To make the gas burn better, the boilers are equipped with draft mechanisms. Air is supplied to the boiler, which serves as an oxidizer during gas combustion. To reduce noise levels, the mechanisms are equipped with noise suppressors. Flue gases generated during fuel combustion are discharged into chimney and disperse into the atmosphere.

The hot gas rushes through the flue and heats the water passing through special boiler tubes. When heated, water turns into superheated steam, which enters the steam turbine. The steam enters the turbine and begins to rotate the turbine blades, which are connected to the generator rotor. Steam energy is converted into mechanical energy. In the generator, mechanical energy is converted into electrical energy, the rotor continues to rotate, creating an alternating electric current in the stator windings.

Through a step-up transformer and a step-down transformer substation Electricity is supplied to consumers via power lines. The steam exhausted in the turbine is sent to the condenser, where it turns into water and returns to the boiler. At a thermal power plant, water moves in a circle. Cooling towers are designed to cool water. CHP plants use fan and tower cooling towers. The water in cooling towers is cooled by atmospheric air. As a result, steam is released, which we see above the cooling tower in the form of clouds. The water in the cooling towers rises under pressure and falls like a waterfall into the front chamber, from where it flows back to the thermal power plant. To reduce droplet entrainment, cooling towers are equipped with water traps.

Water supply is provided from the Moscow River. In the chemical water treatment building, water is purified from mechanical impurities and supplied to groups of filters. In some, it is prepared to the level of purified water to feed the heating network, in others - to the level of demineralized water and is used to feed power units.

The cycle used for hot water supply and district heating is also closed. Part of the steam from the steam turbine is sent to water heaters. Next, the hot water is directed to heating points, where heat exchange occurs with water coming from houses.

Highly qualified Mosenergo specialists support the production process around the clock, providing the huge metropolis with electricity and heat.

How does a combined cycle power unit work?

Purpose of the thermal power plant consists of converting the chemical energy of fuel into electrical energy. Since it turns out to be practically impossible to carry out such a transformation directly, it is necessary to first convert the chemical energy of the fuel into heat, which is produced by burning the fuel, then convert the heat into mechanical energy and, finally, convert this latter into electrical energy.

The figure below shows simplest scheme the thermal part of an electric power plant, often called a steam power plant. Fuel is burned in a furnace. At the same time. The resulting heat is transferred to the water in the steam boiler. As a result, the water heats up and then evaporates, forming so-called saturated steam, that is, steam at the same temperature as boiling water. Next, heat is supplied to the saturated steam, resulting in the formation of superheated steam, i.e. steam that has more high temperature than water evaporating at the same pressure. Superheated steam is obtained from saturated steam in a superheater, which in most cases is a coil made of steel pipes. Steam moves inside the pipes, while on the outside the coil is washed by hot gases.

If the pressure in the boiler were equal to atmospheric pressure, then the water would need to be heated to a temperature of 100 ° C; with further heat it would begin to evaporate quickly. The resulting saturated steam would also have a temperature of 100° C. At atmospheric pressure steam will be overheated when its temperature is above 100 ° C. If the pressure in the boiler is higher than atmospheric, then the saturated steam has a temperature above 100 ° C. The higher the pressure, the higher the temperature of saturated steam. Currently, they are not used in the energy sector at all. steam boilers with pressure close to atmospheric. It is much more profitable to use steam boilers designed for much higher pressure, about 100 atmospheres or more. The temperature of saturated steam is 310° C or more.

From the superheater, superheated water vapor steel pipeline supplied to the heat engine, most often -. In existing steam power plants of power plants, other engines are almost never used. Superheated water vapor entering a heat engine contains a large supply of thermal energy released as a result of fuel combustion. The job of a heat engine is to convert the thermal energy of steam into mechanical energy.

The pressure and temperature of the steam at the inlet to the steam turbine, usually referred to as , are significantly higher than the pressure and temperature of the steam at the outlet of the turbine. The pressure and temperature of the steam at the outlet of the steam turbine, equal to the pressure and temperature in the condenser, are usually called. Currently, as already mentioned, the energy industry uses steam with very high initial parameters, with a pressure of up to 300 atmospheres and a temperature of up to 600 ° C. The final parameters, on the contrary, are chosen low: a pressure of about 0.04 atmospheres, i.e. 25 times less than atmospheric, and the temperature is about 30 ° C, i.e. close to ambient temperature. When steam expands in a turbine, due to a decrease in the pressure and temperature of the steam, the amount of thermal energy contained in it decreases significantly. Since the expansion process of steam occurs very quickly, during this very short time any significant transfer of heat from steam to the environment does not have time to take place. Where does the excess thermal energy go? It is known that, according to the basic law of nature - the law of conservation and transformation of energy - it is impossible to destroy or obtain “out of nothing” any, even the smallest, amount of energy. Energy can only move from one type to another. Obviously, it is precisely this kind of energy transformation that we are dealing with in in this case. The excess thermal energy previously contained in the steam has turned into mechanical energy and can be used at our discretion.

How a steam turbine works is described in the article about.

Here we will only say that the stream of steam entering the turbine blades has a very higher speed, often exceeding the speed of sound. The steam jet rotates the steam turbine disk and the shaft on which the disk is mounted. The turbine shaft can be connected, for example, to an electrical machine - a generator. The task of the generator is to convert the mechanical energy of shaft rotation into electrical energy. Thus, chemical energy fuel in a steam power plant is converted into mechanical and then into electrical energy, which can be stored in an AC UPS.

The steam that has done work in the engine enters the condenser. Cooling water is continuously pumped through the condenser tubes, usually taken from some natural body of water: river, lake, sea. Cooling water takes heat from the steam entering the condenser, as a result of which the steam condenses, i.e. turns into water. The water formed as a result of condensation is pumped into a steam boiler, in which it evaporates again, and the whole process is repeated again.

This is, in principle, the operation of the steam power plant of a thermoelectric station. As can be seen, steam serves as an intermediary, the so-called working fluid, with the help of which the chemical energy of the fuel is converted into thermal energy, is converted into mechanical energy.

One should not think, of course, that the design of a modern, powerful steam boiler or heat engine is as simple as shown in the figure above. On the contrary, the boiler and turbine, which are the most important elements steam power plants have a very complex structure.

We now begin to explain the work.

Electricity is produced in power plants by using the energy hidden in various natural resources. As can be seen from table. 1.2 this happens mainly at thermal power plants (TPPs) and nuclear power plants (NPPs) operating according to the thermal cycle.

Types of thermal power plants

Based on the type of energy generated and released, thermal power plants are divided into two main types: condensing power plants (CHPs), intended only for the production of electricity, and heating plants, or combined heat and power plants (CHPs). Condensing power plants operating on fossil fuels are built near the places of its production, and thermal power plants are located near heat consumers - industrial enterprises and residential areas. CHP plants also operate on fossil fuels, but unlike CPPs, they generate both electrical and thermal energy in the form of hot water and steam for production and heating purposes. The main types of fuel of these power plants include: solid - coals, anthracite, semi-anthracite, brown coal, peat, shale; liquid - fuel oil and gaseous - natural, coke, blast furnace, etc. gas.

Table 1.2. Electricity generation in the world

Nuclear power plants, predominantly of the condensing type, use the energy of nuclear fuel.

Depending on the type of thermal power plant for driving the electric generator, power plants are divided into steam turbine (STU), gas turbine (GTU), combined cycle (CCG) and power plants with engines internal combustion(DES).

Depending on the duration of work TPP throughout the year Based on the coverage of energy load schedules, characterized by the number of hours of use of the installed capacity τ at the station, power plants are usually classified into: basic (τ at the station > 6000 h/year); half-peak (τ at station = 2000 – 5000 h/year); peak (τ at st< 2000 ч/год).

Basic power plants are those that carry the maximum possible constant load for most of the year. In the global energy industry, nuclear power plants, highly economical thermal power plants, and thermal power plants are used as base plants when operating according to a thermal schedule. Peak loads are covered by hydroelectric power plants, pumped storage power plants, gas turbine plants, which have maneuverability and mobility, i.e. quick start and stop. Peaking power plants are switched on during the hours when it is necessary to cover the peak part of the daily electrical load schedule. Half-peak power plants, when the total electrical load decreases, are either transferred to reduced power or put into reserve.

By technological structure Thermal power plants are divided into block and non-block. With a block diagram, the main and auxiliary equipment The steam turbine unit has no technological connections with the equipment of another power plant unit. For fossil fuel power plants, steam is supplied to each turbine from one or two boilers connected to it. With a non-block TPP scheme, steam from all boilers enters a common main and from there is distributed to individual turbines.

At condensing power plants that are part of large energy systems, only block systems with intermediate superheating of steam are used. Non-block circuits with cross-coupling of steam and water are used without intermediate overheating.

Operating principle and main energy characteristics of thermal power plants

Electricity at power plants is produced by using energy hidden in various natural resources (coal, gas, oil, fuel oil, uranium, etc.), according to sufficient simple principle, implementing energy conversion technology. General scheme Thermal power plant (see Fig. 1.1) reflects the sequence of such conversion of some types of energy into others and the use of the working fluid (water, steam) in the cycle of a thermal power plant. The fuel (in this case coal) burns in the boiler, heats the water and turns it into steam. The steam is supplied to turbines, which convert the thermal energy of the steam into mechanical energy and drive generators that produce electricity (see section 4.1).

A modern thermal power plant is a complex enterprise, including large number various equipment. The composition of the power plant equipment depends on the selected thermal circuit, the type of fuel used and the type of water supply system.

The main equipment of the power plant includes: boiler and turbine units with an electric generator and a condenser. These units are standardized in terms of power, steam parameters, productivity, voltage and current, etc. The type and quantity of the main equipment of a thermal power plant correspond to the specified power and the intended operating mode. There is also auxiliary equipment used to supply heat to consumers and use turbine steam to heat boiler feedwater and meet the power plant’s own needs. This includes equipment for fuel supply systems, deaeration and feeding installations, condensing unit, heating plant (for thermal power plants), technical water supply systems, oil supply systems, regenerative heating of feedwater, chemical water treatment, distribution and transmission of electricity (see section 4).

All steam turbine plants use regenerative heating of feed water, which significantly increases the thermal and overall efficiency of the power plant, since in circuits with regenerative heating, the steam flows removed from the turbine to the regenerative heaters perform work without losses in the cold source (condenser). At the same time, for the same electric power of the turbogenerator, the steam flow in the condenser decreases and, as a result, efficiency installations are growing.

The type of steam boiler used (see section 2) depends on the type of fuel used in the power plant. For the most common fuels (fossil coal, gas, fuel oil, milling peat), boilers with a U-, T-shaped and tower layout and a combustion chamber designed in relation to a particular type of fuel are used. For fuels with low-melting ash, boilers with liquid ash removal are used. At the same time, high (up to 90%) ash collection in the firebox is achieved and abrasive wear of heating surfaces is reduced. For the same reasons, steam boilers with a four-pass arrangement are used for high-ash fuels, such as shale and coal preparation waste. Thermal power plants usually use drum or direct-flow boilers.

Turbines and electric generators are matched on a power scale. Each turbine corresponds certain type generator For block thermal condensing power plants, the power of the turbines corresponds to the power of the blocks, and the number of blocks is determined by the given power of the power plant. IN modern blocks Condensing turbines with a capacity of 150, 200, 300, 500, 800 and 1200 MW with intermediate superheating of steam are used.

Thermal power plants use turbines (see subsection 4.2) with back pressure (type P), with condensation and industrial steam extraction (type P), with condensation and one or two heating extractions (type T), as well as with condensation, industrial and heating extraction pair (PT type). PT turbines can also have one or two heating outlets. The choice of turbine type depends on the magnitude and ratio of thermal loads. If the heating load predominates, then in addition to the PT turbines, type T turbines with heating extraction can be installed, and if the industrial load predominates, type PR and R turbines with industrial extraction and back pressure can be installed.

Currently, the most widely used thermal power plants are installations with an electrical capacity of 100 and 50 MW, operating at initial parameters of 12.7 MPa, 540–560°C. For thermal power plants in large cities, installations with an electrical capacity of 175–185 MW and 250 MW (with a T-250-240 turbine) have been created. Installations with T-250-240 turbines are modular and operate at supercritical initial parameters (23.5 MPa, 540/540°C).

A feature of the operation of power stations in the network is that the total number electrical energy generated by them at each moment of time must fully correspond to the energy consumed. The main part of the power plants operates in parallel in the unified energy system, covering the total electrical load of the system, and the thermal power plant simultaneously covers the heat load of its area. There are local power plants designed to serve the area and not connected to the general power grid.

A graphical representation of the dependence of power consumption over time is called electrical load graph. Daily graphs of electrical load (Fig. 1.5) vary depending on the time of year, day of the week and are usually characterized by a minimum load at night and a maximum load during peak hours (the peak part of the graph). Along with daily charts great value have annual charts electrical load (Fig. 1.6), which are built according to daily graphs.

Electrical load graphs are used when planning electrical loads of power plants and systems, distributing loads between individual power plants and units, in calculations for selecting the composition of working and backup equipment, determining the required installed power and the required reserve, the number and unit power of units, when developing equipment repair plans and determining the repair reserve, etc.

When operating at full load, the power plant equipment develops its rated or as long as possible power (performance), which is the main passport characteristic of the unit. On this highest power(performance) the unit must operate for a long time at the nominal values ​​of the main parameters. One of the main characteristics of a power plant is its installed capacity, which is defined as the sum of the rated capacities of all electric generators and heating equipment, taking into account the reserve.

The operation of the power plant is also characterized by the number of hours of use installed capacity, which depends on the mode in which the power plant operates. For power plants carrying base load, the number of hours of use of installed capacity is 6000–7500 h/year, and for those operating in peak load coverage mode – less than 2000–3000 h/year.

The load at which the unit operates with the greatest efficiency is called the economic load. The rated long-term load can be equal to the economic load. Sometimes it is possible to operate equipment for a short time with a load 10–20% higher than the rated load at lower efficiency. If the power plant equipment operates stably with the design load at the nominal values ​​of the main parameters or when they change within acceptable limits, then this mode is called stationary.

Operating modes with steady loads, but different from the design ones, or with unsteady loads are called non-stationary or variable modes. In variable modes, some parameters remain unchanged and have nominal values, while others change within certain acceptable limits. Thus, at partial load of the unit, the pressure and temperature of the steam in front of the turbine can remain nominal, while the vacuum in the condenser and the steam parameters in the extractions will change in proportion to the load. Non-stationary modes are also possible, when all the main parameters change. Such modes occur, for example, when starting and stopping equipment, dumping and increasing the load on a turbogenerator, when operating on sliding parameters and are called non-stationary.

The thermal load of the power plant is used for technological processes and industrial installations, for heating and ventilation of industrial, residential and public buildings, air conditioning and domestic needs. For production purposes, steam pressure of 0.15 to 1.6 MPa is usually required. However, in order to reduce losses during transportation and avoid the need for continuous drainage of water from communications, steam is released from the power plant somewhat overheated. The thermal power plant usually supplies heating, ventilation and domestic needs hot water with temperatures from 70 to 180°C.

Thermal load, determined by the heat consumption for production processes and domestic needs (hot water supply), depends on the outside air temperature. In the conditions of Ukraine in summer, this load (as well as electrical) is less than in winter. Industrial and domestic heat loads change during the day, in addition, the average daily heat load of the power plant, spent on domestic needs, changes on weekdays and weekends. Typical graphs of changes in the daily heat load of industrial enterprises and hot water supply to a residential area are shown in Figures 1.7 and 1.8.

The operating efficiency of thermal power plants is characterized by various technical and economic indicators, some of which assess the perfection of thermal processes (efficiency, heat and fuel consumption), while others characterize the conditions in which the thermal power plant operates. For example, in Fig. 1.9 (a,b) shows approximate heat balances of thermal power plants and CPPs.

As can be seen from the figures, the combined generation of electrical and thermal energy provides a significant increase in the thermal efficiency of power plants due to a reduction in heat losses in turbine condensers.

The most important and complete indicators of the operation of thermal power plants are the cost of electricity and heat.

Thermal power plants have both advantages and disadvantages compared to other types of power plants. The following advantages of TPP can be indicated:

• relatively free territorial distribution associated with the wide distribution of fuel resources;
• the ability (unlike hydroelectric power plants) to generate energy without seasonal power fluctuations;
• the area of ​​alienation and withdrawal from economic circulation of land for the construction and operation of thermal power plants is, as a rule, much smaller than that required for nuclear power plants and hydroelectric power plants;
• Thermal power plants are built much faster than hydroelectric power plants or nuclear power plants, and their specific cost per unit of installed capacity is lower compared to nuclear power plants.
• At the same time, thermal power plants have major disadvantages:
• the operation of thermal power plants usually requires much more personnel than hydroelectric power plants, which is associated with the maintenance of a very large-scale fuel cycle;
• the operation of thermal power plants depends on the supply of fuel resources (coal, fuel oil, gas, peat, oil shale);
• variability of operating modes of thermal power plants reduces efficiency, increases fuel consumption and leads to increased wear and tear of equipment;
• existing thermal power plants are characterized by relatively low efficiency. (mostly up to 40%);
• Thermal power plants have a direct and adverse impact on the environment and are not environmentally friendly sources of electricity.
• The greatest damage to the environment of the surrounding regions is caused by power plants burning coal, especially high-ash coal. Among thermal power plants, the “cleanest” ones are those that use technological process natural gas.

According to experts, thermal power plants around the world annually emit about 200–250 million tons of ash, more than 60 million tons of sulfur dioxide, large amounts of nitrogen oxides and carbon dioxide (causing the so-called greenhouse effect and leading to long-term global climate change), into the atmosphere. absorbing large amounts of oxygen. In addition, it has now been established that the excess radiation background around thermal power plants operating on coal is, on average, 100 times higher in the world than near nuclear power plants of the same power (coal almost always contains uranium, thorium and a radioactive isotope of carbon as trace impurities ). However, well-developed technologies for the construction, equipment and operation of thermal power plants, as well as the lower cost of their construction, lead to the fact that thermal power plants account for the bulk of global electricity production. For this reason, improving TPP technologies and reducing negative influence Their environmental impact has received great attention around the world (see section 6).