A modern chimney is not just a pipe for removing combustion products, but an engineering structure, on which the boiler efficiency, efficiency and safety of the entire heating system directly depend. Smoke, back draft and, finally, fire - all this can happen as a result of an ill-considered and irresponsible attitude to the chimney. That is why you should take seriously the selection of material, components and installation of the chimney. The main purpose of the chimney is to remove fuel combustion products into the atmosphere. The chimney creates a draft, under the action of which air is formed in the firebox, which is necessary for the combustion of fuel, and combustion products are removed from the firebox. The chimney must create conditions for complete combustion fuel and excellent traction. And yet it must be reliable and durable, easy to install and durable. And therefore, choosing a good chimney is not as easy as it seems to us.
Local resistances in a rectangular chimney
Few people know that the only thing correct shape chimney - cylinder. This is due to the fact that the swirls formed in the right angles impede the removal of smoke and lead to the formation of soot. All homemade chimneys are square, rectangular and even triangular shapes not only are they more expensive than even a steel round chimney, but they also create a lot of problems, and most importantly, they can reduce the efficiency of the best boiler from 95 to 60%
Round section of the chimney
Old boilers operated without automatic control and with high flue gas temperatures. As a result, the chimneys almost never cooled down, and the gases did not cool below the dew point and, as a result, did not spoil the chimneys, but at the same time a lot of heat was spent for other purposes. In addition, this type of chimney has a relatively low draft due to its porous and rough surface.
Modern boilers are economical, their power is regulated depending on the needs of the heated room, and therefore, they do not work all the time, but only during periods when the room temperature drops below the set one. Thus, there are periods of time when the boiler does not work and the chimney cools down. The walls of a chimney working with a modern boiler almost never reach a temperature higher than the dew point temperature, which leads to a constant accumulation of water vapor. And this, in turn, leads to damage to the chimney. An old brick chimney can collapse under new operating conditions. Since the exhaust gases contain: CO, CO2, SO2, NOx, the temperature of the exhaust gases of wall-mounted gas boilers is quite low, 70 - 130 ° C. Passing through the brick chimney, the exhaust gases cool down and when the dew point of ~ 55 - 60 oC is reached, condensate falls out. Water, settling on the walls in the upper part of the chimney, will cause them to get wet, in addition, when connected
SO2 + H2O = H2SO4
sulfuric acid is formed, which can lead to the destruction of the brick channel. To avoid condensation, it is advisable to use an insulated chimney or install a stainless steel pipe in the existing brick channel.
At optimal conditions boiler operation (temperature of exhaust gases at the inlet 120-130 ° С, at the exit from the pipe mouth - 100-110 ° С) and the heated chimney, water vapor is carried away together with the flue gases outside. When the temperature on the inner surface of the chimney is below the dew point temperature of gases, water vapor is cooled and settles on the walls in the form of tiny droplets. If this is repeated frequently, the brickwork of the walls of the chimneys and chimneys is saturated with moisture and collapses, and black resinous deposits appear on the outer surfaces of the chimney. In the presence of condensation, the draft weakens sharply, and the smell of burning is felt in the rooms.
Leaving flue gases decrease in volume as they cool down in chimneys, and water vapor, without changing in mass, gradually saturates the flue gases with moisture. The temperature at which water vapor will completely saturate the volume of flue gases, that is, when their relative humidity is 100%, is the dew point temperature: the water vapor contained in the combustion products begins to turn into a liquid state. Dew point temperature of combustion products various gases- 44 -61 ° C.
Condensation
If the gases passing through the flue channels cool down strongly and lower their temperature to 40-50 ° C, then on the walls of the channels and the chimney, water vapor is deposited, formed as a result of the evaporation of water from the fuel and the combustion of hydrogen. The amount of condensate depends on the flue gas temperature.
Cracks and holes in the pipe, through which cold air penetrates, also contribute to the cooling of gases and the formation of condensation. When the cross-section of the channel of the pipe or chimney is higher than the required one, the flue gases rise along it slowly and the cold outside air cools them in the pipe. The surface of the chimney walls also has a great influence on the draft force; the smoother they are, the stronger the draft. Roughness in the pipe reduces draft and retains soot. Condensation also depends on the thickness of the chimney walls. Thick walls warm up slowly and retain heat well. Thinner walls heat up faster, but retain heat poorly, which leads to their cooling. Masonry thickness brick walls chimneys passing through interior walls the building must be at least 120 mm (half a brick), and the thickness of the walls of the smoke and ventilation ducts located in the outer walls of the building should be 380 mm (one and a half bricks).
Outside air temperature has a great influence on the condensation of water vapor contained in gases. In the summer season, when the temperature is relatively high, condensation on the inner surfaces of the chimneys is too low, since their walls cool for a long time, therefore, moisture instantly evaporates from the well-heated surfaces of the chimney and condensation does not form. V winter time years, when the outside temperature has a negative value, the walls of the chimney are strongly cooled and the condensation of water vapor increases. If the chimney is not insulated and is strongly cooled, increased condensation of water vapor occurs on the inner surfaces of the chimney walls. Moisture is absorbed into the walls of the pipe, which causes the masonry to become damp. This is especially dangerous in winter, when ice plugs are formed in the upper sections (at the mouth) under the influence of frosts.
Chimney icing
It is not recommended to attach hinged gas boilers to chimneys of large cross-sections and heights: draft weakens, increased condensation forms on internal surfaces. Condensation is also observed when boilers are connected to very high chimneys, since a significant part of the temperature flue gas spent on heating a large heat absorption surface.
To avoid overcooling of flue gases and condensation on the inner surfaces of the smoke and ventilation ducts, it is necessary to maintain the optimal thickness of the outer walls or insulate them from the outside: plaster, cover with reinforced concrete or slag concrete slabs, shields or clay bricks.
Steel pipes must be pre-insulated or insulated. Any manufacturer will help you choose the type and thickness of insulation.
A beautiful enamelled stove implies a beautiful enameled chimney.
Is it possible to put a stainless steel?
New Product
These enamelled flues are coated with a special compound of high temperature resistance and acid resistance. The enamel can withstand very high flue gas temperatures.
For example, modular chimney systems LOKKI production facilities of the Novosibirsk plant "SibUniversal" have the following data:
In the table, we have collected the temperature readings of the flue gases of various heating devices.
After comparison, it becomes clear to us that working temperature of enameled chimneys 450 ° С not suitable for Russian wood-fired stoves and fireplaces, wood-fired sauna stoves and coal-fired boilers, and this chimney is quite suitable for all other types of heating appliances.
In the descriptions of the chimneys of the system "Locke" it is said so directly that they are intended for connection to any type of heating devices with an operating temperature of exhaust gases from 80 ° C to 450 ° C.
Note. We love to turn our sauna stove red hot to its fullest. And even for a long time. That is why the temperature of the flue gases is so high, and that is why fires occur so often in baths.
In these cases, especially in sauna stoves, you can use thick-walled steel or cast iron pipe as the first element after the oven. The fact is that most of the hot gases are cooled to an acceptable temperature (less than 450 ° C) already at the first pipe element.
Steel is a durable material, but it has a significant drawback - a tendency to corrosion. In order for metal pipes to withstand adverse conditions, they are covered with protective compounds. One of the options for the protective composition is enamel, and since we are talking about chimneys, the enamel must be heat-resistant.
Please note: the enamelled chimneys have a two-layer coating, metal pipe cover first with ground, and then with a cover enamel.
To give the enamel the necessary properties, during its preparation, special additives are introduced into the molten mixture. The basis of the ground and cover enamel is the same; for the manufacture of the charge, a melt is used from:
But additives for cover and ground enamel are used differently. Metal oxides (nickel, cobalt, etc.) are introduced into the soil composition. Thanks to these substances, reliable adhesion of the metal to the enamel layer is ensured.
Titanium and zirconium oxides, as well as fluorides of some alkali metals are added to the cover enamel. These substances provide not only increased heat resistance, but also the strength of the coating. And to give the coating decorative properties during the preparation of the cover enamel, colored pigments are introduced into the molten composition
Attention. Light weight of thin-walled metal and mineral wool allows you to do without a special foundation for the chimney system. The pipes are mounted on brackets on any wall.
In the double-walled version, the space between the pipes is filled with mineral (basalt) wool, which is a non-combustible material with a melting point of more than 1000 degrees.
Manufacturers and suppliers of enamelled chimney systems offer a wide range of accessories:
In any case, we begin to mount the chimney "from the stove", from the heater, that is, from the bottom up.
In the process installation works reasonable care must be taken. It is recommended to use only rubberized tools, this will avoid violating the integrity of the pipe coating (chips, cracks). This is very important, since a corrosive process begins to develop at the place of damage to the enamel, which destroys the pipe.
In general, we can say that such chimneys have undoubted aesthetic advantages over stainless steel. But there are no technical, operational and installation advantages.
The destruction of pipes often occurs due to the use of low-quality bricks (a, b). Moisture-resistant cladding is able to protect the masonry (c). Silicate brick is not suitable for the construction of chimneys (g) 
Outside the window is a chilly autumn evening, and a fire is burning brightly in the fireplace, and a very special warmth fills the room ... For this suburban idyll to become a reality, you need a well-designed and installed chimney, which, unfortunately, is often remembered last.
The degree of reliability and efficiency of the chimney operation largely depends on the heating devices connected to them, and vice versa. Therefore, for each type of fireplace there is the best option chimney.
And finally, the last type is the fireplace stove. home distinctive feature similar devices, making them similar to a real oven, - the presence of a built-in smoke channel, passing through which the flue gases are cooled to a rather low temperature. In this regard, there is a need for a massive masonry or well-insulated modular chimney.
Ethnographic touches
The houses of Korean settlers in the Ussuri region were equipped with very exotic chimneys. Here is how VK Arseniev described them: “Inside ... there is a clay canal. It takes up more than half of the room. Chimneys run under the canal, warming the floors in the rooms and spreading heat throughout the house. The chimneys are led out into a large hollow tree that replaces the chimney. "
Some peoples of the Volga region and Siberia before the 30s. XX century Chuval was widespread - a wall open hearth with a straight chimney hanging over it. The hearth was built of stones or logs covered with a layer of clay, and the chimney was made of hollow wood and thin poles coated with clay. In winter, the chuval was stoked all day, the pipe was plugged at night.
Brick chimneys until recently, both in urban and rural construction there were practically no alternatives. Being versatile construction material, the brick allows you to vary the number of chimney channels and wall thickness (you can make the necessary thickenings in the places of passage of ceilings, roofs, as well as during the construction of the street part of the chimney). Subject to building technologies the brick chimney is very durable. However, it also has disadvantages. Due to the significant mass (pipe with a cross section of 260
For the construction of a brick chimney, a very high qualification of builders is required. What are the most common mistakes when building it? This is a choice of low-quality or unsuitable bricks (poorly fired partition or wall); thickness of masonry joints more than 5 mm; masonry on the edge; the use of stepped ("jagged") masonry in inclined areas; improper preparation of the solution (for example, if the ratio of parts of clay and sand is chosen without taking into account the fat content of the clay), sloppy splitting or cutting of bricks; inattentive filling and bandaging of masonry seams (the presence of voids and double vertical seams); pipe laying close to structures made of combustible materials.
The condition of the brick pipe requires constant monitoring. Before, it was certainly whitewashed, since it is easier to notice soot on a white surface, indicating the presence of cracks.
Expert opinion
The brick chimney has served people with faith and truth for centuries. The laying of stoves and fireplaces from this material is almost an art. The paradox is that during the period of mass dacha construction in our country, this skill suffered serious damage. The consequences of the "work" of numerous would-be stove-makers were sad, and most importantly, they gave rise to distrust of brick furnaces and chimneys. Therefore, favorable conditions have arisen and remain for the promotion of prefabricated chimney systems on the domestic market.
Alexander Zhilyakov,
head of the wholesale department of the company "Saunas and Fireplaces"
Stainless steel pipes can be safely attributed to the most widely used type of chimneys today. Steel modular systems have a number of undeniable advantages. The main ones are low weight, ease of installation, a wide selection of pipes of different diameters and lengths, as well as fittings. Steel chimneys are manufactured in two versions - one- and two-circuit (the latter is in the form of a "sandwich" of two coaxial pipes with a layer of non-combustible thermal insulation). The first ones are designed for installation in heated rooms, connecting the fireplace to an existing chimney, as well as rehabilitating old brick pipes. The latter are a ready-made constructive solution, equally suitable for the installation of a chimney both inside the building and outside. A special type of stainless steel smoke ducts - flexible single- and double-walled (without thermal insulation) corrugated hoses.
For the production of single-circuit chimneys and inner pipes of "sandwich" type chimneys, heat- and acid-resistant alloy steel sheet (usually 0.5-0.6 mm thick) is used. Single-circuit chimneys made of carbon steel, coated on the outside and inside with special black enamel (such as, for example, in the assortment of Bofill, Spain), even surpass stainless steel pipes in heat resistance; they are also not afraid of condensate, but only if the coating is intact, which is easy to damage (say, when cleaning the chimney). The service life of pipes without coating of "black" steel 1 mm thick does not exceed 5 years.
The casing (shell) of "sandwich" pipes, as a rule, is made of ordinary (non-heat-resistant) stainless steel, which is electrochemically polished to a mirror finish, and some manufacturers, such as Jeremias (Germany), offer enamel painting in any color on the scale RAL. The use of a casing made of galvanized steel is justified only when installing a chimney inside a building. Outside, such a pipe, if you actively operate the chimney, will not last long: due to periodic heating, corrosion intensifies.
Stainless steels used for the production of chimneys are divided into two categories: magnetic ferrite (in the American standardization system ASTM - these are AISI 409, 430, 439, etc.) and non-magnetic austenitic (AISI 304, 316, 321, etc.). ). According to our tests of AISI 409 steel (composition: 0.08% C, 1% Mn, 1% Si, 10.5-11.75% Cr, 0.75% Ti), the critical temperature value in the inner pipe of the insulated chimney fragment , at which the effect of intercrystalline corrosion became noticeable, was equal to 800-900
Alexey Matveev,
head of the commercial department of the company "NII KM"
The layer of thermal insulation in the "sandwich" pipes solves three problems at once: it prevents the overcooling of flue gases that negatively affects the draft, does not allow the temperature of the inner walls of the chimney to drop to the dew point, and, finally, ensures the fire-safe temperature of the outer walls. The choice of insulating materials is small: usually it is cotton wool - basalt (Rockwool, Denmark; Paroc, Finland) or organosilicon (Supersil, Elits, both - Russia), pearlite sand (but it can be filled up only during the installation of the chimney).
Such a very important characteristic of the chimney as gas tightness depends on the design of the pipe joints, therefore each manufacturer strives to bring it to perfection. So, the sealing of the chimney Hild (France) is provided by centering couplings; the double annular protrusion formed at the joint is clamped by the clamps supplied with each module. Raab chimneys are provided with a tapered connection in combination with a collar. In Selkirk systems (Great Britain), high gas density can be achieved due to the special design of the clamp. The overwhelming majority of stainless steel chimneys are mounted in the traditional way, and here a lot depends on the quality of the parts. Usually, the upper module is put on the lower one, however, single-circuit ones, and with an external gasket, double-circuit modules should be joined by inserting the upper one into the lower one, which will avoid condensate leaks through the joints.
| Fireplace type | Combustion feature | Efficiency,% | Discharged gas temperature, | Chimney type |
|---|---|---|---|---|
| With open hearth | Air access is unlimited | 15-20 | Up to 600 * | Brick, heat-resistant concrete |
| With a closed firebox | Air access may be restricted | 70-80 | 400-500 | Brick, made of heat-resistant concrete, modular insulated from stainless steel or ceramic, within the heated rooms - single-circuit steel enameled |
| Fireplace stoves | Air access is limited, gases are cooled through integrated ducts | Up to 85 | 160-230** | In addition to those listed above: from talc magnesite or soapstone - massive or with an inner tube (steel, ceramic) |
* - when using hardwoods, coal as fuel, as well as with excessive draft, the temperature may exceed the specified value;
** - for talcomagnesite fireplaces; for metal - up to 400
Ceramic chimneys- these are the same "sandwiches", but "cooked" according to a completely different recipe. The inner tube is made of chamotte pottery, the middle layer is unchanged basalt wool, external - sections of lightweight concrete or mirror stainless steel. Such systems are presented on the domestic market by Schiedel (Germany).
Chimneys made of ceramics are resistant to high temperatures (up to 1000
Ceramic systems also have their drawbacks. Chimneys with a casing made of concrete have a significant mass (1 running meter weighs from 80 kg), can be used only as main (free-standing) ones, do not allow to bypass obstacles. The "weak link" of such chimneys is the connection unit. Manufacturers provide for the use of a metal module (s), which has a shorter service life and therefore will require replacement in the future, which must be foreseen during the construction of the fireplace.
Raab chimneys with stainless steel inner pipe and concrete casing:
with ventilation duct (a)
or without it (b)
Finally, metal does not work well with ceramics, since it has a high coefficient of thermal expansion: around the perimeter steel pipe where it enters the ceramic, it is necessary to leave a rather large (about 10 mm) gap, which is filled with an asbestos cord or heat-resistant sealant.
However, high reliability and durability ceramic chimneys(the factory warranty is 30 years, and the actual service life, according to the manufacturers, is more than 100 years) allow us to close our eyes to the listed disadvantages. Moreover, the price of Schiedel products is quite comparable to the cost of imported stainless steel systems - only a set of the first three meters of the chimney, including a condensate trap, an inspection, a connection unit and a gate, is relatively expensive. For example, a 10 m high chimney of the Uni system with ceramic pipes 200 mm in diameter without a ventilation duct costs about 43 thousand rubles.
| Firm | Country | Thermal insulation thickness, mm | Price (depending on diameter, mm) | ||
|---|---|---|---|---|---|
| 150 | 200 | 250 | |||
| Selkirk, model Europa | United Kingdom | 25 | 6100 | 7500 | 9100 |
| Jeremias | Germany | 32,5 | 3400 | 4300 | 5700 |
| Raab | Germany | 30 | 4450 | 5850 | 7950 |
| Hild | France | 25 | 2850 | 3300 | 5100 |
| Bofill | Spain | 30 | 3540 | 4500 | 5700 |
| Elits | Russia | 30 | 3000 | 3480 | 4220 |
| "NII KM" | Russia | 35 | 2235 | 2750 | 3550 |
| FineLine | Russia | 30 | 2600 | 3410 | 4010 |
| "Baltvent-M" | Russia | 25/50 | 2860/3150 | 3660/4030 | 4460/4910 |
| "Inzhkomtsentr VVD" | Russia | 25 | 1600 | 2000 | - |
| Rosinox | Russia | 25/50 | 2950/3570 | 3900/4750 | 4700/5700 |
| Salner | Russia | 35 | 2550 | 3100 | 4100 |
| "Volcano" | Russia | 50 | 3050 | 3850 | 4550 |
| "Luxury version" | Russia | 35 | 2600 | 3350 | 4120 |
The question of the possibility of connecting two fireplaces to one chimney is a controversial one. According to the requirements of SNiP 41-01-2003, "for each stove, as a rule, a separate chimney or channel should be provided ... It is allowed to connect two stoves located in one apartment on the same floor to one chimney. cuts should be provided (middle walls dividing the chimney into two channels. - Ed.) with a height of at least 1 m from the bottom of the pipe joint. " brick chimney... If the chimney is modular, it is enough to use a tee to connect the pipe of the second furnace to the pipe of the first (if the smoke channels have different diameters, then the smaller one is cut into the larger one), after which it is necessary to increase the channel cross-section. How much? Some experts believe that if the simultaneous operation of the furnaces is planned, then the cross-sectional area is determined by simple summation. Others believe that it is enough to "throw" 30-50%, since two furnaces will heat up the common pipe better and the draft will increase, but this only applies to chimneys with a height of more than 6 m.
When connecting two stoves located on different floors to one chimney, everything is much more complicated. Practice shows that such systems work, but only with careful calculation and numerous additional conditions (increase in the height of the chimney, installation of dampers after the lower firebox and on the inlet pipe of the upper one, observance of the sequence of ignition or complete exclusion of simultaneous operation, etc.).
We draw your attention to the fact that everything said in this section applies only to fireplaces with a closed hearth. An open firebox is more fire hazardous and demanding for draft, therefore it does not allow any "liberties" and requires the construction of a separate chimney.
Poor draft, as a rule, occurs due to errors in the design of the chimney. The desire to explain it unfavorable weather conditions(drops atmospheric pressure and air temperature) is unreasonable, since with a competent decision, these factors are also taken into account. Let's list the reasons for poor traction and its periodic overturning (that is, the occurrence of reverse thrust):
It is much more difficult to determine the cause in each specific case, since often several factors act at once, none of which plays an independent role. To improve draft, it is necessary to change the design of the chimney, sometimes not too much (for example, to increase the thickness of the thermal insulation on the last one and a half to two meters of the pipe). There is also such a problem as excessive thrust. You can deal with it with a gate. It is only necessary to provide for its installation before starting the installation of the chimney.
The main combustion gases of carbonaceous fuels are carbon dioxide and water vapor. In addition, during combustion, the moisture present in the fuel itself (wood) evaporates. As a result of the interaction of water vapor with sulfur and nitrogen oxides, acid vapors of weak concentration are formed, which condense on the inner surface of the chimney when they are cooled to a temperature below the critical temperature (when burning wood - about 50
If you heat a fireplace with a non-insulated outdoor fireplace in the cold season metal chimney, the amount of condensate can be measured in liters per day. A brick pipe is capable of accumulating heat, therefore it behaves differently: condensate is formed only at the stage of heating the pipe (although this is a rather long period of time). In addition, the material partially absorbs condensate, so the latter is not too noticeable, which, however, does not prevent it from having a destructive effect on the masonry. If the intensity of combustion is low and the ambient temperature is low, the brick may cool down and condensation will start to form again. If the thickness of the insulation is insufficient and the temperature of the exhaust gases is low (the firebox is adjusted for long-term burning), condensate can also appear in a modular sandwich-type chimney. One way or another, it is impossible to completely get rid of condensate, you just need to reduce its amount to a minimum (the main means for this is the use of more effective thermal insulation) and prevent leaks.
We have touched on only a small part of the problems associated with the coexistence of chimney and smoke. Trying to answer all the questions that the owners of fireplaces have in one article is an impossible task. An individual approach is often required, and, as experts say, sometimes only experience and professional intuition can suggest the right decision.
The editors would like to thank Raab, Rosinox, Schiedel, Tulikivi, Maestro, NII KM, Saunas and Fireplaces, EcoKamin for their help in preparing the material.
What should be the chimney for gas and diesel boilers?
Chimneys are an important part of heat generators. No boiler can work without a chimney. The function of the chimney is to remove combustion products or flue gases from the combustion chamber of the boiler. In individual houses, chimneys are internal - passing through the ceilings and roof of the building, external - mounted vertically along the outer surface of the wall and horizontal - exhaust gases through outer wall building. The latter type of chimney is used for boilers with forced removal of flue gases and is usually a "pipe in pipe" design. (The combustion products are removed through the inner pipe, air is supplied to the boiler combustion chamber through the outer pipe.) apartment buildings with apartment heating. Chimneys must be designed and selected by a specialist. An incorrectly installed chimney can lead to unstable boiler operation; installed without taking into account the roof configuration can be “blown out” by the wind and extinguish the boiler. It is important for you to know that the internal diameter of the chimney should be no less than the diameter of the boiler neck, that there should be as few bends and bends in the path of the flue gases as possible, and that measures should be taken to prevent the formation of condensation when installing the chimney.
What is condensation and how is it formed?
A feature of modern boilers operating on gas and liquid fuel is low temperature flue gases at the outlet of the boiler - from 100 ° C. In the process of combustion of hydrocarbon fuel - natural gas or diesel fuel, water vapor, carbon dioxide, sulfur dioxide and many other chemical compounds are formed. Going up the chimney, this gas mixture cools down. When its temperature drops to + 55 ° C (dew point temperature), the water vapor present in the gas mixture cools and turns into water - condenses. This water dissolves compounds of sulfur and other chemicals in the flue gases. They form a very aggressive acid mixture, which, flowing down, quickly corrodes the material of the chimneys. The flue gases are usually cooled down to the dew point temperature at a height of 4 - 5 m from the boiler outlet. Therefore, chimneys, the height of which is greater, are made of stainless steel and insulated. A condensate trap is always installed at the bottom of the chimney. For outdoor chimneys, there is a "sandwich" type design - the chimney pipe is placed in a pipe of a larger diameter, and the space between them is filled with a heat insulator. The thickness of the thermal insulation layer is selected depending on the value of the minimum outdoor temperatures.
Stainless steel chimneys are very expensive. Is it possible to use a brick pipe for the chimney, as in wood stove?
This should not be done under any circumstances. First, the acid mixture is so aggressive that brickwork, if not made of special acid-resistant bricks, can be destroyed in one heating season. Secondly, flue gases through inconspicuous cracks in the masonry can penetrate into living quarters and cause harm to human health. If the house has a channel made of brickwork, then it can serve as a chimney only if an inset stainless steel chimney with thermal insulation is placed in it.
Are there - are there any chimney systems that do not use metal?
Yes. Recently on Russian market chimney system appeared original design, which is called "insulated chimney system with ventilation." It consists of individual modules with a height of 0.33 m. Each module is a rectangular block of lightweight concrete, inside which a ceramic pipe is fixed. Between the inner wall of the block and outer wall a ceramic pipe has a channel that plays the role of a ventilation channel, which is not the case with other types of chimneys. The blocks are installed one on top of the other, fastened with a special sealant and mounted in a chimney of any configuration and height. The complete set of the chimney system contains a complete set necessary elements for connecting boiler chimneys, for leading the chimney through the roof and for decorative end of the pipe. Four types of modules allow the construction of one-way and two-way chimneys or chimneys with separate ventilation ducts. This makes the design of the chimney system versatile and versatile. Inner ceramic tube resistant to impact high temperatures and temperature fluctuations; acid-resistant (protected from condensation), hermetically sealed and durable. The system is easy to install and does not require highly qualified specialists. The cost of an insulated chimney system is commensurate with the cost of high-end stainless steel chimneys.
time-nn.ru
Improving the energy efficiency (efficiency) of a combustion plant achieves a reduction in CO2 emissions, provided that this improvement results in a reduction in fuel consumption. In this case, CO2 emissions are reduced in proportion to the reduction in fuel consumption. However, the result of an increase in efficiency can also be an increase in the production of useful energy at a constant fuel consumption (an increase in Hp at a constant Hf in Equation 3.2). This can lead to an increase in the productivity or capacity of the production unit while improving energy efficiency. In this case, there is a reduction in specific CO2 emissions (per unit of production), but the absolute volume of emissions remains unchanged (see section 1.4.1).
Guidelines for energy efficiency (KPIs) and related calculations for various combustion processes are provided in industry Briefing Papers and other sources. In particular, the document EN 12952-15 contains recommendations for calculating the efficiency of water-tube boilers and related auxiliary equipment, and document EN12953-11 - fire-tube boilers.
general characteristics
One of the options for reducing thermal energy losses during combustion is to reduce the temperature of flue gases emitted into the atmosphere. This can be achieved through:
Selection of the optimal dimensions and other characteristics of the equipment based on the required maximum power, taking into account the estimated safety margin;
Intensification of heat transfer to the technological process by increasing the specific heat flux (in particular, using swirlers-turbulators that increase the turbulence of the working fluid flows), increasing the area or improving the heat exchange surfaces;
Recovery of heat from flue gases using an additional technological process (for example, steam production using an economizer, see section 3.2.5);
Installing an air or water heater, or organizing a preheating of fuel due to the heat of flue gases (see 3.1.1). It should be noted that air heating may be necessary if the process requires a high flame temperature (for example, in glass or cement production). The heated water can be used to power the boiler or in hot water supply systems (including centralized heating);
Cleaning of heat exchange surfaces from accumulating ash and carbon particles in order to maintain high thermal conductivity. Particularly in the convection zone, soot blowers can be used periodically. Cleaning of heat exchange surfaces in the combustion zone, as a rule, is carried out during shutdown of equipment for inspection and maintenance, however, in some cases, non-stop cleaning is used (for example, in heaters at a refinery);
Ensuring a level of heat production that meets existing needs (does not exceed them). The heat output of the boiler can be regulated, for example, by selecting the optimum throughput of the nozzles for liquid fuel or the optimum pressure under which the gaseous fuel is supplied.
Environmental benefits
Energy saving.
Impact on various components of the environment
Decrease in flue gas temperature at certain conditions may conflict with air quality objectives, for example:
studfiles.net
Page 3
The temperature of the flue gases at the exit from the furnace must be at least 150 C higher than the initial temperature of the heated raw material in order to prevent intensive corrosive wear of the pipe surfaces in the convection chamber.
Flue gas temperature at the boiler outlet, heated air temperature at the furnace inlet, consumption and thermodynamic parameters of superheated and intermediate steam, feed water for a given load factor are considered unchanged.
The flue gas temperature above the pass wall is especially important. The high temperature of the gases at the pass corresponds to the high heat density of the surface of the radiant tubes, the temperature of their walls, and a high probability of coke formation. Deposing on the inner surface of the pipes, coke hinders heat transfer, which leads to a further increase in the temperature of the walls and to their burnout.
The flue gas temperature in front of the recuperator in heating furnaces reaches 1400 C.
The temperature of the flue gases entering the chimney must be maintained no higher than 500 C by adjusting the flow rate of the cooling air supplied to the flue by the fan.
The flue gas temperature at the inlet to the heat exchanger of the starting heater should not exceed 630 - 650 C. Exceeding this temperature may lead to its premature failure. It is even more important that during the operation of the starting heater, air or gas is always supplied to the shell side of the heat exchanger. When the air or gas is turned off, the temperature of the tube plates and pipes rises sharply and the heat exchanger may fail. In this case, it is necessary to immediately reduce the temperature of the flue gases to 450 C.
The temperature of the flue gases at the entrance to the second chamber is maintained at 850 C. The gases leaving this chamber with a temperature of 200 - 250 C enter the first (along the acid path) chamber, where their temperature drops to 90 - 135 C.
The temperature of the flue gases leaving the convection chamber and going into the chimney depends on the temperature of the raw material entering the furnace and exceeds it by 100 - 150 C. However, when the temperature of the raw material is high for technological reasons (furnaces for heating fuel oil, catalytic reforming furnaces, etc.) ), the flue gases are cooled using their heat in a steamer, air freshener or for underfloor condensate water and obtaining water vapor.
The flue gas temperature above the pass wall is one of the critical indicators... The high temperature of the flue gases above the pass wall corresponds to the high heat density of the radiant tubes, the high temperature of their walls and the likelihood of coke deposition in the furnace tubes, and, consequently, the possibility of their burnout. The high speed of the heated flow of raw materials allows for greater heat removal, lowering the temperature of the pipe walls and, thus, working with a higher temperature of gases over the pass and heat intensity of radiant pipes. An increase in the surface of the radiant tubes also contributes to a decrease in their heat density and a decrease in the temperature of flue gases over the pass. The cleanliness of the inner surface of the coil pipes is also the most important factor influencing the temperature of gases above the pass wall. The temperature of the gases over the pass is carefully controlled and usually does not exceed 850 - 900 C.
The flue gas temperature at the entrance to the radiation zone is 1100 - 1200 С, at the entrance to the convective zone 800 - 850 С.
The flue gas temperature at the outlet of the tube furnace is 900 C.
The flue gas temperature in front of the recuperator will be approximately 1100 C.
Pages: 1 2 3 4
www.ngpedia.ru
And only by shielding the combustion chamber and increasing its volume, normal conditions were created for the operation of the coil. Radiant tube furnaces were created. In early designs of such furnaces, the ceiling screen tubes were protected from the strong effects of the flame by cuffs of flame retardant material. Corrugated cast iron collars on convection pipes raised the heating surface in the convection chamber of the oven. As a result of the shielding of the furnace ceiling, heat transfer by radiation increased, the temperature of the flue gases over the pass decreased, and there was no need for protective cuffs and recirculation of flue gases. For maximum use warmth
Flue gas temperature after the boiler - 210 210 -
Norms technological design it is planned to reduce the temperature of flue gases before entering the chimney with natural draft up to 250 ° С. In the presence of special smoke exhausters, the temperature can be reduced to 180-200 ° C. The heat of flue gases with a temperature of 200-450 ° C (average figure) can be used for heating air, water, oil and for the production of water vapor in the installation. Below are the data on the thermal resources of flue gases at the ELOU-AVT unit with secondary distillation of gasoline with a capacity of 3 million tons / year of sulphurous oil.
average temperature flue gases in 293 305 310 -
The temperature regime of raw heat exchangers is also limited. The maximum allowable temperature at a regeneration pressure of 3.0-4.0 MPa should not exceed 425 ° C, in connection with which the temperature of flue gases leaving the reactors before entering the raw heat exchanger should be reduced by mixing with a cold coolant.
Heat density of pipes, kcal / (m2-h) radiant convection pipes Temperature of flue gases,
Heater surface, Air heating temperature in air heaters, ° С Flue gas temperature, ° С
Usually, the temperature of the flue gases at the pass is automatically controlled with a correction for the temperature of the product at the outlet of the furnace. To control and regulate tube furnaces, the following elements are provided in their piping.
Liquid fuel consumption, kg / h Flue gas temperature at the outlet from the furnace, ° С. ... ... ... Flue gas volume at gas outlet temperature 4000 3130 2200
Flue gas temperature in front of boilers, ° С 375 400 410 -
In drying installations, the processed material is not located in the immediate vicinity of the furnace, as is the case in furnaces for various types of cooking, distillation and other similar boilers. Therefore, the temperature in the combustion chamber of the drying installation can be significantly higher than the temperature in the furnaces, in devices that consume heat are located. However, in this case, the temperature is determined by the properties of the material to be dried and the requirements dictated by the quality of the product.
By the amount of heat given off by a given amount of flue gases in the radiation system, the temperature of the flue gases entering the convective system is determined.
During the operation of the regenerator, the flue gas temperature can exceed normal due to the afterburning of carbon monoxide. With timely detection of this phenomenon, it is necessary to redistribute the air over the sections, reducing the supply era to those sections where there is an excess of oxygen in the flue gases leaving the section, and increasing its input into the sections where there is not enough oxygen. In the event of a sharp increase in the temperature of the flue gases, the air supply to some or all of the sections is temporarily interrupted.
The primary reforming of natural gas with steam is carried out in vertically arranged pipes heated by flue gases, the lower ends of which are introduced directly into the secondary methane reformer. A portion of the flue gases are fed through the perforated plate into the secondary reforming catalyst bed, which makes it possible to obtain a nitrogen-rich gas. Flue gas temperature - 815 ° С
Convection ovens replaced the fire-type stoves, in which the pipe coil is separated from the combustion chamber by a pass wall. During the operation of such furnaces, significant drawbacks were established: high temperature of flue gases above the pass wall, melting and deformation of brickwork, burnout of pipes in the upper rows of the coil. To reduce the temperature in the combustion chamber, recirculation of flue gases was used and the fuel was burned with an increased excess air ratio. However, the increased air consumption reduced the efficiency of the furnaces and did not reduce the burnout of the pipes.
Superheater temperature. In some cases, a coil is mounted in the convection section of the furnace for superheating the water vapor supplied to the distillation columns for stripping low-boiling fractions. The superheater is placed where the flue gas temperature is 450-550 ° C, i.e. in the middle or lower section of the convection chamber. The superheated steam temperature is 350-400 ° C.
The flue gas temperature above the pass wall is especially important. The high temperature of the gases at the pass corresponds to the high heat density of the surface of the radiant tubes, the temperature of their walls, and a high probability of coke formation. Deposing on the inner surface of the pipes, coke hinders heat transfer, which leads to a further increase in the temperature of the walls and to their burnout.
An increase in the speed of movement of heated raw materials in the furnace tubes increases the efficiency of heat removal, lowers the temperature of the walls of the tubes and thus makes it possible to work with higher heat intensity of the radiant tubes and the temperature of the flue gases at the pass.
On a typical unit ELOU - AVT (A-12/9) with a capacity of 3 million tons / year with secondary distillation of gasoline, five furnaces with a total thermal capacity of 81 Gkcal / h are installed. All furnaces burn 11 130 kg of fuel in 1 hour. The flue gas temperature at the outlet of the convection chambers of the ovens is 375-410 ° C. To use the thermal energy of flue gases, before entering them into the chimney, remote heat recovery boilers of the KU-40 type are installed in the furnaces.
The lower the temperature of the flue gases leaving the convection chamber, the more heat is absorbed by the heated oil product. Usually, the temperature of the flue gases at the exit from the convection chamber is taken to be 100-150 ° C higher than the temperature of the raw material entering the furnace. But since the temperature of the raw material entering the furnace is quite high, about 160-200 ° C, and for some processes it reaches 250-300 ° C, an air heater (recuperator) is installed to utilize the heat of the flue gases, in which the air going to the furnace is heated ovens. In the presence of an air heater and a smoke exhauster, it is possible to cool the flue gases before releasing them into the chimney to a temperature of 150 ° C. With natural draft, this temperature is at least 250 ° C.
Convection pipes receive heat due to convection of flue gases, radiation from masonry walls and radiation of triatomic gases. As noted at the beginning of this chapter, heat transfer in a convection chamber depends on the speed and temperature of the flue gases, as well as the temperature of the feedstock, the diameter of the pipes and their layout. The speed of flue gases in a convection shaft usually fluctuates within 3-4 m / s, and in a chimney 4-6 m / s.
Solution. Let us determine the efficiency of the furnace if the temperature of the flue gases at the outlet of the convection chamber is
The temperature of the flue gases at the outlet of the furnace is 500 C. The heat of the flue gases is utilized in a tubular three-way (by air) air heater with a heating surface of 875 m. After the air heater, flue gases at 250 C are removed into the atmosphere through the chimney without the use of forced draft.
Let us set the temperature of the flue gases after the heating section of the radiation chamber r, c = 850 ° C, and after the reaction section ip. c = 750 ° C. Heat content of flue gases but fig. 6.1 at a = 1.1
Distinctive feature waste-heat boilers, as equipment for generating steam, is the need to ensure the passage of a large amount of heating flue gases per unit of generated water vapor (E1 / d.g / C). This ratio is a direct function of the initial temperature of the flue gases at the inlet to the apparatus and their flow rate. Due to the relatively low temperature of flue gases for generating steam, their specific consumption in waste-heat boilers is much higher (8-10 times) than in conventional combustion boilers. The increased specific consumption of heating gases per unit of generated steam predetermines design features waste heat boilers. They have large dimensions, high metal consumption. Overcoming the additional gas-dynamic resistance and creating the required vacuum in the furnace furnace (for draft) requires 10-15% of the equivalent electrical power of the waste heat boiler.
After filling the hopper with the dried catalyst, open the valve under the hopper and pour the catalyst into the calcining column. The volume of the hopper corresponds to the useful volume of the calcining column, i.e. one load. After filling the column with a catalyst, the furnace is ignited under pressure (on liquid fuel), directing the flue gases into the atmosphere. Then, having adjusted the combustion in the furnace, the flue gases are introduced into the casing of the calcining column. Warming up the casing and making sure that the fuel is burning normally, the flue gases are directed to the bottom of the calcining column in the minimum amount necessary only to overcome the resistance of the catalyst bed. Then a slow rise in the temperature of the flue gases at the outlet from the furnace and the heating of the catalyst begin. The heating of the system is continued for about 10-12 hours during this time, such an amount of flue gases is introduced so that there is no carryover of the catalyst from above. Reaching the temperature at the bottom of the column of 600-650 ° C is considered the beginning of the catalyst calcination. The duration of calcination at this temperature is 10 hours.
Then the temperature of the flue gases at the outlet from the furnace is gradually reduced and the fuel supply is stopped at 250-300 ° C, but
The temperature of the gases at the pass, the thermal intensity of the heating surface of the radiant tubes and the direct return coefficient of the furnace are mutually related. The greater the direct return coefficient, the lower, other things being equal, the lower the temperature of the flue gases at n (maturation and the lower the thermal intensity of the heating surface of the radiant tubes and vice versa.
Tubular coil reactors. The vertical tube coil reactor was designed for continuous bitumen production at domestic refineries. Temperature regime reactors. (Kremenchug and Novogorkovsky refineries) is supported by the heat of flue gases coming from the pre-chamber furnace. However, with such a solution, the specificity of the exothermic oxidation process is poorly taken into account. Indeed, to accelerate the heating of the reaction mixture in the first upstream reactor tubes, it is necessary to increase the temperature of the flue gases, but as a result, the oxidizable material in the subsequent tubes overheats, where the oxidation reaction and heat release proceed with high speeds... Thus, it is necessary to maintain some intermediate temperature of the flue gases, neo [tpm], both to heat the reaction mixture to the reaction temperature and to subsequently maintain the temperature at the desired level. For the units of the Angarsk, Kirish, Polotsk, Novoyaroslavl and Syzran refineries, a more successful solution was found, the feedstock is preheated in a tube furnace, and the excess heat of reaction, if necessary, is removed by blowing air into the reactor pipes placed in a common casing (according to the design of the Omsk branch of VNIPIneft, each reactor pipe housed in a separate casing).
If the temperature of the flue gases at the outlet from the common collectors of the regenerator exceeds 650 °, this indicates the beginning of the afterburning of carbon monoxide. To stop it, it is necessary to sharply decrease the air supply to the upper part of the regenerator.
In order to reduce the temperature of flue gases above the pass wall, flue gas recirculation is used in old-design radiant-convection furnaces, especially thermal cracking furnaces. The colder flue gases from the hog furnace are returned to the combustion chamber, which leads to a redistribution of heat between the chambers. In the convection chamber, the thermal stress of the upper pipes decreases, but due to an increase in the volume of flue gases, their speed increases, while heat transfer throughout the convection chamber improves. The recirculation ratio in tube furnaces ranges from 1-3.
The imperfection of the design of the burners of furnaces and boilers for burning fuel and the insufficient tightness of the furnaces do not allow for the time being to work with small excess air. Therefore, it is believed that the temperature of the air heater tubes should be higher than the dew point temperature of aggressive flue gases, i.e. not lower than 130 ° C. For this, preliminary or intermediate heating of cold air or special layouts of the heating surface are used. There are devices that are structurally designed so that the heat exchange surface on the side of the flue gases is much larger than on the side of the atmospheric air, therefore, the sections of air heaters are assembled from pipes with different finning coefficients increasing towards the cold end (to the place where cold air enters), and thus the temperature the pipe walls are approaching the flue gas temperature. According to this principle, Bashorgener-goneft air heaters are designed from cast iron ribbed and ribbed-toothed tubes with good performance.
Heating and calcination of the catalyst is carried out by direct contact with flue gases coming from the furnace, in which gaseous or liquid fuel is burned. The temperature of the flue gases is automatically maintained at the level of 630-650 ° C, while the temperature in the calcination zone is 600-630 ° C. The calcined catalyst enters the cooling chon through the flow tubes of the lower gate lattice, where it moves between the rows of air-cooled tubes and he cools himself to the desired temperature. At the end of the re-grinding tube, a movable metal glass, the position of which regulates the height of the catalyst bed on the conveyor located below and, consequently, the rate of unloading of the product. The unloaded catalyst is fed by a belt conveyor into a screen for screening out fines. Then it is poured into metal drums and delivered to the finished product warehouse.
The higher the temperature of the heated raw material in the radiant tubes and the greater its tendency to coke formation, the lower the heat density should be, and, consequently, the lower the temperature of the flue gases above the pass. For a given furnace, an increase in the surface of the radiant tubes leads to a decrease in the temperature of the flue gases above the pass and the heat congestion of the radiant tubes. Contamination of the inner surface of the pipes with coke or other deposits can lead to an increase in the temperature of the flue gases over the pass and to burnout of the first rows of pipes in the convection chamber of the furnace. The temperature over the pass is carefully controlled and usually does not exceed 850-900 ° C.
The temperature of the flue gases above the pass wall is usually maintained at 700-850 ° C, i.e., high enough to transfer part of the heat by radiation to the upper rows of pipes in the convection chamber. But the main amount of heat in the convection chamber is transferred due to the priming convection of flue gases (created by a chimney or smoke exhauster).
The fraction of the distillate at the exit from the furnace is e = 0.4, the vapor density of the distillate is 0.86. residue density = 0.910. The diameter of the tubes in the radiation chamber is 152 X 6 mm, in the convection chamber is 127 X 6 mm, the useful length of the tubes is 11.5 m, the number of tubes is 90 and 120, respectively. Fuel composition and theoretical air consumption are the same as in examples 6.1 and 6. 2, the heat content of flue gases with an excess of air a = 1.4 is found in Fig. 6. 1. Temperature of flue gases at the pass
The total duration of the hydrothermal treatment, including heating, is approximately one day. After the start of the pressure drop in the apparatus, the temperature of the flue gases at the outlet of the furnace is gradually reduced and, finally, the nozzle is extinguished. The apparatus is cooled with cold air from the firebox through the casing. The dried balls are unloaded and sent to the bunker of the calcining column.
Suction pyrometers. In the practice of measuring high temperatures of flue gases, suction pyrometers are used. The main elements of suction pyrometers are a thermocouple placed in a cooled housing, a system of screens and a device for suction of gases. Thermal electrodes are insulated from one another and from a protective cover with rigid elements (straws, beads, one- and two-channel) of quartz (up to 1100 ° C), porcelain (up to 1200 ° C), porcelain with a high alumina content (up to 1350 ° C) ) ceramic materials and glass enamels applied by broaching methods.
When the nyrozmeeviki coke, there is a gradual increase in the temperature of the pipe wall, the pressure drop increases, and white spots can be observed in the places of overheating of the pipes. The formation of coke deposits in pyrosmeeviks is also judged by the increase in the temperature of the flue gases at the pass of the furnace. Coking of the ZIA is characterized by an increase in the hydraulic resistance of the system with an increase in the temperature of the pyrolysis products after the PIA. An increase in the hydraulic resistance in the pyrosmeevik and ZIA is accompanied by an increase in pressure in the furnace unit and, as a consequence, the contact time increases, and the yield of lower olefins decreases.
Table. B.2
| t, C | , kg / m3 | , J / (kgK) | , [W / (m · K)] | , m2 /with | Pr |
| 100 | 0,950 | 1068 | 0,0313 | 21,54 | 0,690 |
| 200 | 0,748 | 1097 | 0,0401 | 32,80 | 0,670 |
| 300 | 0,617 | 1122 | 0,0484 | 45,81 | 0,650 |
| 400 | 0,525 | 1151 | 0,0570 | 60,38 | 0,640 |
| 500 | 0,457 | 1185 | 0,0656 | 76,30 | 0,630 |
| 600 | 0,505 | 1214 | 0,0742 | 93,61 | 0,620 |
| 700 | 0,363 | 1239 | 0,0827 | 112,1 | 0,610 |
| 800 | 0,330 | 1264 | 0,0915 | 131,8 | 0,600 |
| 900 | 0,301 | 1290 | 0,0100 | 152,5 | 0,590 |
| 1000 | 0,275 | 1306 | 0,0109 | 174,3 | 0,580 |
| 1100 | 0,257 | 1323 | 0,01175 | 197,1 | 0,570 |
| 1200 | 0,240 | 1340 | 0,01262 | 221,0 | 0,560 |
Pipeline wall diameter d=… [Mm] heated to temperature t1 = ... [° C] and has a thermal emissivity. The pipeline is placed in a channel with a cross section bNSh[mm] whose surface has a temperature t2 = ... [° C] and emissivity c2 = … [W / (m2 K4 )] .Calculate the reduced emissivity and heat loss Q pipeline due to radiant heat exchange.
The conditions of the problem are given in Table 5.
The values of the coefficient of thermal radiation of materials are given in Table B.1 of Appendix B.
Table. 5
| №tasks | d, [mm] | t1 , [° C] | t2 , [° C] | c2 , [W / (m2 K4 )]. | bNSh, [mm] | Pipe material |
| 1 | 400 | 527 | 127 | 5,22 | 600x800 | oxidized steel |
| 2 | 350 | 560 | 120 | 4,75 | 480x580 | aluminumrough |
| 3 | 300 | 520 | 150 | 3,75 | 360x500 | concrete |
| 4 | 420 | 423 | 130 | 5,25 | 400x600 | cast iron |
| 5 | 380 | 637 | 200 | 3,65 | 550x500 | oxidized brass |
| 6 | 360 | 325 | 125 | 4,50 | 500x700 | oxidized copper |
| 7 | 410 | 420 | 120 | 5,35 | 650x850 | polished steel |
| 8 | 400 | 350 | 150 | 5,00 | 450x650 | oxidized aluminum |
| 9 | 450 | 587 | 110 | 5,30 | 680x580 | polished brass |
| 10 | 460 | 547 | 105 | 5,35 | 480x600 | polished copper |
| 11 | 350 | 523 | 103 | 5,20 | 620x820 | rough steel |
| 12 | 370 | 557 | 125 | 5,10 | 650x850 | turned cast iron |
| 13 | 360 | 560 | 130 | 4,95 | 630x830 | polished aluminum |
Table continuation. 5
| 14 | 250 | 520 | 120 | 4,80 | 450x550 | rolled brass |
| 15 | 200 | 530 | 130 | 4,90 | 460x470 | polished steel |
| 16 | 280 | 540 | 140 | 5,00 | 480x500 | rough cast iron |
| 17 | 320 | 550 | 150 | 5,10 | 500x500 | oxidized aluminum |
| 18 | 380 | 637 | 200 | 3,65 | 550x500 | polished brass |
| 19 | 360 | 325 | 125 | 4,50 | 500x700 | polished copper |
| 20 | 410 | 420 | 120 | 5,35 | 650x850 | rough steel |
| 21 | 400 | 350 | 150 | 5,00 | 450x650 | turned cast iron |
| 22 | 450 | 587 | 110 | 5,30 | 680x580 | polished aluminum |
| 23 | 460 | 547 | 105 | 5,35 | 480x600 | rolled brass |
| 24 | 350 | 523 | 103 | 5,20 | 620x820 | oxidized steel |
| 25 | 370 | 557 | 125 | 5,10 | 650x850 | aluminumrough |
| 26 | 450 | 587 | 110 | 5,30 | 450x650 | concrete |
| 27 | 460 | 547 | 105 | 5,35 | 680x580 | cast iron |
| 28 | 350 | 523 | 103 | 5,20 | 480x600 | oxidized brass |
| 29 | 370 | 557 | 125 | 5,10 | 620x820 | oxidized copper |
| 30 | 280 | 540 | 140 | 5,00 | 480x500 | polished steel |
Neighboring files in subject [UNSORTED]
Source: https://StudFiles.net/preview/5566488/page:8/
Gazovik - industrial gas equipment Handbook of GOST, SNiP, PB SNiP II-35-76 Boiler plants
7.1. When designing boiler rooms, draft-blowing installations (smoke exhausters and blowing fans) should be adopted in accordance with technical conditions manufacturing plants. As a rule, draft units should be provided individually for each boiler unit.
7.2. Group (for individual groups of boilers) or general (for the entire boiler room) blower installations are allowed to be used in the design of new boiler houses with boilers with a capacity of up to 1 Gcal / h and in the design of reconstructed boiler houses.
7.3. Group or general blower installations should be designed with two smoke exhausters and two blowing fans. The design capacity of the boilers for which these installations are provided is ensured by the parallel operation of two smoke exhausters and two blowing fans.
7.4. The choice of draft units should be made taking into account the safety factors for pressure and productivity in accordance with Appendix. 3 to these rules and regulations.
7.5. When designing blower installations to regulate their performance, guide vanes, induction couplings and other devices should be provided that provide cost-effective control methods and supplied complete with equipment.
7.6.*
The design of the gas-air duct of the boiler houses is carried out in accordance with the normative method of aerodynamic calculation of the boiler plants of the TsKTI im. I. I. Polzunova.
For built-in, attached and roof-mounted boiler rooms, openings for supplying combustion air, located, as a rule, in the upper zone of the room, should be provided in the walls. The dimensions of the free cross-section of the openings are determined on the basis of ensuring the air speed in them is not more than 1.0 m / s.
7.7. The gas resistance of commercially available boilers should be taken according to the manufacturer's data.
7.8. Depending on the hydrogeological conditions and layout solutions of boiler units, external gas ducts should be provided underground or above ground. Gas ducts should be provided with brick or reinforced concrete. The use of above-ground metal gas ducts is allowed as an exception, subject to the availability of an appropriate feasibility study.
7.9. Gas and air ducts inside the boiler room may be designed with steel, round section... Gas and air ducts of rectangular cross-section are allowed to be provided at the points of abutment to rectangular equipment elements.
7.10. For areas of gas ducts where ash accumulation is possible, cleaning devices should be provided.
7.11. For boiler rooms operating on sulphurous fuel, if it is possible for condensate to form in the gas ducts, protection against corrosion of the internal surfaces of the gas ducts should be provided in accordance with building codes and rules for the protection of building structures from corrosion.
7.12. Chimneys of boiler rooms should be constructed according to typical projects... When developing individual projects chimneys must be guided technical solutions adopted in typical projects.
7.13. For the boiler room, it is necessary to provide for the construction of one chimney. It is allowed to provide for two or more pipes with appropriate justification.
7.14.* The height of chimneys with artificial draft is determined in accordance with the Guidelines for calculating the dispersion in the atmosphere of harmful substances contained in the emissions of enterprises and the Sanitary norms for the design of industrial enterprises. The height of chimneys with natural draft is determined on the basis of the results of aerodynamic calculation of the gas-air duct and is checked according to the conditions of dispersion of harmful substances in the atmosphere.
When calculating the dispersion of harmful substances in the atmosphere, the maximum allowable concentrations of ash, sulfur oxides, nitrogen dioxide and carbon monoxide should be taken. In this case, the amount of harmful emissions is taken, as a rule, according to the data of the boiler manufacturers, in the absence of these data, it is determined by calculation.
The height of the mouth of the chimneys for built-in, attached and roof-top boiler rooms must be above the boundary of the wind support, but not less than 0.5 m above the roof, and also at least 2 m above the roof of the higher part of the building or the tallest building within a radius of 10 m.
7.15.* The diameters of the outlets of steel chimneys are determined from the condition of optimal gas velocities on the basis of technical and economic calculations. The diameters of the outlet openings of brick and reinforced concrete pipes are determined on the basis of the requirements of clause 7.16 of these rules and regulations.
7.16. In order to prevent the penetration of flue gases into the thickness of the structures of brick and reinforced concrete pipes, positive static pressure on the walls of the gas outlet is not allowed. To do this, condition R1 must be satisfied, the pipe diameter must be increased or a pipe of a special design (with an internal gas-tight gas outlet, with back pressure between the barrel and the lining) must be used.
7.17. The formation of condensate in the shafts of brick and reinforced concrete pipes, which remove the products of combustion of gaseous fuel, is allowed in all operating modes.
7.18.*
For boiler rooms operating on gaseous fuels, it is allowed to use steel chimneys if it is economically inexpedient to increase the temperature of the flue gases.
For autonomous boiler rooms, chimneys must be gas-tight, made of metal or non-combustible materials. Pipes should generally have external thermal insulation to prevent condensation and inspection and cleaning hatches.
7.19.
The openings for gas ducts in one horizontal section of the pipe trunk or foundation cup must be evenly spaced around the circumference.
The total area of weakening in one horizontal section should not exceed 40% of the total cross-sectional area for a reinforced concrete shaft or foundation glass and 30% for a brick pipe barrel.
7.20. The supply ducts at the junction with the chimney must be designed in a rectangular shape.
7.21. In the conjugation of gas ducts with a chimney, it is necessary to provide for temperature-sedimentary joints or expansion joints.
7.22. The need to use lining and thermal insulation to reduce thermal stresses in the trunks of brick and reinforced concrete pipes is determined by the heat engineering calculation.
7.23. In pipes designed to remove flue gases from the combustion of sulphurous fuel, when condensate forms (regardless of the percentage of sulfur content), a lining of acid-resistant materials should be provided along the entire height of the wellbore. In the absence of condensate on the inner surface of the gas outlet of the pipe in all operating modes, it is allowed to use a lining made of clay brick for chimneys or ordinary clay brick of plastic pressing grade of at least 100 with water absorption of not more than 15% on an alumina or complex solution of grade at least 50.
7.24. The calculation of the height of the chimney and the choice of the structure for protecting the inner surface of its trunk from the aggressive effects of the environment should be carried out based on the conditions of combustion of the main and reserve fuel.
7.25. The height and location of the chimney must be coordinated with the local Office of the Ministry civil aviation... Light barriers of chimneys and external marking color must comply with the requirements of the Manual on Aerodrome Service in Civil Aviation of the USSR.
7.26. Projects should provide for corrosion protection of external steel structures of brick and reinforced concrete chimneys, as well as surfaces of steel pipes.
7.27. In the lower part of the chimney or the foundation, there should be manholes for inspecting the chimney, and, if necessary, devices that provide condensate drainage.
7.28. Boiler houses designed to operate on solid fuels (coal, peat, oil shale and wood waste) must be equipped with installations for cleaning flue gases from ash in cases where
Note... When applying solid fuel installation of ash collectors is not required as an emergency.
7.29.
The choice of the type of ash collectors is made depending on the volume of gases to be cleaned, the required degree of purification and layout possibilities on the basis of a technical and economic comparison of options for installing ash collectors different types.
The following should be taken as ash-collecting devices:
"Wet" ash collectors with low-calorie Venturi pipes with drop catchers can be used in the presence of a hydro-ash removal system and devices that exclude the discharge of harmful substances contained in the ash and slag slurry into water bodies.
The volumes of gases are taken at their operating temperature.
7.30. The cleaning coefficients of ash-collecting devices are taken by calculation and must be within the limits established by app. 4 to these rules and regulations.
7.31. The installation of ash collectors must be provided on the suction side of the smoke exhausters, as a rule, on open areas... With appropriate justification, it is allowed to install ash collectors indoors.
7.32. Ash collectors are provided individually for each boiler unit. In some cases, it is allowed to provide for several boilers a group of ash collectors or one sectioned apparatus.
7.33. When operating a boiler house on solid fuel, individual ash collectors should not have bypass ducts.
7.34.
The shape and inner surface of the ash collector bunker must ensure complete ash drainage by gravity, while the angle of inclination of the bunker walls to the horizon is taken as 600 and, in justified cases, at least 550 is allowed.
Ash collector bins must have hermetic seals.
7.35. The gas velocity in the inlet gas duct of ash-collecting installations should be taken at least 12 m / s.
7.36. "Wet" spark arresters should be used in boiler rooms designed to operate on wood waste, in cases where ArB≤5000. Spark arresters are not installed after the ash collectors.
Source: https://gazovik-gas.ru/directory/add/snip_2_35_76/trakt.html
14.02.2013
A. Batsulin
To understand the process of condensation formation in stove chimneys, it is important to understand the concept of dew point. Dew point is the temperature at which water vapor in the air condenses into water.
At each temperature, no more than a certain amount water vapor. This quantity is called the density of saturated vapor for a given temperature and is expressed in kilograms per cubic meter.
In fig. 1 shows a graph of the dependence of the density of saturated steam on temperature. The partial pressures corresponding to these values are marked on the right. The data in this table are taken as a basis. In fig. 2 shows the initial section of the same graph.
Rice. 1.
Saturated water vapor pressure.
Rice. 2.
Saturated water vapor pressure, temperature range 10 - 120 * С
Let's explain how to use the chart with a simple example. Take a pot of water and cover it with a lid. After some time, under the lid, an equilibrium will be established between water and saturated water vapor. Let the temperature of the pan be 40 * C, then the vapor density under the lid will be about 50 g / m3. The partial pressure of water vapor under the cover according to the table (and the graph) will be 0.07 atm, the remaining 0.93 atm will be the air pressure.
(1 bar = 0.98692 atm). Let's start slowly heating the pan, and at 60 * C, the density of saturated steam under the lid will already be 0.13 kg / m3, and its partial pressure will be 0.2 atm. At 100 * C, the partial pressure of saturated vapor under the lid will reach one atmosphere (i.e., external pressure), which means that there will be no more air under the lid. The water will start to boil and steam will escape from under the lid.
In this case, the density of saturated steam under the lid will be 0.59 kg / m3. Now we close the lid tightly (i.e. turn it into an autoclave) and insert a safety valve into it, for example, at 16 atm, and continue heating the pan itself. The boiling of water will stop, and the pressure and density of the vapor under the lid will increase, and when it reaches 200 * C, the pressure will reach 16 atm (see graph). In this case, the water will boil again, and the steam will come out from under the valve.
The vapor density under the cover is now 8 kg / m3.
In the case of consideration of condensate fallout from flue gases (DG), only a part of the graph up to a pressure of 1 atm is of interest, since the furnace is in communication with the atmosphere and the pressure in it is equal to atmospheric with an accuracy of several Pa. It is also obvious that the dew point of the DG is below 100 * C.
To determine the dew point of flue gases (i.e. the temperature at which condensate falls out of the DG), it is necessary to know the density of water vapor in the DG, which depends on the composition of the fuel, its moisture content, the excess air ratio and temperature. The vapor density is equal to the mass of water vapor contained in 1 m3 of flue gases at a given temperature.
Formulas for the volume of a DW were derived in this work, Section 6.1, formulas A1.3 - A1.8. After transformations, we obtain an expression for the vapor density in flue gases depending on the moisture content of the wood, the excess air ratio and temperature. The humidity of the source air makes a small correction and is not taken into account in this expression.
The formula has a simple physical meaning. If we multiply the numerator of the large fraction by 1 / (1 + w), then we get the mass of water in DG, in kg per kg of wood. And if we multiply the denominator by 1 / (1 + w), then we get the specific volume of the DW in nm3 / kg. The multiplier with temperatures is used to convert normal cubic meters into real ones at a temperature T. After substituting the numbers, we get the expression:
The dew point of flue gases can now be determined graphically. Let us superimpose the graph of the steam density in the DG on the graph of the density of saturated water vapor. The intersection of the graphs will correspond to the dew point of the DG with the corresponding humidity and excess air. In fig. Figures 3 and 4 show the result.
Rice. 3.
The dew point of flue gases with excess air unit and different moisture content of the wood.
From fig. 3 it follows that in the most unfavorable case, when burning wood with a moisture content of 100% (half of the mass of the samples is water) without excess air, condensation of water vapor will begin at about 70 * C.
Under conditions typical for batch furnaces (wood moisture content of 25% and an excess of air of about two), condensation will begin when the flue gases are cooled to 46 * C. (see fig. 4)
Rice. 4.
Flue gas dew point at 25% wood moisture and various excess air.
From fig. 4 it is also clearly seen that excess air significantly lowers the temperature of condensation. Adding excess air into the chimney is one of the ways to eliminate condensation in pipes.
All the above considerations are valid if the composition of the fuel remains unchanged over time, for example, gas is burned in the trough or pellets are fed continuously. In the case of burning firewood in a batch oven, the composition of the flue gases changes over time. First, volatiles burn out and moisture evaporates, and then the carbon residue burns out. Obviously, in the initial period, the content of water vapor in the DG will be significantly higher than the calculated one, and at the stage of combustion of the coal residue it will be lower. Let's try to roughly estimate the dew point temperature in the initial period.
Let the volatiles burn out from the bookmark in the first third of the heating process, also all the moisture contained in the bookmark evaporates during this time. Then the concentration of water vapor in the first third of the process will be three times higher than the average. At 25% wood moisture content and a 2-fold excess of air, the vapor density will be 0.075 * 3 = 0.225 kg / m3. (see FIGURE, blue graph). In this case, the condensation temperature will be 70-75 * С. This is an approximate estimate, since it is not known how, in reality, the composition of the DG changes as the bookmark burns out.
In addition, unburned volatiles condense from the flue gases together with water, which, apparently, will slightly increase the dew point of the DG.
Flue gases, rising through the chimney, are gradually cooled. When cooling below the dew point, condensation begins to form on the walls of the chimney. The cooling rate of the DG in the chimney depends on the flow section of the pipe (the area of its inner surface), the pipe material and its filling, as well as the intensity of combustion. The higher the combustion rate, the greater the flue gas flow, which means that, other things being equal, the gases will cool more slowly.
The formation of condensation in the chimneys of stoves or intermittent fireplaces is cyclical. At the initial moment, while the pipe is not yet warmed up, condensate falls on its walls, and as the pipe warms up, the condensate evaporates. If the water from the condensate has time to evaporate completely, then it gradually soaks brickwork chimney, and black resinous deposits appear on the outer walls. If this happens on the outside of the chimney (outside or in a cold attic), then constant moistening of the masonry in winter will lead to the destruction of the oven bricks.
The temperature drop in the chimney depends on its design and the size of the DG flow (fuel combustion rate). In brick chimneys, the drop in T can reach 25 * C per linear meter. This justifies the requirement to have the temperature of the DG at the outlet of the furnace ("on the view") 200-250 * C, with the aim that at the pipe head it was 100-120 * C, which is obviously higher than the dew point. The temperature drop in insulated sandwich-type chimneys is only a few degrees per meter, and the temperature at the oven outlet can be reduced.
Condensation, forming on the walls of a brick chimney, is absorbed into the masonry (due to the porosity of the brick), and then evaporates. In stainless steel chimneys (sandwich), even a small amount of condensate formed in the initial period immediately begins to flow downward, therefore, in order to avoid condensate flowing into the chimney insulation, inner pipes assembled in such a way that the upper pipe is inserted into the lower one, i.e. "By condensate".
Knowing the speed of burning firewood in the stove and the cross-section of the chimney, you can estimate the temperature drop in the chimney per linear meter using the formula:
q is the heat absorption coefficient of the walls of a brick chimney, 1740 W / m2 S is the area of the heat-absorbing surface of 1 m of the chimney, m2 s is the heat capacity of waste gases, 1450 J / nm3 * СF is the waste gas flow, nm3 / h V is the specific volume of the DG, at 25% humidity wood and 2-fold excess of air, 8 Nm3 / kg Bh - hourly fuel consumption, kg / h
The heat absorption coefficient of the chimney walls is conventionally taken as 1500 kcal / m2 hour, because for the last flue of the furnace in the literature, a value of 2300 kcal / m2h is given. The calculation is indicative and intended to show general patterns... In fig. 5 shows a graph of the dependence of the temperature drop in chimneys with a cross section of 13 x 26 cm (five) and 13 x 13 cm (four), depending on the speed of burning firewood in the firebox of the stove.
Rice. 5.Temperature drop in a brick chimney per linear meter depending on the burning rate of wood in the stove (flue gas flow). The excess air ratio is taken equal to two.
The numbers at the beginning and at the end of the graphs indicate the speed of the DG in the chimney, calculated on the basis of the flow of the DG, reduced to 150 * C, and the cross section of the chimney. As you can see, for speeds of about 2 m / s recommended by GOST 2127-47, the temperature drop of the diesel generator is 20-25 * C. It is also clear that the use of chimneys with a cross-section greater than the required one can lead to strong cooling of the DG and, as a result, condensation.
As follows from Fig. 5, a decrease in the hourly consumption of firewood leads to a decrease in the flow of exhaust gases, and, as a consequence, to a significant drop in temperature in the chimney. In other words, the temperature of the exhaust gases, for example, at 150 * C for a batch-type brick oven, where firewood is actively burning, and for a slow-burning (smoldering) oven, is not at all the same thing. Somehow I had to observe such a picture, fig. 6.
Rice. 6.
Condensation in a brick chimney from a stove long burning.
Here the smoldering furnace was connected to brick pipe section in brick. The burning rate in such a furnace is very low - one tab can burn for 5-6 hours, i.e. the burning rate will be about 2 kg / h. Of course, the gases in the chimney cooled below the dew point and condensate began to form in the chimney, which soaked the chimney through and through, and when the furnace was fired, it dripped onto the floor in drops. Thus, long-burning stoves can only be connected to insulated sandwich-type chimneys.
