Thermal power plants. Thermal power plants (TPP, IES, CHP) What do thermal power plants operate on?

The impeller blades of this steam turbine are clearly visible.

A thermal power plant (CHP) uses the energy released by burning fossil fuels - coal, oil and natural gas - to convert water into high-pressure steam. This steam, having a pressure of about 240 kilograms per square centimeter and a temperature of 524°C (1000°F), drives the turbine. The turbine spins a giant magnet inside a generator, which produces electricity.

Modern thermal power plants convert about 40 percent of the heat released during fuel combustion into electricity, the rest is discharged into the environment. In Europe, many thermal power plants use waste heat to heat nearby homes and businesses. Combined heat and power generation increases the energy output of the power plant by up to 80 percent.

Steam turbine plant with electric generator

A typical steam turbine contains two sets of blades. High-pressure steam coming directly from the boiler enters the flow path of the turbine and rotates the impellers with the first group of blades. The steam is then heated in the superheater and again enters the turbine flow path to rotate impellers with a second group of blades, which operate at a lower steam pressure.

Sectional view

A typical thermal power plant (CHP) generator is driven directly by a steam turbine, which rotates at 3,000 revolutions per minute. In generators of this type, the magnet, also called the rotor, rotates, but the windings (stator) are stationary. The cooling system prevents the generator from overheating.

Power generation using steam

At a thermal power plant, fuel burns in a boiler, producing a high-temperature flame. The water passes through the tubes through the flame, is heated and turns into high-pressure steam. The steam spins a turbine, producing mechanical energy, which a generator converts into electricity. After leaving the turbine, the steam enters the condenser, where it washes the tubes with cold running water, and as a result turns into a liquid again.

Oil, coal or gas boiler

Inside the boiler

The boiler is filled with intricately curved tubes through which heated water passes. The complex configuration of the tubes allows you to significantly increase the amount of heat transferred to the water and, as a result, produce much more steam.

What is it and what are the operating principles of thermal power plants? The general definition of such objects sounds approximately as follows - these are power plants that process natural energy into electrical energy. Fuel of natural origin is also used for these purposes.

The operating principle of thermal power plants. Brief description

Today, it is precisely at such facilities that combustion is most widespread that releases thermal energy. The task of thermal power plants is to use this energy to produce electrical energy.

The operating principle of thermal power plants is not only the generation but also the production of thermal energy, which is also supplied to consumers in the form of hot water, for example. In addition, these energy facilities generate about 76% of all electricity. This widespread use is due to the fact that the availability of fossil fuels for the operation of the station is quite high. The second reason was that transporting fuel from the place of its extraction to the station itself is a fairly simple and streamlined operation. The operating principle of thermal power plants is designed in such a way that it is possible to use the waste heat of the working fluid for its secondary supply to the consumer.

Separation of stations by type

It is worth noting that thermal stations can be divided into types depending on what kind of heat they produce. If the principle of operation of a thermal power plant is only to produce electrical energy (that is, it does not supply thermal energy to the consumer), then it is called condensing power plant (CES).

Facilities intended for the production of electrical energy, for the supply of steam, as well as the supply of hot water to the consumer, have steam turbines instead of condensing turbines. Also in such elements of the station there is an intermediate steam extraction or a backpressure device. The main advantage and operating principle of this type of thermal power plant (CHP) is that waste steam is also used as a heat source and supplied to consumers. This reduces heat loss and the amount of cooling water.

Basic operating principles of thermal power plants

Before moving on to considering the principle of operation itself, it is necessary to understand what kind of station we are talking about. The standard design of such facilities includes a system such as intermediate superheating of steam. It is necessary because the thermal efficiency of a circuit with intermediate superheating will be higher than in a system without it. In simple terms, the operating principle of a thermal power plant with such a scheme will be much more efficient with the same initial and final specified parameters than without it. From all this we can conclude that the basis of the station’s operation is organic fuel and heated air.

Operation scheme

The operating principle of the thermal power plant is constructed as follows. The fuel material, as well as the oxidizer, the role of which is most often played by heated air, is fed in a continuous flow into the boiler furnace. Substances such as coal, oil, fuel oil, gas, shale, and peat can act as fuel. If we talk about the most common fuel on the territory of the Russian Federation, it is coal dust. Further, the operating principle of thermal power plants is constructed in such a way that the heat generated by burning fuel heats the water in the steam boiler. As a result of heating, the liquid is converted into saturated steam, which enters the steam turbine through the steam outlet. The main purpose of this device at the station is to convert the energy of the incoming steam into mechanical energy.

All elements of the turbine that can move are closely connected to the shaft, as a result of which they rotate as a single mechanism. To make the shaft rotate, a steam turbine transfers the kinetic energy of steam to the rotor.

Mechanical part of the station

The design and principle of operation of a thermal power plant in its mechanical part is associated with the operation of the rotor. The steam that comes from the turbine has very high pressure and temperature. Because of this, high internal energy of steam is created, which flows from the boiler into the turbine nozzles. Jets of steam, passing through the nozzle in a continuous flow, at high speed, which is most often even higher than sound speed, act on the turbine blades. These elements are rigidly fixed to the disk, which, in turn, is closely connected to the shaft. At this point in time, the mechanical energy of the steam is converted into the mechanical energy of the rotor turbines. If we talk more precisely about the principle of operation of thermal power plants, then the mechanical impact affects the rotor of the turbogenerator. This is due to the fact that the shaft of a conventional rotor and generator are tightly coupled to each other. And then there is a fairly well-known, simple and understandable process of converting mechanical energy into electrical energy in a device such as a generator.

Steam movement after the rotor

After the water vapor passes the turbine, its pressure and temperature drop significantly, and it enters the next part of the station - the condenser. Inside this element, the vapor is converted back into liquid. To perform this task, there is cooling water inside the condenser, which is supplied there through pipes running inside the walls of the device. After the steam is converted back into water, it is pumped out by a condensate pump and enters the next compartment - the deaerator. It is also important to note that the pumped water passes through regenerative heaters.

The main task of the deaerator is to remove gases from the incoming water. Simultaneously with the cleaning operation, the liquid is heated in the same way as in regenerative heaters. For this purpose, the heat of the steam is used, which is taken from what goes into the turbine. The main purpose of the deaeration operation is to reduce the oxygen and carbon dioxide content in the liquid to acceptable values. This helps reduce the rate of corrosion on the paths through which water and steam are supplied.

Coal stations

There is a high dependence of the operating principle of thermal power plants on the type of fuel used. From a technological point of view, the most difficult substance to implement is coal. Despite this, raw materials are the main source of power at such facilities, the number of which is approximately 30% of the total share of stations. In addition, it is planned to increase the number of such objects. It is also worth noting that the number of functional compartments required for the operation of the station is much greater than that of other types.

How do thermal power plants run on coal fuel?

In order for the station to operate continuously, coal is constantly brought in along the railway tracks, which is unloaded using special unloading devices. Then there are elements such as through which unloaded coal is supplied to the warehouse. Next, the fuel enters the crushing plant. If necessary, it is possible to bypass the process of delivering coal to the warehouse and transfer it directly to the crushers from unloading devices. After passing this stage, the crushed raw materials enter the raw coal bunker. The next step is to supply the material through feeders to the pulverized coal mills. Next, the coal dust, using a pneumatic transportation method, is fed into the coal dust bunker. Along this path, the substance bypasses elements such as a separator and a cyclone, and from the hopper it already flows through the feeders directly to the burners. The air passing through the cyclone is sucked in by the mill fan and then fed into the combustion chamber of the boiler.

Further, the gas movement looks approximately as follows. The volatile substance formed in the chamber of the combustion boiler passes sequentially through such devices as the gas ducts of the boiler plant, then, if a steam intermediate superheater system is used, the gas is supplied to the primary and secondary superheater. In this compartment, as well as in the water economizer, the gas gives up its heat to heat the working fluid. Next, an element called an air superheater is installed. Here the thermal energy of the gas is used to heat the incoming air. After passing through all these elements, the volatile substance passes into the ash collector, where it is cleaned of ash. After this, smoke pumps draw the gas out and release it into the atmosphere using a gas pipe.

Thermal power plants and nuclear power plants

Quite often the question arises about what is common between thermal power plants and whether there are similarities in the operating principles of thermal power plants and nuclear power plants.

If we talk about their similarities, there are several of them. Firstly, both of them are built in such a way that for their work they use a natural resource that is fossil and excreted. In addition, it can be noted that both objects are aimed at generating not only electrical energy, but also thermal energy. The similarities in operating principles also lie in the fact that thermal power plants and nuclear power plants have turbines and steam generators involved in the operation process. Further there are only some differences. These include the fact that, for example, the cost of construction and electricity obtained from thermal power plants is much lower than from nuclear power plants. But, on the other hand, nuclear power plants do not pollute the atmosphere as long as the waste is disposed of correctly and no accidents occur. While thermal power plants, due to their operating principle, constantly emit harmful substances into the atmosphere.

Here lies the main difference in the operation of nuclear power plants and thermal power plants. If in thermal facilities the thermal energy from fuel combustion is most often transferred to water or converted into steam, then at nuclear power plants the energy is taken from the fission of uranium atoms. The resulting energy is used to heat a variety of substances and water is used here quite rarely. In addition, all substances are contained in closed, sealed circuits.

District heating

At some thermal power plants, their design may include a system that handles heating of the power plant itself, as well as the adjacent village, if there is one. To the network heaters of this installation, steam is taken from the turbine, and there is also a special line for condensate removal. Water is supplied and discharged through a special pipeline system. The electrical energy that will be generated in this way is removed from the electrical generator and transmitted to the consumer, passing through step-up transformers.

Main equipment

If we talk about the main elements operated at thermal power plants, these are boiler houses, as well as turbine units paired with an electric generator and a capacitor. The main difference between the main equipment and the additional equipment is that it has standard parameters in terms of its power, productivity, steam parameters, as well as voltage and current, etc. It can also be noted that the type and number of main elements are selected depending on how much power needs to be obtained from one thermal power plant, as well as its operating mode. An animation of the operating principle of thermal power plants can help to understand this issue in more detail.

Electricity is produced in power plants by using the energy hidden in various natural resources. As can be seen from table. 1.2 this occurs 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 stations operating on fossil fuels are built near the places of its production, and combined heat and 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 - hard coal, 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 an electric generator, power plants are divided into steam turbine (STU), gas turbine (GTU), combined cycle (CCG) and power plants with internal combustion engines (ICE).

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 turned on at 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.

According to the technological structure, thermal power plants are divided into block and non-block. With a block diagram, the main and auxiliary equipment of a steam turbine plant does not have technological connections with the equipment of another installation of the power plant. 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 a fairly simple principle, implementing energy conversion technology. The general diagram of a thermal power plant (see Fig. 1.1) reflects the sequence of such conversion of one type of energy into another 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 that includes a large number of different 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, a deaeration-feeding unit, a condensation unit, a heating unit (for thermal power plants), technical water supply systems, oil supply systems, regenerative heating of feed water, 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 has a specific type of 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. Modern units use condensing turbines with a capacity of 150, 200, 300, 500, 800 and 1200 MW with intermediate superheating of steam.

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 amount of 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 graphs, annual graphs of electrical load (Fig. 1.6), which are constructed based on data from daily graphs, are of great importance.

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. At this maximum 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 hot water with a temperature of 70 to 180°C for heating, ventilation and domestic needs.

The heat 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);
• variable operating modes of thermal power plants reduce efficiency, increase fuel consumption and lead 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 natural gas in their technological process.

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, much attention is paid to improving TPP technologies and reducing their negative impact on the environment around the world (see section 6).

A thermal power plant is a power plant for converting fuel energy into mechanical energy

IA website. Thermal power plant (thermal power plant) is a power plant that generates electrical energy by converting the chemical energy of fuel into the mechanical energy of rotation of the electric generator shaft.

The coal is transported (14) from an external shaft and ground into a very fine powder by large metal spheres in a mill (16).

There it is mixed with preheated air (24), forced by the blower fan (20).

The hot air-fuel mixture is forced, at high pressure, into the boiler, where it quickly ignites.

Water flows vertically up the tubular walls of the boiler, where it turns into steam and enters the boiler drum (17), in which the steam is separated from the remaining water.

The steam passes through a manifold in the drum cover into the suspended heater (19), where its pressure and temperature quickly increase to 200 bar and 570°C, sufficient to cause the tube walls to glow a dull red color.

The steam then enters the high pressure turbine (11), the first of three in the electricity generation process.

The steam supply control valve (10) provides both manual control of the turbine and automatic control according to the specified parameters.

Steam is released from the high-pressure turbine with both a decrease in pressure and temperature, after which it returns to the intermediate superheater (21) of the boiler for heating.

TPPs are the main type of power plants in Russia; the share of electricity they generate is 67% as of 2000.

In industrialized countries this figure reaches 80%.

Thermal energy at thermal power plants is used to heat water and produce steam - in steam turbine power plants or to produce hot gases - in gas turbine power plants.

To produce heat, organic fuel is burned in boiler units of thermal power plants.

The fuel used is coal, peat, natural gas, fuel oil, and oil shale.

1. Boiler-turbine power plants

1.1. Condensing power plants (CPS, historically called GRES - state district power plant)

1.2. Combined heat and power plants (cogeneration power plants, combined heat and power plants)

2. Gas turbine power plants

3. Power plants based on combined cycle gas plants

4. Power plants based on piston engines

5. Combined cycle

Abstract on the discipline “Introduction to Direction”

Completed by student Mikhailov D.A.

Novosibirsk State Technical University

Novosibirsk, 2008

Introduction

An electric power plant is a power plant used to convert natural energy into electrical energy. The type of power plant is determined primarily by the type of natural energy. The most widespread are thermal power plants (TPPs), which use thermal energy released by burning fossil fuels (coal, oil, gas, etc.). Thermal power plants generate about 76% of the electricity produced on our planet. This is due to the presence of fossil fuels in almost all areas of our planet; the possibility of transporting organic fuel from the extraction site to a power plant located near energy consumers; technical progress at thermal power plants, ensuring the construction of thermal power plants with high power; the possibility of using waste heat from the working fluid and supplying it to consumers, in addition to electrical energy, also thermal energy (with steam or hot water), etc. Thermal power plants intended only for the production of electricity are called condensing power stations (CPP). Power plants designed for combined generation of electrical energy and supply of steam, as well as hot water to thermal consumers, have steam turbines with intermediate steam extraction or with back pressure. In such installations, the heat of exhaust steam is partially or even completely used for heat supply, as a result of which heat losses with cooling water are reduced. However, the share of steam energy converted into electricity, with the same initial parameters, in installations with heating turbines is lower than in installations with condensing turbines. Thermal power plants in which exhaust steam, along with generating electricity, is used for heat supply are called combined heat and power plants (CHP).

Basic operating principles of thermal power plants

Figure 1 shows a typical thermal diagram of a condensing unit running on organic fuel.

Fig.1 Schematic thermal diagram of thermal power plant

1 – steam boiler; 2 – turbine; 3 – electric generator; 4 – capacitor; 5 – condensate pump; 6 – low pressure heaters; 7 – deaerator; 8 – feed pump; 9 – high pressure heaters; 10 – drainage pump.

This circuit is called a circuit with intermediate superheating of steam. As is known from the thermodynamics course, the thermal efficiency of such a circuit with the same initial and final parameters and the correct choice of intermediate overheating parameters is higher than in a circuit without intermediate overheating.

Let's consider the principles of operation of thermal power plants. Fuel and oxidizer, which is usually heated air, continuously flow into the boiler furnace (1). The fuel used is coal, peat, gas, oil shale or fuel oil. Most thermal power plants in our country use coal dust as fuel. Due to the heat generated as a result of fuel combustion, the water in the steam boiler is heated, evaporates, and the resulting saturated steam flows through the steam line into the steam turbine (2). The purpose of which is to convert the thermal energy of steam into mechanical energy.

All moving parts of the turbine are rigidly connected to the shaft and rotate with it. In the turbine, the kinetic energy of the steam jets is transferred to the rotor as follows. Steam of high pressure and temperature, which has high internal energy, enters the nozzles (channels) of the turbine from the boiler. A jet of steam at a high speed, often above the sound speed, continuously flows out of the nozzles and enters the turbine blades mounted on a disk rigidly connected to the shaft. In this case, the mechanical energy of the steam flow is converted into mechanical energy of the turbine rotor, or more precisely, into the mechanical energy of the turbogenerator rotor, since the shafts of the turbine and electric generator (3) are interconnected. In an electric generator, mechanical energy is converted into electrical energy.

After the steam turbine, water vapor, already at low pressure and temperature, enters the condenser (4). Here, the steam, with the help of cooling water pumped through the tubes located inside the condenser, is converted into water, which is supplied to the deaerator (7) by a condensate pump (5) through regenerative heaters (6).

The deaerator is used to remove gases dissolved in it from water; at the same time, in it, just like in regenerative heaters, the feed water is heated by steam, taken for this purpose from the turbine outlet. Deaeration is carried out in order to bring the content of oxygen and carbon dioxide in it to acceptable values ​​and thereby reduce the rate of corrosion in water and steam paths.

Deaerated water is supplied to the boiler plant by a feed pump (8) through heaters (9). The condensate of the heating steam formed in the heaters (9) is passed in cascade to the deaerator, and the condensate of the heating steam of the heaters (6) is supplied by the drain pump (10) to the line through which the condensate from the condenser (4) flows.

The most difficult technically is the organization of the operation of coal-fired thermal power plants. At the same time, the share of such power plants in the domestic energy sector is high (~30%) and it is planned to increase it.

The technological diagram of such a coal-fired power plant is shown in Fig. 2.

Fig.2 Technological diagram of a pulverized coal-fired thermal power plant

1 – railway cars; 2 – unloading devices; 3 – warehouse; 4 – belt conveyors; 5 – crushing plant; 6 – raw coal bunkers; 7 – pulverized coal mills; 8 – separator; 9 – cyclone; 10 – coal dust bunker; 11 – feeders; 12 – mill fan; 13 – combustion chamber of the boiler; 14 – blower fan; 15 – ash collectors; 16 – smoke exhausters; 17 – chimney; 18 – low pressure heaters; 19 – high pressure heaters; 20 – deaerator; 21 – feed pumps; 22 – turbine; 23 – turbine condenser; 24 – condensate pump; 25 – circulation pumps; 26 – receiving well; 27 – waste well; 28 – chemical shop; 29 – network heaters; 30 – pipeline; 31 – condensate drain line; 32 – electrical switchgear; 33 – sump pumps.

Fuel in railway cars (1) is supplied to unloading devices (2), from where it is sent to the warehouse (3) using belt conveyors (4), and from the warehouse the fuel is supplied to the crushing plant (5). It is possible to supply fuel to the crushing plant and directly from unloading devices. From the crushing plant, fuel flows into raw coal bunkers (6), and from there through feeders into pulverized coal mills (7). Coal dust is pneumatically transported through a separator (8) and a cyclone (9) to a coal dust hopper (10), and from there by feeders (11) to the burners. Air from the cyclone is sucked in by the mill fan (12) and supplied to the combustion chamber of the boiler (13).

The gases formed during combustion in the combustion chamber, after exiting it, pass successively through the gas ducts of the boiler installation, where in the steam superheater (primary and secondary, if a cycle with intermediate superheating of steam is carried out) and the water economizer they give off heat to the working fluid, and in the air heater - supplied to the steam boiler to air. Then, in ash collectors (15), the gases are purified from fly ash and released into the atmosphere through the chimney (17) by smoke exhausters (16).

Slag and ash falling under the combustion chamber, air heater and ash collectors are washed off with water and flow through channels to the slag pumps (33), which pump them to ash dumps.

The air required for combustion is supplied to the air heaters of the steam boiler by a blower fan (14). Air is usually taken from the top of the boiler room and (for high-capacity steam boilers) from outside the boiler room.

Superheated steam from the steam boiler (13) enters the turbine (22).

Condensate from the turbine condenser (23) is supplied by condensate pumps (24) through low-pressure regenerative heaters (18) to the deaerator (20), and from there by feed pumps (21) through high-pressure heaters (19) to the boiler economizer.

In this scheme, the losses of steam and condensate are replenished with chemically demineralized water, which is supplied to the condensate line behind the turbine condenser.

Cooling water is supplied to the condenser from the receiving well (26) of the water supply by circulation pumps (25). The heated water is discharged into a waste well (27) of the same source at a certain distance from the point of intake, sufficient to ensure that the heated water does not mix with the taken water. Devices for chemical treatment of make-up water are located in the chemical workshop (28).

The schemes may provide for a small network heating installation for district heating of the power plant and the adjacent village. Steam is supplied to the network heaters (29) of this installation from turbine extractions, and condensate is discharged through line (31). Network water is supplied to the heater and removed from it through pipelines (30).

The generated electrical energy is removed from the electrical generator to external consumers through step-up electrical transformers.

To supply electric motors, lighting devices and devices of the power plant with electricity, there is an auxiliary electrical switchgear (32).

Conclusion

The abstract presents the basic principles of operation of thermal power plants. The thermal diagram of a power plant is considered using the example of the operation of a condensing power station, as well as a technological diagram using the example of a coal-fired power plant. The technological principles of production of electrical energy and heat are shown.