Convective heating surface of the boiler. The main heating surfaces of the steam boiler, purpose

Elements of heating surfaces are the main ones in the boiler unit and their serviceability primarily determines the efficiency and reliability of the boiler plant.

The placement of elements of the heating surface of a modern boiler is shown in the figure:

This boiler is U-shaped. The left vertical chamber 2 forms a furnace, all its walls are covered with pipes. Pipes located on the walls and ceiling in which water evaporates are called screens. Screen pipes, as well as parts of the superheater located on the walls of the furnace, are called radiation heating surfaces, since they absorb heat from flue gases mainly due to radiation or radiation.

The lower part 9 of the combustion chamber is commonly referred to as the cold funnel. In it, ash particles fall out of the furnace torch. Cooled and hardened ash particles in the form of sintered lumps (slag) are removed through the device 8 into the hydraulic ash removal system.

The upper part of the furnace passes into a horizontal gas duct, in which the screen 3 and convective 5 superheaters are located. The side walls and ceiling of the horizontal duct are usually also covered with superheater pipes. These elements of the superheater are called semi-radiation, since they perceive heat from flue gases both as a result of radiation and convection, i.e., heat exchange that occurs when hot gases come into contact with pipes.

After the horizontal flue behind the rotary chamber, the right vertical part of the boiler begins, called the convective shaft. In it, steps, air heater steps, and in some designs, coils are placed in a different sequence.

The layout of the boiler depends on its design and power, as well as steam pressure. In outdated low and medium pressure three-drum boilers, water is heated and evaporated not only in the screens, but also in the boiler pipes located between the upper and lower drums.

Through the lower 3 bundle of boiler pipes, water from the rear drum descends into the lower drum; these pipes play the role of culverts. A slight heating of these pipes by flue gases does not disturb the circulation of water in the boiler, since at low and medium pressures the difference in specific gravity water and steam is large, which provides a fairly reliable circulation. Water is supplied to the lower chambers of the screens 7 from the upper drums 2 through external unheated culverts.

In medium-pressure boilers, the share of heat used to superheat steam is relatively small (less than 20% of the total heat absorbed by the boiler unit from flue gases), so the heating surface of the superheater is also small and it is placed between the bundles of boiler tubes.

In single-drum medium-pressure boilers of later releases, the main evaporative surface is placed on the walls of the furnace in the form of screens 6, and a small convective beam 10 is made of pipes separated with a large pitch, which represent the semi-radiant part of the boiler.

Boilers high pressure are usually made with one drum and do not have convective bundles. The entire evaporative heating surface is made in the form of screens, which are fed with water through external unheated culverts.

AT once-through boiler x drum missing.

Water from the economizer 3 flows through the supply pipes 7 to the lower chamber 6, and then to the radiation part 5, which is the evaporation pipes (coils) located along the walls of the furnace. Passing through the coils most of water turns into steam. Water completely evaporates in the transition zone 2, which is located in an area more low temperatures flue gases. From the transition zone, steam enters the superheater 1.

Thus, in once-through boilers there is no circulation of water with its return movement. Water and steam pass through the pipes only once.

A superheater is a heating surface of a steam boiler in which the steam is superheated to a predetermined temperature. Modern steam boilers large steam capacity have two superheaters - primary and secondary (intermediate). Saturated steam at the temperature of boiling water enters the primary superheater from the boiler drum or the transition zone of the once-through boiler. Steam enters the secondary superheater from for reheating.

To overheat steam in high-pressure boilers, up to 35% of heat is consumed, and in the presence of secondary overheating, up to 50% of the heat perceived by the boiler unit from flue gases. In boilers with a pressure of more than 225 atm, this proportion of heat increases to 65%. As a result, the heating surfaces of superheaters increase significantly, and in modern boilers they are placed in the radiation, semi-radiation and convective parts of the boiler.

The figure below shows a diagram of a modern boiler superheater.

The steam from the drum 7 is directed to the wall tube panels of the radiation part 2 and 4, then to the ceiling tube panels 5. From the desuperheater 8, the steam enters the screens 6, and then to the coils 10 of the convective part of the superheater. The screen is a package of U-shaped pipes located in the same plane, which are rigidly fastened together with almost no gap. The steam enters one chamber of the screen, passes through the pipes and exits through the second chamber. The layout of the screens in the boiler is shown in the figure:

Water economizers, together with air heaters, are usually located in convection shafts. These elements of the heating surface are called tail elements, since they are located last along the path of flue gases. Water economizers are mainly made of steel pipes. On low and medium pressure boilers, cast iron economizers are installed, made up of cast iron ribbed tubes. The pipes are connected with cast-iron bends (kalachs).

Steel economizers can be of boiling and non-boiling types. In boiling type economizers, part of the heated water (up to 25%) is converted into steam.

Modern boilers, unlike those used a few years ago, can use not only gas, coal, fuel oil, etc. as fuel. Pellets are used more and more often as an environmentally friendly fuel. You can order pellets for your pellet boiler here - http://maspellet.ru/zakazat-pellety.

Convective heating surfaces of boilers using finned tubes, produced at the UralKotloMashZavod enterprise, are modernized models that have incorporated our rich experience in this industry and new high-tech research to increase the efficiency and wear resistance of these boiler equipment units.

To date, it is generally recognized that the convective heating surface in hot water boilers PTVM and KVGM is the weakest link. Many boiler plants, a number of design organizations and repair enterprises have their own projects for its modernization. The most perfect development should be recognized as the development of JSC "Machine-building plant" ZIO-Podolsk ". The developers approached the solution of the problem in a complex way. In addition to increasing the diameter of pipes from 28 mm to 38 mm and doubling their transverse pitch, traditional smooth-walled pipes have been replaced with finned ones. Membrane and transverse-spiral finning is used. According to the developers, replacement in PTVM-100 boilers old design the new one will allow to obtain fuel savings of up to 2.4%, and most importantly, to increase the operational reliability and service life of the convective surface by 3 times.
Below are the results of further improvement of the convective surface, aimed at the possibility of abandoning the membrane fins in the high-temperature part of the surface in order to reduce its metal consumption. Instead of membranes, short spacers are welded between the pipes. They form three stiffening belts along the length of the sections and therefore spacer posts are not required. Exactly the same short spacer inserts are used in the low-temperature part of the surface of pipes with transverse spiral fins. They replaced the bulky stamped racks. The ranking of the transverse pitch of the pipes and, accordingly, the sections among themselves is carried out by combs in the area of ​​the stiffening belts. Combs fix only the outer rows of pipes of each section. Inside the heating surface assembled from sections, the pipes are ranked according to the transverse pitch due to the rigid design of the sections.
Spacing inserts welded between coil tubes have been used for more than 20 years instead of traditional racks. The result is positive. Spacer inserts securely cool and do not cause deformation of the pipes. There have been no cases of fistulas on the pipes due to the use of inserts over the entire long-term practice.
The rejection of membrane finning of pipes in the high-temperature part of the heating surface and the return to a smooth-tube design made it possible to reduce its metal consumption with virtually no change in heat absorption. In the first projects, the step between the transverse-spiral fins in the low-temperature part was taken to be 6.5 mm, and in later projects it was reduced to 5 mm. Practice shows that when burning only natural gas in hot water boilers, this step can be further reduced and additional fuel savings can be obtained.
In the period from 2002 to 2010, modernized convective heating surfaces for PTVM-100 boilers were introduced at the Gurzuf district boiler house (Yekaterinburg) - 4 boilers; CHPP of the Nizhny Tagil Iron and Steel Works (Nizhny Tagil) -3 boilers; Sverdlovsk CHPP (OAO Uralmash, Yekaterinburg) - 2 boilers; for PTVM-180: Saratov CHPP-5 (Saratov) - 2 boilers; KVGM-100 ( Rostov region) - 2 boilers.
There are no remarks from the side of operation on the newly developed and installed heating surfaces in hot water boilers. A significant reduction in hydraulic and aerodynamic resistances has been confirmed. The boilers easily reach the rated load and operate stably in this mode. Used spacers are reliably cooled. There are no deformations of pipes and sections themselves in the modernized heating surfaces. The flue gas temperature at the nominal factory heat output decreased by 15°C for boilers with a pitch between transverse-spiral fins of 6.5 mm and by 18°C ​​for boilers with a pitch between fins of 5 mm.

You can order, clarify the cost, prices by sending a message from the site!

The heating surface of the boiler is an important part, it is the metal walls of its elements, which are washed by the gases coming directly from the furnace, on the one hand, and the steam-water mixture, on the other. Usually its components are the surfaces of the economizer, the superheater and the steam boiler itself. Its size can vary - from 2-3m2 to 4000m2, it depends on the scope of the boiler and its purpose.

Types of boiler heating surfaces

The production of boiler heating surfaces is quite developed and allows you to make them of various configurations:

Screen-pipe - seamless pipes located in the boiler furnace are the basis of such a surface. As a rule, the type of boiler determines which screen is needed - rear, side right or left.

Convective - boiling bundles of steel seamless pipes, which are placed as a standard in the gas outlets of a stationary boiler. Heat in this case is obtained by convection.

Convective boiler heating surfaces are widely used in thermal power engineering, in particular, in the production of steam generators. This type includes such heat-receiving surfaces as economizers, air heaters and other heating surfaces of a hot water and steam boiler, with the exception of the surfaces of furnace screens, as well as radiation-convective screen superheaters located in the first flue and furnace. The invention of this type of heat-receiving surface has significantly increased the manufacturability of both installation and subsequent repair.

Heating surfaces for steam boilers

Heating surfaces of steam boilers in a variety of industrial systems have significant differences from each other. Only the location is identical - basically it is a firebox, and the way heat is perceived by radiation. The amount of heat perceived by the combustion screens directly depends on the type of fuel that is burned. So, for a steam-forming surface, the perception ranges from 40 to 50% of the heat given off to the working medium in the boiler.

Modernization of convective surfaces: efficiency and durability

Nevertheless, the convective heating surfaces of hot water boilers are a rather vulnerable place, so projects for its improvement are constantly being created. The most effective development was the decision to increase the diameter of the pipes and replace standard smooth-tube structures with finned ones, which made it possible to save fuel consumption and triple the service life and general term operation, as well as the reliability of the convective surface. It should be noted that in this case, specialists used membrane and transverse-spiral finning technology.

To reduce metal consumption, quite successful projects have also been developed to replace membrane fins in that part of the surface that interacts with high temperatures with small spacer inserts. As a result, resistance decreased, both hydraulic and aerodynamic, metal consumption, and heat absorption remained at the same level.

The company "UralKotloMashZavod" supplies modernized convective heating surfaces, manufactured using the technology of pipe finning, which allows to increase the efficiency and wear resistance of such vulnerable parts of boiler equipment. The company has many years of experience in the production and sale of high-tech surfaces that have proven themselves in the industrial market.

Boiler classification

Boiler units are divided into steam, designed to produce steam, and hot water, designed to produce hot water.

According to the type of fuel burned and the corresponding fuel path, boilers for gaseous, liquid and solid fuel.

According to the gas-air path, boilers are distinguished with natural and balanced draft and with pressurization. In the boiler with natural draft the resistance of the gas path is overcome under the action of the density difference atmospheric air and gas in the chimney. If the resistance of the gas path (as well as the air path) is overcome with the help of a blower fan, then the boiler operates with pressurization. In a balanced draft boiler, the pressure in the furnace and at the beginning of the flue is maintained close to atmospheric joint work blower fan and smoke exhauster. At present, all manufactured boilers, including those with balanced draft, are being strived to be gas-tight.

According to the type of steam-water path, drum ones are distinguished (Fig. 3.1, a, b) and straight-through (Fig. 3.1, in) boilers. In all types of boilers, water and steam pass through economizer 1 and superheater 6 once. In drum boilers, the steam-water mixture repeatedly circulates in the evaporative heating surfaces 5 (from drum 2 through drain pipes 3 to collector 4 and drum 2). Moreover, in boilers with forced circulation (Fig. 3.1, b) an additional pump 8 is installed before the water enters the evaporation surfaces 5. In once-through boilers (Fig. 3.1, in) the working fluid passes through all heating surfaces once under the action of pressure developed by the feed pump 7.

In boilers with recirculation and combined circulation, to increase the speed of water movement in some heating surfaces, when starting a once-through boiler or operating at reduced loads, forced water recirculation is provided by a special pump 8 (Fig. 3.1, G).

According to the phase state of the slag removed from the furnace, boilers with solid and liquid slag removal are distinguished. In boilers with solid ash removal (TShU), slag is removed from the furnace in the solid state, and in boilers with liquid ash removal (LShU) - in the molten state.

Rice. 3.1. Schemes of the steam-water path of the boiler: a- drum with natural circulation;
b - drum with forced circulation; in- straight-through; G- direct-flow
with forced circulation: 1 – economizer; 2 - boiler drum; 3 - culverts;
4 – collector of screen pipes; 5 – evaporative heating surfaces; 6 - superheater;
7 – feed pump; 8 – circulation pump

Hot water boilers characterized by their heat output, temperature and pressure of heated water, as well as by the type of metal from which it is made.

Hot water boilers are steel and cast iron.

Cast iron boilers are made for heating individual residential and public buildings. Their heat output does not exceed 1 - 1.5 Gcal / h, pressure - 0.3 - 0.4 MPa, temperature - 115 ° C. Steel hot water boilers large heating capacity is installed in large quarterly or district boiler houses, which can provide heat supply to large residential areas.

Steam boiler units They are produced in different types, steam capacities and parameters of produced steam.

By steam capacity, boilers are distinguished with low productivity - 15 - 20 t / h, medium productivity - from 25 - 35 to 160 - 220 t / h and high productivity from 220 - 250 t / h and above.

Under nominal steam capacity understand the maximum load (in t/h or kg/s) of a stationary boiler with which it can operate during long-term operation when burning the main type of fuel or when supplying a nominal amount of heat at nominal values ​​of steam and feed water subject to allowable deviations.

Steam pressure and temperature ratings- these are the parameters that must be ensured immediately before the steam pipeline to the steam consumer at the nominal steam output of the boiler (and the temperature also at the nominal pressure and temperature of the feed water).

Rated feed water temperature- this is the water temperature that must be provided before entering the economizer or other boiler feed water heater (or in their absence - before entering the drum) at a nominal steam capacity.

According to the pressure of the working fluid, boilers of low (less than 1 MPa), medium
(1 - 10 MPa), high (10 - 25 MPa) and supercritical pressure (more than 25 MPa).

Boiler units produce saturated or superheated steam with temperatures up to 570 °C.

According to their purpose, steam boilers can be divided into industrial boilers installed in production, production and heating and heating boilers, and energy boilers installed in boilers of thermal power plants.

According to the type of layout, boilers can be divided into vertical-cylindrical, horizontal layout (with a developed evaporative heating surface) and vertical layout.

Drum steam boilers

Drum boilers are widely used at thermal power plants and in boiler houses. The presence of one or more drums with a fixed interface between steam and water is hallmark these boilers. Feed water in them, as a rule, after economizer 1 (see Fig. 3.1, a) is fed into drum 2, where it is mixed with boiler water (water filling the drum and screens). The mixture of boiler and feed water through unheated downpipes 3 from the drum enters the lower distribution manifolds 4, and then into screens 5 (evaporation surfaces). In the screens, water receives heat Q from the products of combustion of fuel and boils. The resulting steam-water mixture rises into the drum. This is where the separation of steam and water takes place. Steam through pipes connected to top drum, is sent to the superheater 6, and the water again to the downpipes 3.

In the screens, only a part (from 4 to 25%) of the water entering them evaporates in one pass. This ensures sufficiently reliable cooling of the pipes. Prevent the accumulation of salts deposited during the evaporation of water on inner surface pipes, is possible due to the continuous removal of part of the boiler water from the boiler. Therefore, to feed the boiler, it is allowed to use water with a relatively high content of salts dissolved in it.

closed system, consisting of a drum, downpipes, a collector and evaporative surfaces, along which the working fluid repeatedly moves, is commonly called circulation circuit, and the movement of water in it is circulation. The movement of the working medium, due only to the difference in the weight of the water columns in the downcomers and the steam-water mixture in the lifts, is called natural circulation, and the steam boiler is drum type with natural circulation. natural circulation possible only in boilers with a pressure not exceeding 18.5 MPa. At a higher pressure, due to the small difference in the densities of the steam-water mixture and water, it is difficult to ensure the steady movement of the working medium in the circulation circuit. If the movement of the medium in the circulation circuit is created by pump 8 (see Fig. 3.1, b), then the circulation is called forced, and the steam boiler - drum with forced circulation. Forced circulation makes it possible to make screens from pipes of smaller diameter with both upward and downward movement of the medium in them. The disadvantages of such circulation include the need to install special pumps (circulation), which have complex structure, and additional energy consumption for their work.

The simplest drum boiler used to produce steam consists of a horizontal cylindrical drum 1 with elliptical bottoms, 3/4 filled with water, and a furnace 2 underneath (Fig. 3.2, a). The walls of the drum, heated from the outside by the combustion products of the fuel, play the role of a heat exchange surface.

With the growth of steam production, the size and weight of the boiler increased sharply. The development of boilers, aimed at increasing the heating surface while maintaining the water volume, went in two directions. According to the first direction, an increase in the heat exchange surface was achieved due to the placement of pipes in the water volume of the drum, heated from the inside by combustion products. So, fire tubes appeared (Fig. 3.2, b), then flue and, finally, combined gas-tube boilers. In fire-tube boilers in the water volume of the drum 1, one or more flame tubes 3 of large diameter (500 - 800 mm) are placed parallel to its axis, in fire tubes - a whole bundle of pipes 3 of small diameter. In combined gas-tube boilers (Fig. 3.2, in) in the initial part of the flame tubes there is a furnace 2, and the convective surface is made of fire tubes 3. The performance of these boilers was low, due to disabilities placement of flame and smoke tubes in the water volume of the drum 1. They were used in ship installations, locomotives and steam locomotives, as well as to produce steam for the company's own needs.

Rice. 3.2. Boiler schemes: a- the simplest drum; b - fire-tube; in– combined gas-pipe; G- water pipe; d- vertical water pipe; e- drum modern design

The second direction in the development of boilers is associated with the replacement of one drum with several smaller diameter ones filled with water and a steam-water mixture. An increase in the number of drums led first to the creation of battery boilers, and the replacement of part of the drums with smaller diameter pipes located in the flue gas flow led to water-tube boilers. Thanks to great opportunities increasing steam production this direction has been widely developed in the energy sector. First water tube boilers had bundles of pipes 3 inclined to the horizontal (at an angle of 10 - 15 °), which, using chambers 4, were connected to one or more horizontal drums 1 (Fig. 3.2, G). Boilers of this design are called horizontal water pipe. Among them, the boilers of the Russian designer V. G. Shukhov should be highlighted. The progressive idea associated with the division of common chambers, drums and tube bundles into the same type groups (sections) of the same length and the same number of pipes, incorporated into the design, made it possible to assemble boilers of different steam capacities from standard parts.
But such boilers could not work under variable loads.

The creation of vertical water tube boilers is the next stage in the development of boilers. Bundles of pipes 3 connecting the upper and lower horizontal drums 1 began to be placed vertically or at a large angle to the horizon (Fig. 3.2, d). The reliability of the circulation of the working medium has increased, access to the ends of the pipes has been provided, and thereby the processes of rolling and cleaning of pipes have been simplified. Improving the design of these boilers, aimed at increasing the reliability and efficiency of their work, has led to the emergence of a modern boiler design (Fig. 3.2, e): single-drum with a lower collector 5 of small diameter; downpipes 6 and drum 1 taken out of the heating zone beyond the boiler lining; complete shielding of the firebox; convective tube bundles with transverse washing by combustion products; preheating of air 9, water 8 and superheating of steam 7.

Structural scheme of a modern drum boiler is determined by its power and steam parameters, the type of fuel burned and the characteristics of the gas-air path. Thus, with increasing pressure, the ratio between the areas of heating, evaporating and superheating surfaces changes. Increasing the pressure of the working fluid from
R= 4 MPa up to R= 17 MPa leads to a decrease in the proportion of heat q, water spent on evaporation from 64 to 38.5%. The share of heat consumed for heating water increases from 16.5 to 26.5%, and for steam superheating - from 19.5 to 35%. . Therefore, with an increase in pressure, the areas of the heating and superheating surfaces increase, and the area of ​​the evaporation surface decreases.

In domestic industrial and industrial heating boilers, boiler units of the DKVR type (double-drum boiler, water-tube, reconstructed) with a nominal steam output of 2.5 are widespread; 4; 6.5; 10 and 20 t/h manufactured by the Biysk Boiler Plant.

Boilers of the DKVR type (Fig. 3.3 and 3.4) are manufactured mainly for operating steam pressure
14 kgf/cm 2 for the production of saturated steam and with a superheater for the production of superheated steam with a temperature of 250 °C. In addition, boilers with a steam capacity of 6.5 and 10 t/h are manufactured for a pressure of 24 kgf/cm 2 for the production of steam superheated to 370 ° C, and boilers with a steam capacity of 10 t/h are also made for a pressure of 40 kgf/cm 2 for the production of steam, superheated to 440 °C.

Boilers of the DKVR type are produced in two modifications along the length of the upper drum.
For boilers with a steam capacity of 2.5; 4.0 and 6.5 t/h, as well as in an earlier modification of the boiler with a steam capacity of 10 t/h, the upper drum is made much longer than the lower one. The drums are connected by a system of bent seamless steel boiler tubes with an outer diameter of 51×2.5 mm, forming a developed convective heating surface. The pipes are arranged in a corridor order and their ends are rolled into drums. In the longitudinal direction, the pipes are located at a distance between the axes (pitch) 110, and in the transverse direction - 100 mm.

The superheater in boilers of the DKVR type is made as a vertical coil of seamless steel pipes with an outer diameter of 32 mm. It is placed at the beginning of the boiler bundle, separated from the afterburner by two rows of boiler pipes. In order to be able to place a superheater, some of the boiler pipes are not installed. The tube bundle and screens assembled with drums, collectors and the support frame of these boilers fit into the railway gauge; this makes it possible to assemble the metal part of the boiler at the factory and deliver it to the installation site assembled, which simplifies installation.

When installing boilers of the DKVR type with low-temperature heating surfaces, it is advisable to provide only a water economizer or only an air heater so as not to complicate the layout and operation of the boiler unit. Such a solution is also advisable because the flue gas temperature behind boilers with developed heating surfaces is relatively low and amounts to approximately 250–300 °C, as a result of which the amount of heat carried away by flue gases is relatively small. It is more expedient to install water economizers, then the unit is compact and easy to operate. At the same time, it is preferable to choose cast-iron ribbed economizers, since they are made from non-deficient material and they suffer less from corrosion.

Boilers of the DKVR type are quite sensitive to the quality of feed water, so the water used to feed them must be softened and deaerated. The operation of boiler plants with boilers of the DKVR type is easy to automate, especially when burning liquid and gaseous fuels.

Steam generators of the DKVR series are well combined with layered furnace devices and were originally designed for burning solid fuels. Later, a number of steam generators were transferred to burning liquid and gaseous fuel. When operating on liquid and gaseous fuels, the performance of steam generators can be 30–50% higher than the nominal one. Bottom part the upper drum, located above the combustion chamber, must be protected refractory brick or shotcrete.

The work was examined at CKTI a large number industrial boiler houses in which steam generators of the DKVR series were operated. As a result of the survey, it was found that 85% of steam generators use gas and fuel oil. In addition, shortcomings in the operation of steam generators were identified: large air suction into the convective part of the heating surface and a water economizer, insufficient degree of factory readiness, lower operational efficiency compared to the calculated ones.

When developing new design gas-oil steam generators of the DE series (Fig. 3.5) Special attention It was focused on increasing the degree of factory readiness of steam generators in conditions of large-scale production, reducing the metal consumption of the structure, and bringing operational indicators closer to the calculated ones.

In all standard sizes of the series from 4 to 25 t/h, the diameter of the upper and lower drums of steam generators is assumed to be 1000 mm. The wall thickness of both drums at a pressure of 1.37 MPa is 13 mm. The length of the cylindrical part of the drums, depending on the capacity, varies from 2240 mm (steam generator with a capacity of 4 t/h) to 7500 mm (steam generator with a capacity of 25 t/h). Manhole locks are installed in each drum in the front and rear bottoms, which provides access to the drums during repairs.

The combustion chamber is separated from the convective heating surface by a gas-tight partition.

All steam generators of the series have two-stage evaporation. Part of the tubes of the convective bundle is separated into the second stage of evaporation. The common downstream link of all circuits of the first stage of evaporation are the last (along the combustion products) tubes of the convective bundle. The downcomers of the second stage of evaporation are placed outside the flue.

The steam generator with a capacity of 25 t/h has a superheater that provides a small overheating of the steam, up to 225 °C.

The GM-10 type boiler unit is intended for the production of superheated steam with pressures of 1.4 and 4 MPa and temperatures of 250 and 440 °C, respectively. The boiler is designed to work on natural gas and fuel oil and differs in that it works with pressurization, i.e. with excess pressure in the furnace. This allows you to work without a smoke exhauster.

In order to avoid knocking out flue gases in environment the boiler is made with double steel casing. The air supplied by the draft fan passes through the space formed by the sheathing sheets, as a result of which only cold air can escape through random leaks into the environment.

According to its layout, the boiler is double-drum asymmetric: the boiler bundle and the superheater are placed next to the furnace. Fuel and air enter the furnace through combined burners, the design of which ensures a quick transition from burning one type of fuel to burning another.

Usage: in thermal power engineering, in particular, in the manufacture of steam generators. The essence of the invention: the increase in installation and repair manufacturability is ensured by the fact that in the convective heating surface containing the inlet 1 and outlet 2 collectors, vertically installed heated pipes 3, spacer pipes 4, located in horizontal tiers 5 on straight vertical sections of the heated pipes 4 and are rigidly fastened in pairs between themselves along the periphery of the convective surface, and a pair of spacer pipes 4 covers only one row of heated pipes 3. 4 ill.

SUBSTANCE: invention relates to heat power engineering and can be used in steam generator building. During the operation of the steam generator, especially on slagging fuel or high-sulphur fuel oil, on the vertical heating surfaces, located, as a rule, in a horizontal flue, a large number of slag. The centers for intensive slagging are places where the transverse steps between vertical pipes are reduced due to their exit from the design plane (out of range). In these places, the flow rate and speed of flue gases are sharply reduced, and this further contributes to the slagging of heating surfaces. In addition, the external ranking of pipes, especially in the transverse direction of movement of the heating gases, worsens the conditions for cleaning with blowers or other devices. Currently used various uncooled devices made of heat-resistant materials quickly burn out under the influence of high temperatures and aggressive components (sulfur, vanadium) of heating gases. Application of own, ie. connected in parallel with the heated pipes of the heating surface, spacer heated pipes leads to uneven conditions for their operation, because. spacer pipes necessarily differ in length and configuration from the main pipes, which reduces the reliability of the heating surface. Known design of the convective heating surface, in which the spacing of heated pipes is carried out by uncooled spacer bars made of heat-resistant cast iron. For example, on the TGMP-204 boiler. The disadvantage of this design is the fragility of the spacer bars, since under conditions of high temperatures of gases and aggressive components of the combustion products of the fuel, they quickly burn and collapse, which leads to a violation of the distances between the heated pipes of the heating surface, contributes to their drift with ash and slag, deterioration of heat transfer and decrease in the reliability of the steam generator. The closest to the claimed one is the design of the convective heating surface, containing the inlet and outlet collectors, vertically arranged heated pipes and horizontal tiers of spacer pipes installed, cooled by the working medium and equipped with spikes forming cells, each of which houses one vertical pipe. In general, all spacer pipes interconnected with spikes form a horizontal rigid grid through which the heated pipes of the heating surface are passed. heating surfaces, it is absolutely impossible to push the heated vertical pipes to facilitate access to the damaged area. This applies equally to the spacing pipes themselves, equipped with spikes. To access the damaged area, it is necessary to cut a large number of undamaged pipes in accessible places with their subsequent restoration. The experience of operating this surface on TGMP-204 boilers confirms the above. The aim of the invention is to eliminate these shortcomings, as well as to improve the assembly and repair manufacturability. This goal is achieved by the fact that in the convective heating surface containing the inlet and outlet collectors, vertically installed heated pipes and spacer pipes located in horizontal tiers, spacer pipes in the form of horizontal tiers are placed on straight vertical sections of heated pipes, rigidly connected in pairs along the periphery convective surface, and each mentioned pair covers only one row of heated pipes. The essence of the invention is illustrated by drawings, which show: in Fig. one general form convective heating surface, in Fig. 2 section along A-A of Fig. 1 in FIG. 3 is a section along B-B in Fig. 2 in FIG. 4 is a section along B-B of FIG. 2. The convective heating surface contains inlet 1 and outlet 2 collectors, vertically installed heated pipes 3, spacer pipes 4, made in the form of horizontal tiers 5, placed on straight sections of pipes 3 along the height of the surface parallel to the movement of heating gases and in pairs covering each row of these pipes . Pipes 4 are rigidly interconnected by welding 6 along the periphery of the heating surface. Convective heating surface works in the following way. When the thermal state of the steam generator changes, the spacer pipes 4 keep each row of heated pipes 3 in the same plane, tending to go out of range due to uneven heating. Keeping pipe ranking 3 ensures uniform speeds gases across the entire width of the gas duct, reduces the possibility of ash drifting of its individual sections, and also improves the conditions for cleaning with the help of blowers or other devices. Keeping heated pipes 3 in rank significantly improves the conditions for their inspection and repair.,

The calculation of convective evaporative heating surfaces is recommended to be performed in the following sequence.

1. According to the drawing and technical specifications boiler unit (Section 2, Tables 1.2-1.13) determine the design characteristics of the calculated flue: the heating surface area H, the diameter of the pipes in the bundle d, the transverse pitch of the pipes s 1 (in the transverse direction with respect to the flow direction Fig. 6.1), the longitudinal pitch of the pipes s 2 (in the longitudinal direction with respect to the flow, Fig. 6.1.), m; z 1 - the number of pipes in a row, z 2 - the number of rows of pipes along the combustion products. Then the relative transverse step is calculated

and relative pitch

Heating surface area located in the gas duct, m 2

where l is the length of the pipes located in the gas duct, m, n is the total number of pipes located in the gas duct.

Square cross section for the passage of combustion products, m 2: with transverse washing of smooth pipes

for transverse washing of smooth pipes

, (6.5)

where and are the dimensions of the gas duct in the calculated sections, m; - illuminated pipe length (pipe projection length), m; - the number of pipes in the bundle.

2. Preliminarily, two values ​​of the temperature of the combustion products at the outlet of the calculated flue are taken. AT further all the calculation is carried out for two values ​​of previously accepted temperatures .

3. The heat absorption of the surface is determined according to the heat balance equation, kJ / kg, kJ / m 3,

where is determined by formula (4.11); - is determined from the diagram at temperature and coefficient of excess air at the inlet to the heating surface ; - is determined from the diagram at the temperature and excess air coefficient at the exit from the heating surface; the amount of air suction in the calculated gas duct; taken according to the table for air temperature \u003d 30 ° C.

4. The average temperature of the flow of combustion products in the gas duct is calculated, o C

where is the temperature of the combustion products at the entrance to the surface and at the exit from it.

5. The temperature difference is determined, o C

where k is the water temperature at the saturation line at the pressure in the boiler drum, o C, is determined from the tables of water and steam.

6. The average velocity of combustion products in the flue is calculated, m/s

(6.9)

where V g is the volume of combustion products per 1 kg of solid or liquid fuel or per 1 m 3 of gaseous fuel, taken according to table. 3.3 for the relevant flue.

7. The coefficient of heat transfer by convection from the combustion products to the heating surface is determined:

for transverse washing of corridor and chess beams and screens

with longitudinal washing

where is the heat transfer coefficient determined from the nomogram: for transverse washing of in-line beams - according to Fig. 6.1, for transverse washing of staggered beams - according to Fig. 6.2, for longitudinal washing - according to Fig. 6.3; c z - correction for the number of rows of pipes along the combustion products, is determined: for transverse washing of in-line bundles according to Fig. 6.1, for transverse washing of staggered bundles according to Fig. 6.2; c s - correction for the geometric layout of the tube bundle, determined for in-line and staggered bundles with transverse washing according to Fig. 6.1 and 6.2, respectively; c f - coefficient taking into account the effect of changes in the physical parameters of the flow, is determined for in-line and staggered beams with transverse washing according to Fig. 6.1 and 6.2, respectively; c l - correction for relative length, entered at and determined in the case of a direct entry into the pipe, without rounding; in the case of longitudinal washing with combustion products, the correction is introduced for boiler bundles and is not introduced for screens.

Fig.6.1. Heat transfer coefficient by convection during transverse washing of in-line smooth-tube bundles.

Fig.6.2. Heat transfer coefficient for transverse washing of staggered smooth-tube bundles

Fig.6.3. Heat transfer coefficient by convection during transverse washing for air and combustion products

When cooling products of combustion and air, W / (m 2 K), when heating air, W / (m 2 K)

Fig.6.4. Radiant heat transfer coefficient

8. The degree of blackness of the gas flow is determined according to the nomogram Fig.5.5. To determine the degree of emissivity according to the nomogram, it is necessary to calculate the total optical thickness of the attenuation of the rays

where k g r p is the attenuation coefficient of rays by triatomic gases, k g is determined in accordance with formula (5.6) or according to the nomogram (Fig. 5.4), r p - from table. 3.3; k zl - the coefficient of attenuation of the rays by ash particles, is determined from fig. 5.3 when burning solid fuel in pulverized coal furnaces; when burning gas, liquid fuels and solid fuels in layer and torch-layer furnaces k zl =0; - concentration of ash particles, taken according to table 3.3; p - pressure in the gas duct, for boilers operating without pressurization, is assumed to be 0.1 MPa.

Radiating layer thickness for smooth tube bundles, m

. (6.13)

9. The coefficient of heat transfer by radiation from the products of combustion to the surface of convective beams, W / (m 2 K) is determined:

for dusty flow (when burning solid fuels)

for dust-free flow (when burning liquid and gaseous fuels)

where is the coefficient of heat transfer by radiation, determined by the nomogram in Fig. 6.4; - degree of emissivity, determined according to Fig.5.5; c r is the coefficient determined according to Fig. 6.4.

To determine the coefficient c r, it is necessary to know the temperature of the contaminated wall, o C

where t is the average temperature of the steam-water mixture, is assumed to be equal to the saturation temperature at the pressure in the boiler drum, o C; t when burning solid and liquid fuels is taken equal to 60 o C, when burning gas 25 o C.

10. The total heat transfer coefficient from the combustion products to the heating surface is calculated, W / (m 2 K):

(6.17)

where is the utilization factor, taking into account the decrease in heat absorption of the heating surface due to the uneven washing of it by combustion products, the formation of stagnant zones, for transversely washed beams = 1.0, for difficultly washed beams = 0.95.

11. The heat transfer coefficient is calculated, W / (m 2 K):

where is the coefficient of thermal efficiency, determined according to tables 6.1 and 6.2.

Table 6.1.

Thermal efficiency coefficient for convective heating surfaces* when burning various solid fuels

*Festoons of steam generators high power, developed boiler bundles of boilers low power, convective superheaters and economizers with in-line pipe arrangement.

For all types of solid fuels, except for coal near Moscow, cleaning of convective heating surfaces is required.

Table 6.2.

Thermal efficiency coefficient for convective surfaces when burning gas and fuel oil

Note. 1. When burning gas after burning fuel oil, the coefficient of thermal efficiency is taken as the average between the values ​​for gas and fuel oil. 2. When burning gas after solid fuel (without stopping the boiler), the coefficient of thermal efficiency is taken as for solid fuel. 3. A larger thermal efficiency coefficient is assumed for a lower speed.