The technological process of converting the feedstock (fuel) into the final product (electricity) is reflected in the technological schemes of power plants.

Process flow diagram of a coal-fired TPP is shown in Figure 3.4. It is a complex complex of interconnected paths and systems: a dust preparation system; fuel supply and fuel ignition system (fuel path); ash removal system; gas-air tract; a steam-water path system, including a steam-water boiler and a turbine unit; system for preparation and supply of additional water to replenish feed water losses; technical water supply system for steam cooling; system of network water heating installations; electric power system, including a synchronous generator, step-up transformer, high-voltage switchgear, etc.

Below is a brief description of the main systems and paths of the technological scheme of a TPP using the example of a coal-fired TPP.

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

1. Dust preparation system. Fuel path... Solid fuel delivery is carried out by rail in special open wagons 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 hothouse, in which the gondola car walls 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; the coal is discharged onto the grates overlapping the receiving bunkers. Coal from bunkers is fed by feeders to a conveyor 4 , through which it enters either the coal warehouse 3 , or through the crushing department 5 in the raw coal bunker boiler room 6 , which can also be delivered from a coal warehouse.

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

This entire fuel path, together with the coal storage, belongs to the fuel supply system, which is maintained by the personnel of the fuel and transport department of the TPP.

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

At TPPs that burn gas and oil fuel, the fuel economy is significantly simplified in comparison with pulverized coal TPPs. The coal storage, the crushing department, the conveyor system, the raw coal and dust bunker, as well as the ash collection and ash removal systems are becoming unnecessary.

2... Air-gas path. Slag ash removal system. The air required for combustion is supplied to the air duct.

blower steam boiler heaters 14 ... Air is usually taken from the upper part of the boiler room and (with steam boilers of high capacity) from the outside of the boiler room.

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

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

3... Steam-water tract. Steam superheated in a superheater from a steam boiler 13 through steam lines and a nozzle system to the turbine 22 .

Condensate from condenser 23 turbines are supplied by condensate pumps 24 through regenerative low pressure heaters 18 into the deaerator 20 , in which the 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. From the deaerator, water is supplied by feed pumps 21 through high pressure heaters 19 into the boiler economizer, providing preheating of water and significantly increasing the efficiency of the TPP.

The steam-water path of the TPP is the most complex and responsible, since this path has the highest metal temperatures and the highest steam and water pressures.

To ensure the functioning of the steam-water tract, a system for the preparation and supply of additional water to replenish the losses of the working fluid is required, as well as a system of technical water supply of the TPP to supply cooling water to the turbine condenser.

4... Additional water preparation and supply system. Additional water is obtained as a result of chemical purification of raw water, carried out in special ion-exchange filters for chemical water purification.

Steam and condensate losses 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 shop).

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

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. The water supply system with cooling towers is mainly used at CHP plants. IES uses a water supply system with cooling ponds. With evaporative cooling of water, the vapor is approximately equal to the amount of steam condensing in the turbine condensers. Therefore, replenishment of the water supply systems is required, usually with water from the river.

6. System of networked water heating installations. The schemes may include a small network heating unit for heating the power plant and the adjacent village. To network heaters 29 In this unit, steam comes from the turbine extractions, condensate is removed through the line 31 ... Mains water is supplied to the heater and removed from it through pipelines 30 .

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

In special cases (emergency situations, load shedding, start-up and shutdowns), auxiliary power supply is provided through the standby switchgear bus transformer. Reliable power supply of electric motors of auxiliary units ensures the reliability of operation of power units and TPPs as a whole. Interruption of 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 one 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 unit (Fig. 3.5) consists of a combustion chamber, 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 of the combustor. Fuel (for example, diesel oil, natural or industrial gas) also gets into the combustion chamber and is burned in compressed air.

Rice. 3.4. Simplified process flow diagram of a gas turbine

power plants on liquid or gas fuel: T - fuel; V -

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

The main advantages of gas turbine units in comparison with steam turbine units are:

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

2) significantly less demand for cooling water, which makes it possible to use GTU in areas with limited water resources;

3) significantly fewer operating personnel;

4) quick start-up;

5) lower cost of generated electricity.
3.1.3. Layout diagrams of TPP
TPPs by type (structure) of the thermal scheme are subdivided into block and non-block.

With a block scheme All the main and auxiliary equipment of the plant has no technological connections with the equipment of another plant of the power plant. In fossil fuel power plants, steam is supplied to each turbine only from one or two connected boilers. A steam turbine plant, the turbine of which is powered by steam from one steam boiler, is called monoblock, in the presence of two boilers for one turbine - double-block.

With a non-block diagram TPP steam from all steam boilers enters a common mainline and only from there is distributed to individual turbines. In some cases, it is possible to direct steam directly from steam boilers to turbines, however, the common connecting line is preserved, so you can always use steam from all boilers to power any turbine. The lines carrying water to the steam boilers (feed lines) are also cross-linked.

Block TPPs are cheaper than non-block ones, since the pipeline diagram 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 work of one block does not affect the neighboring blocks. When expanding the power plant, the subsequent unit can have a different capacity and operate at new parameters. This makes it possible to install more powerful equipment with higher parameters at the expandable station, i.e. allows to improve the equipment and improve the technical and economic indicators of the power plant. At the same time, the processes of setting up new equipment do not affect the operation of previously installed units. However, for normal operation of block TPPs, the reliability of their equipment should be much higher than that of non-block ones. There are no standby steam boilers in the units; if the possible productivity of the boiler is higher than the flow rate required for a given turbine, part of the steam (the so-called hidden reserve, which is widely used at non-block TPPs) cannot be transferred here to another unit. For steam turbine plants with intermediate superheating of steam, the block scheme is practically the only possible one, since the non-block scheme of the station in this case will turn out to be overly complicated.

In our country, steam turbine units of TPPs without controlled extraction of steam with an initial pressure P 0 ≤8.8 MPa and installations with controlled extractions at P 0 ≤12.7 MPa, operating in cycles without intermediate superheating of steam, are built non-block. At higher pressures (at KES at P 0 ≥12.7 MPa, and at CHPP at P 0 = 23.5 MPa) all steam turbine units operate in cycles with reheating, and stations with such installations are built in modular units.

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 the layout of the main building of the power plant.

The main building of a power plant usually consists of a turbine room, a boiler room (with a bunker room for solid fuel operation) or a reactor room at a nuclear power plant and a deaerator room. In the engine room, along with the main equipment (primarily turbine units), there are: condensate pumps, regenerative low and high pressure heaters, feed pumping units, evaporators, steam converters, network heaters (at CHP), auxiliary heaters and other heat exchangers.

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

In fig. 3.6. the layout diagram of the power unit of the pulverized-coal power plant is shown: I - room for steam generators; 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 –The steam generator; 9 - mill fan; 10 - bunker of coal dust; 11 - dust feeders; 12 - pipelines for reheat steam; 13 - deaerator; 14 - steam turbine; 15 - electric generator; 16 - a step-up electrical transformer; 17 - capacitor; 18 - supply and drain pipelines of cooling water; 19 - condensate pumps; 20 - regenerative HDPE; 21 - feed pump; 22 - regenerative LDPE; 23 - blower fan; 24 - ash collector; 25 - slag and ash 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 location of only the main and part of the auxiliary equipment, as well as the dimensions of the structures (m): 1 - boiler room; 2 –Turbine department; 3 - condenser compartment; 4 - generator compartment; 5 - deaerator department; 6 - blower fan; 7 - regenerative air heaters; 8 - auxiliary switchgear (RUSN); 9 - chimney.

Rice. 3.7. Layout of the main building of the gas-oil

power plants with a capacity of 2400 MW
The main equipment of the IES (boiler and turbine units) is located in the main building, boilers and a pulverized plant (at IESs 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 the IES, mainly one boiler is installed per turbine. The boiler with the turbine unit and their auxiliary equipment form a separate part - the monoblock of the power plant.

For turbines with a capacity of 150–1200 MW, boilers with a capacity of 500–3600 m 3 / h of steam, respectively, are required. Previously, the state district power station used two boilers per turbine, i.e. double-blocks . At the IES without intermediate superheating of steam 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 line, and from it is distributed between the turbines.

The dimensions of the main building depend on the capacity 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 turbine hall is about 30 m, the boiler room is 50 m more. The efficiency of the layout of the main building is estimated approximately by the specific cubic capacity, which is about 0.7-0.8 m 3 / kW at a pulverized coal power plant. , and at the gas-oil plant - about 0.6–0.7 m 3 / kW. Part of the auxiliary equipment of the boiler room (smoke exhausters, blowing fans, ash collectors, dust cyclones and dust separators of the dust preparation system) are often installed outside the building, in the open air.

IES is built directly at water supply sources (river, lake, sea); often a reservoir (pond) is created next to the IES. On the territory of the IES, in addition to the main building, 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 serving the IES are located. Fuel is usually delivered to the IES territory by train. Ash and slag from the combustion chamber and ash collectors are removed hydraulically. On the territory of the IES, railways and highways are laid, conclusions are being built power lines, engineering ground and underground communications. The area of the territory occupied by the IES facilities is, depending on the power plant capacity, fuel type and other conditions, 25–70 hectares .

Large-scale 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 IES with a capacity of 3,000 MW); in addition, maintenance personnel are required.

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

Controlling a wide variety of IES equipment is possible only on the basis of comprehensive automation of production processes. Modern condensing turbines are fully automated. The boiler unit has automated control over the processes of fuel combustion, supplying the boiler unit with water, maintaining the temperature of steam overheating, etc. Other processes of the IES are also automated: maintaining the specified operating modes, starting and stopping units, protecting equipment in case of abnormal and emergency conditions.
3.1.4. The main equipment of TPP
To the main equipment of TPP include steam boilers (steam generators), turbines, synchronous generators, transformers.

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

At present, serial domestic condensing power units of thermal power plants with a capacity of 200, 300, 500, 800 and 1200 MW are being produced. For the CHPP, 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 equipment cross-links.

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

The characteristics of the PC are:

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

The steam flow rate for the turbine is usually set for the winter operation of the power plant. The capacity of the steam boiler should be selected taking into account the increase in steam consumption to the turbine due to the increase in pressure in the condenser in the summer season, steam and condensate leaks, the inclusion of network installations for heat supply and other costs. In accordance with this, the productivity of the steam boiler is selected according to the maximum flow of fresh steam through the turbine, taking into account the steam consumption for the auxiliary needs of the power plant and providing a certain margin for using the rotating reserve and other purposes.

Weight, dimensions, metal consumption and available equipment for mechanization and automation of service are also characteristic of the PC.

The first PCs were spherical. The PC built in 1765 by I. Polzunov, who created the first universal steam engine and thus laid the foundation for the energy use of water vapor, also had such a shape. At first, PCs were made from copper, then from cast iron. At the end of the 18th century, the level of development of ferrous metallurgy made it possible to make steel cylindrical PCs from sheet material by riveting. Gradual changes in PC designs have led to numerous variations. 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 the 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 increase the parameters of the PC led to an increase in the size and an increase in the number of flows of water and steam. 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 the dimensions and, first of all, in the height of the PC. PC efficiency reached 93–95%.

Originally, water tube PCs were PCs only bar aban 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 - downpipes; 6 - superheater; 7 - secondary (intermediate) superheater; 8 - economizer; 9 - air heater.
In the combustion chamber 1 the burners are located 2, through which a mixture of fuel with heated air enters the furnace. The number and type of burners depend on their performance, unit power and type of fuel. The three most common fuels are coal, natural gas and fuel oil. The coal is preliminarily converted into coal dust, which is blown into the furnace with the help of air through the burners.

The walls of the combustion chamber are covered with pipes from the inside (screens) 3, which absorb heat from hot gases. Water enters the screen pipes through unheated down pipes 5 out of the drum 4, in which the given level is constantly maintained . In the wall tubes, water boils and moves upward in the form of a steam-water mixture, then getting into the steam space of the drum. Thus, during the operation of the boiler, there is a natural circulation of water with steam in the circuit: drum - downpipes - screen pipes - drum. Therefore, the boiler shown in fig. 3.8 is called a natural circulation drum boiler. The steam outlet to the turbine is replenished by supplying feed water to the boiler drum using pumps.

The steam supplied from the wall tubes to the steam space of the drum is saturated and in this form, although it has a full working pressure, is not yet suitable for use in a turbine, since it has a relatively small operability. In addition, the moisture content of saturated steam during expansion in the turbine increases to the limits that are dangerous for the reliability of the rotor blades. Therefore, steam is sent from the drum to the superheater 6, where an additional amount of heat is given to it, due to which it becomes superheated from saturated. At the same time, its temperature rises to about 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 carried out in it, there are radiation, screen (semi-radiation) and convective superheaters.

Radiant superheaters placed on the ceiling of the combustion chamber or on its walls, often between the pipes of the screens. They, like the evaporative screens, perceive the heat emitted by the torch of the combusted fuel. Screen steam superheaters, made in the form of separate flat screens of pipes connected in parallel, are reinforced at the outlet 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 boiler unit flue, usually behind screens or behind the firebox; they are multi-row coil packs. Superheaters consisting only of convective stages are usually installed in medium and low pressure boilers at a superheated steam temperature not exceeding 440–510 ºС. In high-pressure boilers with significant steam superheating, combined superheaters are used, including convective, screen, and sometimes radiation parts.

At a steam pressure of 14 MPa (140 kgf / cm 2) and above, a secondary (intermediate) superheater is usually installed behind the primary superheater 7 ... It, like the primary one, is formed of steel pipes bent into coils. Steam is sent here, which has been exhausted 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. . In the secondary (intermediate) superheater, the temperature of this steam rises again to 560 ° C, and its efficiency 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 reheating of steam, despite the complexity of the boiler and turbine design and a significant increase in the number of steam pipelines, has great economic advantages over boilers without reheating of steam. The steam consumption for the turbine is approximately halved, while the fuel consumption is reduced by 4–5%. The presence of intermediate superheating of steam also reduces the moisture content of the steam in the last stages of the turbine, due to which the wear of the blades by water droplets decreases and the efficiency of the LPC of the turbine slightly increases.

Further, in the tail section of the boiler, there are auxiliary surfaces designed to use the heat of flue gases. This convection part of the boiler contains a water economizer. 8, where the feed water is heated before entering the drum, and the air heater 9, used for heating air before supplying 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 out by a smoke exhauster into the chimney.

Further improvement of water-tube PC made it possible to create a PC consisting entirely of steel pipes of small diameter, into which water under pressure enters from one end, and steam of specified parameters comes out from the other - the so-called direct-flow boiler (fig. 3.9). Thus, this is a PC, in which the complete evaporation of water occurs during a single (direct-flow) passage of water through the evaporating heating surface. In the direct-flow PC, water is supplied by a feed pump through an economizer. There is no drum or standpipes in such a boiler.

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 HPC for secondary overheating; 11 - steam removal to the central heating system after secondary overheating; 12 - discharge of flue gases to the air heater
The heating surface of the boiler can be thought of as a series of parallel coils, in which the water heats up as it moves, turns into steam, and then the steam is overheated to the required temperature. These coils are located both on the walls of the combustion chamber and in the boiler gas ducts. Combustion devices, secondary superheater and air preheater of once-through 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 proportion of this boiler water in an amount of about 0.5% must be discharged from the boiler all the time in order to prevent the salt concentration from building up above a certain limit. This process is called blowdown boiler. For once-through boilers, this method of removing accumulated salts is inapplicable due to the lack of water volume, and therefore the feed water quality standards for them are much more stringent.

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

Direct-flow PCs are installed, as a rule, on a condensation power plants where the boilers are powered by demineralized water. Their use at combined heat and power plants is associated with increased costs for chemical treatment of additional (make-up) water. The most effective direct-flow PS for supercritical pressures (above 22 MPa), where other types of boilers are inapplicable.

In power units, either one boiler is installed per turbine ( monoblocks), or two boilers of half capacity. To the benefits double-blocks can be attributed to the possibility of operation of the unit with half load on the turbine in the event of damage to one of the boilers. However, the presence of two boilers in the 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 very uneconomical. The experience of a number of stations has shown that monoblocks can operate no less reliably than double-blocks.

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

Heating boiler - This is a boiler unit of a combined heat and power plant (CHP), which provides a simultaneous supply of steam to heating turbines and the production of steam or hot water for technological, heating and other needs. In contrast to KES boilers, in heating boilers, the returned contaminated condensate is usually used as a water feeder. For such operating conditions, drum-type boilers with staged evaporation are most suitable. In most CHP plants, cogeneration boilers are cross-linked by steam and water. Drum boilers with a steam capacity of 420 t / h (steam pressure 14 MPa, temperature 560 ºС) are the most common in the Russian Federation at CHPPs. Since 1970, monoblocks with once-through boilers with a steam capacity of 545 t / h (25 MPa , 545 ° C).

Cogeneration PCs also include peak hot water boilers, which are used for additional heating of water with an increase in heat load in excess of the maximum provided by the extraction of turbines. 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 CHPP. The use of comparatively cheap peak hot water heating boilers for removing short-term peaks of heat loads allows to dramatically increase the number of hours of use of the main heating equipment and to increase the efficiency of its operation.

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

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

They tried to create a PT for a long time. Known is the description of the 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 reached a sufficient level, K.G. Laval (Sweden) and C.A. Parsons (Great Britain) independently created industrially suitable PTs in 1884-1889.

Laval applied steam expansion in conical fixed nozzles in one step from initial to final pressure and directed the resulting jet (with a supersonic outflow velocity) onto one row of rotor blades mounted on a disk. PTs operating on this principle are called active Fri. The impossibility of obtaining high aggregate power and the very high rotational 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 the drive of auxiliary mechanisms.

Parsons created a multistage reactive PT, in which the expansion of steam was carried out in a large number of successively located stages, not only in the channels of the stationary (guide) blades, but also between the movable (working) blades. The Parsons' rocket tank 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 FH power plants developed in the direction of creating multistage structures, in which the expansion of steam was carried out in a number of successively located stages. This made it possible to significantly increase the unit power of the PT, while maintaining a moderate rotational speed required for direct connection of the PT shaft with the mechanism it rotates, in particular, an electric generator.

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

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

By the number of bodies (cylinders) PT is subdivided into monohull, double-hull and three-case(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 the bifurcation of the steam flow in the low-pressure part. At the same time, such a PT turns out to be more expensive, heavy and complex.

According to the number of shafts distinguish 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-placed single-shaft PTs, connected by a common thermal process, and in ship PTs also by a common gear transmission (reducer).

The stationary part of the PT (housing) is split in the horizontal plane for the possibility of mounting the rotor. The body has grooves for installing diaphragms, the connector of which coincides with the plane of the body connector. Along the periphery of the diaphragms, there are nozzle channels formed by curved blades that are poured 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 leaks outward (from the high pressure side) and air suction into the housing (from the low side). Labyrinth seals are also installed in the places where the rotor passes through the diaphragms in order to avoid steam flow 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 speed increases by 10-12% above the nominal. The rear end of the rotor is equipped with a barring device with an electric drive for slow (4–6 rpm) rotation of the rotor after stopping the PT, which is necessary for its uniform cooling.

In fig. 3.10 schematically shows the device of one of the intermediate stages of a modern steam turbine at a TPP. The stage consists of a disc with blades and a diaphragm. The diaphragm is a vertical partition between two discs, in which stationary guide vanes are located along the entire circumference against the rotor blades, forming nozzles for steam expansion. The diaphragms are made of two horizontally split halves, each of which is fixed in the corresponding half of the turbine housing.

Rice. 3.10. Device of one of the stages of multistage

turbines: 1 - shaft; 2 - disk; 3 - working blade; 4 - the wall of the turbine cylinder; 5 - nozzle grill; 6 - diaphragm;

7 - diaphragm seal
A large number of stages forces the turbine to be made of several cylinders, placing 10-12 stages in each. Turbines with reheating of steam in the first high pressure cylinder (HPC) usually have a group of stages that convert the energy of the steam from the initial parameters to the pressure at which the steam is supplied for reheating. After the reheating of steam in turbines with a capacity of 200 and 300 MW, steam is supplied to two more cylinders - the LPC and the LPC.