Boiler installations of thermal power plants. General information. Steam boilers of thermal power plants (TPP)

General information. The boiler installation consists of a boiler and auxiliary equipment

MAIN EQUIPMENT OF THERMAL

ELECTRIC STATIONS

Chapter 7

BOILER UNITS OF THERMAL POWER PLANTS

General information

The boiler installation consists of a boiler and auxiliary equipment. Devices designed to produce steam or hot water at high pressure due to the heat released during fuel combustion or heat supplied from external sources (usually with hot gases) are called boiler units. They are divided respectively into steam boilers and hot water boilers. Boiler units that use (i.e. utilize) the heat of exhaust gases from furnaces or other main and by-products of various technological processes are called waste heat boilers.

The boiler includes: firebox, superheater, economizer, air heater, frame, lining, thermal insulation, casing.

Auxiliary equipment includes: draft machines, devices for cleaning heating surfaces, fuel preparation and fuel supply equipment, slag and ash removal equipment, ash collection and other gas cleaning devices, gas and air pipelines, water, steam and fuel pipelines, fittings, fittings, automation, instruments and control devices protection, water treatment equipment and chimney.

Valves include control and locking devices, safety and water testing valves, pressure gauges, water indicating devices.

The set includes manholes, peepholes, hatches, gates, and dampers.

The building in which the boilers are located is called boiler room

A set of devices, including a boiler unit and auxiliary equipment, is called a boiler installation. Depending on the type of fuel burned and other conditions, some of the specified accessories may not be available.

Boiler plants that supply steam to the turbines of thermal power plants are called power plants. To supply steam to industrial consumers and heat buildings, in some cases special industrial and heating boiler installations are created.

Natural and artificial fuels (coal, liquid and gaseous products of petrochemical processing, natural and blast furnace gases, etc.), waste gases of industrial furnaces and other devices are used as heat sources for boiler plants.

The technological diagram of a boiler plant with a drum steam boiler operating on pulverized coal is shown in Fig. 7.1. After crushing, fuel from the coal warehouse is fed by a conveyor into fuel bunker 3, from which it is sent to a dust preparation system equipped with a coal grinding mill. 1 . Pulverized fuel using a special fan 2 transported through pipes in the air flow to burners 3 of the furnace of boiler 5 located in the boiler room 10. Secondary air is also supplied to the burners by a blower fan. 15 (usually through an air heater 17 boiler). Water to feed the boiler is supplied to its drum 7 by a feed pump 16 feed water tank 11, having a deaeration device. Before water is supplied to the drum, it is heated in a water economizer 9 boiler Water evaporation occurs in a pipe system 6. Dry saturated steam from the drum enters the superheater 8 , then sent to the consumer.

Rice. 7.1. Technological diagram of the boiler plant:

1 - coal grinding mill; 2 - mill fan; 3 - fuel bunker; 7 - burner; 5 - circuit of the furnace and gas ducts of the boiler unit; 6 - pipe system - firebox screens; 7 - drum; 8 - superheater; 9 - water johnomizer; 10 - outline of the boiler house building (boiler room premises); 11 - water reserve tank with deaeration device; 12 - chimney; 13 - pump; 14- ash collection device; 15- fan; 16- nutritious cicoc; 17 - air heater; 18 - pump for pumping out ash and slag pulp; / - water path; b– superheated steam; V- fuel path; G - air movement path; d - combustion products path; e - path of ash and slag

The fuel-air mixture supplied by the burners into the combustion chamber (furnace) of the steam boiler burns, forming a high-temperature (1500 °C) torch that radiates heat to the pipes 6, located on inner surface firebox walls. These are evaporative heating surfaces called screens. Having transferred part of the heat to the screens, flue gases with a temperature of about 1000 ° C pass through the upper part of the rear screen, the pipes of which are located here at large intervals (this part is called a festoon), and wash the superheater. Then the combustion products move through the water economizer, air heater and leave the boiler with a temperature slightly exceeding 100 °C. Gases leaving the boiler are cleaned of ash in an ash collection device 14 and a smoke exhauster 13 released into the atmosphere through a chimney 12. The pulverized ash collected from the flue gases and the slag that falls into the lower part of the furnace are removed, as a rule, in a stream of water through channels, and then the resulting pulp is pumped out with special pumps. 18 and is removed through pipelines.

The drum boiler unit consists of a combustion chamber and; flues; drum; heating surfaces under pressure from the working medium (water, steam-water mixture, steam); air heater; connecting pipelines and air ducts. The pressurized heating surfaces include the water economizer, evaporative elements formed primarily by the firebox screens and festoon, and the superheater. All heating surfaces of the boiler, including the air heater, are usually tubular. Only a few powerful steam boilers have air heaters of a different design. The evaporating surfaces are connected to the drum and, together with the lowering pipes connecting the drum with the lower screen collectors, form a circulation circuit. The separation of steam and water occurs in the drum; in addition, a large supply of water in it increases the reliability of the boiler.

The lower trapezoidal part of the furnace of the boiler unit (see Fig. 7.1) is called a cold funnel - the partially sintered ash residue falling from the torch is cooled in it, which falls in the form of slag into a special receiving device. Gas-oil boilers do not have a cold funnel. The gas duct in which the water economizer and air heater are located is called convective (convective shaft), in which heat is transferred to water and air mainly by convection. The heating surfaces built into this flue and called tail surfaces make it possible to reduce the temperature of combustion products from 500...700 °C after the superheater to almost 100 °C, i.e. use the heat of the burned fuel more fully.

The entire pipe system and the boiler drum are supported by a frame consisting of columns and cross beams. The firebox and flues are protected from external heat loss by lining - a layer of fireproof and insulating materials. On the outside of the lining, the boiler walls are lined with a gas-tight steel sheet in order to prevent excess air from being sucked into the firebox and dusty hot combustion products containing toxic components being knocked out.

7.2. Purpose and classification of boiler units

The boiler unit is called energy device productivity D(t/h) to produce steam at a given pressure R(MPa) and temperature t(°C). This device is often called a steam generator, because steam is generated in it, or simply steam boiler. If the end product is hot water of specified parameters (pressure and temperature), used in industrial technological processes and for heating industrial, public and residential buildings, then the device is called hot water boiler. Thus, all boiler units can be divided into two main classes: steam and hot water.

According to the nature of the movement of water, steam-water mixture and steam, steam boilers are divided as follows:

· drum with natural circulation (Fig. 7.2,a);

drum with multiple forced circulation(Fig. 7.2, b);

direct-flow (Fig. 7.2, V).

In drum boilers with natural circulation(Fig. 7.3) due to the difference in the densities of the steam-water mixture in the left pipes 2 and fluids in the right pipes 4 the steam-water mixture in the left row will move upward, and the water in the right row will move downward. The pipes of the right row are called lowering, and those of the left are called lifting (screen).

The ratio of the amount of water passing through the circuit to the steam output of the circuit D over the same period of time is called circulation ratio K ts . For boilers with natural circulation K tz ranges from 10 to 60.

Rice. 7.2. Schemes for generating steam in steam boilers:

A- natural circulation; b- multiple forced circulation; V- direct-flow circuit; B - drum; ISP - evaporative surfaces; PE - steam superheater; EC - water economizer; PN - feed pump; CN - circulation pump; NK - lower collector; Q- heat supply; OP - downpipes; POD – lifting pipes; D n - steam consumption; D pw - feed water consumption

The difference in weights of two columns of liquids (water in the downdraft pipes and a steam-water mixture in the riser pipes) creates a driving pressure D R, N/m 2, water circulation in the boiler pipes

Where h- contour height, m; r in and r cm - densities (volumetric masses) of water and steam-water mixture, kg/m 3.

In boilers with forced circulation, the movement of water and steam-water mixture (see Fig. 7.2, b)is carried out forcibly with the help of a central circulation pump, the driving pressure of which is designed to overcome the resistance of the entire system.

Rice. 7.3. Natural circulation of water in the boiler:

1 - lower manifold; 2 - left pipe; 3 - boiler drum; 4 - right pipe

In once-through boilers (see Fig. 7.2, V) there is no circulation circuit, there is no multiple circulation of water, there is no drum, water is pumped by the feed pump PN through the economizer EK, evaporating surfaces ISP and steam transfer unit PE, connected in series. It should be noted that once-through boilers use water of higher quality; all water entering the evaporation tract is completely converted into steam at its exit, i.e. in this case the circulation rate K ts = 1.

A steam boiler unit (steam generator) is characterized by steam output (t/h or kg/s), pressure (MPa or kPa), temperature of the steam produced and temperature of the feed water. These parameters are listed in table. 7.1.

Table 7.1. Summary table of boiler units produced by domestic industry, indicating the scope of application

Pressure, MPa(at)	Boiler steam production, t/h	Steam temperature, °C	Feedwater temperature, °C	Application area
0,88 (9)	0,2; 0,4; 0,7; 1,0	Saturated		Satisfying the technological and heating needs of small industrial enterprises
1,37 (14)	2,5	Saturated		Meeting the technological and heating needs of larger industrial enterprises
	4; 6,5; 10; 15; 20	Saturated or overheated, 250		Quarterly heating boiler houses
2,35 (24)	4; 6,5; 10; 15; 20	Saturated or superheated, 370 and 425		Meeting the technological needs of some industrial enterprises
3,92 (40)	6,5; 10; 15; 20; 25; 35; 50; 75			Supply of steam to turbines with a capacity of 0.75 to 12.0 MW at power plants low power
9,80 (100)	60; 90; 120; 160; 220			Supply of steam to turbines with a capacity of 12 to 50 MW at power plants
13,70 (140)	160; 210; 320; 420; 480			Supply of steam to turbines with a capacity of 50 to 200 MW at large power plants
	320; 500; 640
25,00 (255)	950; 1600; 2500	570/570 (with secondary overheating)		Supply of steam to turbines with a capacity of 300, 500 and 800 MW at the largest power plants

Based on steam output, boilers are divided into low steam output (up to 25 t/h), medium steam output (from 35 to 220 t/h) and high steam output (from 220 t/h or more).

Based on the pressure of the steam produced, boilers are distinguished: low pressure (up to 1.37 MPa), medium pressure (2.35 and 3.92 MPa), high pressure(9.81 and 13.7 MPa) and supercritical pressure (25.1 MPa). The boundary separating low-pressure boilers from medium-pressure boilers is arbitrary.

Boiler units produce either saturated steam or steam superheated to different temperatures, the magnitude of which depends on its pressure. Currently, in high-pressure boilers the steam temperature does not exceed 570 °C. The temperature of the feed water, depending on the steam pressure in the boiler, ranges from 50 to 260 °C.

Hot water boilers are characterized by their heating output (kW or MW, in the MKGSS system - Gcal/h), the temperature and pressure of the heated water, as well as the type of metal from which the boiler is made.

7.3. Main types of boiler units

Energy boiler units. Boiler units with a steam capacity from 50 to 220 t/h at a pressure of 3.92... 13.7 MPa are made only in the form of drums, operating with natural circulation of water. Units with a steam capacity from 250 to 640 t/h at a pressure of 13.7 MPa are made both in the form of drum and direct-flow, and boiler units with a steam capacity of 950 t/h and more at a pressure of 25 MPa are made only in the form of direct-flow, since at supercritical pressure natural circulation cannot be achieved.

A typical boiler unit with a steam capacity of 50...220 t/h at a steam pressure of 3.97...13.7 MPa at an overheating temperature of 440...570 °C (Fig. 7.4) is characterized by the arrangement of its elements in the form of the letter P, in As a result, two flue gas passages are formed. The first move is a shielded firebox, which determined the name of the type of boiler unit. The screening of the firebox is so significant that all the heat required to convert the water entering the boiler drum into steam is transferred to the screen surfaces. Coming out of the combustion chamber 2, flue gases enter a short horizontal connecting flue where the superheater is located 4, separated from the combustion chamber only by a small scallop 3. After this, the flue gases are directed into the second - downward gas duct, in which water economizers 5 and air heaters are located in a cut. 6. Burners 1 There can be either swirling ones, located on the front wall or on the side walls opposite, and angular ones (as shown in Fig. 7.4). With a U-shaped layout of the boiler unit operating with natural circulation of water (Fig. 7.5), the drum 4 the boiler is usually placed relatively high above the firebox; Steam separation in these boilers is usually carried out in remote devices - cyclones 5.

Rice. 7.4. Boiler unit with a steam capacity of 220 t/h with a steam pressure of 9.8 MPa and a superheated steam temperature of 540 °C:

1 - burners; 2 - combustion chamber; 3 - festoon; 4 - superheater; 5 - water economizers; 6 - air heaters

When burning anthracite, a semi-open, fully shielded firebox is used. 2 with counter-arranged burners 1 on the front and rear walls and the bottom, intended for liquid slag removal. Studded screens insulated with a fire-resistant mass are placed on the walls of the combustion chamber, and open screens are placed on the walls of the cooling chamber. A combined superheater is often used 3, consisting of a ceiling radiation part, semi-radiation screens and a convective part. In the downward part of the unit, a water economizer is placed in a dissected manner, i.e. alternating 6 second stage (along the water path) and a tubular air heater 7 of the second stage (along the air path), and behind them a water economizer 8 w air heater 9 first stage.

Rice. 7.5. Boiler unit with a steam capacity of 420 t/h with a steam pressure of 13.7 MPa and a superheated steam temperature of 570 °C:

1 - burners; 2 - shielded firebox; 3 ~- superheaters; 4 - drum;

5 - cyclone; 6, 8 - economizers; 7, 9 - air heaters

Boiler units with a steam capacity of 950, 1600 and 2500 t/h and a steam pressure of 25 MPa are designed to operate in a unit with turbines with a capacity of 300, 500 and 800 MW. The layout of boiler units of the named steam capacity is U-shaped with an air heater located outside the main part of the unit. Double steam superheat. Its pressure after the primary superheater is 25 MPa, temperature 565 °C, after the secondary superheater - 4 MPa and 570 °C, respectively.

All convective heating surfaces are made in the form of packages of horizontal coils. Outside diameter heating surface pipes is 32 mm.

Steam boilers for industrial boiler houses. Industrial boiler houses that supply industrial enterprises with low-pressure steam (up to 1.4 MPa) are equipped with steam boilers manufactured by domestic industry with a capacity of up to 50 t/h. Boilers are produced for burning solid, liquid and gaseous fuels.

A number of industrial enterprises use medium-pressure boilers when technologically necessary. Single-drum vertical water-tube boiler BK-35 (Fig. 7.6) with a capacity of 35 t/h at an excess pressure in the drum of 4.3 MPa (steam pressure at the outlet of the superheater 3.8 MPa) and a superheat temperature of 440 °C consists of two vertical gas ducts - a lift and lower, connected at the top by a small horizontal gas duct. This boiler layout is called U-shaped.

The boiler has a highly developed screen surface and a relatively small convective beam. Screen pipes 60 x 3 mm are made of steel grade 20. The rear screen pipes in the upper part are spread out, forming a scallop. The lower ends of the screen pipes are flared in the collectors, and the upper ends are rolled into the drum.

The main type of low-capacity steam boilers, widespread in various industries, transport, utilities and agriculture(steam is used for technological and heating and ventilation needs), as well as at low-power power plants, are vertical water tube boilers DKVR. The main characteristics of DKVR boilers are given in table. 7.2.

Hot water boilers. It was previously indicated that at thermal power plants with a large heat load, instead of peak network water heaters, high-power hot water boilers are installed for centralized heat supply of large industrial enterprises, cities and individual regions.

Rice. 7.6. Single-drum steam boiler BK-35 with gas-oil furnace:

1 - gas-oil burner; 2 - side screen; 3 - front screen; 4 - gas supply; 5 - air duct; 6 - down pipes; 7 - frame; 8 - cyclone; 9 - boiler drum; 10 - water supply; 11 - superheater manifold; 12 - steam output; 13 - surface steam cooler; 14 - steam superheater; 15 - coil economizer; 16 - flue gas outlet; 17 - tubular air heater; 18 - rear screen; 19 - combustion chamber

Table 7.2. Main characteristics of DKVR boilers, production

"Uralkotlomash" (liquid and gaseous fuel)

Brand	Steam capacity, t/h	Steam pressure, MPa	Temperature, °C	Efficiency, % (gas/fuel oil)	Dimensions, mm	Weight, kg
Length	Width	Height
DKVR-2.5-13	2,5	1,3		90,0/883
DKVR-4-13	4,0	1,3		90,0/888
DKVR-6; 5~13	6,5	1,3		91,0/895
DKVR-10-13	10,0	1,3		91,0/895
DKVR-10-13	10,0	1,3		90,0/880
DKVR-Yu-23	10,0	2,3		91,0/890
DKVR-10-23	10,0	2,3		90,0/890
DKVR-10-39	10,0	3,9		89,0
DKVR-10-39	10,0	3,9		89,0
DKVR-20-13	20,0	1,3		92,0/900			43 700
DKVR-20-13	20,0	1,3		91,0/890
DKVR-20-23	20,0	2,3		91,0/890			44 4001

Hot water boilers are designed to produce hot water of specified parameters, mainly for heating. They operate on a direct-flow basis with constant water flow. The final heating temperature is determined by the conditions for maintaining a stable temperature in living and working spaces heated by heating devices, through which the water heated in the hot water boiler circulates. Therefore, with a constant surface heating devices the temperature of the water supplied to them increases as the ambient temperature decreases. Typically, heating network water in boilers is heated from 70... 104 to 150... 170 °C. Recently, there has been a tendency to increase the temperature of water heating to 180... 200 °C.

To avoid condensation of water vapor from the flue gases and the associated external corrosion of heating surfaces, the water temperature at the inlet to the unit must be higher than the dew point for combustion products. In this case, the temperature of the pipe walls at the water entry point will also not be lower than the dew point. Therefore, the inlet water temperature should not be lower than 60 °C when operating on natural gas, 70 °C when operating on low-sulfur fuel oil and 110 °C when using high-sulfur fuel oil. Since water in the heating network can be cooled to a temperature below 60 ° C, before entering the unit, a certain amount of (direct) water already heated in the boiler is mixed into it.

Rice. 7.7. Gas-oil water heating boiler type PTVM-50-1

A gas-oil water heating boiler of the PTVM-50-1 type (Fig. 7.7) with a heating capacity of 50 Gcal/h has proven itself well in operation.

7.4. Main elements of the boiler unit

The main elements of the boiler are: evaporative heating surfaces (screen tubes and boiler bundle), a superheater with a steam superheat regulator, a water economizer, an air heater and draft devices.

Evaporating surfaces of the boiler. Steam-generating (evaporation) heating surfaces differ from each other in boilers of different systems, but, as a rule, they are located mainly in the combustion chamber and receive heat by radiation - radiation. These are screen pipes, as well as a convective (boiler) bundle installed at the exit from the furnace of small boilers (Fig. 7.8, A).

Rice. 7.8. Evaporator layout diagrams (A) and superheating (b) surfaces of the drum boiler unit:

/ - contour of the firebox lining; 2, 3, 4 - side screen panels; 5 - front screen; 6, 10, 12 - collectors of screens and convective beam; 7 - drum; 8 - festoon; 9 - boiler bundle; 11 - rear screen; 13 - wall-mounted radiation superheater; 14 - screen semi-radiative superheater; 15 ~~ ceiling radiant superheater; 16 ~ overheating regulator; 17 - removal of superheated steam; 18 - convective superheater

The screens of boilers with natural circulation, operating under vacuum in the furnace, are made of smooth pipes (smooth tube screens) with an internal diameter of 40...60 mm. The screens are a series of parallel vertical rise pipes connected to each other by collectors (see Fig. 7.8, A). The gap between the pipes is usually 4...6 mm. Some screen pipes are inserted directly into the drum and do not have overhead collectors. Each screen panel, together with lowering pipes located outside the furnace lining, forms an independent circulation circuit.

The rear screen pipes at the point where combustion products exit the furnace are arranged in 2-3 rows. This discharge of pipes is called scalloping. It allows you to increase the cross-section for the passage of gases, reduce their speed and prevent clogging of the gaps between the pipes, hardened during cooling by molten ash particles carried by gases from the furnace.

In high-power steam generators, in addition to wall-mounted ones, additional screens are installed that divide the firebox into separate compartments. These screens are illuminated by torches on both sides and are called double-light. They perceive twice as much heat as wall-mounted ones. Double-light screens, while increasing the overall heat absorption in the firebox, make it possible to reduce its size.

Superheaters. The superheater is designed to increase the temperature of the steam coming from the boiler evaporation system. It is one of the most critical elements of the boiler unit. With an increase in steam parameters, the heat absorption of superheaters increases to 60% of the total heat absorption of the boiler unit. The desire to obtain high superheat of steam forces part of the superheater to be located in the zone of high temperatures of combustion products, which naturally reduces the strength of the pipe metal. Depending on the determining method of heat transfer from gases, superheaters or their individual stages (Fig. 7.8, b) are divided into convective, radiative and semi-radiative.

Radiation superheaters are usually made from pipes with a diameter of 22...54 mm. At high steam parameters, they are placed in the combustion chamber, and they receive most of the heat by radiation from the torch.

Convective steam superheaters are located in a horizontal gas duct or at the beginning of a convective shaft in the form of dense packages formed by coils with a step along the width of the gas duct equal to 2.5...3 pipe diameters.

Convective superheaters, depending on the direction of steam movement in the coils and the flow of flue gases, can be counter-current, direct-flow or with a mixed direction of flow.

The temperature of the superheated steam must always be maintained constant, regardless of the operating mode and load of the boiler unit, since when it decreases, the moisture content of the steam in the last stages of the turbine increases, and when the temperature rises above the design value, there is a danger of excessive thermal deformation and a decrease in strength individual elements turbines. The steam temperature is maintained at a constant level using control devices - desuperheaters. The most widely used desuperheaters are the injection type, in which control is carried out by injecting demineralized water (condensate) into the steam flow. When water evaporates, it takes away some of the heat from the steam and reduces its temperature (Fig. 7.9, A).

Typically, an injection desuperheater is installed between the individual parts of the superheater. Water is injected through a series of holes around the circumference of the nozzle and sprayed inside a jacket consisting of a diffuser and a cylindrical part that protects the body, which has a higher temperature, from splashing water from it to prevent the formation of cracks in the metal of the body due to a sudden change in temperature.

Rice. 7.9. Desuperheaters: A - injecting; b - surface with steam cooling feed water; 1 – hatch for measuring instruments; 2 – cylindrical part of the shirt; 3 - desuperheater housing; 4 - diffuser; 5 - holes for spraying water in steam; 6 - desuperheater head; 7-pipe board; 8 - collector; 9 - a jacket that prevents steam from washing the tube sheet; 10, 14 - pipes supplying and discharging steam from the desuperheater; 11 - distance partitions; 12 - water coil; 13 - longitudinal partition that improves steam washing of coils; 15, 16 - pipes supplying and discharging feedwater

In boilers of medium steam capacity, surface desuperheaters are used (Fig. 7.9, b), which are usually placed at the steam entry into the superheater or between its individual parts.

Steam is supplied and discharged to the collector through coils. Inside the collector there are coils through which feed water flows. The temperature of the steam is controlled by the amount of water entering the desuperheater.

Water economizers. These devices are designed to heat feed water before it enters the evaporating part of the boiler unit by using the heat of the flue gases. They are located in a convective flue and operate at relatively low temperatures of combustion products (flue gases).

Rice. 7.10. Steel coil economizer:

1 - lower manifold; 2 - upper collector; 3 - support post; 4 - coils; 5 -- support beams (cooled); 6 - draining water

Most often, economizers (Fig. 7.10) are made from steel pipes with a diameter of 28...38 mm, bent into horizontal coils and arranged in bags. The pipes in the packages are staggered quite tightly: the distance between the axes of adjacent pipes across the flow of flue gases is 2.0... 2.5 pipe diameters, along the flow - 1.0... 1.5. Fastening of the coil pipes and their spacing is carried out by support posts, fixed in most cases to hollow (for air cooling) frame beams insulated from the hot gas side.

Depending on the degree of water heating, economizers are divided into non-boiling and boiling. In a boiling economizer, up to 20% of the water can be converted into steam.

The total number of parallel operating pipes is selected based on a water speed of at least 0.5 m/s for non-boiling economizers and 1 m/s for boiling economizers. These speeds are due to the need to wash away air bubbles from the pipe walls, which promote corrosion and prevent stratification of the steam-water mixture, which can lead to overheating of the upper wall of the pipe, which is poorly cooled by steam, and its rupture. The movement of water in the economizer is necessarily upward. The number of pipes in the package in the horizontal plane is selected based on the speed of combustion products 6...9 m/s. This speed is determined by the desire, on the one hand, to protect the coils from being carried by ash, and on the other, to prevent excessive ash wear. Heat transfer coefficients under these conditions are usually 50... 80 W/(m 2 - K). For ease of repair and cleaning of pipes from external contaminants, the economizer is divided into packages with a height of 1.0... 1.5 m with gaps between them of up to 800 mm.

External contamination from the surface of the coils is removed by periodically turning on the shot cleaning system, when metal shot is passed (falls) from top to bottom through convective heating surfaces, knocking off deposits adhering to the pipes. Ash adhesion may be a result of dew from the flue gases depositing on the relatively cold surface of the pipes. This is one of the reasons for preheating the feedwater supplied to the economizer to a temperature above the dew point of water vapor or sulfuric acid vapor in the flue gases.

The upper rows of economizer pipes when the boiler operates on solid fuel, even at relatively low gas velocities, are subject to noticeable ash wear. To prevent ash wear, these pipes are attached various kinds protective pads.

Air heaters. They are installed to heat the air directed into the furnace in order to increase the efficiency of fuel combustion, as well as into coal grinding devices.

The optimal amount of air heating in the air heater depends on the floor of the fuel being burned, its humidity, the type of combustion device and is 200 ° C for coal burned on a chain grate (to avoid overheating of the grates), 250 ° C for peat burned on the same grates, 350 ...450 °C for liquid or pulverized fuel burned in chamber furnaces.

To obtain a high air heating temperature, two-stage heating is used. To do this, the air heater is divided into two parts, between which a part of the water economizer is installed (“in the cut”).

The temperature of the air entering the air heater must be 10... 15 °C above the dew point of the flue gases in order to avoid corrosion of the cold end of the air heater as a result of condensation of water vapor contained in the flue gases (in contact with the relatively cold walls of the air heater), and also clogging the passage channels for gases with ash sticking to the wet walls. These conditions can be met in two ways: either by increasing the temperature of the flue gases and losing heat, which is economically unprofitable, or by installing special devices for heating the air before it enters the air heater. For this purpose, special air heaters are used, in which the air is heated by selected steam from turbines. In some cases, air heating is carried out by recirculation, i.e. Part of the air heated in the air heater returns through the suction pipe to the blower fan and mixes with cold air.

According to the operating principle, air heaters are divided into recuperative and regenerative. In recuperative air heaters, heat is transferred from gases to air through a stationary metal pipe wall separating them. As a rule, these are steel tubular air heaters (Fig. 7.11) with a tube diameter of 25...40 mm. The tubes in it are usually located vertically, combustion products move inside them; the air washes them with a transverse flow in several passages, organized through air bypass ducts (ducts) and intermediate partitions.

The gas in the tubes moves at a speed of 8... 15 m/s, the air between the tubes is twice as slow. This allows you to have approximately equal heat transfer coefficients on both sides of the pipe wall.

Thermal expansion the air heater is perceived by the lens compensator 6 (see Fig. 7.11), which is installed above the air heater. Using flanges, it is bolted from below to the air heater, and from above to the transition frame of the previous flue of the boiler unit.

Rice. 7.11. Tubular air heater:

1 - Column; 2 – support frame; 3, 7 – air bypass boxes; 4 – steel

pipes 40´1.5 mm; 5, 9 – upper and lower tube sheets with a thickness of 20...25 mm;

6 – thermal expansion compensator; 8 – intermediate tube sheet

In a regenerative air heater, heat is transferred by a metal nozzle, which is periodically heated by gaseous combustion products, after which it is transferred into the air flow and releases the accumulated heat to it. The regenerative air heater of the boiler is a slowly rotating (3...5 rpm) drum (rotor) with a packing (nozzle) made of corrugated thin steel sheets, enclosed in a stationary housing. The housing is divided into two parts by sector plates - air and gas. As the rotor rotates, the packing alternates between gas and air flow. Despite the fact that the packing operates in a non-stationary mode, heating of the continuous flow of air is carried out continuously without temperature fluctuations. The movement of gases and air is countercurrent.

The regenerative air heater is compact (up to 250 m 2 of surface in 1 m 3 of packing). It is widely used in powerful power boilers. Its disadvantage is large (up to 10%) air flows into the gas path, which leads to overloads of blower fans and smoke exhausters and increased losses with flue gases.

Draft and blowing devices of the boiler unit. In order for fuel combustion to occur in the furnace of a boiler unit, air must be supplied to it. To remove gaseous combustion products from the furnace and ensure their passage through the entire system of heating surfaces of the boiler unit, draft must be created.

Currently, there are four schemes for supplying air and removing combustion products in boiler plants:

· with natural draft created by the chimney and natural suction of air into the firebox as a result of the vacuum in it created by the draft of the pipe;

·artificial draft created by the smoke exhauster and air suction into the firebox as a result of the vacuum created by the smoke exhauster;

·artificial draft created by a smoke exhauster and forced air supply into the firebox by a blower fan;

· supercharging, in which the entire boiler installation is sealed and placed under a certain excess pressure created by a blower fan, which is enough to overcome all the resistance of the air and gas paths, which eliminates the need to install a smoke exhauster.

In all cases of artificial draft or operation under pressurization, the chimney is preserved, but the main purpose of the chimney is to remove flue gases to higher layers of the atmosphere in order to improve the conditions for their dispersion in space.

In boiler installations with large steam production, artificial draft with artificial blast is widely used.

Chimneys are made of brick, reinforced concrete and iron. Pipes up to 80 m high are usually constructed from brick. Higher pipes are made of reinforced concrete. Iron pipes are installed only on vertical cylindrical boilers, as well as on powerful steel tower-type hot water boilers. To reduce costs, one common chimney is usually built for the entire boiler room or for a group of boiler plants.

The principle of operation of the chimney remains the same in installations operating with natural and artificial draft, with the peculiarity that with natural draft the chimney must overcome the resistance of the entire boiler installation, and with artificial draft it creates additional draft to the main one created by the smoke exhauster.

In Fig. 7.12 shows a diagram of a boiler with natural draft created by a chimney 2 . It is filled with flue gases (combustion products) with a density r g, kg/m 3, and communicates through the boiler flues 1 with atmospheric air, the density of which is r in, kg/m 3. Obviously, r in > r g.

At chimney height N difference in pressure between air columns gH r in and gases gН r g at the level of the base of the pipe, i.e. the amount of thrust D S, N/m 2, has the form

where p and Pr are the densities of air and gas under normal conditions, kg/m; IN- barometric pressure, mm Hg. Art. Substituting the values of r into 0 and r g 0, we get

From equation (7.2) it follows that the greater the natural thrust more height pipes and flue gas temperature and the lower the ambient temperature.

Minimum permissible height pipes are regulated for sanitary reasons. The diameter of the pipe is determined by the rate of flue gases flowing out of it at the maximum steam production of all boiler units connected to the pipe. With natural draft, this speed should be within 6... 10 m/s, without becoming less than 4 m/s, in order to avoid disruption of the draft by the wind (pipe blowing). With artificial draft, the speed of exhaust gases from the pipe is usually taken to be 20...25 m/s.

Rice. 7.12. Diagram of a boiler with natural draft created by a chimney:

1 - boiler; 2 - chimney

Centrifugal smoke exhausters and blower fans are installed for boiler units, and for steam generators with a capacity of 950 t/h or more - axial multi-stage smoke exhausters.

Smoke exhausters are placed behind the boiler unit, and in boiler installations intended for burning solid fuels, smoke exhausters are installed after ash removal in order to reduce the amount of fly ash passing through the smoke exhauster, and thereby reduce abrasion of the smoke exhauster impeller by ash. n

The vacuum that must be created by the smoke exhauster is determined by the total aerodynamic resistance of the gas path of the boiler installation, which must be overcome provided that the vacuum of the flue gases at the top of the furnace is equal to 20...30 Pa and the necessary velocity pressure is created at the outlet of the flue gases from the flue pipes. In small boiler installations, the vacuum created by the smoke exhauster is usually 1000...2000 Pa, and in large installations 2500... 3000 Pa.

Blower fans installed in front of the air heater are designed to supply unheated air into it. The pressure created by the fan is determined by the aerodynamic resistance of the air path, which must be overcome. It usually consists of the resistance of the suction air duct, the air heater, the air ducts between the air heater and the firebox, as well as the resistance of the grate and the fuel layer or burners. In total, these resistances amount to 1000... 1500 Pa for low-capacity boiler plants and increase to 2000... 2500 Pa for large boiler plants.

7.5. Heat balance of the boiler unit

Thermal balance of a steam boiler. This balance consists of establishing equality between the amount of heat entering the unit during fuel combustion, called available heat Q r r , and the amount of heat used Q 1 and heat losses. Based on the heat balance, efficiency and fuel consumption are determined.

Under steady-state operating conditions of the unit, the heat balance for 1 kg or 1 m 3 of burned fuel is as follows:

Where Q r r - available heat per 1 kg of solid or liquid fuel or 1 m 3 of gaseous fuel, kJ/kg or kJ/m 3 ; Q 1 - used heat; Q 2 - heat loss with gases leaving the unit; Q 3 - heat loss from chemical incomplete combustion of fuel (underburning); Q 4 - heat loss from mechanical incomplete combustion; Q 5 - heat loss to the environment through the external enclosure of the boiler; Q 6 - heat loss with slag (Fig. 7.13).

Typically, calculations use the heat balance equation, expressed as a percentage relative to the available heat, taken as 100% ( Q p p = 100):

Where q 1 = Q 1 × 100/Q p p; q 2= Q 2 × 100/Q r r etc.

Available heat includes all types of heat introduced into the furnace along with fuel:

Where Q n r – lower working heat of combustion of fuel; Q ft - physical heat of fuel, including that obtained during drying and heating; Q v.vn - the heat of the air received by it when heated outside the boiler; Q f - heat introduced into the furnace with atomizing nozzle steam.

The heat balance of the boiler unit is relative to a certain temperature level or, in other words, relative to a certain starting temperature. If we take as this temperature the temperature of the air entering the boiler unit without heating outside the boiler, do not take into account the heat of the steam blast in the nozzles and exclude the value Q ft, since it is negligible compared to the heat of combustion of the fuel, then we can accept

Expression (7.5) does not take into account the heat introduced into the furnace by the hot air of its own boiler. The fact is that the same amount of heat is given off by combustion products to the air in the air heater within the boiler unit, i.e., a kind of recirculation (return) of heat is carried out.

Rice. 7.13. The main heat losses of the boiler unit

Used heat Q 1 is perceived by the heating surfaces in the combustion chamber of the boiler and its convective flues, transferred to the working fluid and spent on heating water to the phase transition temperature, evaporation and superheating of steam. The amount of heat used per 1 kg or 1 m 3 of burned fuel,

Where D 1 , D n, D pr, - respectively, the productivity of the steam boiler (superheated steam consumption), saturated steam consumption, boiler water consumption for blowing, kg/s; IN- fuel consumption, kg/s or m 3 /s; i pp, i", i", i pv - respectively, the enthalpy of superheated steam, saturated steam, water on the saturation line, feed water, kJ/kg. At the blowing rate and in the absence of saturated steam consumption, formula (7.6) takes the form

For boiler units that are used to produce hot water (hot water boilers),

Where G c - hot water consumption, kg/s; i 1 and i 2 - respectively, specific enthalpies of water entering and exiting the boiler, kJ/kg.

Heat losses of a steam boiler. The efficiency of fuel use is determined mainly by the completeness of fuel combustion and the depth of cooling of combustion products in the steam boiler.

Heat loss with flue gases Q 2 are the largest and are determined by the formula

Where Iух - enthalpy of flue gases at flue gas temperature q ух and excess air in flue gases α ух, kJ/kg or kJ/m 3 ; Iхв - enthalpy of cold air at cold air temperature t xv and excess air α xv; (100- q 4) - the proportion of burned fuel.

For modern boilers the value q 2 is within 5...8% of available heat, q 2 increases with increasing qух, αух and the volume of exhaust gases. A decrease in qх by approximately 14... 15 °C leads to a decrease q 2 to 1%.

In modern energy boiler units qух is 100... 120 °C, in industrial heating units - 140... 180 °C.

Heat loss from chemical incomplete combustion of fuel Q 3 is the heat that remains chemically bound in the products of incomplete combustion. It is determined by the formula

where CO, H 2, CH 4 - volumetric content of products of incomplete combustion in relation to dry gases,%; the numbers in front of CO, H 2, CH 4 are the heat of combustion of 1 m 3 of the corresponding gas reduced by 100 times, kJ/m 3.

Heat losses from chemical incomplete combustion usually depend on the quality of mixture formation and local insufficient amounts of oxygen for complete combustion. Hence, q 3 depends on α t. The smallest values of α t , at which q 3 are practically absent, depend on the type of fuel and the organization of the combustion regime.

Chemical incomplete combustion is always accompanied by soot formation, which is unacceptable in boiler operation.

Heat loss from mechanical incomplete combustion of fuel Q 4 - This is the heat of the fuel, which, during chamber combustion, is carried away along with the combustion products (entrainment) into the boiler flues or remains in the slag, and during layer combustion - in the products falling through the grate (failure):

Where a shl+pr, a un - respectively, the share of ash in the slag, sinkhole and entrainment, determined by weighing from the ash balance A shl+pr + a un = 1 in fractions of one; G shl+pr, G un – the content of combustible substances in the slag, sinkhole and entrainment, respectively, is determined by weighing and afterburning in laboratory conditions samples of slag, failure, entrainment, %; 32.7 kJ/kg - heat of combustion of combustibles in slag, sinkhole and entrainment, according to VTI data; A r - ash content of the working mass of fuel, %. Magnitude q 4 depends on the combustion method and the method of slag removal, as well as the properties of the fuel. With a well-established combustion process of solid fuel in chamber furnaces q 4 "0.3...0.6 for fuels with a high yield of volatile substances, for anthracite pellet (AS) q 4 > 2%. In layer combustion for hard coals q 4 = 3.5 (of which 1% is due to losses with slag, and 2.5% due to entrainment), for brown - q 4 = 4%.

Heat loss to the environment Q 5 depend on the area of the outer surface of the unit and the temperature difference between the surface and the surrounding air (q 5"0.5...1.5%).

Heat loss from slag Q 6 occur as a result of removing slag from the furnace, the temperature of which can be quite high. In pulverized coal furnaces with solid slag removal, the slag temperature is 600...700°C, and with liquid slag removal - 1500...1600°C.

These losses are calculated using the formula

Where With shl - heat capacity of the slag, depending on the temperature of the slag t Shl. So, at 600°C With shl = 0.930 kJ/(kg×K), and at 1600°C With shl = 1.172 kJ/(kg×K).

Coefficient useful action boiler and fuel consumption. The perfection of the thermal operation of a steam boiler is assessed by the gross efficiency h to br,%. Yes, according to direct balance

Where Q To - heat usefully transferred to the boiler and expressed through the heat perception of heating surfaces, kJ/s:

Where Q st - heat content of water or air heated in the boiler and transferred to the side, kJ/s (purge heat is taken into account only for D pr > 2% of D).

The efficiency of the boiler can also be calculated using the reverse balance:

The direct balance method is less accurate, mainly due to the difficulties in determining large masses of fuel consumed in operation. Heat losses are determined with greater accuracy, so the reverse balance method has found widespread use in determining efficiency.

In addition to the gross efficiency, the net efficiency is used, which shows the operational excellence of the unit:

Where q s.n - total heat consumption for the boiler’s own needs, i.e. consumption electrical energy for driving auxiliary mechanisms (fans, pumps, etc.), steam consumption for blowing and fuel oil spray, calculated as a percentage of the available heat.

From expression (7.13) the consumption of fuel supplied to the furnace is determined B kg/s,

Since part of the fuel is lost due to mechanical underburning, the calculated fuel consumption is used for all calculations of air volumes and combustion products, as well as enthalpies B R , kg/s, taking into account the mechanical incompleteness of combustion:

When burning liquid and gaseous fuels in boilers Q 4 = 0

Control questions

1. How are boiler units classified and what is their purpose?

2. Name the main types of boiler units and list their main elements.

3. Describe the evaporating surfaces of the boiler, list the types of superheaters and methods for regulating the temperature of superheated steam.

4. What types of water economizers and air heaters are used in boilers? Tell us about the principles of their design.

5. How is air supplied and flue gases removed in boiler units?

6. Tell us about the purpose of the chimney and the determination of its gravity; indicate the types of smoke exhausters used in boiler installations.

7. What is the heat balance of a boiler unit? List the heat losses in the boiler and indicate their causes.

8. How is the efficiency of a boiler unit determined?

Steam boilers and steam turbines are the main units of a thermal power plant (TPP).

Steam boiler- this is a device that has a system of heating surfaces for producing steam from feed water continuously supplied to it by using the heat released during the combustion of organic fuel (Fig. 1).

In modern steam boilers it is organized flare combustion of fuel in a chamber furnace, which is a prismatic vertical shaft. The flare combustion method is characterized by the continuous movement of fuel along with air and combustion products in the combustion chamber.

Fuel and the air necessary for its combustion are introduced into the boiler furnace through special devices — burners. The firebox in the upper part is connected to a prismatic vertical shaft (sometimes with two), named after the main type of heat exchange taking place convective shaft.

In the firebox, horizontal flue and convective shaft there are heating surfaces made in the form of a system of pipes in which the working medium moves. Depending on the preferred method of heat transfer to heating surfaces, they can be divided into the following types: radiation, radiation-convective, convective.

In the combustion chamber, flat pipe systems are usually located along the entire perimeter and along the entire height of the walls - combustion screens , which are radiation heating surfaces.

Rice. 1. Diagram of a steam boiler at a thermal power plant.

1 - combustion chamber (furnace); 2 - horizontal gas duct; 3 - convective shaft; 4 - combustion screens; 5 - ceiling screens; 6 — drain pipes; 7 - drum; 8 – radiation-convective superheater; 9 — convective superheater; 10 - water economizer; 11 — air heater; 12 — blower fan; 13 — lower screen collectors; 14 - slag chest of drawers; 15 — cold crown; 16 - burners. The diagram does not show the ash collector and smoke exhauster.

IN modern designs boilers, combustion screens are made either from ordinary pipes (Fig. 2, A), or from fin tubes, welded together along the fins and forming a continuous gas-tight shell(Fig. 2, b).

A device in which water is heated to saturation temperature is called economizer; steam formation occurs in the steam-forming (evaporation) heating surface, and its overheating occurs in superheater.

Rice. 2. Scheme of combustion screens
a - from ordinary pipes; b - from fin tubes

The system of pipe elements of the boiler, in which feed water, steam-water mixture and superheated steam move, forms, as already indicated, its water-steam path.

To continuously remove heat and ensure an acceptable temperature regime for the metal of the heating surfaces, continuous movement of the working medium is organized in them. In this case, water in the economizer and steam in the superheater pass through them once. The movement of the working medium through the steam-generating (evaporating) heating surfaces can be either single or multiple.

In the first case, the boiler is called direct-flow, and in the second - a boiler with multiple circulation(Fig. 3).

Rice. 3. Diagram of water-steam paths of boilers
a - direct-flow circuit; b - scheme with natural circulation; c - scheme with multiple forced circulation; 1 - feed pump; 2 - economizer; 3 - collector; 4 — steam-generating pipes; 5 — steam superheater; 6 - drum; 7 — lowering pipes; 8 - multiple forced circulation pump.

The water-steam path of a once-through boiler is an open-loop hydraulic system, in all elements of which the working medium moves under the pressure created feed pump. In direct-flow boilers there is no clear separation of the economizer, steam-generating and superheating zones. Once-through boilers operate at subcritical and supercritical pressure.

In boilers with multiple circulation, there is a closed loop formed by a system of heated and unheated pipes connected at the top drum, and below - collector. The drum is a cylindrical horizontal vessel having water and steam volumes, which are separated by a surface called mirror of evaporation. The collector is a large-diameter pipe plugged at the ends, into which pipes of smaller diameter are welded along its length.

In boilers with natural circulation(Fig. 3, b) feed water supplied by the pump is heated in the economizer and enters the drum. From the drum, water flows through lower unheated pipes into the lower collector, from where it is distributed into heated pipes, in which it boils. Unheated pipes are filled with water having a density ρ´ , and the heated pipes are filled with a steam-water mixture having a density ρ cm, whose average density is less ρ´ . The lowest point of the circuit - the collector - on one side is subjected to the pressure of the column of water filling the unheated pipes, equal to Hρ´g, and on the other - pressure Hρ cm g column of steam-water mixture. The resulting pressure difference H(ρ´ - ρ cm)g causes movement in the circuit and is called driving pressure of natural circulation S door(Pa):

S dv =H(ρ´ - ρ cm)g,

Where H— contour height; g- acceleration of gravity.

In contrast to the single movement of water in the economizer and steam in the superheater, the movement of the working fluid in the circulation circuit is multiple, since when passing through the steam-generating pipes, the water does not evaporate completely and the steam content of the mixture at the outlet is 3-20%.

Attitude mass flow circulating water in the circuit to the amount of steam formed per unit time is called the circulation ratio

R = m in / m p.

In boilers with natural circulation R= 5-33, and in boilers with forced circulation - R= 3-10.

In the drum, the resulting steam is separated from the water droplets and enters the superheater and then into the turbine.

In boilers with multiple forced circulation (Fig. 3, V) to improve circulation is installed additionally circulation pump. This allows for a better layout of the heating surfaces of the boiler, allowing the movement of the steam-water mixture not only through vertical steam-generating pipes, but also along inclined and horizontal ones.

Since the presence of two phases in vapor-forming surfaces - water and steam - is possible only at subcritical pressure, drum boilers operate at pressures less than critical.

The temperature in the furnace in the torch combustion zone reaches 1400-1600°C. Therefore, the walls of the combustion chamber are laid out from refractory material, and their outer surface is covered with thermal insulation. The combustion products, partially cooled in the furnace with a temperature of 900-1200°C, enter the horizontal flue of the boiler, where they wash the superheater, and then are sent to the convective shaft in which they are placed reheater, water economizer and the last heating surface along the flow of gases is air heater, in which the air is heated before it is supplied to the boiler furnace. The combustion products behind this surface are called flue gases: they have a temperature of 110-160°C. Since further heat recovery at such a low temperature is unprofitable, the flue gases are removed into the chimney using a smoke exhauster.

Most boiler fireboxes operate under a slight vacuum of 20-30 Pa (2 - 3 mm water column) in the upper part of the combustion chamber. As combustion products flow, the vacuum in the gas path increases and reaches 2000-3000 Pa in front of the smoke exhausters, which causes atmospheric air to enter through leaks in the boiler walls. They dilute and cool combustion products, reducing the efficiency of heat use; In addition, this increases the load of the smoke exhausters and increases the energy consumption for their drive.

Recently, boilers have been created that operate under pressurization, when the combustion chamber and flues operate under excess pressure created by fans, and smoke exhausters are not installed. For the boiler to operate under pressurization, it must be carried out gas-tight.

Boiler heating surfaces are made of steel various brands depending on the parameters (pressure, temperature, etc.) and the nature of the medium moving in them, as well as on the temperature level and aggressiveness of the combustion products with which they are in contact.

The quality of the feed water is important for reliable operation of the boiler. A certain amount of suspended solids and dissolved salts, as well as iron and copper oxides formed as a result of corrosion of power plant equipment, continuously enters the boiler with it. A very small part of the salts is carried away by the generated steam. In boilers with multiple circulation, the bulk of salts and almost all solid particles are retained, which is why their content in the boiler water gradually increases. When water boils in a boiler, salts fall out of solution and scale appears on the inner surface of the heated pipes, which does not conduct heat well. As a result, pipes coated with a layer of scale on the inside are not sufficiently cooled by the medium moving in them, are heated by combustion products to a high temperature, lose their strength and can collapse under the influence of internal pressure. Therefore, part of the water with a high concentration of salts must be removed from the boiler. Feed water with a lower concentration of impurities is supplied to replenish the removed amount of water. This process of replacing water in a closed loop is called continuous blowing. Most often, continuous blowing is carried out from the boiler drum.

In direct-flow boilers, due to the absence of a drum, there is no continuous blowing. Therefore, particularly high demands are placed on the quality of the feed water of these boilers. They are achieved by cleaning turbine condensate after the condenser in special condensate treatment plants and appropriate treatment of make-up water in water treatment plants.

The steam produced by a modern boiler is probably one of the purest products produced by industry in large quantities.

So, for example, for a once-through boiler operating at supercritical pressure, the contaminant content should not exceed 30-40 μg/kg of steam.

Modern power plants operate with sufficient high efficiency. The heat spent on heating the feed water, evaporating it and producing superheated steam is useful heat Q 1.

The main heat loss in the boiler occurs with exhaust gases Q 2. In addition, there may be losses Q 3 from chemical incomplete combustion caused by the presence of CO in the exhaust gases , H 2 , CH4; losses due to mechanical underburning of solid fuel Q 4 associated with the presence of unburned carbon particles in the ash; losses to the environment through the boiler enclosing structure and gas ducts Q 5; and, finally, losses with the physical heat of the slag Q 6.

Designating q 1 = Q 1 / Q , q 2 = Q 2 / Q etc., we get the boiler efficiency:

η k =Q 1 /Q= q 1 =1-(q 2 +q 3 +q 4 +q 5 +q 6 ),

Where Q- the amount of heat released during complete combustion of fuel.

Heat loss with flue gases is 5-8% and decreases with decreasing excess air. Smaller losses practically correspond to combustion without excess air, when only 2-3% more air is supplied to the firebox than is theoretically necessary for combustion.

Actual air volume ratio V D supplied to the furnace to the theoretically necessary V T for fuel combustion is called the excess air coefficient:

α = V D /V T ≥ 1 .

Decrease α may lead to incomplete combustion of fuel, i.e. to an increase in losses due to chemical and mechanical underburning. Therefore, taking q 5 And q 6 constant, establish such an excess of air a, at which the sum of losses

q 2 + q 3 + q 4 → min.

Optimal excess air is maintained using electronic automatic regulators combustion process, changing the supply of fuel and air when the boiler load changes, while ensuring the most economical mode of its operation. The efficiency of modern boilers is 90-94%.

All elements of the boiler: heating surfaces, collectors, drums, pipelines, lining, platforms and service ladders are mounted on a frame, which is a frame structure. The frame rests on the foundation or is suspended from beams, i.e. based on bearing structures building. The mass of the boiler together with the frame is quite significant. So, for example, the total load transmitted to the foundations through the columns of the boiler frame with steam capacity D=950 t/h, is 6000 t. The boiler walls are covered from the inside fireproof materials, and on the outside - thermal insulation.

The use of gas-tight screens leads to savings in metal for the manufacture of heating surfaces; in addition, in this case, instead of fire-resistant brick lining, the walls are covered only with soft thermal insulation, which makes it possible to reduce the weight of the boiler by 30-50%.

Energy stationary boilers, produced by Russian industry, are marked as follows: E - steam boiler with natural circulation without intermediate steam overheating; Ep - steam boiler with natural circulation with intermediate overheating pair; PP is a direct-flow steam boiler with intermediate steam superheating. The letter designation is followed by numbers: the first is steam production (t/h), the second is steam pressure (kgf/cm 2). For example, PC - 1600 - 255 means: a steam boiler with a chamber combustion chamber with dry slag removal, steam capacity 1600 t/h, steam pressure 255 kgf/cm2.

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1. Statistical characteristicsboiler when the feed water temperature changes

drum boiler turbine battery

During the operation of the boiler, its performance may vary within the limits determined by the operating mode of consumers. The temperature of the feed water and the air regime of the furnace may also change. Each boiler operating mode corresponds to certain values of coolant parameters in the water-steam and gas paths, heat losses and efficiency. One of the tasks of the personnel is to maintain the optimal boiler mode under given operating conditions, which corresponds to the maximum possible net boiler efficiency value. In this regard, there is a need to determine the influence of the static characteristics of the boiler - load, feed water temperature, air mode of the furnace and fuel characteristics - on its performance when changing the values of the listed parameters. During short periods of transition of the boiler operation from one mode to another, a change in the amount of heat, as well as a delay in the system of its regulation, causes a violation of the material and energy balances of the boiler and a change in the parameters characterizing its operation. Violation of the stationary operating mode of the boiler during transition periods can be caused by internal (for the boiler) disturbances, namely a decrease in the relative heat release in the furnace and a change in it. air mode and water supply mode, and external disturbances - changes in steam consumption and feed water temperature. The time dependences of the parameters that characterize the operation of the boiler during the transition period are called its dynamic characteristics.

Dependence of parameters on feed water temperature. The boiler operation is significantly affected by the temperature of the feed water, which can change during operation depending on the operating mode of the turbines. A decrease in the temperature of the feed water at a given load and other conditions unchanged determines the need to increase heat release in the furnace, i.e. fuel consumption, and as a result of this redistribution of heat transfer to the heating surfaces of the boiler. The superheating temperature of steam in a convective superheater increases due to an increase in the temperature of combustion products and their speed, and the temperature of heating water and air increases. The temperature of the flue gases and their volume increase. Accordingly, the loss with exhaust gases increases.

2 . Starting the drum boiler

During startup, as a result of uneven heating of the metal, thermal stresses additionally arise in the surfaces: y t = e t ·E t ·?t

e t - linear expansion coefficient.

E t - elastic modulus of steel.

y t increases with u. Therefore, kindling is carried out slowly and carefully so that the speed and thermal stress do not exceed permissible values. , . Starting circuit.

RKNP - continuous blowdown control valve.

B-air balloon.

rec. - recirculation line.

Drains.

PP - superheater purge.

GPZ - main steam valve.

SP - connecting steam line.

PP - kindling expander.

RROU - kindling reduction-cooling unit.

K.S.N. - collector of own needs.

K.O.P. - live steam collector.

RPK - control feed valve.

RU - kindling unit.

PM - nutritional line.

Start sequence

1. External inspection (heating surfaces, lining, burners, safety valves, water indicating devices, regulators, fan and exhaust fan).

2. Close the drains. Open the air vent and purge the superheater.

3. The boiler is filled through the lowest points with deaerated water at a temperature corresponding to the condition: (vу t).

4. Filling time 1-1.5 hours. Filling ends when water closes the downpipes. When filling out, make sure that< 40єC.

5. Turn on the smoke exhauster and fan and ventilate the firebox and flues for 10-15 minutes.

6. Set the vacuum at the outlet of the furnace kg/m2, set the flow rate.

7. The heat released during fuel combustion is spent on heating heating surfaces, lining, water, and on steam generation. With increasing duration of kindling ^Q steam generation. and vQ load.

8. When steam appears from the vents, close them. Cooling of the superheater is carried out with pilot steam, releasing it through the PP. Purge line resistance ~ > ^P b.

9. At P = 0.3 MPa, the lower points of the screens and air indicators are blown. At P = 0.5 MPa, close the PP, open GPZ-1 and warm up the SP, releasing steam through the ignition expander.

10. Periodically replenish the drum with water and control the water level.

11. Increase fuel consumption. єС/min.

12. At P = 1.1 MPa turn on continuous blowing and use a recirculation line (to protect the ECO from burnout).

13. At P = 1.4 MPa, close the ignition expander and open the ignition reduction-cooling units. Increases fuel consumption.

14. At P = P nom - 0.1 MPa and t p = t nom - 5°C, check the quality of the steam, increase the load to 40%, open the GPZ-2 and turn on the boiler to the live steam manifold.

15. Turn on the main fuel supply and increase the load to the nominal one.

16. Switch to power supply to the boiler through the control feed valve and fully load the desuperheater.

17. Turn on the automation.

3. Features of starting heating turbines

Start turbines with steam extraction are carried out in basically the same way as starting cleanly condensation turbines. Regulatory valves The low pressure parts (extraction control) must be fully open, the pressure regulator is turned off and the valve in the extraction line is closed. Obviously, under these conditions, any turbine with steam extraction operates as a purely condensing turbine and can be put into operation in the manner described above. However, special attention should be paid to those drain lines that are not present at the condensing turbine, in particular the drain line of the extraction line and safety valve. As long as the pressure in the sampling chamber is below atmospheric pressure, these drain lines must be open to the condenser. After the turbine with steam extraction is deployed to full number rpm, the generator is synchronized, connected to the network and some load has been accepted, you can turn on the pressure regulator and slowly open the shut-off valve on the extraction line. From this point on, the pressure regulator comes into action and must maintain the desired extraction pressure. For turbines with coupled speed and extraction control, the transition from purely condensing regime to work with steam extraction is usually accompanied by only slight fluctuations in load. However, when turning on the pressure regulator, you must carefully ensure that the bypass valves do not immediately close completely, as this will create a sharp increase (push) in pressure in the extraction chamber, which can cause a turbine failure. In turbines with uncoupled regulation, each of the regulators receives an impulse under the influence of the action of the other regulator. Therefore, load fluctuations at the time of transition to operation with steam extraction may be more significant. A turbine with back pressure is usually started to exhaust into the atmosphere, for which the exhaust valve is first opened by hand with the valve closed. For the rest, they are guided by the above rules for starting condensing turbines. Switching from exhaust operation to backpressure operation (to the production line) is usually made when the turbine reaches its normal speed. To switch, first gradually close the exhaust valve to create a back pressure behind the turbine that is slightly higher than the back pressure in the production line on which the turbine will operate, and then slowly open the valve of this line. The valve must be completely closed by the time the production line valve is fully open. The pressure regulator is turned on after the turbine takes on a small thermal load and the generator is connected to the network; It is usually more convenient to switch on at a time when the back pressure is slightly lower than normal. From the moment the desired back pressure is established in the exhaust pipe, the speed regulator is turned off and the turbine begins to operate thermal chart controlled by a pressure regulator.

4. Aboiler storage capacity

In an operating boiler unit, heat is accumulated in the heating surfaces, in water and steam located in the volume of the boiler heating surface. With the same productivity and steam parameters, more heat is accumulated in drum boilers, which is primarily explained by the large water volume. For drum boilers, 60-65% of heat is accumulated in water, 25-30% in metal, 10-15% in steam. For direct-flow boilers, up to 65% of the heat is accumulated in the metal, the remaining 35% in steam and water.

When the vapor pressure decreases, part of the accumulated heat is released due to a decrease in the saturation temperature of the medium. This produces additional steam almost instantly. The amount of additional steam produced when the pressure decreases by 1 MPa is called storage capacity of the boiler unit:

where Q ak is the heat released in the boiler unit; q is the heat consumption to produce 1 kg of steam.

For drum boilers with steam pressure above 3 MPa, the storage capacity can be found from the expression

where r is the latent heat of vaporization; G m - mass of metal of evaporative heating surfaces; С m, С в - heat capacity of metal and water; Dt n - change in saturation temperature with a change in pressure by 1 MPa; V in, V p - water and steam volumes of the boiler unit; - change in vapor density with a decrease in pressure by 1 MPa; - density of water. The water volume of the boiler unit includes the water volume of the drum and circulation circuits, the steam volume includes the volume of the drum, the volume of the superheater, as well as the volume of steam in the evaporator tubes.

The permissible rate of pressure reduction, which determines the degree of increase in the steam output of the boiler unit, is also of practical importance.

A once-through boiler allows very high speeds reducing pressure. At a speed of 4.5 MPa/min, an increase in steam production by 30-35% can be achieved, but within 15-25 s. A drum boiler allows a lower rate of pressure reduction, which is associated with swelling of the level in the drum and the danger of steam formation in the sink pipes. At a pressure reduction rate of 0.5 MPa/min, drum boilers can operate with an increase in steam production by 10-12% within 2-3 minutes.

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RD 153-34.1-26.303-98

ORGRES

Moscow 2000

Developed by the Open Joint Stock Company "Company for setting up, improving technology and operating power plants and networks of ORGRES" Performed by G.T. LEVIT Approved by the Department of Development Strategy and Scientific and Technical Policy of RAO "UES of Russia" 01.10.98 First Deputy Head A.P. BERSENEV The guidance document was developed by JSC Firm ORGRES on behalf of the Department of Development Strategy and Scientific and Technical Policy and is the property of RAO UES of Russia.

METHODOLOGICAL INSTRUCTIONS FOR CONDUCTING OPERATIONAL TESTS OF BOILER INSTALLATIONSTO EVALUATE THE QUALITY OF REPAIR

RD 153-34.1-26.303-98

Put into effect
from 04/03/2000

1. GENERAL PART

1.1. The tasks of operational tests (acceptance tests) are determined by the “Methodology for assessing the technical condition of boiler installations before and after repairs” [1], according to which, when conducting tests after major repairs, they must be identified and compared with the requirements of normative and technical documentation (NTD) and test results after previous repair, the values of the indicators listed in table. 1 of these Guidelines. The specified Methodology also defines as desirable tests before repair to clarify the scope of the upcoming repair. 1.2. According to the rules [2], the technical condition of the boiler installation is assessed based on the results of acceptance tests (during start-up and under load) and controlled operation. The duration of controlled operation when working according to a regime map at loads corresponding to the dispatch schedule is set equal to 30 days, and acceptance tests under rated load, also when working according to a regime map, is set to 48 hours.

Table 1

Statement of technical condition indicators of the boiler installation

Index

Indicator value

after the last major renovation

after real renovation

before the current renovation

1. Fuel, its characteristics

2. Number of operating dust preparation systems*

3. Dust fineness R 90 (R 1000)*, %

4. Number of working burners*

5. Excess air behind the superheater *

6. Steam production, reduced to nominal parameters, t/h

7. Temperature of superheated steam, °C

8. Temperature of reheat steam, °C

9. Feedwater temperature, °C

10. Temperature at control points of the high pressure steam-water path. and intermediate superheater, °C

11. Maximum measurement of the temperature of the walls of the heating surface coils in characteristic places

12. Suction of cold air into the firebox

13. Cold air suctions into dust preparation systems

14. Suction cups in the convective flue ducts of the boiler

15. Suction cups in the flue ducts from the air heater to the smoke exhausters

16. Vacuum in front of the guide vanes of smoke exhausters, kg/m2

17. Degree of opening of the guide vanes of smoke exhausters, %

18. Degree of opening of fan guide vanes, %

19. Flue gas temperature, °C

20. Heat loss with flue gases, %

21. Heat loss with mechanical incomplete combustion, %

22. Efficiency boiler "gross", %

23. Specific electricity consumption for dust preparation, kW h/t of fuel

24. Specific electricity consumption for traction and blast, kW h/t steam

25. Content of NO x in flue gases (at α = 1.4), mg/nm 3

* Accepted with a regime card

1.3. The boiler installation should be tested at its rated output. For installations where there is a load limitation for any reason, approved in accordance with existing regulations by a higher organization, the operating characteristic at the achievable load is used as a basis. Tests are preferably carried out at the nominal value of the feed water temperature, since this determines the temperature of the flue gases and, in addition, for drum boilers the temperature of the superheated steam depends on this, and for direct-flow boilers - the temperature at the control points of the steam-water path. If it is not possible to maintain the nominal feed water temperature, the flue gas temperature should be adjusted in accordance with amendments to the regulatory characteristics. Amendments to these characteristics should also be used to take into account the influence of changes in the temperature of cold air and air at the inlet to the air heater. 1.4. To eliminate unjustified differences in the performance of the boiler installation due to unclear organization of its operating mode, one should, according to the recommendations [3], during testing strive to maintain at the level specified in the technical specifications (regime map): the upper load limit; excess air behind the superheater (in the control section); number of operating dust preparation systems and burners; fine dust; distribution of air and fuel among burners; quantity of recirculation gases (number of working recirculation smoke exhausters); vacuum in the upper part of the furnace; air temperature at the air heater inlet; heating cold air due to recirculation, etc. 1.5. Before conducting a long-term (48 hours) experiment at rated load, it is necessary that the boiler operate for at least 2 days after lighting, of which at least 4 hours at rated load. In addition, before the start of the main experiment, preliminary experiments should be carried out to identify the need to adjust the instructions of the regime map due to increased (lowered) steam temperature, decreased efficiency, excessive content of nitrogen oxides in the flue gases, intensive slagging of heating surfaces, etc. During estimation experiments, it is necessary to achieve minimal distortions in the temperature and composition of the flue gases, as well as the steam temperature along the flows of the steam-water path and within each of the flows. Elimination of distortions along the gas path should be preceded by equalizing the distribution of fuel and air among the burners, adjusting the air distribution among nozzles, slots, etc. 1.6. When carrying out the main long-term experiment on slag fuel, all blowers should be used with a frequency of switching on that ensures the absence of progressive slagging, which can be judged by the stability over time of the temperature of the flue gases and steam (the degree of use of desuperheaters). The number of blowers used must be recorded. It is also necessary to record the serviceability of slag removal devices. 1.7. Installations operating on several types of fuel should be tested on the fuel (fuel mixture) that was used in the preparation of the technical documentation and on which the test was carried out after the previous repair. 1.8. In addition to the main and preliminary experiments, in accordance with clause 1.5 of these Guidelines, experiments must be carried out to identify cold air suction into the furnace and superheater, the gas path from the superheater to the smoke exhauster (on the discharge side), and into dust preparation systems. They should be carried out at the same load as during the main experiment, but separately from the main experiment, since this requires the participation of an additional number of laboratory assistants. 1.9. When conducting operational tests, standard instruments are mainly used. Additionally, gas analyzers GKhP-ZM (Orsa) or portable automatic gas analyzers of the "type" are used Testo-Term". The quality of fuel is determined by the average daily samples of the power plant. In cases where the power plant consumes a mixture of solid fuels or the quality (brand) of solid fuel is not constant, a fuel sample should be taken from the leaks of the fuel feeders. The methodology for collecting and cutting fuel samples for analysis is set out in [4 ] 1.10. To prepare for testing during repairs, the following must be checked, including checking the sensors for the gas-air, steam-water and fuel paths, as well as the correctness of their installation. In particular, the gas intake pipes and oxygen meter sensors must be checked. should be installed at points in the flow at which the measured parameter corresponds to the average value of the flow as a whole; gate valves installed on the gas-air path, guide devices and the flow part of the draft machines, slots, nozzles, etc.; synchronization of the rotational speed of fuel or dust feeders, the range of variation of this frequency and its compliance with the needs of the boiler; state of devices regulating the height of the fuel layer on fuel feeders; condition of the metering wheels of dust feeders, as well as valves regulating the supply of gaseous and liquid fuels, etc.); compliance with the design of dust preparation system units. determining the quality of dust and its uniform distribution. 1.11. It is recommended to use [4] as reference literature when organizing and conducting operational tests, and [5] when carrying out calculations. 1.12. With the publication of these Guidelines, the “Instructions and guidelines on conducting operational express tests of boiler units to assess the quality of repairs" (Moscow: STSNTI ORGRES, 1974).

2. DETERMINATION OF EXCESS AIR AND COLD AIR SUCKS

2.1. Determination of excess air

Excess air α is determined with sufficient accuracy for practical purposes using the equation

The error in calculations using this equation does not exceed 1% if α is less than 2.0 for solid fuels, 1.25 for fuel oil and 1.1 for natural gas. A more accurate determination of excess air α can be performed using the equation

Where K α- correction factor determined from Fig. 1. Introduction of amendment K α may be required for practical purposes only when there is a large excess of air (for example, in flue gases) and when burning natural gas. The influence of incomplete combustion products in these equations is very small. Since gas analysis is usually carried out using Orsa chemical gas analyzers, it is advisable to check the correspondence between the values ABOUT 2 and RABOUT 2 because ABOUT 2 is determined by the difference [( R.O. 2 + ABOUT 2) - ABOUT 2 ], and the value ( R.O. 2 + O 2) largely depends on the absorption abilities of pyrogallol. Such a check, in the absence of chemical incompleteness of combustion, can be performed by comparing the excess air determined by the oxygen formula (1) with the excess determined by the carbon dioxide formula:

When conducting operational tests, the value for hard and brown coals can be taken equal to 19%, for AS 20.2%, for fuel oil 16.5%, for natural gas 11.8% [5]. Obviously, when burning a mixture of fuels with different values, it is impossible to use equation (3).

Rice. 1. Dependence of the correction factor TOα from excess air coefficient α :

1 - solid fuels; 2 - fuel oil; 3 - natural gases

The correctness of the gas analysis can also be checked using the equation

(4)

Or using the graph in Fig. 2.

Rice. 2. Content dependency CO 2 andO 2 in combustion products various types fuel from excess air coefficient α:

1, 2 and 3 - city gas (respectively 10.6, 12.6 and 11.2%); 4 - natural gas; 5 - coke oven gas; 6 - oil gas; 7 - water gas; 8 and 9 - fuel oil (from 16.1 to 16.7%); 10 and 11 - solid fuel group (from 18.3 to 20.3%)

When using devices like " Testo-Term" the definition of content is taken as a basis ABOUT 2, since in these devices the value R.O. 2 is determined not by direct measurement, but by calculation based on an equation similar to (4). Absence of noticeable chemical incompleteness of combustion ( CO) is usually determined using indicator tubes or devices like " Testo-Term". Strictly speaking, to determine the excess air in a particular section of a boiler installation, it is necessary to find such cross-sectional points, the analysis of gases in which in most modes would reflect the average values for the corresponding part of the section. However, for operational tests it is sufficient as a control, the closest to the firebox section, take the gas duct behind the first convective surface in the lowering gas duct (conditionally - behind the superheater), and the sampling location for the U-shaped boiler is in the center of each (right and left) half of the section. For the T-shaped boiler, the number of gas sampling locations follows. double.

2.2. Determination of air suction into the firebox

To determine air suction into the furnace, as well as into gas ducts up to the control section, in addition to the YuzhORGRES method with placing the furnace under pressure [4], it is recommended to use the method proposed by E.N. Tolchinsky [6]. To determine the suction cups, two experiments should be carried out with different flow rates of organized air at the same load, at the same vacuum at the top of the furnace and at a constant position of the dampers on the air path after the air heater. It is advisable to take the load as close as possible to the final load so that there is a possibility (were sufficient reserves in the performance of smoke exhausters and the supply of blower fans) vary the excess air within a wide range. For example, for a pulverized coal boiler, have α" = 1.7 behind the superheater in the first experiment, and α" = 1.3 in the second. The vacuum at the top of the furnace is maintained at the normal level for this boiler. Under these conditions, the total air suction (Δα t), suction into the furnace (Δα top) and the gas duct of the superheater (Δα pp) are determined by the equation

(5)

(6)

Here and are the excess air supplied into the furnace in an organized manner in the first and second experiments; - pressure difference between the air box at the outlet of the air heater and the vacuum in the furnace at the level of the burners. When performing experiments, it is necessary to measure: boiler steam output - D k; temperature and pressure of fresh steam and reheat steam; content in flue gases ABOUT 2 and, if necessary, products of incomplete combustion ( CO, N 2); vacuum in the upper part of the furnace and at the level of the burners; pressure behind the air heater. In the event that the boiler load D experiment differs from the nominal D nom, the reduction is made according to the equation

(7)

However, equation (7) is valid if in the second experiment the excess air corresponded to the optimal one at the rated load. Otherwise, the reduction should be performed using the equation

(8)

Estimation of changes in the flow rate of organized air into the furnace by value is possible if the position of the dampers on the path after the air heater remains unchanged. However, this is not always feasible. For example, on a pulverized coal boiler equipped with a direct injection pulverized preparation circuit with the installation of individual fans (IF) in front of the mills, the value characterizes the air flow only through the secondary air path. In turn, the flow rate of primary air, with the position of the dampers on its path unchanged, will change during the transition from one experiment to the second to a significantly lesser extent, since a large proportion of the resistance is overcome by the IOP. The same thing happens in a boiler equipped with a dust preparation circuit with a dust hopper with hot air transport of dust. In the situations described, the change in the flow rate of organized air can be judged by the pressure difference across the air heater, replacing the indicator in equation (6) with the value or difference on the measuring device on the fan suction box. However, this is possible if during the experiments the air recirculation through the air heater is closed and there are no significant leaks in it. The problem of determining air suction into the furnace on gas-oil boilers is solved more simply: to do this, it is necessary to stop the supply of recirculation gases to the air tract (if such a scheme is used); pulverized coal boilers should be switched to gas or fuel oil during the experiments, if possible. And in all cases, it is easier and more accurate to determine the suction cups if there are direct measurements of the air flow after the air heater (total or by adding the flow rates for individual flows), determining the parameter WITH in equation (5) according to the formula

(9)

Availability of direct measurements Q c allows you to determine the suction cups by comparing its value with the values determined by the heat balance of the boiler:

; (10)

(11)

In equation (10): and - consumption of fresh steam and reheat steam, t/h; and - increment of heat absorption in the boiler along the main path and the reheat steam path, kcal/kg; - boiler efficiency, gross, %; - reduced air consumption (m 3) under normal conditions per 1000 kcal for a specific fuel (Table 2); - excess air behind the superheater.

table 2

The theoretically required volumes of air for combustion of various fuels

Pool, fuel type

Fuel characteristics

Volume of air per 1000 kcal (at α = 1), 10 3 m 3 /kcal

Donetsk

Kuznetsky

Karaganda

Ekibastuz

ss

Podmoskovny

Raichikhisky

Irsha-Borodinsky

Berezovsky

Slates

Milled peat

Fuel oil

Gas Stavropol-Moscow

Calculations using this make it possible not to determine the heat of combustion and V 0 of the fuel burned during the experiments, since the value of this value within one type of fuel (a group of fuels with a similar reduced humidity) changes insignificantly. When determining suction cups using equation (11), one should keep in mind the possibility of large errors - according to [4], about 5%. However, if during testing, in addition to determining the suction cups, the task is to identify the distribution of air entering the furnace along the flows, i.e. meaning Q As is known, the determination by (11) should not be neglected, especially if the suction cups are large. A simplification of the methodology outlined in [6] was carried out under the assumption that the suction in the gas duct from the measurement point at the top of the furnace to the control section (behind the superheater or further along the duct), where gas samples are taken for analysis, are small and change little from experiment to experiment. experience due to the low resistance of heating surfaces in this area. In cases where this assumption is not satisfied, the method [6] should be used without simplifications. This requires not two, but three experiments. Moreover, the two experiments described above (hereinafter with the superscripts " and "") must be preceded by an experiment (with the index ") with the same flow rate of organized air as in the experiment with the index ("), but with a higher load. In addition to the vacuum at the top fireboxes S t in experiments the vacuum in the control section should be determined S j. Calculations are carried out according to the formulas:

(12)

. (13)

2.3. Determination of air suction into the flues of a boiler installation

With moderate suction, it is advisable to organize the determination of excess air in the control section (behind the superheater), behind the air heater and behind the smoke exhausters. If the suctions significantly (twice or more) exceed the standard ones, it is advisable to organize measurements in a large number of sections, for example, before and after an air heater, especially a regenerative one, before and after an electric precipitator. In the above sections, it is advisable, as well as in the control section, to organize measurements on the right and left sides of the boiler (both gas ducts of the T-shaped boiler), bearing in mind what was stated in Section. 2.1 considerations regarding the representativeness of the sampling site for analysis. Since it is difficult to organize simultaneous analysis of gases in many sections, measurements are usually taken first on one side of the boiler (in the control section, behind the air heater, behind the smoke exhauster), then on the other. Obviously, during the entire experiment it is necessary to ensure stable operation of the boiler. The value of suction cups is determined as the difference in the values of excess air in the compared sections,

2.4. Determination of air suction into dust preparation systems

Suction cups should be determined according to [7] in installations with a drying hopper, as well as with direct injection during drying with flue gases. In gas drying, in both cases, suction is determined, as in the boiler, on the basis of gas analysis at the beginning and end of the installation. Calculation of suction cups in relation to the volume of gases at the beginning of installation is carried out according to the formula

(14)

When drying with air in dust preparation systems with a drying hopper, to determine suction, it is necessary to organize the measurement of air flow at the entrance to the dust preparation system and the wet drying agent on the suction or discharge side of the mill fan. When determining at the inlet of the mill fan, the recirculation of the drying agent into the inlet pipe of the mill should be closed during the determination of the suction cups. The flow rates of air and wet drying agent are determined using standard measuring devices or using multipliers calibrated with Prandtl tubes [4]. Calibration of multipliers should be carried out in conditions as close as possible to operating conditions, since the readings of these devices are not strictly subject to the laws inherent in standard throttling devices. To bring the volumes to normal conditions, the temperature and pressure of the air at the inlet to the installation and the wet drying agent at the mill fan are measured. Air density (kg/m3) in the section in front of the mill (at the usually accepted water vapor content (0.01 kg/kg dry air):

(15)

Where is the absolute air pressure in front of the mill at the location where the flow is measured, mmHg. Art. The density of the drying agent in front of the mill fan (kg/m3) is determined by the formula

(16)

Where is the increase in water vapor content due to evaporated fuel moisture, kg/kg dry air, determined by the formula

(17)

Here IN m - mill productivity, t/h; μ - fuel concentration in the air, kg/kg; - air flow in front of the mill under normal conditions, m 3 /h; - the proportion of evaporated moisture in 1 kg of original fuel, determined by the formula

(18)

In which is the working moisture of the fuel, %; - dust moisture, %. Calculations when determining suction cups are carried out using the formulas:

(20)

(21)

The value of the suction cups in relation to the air flow theoretically required for fuel combustion is determined by the formula

(22)

Where is the average value of suction for all dust preparation systems, m 3 /h; n- average number of operating dust preparation systems at rated boiler load; IN k - fuel consumption per boiler, t/h; V 0 - theoretically required air flow for burning 1 kg of fuel, m 3 /kg. To identify the value based on the value of the coefficient determined by formula (14), it is necessary to determine the amount of drying agent at the entrance to the installation and then carry out calculations based on formulas (21) and (22). If determining the value is difficult (for example, in dust preparation systems with fan mills due to high gas temperatures), then this can be done based on the gas flow rate at the end of the installation - [we retain the designation of formula (21)]. To do this, it is determined in relation to the section behind the installation using the formula

(23)

In this case

Further determined by formula (24). When determining the consumption of the drying-ventilating agent during gas drying, it is advisable to determine the density using formula (16), substituting . The latter can, according to [5], be determined by the formulas:

(25)

Where is the density of gases at α = 1; - reduced fuel humidity, % per 1000 kcal (1000 kg·% / kcal); and - coefficients having the following meanings:

3. DETERMINATION OF HEAT LOSS AND EFFICIENCY BOILER

3.1. Calculations to determine the components of the heat balance are carried out using the given fuel characteristics [5] in the same way as is done in [8]. The efficiency (%) of the boiler is determined by the reverse balance using the formula

Where q 2 - heat loss with flue gases, %; q 3 - heat loss with chemical incomplete combustion,%; q 4 - heat loss with mechanical incomplete combustion, %; q 5 - heat loss to the environment, %; q 6 - heat loss with physical heat of the slag, %. 3.2. Due to the fact that the purpose of these Guidelines is to assess the quality of repairs, and comparative tests are carried out under approximately the same conditions, heat losses with flue gases can be determined with sufficient accuracy using a somewhat simplified formula (in comparison with that adopted in [8]):

Where is the coefficient of excess air in the exhaust gases; - flue gas temperature, °C; - cold air temperature, °C; q 4 - heat loss with mechanical incomplete combustion, %; TOQ- correction factor taking into account the heat introduced into the boiler with heated air and fuel; TO , WITH, b- coefficients depending on the type and reduced moisture content of the fuel, the average values of which are given in table. 3.

Table 3

Average values of coefficients K, C and d for calculating heat loss q 2

Fuel

WITH

Anthracites,

3.5 + 0.02 W p ≈ 3.53

0.32 + 0.04 W p ≈ 0.38

semi-anthracite,

skinny coals

Stone coals

Brown coals

3.46 + 0.021 W p

0.51 +0.042 W p

0.16 + 0.011 W p

Slates

3.45 + 0.021 W p

0.65 +0.043 W p

0.19 + 0.012 W p

Peat

3.42 + 0.021 W p

0.76 + 0.044 W p

0.25 + 0.01 W p

Firewood

3.33 + 0.02 W p

0.8 + 0.044 W p

0.25 + 0.01 W p

Fuel oil, oil

Natural gases

Associated gases

*At W n ≥ 2 b = 0,12 + 0,014 W P.

The cold air temperature (°C) is measured on the suction side of the blower fan before the control hot air is introduced. Correction factor K Q determined by the formula

(29)

It makes sense to take physical heat of fuel into account only when using heated fuel oil. This value is calculated in kJ/kg (kcal/kg) using the formula

(30)

Where is the specific heat capacity of fuel oil at the temperature at which it enters the furnace, kJ/(kg °C) [kcal/(kg °C)]; - temperature of fuel oil entering the boiler, heated outside it, °C; - The share of fuel oil by heat in the fuel mixture. Specific heat consumption per 1 kg of fuel introduced into the boiler with air (kJ/kg) [(kcal/kg)] when preheating it in air heaters is calculated by the formula

Where is the excess air entering the boiler in the air path in front of the air heater; - increase in air temperature in heaters, °C; - reduced fuel humidity, (kg % 10 3) / kJ [(kg % 10 3) / kcal]; - physical constant equal to 4.187 kJ (1 kcal); - lower calorific value, kJ (kcal/kg). The reduced humidity of solid fuel and fuel oil is calculated based on the current average data at the power plant using the formula

(32)

Where is the fuel moisture per working mass, %, for the co-combustion of fuel of different types and brands, if the coefficients K, S And b for different grades of solid fuel differ from one another, the given values of these coefficients in formula (28) are determined by the formula

Where a 1 a 2 ... a n are the thermal fractions of each of the fuels in the mixture; TO 1 TO 2 ...TO n - coefficient values TO (WITH,b) for each of the fuels. 3.3. Heat losses with chemical incomplete combustion of fuel are determined by the formulas: for solid fuel

For fuel oil

For natural gas

The coefficient is taken equal to 0.11 or 0.026 depending on in what units it is determined - in kcal/m3 or kJ/m3. The value is determined by the formula

When calculating in kJ/m 3, the numerical coefficients in this formula are multiplied by the coefficient K = 4.187 kJ/kcal. In formula (37) CO, N 2 and CH 4 - volumetric contents of products of incomplete combustion of fuels as a percentage relative to dry gases. These values are determined using chromatographs using previously selected gas samples [4]. For practical purposes, when the boiler operating mode is carried out with excess air, providing a minimum value q 3, it is quite enough to substitute only the value into formula (37) CO. In this case, you can get by with simpler gas analyzers like " Testo-Term". 3.4. Unlike other losses, determining heat losses with mechanical incomplete combustion requires knowledge of the characteristics of the solid fuel used in specific experiments - its calorific value and working ash content A R. When burning bituminous coals of unknown suppliers or brands, it is useful to know the volatile yield, since this value can affect the degree of fuel burnout - the content of combustible substances in the entrainment of the guns and slag Gsl. Calculations are carried out according to the formulas:

(38)

Where and is the proportion of fuel ash falling into a cold funnel and carried away by flue gases; - heat of combustion of 1 kg of fuel, equal to 7800 kcal/kg or 32660 kJ/kg. It is advisable to calculate heat losses with entrainment and slag separately, especially with large differences in G un and G Shl. In the latter case, it is very important to clarify the value of , since the recommendations [9] on this issue are very approximate. In practice and G shl depend on the dust size and the degree of contamination of the furnace with slag deposits. To clarify the value, it is recommended to carry out special tests [4]. When burning solid fuel in a mixture with gas or fuel oil, the value (%) is determined by the expression

Where is the share of solid fuel by heat in total fuel consumption. When several grades of solid fuel are simultaneously burned, calculations using formula (39) are carried out using weighted average values and A R. 3.5. Heat losses to the environment are calculated based on recommendations [9]. When conducting experiments at a load D less than the nominal one, recalculation is carried out using the formula

3.6. Heat losses with the physical heat of the slag are significant only with liquid slag removal. They are determined by the formula

(42)

Where is the enthalpy of ash, kJ/kg (kcal/kg). Determined according to [9]. The ash temperature for solid slag removal is assumed to be equal to 600°C, for liquid ash removal - equal to the temperature of normal liquid slag removal t nz or t zl + 100°С, which are determined by [9] and [10]. 3.7. When conducting experiments before and after repairs, it is necessary to strive to maintain the same maximum number of parameters (see paragraph 1.4 of these Guidelines) in order to minimize the number of corrections that need to be introduced. Only an amendment to q 2 for cold air temperature t x.c, if the temperature at the inlet to the air heater is maintained at a constant level. This can be done based on formula (28), defining q 2 at different meanings t x.v. Taking into account the influence of deviations of other parameters requires experimental verification or machine calibration calculations of the boiler.

4. DETERMINATION OF HARMFUL EMISSIONS

4.1. The need to determine the concentrations of nitrogen oxides ( NO x), and also SO 2 and CO is dictated by the urgency of the problem of reducing harmful emissions from power plants, which over the years has received all the attention more attention[11, 12]. This section is missing in [13]. 4.2. To analyze flue gases for the content of harmful emissions, portable gas analyzers from many companies are used. The most common electrochemical devices at Russian power plants are from the German company " Testo"The company produces devices of various classes. Using the simplest device" Testo 300M" can determine the content in dry flue gases ABOUT 2 in % and volume fractions ( ppt)* CO And NO x and automatically convert the volume fractions to mg/nm 3 at α = 1.4. Using a more complex device " Testo- 350" you can, in addition to the above, determine the temperature and gas velocity at the probe insertion point, determine by calculation the efficiency of the boiler (if the probe is inserted into the gas duct behind the boiler), determine separately using an additional block (" Testo- 339") content NO And NO 2, as well as when using heated hoses (up to 4 m long) SO 2 . ___________ *1 ppt= 1/10 6 volume. 4.3. In boiler furnaces, during fuel combustion, nitrogen monoxide is mainly formed (95 - 99%) NO, and the content of more toxic dioxide NO 2 is 1 - 5%. Partial uncontrolled additional oxidation occurs in the boiler flues and further in the atmosphere. NO V NO 2 Therefore, conditionally when converting the volume fraction ( ppt) NO x to a standard mass value (mg/nm 3) at α = 1.4, a conversion factor of 2.05 is applied (and not 1.34, as for NO). The same coefficient is also adopted in instruments " Testo" when converting values from ppt in mg/nm3. 4.4. The content of nitrogen oxides is usually determined in dry gases, therefore water vapor contained in flue gases must be condensed and removed as much as possible. For this purpose, in addition to the condensate drain with which the devices are equipped, " Testo", it is advisable for short lines to install a Drexler flask in front of the device to organize gas bubbling through the water. 4.5. Representative gas sample for determination NO x and also S O 2 and CO can be taken only in the section behind the smoke exhauster, where the gases are mixed, while in sections closer to the firebox, distorted results can be obtained due to sampling from a plume of flue gases characterized by increased or decreased content NO X, SO 2 or CO. At the same time, with a detailed study of the reasons for the increased values NO x It is useful to take samples from several points along the width of the duct. This allows you to associate values NO x with the organization of combustion mode, find modes characterized by a smaller spread of values NO x and, accordingly, a smaller average value. 4.6. Definition NO x before and after repair, as well as the determination of other boiler indicators, should be carried out at rated load and in the modes recommended by the operating map. The latter, in turn, should be focused on the use of technological methods for suppressing nitrogen oxides - organizing staged combustion, introducing recirculation gases into burners or into air ducts in front of the burners, different supplies of fuel and air to different tiers of burners, etc. 4.7. Conducting experiments on maximum reduction NO x, which is often achieved by reducing the excess air in the control section (behind the superheater), an increase in CO. The limit values for newly designed or reconstructed boilers, according to [12], are: for gas and fuel oil - 300 mg/nm 3, for pulverized coal boilers with solid and liquid slag removal - 400 and 300 mg/nm 3, respectively. Recalculation CO And SO 2 of ppt in mg/nm 3 is produced by multiplying by specific gravity 1.25 and 2.86. 4.8. To eliminate errors when determining the content in flue gases SO 2 it is necessary to sample gases downstream of the smoke exhauster and, in addition, to prevent condensation of water vapor contained in the flue gases, since SO 2 dissolves well in water to form H 2 SO 3 To do this, when high temperature exhaust gases, eliminating the condensation of water vapor in the gas intake tube and hose, make them as short as possible. In turn, in case of possible moisture condensation, heated hoses (up to a temperature of 150°C) and an attachment for drying flue gases should be used. 4.9. Sampling behind the smoke exhauster involves quite a period of time. long period with sub-zero ambient temperatures, and the devices " Testo" are designed to operate in the temperature range +4 ÷ + 50 ° C, therefore, for measurements behind the smoke exhauster in winter, it is necessary to install insulated cabins. For boilers equipped with wet ash collectors, the definition SO 2 behind the smoke exhauster allows you to take into account partial absorption SO 2 in scrubbers. 4.10. To eliminate systematic errors in determining NO x and SO 2 and comparing them with generalized materials, it is advisable to compare the experimental data with the calculated values. The latter can be determined from [13] and [14].4.11. The quality of repair of a boiler installation, among other indicators, is characterized by emissions of solid particles into the atmosphere. If it is necessary to determine these emissions, [15] and [16] should be used.

5. DETERMINATION OF STEAM TEMPERATURE LEVEL AND ITS REGULATION RANGE

5.1. When conducting operational tests, it is necessary to identify the possible range of steam temperature control using desuperheaters and, if this range is insufficient, determine the need to intervene in the combustion mode to ensure the required level of superheat, since these parameters determine the technical condition of the boiler and characterize the quality of repairs. 5.2. The steam temperature level is assessed based on the value of the conditional temperature (steam temperature in the event of desuperheater shutdown). This temperature is determined from tables of water vapor based on conventional enthalpy:

(43)

Where is the enthalpy of superheated steam, kcal/kg; - decrease in steam enthalpy in the desuperheater, kcal/kg; TO- coefficient that takes into account the increase in heat absorption of the superheater due to an increase in temperature pressure when the desuperheater is turned on. The value of this coefficient depends on the location of the desuperheater: the closer the desuperheater is located to the outlet of the superheater, the closer the coefficient is to unity. When installing a surface desuperheater on saturated steam TO is taken to be 0.75 - 0.8. When using a surface desuperheater to regulate the steam temperature, in which the steam is cooled by passing part of the feed water through it,

(44)

Where and is the enthalpy of feed water and water at the inlet to the economizer; - enthalpy of steam before and after the desuperheater. In cases where there are several injections on the boiler, formula (46) determines the water consumption for the last injection along the steam flow. For the previous injection, instead of in formula (46), one should substitute ( - ) and the values of the enthalpy of steam and condensate corresponding to this injection. Formula (46) is written similarly for the case when the number of injections is more than two, i.e. is substituted ( - - ), etc. 5.3. The range of boiler loads within which the nominal fresh steam temperature is provided by devices designed for this purpose without interfering with the operating mode of the furnace is determined experimentally. The limitation for a drum boiler when the load decreases is often associated with leakage of the control valves, and when the load increases, it can be a consequence of the lower feedwater temperature due to the relatively lower steam flow through the superheater at a constant fuel consumption. To take into account the influence of feed water temperature, you should use a graph similar to that shown in Fig. 3, and to convert the load to the nominal temperature of the feed water - in Fig. 4. 5.4. When conducting comparative tests of the boiler before and after repair, the load range at which the nominal temperature of the reheat steam is maintained must also be experimentally determined. This means the use of design means for regulating this temperature - a steam-steam heat exchanger, gas recirculation, gas bypass in addition to the industrial steam superheater (boilers TP-108, TP-208 with split tail), injection. The assessment should be carried out with high-pressure heaters turned on (design feed water temperature) and taking into account the steam temperature at the inlet to the reheater, and for double-shell boilers - with equal loading of both buildings.

Rice. 3. An example of determining the necessary additional decrease in the temperature of superheated steam in desuperheaters while lowering the temperature of the feed water and maintaining a constant steam flow

Note. The graph is based on the fact that when the feed water temperature decreases, for example from 230 to 150°C, and the boiler steam output and fuel consumption remain unchanged, the enthalpy of steam in the superheater increases (at R p.p = 100 kgf/cm2) a 1.15 times (from 165 to 190 kcal/kg), and steam temperature from 510 to 550°C

Rice. 4. An example of determining the boiler load, reduced to the nominal feed water temperature of 230 °C (att p.v.= 170 °C and Dt= 600 t/h D nom = 660 t/h)

Note . The graph was built under the following conditions: t p.e = 545/545°C; R p.p = 140 kgf/cm 2 ; R"industrial = 28 kgf/cm2; R"prom = 26 kgf/cm 2; t"prom = 320°C; D prom/D pp = 0.8

List of used literature

1. Methodology for assessing the technical condition of boiler plants before and after repair: RD 34.26.617-97.- M.: SPO ORGRES, 1998. 2. Rules for organizing maintenance and repair of equipment, buildings and structures of power plants and networks: RD 34.38.030 -92. - M.: TsKB Energoremonta, 1994. 3. Guidelines for drawing up operational maps of boiler installations and optimizing their management: RD 34.25.514-96. - M.: SPO ORGRES, 1998. 4. Trembovlya V.I., Finger E.D., Avdeeva A.A. Thermal testing of boiler installations. - M.: Energoatomizdat, 1991. 5. Pekker Ya.L. Thermal engineering calculations based on the given fuel characteristics. - M.: Energy, 1977. 6. Tolchinsky E.N., Dunsky V.D., Gachkova L.V. Determination of air suction into the combustion chambers of boiler installations. - M.: Electric Stations, No. 12, 1987. 7. Rules for the technical operation of power stations and networks of the Russian Federation: RD 34.20.501-95. - M.: SPO ORGRES, 1996. 8. Guidelines for the preparation and content of energy characteristics of equipment for thermal power plants: RD 34.09.155-93. - M.: SPO ORGRES, 1993. 9. Thermal calculation of boiler units (Normative method). - M.: Energy, 1973. 10. Energy fuel of the USSR: Directory. - M.: Energoatomizdat, 1991. 11. Kotler V.R. Nitrogen oxides in boiler flue gases. - M.: Energoatomizdat, 1987. 12. GOST R 50831-95. Boiler installations. Heating equipment. General technical requirements. 13. Methodology for determining gross and specific emissions harmful substances into the atmosphere from boilers of thermal power plants: RD 34.02.305-90. - M.: Rotaprint VTI, 1991. 14. Guidelines for calculating emissions of nitrogen oxides from flue gases of boilers of thermal power plants: RD 34.02.304-95. - M.: Rotaprint VTI, 1996. 15. Methodology for determining the degree of purification of flue gases in ash collection plants (express method): RD 34.02.308-89. - M.: SPO Soyuztekhenergo, 1989. RD 153-34.0-02.308-98 16. Methodology for testing ash collection installations of thermal power plants and boiler houses: RD 34.27.301-91. - M.: SPO ORGRES, 1991.

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Boiler installations of thermal power plants. General information. Steam boilers of thermal power plants (TPP)

General information. The boiler installation consists of a boiler and auxiliary equipment

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RD 153-34.1-26.303-98

RD 153-34.1-26.303-98

1. GENERAL PART

Table 1

Statement of technical condition indicators of the boiler installation

2. DETERMINATION OF EXCESS AIR AND COLD AIR SUCKS

2.1. Determination of excess air

The correctness of the gas analysis can also be checked using the equation

2.2. Determination of air suction into the firebox

ss

2.3. Determination of air suction into the flues of a boiler installation

2.4. Determination of air suction into dust preparation systems

3. DETERMINATION OF HEAT LOSS AND EFFICIENCY BOILER

Table 3

Fuel

4. DETERMINATION OF HARMFUL EMISSIONS

5. DETERMINATION OF STEAM TEMPERATURE LEVEL AND ITS REGULATION RANGE

List of used literature