YOUTH AND SPORTS OF UKRAINE

YU.A. GICHEV

THERMAL POWER PLANTS

Frequentlyb I

Dnepropetrovsk NMetAU 2011

MINISTRY OF EDUCATION AND SCIENCE,

YOUTH AND SPORTS OF UKRAINE

NATIONAL METALLURGICAL ACADEMY OF UKRAINE

YU.A. GICHEV

THERMAL POWER PLANTS

Frequentlyb I

Ill. 23. Bibliography: 4 names.

Responsible for the issue, Dr. Tech. sciences, prof.

Reviewer: , Dr. Tech. sciences, prof. (DNUZHT)

Cand. tech. Sciences, Associate Professor (NMetAU)

© National Metallurgical

Academy of Ukraine, 2011

INTRODUCTION…………………………………………………………………………………..4

1 GENERAL INFORMATION ABOUT THERMAL POWER PLANTS………………...5

1.1 Definition and classification of power plants………………………….5

1.2 Technological diagram of a thermal power plant………………………8

1.3 Technical and economic indicators of thermal power plants……………………………….11

1.3.1 Energy indicators…………………………………….11

1.3.2 Economic indicators…………………………………….13

1.3.3 Performance indicators……………………………...15

1.4 Requirements for thermal power plants………………………………………………………16

1.5 Features of industrial thermal power plants………………16

2 CONSTRUCTION OF THERMAL DIAGRAMS OF TPP………………………………………………………...17

2.1 General concepts about thermal circuits………………………………………………………17

2.2 Initial steam parameters…………………………………………….18

2.2.1 Initial steam pressure…………………………………….18

2.2.2 Initial steam temperature…………………………………...20

2.3 Intermediate superheating of steam…………………………………………..22

2.3.1 Energy efficiency of intermediate superheating...24

2.3.2 Intermediate superheat pressure…………………………26

2.3.3 Technical implementation of intermediate superheating……27

2.4 Final steam parameters………………………….……………………….29

2.5 Regenerative heating of feedwater……………………………...30

2.5.1 Energy efficiency of regenerative heating..30

2.5.2 Technical implementation of regenerative heating.......34

2.5.3 Temperature of regenerative heating of feedwater..37

2.6 Construction of thermal diagrams of thermal power plants based on the main types of turbines……..39

2.6.1 Construction of a thermal circuit based on turbine “K”…………...39

2.6.2 Construction of a thermal circuit based on turbine “T”….………..41

LITERATURE………………………………………………………………………………...44

INTRODUCTION

The discipline “Thermal Power Plants” for a number of reasons is of particular importance among the disciplines taught for specialty 8(7). - thermal power engineering.

Firstly, from a theoretical point of view, the discipline accumulates the knowledge acquired by students in almost all the main previous disciplines: “Fuel and its combustion”, “Boiler plants”, “Superchargers and heat engines”, “Heat supply sources for industrial enterprises” , “Gas purification” and others.

Secondly, from a practical point of view, thermal power plants (TPPs) are a complex energy enterprise that includes all the main elements of the energy economy: a fuel preparation system, a boiler shop, a turbine shop, a system for converting and supplying thermal energy to external consumers, recycling and neutralization systems harmful emissions.

Thirdly, from an industrial point of view, thermal power plants are the dominant power generating enterprises in the domestic and foreign energy sector. Thermal power plants account for about 70% of the installed electricity generating capacity in Ukraine, and taking into account nuclear power plants, where steam turbine technologies are also implemented, the installed capacity is about 90%.

This lecture notes have been developed in accordance with the work program and curriculum for specialty 8(7). - thermal power engineering and includes as main topics: general information about thermal power plants, principles of constructing thermal circuits of power plants, selection of equipment and calculations of thermal circuits, layout of equipment and operation of thermal power plants.

The discipline “Thermal Power Plants” helps to systematize the knowledge acquired by students, expand their professional horizons and can be used in coursework in a number of other disciplines, as well as in the preparation of theses for specialists and graduate theses for masters.

1 GENERAL INFORMATION ABOUT THERMAL POWER PLANTS

1.1 Definition and classification of power plants

Power station– an energy enterprise designed to convert various types of fuel and energy resources into electricity.

Main options for classifying power plants:

I. Depending on the type of converted fuel and energy resources:

1) thermal power plants (TPPs), in which electricity is produced by converting hydrocarbon fuels (coal, natural gas, fuel oil, combustible RES and others);

2) nuclear power plants (NPP), in which electricity is produced by converting atomic energy from nuclear fuel;

3) hydroelectric power plants (HPP), in which electricity is produced by converting the mechanical energy of the flow of a natural source of water, primarily rivers.

This classification option can also include power plants using non-traditional and renewable energy sources:

· solar power plants;

· geothermal power plants;

· wind power stations;

· tidal power stations and others.

II. For this discipline, a more in-depth classification of thermal power plants is of interest, which, depending on the type of heat engines, are divided into:

1) steam turbine power plants (STP);

2) gas turbine power plants (GTU);

3) combined cycle power plants (CGE);

4) power plants using internal combustion engines (ICE).

Among these power plants, steam turbine power plants are dominant, accounting for over 95% of the total installed capacity of thermal power plants.

III. Depending on the type of energy supplied to external consumers, steam turbine power plants are divided into:

1) condensing power plants (CPS), which supply exclusively electricity to external consumers;

2) combined heat and power plants (CHPs), which supply both thermal and electrical energy to external consumers.

IV. Depending on their purpose and departmental subordination, power plants are divided into:

1) district power plants, which are designed to provide electricity to all consumers in the region;

2) industrial power plants, which are part of industrial enterprises and are intended to provide electricity primarily to consumers of enterprises.

V. Depending on the duration of use of the installed capacity during the year, power plants are divided into:

1) basic (B): 6000÷7500 hours/year, i.e. over 70% of the duration of the year;

2) semi-basic (P/B): 4000÷6000 h/year, 50÷70%;

3) half-peak (P/P): 2000÷4000 h/year, 20÷50%;

4) peak (P): up to 2000 hours/year, up to 20% of the year.

This classification option can be illustrated using the example of a graph of the duration of electrical loads:

Figure 1.1 – Graph of duration of electrical loads

VI. Depending on the steam pressure entering the turbines, steam turbine thermal power plants are divided into:

1) low pressure: up to 4 MPa;

2) medium pressure: up to 9 – 13 MPa;

3) high pressure: up to 25 – 30 MPa, including:

● subcritical pressure: up to 18 – 20 MPa

● critical and supercritical pressure: over 22 MPa

VII. Depending on the power, steam turbine power plants are divided into:

1) low-power power plants: total installed capacity up to 100 MW with a unit power of installed turbogenerators up to 25 MW;

2) medium power: total installed capacity up to 1000 MW with a unit power of installed turbogenerators up to 200 MW;

3) high power: total installed capacity over 1000 MW with a unit power of installed turbogenerators over 200 MW.

VIII. Depending on the method of connecting steam generators to turbogenerators, thermal power plants are divided into:

1) centralized (non-unit) thermal power plants, in which steam from all boilers enters one central steam pipeline and is then distributed among turbine generators (see Fig. 1.2);

1 – steam generator; 2 – steam turbine; 3 - central (main) steam line; 4 – steam turbine condenser; 5 – electric generator; 6 – transformer.

Figure 1.2 - Schematic diagram of a centralized (non-block) thermal power plant

2) block thermal power plants, in which each of the installed steam generators is connected to a very specific turbogenerator (see Fig. 1.3).

1 – steam generator; 2 – steam turbine; 3 – intermediate superheater; 4 – steam turbine condenser; 5 – electric generator; 6 – transformer.

Figure 1.3 - Schematic diagram of a block thermal power plant

In contrast to the non-block design, the block design of thermal power plants requires less capital costs, is easier to operate and creates conditions for full automation of the steam turbine installation of the power plant. In the block diagram, the number of pipelines and production volumes of the station for the placement of equipment are reduced. When using intermediate superheating of steam, the use of block diagrams is mandatory, since otherwise it is not possible to control the flow of steam released from the turbine for superheating.

1.2 Technological diagram of the thermal power plant

The technological diagram depicts the main parts of the power plant, their interconnection and, accordingly, shows the sequence of technological operations from the moment of delivery of fuel to the station to the supply of electricity to the consumer.

As an example, Figure 1.4 shows a technological diagram of a pulverized-coal steam turbine power plant. This type of thermal power plant predominates among the existing basic thermal power plants in Ukraine and abroad.

Sun – fuel consumption at the station; Dp. g. – steam generator productivity; Ds. n. – conditional steam consumption for the station’s own needs; Dt – steam consumption per turbine; Evir – amount of generated electricity; Esn - electricity consumption for the station’s own needs; Eotp is the amount of electricity supplied to external consumers.

Figure 1.4 – Example of a technological diagram of a steam turbine pulverized coal power plant

The technological diagram of a thermal power plant is usually divided into three parts, which are marked with dotted lines in Figure 1.4:

I … Fuel-gas-air path, which includes:

1 – fuel facilities (unloading device, raw coal warehouse, crushing plants, crushed coal bunkers, cranes, conveyors);

2 – dust preparation system (coal mills, fine fans, coal dust bins, feeders);

3 – blower fan for supplying air for fuel combustion;

4 – steam generator;

5 – gas cleaning;

6 – smoke exhauster;

7 – chimney;

8 – slag pump for transporting hydroash and slag mixture;

9 – supply of hydroash and slag mixture for disposal.

In general, the fuel-gas-air path includes : fuel facilities, dust preparation system, draft means, boiler flues and ash and slag removal system.

II … Steam-water path, which includes:

10 – steam turbine;

11 – steam turbine condenser;

12 – circulation pump of the circulating water supply system for cooling the condenser;

13 – cooling device of the circulating system;

14 – supply of additional water to compensate for water losses in the circulating system;

15 – supply of raw water for the preparation of chemically purified water, compensating for the loss of condensate at the station;

16 – chemical water treatment;

17 – chemical water treatment pump supplying additional chemically treated water to the exhaust steam condensate stream;

18 – condensate pump;

19 – regenerative low-pressure feedwater heater;

20 – deaerator;

21 – feed pump;

22 – regenerative high-pressure feedwater heater;

23 – drainage pumps to remove heating steam condensate from the heat exchanger;

24 – regenerative steam extraction;

25 – intermediate superheater.

In general, the steam-water path includes: steam-water part of the boiler, turbine, condensate unit, systems for preparing cooling circulating water and additional chemically purified water, a system for regenerative heating of feed water and deaeration of feed water.

III … Electrical part which includes:

26 – electric generator;

27 – step-up transformer for electricity supplied to external consumers;

28 – buses of the open switchgear of the power plant;

29 – transformer for electricity for the power plant’s own needs;

30 – busbars of the distribution device for auxiliary electricity.

Thus, the electrical part includes: electric generator, transformers and switchgear buses.

1.3 Technical and economic indicators of thermal power plants

Technical and economic indicators of thermal power plants are divided into 3 groups: energy, economic and operational, which, respectively, are intended to assess the technical level, efficiency and quality of operation of the station.

1.3.1 Energy performance

The main energy indicators of thermal power plants include: efficiency power plants (), specific heat consumption (), specific fuel consumption for electricity generation ().

These indicators are called the thermal efficiency indicators of the plant.

Based on the results of the actual operation of the power plant, efficiency is determined by the relations:

; (1.1)

; (1.2)

When designing a power plant and analyzing its operation, efficiency. determined by products taking into account efficiency. individual elements of the station:

where ηcat, ηturb – efficiency. boiler and turbine shops;

ηt. p. – k.p.d. heat flow, which takes into account heat loss by coolants inside the station due to heat transfer to environment through the walls of the pipeline and coolant leaks, ηt. n. = 0.98...0.99 (average 0.985);

esn is the share of electricity spent on the power plant’s own needs (electric drive in the fuel preparation system, drive of the boiler shop draft equipment, pump drive, etc.), esn = Esn/Evir = 0.05...0.10 (cf. 0.075);

qсн – share of heat consumption for own needs (chemical water treatment, deaeration of feed water, operation of steam ejectors providing vacuum in the condenser, etc.), qсн = 0.01...0.02 (cf. 0.015).

K.p.d. boiler shop can be represented as efficiency steam generator: ηcat = ηp. g = 0.88…0.96 (average 0.92)

K.p.d. turbine shop can be represented as absolute electrical efficiency. turbogenerator:

ηturb = ηt. g. = ηt · ηoi · ηм, (1.5)

where ηt is thermal efficiency. cycle of a steam turbine plant (ratio of heat used to heat supplied), ηt = 0.42...0.46 (cf. 0.44);

ηoi – internal relative efficiency. turbines (takes into account losses inside the turbine due to steam friction, cross-flows, ventilation), ηoi = 0.76...0.92 (cf. 0.84);

ηm – electromechanical efficiency, which takes into account losses during the transfer of mechanical energy from the turbine to the generator and losses in the electric generator itself, ηen = 0.98...0.99 (cf. 0.985).

Taking into account the product (1.5), expression (1.4) for the efficiency net power plant takes the form:

ηsnetto = ηпг·ηt· ηoi· ηм· ηтп·(1 – есн)·(1 – qсн); (1.6)

and after substituting the average values ​​it will be:

ηsnetto = 0.92·0.44·0.84·0.985·0.985·(1 – 0.075)·(1 – 0.015) = 0.3;

In general, for a power plant the efficiency is net varies within the range: ηsnet = 0.28…0.38.

The specific heat consumption for electricity generation is determined by the ratio:

, (1.7)

where Qfuel is the heat obtained from fuel combustion .

; (1.8)

where pH is the standard investment efficiency ratio, year-1.

The inverse value pH gives the payback period for capital investments, for example, with pH = 0.12 year-1, the payback period will be:

The given costs are used to select the most economical option for constructing a new or reconstructing an existing power plant.

1.3.3 Performance

Operational indicators assess the quality of operation of the power plant and specifically include:

1) staffing coefficient (number of service personnel per 1 MW of installed power of the station), W (persons/MW);

2) utilization factor of the installed capacity of the power plant (the ratio of actual electricity production to the maximum possible generation)

; (1.16)

3) number of hours of use of installed capacity

4) equipment availability rate and equipment technical utilization rate

; (1.18)

Equipment availability factors for boiler and turbine shops are: Kgotkot = 0.96...0.97, Kgotturb = 0.97...0.98.

The utilization rate of equipment for thermal power plants is: KispTPP = 0.85…0.90.

1.4 Requirements for thermal power plants

The requirements for thermal power plants are divided into 2 groups: technical and economic.

Technical requirements include:

· reliability (uninterrupted power supply in accordance with consumer requirements and dispatch schedule of electrical loads);

· maneuverability (the ability to quickly increase or remove the load, as well as start or stop units);

· thermal efficiency (maximum efficiency and minimum specific fuel consumption under various operating modes of the plant);

· environmental friendliness (minimal harmful emissions into the environment and not exceeding permissible emissions under various operating modes of the plant).

Economic requirements are reduced to the minimum cost of electricity, subject to compliance with all technical requirements.

1.5 Features of industrial thermal power plants

Among the main features of industrial thermal power plants are:

1) two-way communication of the power plant with the main technological workshops (the power plant provides the electrical load of the technological workshops and, in accordance with the need, changes the supply of electricity, and the workshops in some cases are sources of thermal and combustible renewable energy resources that are used at power plants);

2) the commonality of a number of systems of power plants and technological workshops of the enterprise (fuel supply, water supply, transport facilities, repair base, which reduces the costs of plant construction);

3) the presence at industrial power plants, in addition to turbogenerators, of turbocompressors and turboblowers for supplying process gases to the workshops of the enterprise;

4) the predominance of combined heat and power plants (CHP) among industrial power plants;

5) relatively small capacity of industrial thermal power plants:

70…80%, ≤ 100 MW.

Industrial thermal power plants provide 15...20% of the total electricity generation.

2 CONSTRUCTION OF THERMAL DIAGRAMS OF TPP

2.1 General concepts about thermal circuits

Thermal diagrams relate to steam-water paths of power plants and show :

1) relative position of the main and auxiliary equipment of the station;

2) technological connection of equipment through coolant pipeline lines.

Thermal circuits can be divided into 2 types:

1) fundamental;

2) expanded.

The schematic diagrams show the equipment to the extent necessary for calculating the thermal circuit and analyzing the calculation results.

Based on the circuit diagram, the following tasks are solved:

1) determine the costs and parameters of coolants in various elements of the circuit;

2) choose equipment;

3) develop detailed thermal circuits.

Expanded Thermal Circuits include all station equipment, including backup equipment, all station pipelines with shut-off and control valves.

Based on the developed schemes, the following tasks are solved:

1) mutual placement of equipment when designing power plants;

2) execution of working drawings during design;

3) operation of stations.

The construction of thermal diagrams is preceded by solving the following issues:

1) selection of the type of station, which is carried out based on the type and quantity of expected energy loads, i.e. CPP or CHP;

2) determine the electrical and thermal power of the station as a whole and the power of its individual blocks (units);

3) select the initial and final steam parameters;

4) determine the need for intermediate superheating of steam;

5) choose the types of steam generators and turbines;

6) develop a scheme for regenerative heating of feedwater;

7) compose the main technical solutions for the thermal scheme (unit power, steam parameters, type of turbines) with a number of auxiliary issues: preparation of additional chemically purified water, water deaeration, recycling of steam generator blow-off water, drive of feed pumps and others.

The development of thermal circuits is mainly influenced by 3 factors:

1) the value of the initial and final parameters of steam in a steam turbine installation;

2) intermediate superheating of steam;

3) regenerative heating of feedwater.

2.2 Initial steam parameters

The initial steam parameters are the pressure (P1) and temperature (t1) of the steam before the turbine stop valve.

2.2.1 Initial steam pressure

The initial steam pressure affects the efficiency. power plants and, first of all, through thermal efficiency. cycle of a steam turbine plant, which, when determining the efficiency power plant has a minimum value (ηt = 0.42…0.46):

To determine thermal efficiency can be used iS– water vapor diagram (see Fig. 2.1):

(2.2)

where Above is the adiabatic heat loss of steam (for an ideal cycle);

qsupply is the amount of heat supplied to the cycle;

i1, i2 – enthalpy of steam before and after the turbine;

i2" – enthalpy of condensate of steam exhausted in the turbine (i2" = cpt2).

Figure 2.1 – Towards the determination of thermal efficiency.

The results of the calculation using formula (2.2) give the following efficiency values:

ηt, fractions of units

Here 3.4...23.5 MPa are the standard steam pressures adopted for steam turbine power plants in the energy sector of Ukraine.

From the calculation results it follows that with an increase in the initial steam pressure, the value of efficiency. increases. Together with that, An increase in pressure has a number of negative consequences:

1) with increasing pressure, the volume of steam decreases, the flow area of ​​the turbine flow part and the length of the blades decrease, and, consequently, the flow of steam increases, which leads to a decrease in the internal relative efficiency. turbines (ηоі);

2) an increase in pressure leads to an increase in steam losses through the turbine end seals;

3) metal consumption for equipment and the cost of a steam turbine plant increases.

To eliminate the negative impact Along with an increase in pressure, the turbine power should be increased, which ensures :

1) increase in steam flow (excludes a decrease in the flow area in the turbine and the length of the blades);

2) reduces the relative escape of steam through the mechanical seals;

3) an increase in pressure together with an increase in power makes it possible to make pipelines more compact and reduce metal consumption.

The optimal ratio between the initial steam pressure and turbine power, obtained based on an analysis of the operation of existing power plants abroad, is presented in Figure 2.2 (the optimal ratio is marked by shading).

Figure 2.2 – Relationship between turbogenerator power (N) and initial steam pressure (P1).

2.2.2 Initial steam temperature

As the initial steam pressure increases, the humidity of the steam at the turbine outlet increases, which is illustrated by the graphs on the iS diagram (see Fig. 2.3).

Р1 > Р1" > Р1"" (t1 = const, P2 = const)

x2< x2" < x2"" (y = 1 – x)

y2 > y2" > y2""

Figure 2.3 – The nature of the change in the final moisture content of steam with an increase in the initial steam pressure.

The presence of steam moisture increases friction losses and reduces internal relative efficiency. and causes droplet erosion of the blades and other elements of the turbine flow path, which leads to their destruction.

The maximum permissible steam humidity (y2add) depends on the length of the blades (ll); For example:

ll ≤ 750…1000 mm y2add ≤ 8…10%

ll ≤ 600 mm y2add ≤ 13%

To reduce the humidity of steam, the temperature should be increased along with an increase in steam pressure, which is illustrated in Figure 2.4.

t1 > t1" > t1"" (P2 = const)

x2 > x2" > x2"" (y = 1 - x)

y2< y2" < y2""

Figure 2.4 – The nature of the change in the final moisture content of steam with an increase in the initial temperature of steam.

The steam temperature is limited by the heat resistance of the steel from which the superheater, pipelines, and turbine elements are made.

It is possible to use steels of 4 classes:

1) carbon and manganese steels (with maximum temperature tpr ≤ 450...500°C);

2) chrome-molybdenum and chrome-molybdenum-vanadium steels of the pearlitic class (tpr ≤ 570...585°C);

3) high-chromium steels of the martensitic-ferritic class (tpr ≤ 600...630°C);

4) stainless chromium-nickel steels of the austenitic class (tpr ≤ 650...700°C).

When moving from one class of steel to another, the cost of equipment increases sharply.

Steel grade

Relative cost

At this stage, from an economic point of view, it is advisable to use pearlitic steel with an operating temperature tr ≤ 540°C (565°C). Steels of the martensitic-ferritic and austenitic class lead to a sharp increase in the cost of equipment.

It should also be noted the influence of the initial steam temperature on thermal efficiency. cycle of a steam turbine plant. An increase in steam temperature leads to an increase in thermal efficiency:

Technological diagram of a thermal power plant operating on coal , is shown in Figure 3.4. It is a complex set of interconnected paths and systems: a dust preparation system; fuel supply and ignition system (fuel path); slag and ash removal system; gas-air path; a steam-water path system, including a steam-water boiler and a turbine unit; a system for preparing and supplying additional water to replenish losses of feedwater; technical water supply system providing steam cooling; network water heating system; an electrical power system, including a synchronous generator, step-up transformer, high-voltage switchgear, etc.

Below is given a brief description of the main systems and paths of the technological scheme of a thermal power plant using the example of a coal-fired thermal power plant.

Rice. 3.3. Process diagram of a pulverized coal power plant

1. Dust preparation system. Fuel path. Solid fuel is delivered by rail in special gondola cars. 1 (see Fig. 3.4). Gondola cars with coal are weighed on railway scales. In winter, gondola cars with coal are passed through a defrosting greenhouse, in which the walls of the gondola car are heated with heated air. Next, the gondola car is pushed into an unloading device - a car dumper 2 , in which it rotates around the longitudinal axis at an angle of about 180 0; coal is dumped onto grates covering the receiving hoppers. Coal from the bunkers is fed by feeders to the conveyor 4 , through which it arrives either to the coal warehouse 3 , or through the crushing department 5 in the raw coal bunker of the boiler room 6 , to which it can also be delivered from a coal warehouse.

From the crushing plant, fuel enters the raw coal bunker 6 , and from there through feeders - into pulverized coal mills 7 . Coal dust is pneumatically transported through the separator 8 and cyclone 9 into the coal dust bin 10 , and from there feeders 11 supplied to the burners. Air from the cyclone is sucked in by the mill fan 12 and fed into the combustion chamber of the boiler 13 .

This entire fuel path, together with the coal warehouse, belongs to the fuel supply system, which is serviced by the personnel of the fuel transport department of the thermal power plant.

Pulverized coal boilers also have a starting fuel, usually fuel oil. Fuel oil is delivered in railway tanks, in which it is heated with steam before being discharged. Using the first and second lift pumps, it is supplied to the fuel oil nozzles. The starting fuel can also be natural gas supplied from the gas pipeline through the gas control point to the gas burners.

At thermal power plants that burn gas and oil fuel, the fuel economy is significantly simplified compared to pulverized coal thermal power plants. The coal warehouse, crushing department, conveyor system, raw coal and dust bunkers, as well as ash collection and ash removal systems become unnecessary.

2. Gas-air path. Slag and ash removal system. The air required for combustion is supplied to the air supply

steam boiler heaters with 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.

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, heat is transferred to the working fluid, and the air heater is supplied to the steam boiler air. Then in ash collectors (electric precipitators) 15 gases are purified from fly ash and through the chimney 17 smoke exhausters 16 are released into the atmosphere.

Slag and ash falling under the combustion chamber, air heater and ash collectors are washed off with water and supplied through channels to the blast pumps. 33 , which pump them into ash dumps.

3. Steam-water path. Steam superheated in a superheater from a steam boiler 13 through steam pipelines and a system of nozzles it flows to the turbine 22 .

Condensation from the condenser 23 turbines are supplied by condensate pumps 24 through low pressure regenerative heaters 18 into the deaerator 20 , in which water is brought to a boil; at the same time, it is freed from the aggressive gases O 2 and CO 2 dissolved in it, which prevents corrosion in the steam-water path. Water is supplied from the deaerator by feed pumps 21 through high pressure heaters 19 into the boiler economizer, providing preheating of water and significantly increasing the efficiency of the thermal power plant.

The steam-water path of a thermal power plant is the most complex and responsible, since in this path the highest metal temperatures and the highest steam and water pressures occur.

To ensure the functioning of the steam-water path, a system for preparing and supplying additional water to replenish losses of the working fluid, as well as a technical water supply system for thermal power plants to supply cooling water to the turbine condenser are required.

4. System for preparing and supplying additional water. Additional water is obtained as a result of chemical purification of raw water, carried out in special ion exchange filters for chemical water treatment.

Losses of steam and condensate due to leaks in the steam-water path are replenished in this scheme with chemically demineralized water, which is supplied from the demineralized water tank by a transfer pump to the condensate line behind the turbine condenser.

Devices for chemical treatment of make-up water are located in the chemical workshop 28 (chemical water treatment workshop).

5. Steam cooling system. Cooling water is supplied to the condenser from the water supply well 26 circulation pumps 25 . The cooling water heated in the condenser is discharged into a collecting well 27 the same source of water at a certain distance from the point of intake, sufficient to ensure that the heated water does not mix with the taken water.

In many technological schemes of thermal power plants, cooling water is pumped through the condenser tubes by circulation pumps 25 and then enters the cooling tower (cooling tower), where, due to evaporation, the water is cooled by the same temperature difference by which it was heated in the condenser. A water supply system with cooling towers is used mainly in thermal power plants. The IES uses a water supply system with cooling ponds. When evaporative cooling of water occurs, the evaporation is approximately equal to the amount of steam condensing in the turbine condensers. Therefore, water supply systems need to be recharged, usually with river water.

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

7. Electric power system. An electric generator rotated by a steam turbine produces alternating electric current, which goes through a step-up transformer to the busbars of the open switchgear (OSD) of the thermal power plant. The buses of the auxiliary system are also connected to the generator terminals through an auxiliary transformer. Thus, the auxiliary consumers of the power unit (electric motors of auxiliary units - pumps, fans, mills, etc.) are powered by the power unit generator. To supply electricity to electric motors, lighting devices and devices of the power plant, there is an auxiliary electrical switchgear 32 .

In special cases (emergency situations, load shedding, start-up and shutdown), auxiliary power supply is provided through a backup busbar transformer of the outdoor switchgear. Reliable power supply to electric motors of auxiliary units ensures reliable operation of power units and thermal power plants as a whole. Disruption of the power supply for own needs leads to failures and accidents.

The fundamental difference between the technological scheme of a gas turbine power plant (GTU) and a steam turbine is that in a GTU the chemical energy of the fuel is converted into mechanical energy in one unit - a gas turbine, as a result of which there is no need for a steam boiler.

The gas turbine installation (Fig. 3.5) consists of a combustion chamber KS, a gas turbine GT, an air compressor K and an electric generator G. Compressor K sucks in atmospheric air, compresses it to an average of 6–10 kg/cm 2 and supplies it to the combustion chamber KS. Fuel (for example, solar oil, natural or industrial gas) also enters the combustion chamber, which burns in a compressed air environment.


Rice. 3.4. Simplified technological diagram of a gas turbine

power plants using liquid or gas fuel: T – fuel; IN -

air; KS – combustion chamber; GT – gas turbine; K – air compressor; G – electric generator
Hot gases with a temperature of 600–800 °C from the combustion chamber enter the gas turbine GT. Passing through the turbine, they expand to atmospheric pressure and, moving at high speed between the blades, rotate the turbine shaft. Exhaust gases escape into the atmosphere through the exhaust pipe. A significant part of the power of a gas turbine is spent on rotating the compressor and other auxiliary devices.

The main advantages of gas turbine units compared to steam turbine units are:

1) lack of a boiler plant and chemical water treatment;

2) significantly lower need for cooling water, which makes it possible to use gas turbine units in areas with limited water resources;

3) significantly smaller number of operating personnel;

4) quick start-up;

5) lower cost of generated electricity.
3.1.3. Layout diagrams of thermal power plants
TPPs are divided into block and non-block based on the type (structure) of the thermal circuit.

With a block diagram all main and auxiliary equipment of the installation have no technological connections with the equipment of another installation of the power plant. In fossil fuel power plants, each turbine is supplied with steam only from one or two boilers connected to it. A steam turbine plant, the turbine of which is powered by steam from one steam boiler, is called monoblock, if there are two boilers per turbine – double-block.

With a non-block scheme TPP steam from all steam boilers enters a common main and only from there is distributed to individual turbines. In some cases, it is possible to direct steam directly from steam boilers to turbines, but the common connecting line is preserved, so you can always use steam from all boilers to power any turbine. The lines through which water is supplied to steam boilers (feed pipelines) also have cross connections.

Block thermal power plants are cheaper than non-block thermal power plants, since the pipeline layout is simplified and the number of fittings is reduced. It is easier to control individual units at such a station; block-type installations are easier to automate. In operation, the operation of one unit does not affect neighboring units. When expanding a power plant, the subsequent unit may have a different power and operate at new parameters. This makes it possible to install more powerful equipment with higher parameters at the expandable station, i.e. allows you to improve equipment and increase the technical and economic performance of the power plant. The process of setting up new equipment does not affect the operation of previously installed units. However, for normal operation of block thermal power plants, the reliability of their equipment must be significantly higher than that of non-block thermal power plants. The units do not have backup steam boilers; if the possible boiler productivity is higher than the flow rate required for a given turbine, part of the steam (the so-called hidden reserve, which is widely used in non-unit thermal power plants) cannot be transferred to another installation. For steam turbine plants with intermediate superheating of steam, a block diagram is practically the only possible one, since a non-block plant diagram in this case will be overly complex.

In our country, steam turbine installations of thermal power plants without controlled steam extraction with initial pressure P 0 ≤8.8 MPa and installations with controlled extractions at P 0 ≤12.7 MPa, operating in cycles without intermediate steam superheating, are built non-block. At higher pressures (at IES at P 0 ≥12.7 MPa, and at thermal power plants at P 0 = 23.5 MPa) all steam turbine units operate in cycles with intermediate overheating, and stations with such installations are built in blocks.

The main building (main building) houses the main and auxiliary equipment directly used in the technological process of the power plant. The mutual arrangement of equipment and building structures is called layout of the main power plant building.

The main building of a power plant usually consists of a turbine room, a boiler room (with a bunker room when operating on solid fuel) or a reactor room in a nuclear power plant and a deaerator room. In the machine room, along with the main equipment (primarily turbine units), the following are located: condensate pumps, low and high pressure regenerative heaters, feed pump units, evaporators, steam converters, network heaters (at thermal power plants), auxiliary heaters and other heat exchangers.

In warm climates (for example, in the Caucasus, Central Asia, etc.), in the absence of significant precipitation, dust storms, etc. CPPs, especially gas and oil plants, use an open layout of equipment. At the same time, canopies are installed over the boilers, and the turbine units are protected with light shelters; auxiliary equipment of the turbine unit is placed in a closed condensation room. The specific cubic capacity of the main building of a CPP with an open layout is reduced to 0.2–0.3 m 3 /kW, which reduces the cost of constructing a CPP. Overhead cranes and other lifting mechanisms are installed in the power plant premises for the installation and repair of power equipment.

In Fig. 3.6. The layout diagram of the power unit of a pulverized coal power plant is shown: I – steam generator room; II – machine room, III – cooling water pumping station; 1 – unloading device; 2 – crushing plant; 3 – water economizer and air heater; 4 – steam superheaters; 5 , 6 – combustion chamber; 7 – pulverized coal burners; 8 – steam generator; 9 – mill fan; 10 – coal dust bunker; 11 – dust feeders; 12 – intermediate superheat steam pipelines; 13 – deaerator; 14 - steam turbine; 15 – electric generator; 16 – step-up electrical transformer; 17 – capacitor; 18 – cooling water supply and drain pipelines; 19 – condensate pumps; 20 – regenerative HDPE; 21 – feed pump; 22 – regenerative LDPE; 23 – blower fan; 24 – ash catcher; 25 – slag and ash removal channels; EE– high voltage electricity.

In Fig. 3.7 shows a simplified layout diagram of a gas-oil power plant with a capacity of 2400 MW, indicating the placement of only the main and part of the auxiliary equipment, as well as the dimensions of the structures (m): 1 – boiler room; 2 – turbine compartment; 3 – condenser compartment; 4 – generator compartment; 5 – deaerator compartment; 6 – blower fan; 7 – regenerative air heaters; 8 – distribution system for own needs (RUSN); 9 - chimney.

Rice. 3.7. Layout of the main building of the gas and oil plant

power plants with a capacity of 2400 MW
The main equipment of IES (boiler and turbine units) is located in the main building, boilers and a dust preparation unit (at IES that burn, for example, coal in the form of dust) - in the boiler room, turbine units and their auxiliary equipment - in the turbine room of the power plant. At CPPs, mainly one boiler per turbine is installed. The boiler with the turbine unit and their auxiliary equipment form a separate part - a monoblock power plant.

Turbines with a capacity of 150–1200 MW require boilers with a capacity of 500–3600 m 3 /h of steam, respectively. Previously, state district power plants used two boilers per turbine, i.e. double-blocks . At CPPs without intermediate steam superheating with turbine units with a capacity of 100 MW or less, a non-block centralized scheme was used, in which steam from the boilers is diverted into a common steam main, and from it is distributed between the turbines.

The dimensions of the main building depend on the power of the equipment placed in it: the length of one block is 30–100 m, the width is 70–100 m. The height of the machine room is about 30 m, the boiler room is more than 50 m. The cost-effectiveness of the layout of the main building is estimated approximately by the specific cubic capacity, equal to about 0.7–0.8 m 3 /kW at a pulverized coal-fired power plant , and in gas-oil - about 0.6–0.7 m 3 / kW. Some of the auxiliary equipment of the boiler room (smoke exhausters, blower fans, ash collectors, dust cyclones and dust separators of the dust preparation system) are often installed outside the building, in the open air.

CESs are built directly near water supply sources (river, lake, sea); Often a reservoir (pond) is created next to the CPP. On the territory of the IES, in addition to the main building, there are structures and devices for technical water supply and chemical water treatment, fuel facilities, electrical transformers, switchgears, laboratories and workshops, material warehouses, office premises for personnel servicing the IES. Fuel is usually supplied to the CPP territory by trains. Ash and slag from the combustion chamber and ash collectors are removed hydraulically. On the territory of the IES, railway tracks and roads are laid, and conclusions are built power lines, engineering ground and underground communications. The area of ​​territory occupied by CPP structures is, depending on the power plant capacity, type of fuel and other conditions, 25–70 hectares .

Large pulverized coal-fired power plants in Russia are serviced by personnel at the rate of 1 person for every 3 MW of capacity (approximately 1000 people at a power plant with a capacity of 3000 MW); In addition, maintenance personnel are required.

The power of IES depends on water and fuel resources, as well as environmental protection requirements: ensuring normal cleanliness of air and water basins. Emissions of fuel combustion products in the form of solid particles into the air in the CPP area are limited by the installation of advanced ash collectors (electric precipitators with an efficiency of about 99%). The remaining impurities, oxides of sulfur and nitrogen, are dispersed using high chimneys, which are built to remove harmful impurities to higher layers of the atmosphere. Chimneys with a height of up to 300 m or more are constructed of reinforced concrete or with 3–4 metal trunks inside a reinforced concrete shell or a common metal frame.

Control of numerous diverse IES equipment is possible only on the basis of comprehensive automation of production processes. Modern condensing turbines are fully automated. The boiler unit automatically controls the processes of fuel combustion, feeding the boiler unit with water, maintaining the steam superheat temperature, etc. Other IES processes are also automated: maintaining specified operating modes, starting and stopping units, protecting equipment during abnormal and emergency conditions.
3.1.4. Main equipment of thermal power plants
To the main equipment of thermal power plants include steam boilers (steam generators), turbines, synchronous generators, transformers.

All listed units are standardized according to the relevant indicators. The choice of equipment is determined primarily by the type of power plant and its power. Almost all newly designed power plants are block-type, their main characteristic is the power of turbine units.

Currently, serial domestic condensing power units of thermal power plants with a capacity of 200, 300, 500, 800 and 1200 MW are produced. For thermal power plants, along with units with a capacity of 250 MW, turbine units with a capacity of 50, 100 and 175 MW are used, in which the block principle is combined with individual cross-links of equipment.

For a given power plant power, the range of equipment included in the power units is selected according to its power, steam parameters and the type of fuel used.
3.1.4.1. Steam boilers
Steam boiler(PC) – heat exchanger for producing steam with a pressure exceeding atmospheric pressure, forming together with auxiliary equipment boiler unit.

PC characteristics are:

• 
  steam production;
• 
  steam operating parameters (temperature and pressure) after the primary and intermediate superheaters;
• 
  heating surface, i.e. a surface washed by flue gases on one side and feed water on the other;
• 
  Efficiency, i.e. the ratio of the amount of heat contained in steam to the calorific value of the fuel used to produce this steam.

Characteristic for PCs are also weight, dimensions, metal consumption and available equipment for mechanization and automation of maintenance.

The first PCs were spherical in shape. The PC built in 1765 by I. Polzunov, who created the first universal steam engine and thereby laid the foundation for the energy use of water steam, also had this form. At first PCs were made of copper, then of cast iron. At the end of the 18th century, the level of development of ferrous metallurgy made it possible to produce steel cylindrical PCs from sheet material by riveting. Gradual changes in PC designs have led to numerous varieties. The cylindrical boiler, which had a diameter of up to 0.9 m and a length of 12 m, was mounted using brick lining, in which all gas channels were laid out. The heating surface of such a PC was formed only in the lower part of the boiler.

The desire to improve PC parameters has led to an increase in dimensions and an increase in the number of water and steam flows. The increase in the number of threads went in two directions: development gas tube boilers, in particular locomotive gas-tube steam boilers, and the development water tube boilers, which are the basis of modern boiler units. An increase in the heating surface of water tube boilers was accompanied by an increase in dimensions and, first of all, the height of the boiler. PC efficiency reached 93–95%.

Initially, water-tube PCs were PCs only bar banal type , in which bundles of straight or curved pipes (coils) were combined with cylindrical steel drums (Fig. 3.8).

Rice. 3.8. Schematic diagram of a drum-type PC:

1 – combustion chamber; 2 – burner; 3 – screen pipes; 4 -drum;

5 – lowering pipes; 6 – steam superheater; 7 – secondary (intermediate) superheater; 8 – economizer; 9 – air heater.
In the combustion chamber 1 burners are located 2, through which a mixture of fuel and heated air enters the firebox. The number and type of burners depend on their performance, unit power and type of fuel. The three most common types of fuel are coal, natural gas and fuel oil. The coal is first converted into coal dust, which is blown through the burners into the firebox using air.

The walls of the combustion chamber are covered from the inside with pipes (screens) 3, which absorb heat from hot gases. Water enters the screen pipes through lower unheated pipes 5 from the drum 4, in which a given level is constantly maintained . Water boils in the screen pipes and moves upward in the form of a steam-water mixture, then entering the steam space of the drum. Thus, during operation of the boiler, a natural circulation of water and steam occurs in the circuit: drum - lower pipes - screen pipes - drum. Therefore, the boiler shown in Fig. 3.8, is called a drum boiler with natural circulation. The removal of steam to the turbine is replenished by supplying feedwater to the boiler drum using pumps.

The steam coming from the screen pipes into the steam space of the drum is saturated and in this form, although it has full operating pressure, is not yet suitable for use in a turbine, since it has a relatively low efficiency. In addition, the humidity of saturated steam during expansion in the turbine increases to limits that are dangerous for the reliability of the rotor blades. Therefore, steam from the drum is directed to the superheater 6, where an additional amount of heat is imparted to it, due to which it becomes overheated from saturated. At the same time, its temperature rises to approximately 560 ° C and, accordingly, its performance increases. Depending on the location of the superheater in the boiler and, consequently, on the type of heat exchange taking place in it, radiation, screen (semi-radiation) and convective superheaters are distinguished.

Radiation superheaters placed on the ceiling of the combustion chamber or on its walls, often between the screen pipes. They, like evaporation screens, perceive the heat emitted by the torch of burned fuel. Screen superheaters, made in the form of separate flat screens from parallel-connected pipes, are strengthened at the exit from the furnace in front of the convective part of the boiler. Heat exchange in them is carried out both by radiation and convection. Convective superheaters located in the flue of the boiler unit, usually behind screens or behind the firebox; they are multi-row packages of coils. Superheaters consisting only of convective stages are usually installed in medium and low pressure boilers at a superheated steam temperature of no higher than 440–510 ºС. In high-pressure boilers with significant steam superheating, combined steam superheaters are used, including convective, screen, and sometimes radiation parts.

At a steam pressure of 14 MPa (140 kgf/cm2) and higher, a secondary (intermediate) superheater is usually installed behind the primary superheater 7 . It, like the primary one, is formed from steel pipes bent into coils. Steam that has worked in the high pressure cylinder (HPC) of the turbine and has a temperature close to the saturation temperature at a pressure of 2.5–4 MPa is sent here . In the secondary (intermediate) superheater, the temperature of this steam again rises to 560 °C, and its performance increases accordingly, after which it passes through a medium pressure cylinder (MPC) and a low pressure cylinder (LPC), where it expands to the exhaust steam pressure (0.003–0.007 MPa ). The use of intermediate superheating of steam, despite the complexity of the design of the boiler and turbine and a significant increase in the number of steam lines, has great economic advantages compared to boilers without intermediate superheating of steam. The steam consumption per turbine is approximately halved, and fuel consumption is reduced by 4–5%. The presence of intermediate superheating of the steam also reduces the humidity of the steam in the last stages of the turbine, due to which the wear of the blades by water droplets is reduced and the efficiency of the low pressure turbine turbine is slightly increased.

Further, in the tail part of the boiler there are auxiliary surfaces designed to use the heat of the flue gases. In this convective part of the boiler there is a water economizer 8, where the feed water is heated before entering the drum, and the air heater 9, serving to heat the air before feeding it to the burners and to the dust preparation circuit, which increases the efficiency of the PC. Cooled flue gases with a temperature of 120–150 °C are sucked by a smoke exhauster into the chimney.

Further improvement of water-pipe PCs made it possible to create a PC consisting entirely of small-diameter steel pipes, into which water under pressure enters from one end, and steam of specified parameters exits from the other - the so-called once-through boiler (Fig. 3.9). Thus, this is a PC in which complete evaporation of water occurs during a single (direct-flow) passage of water through the evaporative heating surface. Water is supplied to the direct-flow PC using a feed pump through an economizer. This type of boiler does not have a drum or down pipes.

Rice. 3.9. Schematic diagram of a direct-flow PC:

1 – screens of the lower radiation part; 2 – burners; 3 – screens of the upper radiation part; 4 – screen steam superheater; 5 – convective superheater; 6 – secondary superheater; 7 – water economizer; 8 – feed water supply; 9 – steam removal to the turbine; 10 – steam supply from the HPC for secondary superheating; 11 – steam removal to the central heating chamber after secondary overheating; 12 – removal of flue gases to the air heater
The heating surface of the boiler can be imagined as a series of parallel coils, in which the water heats up as it moves, turns into steam, and then the steam is superheated to the desired temperature. These coils are located both on the walls of the combustion chamber and in the boiler flues. The combustion devices, secondary superheater and air heater of direct-flow boilers do not differ from drum boilers.

In drum boilers, as the water evaporates, the concentration of salts in the remaining boiler water increases, and a small portion of this boiler water, approximately 0.5%, must always be thrown out of the boiler in order to prevent the salt concentration from increasing above a certain limit. This process is called purging boiler For direct-flow boilers, this method of removing accumulated salts is not applicable due to the lack of water volume, and therefore the feedwater quality standards for them are much more stringent.

Another disadvantage of direct-flow PCs is the increased energy consumption to drive the feed pump.

Direct-flow PCs are usually installed on condensation power plants, where the boilers are fed with demineralized water. Their use in thermal power plants is associated with increased costs for chemical purification of additional (make-up) water. The most effective direct-flow boilers are for supercritical pressures (above 22 MPa), where other types of boilers are not applicable.

In power units, either one boiler is installed per turbine ( monoblocks), or two boilers of half capacity. To the benefits double-blocks This may include the possibility of operating the unit at half load on the turbine in the event of damage to one of the boilers. However, the presence of two boilers in a block significantly complicates the entire circuit and control of the block, which in itself reduces the reliability of the block as a whole. In addition, operating the unit at half load is highly uneconomical. The experience of a number of stations has shown that monoblocks can operate no less reliably than double blocks.

In block installations for pressures up to 130 kgf/cm 2 (13 MPa) boilers of both drum and direct-flow types are used. In installations for pressure 240 kgf/cm 2 (24 MPa) and higher Only direct-flow boilers are used.

Cogeneration boiler is a boiler unit of a combined heat and power plant (CHP), providing simultaneous supply of steam to heating turbines and the production of steam or hot water for technological, heating and other needs. Unlike IES boilers, district heating boilers usually use returned contaminated condensate as a water feeder. For such operating conditions, drum boilers with staged evaporation are most suitable. At most thermal power plants, heating boilers have cross-connections for steam and water. In the Russian Federation, at thermal power plants the most common are drum boilers with a steam capacity of 420 t/h (steam pressure 14 MPa, temperature 560 ºC). Since 1970, at powerful thermal power plants with prevailing heating loads, when almost all condensate is returned in its pure form, monoblocks with direct-flow boilers with a steam capacity of 545 t/h (25 MPa) have been used , 545 ºС).

Heating PCs can also include peak hot water boilers, which are used for additional heating of water when the thermal load increases beyond the maximum provided by turbine extractions. In this case, the water is heated first by steam in boilers to 110–120 ºС, and then in boilers to 150–170 ºС. In our country, these boilers are usually installed next to the main building of the thermal power plant. The use of relatively cheap peak hot water heating boilers to relieve short-term peaks in heat loads can dramatically increase the number of hours of use of the main heating equipment and increase the efficiency of its operation.

For heat supply to residential areas, water-heating gas-oil boilers of the KVGM type, operating on gas, are often used. As a reserve fuel for such boilers, fuel oil is used, which is heated by gas-oil drum steam boilers.

3.1.4.2. Steam turbines
Steam turbine(PT) is a heat engine in which the potential energy of steam is converted into the kinetic energy of a steam jet, and the latter is converted into mechanical energy of rotation of the rotor.

They have been trying to create a PT since ancient times. There is a known description of a primitive PT made by Heron of Alexandria (1st century BC). However, only at the end of the 19th century, when thermodynamics, mechanical engineering and metallurgy had reached a sufficient level, K.G. Laval (Sweden) and C.A. Parsons (Great Britain) independently created industrially suitable PTs in 1884–1889.

Laval used steam expansion in conical stationary nozzles in one step from the initial to the final pressure and directed the resulting jet (with supersonic exhaust velocity) onto one row of working blades mounted on a disk. PTs operating on this principle are called active PT. The impossibility of obtaining large aggregate power and the very high rotation speed of single-stage Laval PTs (up to 30,000 rpm for the first samples) led to the fact that they retained their importance only for driving auxiliary mechanisms.

Parsons created a multi-stage jet PT, in which steam expansion was carried out in a large number of successively located stages not only in the channels of fixed (guide) blades, but also between movable (working) blades. The Parsons jet PT was used for some time mainly on warships, but gradually gave way to more compact combined active-reactive PTs in which the high-pressure reactive part is replaced by an active disk. As a result, losses due to steam leakage through the gaps in the blade apparatus have decreased, the turbine has become simpler and more economical.

Active PT power plants have evolved towards the creation of multi-stage designs, in which steam expansion is carried out in a number of sequential stages. This made it possible to significantly increase the unit power of the PT, while maintaining a moderate rotation speed necessary for the direct connection of the PT shaft with the mechanism it rotates, in particular, an electric generator.

There are several design options for steam turbines, allowing them to be classified according to a number of characteristics.

According to the direction of travel steam flow is distinguished axial PT, in which the steam flow moves along the axis of the turbine, and radial PT, the direction of steam flow in which is perpendicular, and the working blades are located parallel to the axis of rotation. In the Russian Federation, only axial PTs are built.

By number of bodies (cylinders) PT is divided into single-hull, double-hull And three-hull(with high, medium and low pressure cylinders) . The multi-casing design allows the use of large available enthalpy differences by placing a large number of pressure stages, the use of high-quality metals in the high-pressure part and a bifurcation of the steam flow in the low-pressure part. At the same time, such a PT turns out to be more expensive, heavier and more complex.

By number of shafts differentiate single-shaft PT, in which the shafts of all housings are on the same axis, as well as twin-shaft or three-shaft, consisting of two or three parallel single-shaft PTs connected by a common thermal process, and for ship PTs also by a common gear drive (gearbox).

The fixed part of the PT (housing) is detachable in a horizontal plane to allow installation of the rotor. The housing has recesses for installing diaphragms, the connector of which coincides with the plane of the housing connector. Along the periphery of the diaphragms there are nozzle channels formed by curved blades cast into the body of the diaphragms or welded to it. In places where the shaft passes through the walls of the housing, labyrinth-type end seals are installed to prevent steam leakage to the outside (from the high pressure side) and air suction into the housing (from the low pressure side). Labyrinth seals are also installed in places where the rotor passes through the diaphragms to prevent steam from flowing from stage to stage, bypassing the nozzles. A limit regulator (safety regulator) is installed at the front end of the shaft, which automatically stops the PT when the rotation speed increases by 10–12% above the nominal one. The rear end of the rotor is equipped with an electrically driven shaft turning device to slowly (4–6 rpm) turn the rotor after stopping the PT, which is necessary for its uniform cooling.

In Fig. Figure 3.10 schematically shows the structure of one of the intermediate stages of a modern steam turbine at a thermal power plant. The stage consists of a disk with blades and a diaphragm. The diaphragm is a vertical partition between two disks, in which fixed guide vanes are located along the entire circumference opposite the working blades, forming nozzles for steam expansion. The diaphragms are made of two halves with a horizontal split, each of which is fixed in the corresponding half of the turbine housing.

Rice. 3.10. Construction of one of the stages of a multi-stage

turbines: 1 – shaft; 2 – disk; 3 – working blade; 4 – turbine cylinder wall; 5 – nozzle grille; 6 – diaphragm;

7 – diaphragm seal
A large number of stages forces the turbine to be made from several cylinders, placing 10–12 stages in each. In turbines with intermediate superheating of steam, a group of stages is usually located in the first high-pressure cylinder (HPC), which converts the steam energy from the initial parameters to the pressure at which the steam enters the intermediate superheating. After intermediate superheating of the steam in turbines with a power of 200 and 300 MW, the steam enters two more cylinders - the CSD and the LPC.

Test

Electric stations

1 general characteristics power stations

2.1 Condensing thermal power plants (CHPS)

2.3 Hydroelectric power plants

2.5 Gas turbine power plants (GTPP)

2.6 Pumped storage power plants (PSPPs)

3.1 Fuel transport

3.3 Power sources for the auxiliary needs of power plants

1 General characteristics of power plants

A power plant is an industrial enterprise that produces electrical and, in some cases, thermal energy based on the conversionprimary energy resources.

Depending on the types of natural energy sources (solid fuel, liquid, gaseous, nuclear, water energy), stations are divided into thermal (thermal power plants), hydraulic (hydroelectric power plants), nuclear power plants (nuclear power plants). Stations at which thermal energy is also generated simultaneously with electrical energy, are called combined heat and power plants (CHP).

For each type of station, its own technological scheme is developed for converting primary energy into electricity, and for thermal power plants - into heat. The technological scheme characterizes the sequence of the process of producing electrical and thermal energy and equipping the conversion process with basic equipment (steam boilers, nuclear reactors, steam or hydraulic turbines, electric generators), as well as various auxiliary equipment and provides for a high degree of mechanization and automation of the process. The equipment is located in special buildings, in open areas or underground. The units are interconnected both in the thermal and electrical parts. These connections are reflected accordingly in technological, thermal and electrical diagrams. In addition, the stations provide for numerous communications of secondary devices, control systems, protection and automation, interlocking, alarm systems, etc.

Participation of various power plants in the generation of electrical energy:

• TPP (combined CPP and CHP) approximately 65-67%;
• Hydroelectric power plantsapproximately 13-15%;
• NPPapproximately 10-12%
• other types of power plants 6-8%.

The energy system is understood asa set of power plants, electrical and thermal networks interconnected and connected by a common mode in the continuous process of production, transformation and distribution of electrical energy and heat with general control of this mode (GOST 21027-75).

The energy system can be roughly represented by the following block diagram (Figure 1.1):

Figure 1Structural diagram of the energy system.

In an energy system, all power plants in the electrical part operate in parallel, i.e. integrated into a common electrical system. Separate power plants operate separately on the thermal side, creating autonomous heating networks.

The integration of individual power plants into a common energy system of any region provides significant technical and economic advantages:

Increases the reliability and efficiency of power supply;

Allows for such load distribution between stations that achieves the most economical generation of electricity for the system as a whole with the best use of the area’s energy resources (fuel, water energy);

Improves the quality of electricity, i.e. ensures constant frequency and voltage, since load fluctuations are perceived by a large number of units;

When several stations operate in parallel, there is no need to install backup units at each station, but it is sufficient to have a reserve power common to the entire power system, the value of which is usually about 1012% of the power of the system units, but not less than the power of the largest unit installed at the stations of the system ( in case of emergency shutdown or scheduled repair of this unit);

Energy resources are used more fully, since the peak part of the power system load schedule can be covered by hydraulic power plants, and the base part by thermal ones, to increase the power of which during peak load hours additional fuel must be spent;

The efficiency of electricity generation increases, since first of all it is possible to increase the power of more economical stations that have less equivalent fuel consumption to generate 1 kWh of electricity;

Allows you to increase the unit capacity of units that have the best technical and economic indicators;

Allows you to reduce the number of repair personnel by concentrating equipment power, centralizing repairs, and automating production processes.

To the disadvantages of energy systems are considered more likely to be false relay protection , automation and mode control.

2 Technological mode of the main types of power plants

2.1 Condensing thermal power plants (CHPS).

Figure 2 Technological diagram of IES

IES produces only electrical energy. The basic technological diagram of the IES is shown in Figure 2.

To steam generator 4 (boiler) fuel is supplied fromworkshops for its transportation and preparation 1 . In the steam generator with blower fans 2 heated air and feed water are supplied by feed pumps 16. The gases generated during fuel combustion are sucked out of the boiler by a smoke exhauster. 3 and are released through a chimney (100-250 m high) into the atmosphere. Live steam from the boiler is supplied to the steam turbine 5, where, passing through a series of stages, it performs mechanical work rotates the turbine and the generator rotor rigidly connected to it 6 . The exhaust steam enters the condenser 9 (heat exchanger); here it condenses due to the passage of a significant amount of cold (5-20 O C) circulating water supplied by circulation pumps 10 from a cold water source 11 . Sources of cold water can be a river, lake, artificial reservoir, as well as special installations with cooling towers (cooling towers) or spray pools. Air entering the condenser through non-densities is removed using an ejector 12. Condensate formed in the condenser using condensate pumps 13 fed to the deaerator 14 , which is designed to remove gases from the feedwater, and primarily oxygen, which causes increased corrosion of boiler pipes. The deaerator is also supplied with water from a chemical water purification device. 15 (HOV). After the deaerator, feed water is supplied by a feed pump 16 to the boiler. 17 ash removal.

Passing the bulk of the steam through the condenser leads to the fact that

60-70% of the thermal energy generated by the boiler is uselessly carried away by circulating water.

Electrical energy generated by a generator 6, through The communication transformer is supplied to the network (35-220 kV). The station receives electrical energy to support the technological process from its own transformers 8 . Which can be powered from the generator voltage network or from an external network. The generated electrical energy is transmitted to the external network through a communication transformer 7 .

The features of IES are as follows:

They are built as close as possible to fuel deposits;

The overwhelming majority of the generated electricity is supplied to the high-voltage electrical network (110-750 kV);

They work according to a free (i.e. not limited by heat consumers) electricity generation schedule; power can vary from the calculated maximum to the so-called technological minimum;

Low maneuverability: turning the turbines and loading the load from a cold state requires approximately 410 hours;

They have a relatively low efficiency (η=30÷40%).

2.2 Cogeneration power plantsCHP

Unlike CPPs, CHP plants have significant withdrawals of steam, partially exhausted in the turbine, for production and domestic needs. (Figure 3). Municipal consumers receive thermal energy from network heaters 18 (boilers) and network pumps 19 , ensuring coolant circulation in heating networks. Steam extraction for production needs is carried out at the high pressure stage 20 . Condensate from network heaters enters the deaerator. When the electrical load of a thermal power plant is reduced below the heat consumption power, the thermal energy required for the consumer can be obtained using a reduction-cooling unit (RCU) 21 .

Figure 3Technological process diagram at a thermal power plant: 1 - fuel supply units; 2 - blower fan; 3 - smoke exhausters; 4 -steam generator (boiler); 5 - turbine; 6 - generator; 7 -communication transformer; 8 -own needs; 9 -consumers powered from the generator voltage network, 10 - capacitor; eleven -circulation pumps; 12 -a source of cold water; 13 - ejector; 14 - condensation pumps; 15 - deaerator; 16 -chemical water purification units; 17 -feeding pumps; 18 - network heaters (boilers); 19 - network pumps; 20 -high pressure stages; 21 - reduction-cooling unit (ROU); 22 - ash removal devices; 23- slag removal device

The greater the extraction of steam from the turbine for heating needs, the less thermal energy is lost with the circulating water and, consequently, the higher the efficiency of the power plant. It should be noted that in order to avoid overheating of the tail section of the turbine, a certain amount of steam must be passed through it in all modes. Due to the discrepancy between the capacities of consumers of thermal and electrical energy, thermal power plants often operate in condensation (mixed) mode, which reduces their efficiency.

The features of the thermal power plant are as follows:

They are built near thermal energy consumers;

They usually run on imported fuel;

Most of the generated electricity is distributed to consumers in the nearby area (at generator or increased voltage);

They work according to a partially forced electricity generation schedule (i.e. the schedule depends on the generation of heat consumption);

Low maneuverability (same as IES);

They have a relatively high total efficiency (with significant steam extraction for industrial and domestic needs η =60÷70%).

2.3 Hydroelectric power plants

The power of a hydroelectric power station depends on the water flow through the turbine and the pressure N. This kW power is determined by the expression

where Q water consumption, m 3 / s;

N pressure, m;

η Σ total efficiency;

η C Efficiency of water supply structures;

η T hydraulic turbine efficiency;

η Г Hydrogen generator efficiency;

At low pressures, run-of-river hydroelectric power stations are built, at high pressures

they build dam hydroelectric power stations, and construct diversion stations in mountainous areas.

Features of the hydroelectric power station are as follows:

They build where there are water resources and conditions for construction, which usually does not coincide with the location of the electrical load;

Most of the generated electricity is sent to high-voltage electrical networks;

They work on a flexible schedule (if there are reservoirs);

Highly maneuverable (turning and loading takes 35 minutes);

Have high efficiency(η Σ ≈85% ).

As you can see, hydroelectric power plants have a number of advantages over thermal power plants in terms of operating parameters. However, thermal and nuclear power plants are currently being built. The determining factors here are the size of capital investments and the time of construction of power plants.

The diagram of the hydroelectric power station is shown in the figure

Figure 4Scheme of hydroelectric power station

2.4 Nuclear power plants (NPPs)

Nuclear power plants are thermal stations that use the energy of a nuclear reaction. The uranium isotope U-235, the content of which in natural uranium is 0.714%, is usually used as nuclear fuel. The bulk of the uranium isotope U-238 (99.28% of the total mass) is converted into secondary fuel plutonium when neutrons are captured.

Pu-239. The fission reaction occurs in nuclear reactor. Nuclear fuel is usually used in solid form. It is enclosed in a protective shell. These types of fuel elements are called fuel rods. They are installed in the working channels of the reactor core. Thermal energy, released during the fission reaction, is removed from the reactor core using coolant, which is pumped under pressure through each working channel or through the entire core.

Figure 5Nuclear power plant diagrams:a) - single-circuit; b) - double-circuit; c) - three-circuit. 1 - reactor; 2 - turbine; 3 - capacitor; 4 and 6 -feeding pumps; 5 and 8 - heat exchangers of active circuits; 7 -feed pumps of active circuits; 9 - volume compensators for active circuit coolants

Figure 5 (a, b, c) shows the technological diagrams of the nuclear power plant.

RBMKhigh-power channel reactor, thermal neutrons, water-graphite.

VVERwater power reactor, thermal neutrons, vessel type.

BNfast neutron reactor with liquid metal sodium coolant.

Features of the nuclear power plant are as follows:

They can be built in any geographical location, including hard-to-reach ones;

By their mode they are autonomous from a number of external factors;

Requires a small amount of fuel;

Can work according to a free load schedule (with the exception of nuclear power plants);

Sensitive to alternating mode, especially nuclear power plants with fast neutron reactors; for this reason, as well as taking into account the requirements for economical operation, the basic part of the power system load schedule is allocated for nuclear power plants;

Lightly pollutes the atmosphere; emissions of radioactive gases and aerosols are insignificant and do not exceed the values ​​​​permissible by sanitary standards. In this regard, nuclear power plants are cleaner than thermal power plants.

2.5 Gas turbine power plants (GTPP)

The basic technological diagram of a gas turbine power station is shown in Figure 6.

Figure 6GTPP diagram

Fuel (gas, diesel fuel, fuel oil) is supplied to the combustion chamber 1 , there with the compressor - 3 compressed air is injected. Combustible combustion products give off their energy to the gas turbine 2 , which rotates the compressor and generator The installation is started by an accelerating motor 5 and lasts 1-3 minutes, due to which gas turbine units are considered highly maneuverable and suitable for covering peak loads in power systems. The generated electricity is supplied to the network from the communication transformer 6.

To increase the efficiency of gas turbines, combined cycle gas turbine units (CCGTs) have been developed. In them, fuel is burned in the furnace of a steam generator, the steam from which is sent to a steam turbine. The combustion products from the steam generator, after they have been cooled to the required temperature, are sent to the gas turbine. Thus, CCGTs have two electrical generator, driven into rotation: one by a gas turbine, the other by a steam turbine. The power of a gas turbine is about 20% of that of a steam turbine. The CCGT diagram is shown in the figure 7.

Figure 7CCGT diagram

2.6 Pumped storage power plants (PSPP)

The purpose of pumped storage power plants is to level out the daily load patterns of the electrical system and increase the efficiency of thermal power plants and nuclear power plants. During the hours of minimum load, the PSPP unit systems operate in pump mode, pumping water from the lower reservoir to the upper one and thereby increasing the load of thermal power plants and nuclear power plants; During the hours of maximum system load, they operate in turbine mode, drawing water from the upper reservoir and thereby unloading thermal power plants and nuclear power plants. PSPP units are highly maneuverable and can be quickly transferred from turbine mode to pump mode and, if necessary, to synchronous compensator mode. The efficiency of pumped storage power plants is 70-75%, they require little maintenance personnel and can be built where it is possible to create a pressure reservoir. The diagram of the pumped storage power plant is shown in Figure 8.

Figure 8 Scheme of a pumped storage power plant

In addition to the types of power plants considered, there are low-power power plants that produce electrical energy using non-traditional methods. These include: wind power plants, solar power plants (with a steam boiler, with silicon solar cells), geothermal power plants, tidal power plants.

3 Own needs (s.n.) of thermal power plants

Consumers of electrical energy of stations belong to consumers of the 1st category in terms of power reliability and require power supply from two independent sources. Consumers s.n. thermal power plants of the 1st category are divided into responsible and non-responsible.

Responsible are those SN mechanisms, a short-term stop of which leads to an emergency shutdown or unloading of the main units of the station. Short-term interruption of power supply to irresponsible consumers s.n. does not lead to an immediate emergency stop of the main equipment. However, in order not to disrupt the technological cycle of electricity production, their power supply must be restored after a short period of time.

Figure 9 Scheme of fuel transportation at a thermal power plant

3.1 Fuel transport

From the extraction site, solid fuel is delivered to the power plant by rail (Figure 9) in special self-unloading cars(1). The car enters a closed unloading device(2) with a car dumper, where fuel is poured into a receiving hopper located under the car dumper, from which it is supplied to a conveyor belt(3). In winter, wagons with frozen coal are first fed into a defrosting device(4). The conveyor delivers coal to the coal warehouse)(5), which is served by an overhead grab crane(6). Or through a crushing plant(7) into raw coal bunkers(8), installed in front of the boiler units. Coal can also be supplied to these bunkers from the warehouse(5). To account for the consumption of fuel entering the boiler room of the power plant, scales for weighing this fuel are installed on the fuel path to the boiler room bunkers. From raw coal bunkers(8) fuel enters the pulverized preparation system: raw coal feeders(9), and then to coal grinding mills(10) , from which coal dust is pneumatically transported through the mill separator(11) , into a dust cyclone(12) and dust augers (13) and then in the dust the storage bunker(14), where are the dust feeders from?(15) to boiler burners(16). All pneumatic transport of dust from the mill to the furnace is carried out by a mill fan(17). The air required for fuel combustion is taken in by a blower fan(18) and fed into the air heater(19), from where, after heating, it is partially pumped into the mill(10) for drying and transporting fuel to the furnace of the boiler unit (primary air) and directly to the pulverized coal burners (secondary air).

3.2 Production of steam, heat and electrical energy

Steam at a thermal power plant is produced by a steam generator (boiler). The normal operation of the boiler is ensured by various types of units, working machines, which are driven by electric motors of various types of current, voltage and power. The scheme for generating steam, heat and electrical energy is shown in Figure 10.

Figure 10Scheme for generating steam, heat and electricity. energy: 2 - blower fans; 3 - chimney; 5 - turbine; 6 - generator; 7 -communication transformer; 8 - supplying consumers with their own needs; 9 -consumers powered by generator voltage; 10 - capacitor; eleven - circulation pumps supplying cold water to the condenser to cool the exhaust steam; 12 - a source of cold water; 14 - condensate pumps supplying water to the deaerator; 16 - pumps that replenish the boiler with chemically purified water; 17 - feed pumps supplying prepared water to the boiler; 18 - heating network boiler; 19 - network pumps supplying hot water to the heating network; 20 - steam extraction for production needs; 21 - reduction-cooling device; 22 - gaff pumps for hydro-ash removal devices; 23 - engines of slag removal units; 24 - oil pumps that provide lubrication to the rotating parts of the turbine and generator; 25 - dust feeders

In addition, there is a large number of electric motors of non-main equipment that ensure the operation of automation, opening and closing gates and valves, room ventilation, etc.

Thermal power plants, especially CHP, are the most energy-intensive. The own needs of the thermal power plant consume 12-14% of the electricity generated by the station, and the units of the non-electrical units. are consumers of the 1st and 2nd categories in terms of reliability of power supply and electricity consumption is greater than in any industry.

3.3 Power supplies for auxiliary systems of power plants

The main power sources of the system are s.n. are step-down transformers or reacted lines connected directly to the terminals of generators or to their switchgears. Start-up backup power supplies s.n. are also connected to the general electrical network, as they are usually connected to station switchgears, nearby substations, and tertiary windings of communication autotransformers. Recently, gas turbine units have begun to be installed at thermal stations to power the solar power system. in emergency conditions.

In addition, at power plants of all types, energy sources independent of the power system are provided, ensuring shutdown and cooling of the station without damage to equipment in the event of loss of the main and backup sources of power. At hydroelectric power stations and conventional thermal power plants, batteries are sufficient for this purpose. At powerful CPPs and nuclear power plants, the installation of diesel generators with power corresponding to the technological process is required.

The main requirements for the s.n. system are to ensure the reliability and efficiency of the s.n. mechanisms. the first requirement is the most important, since disruption of the mechanisms of the s.n. entails disruption of the complex technological cycle of electricity production, disruption of the operation of the main equipment, and sometimes the station as a whole, and the development of an accident into a system one. It is now generally accepted that the power supply of s.n. mechanisms. thermal power plants using fossil and nuclear fuel and hydroelectric power plants can be provided most simply, reliably and economically from generator stations and the power system(Figure 11).

Figure 11General power supply diagram for the TPP’s own needs: 1 - backup power line; 2 - starting-backup transformer s.n.; 3 - high voltage switchgear of the station; 4 - generator-transformer unit; 5 - working transformer s.n.; 6 - switchgear s.n.

This system power supply circuit s.n. stations of all types currently ensure reliability and efficiency:

Widespread use of asynchronous motors with a squirrel-cage rotor in the auxiliary system, starting them from full mains voltage without any control devices and refusal to protect the minimum voltage on critical mechanisms;

Successful self-start of electric motors when voltage is restored after disconnecting short circuits in the power system and in the network;

The use of high-speed relay protections and switches on all elements of the system and connections of the SN;

Widespread introduction of system automation devices (AChR, AVR, AVR generators).

All types of nuclear power plants in our country are required to be supplied with emergency power sources in the form of diesel generators or gas turbine units. Their power is selected based on covering the loads of the NPP cooling system and safety devices, but it is not sufficient to power the SN mechanisms. in normal mode.

List of sources used

1. Alexandrov, K.K.Electrical drawings and diagrams. [Text] / K.K. Alexandrov, E.G. Kuzmina. M.: Energoatomizdat, 1990. 285 p.

2. GOST 2.10595. Interstate standard. ESKD. General requirements for text documents [Text].– Instead of GOST 2.10579, GOST 2.90671; input 19960701. Minsk: Interstate. Council for Standardization, Metrology and Certification; M.: Publishing House of Standards, 2002. 26 p.

3. GOST 2.10696 ESKD. Text documents [Text]. Instead of GOST 2.10668, GOST 2.10868, GOST 2.11270; input 19970701. M.: Publishing House of Standards, 2004. 40 p.

4. GOST 7.322003. Bibliographic record. Bibliographic description. General requirements and rules for compiling [Text]. Instead of GOST 7.1-84, GOST 7.16-79, GOST 7.18-79, GOST 7.34-81, GOST 7.40-82; input 20040701. M.: IPK Publishing House of Standards, 2004. 84 p.

5. GOST 7.822001. Bibliographic record. Bibliographic description of electronic resources [Text]. entered. 20020701. M.: IPK Publishing House of Standards, 2001. 33 p.

6. GOST 7.832001. Electronic publications. Basic types and output information [Text]. entered. 20020701. M.: IPK Publishing House of Standards, 2002. 16 p.

7. GOST 2.70184 ESKD . General requirements for text documents [Text]. Instead of GOST 2.701 86; input 19850701. M.: Publishing house of standards, 1985. 16 p.

8. GOST 2.70275 ESKD . Rules for executing electrical circuits [Text]. Enter. 19770701. M.: Publishing House of Standards, 1976. 23 p.

9. GOST 21.613 88. System of design documents for construction. Power equipment. Working drawings [Text].– Enter. 880701. M.: Publishing house of standards, 1988. 16 p.

10. GOST 21.61488. System of design documents for construction. Conventional graphic images of electrical equipment and wiring on plans [Text].– Enter. 19880701. M.: Publishing House of Standards, 1988. 18 p.

11. GOST 2.10979 ESKD. Basic requirements for drawings [Text]. Instead of GOST 2.10768, GOST 2.10968; input 19740701. M.: Standards Publishing House, 2001. 38 p.

12. GOST 2.710 81. Alphanumeric designations in electrical circuits. M.: Publishing house of standards, 1985. 13 p.

13. GOST 2.722 68. Conditional graphic designations in schemes. Electrical machines [Text].– Enter. 01/01/87. M.: Publishing house in standards, 1988. 85 p.

14. GOST 2.747-68. Conditional graphic designations in schemes. Dimensions of graphic symbols [Text].– Enter. 01/01/71. M.: Publishing house of standards. 13 p. (Changes to it No. 1 dated 01/01/91)

15. GOST 2.30168. ESKD. Formats [Text]. M.: Standards Publishing House, 1981. 3 p.

16. GOST 2.30481 ESKD. Drawing fonts [Text]. M.: Publishing House of Standards, 1982. 8 p.

17. GOST 2.72874 ESKD. Conditional graphic designations in schemes. Resistors. Capacitors [Text]. M.: Publishing house in standards, 1985. 9 p.

18. GOST 2.72174 ESKD. Conditional graphic designations in schemes. Designations for general use. [Text]. M.: Publishing house in standards, 1986. 12 p.

19. GOST 2.70972 ESKD. System for designating circuits in electrical circuits. [Text]. M.: Publishing house in standards, 1987. 13 p.

20.GOST 2.10468 ESKD. Main inscriptions [Text]. M.: Publishing house in standards, 1988. 5 p.

21.STP 1220098 Enterprise standard [Text]. Instead of STP AltSTU 12 20096; . Barnaul. : AltSTU Publishing House, 1998. 30 p.

A thermal power plant is an enterprise for generating electricity and heat. When building a power plant, they are guided by the following, which is more important: the location of a fuel source nearby or the location of a nearby source of energy consumption.

Placement of thermal power plants depending on the fuel source.

Let's imagine that, let's say, we have a large coal deposit. If we build a thermal power plant here, we will reduce the costs of fuel transportation. If we take into account that the transport component in the cost of fuel is quite large, then it makes sense to build thermal power plants near mining sites. But what will we do with the resulting electricity? It’s good if there is somewhere nearby to sell it, there is a shortage of electricity in the area.

What to do if there is no need for new electrical power? Then we will be forced to transmit the resulting electricity via wires over long distances. And in order to transmit electricity over long distances without large losses, it is necessary to transmit it through high-voltage wires. If they are not there, then they will need to be pulled. In the future, power lines will require maintenance. All this will also require money.

Placement of thermal power plants depending on the consumer.

Most new thermal power plants in our country are located in close proximity to the consumer.

This is due to the fact that the benefit of placing thermal power plants in close proximity to the fuel source is eaten up by the cost of transportation over long distances via power lines. Moreover, in this case, there are large losses.

When placing a power plant directly next to the consumer, you can also win if you build a thermal power plant. You can read in more detail. In this case, the cost of supplied heat is significantly reduced.

If placed directly next to the consumer, there is no need to build high-voltage power lines; a voltage of 110 kV will be sufficient.

From everything written above we can draw a conclusion. If the fuel source is far away, then in the current situation it is better to build thermal power plants, however, close to the consumer. Greater benefits are obtained if the source of fuel and the source of electricity consumption are nearby.

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The process of converting thermal energy into electrical energy is reflected in simplified (principal) or complete thermal diagrams.

Schematic thermal diagram of thermal power plant shows the main flows of coolants associated with the main and auxiliary equipment in the processes of converting the heat of burned fuel for the generation and supply of electricity and heat to consumers. In practice, the basic thermal diagram is reduced to a diagram of the steam-water path of a thermal power plant (power unit), the elements of which are usually represented in conventional images.

A simplified (principal) thermal diagram of a coal-fired thermal power plant is shown in Fig. 3.1.

Coal is fed into the fuel bunker 1 , and from it - into the crushing plant 2 where it turns to dust. Coal dust enters the furnace of the steam generator (steam boiler) 3 , having a system of tubes in which chemically purified water, called nutrient water, circulates. There is water in the boiler

Rice. 3.1. Simplified thermal diagram of a steam turbine

pulverized coal thermal power plant and the appearance of the steam turbine wheel

heats up, evaporates, and the resulting saturated steam is brought to a temperature of 400-650 °C in a superheater and, under a pressure of 3...25 MPa, enters the steam turbine through a steam line 4 . Superheated steam parameters T 0 , P 0 (temperature and pressure at the turbine inlet) depend on the power of the units. At the CPP, all the steam is used to generate electricity. In a thermal power plant, one part of the steam is used entirely in a turbine to generate electricity in a generator 5 and then goes to the capacitor 6 , and the other, which has a higher temperature and pressure, is taken from the intermediate stage of the turbine and is used for heat supply (dashed line in Fig. 3.1). Condensate pump 7 through a deaerator 8 and then by the feed pump 9 supplied to the steam generator. The amount of steam taken depends on the thermal energy needs of enterprises.

Complete Thermal Circuit (TCS) differs from the fundamental one in that it completely displays equipment, pipelines, shut-off, control and protective valves. The complete thermal diagram of a power unit consists of diagrams of individual units, including a general station unit (spare condensate tanks with transfer pumps, heating network replenishment, raw water heating, etc.). Auxiliary pipelines include bypass, drainage, drain, auxiliary, and steam-air mixture suction pipelines. The designations of PTS lines and fittings are as follows:

3.1.1.1. Thermal circuits kes

Most CPPs in our country use coal dust as fuel. To generate 1 kWh of electricity, several hundred grams of coal are consumed. In a steam boiler, over 90% of the energy released by the fuel is transferred to steam. In the turbine, the kinetic energy of the steam jets is transferred to the rotor (see Fig. 3.1). The turbine shaft is rigidly connected to the generator shaft. Modern steam turbines for thermal power plants are high-speed (3000 rpm), highly economical machines with a long service life.

High-power CPPs using organic fuel are currently being built mainly for high initial steam parameters and low final pressure (deep vacuum). This makes it possible to reduce heat consumption per unit of generated electricity, since the higher the initial parameters P 0 And T 0 in front of the turbine and below the final steam pressure P k, the higher the efficiency of the installation. Therefore, the steam entering the turbine is brought to high parameters: temperature - up to 650 ° C and pressure - up to 25 MPa.

Figure 3.2 shows typical simplified thermal diagrams of IES running on fossil fuels. According to the diagram in Figure 3.2, A Heat is supplied to the cycle only when steam is generated and heated to the selected superheat temperature t lane; according to the diagram in Figure 3.2, b Along with the transfer of heat under these conditions, heat is supplied to the steam after it has worked in the high pressure part of the turbine.

The first circuit is called a circuit without intermediate overheating, the second - a circuit with intermediate superheating of steam. As is known from the thermodynamics course, the thermal efficiency of the second scheme is higher with the same initial and final parameters and the correct choice of intermediate overheating parameters.

According to both schemes, steam from a steam boiler 1 goes to the turbine 2 located on the same shaft with the electric generator 3 . The exhaust steam is condensed in the condenser 4 , cooled by technical water circulating in the tubes. Turbine condensate by condensate pump 5 through regenerative heaters 6 fed into the deaerator 8 .

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 of water 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 metal corrosion in the water and steam paths. At the same time, a deaerator may be absent in a number of thermal circuits of IES. In this so-called neutral-oxygen water regime, a certain amount of oxygen, hydrogen peroxide or air is supplied to the feed water; a deaerator is not needed in the circuit.

R
is. 3.1. Typical thermal circuits of steam turbines

condensing units running on fossil fuels without

intermediate superheating of steam ( A) and with intermediate

overheating ( b)

Deaerated water by feed pump 9 through heaters 10 supplied to the boiler plant. Heating steam condensate formed in heaters 10 , cascades to the deaerator 8 , and the condensate of the heating steam of heaters 6 is supplied by a drain pump 7 into the line through which condensate flows from the condenser 4 .

The described thermal schemes are largely typical and change slightly with increasing unit power and initial steam parameters.

The deaerator and feed pump divide the regenerative heating circuit into groups HPH (high pressure heater) and LPH (low pressure heater). The HPH group consists, as a rule, of 2–3 heaters with cascade drainage down to the deaerator. The deaerator is fed with steam of the same extraction as the upstream HPH. This scheme for switching on a deaerator using steam is widespread. Since a constant steam pressure is maintained in the deaerator, and the pressure in the extraction is reduced in proportion to the decrease in steam flow to the turbine, this scheme creates a pressure reserve for the extraction, which is realized in the upstream HPH. The HDPE group consists of 3–5 regenerative and 2–3 auxiliary heaters. If there is an evaporative installation (cooling tower), the evaporator condenser is connected between the HDPE.

IES that produce only electricity have low efficiency (30–40%), since a large amount of generated heat is discharged into the atmosphere through steam condensers, cooling towers, and is lost with flue gases and condenser cooling water.