 0.

After platinum come metals with a negative thermoelectric power:

Cobalt -1.54, nickel -1.64, constantan (an alloy of copper and nickel) -3.4, bismuth -6.5.

Using this scale, it is very easy to determine the thermopower value developed by a thermocouple made up of various metals. To do this, it is enough to calculate the algebraic difference between the values ​​of the metals from which the thermoelectrodes are made.

For example, for a pair of antimony - bismuth, this value will be +4.7 - (- 6.5) \u003d 11.2 mV. If an iron-aluminum pair is used as electrodes, then this value will be only +1.6 - (+0.38) = 1.22 mV, which is almost ten times less than that of the first pair.

If the cold junction is maintained at a constant temperature, for example 0 degrees, then the thermoelectric power of the hot junction will be proportional to the change in temperature, which is used in thermocouples.

How thermogenerators were created

Already in the middle of the 19th century, numerous attempts were made to create thermogenerators- devices for generating electrical energy, that is, for supplying various consumers. As such sources, it was supposed to use batteries of series-connected thermoelements. The design of such a battery is shown in Figure 2.

Figure 2. Thermopile, schematic device

First t thermoelectric battery created in the middle of the 19th century by the physicists Oersted and Fourier. Bismuth and antimony were used as thermoelectrodes, just the same pair of pure metals, which has the maximum thermoelectric power. Hot junctions heated up gas burners, and the cold ones were placed in a vessel with ice.

In the process of experiments with thermoelectricity, thermopiles were later invented, suitable for use in some technological processes and even lighting. An example is the Clamont battery, developed in 1874, whose power was quite enough for practical purposes: for example, for electroplating gilding, as well as for use in printing houses and photogravure workshops. At about the same time, the scientist Noe was also engaged in the study of thermopiles, his thermobatteries were also widely distributed at one time.

But all these experiments, although successful, were doomed to failure, since thermopiles based on pure metal thermoelements had a very low efficiency, which hindered their practical application. Pure metal vapors have an efficiency of only a few tenths of a percent. Semiconductor materials have a much higher efficiency: some oxides, sulfides and intermetallic compounds.

Semiconductor thermoelements

A genuine revolution in the creation of thermoelements was made by the works of Academician A.I. Ioffe. In the early 30s of the XX century, he put forward the idea that with the help of semiconductors it is possible to convert thermal energy, including solar energy, into electrical energy. Thanks to the research, already in 1940, a semiconductor photocell was created to convert solar light energy into electrical energy.

First practical application semiconductor thermoelements it should be considered, apparently, a partisan kettle, which made it possible to provide power to some portable partisan radio stations.

The thermogenerator was based on elements from constantan and SbZn. The temperature of the cold junctions was stabilized by boiling water, while the hot junctions were heated by a fire flame, thus ensuring a temperature difference of at least 250,300 degrees. The efficiency of such a device was no more than 1.5-2.0%, but there was enough power to power the radio stations. Of course, in those war times, the design of the bowler hat was a state secret, and even now its device is being discussed on many forums on the Internet.

Household thermogenerators

Already in the post-war fifties Soviet industry started production thermogenerators TGK - 3. Its main purpose was to power battery radios in non-electrified rural areas. The generator power was 3 W, which made it possible to power battery receivers, such as Tula, Iskra, Tallinn B-2, Rodina - 47, Rodina - 52 and some others.

Appearance thermogenerator TGK-3 is shown in Figure 3.

Figure 3. Thermogenerator TGK-3

Thermogenerator design

As already mentioned, the thermogenerator was intended for use in rural areas, where kerosene lamp lightning. Such a lamp, equipped with a thermogenerator, became not only a source of light, but also electricity.

At the same time, additional fuel costs were not required, because it was precisely that part of the kerosene that simply flew into the pipe that turned into electricity. In addition, such a generator was always ready to work, its design was such that there was simply nothing to break in it. The generator could just lie idle, work without load, was not afraid short circuits. The service life of the generator, in comparison with galvanic batteries, seemed simply eternal.

The role of the exhaust pipe for a kerosene lamp is played by an elongated cylindrical part of the glass. When using a lamp together with a thermogenerator, the glass was made shortened, and a metal heat transfer device 1 was inserted into it, as shown in Figure 4.

Figure 4 Kerosene lamp with thermoelectric generator

The outer part of the heat transfer device has the shape of a polyhedral prism on which thermopiles are installed. To increase the efficiency of heat transfer, the heat transfer device had several longitudinal channels inside. Passing through these channels, hot gases went into exhaust pipe 3, simultaneously heating the thermopile, more precisely, its hot junctions.

A radiator was used to cool the cold junctions. air cooling. It consists of metal ribs attached to external surfaces thermopile blocks.

Thermogenerator - TGK3 consisted of two independent sections. One of them generated a voltage of 2V at a load current of up to 2A. This section was used to obtain the anode voltage of the lamps using a vibration transducer. Another section at a voltage of 1.2V and a load current of 0.5A was used to power the filaments of the lamps.

It is easy to calculate that the power of this thermogenerator did not exceed 5 watts, but it was quite enough for the receiver, which made it possible to brighten up long winter evenings. Now, of course, it seems simply ridiculous, but in those distant times such a device was undoubtedly a miracle of technology.

In 1834, the Frenchman Jean Charles Athanase Peltier discovered an effect opposite to the Seebik effect. The meaning of the discovery is that when current passes through a junction of dissimilar materials (metals, alloys, semiconductors), heat is released or absorbed, which depends on the direction of the current and the types of materials. This is described in detail here: Peltier effect: the magical effect of electric current

Tags: nanotechnology, physics

Physicists from Spain, USA and Switzerland have created a microscopic device for converting heat into electricity. It is based on the so-called quantum dots.

In the pages of Physical Review B, the researchers described the system they had developed. which allows you to convert thermal energy into electrical energy - however, for this, heating must be uneven. Around the heated area are the so-called quantum dots, between which electrons can move; they are placed so that thermal vibrations transfer charge carriers only in a certain direction.

Quantum dots, in turn, are tiny (less than 10 nm - 50 atoms - across) pieces of semiconductor material. Due to their very small size, they no longer behave like a solid block of material, but as analogues of individual atoms, they have their own energy levels and electrons at such points can only be in states with a certain energy. And, accordingly, to move from one state to another, from one energy level to another.

The presence of individual energy levels also means that when going from higher levels to lower quantum dots, they can fluoresce beautifully. Moreover, the size of the gap depends only on the size of the quantum dots, so you can get any desired color luminescence quantum dots are already actively used as special dyes. Photo: Wikimedia/Travis.jennings

A heated quantum dot is a dot that has received a certain portion of energy, because temperature, by definition, is the average energy of microscopic particles. The laws of thermodynamics also cause this energy to dissipate (which is why all heated objects cool down), but here the quantum properties of nanodots come to the fore. Since they have only a limited number of energy levels, they cannot let through all the electrons, but only those particles whose energy corresponds to the difference between one level and another.

There are such electrons in the heated region and they safely overcome the barrier. After that, they give off energy in the cold section, but it is no longer possible to go back due to a lack of energy. As a result, an electric charge accumulates at one end of the chain of quantum dots. Where is the charge - there and electric field with its tension and potential where the potential difference, there is voltage. Battery is ready!

Solar panels, recall, use similar principle: light quanta first transfer electrons through some energy barrier, and then the electrons accumulate in one area, creating an electric field and a potential difference. A new study has made it possible to transfer this approach to nanosystems and thermal energy, so no overturning of the foundations and a perpetual motion machine is expected here. Only devices are foreseen that will utilize thermal energy, turning it into electricity directly, bypassing complex mechanical devices like a Stirling engine.

No, this is not your case.

Note that this work has nothing to do with all kinds of inventions with an efficiency of over 100%. It in no way confirms the correctness of all home-grown debunkers of the foundations, if only because the theoretical efficiency of a nanoconverter is accurately described by the school formula - the temperature of the heater in degrees Kelvin divided by the temperature difference between the heater and the refrigerator. In the nanoworld, random and local violations the laws of thermodynamics (say, gas molecules will gather in one half of the vessel. all five molecules at once) - but this also cannot be used to build a perpetual motion machine.

As you know, all bodies are made up of molecules, and these molecules are not at rest, but are constantly moving. The higher the temperature of the body, the faster the movement of the molecules of the substance of this body. When an electric current passes through a conductor, the electrons collide with the moving molecules of the conductor and increase their movement, which leads to heating of the conductor.

An increase in the temperature of the conductor occurs as a result of the conversion of electrical energy into thermal energy. Earlier (see § 13) an expression was obtained for the work of an electric current (electrical energy)

A \u003d I 2 rt joules.

This relationship was initially (in 1841) established as a result of experiments by the English physicist Joule and somewhat later (in 1844) independently by the Russian academician Lenz.

In order for the amount of received thermal energy to be expressed in calories, it is necessary to additionally enter a factor of 0.24, since 1 J = 0.24 cal. Then Q = 0.24I 2 rt. This equation expresses the Joule-Lenz law.

Emil Khristianovich Lenz (1804-1865) established laws thermal action current, generalized experiments on electromagnetic induction, setting out this generalization in the form of "Lenz's rule". In his writings on the theory electrical machines Lenz described the phenomenon of "armature reaction" in DC machines, proved the principle of reversibility of electrical machines. Lenz, working with Jacobi, investigated the force of attraction of electromagnets, established the dependence of the magnetic moment on the magnetizing force.

Thus, the amount of heat generated by the current when passing through the conductor depends on the resistance r of the conductor itself, the square of the current I 2 and the duration of its passage t.

Example 1. Determine how much heat a current of 6 A will release, passing through a conductor with a resistance of 2 ohms for 3 minutes.

Q \u003d I 2 rt \u003d 36 ⋅ 2 ⋅ 180 \u003d 12960 J.

The formula for the Joule-Lenz law can be written as follows.

INVENTION
Patent Russian Federation RU2121246

METHOD OF CONVERTING ELECTRIC ENERGY INTO HEAT
AND CREATING THE HEAT TRANSFER

Inventor's name: Kukushin Viktor Panteleevich
Name of the patentee: Kukushin Viktor Panteleevich
Address for correspondence:
Start date of the patent: 1997.04.16

The method is carried out by using one or more closed turns of an electric current conductor as a heating element, which form the secondary winding of an electric transformer, and by introducing the coolant into contact with the surfaces of the conductor. EFFECT: invention improves the reliability of electrical energy conversion during heat exchange.

DESCRIPTION OF THE INVENTION

The invention relates to a technology for converting electrical energy into thermal energy and creating heat transfer. It can be used for liquid heating in systems of preheating of internal combustion engines, heating and hot water supply of industrial enterprises and residential buildings, for heating plasma and other substances.

A known method of converting electrical energy into thermal energy and creating heat transfer, based on the direct transmission of electric current through the coolant, created by supplying the mains voltage through the current leads to the electrodes ( see A.P. Althausen et al., "Low-temperature electric heating", Moscow, Energia, 1968). It is used to heat liquids, concrete, to thaw soils, ore, sand and other substances. The main disadvantages of this method are increased electrical hazard due to relatively high voltages ( 380V or 220V), as well as the dependence of electric heating and heat transfer on the electrical resistance of the coolant. In particular, special additives are added to the heated water in order to provide a given value of electrical resistance.

There is a known method of converting electrical energy into thermal energy and creating heat exchange between the heating element and the coolant, including supplying power to the heating element, which is a metal tube, inside which there is a heating coil pressed into a special filler, passing electric current through the heating coil ( see A.P. Althausen et al., "Low-temperature electric heating", Moscow, Energia, 1968). This method has become widespread in various fields. National economy. Tubular electric heater ( heating element) can be placed in water, salt, liquid metal, mold, crankcase of an internal combustion engine, etc. However, electrical voltage is supplied to the heated coil directly from the mains, and the relatively high electrical resistance of the coil does not allow to reduce the applied voltage, which entails the need for electrical insulation of the coil to ensure electrical safety and which in turn reduces the thermal conductivity between the coil and the metal tube, and therefore worsens heat transfer. between heating element (ohm) and coolant in general. The electrical insulation of the spiral does not exclude the possibility of its electrical breakdown and contact with a metal tube TEN (a) high electrical potential, which leads to the need for its grounding. Besides, heating element(s) have a limited service life due to coil burnout.

A known method of converting electrical energy into thermal energy and creating heat transfer, called "Contact welding" (see N.S. Kabanov, "Welding on contact machines", Moscow, ed. "Higher School", 1985; Yu.N. Bobrinsky and N.P. Sergeev, "Design and adjustment contact welding machines", Moscow, ed. "Engineering", 1967; V.G. Gevorkyan, "Fundamentals of Welding", Moscow, ed. "Higher School", 1991). In this method, the heating element and the coolant is the metal being welded, which closes the secondary winding of the welding transformer, as a result of which an electric current flows through the closed circuit, sufficient to heat and weld the metal. In this case, each turn of the secondary winding of the transformer is a separate source of electricity, since it covers the same magnetic flux created in the magnetic circuit by the primary winding of the transformer.

This method is a prototype. The disadvantage of this method is that it is applicable only to coolants with relatively low electrical resistance. In the case of using a liquid, for example water, it would be necessary to refuse to lower the voltage using a transformer, and the method would turn into the first one considered with all its shortcomings.

The safety and reliability of converting electrical energy into thermal energy, the efficiency of heat transfer in the proposed method are achieved by using a closed loop of an electric current conductor or several turns forming the secondary winding of the transformer as a heating element, and introducing the coolant into contact with the surfaces of the conductor. When closing the coil of the conductor, covering the magnetic circuit of the transformer, it is induced EMF less than the number of turns supplied to the primary winding, which ensures electrical safety, and the current flowing through the closed coil increases sharply due to the low electrical resistance of the coil and heats it regardless of the electrical resistance of the coolant. At the same time, the direct contact of the coolant with the surfaces of a closed loop of the conductor increases the efficiency of heat transfer due to a sharp decrease in heat losses. Conditions can be created that exclude the possibility of coil burnout, which ensures the reliability of the conversion.

The drawing shows an example of equipment that implements the proposed method.

The method is carried out as follows. With the switch K the primary winding of the transformer with the number of turns W 1 connect to the network alternating current. In the magnetic circuit 1, an alternating magnetic flux occurs, which induces EMF in closed turns of conductors 2 and 3 and induces an electric current in them, heating them. Conductor 2 is made in the form of a pipe, conductor 3 is made of a closed bundle copper wires. A cold coolant is introduced at inlet A, for example, water, which enters the conductor 2 and washes the conductor 3 from the outside. Heat exchange occurs through the interfaces of conductors 2 and 3 and the coolant, the coolant heats up and, due to convection, enters the outlet B. In one particular case, conductor 3 may be absent (it is needed when the electrical resistance of conductor 2 is not consistent with the power of the transformer). In another particular case, in order to prevent heat dissipation from the outer surface of conductor 2, instead of conductor 2, an electrical insulating pipe can be used, and then heat will flow into the coolant only from conductor 3. In the third case, the coolant itself, placed inside the insulating pipe, can be the conductor or in the volume of another form, covering the magnetic core.

EXAMPLE OF SPECIFIC IMPLEMENTATION OF THE METHOD

A stamped steel radiator of the 2M3-500 brand was taken (see p. 189, Handbook of Special Works edited by N.A. Kokhanenko, Moscow, building literature ed., 1964) with an equivalent heating surface 3.53 ekm(equivalent to 11 - sectional cast iron radiatorM-140 according to GOST 8690-58) with capacity 13.3 l. From a steel pipe with a diameter 3/4"" a closed coil was made, covering the magnetic circuit of the power supply transformer with a power of 1.5 kW. The inlet of coil A was connected to the outlet (pipe at the bottom of the vertically mounted radiator), and the outlet of coil B was connected to the inlet of the radiator (pipe at the top) using rubber hoses. An expansion tank was installed at the top of the radiator with a capacity of 0.25 l. Then the system (radiator - turn) was filled with water and the primary winding of the transformer was connected to the network with voltage 220 V. The temperature surrounding the radiator before turning on the transformer was 4.5°C in the volume of the room 300 m 3. After switching on the transformer, the electric voltage on the coil was measured 0.8 V and the electric current passing through the coil, which amounted to 1875 A. Through 20 minutes the temperature of the water in the radiator has risen to 96oC(the initial water temperature was 12oC), after which, with the help of a thyristor control system, the power consumed from the network was initially reduced to 800 W 82oC and then through 2 hours up to 500 W, which ensured that the water temperature was maintained at 60oC. As a result of a 4-hour test, the room temperature reached 18oC. The next day the system was turned on for power consumption. 1.5 kW. Through 4 hours the room temperature has reached 23oC, after which the system was switched to consumption 500 W and is operated for 1 month as a heating device.

Tests were carried out on heating the heating system with a capacity 150 l according to the proposed method with power consumption 800 W. During the tests, water heating from 16 o C to 58.5 o C for 7 hours, after which the system was switched to a mode that maintains the temperature at 58oC at power consumption 500 W.

Tests were carried out on the introduction inside a closed coil of a steel pipe bundle of copper wires closed by soldering (conductor 3). As a result of the tests, it was established that, using conductor 3, it is possible to reduce the equivalent electrical resistance of closed turns in almost any range and increase the power consumption until the transformer is fully loaded.

Tests have shown the possibility of reducing electricity consumption in 1,5 -2 times when using the proposed method in comparison with traditional ones.

CLAIM

A method for converting electrical energy into thermal energy and creating heat exchange between a heating element and a heat carrier, using as a heating element the secondary winding of an electrical transformer, made in the form of a closed loop of a conductor in the form of a pipe with an inlet and outlet of the coolant, characterized in that the convention of the coolant is provided through a heating element by connecting its inlet to the coolant outlet from the radiator, and the coolant outlet from the heating element to the radiator inlet, the connections are made with hoses, the radiator is installed vertically so that the coolant outlet from the radiator is in its lower part, an expansion tank is installed in the upper part of the radiator and the entire the system is filled with coolant and the transformer is connected to the network.

The method according to claim 1, characterized in that the closed coil in the form of a pipe is made of an electrically insulating material, and one or more closed coils of the conductor are installed inside it.

Thermal energy occupies a special place in human activity, since it is used in all sectors of the economy, accompanies most industrial processes and people's livelihoods. In most cases, waste heat is lost irrevocably and without any economic benefit. This lost resource is no longer worth anything, so reusing it will help both reduce the energy crisis and protect the environment. Therefore, new ways of converting heat into electrical energy and the conversion of waste heat into electricity is more relevant today than ever.

Converting natural energy sources into electricity, heat or kinetic energy requires maximum efficiency, especially in gas and coal-fired power plants, to reduce CO 2 emissions. Exist various ways conversion of thermal energy into electrical energy, depending on the types of primary energy.

Among the energy resources, coal and natural gas are used to generate electricity by combustion (thermal energy) and uranium by nuclear fission (nuclear energy) to use steam power to turn a steam turbine. Ten largest countries electricity producers for 2017 are shown in the photo.

Performance Table existing systems conversion of thermal energy into electrical energy.

The choice of a method for converting thermal energy into electrical energy and its economic feasibility depend on the needs for energy carriers, the availability of natural fuel and the sufficiency of the construction site. The type of generation varies throughout the world, resulting in a wide range of electricity prices.

Technologies for converting thermal energy into electrical energy, such as TPP, NPP, KES, GTPP, TEP, thermoelectric generators, MHD generators have different benefits and disadvantages. Research institute Energy Industry (EPRI) illustrates the pros and cons of natural energy generation technologies, looking at critical factors such as construction and costs of electricity, land, water requirements, CO 2 emissions, waste, affordability and flexibility.

The EPRI results highlight that there is no one-size-fits-all approach when considering power generation technologies, but that natural gas still has more advantages, being affordable for construction, having a low cost of electricity, and creating less emissions than coal. However, not all countries have access to abundant and cheap natural gas. In some cases, access to natural gas is under threat due to geopolitical tensions, as was the case with Eastern Europe and some Western European countries.

Renewable energy technologies such as solar photovoltaic modules produce radiant electricity. However, they tend to require a lot of land, and the results of their effectiveness are unstable and depend on the weather. Coal, the main source of heat, is the most problematic. It leads in CO 2 emissions, requires a lot of clean water for cooling the coolant and takes large area for the construction of the station.

New technologies aim to reduce a number of problems associated with power generation technologies. For example, gas turbines combined with a backup battery provide contingency backup without burning fuel, and intermittent renewable resource problems can be mitigated by creating affordable large-scale energy storage. Thus, today there is no one perfect way to convert thermal energy into electrical energy, which could provide reliable and cost-effective electricity with minimal impact on environment.

Thermal power plants

At thermal power plants, high-pressure and high-temperature steam obtained from water heating during combustion solid fuel(mainly coal), rotates a turbine connected to a generator. Thus, it converts its kinetic energy into electrical energy. Operating components of a thermal power plant:

1. Boiler with gas fire.
2. Steam turbine.
3. Generator.
4. Capacitor.
5. Cooling towers.
6. Circulating water pump.
7. Boiler water supply pump.
8. Forced exhaust fans.
9. Separators.

A typical diagram is shown below.

The steam boiler is used to convert water into steam. This process is carried out by heating water in pipes with heating from fuel combustion. Combustion processes are continuously carried out in the fuel combustion chamber with air supply from outside.

The steam turbine transfers steam energy to rotate the generator. Steam with high pressure and temperature pushes the turbine blades mounted on the shaft so that it begins to rotate. In this case, the parameters of the superheated steam entering the turbine are reduced to a saturated state. The saturated steam enters the condenser, and the rotary power is used to rotate the generator, which produces current. Almost all steam turbines today are of the condenser type.

Condensers are devices for converting steam into water. The steam flows outside the pipes and the cooling water flows inside the pipes. This design is called a surface capacitor. The rate of heat transfer depends on the flow of the cooling water, the surface area of ​​the pipes and the temperature difference between the water vapor and the cooling water. The process of changing water vapor occurs at saturated pressure and temperature, in this case the condenser is under vacuum, because the temperature of the cooling water is equal to the external temperature, Maximum temperature water condensate near outdoor temperature.

The generator converts mechanical energy into a stator and rotor. The stator consists of a housing that contains the coils, and the magnetic field rotary station consists of a core containing the coil.

According to the type of energy produced, thermal power plants are divided into condensing condensing power plants, which produce electrical energy and combined heat and power plants, which jointly produce heat (steam and hot water) and electricity. The latter have the ability to convert thermal energy into electrical energy with high efficiency.

Nuclear power plants

Nuclear power plants use the heat released during nuclear fission to heat water and produce steam. The steam is used to turn large turbines that generate electricity. In fission, atoms split to form smaller atoms, releasing energy. The process takes place inside the reactor. In its center is the core, which contains uranium 235. Fuel for nuclear power plants is obtained from uranium, which contains the isotope 235U (0.7%) and non-fissile 238U (99.3%).

The nuclear fuel cycle is a series of industrial steps involved in the production of electricity from uranium in nuclear power reactors. Uranium is a relatively common element found all over the world. It is mined in a number of countries and processed before being used as a fuel.

Activities related to the production of electricity, in the aggregate, relate to the nuclear fuel cycle for the conversion of thermal energy into electrical energy at nuclear power plants. The nuclear fuel cycle begins with the extraction of uranium and ends with the disposal of nuclear waste. When reprocessing used fuel as an option for nuclear power, its steps form a veritable cycle.

To prepare fuel for use at nuclear power plants, processes are carried out for the extraction, processing, conversion, enrichment and production of fuel elements. Fuel cycle:

1. Burnup of uranium 235.
2. Slagging - 235U and (239Pu, 241Pu) from 238U.
3. In the process of decay of 235U, its consumption decreases, and isotopes are obtained from 238U during the generation of electricity.

The cost of fuel rods for VVR is approximately 20% of the cost of generated electricity.

After the uranium has spent about three years in the reactor, the used fuel can go through another process of use, including temporary storage, reprocessing and recycling before waste disposal. Nuclear power plants provide direct conversion of thermal energy into electrical energy. The heat released during nuclear fission in the reactor core is used to turn water into steam, which turns steam turbine blades, driving generators to generate electricity.

The steam is cooled by turning into water in a separate structure in a power plant called a cooling tower, which uses water from ponds, rivers or the ocean to cool the clean water of the steam power circuit. The chilled water is then reused to produce steam.

The share of electricity generation at nuclear power plants, in relation to the total balance of their generation different types resources, in the context of some countries and in the world - in the photo below.

The principle of operation of a gas turbine power plant is similar to that of a steam turbine power plant. The only difference is that in a steam turbine power plant, compressed steam is used to turn the turbine, while in a gas turbine power plant, gas is used.

Consider the principle of converting thermal energy into electrical energy in a gas turbine power plant.

In a gas turbine power plant, air is compressed in a compressor. Then this compressed air passes through the combustion chamber, where a gas-air mixture is formed, the temperature rises compressed air. This high temperature, high pressure mixture is passed through a gas turbine. In the turbine, it expands sharply, receiving sufficient kinetic energy to rotate the turbine.

In a gas turbine power plant, the turbine shaft, alternator and air compressor are common. The mechanical energy generated in the turbine is partly used to compress the air. Gas turbine power plants are often used as a back-up auxiliary energy supplier to hydroelectric power plants. It generates auxiliary power during the start-up of the hydroelectric plant.

The design of a gas turbine power plant is much simpler than that of a steam turbine power plant. The size of a gas turbine power plant is smaller than that of a steam turbine power plant. There is no boiler component and hence the system is less complicated. No steam, so no condenser or cooling tower required.

The design and construction of large gas turbine power plants is much easier and cheaper, capital costs and operating costs are largely less cost similar steam turbine power plant.

The permanent losses in a gas turbine power plant are much lower than in a steam turbine power plant, since in a steam turbine the boiler power plant must operate continuously even when the system is not supplying a load to the grid. A gas turbine power plant can be started almost instantly.

Disadvantages of a gas turbine power plant:

1. The mechanical energy generated in the turbine is also used to run the air compressor.
2. Since most of the mechanical energy generated in the turbine is used to drive air compressor, the overall efficiency of a gas turbine power plant is not as high as an equivalent steam turbine power plant.
3. Exhaust gases in a gas turbine power plant are very different from a boiler.
4. Before the turbine is actually started, the air must be pre-compressed, which requires an additional power source to start the gas turbine power plant.
5. The temperature of the gas is quite high in a gas turbine power plant. This results in a shorter system life than an equivalent steam turbine.

Due to its lower efficiency, a gas turbine power plant cannot be used for commercial power generation, it is usually used to supply auxiliary power to other conventional power plants such as a hydroelectric power plant.

Thermionic transducers

They are also called thermionic generator or thermoelectric motor, which directly convert heat into electricity using thermal emission. Thermal energy can be converted into electrical energy at very high efficiency through a temperature-induced electron flow process known as thermionic radiation.

The basic principle of operation of thermionic energy converters is that electrons evaporate from the surface of a heated cathode in a vacuum and then condense on a colder anode. Since the first practical demonstration in 1957, thermionic power converters have been used with various sources heat, but they all require work at high temperatures- above 1500 K. While operation of thermionic energy converters at a relatively low temperature (700 K - 900 K) is possible, the efficiency of the process, which is usually > 50%, is significantly reduced, since the number of emitted electrons per unit area from the cathode depends on heating temperature.

For traditional cathode materials such as metals and semiconductors, the number of electrons emitted is proportional to the square of the cathode temperature. However, a recent study demonstrates that the heat temperature can be reduced by an order of magnitude by using graphene as a hot cathode. The data obtained show that a graphene-based cathode thermionic converter operating at 900 K can achieve an efficiency of 45%.

circuit diagram the process of electronic thermionic emission is shown in the photo.

Graphene-based TIC, where Tc and Ta are the cathode and anode temperatures, respectively. Based on the new mechanism of thermionic emission, the researchers suggest that the graphene-based cathode energy converter could find its application in the recycling of industrial waste heat, which often reaches a temperature range of 700 to 900 K.

The new model presented by Liang and Eng could benefit the design of a graphene-based energy converter. Solid state power converters, which are basically thermoelectric generators, usually operate inefficiently in the low temperature range (less than 7% efficiency).

Energy waste recycling has become a popular goal for researchers and scientists who come up with innovative methods to achieve this goal. One of the most promising areas is thermoelectric devices based on nanotechnology, which looks like a new approach to energy saving. The direct conversion of heat into electricity or electricity into heat is known as thermoelectricity based on the Peltier effect. To be precise, the effect is named after two physicists - Jean Peltier and Thomas Seebeck.

Peltier discovered that a current sent to two different electrical conductors that are connected at two junctions will cause one junction to heat up while the other junction cools down. Peltier continued his research and found that a drop of water could be made to freeze at a bismuth-antimony (BiSb) junction by simply changing the current. Peltier also discovered that an electric current can flow when a temperature difference is placed across the junction of different conductors.

Thermoelectricity is an extremely interesting source of electricity due to its ability to convert heat flow directly into electricity. It is an energy converter that is highly scalable and has no moving parts or liquid fuel, making it suitable for almost any situation where a large number of The heat is usually sent to waste, from clothing to large industrial facilities.

Nanostructures used in semiconductor thermocouple materials will help maintain good electrical conductivity and reduce thermal conductivity. Thus, the performance of thermoelectric devices can be increased through the use of materials based on nanotechnology, using the Peltier effect. They have improved thermoelectric properties and good absorption capacity of solar energy.

Applications of thermoelectricity:

1. Energy providers and sensors in ranges.
2. A burning oil lamp that controls a wireless receiver for remote communication.
3. Application of small electronic devices such as MP3 players, digital clocks, GPS/GSM chips and pulse meters with body heat.
4. Fast cooling seats in luxury cars.
5. Cleaning up waste heat in vehicles by converting it into electricity.
6. Converting waste heat in factories or industrial facilities into additional power.
7. Solar thermoelectrics can be more efficient than photovoltaic cells for generating electricity, especially in areas with less sunlight.

Magnetohydrodynamic power generators generate electricity through the interaction of a moving fluid (usually an ionized gas or plasma) and magnetic field. Since 1970, MHD research programs have been carried out in several countries, with particular emphasis on the use of coal as a fuel.

The underlying principle behind the generation of MHD technologies is elegant. As a rule, an electrically conductive gas is formed when high pressure by burning fossil fuels. The gas is then directed through a magnetic field, causing an electromotive force to act within it in accordance with Faraday's law of induction (named after the 19th-century English physicist and chemist Michael Faraday).

The MHD system is a heat engine that includes gas expansion from high to low pressure in the same way as in a conventional gas turbine generator. In the MHD system kinetic energy gas is converted directly into electrical energy, as it is allowed to expand. The interest in generating MHD was initially sparked by the discovery that the interaction of a plasma with a magnetic field can occur at much higher temperatures than is possible in a rotating mechanical turbine.

Performance limits in terms of efficiency in heat engines have been set in early XIX century by the French engineer Sadi Carnot. The output power of the MHD generator for each cubic meter its volume is proportional to the gas conductivity product, the square of the gas velocity and the square of the strength of the magnetic field through which the gas passes. In order for MHD generators to operate competitively, with good performance and reasonable physical dimensions, the electrical conductivity of the plasma must be in the temperature range above 1800 K (about 1500 C or 2800 F).

The choice of the type of MHD generator depends on the fuel used and the application. The abundance of coal reserves in many countries of the world contribute to the development of MHD carbon systems for electricity generation.