The main function that the chimney should perform for the boiler room is to exhaust the flue gases from the boilers into the atmosphere and dissipate them in this space. She also has an additional function: they should create natural cravings resulting from the difference between the temperature in the firebox and the outside.
We will introduce you to the varieties of smoke channels, which are classified on the basis of design features and pipe material. Here you will learn how to calculate the geometric parameters for a specific example. Our tips will help determine the type and size of the chimney.
The content of the article:
Types of chimneys
- Self-supporting boiler tubes
- Column smoke structures
- Features of facade and facade chimneys
- Truss pipes
- Mast chimney pipes
- Materials for the construction of pipes boiler
Calculation of pipe parameters
- Determination of the height of the pipe during natural thrust
- Pipe diameter calculation
- Conclusions and useful video on the topic
Types of chimneys
In large boilers, natural draft cannot ensure proper combustion; here it is forcedly created using smoke pumps. The combustion process and the discharge of its products into the atmosphere should bring as little harm to the surrounding the environment and not cause emergency situations as a result of pressure in the furnaces exceeding the norm.
Constructional pipes for boiler rooms very different from each other and in the form of the supporting structure, and the material of manufacture. On the first sign, there are several types of pipes.
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Chimney is a significant constructive component of a boiler house of an enterprise and a private house. It depends on the efficiency of the unit
The height and dimensions of the smoke channel must be calculated with extreme precision, since the size of the channel depends on the combustion process
For the formation of impeccable thrust required to take into account the wind rose in the region, barometric pressure and the average data on air temperature
The design of the chimney should provide full flue gas without causing harm to the owners and users of closely located buildings and the environment
Means and devices for maintenance of the chimney should be thought out, envisaged and designed.
When designing a chimney, it is mandatory to take into account the type of the boiler and the type of fuel. In the case of using a combined unit, the pipe is selected, focusing on the safe removal of gases of maximum temperature
The flow capacity of the chimney is determined taking into account the volume of combustion products at maximum load of the unit
The boiler room pipe is a rather high structure exposed to natural phenomena. The design is designed to ensure stability in strong winds and the ability to extinguish lightning strikes.
An important component of boiler room equipment
The need for accurate calculations of pipe dimensions
Significance of design before installation
Chimney construction requirements
Matching chimney to boiler type
Stability and lightning protection
Self-supporting boiler tubes
Such vertical constructions are single- or multi-barreled. They divert combustion products from boilers and boilers.
They are used regardless of the type of fuel, but subject to certain requirements:
- The temperature of the flue gases passing through the self-supporting pipes should not exceed 350 degrees C.
- Combustion products must not be chemically aggressive.
- The optimal snow load for self-supporting structures is 250 kg per kW. cm, wind - 30 kg per kV. cm in the conditions of the II wind region.
Install a self-supporting pipe on the roof, and fix inside the building. Its design features provide the possibility of transportation and installation on site, because it consists of separate sections representing 3-ply sandwich pipe. The foundation is attached to the foundation using anchors.
Inside the pipe there is a layer made of strong steel that is not amenable to the effects of substances released during combustion. The outer layer protects against weathering.
Chimneys for large boiler houses are often self-supporting. This building, built on an individual project and having its own infrastructure
The parameters of smoke structures must comply with the requirements set forth in regulatory documents. Their calculation is based on such factors as the number of boilers, power, type of fuel. Be sure to take into account standards for emissions into the atmosphere. In some cases, chimneys are equipped with a platform, a ladder, an inspection hatch, light fencing.
Column smoke structures
The pipe of this type consists of an outer shell of high carbon steel and inserted into it internal trunks of different diameters of stainless steel for the removal of gases. The design is fixed in an anchor basket embedded in the foundation. They can be either 1 or several. That inside did not settle a condensate, use heat insulation.
Part of the column tube. Here in the section you can see that several trunks of various diameters of stainless steel are placed inside
The advantage of this design solution is a long operational period, the prospect of connecting several boilers. The thickness of the steel and the brand is chosen based on the temperature and aggressiveness of the combustion products.
The diameter of each barrel can reach one and a half meters, and if you plan to use a common gas duct for several boilers, then a diameter of about 3 m is needed. To avoid condensation, barrels are covered thermal insulation.
Features of facade and facade chimneys
Install near-front chimneys for boiler rooms attached to the house or built-in ones. Attach them to the wall of the building with the use of brackets. Components of the chimney are trunks and frame or anchor fasteners.
The barrel has 3 layers: inside is stainless steel, then heat insulation and galvanized steel. Pipes are intended for boiler rooms where boilers work on gas or liquid fuel.
The most common facade pipes are located along the outer wall of the building. When choosing a steel grade and pipe wall thickness, take into account the chemical composition of the exhaust gases and their temperature
Near-facade and facade pipes transfer the weight load through an additional lower foundation and wind one through vibration-proof fastenings. This type of chimneys, in terms of material costs, is the most economical due to the lack of supporting structures and a solid foundation.
The modular system used to create the exhaust barrels allows for easy replacement of damaged parts.
Such a metal structure consists of pipes mounted on a durable self-supporting truss-type column. The farm, in turn, is fixed in an anchor basket, poured into the foundation. Farm type flues are suitable for use in regions with dangerous seismological conditions.
Farm type construction includes from 1 to 6 stems. The column is made of rolled steel. The profile pipe can have a square or a triangle in cross section. It depends on the number of trunks.
To prevent corrosion, gas vents are coated with a primer, then painted.
The barrel for removal of gases is composed of modules consisting of 3 layers:
- internal, in contact with the combustion products directly and made of special-grade stainless steel;
- 5-6 cm thick, playing the role of thermal insulation;
- external, protecting the insulating layer from the negative effects of the environment.
For anti-corrosion coatings use paints containing a large percentage of zinc. In some structures inside the column there may be stairs and platforms that facilitate maintenance. Structural elements of pipes of this type are relatively lightweight and this facilitates both their transportation and installation work.
Mast chimney pipes
The central element of the mast pipe is a supporting tower - a three- or four-masted tower, to which chimneys are attached. All components of the construction are assembled on the basis in the form of a concrete pad, starting from the bottom and gradually moving upwards. Used when assembling a rivet connection or use screws.
The supporting structure of the mast pipe is assembled from steel profiles interconnected by braces and corners. With its base, the column rests on the foundation, and is fixed by its anchoring.
Usually, individual elements are transported to the installation site and assembled as a designer. It takes this process quite a bit of time - a few hours. The height of the chimney can reach a maximum of 28.5 m. Stability of the chimney provide stiffeners - steel delays with a cross section of 1.6 to 2 cm. They compensate for the action of transverse forces.
Materials for the construction of pipes boiler
Smoke extraction systems are made of different materials - bricks, steel, ceramics, and polymer. Brick chimneybuilt over brick stoves and fireplaces, it has good mechanical strength, excellent heat capacity, a sufficiently high degree of fire safety.
There are also a lot of flaws in these structures, so in modern construction fully brick chimneys are becoming increasingly rare. Regulatory documents limit the height of brick pipes 30-70 m, and a diameter of 0.6-8 m.
On the walls of a brick pipe with a lot of protrusions and recesses inside, there is always a lot of condensate, soot containing sulfur oxides. The latter, reacting with water, forms acids that actively destroy the brick.
Surface irregularities, narrowing of the passage as a result of the gradual increase of the soot layer, cause a decrease in the speed of passage of smoke and tipping over in the flue duct.
More resistant to condensation and external factors ceramic flues, they have high refractoriness. But this system is heavy, because inside there are metal rods, giving it extra strength. Hence the requirements for the mandatory installation of a separate foundation, supports, which increases the complexity and cost of installation.
Polymer flue pipes are appropriate in boiler rooms with a maximum temperature of 250 degrees C, during installation gas water heaters. They are lightweight, flexible and durable, but relevant only for gas equipment.
A device for the exhaust of stainless steel - an assembly consisting of individual elements of the chimney, interconnected by means of fittings: tees, nozzles, deflectors, tees, taps. Steel chimneys equip mainly gas boilers.
Installation of such a chimney can be performed after the construction of the building in a short time. There is a wide range of fittings, so the pipe can be given any configuration.
The modular chimney can be easily dismantled and moved to another location. The advantage of the design is its low weight, which allows to do without the foundation, resistance to moisture, slight soot deposition on the inner walls, high flue passage rate gases.
Sanitary standards allow the use of steel pipes for the construction of chimneys with a height of more than 30 m, an exception is possible only if less than 5 tons of multi-ash is used per day. fuel. The reason is that the service life of such facilities is 10 years, and if high sulfur fuel is used, it is significantly reduced.
The varieties, the body of which is made of steel alloy, are coaxial chimneys, with design specifics and features of operation which we recommend to get acquainted.
Calculation of pipe parameters
To determine the height and diameter of the chimney for the boiler room, it is necessary to perform aerodynamic design calculations. The diameter depends on the capacity of individual boilers or the whole boiler room.
The combustion of fuel and the effective removal of smoke is greatly influenced by thrust, which requires constant air supply to the firebox to create. This is provided both naturally and artificially.
If a smoke pump is built into the system, then the height of the pipe is not critical. This parameter is important mainly to account for harmful emissions into the atmosphere. To determine samotyagu, you need a mandatory calculation of the height and section of the pipe.
Determination of the height of the pipe during natural thrust
To create a normal natural thrust, it is necessary to observe the condition of equality of the thrust force and the total resistance that occurs during the movement of flue gases through the gas channels of the boiler and the path chimney. To provide such a thrust is possible under the condition of a small gas resistance, when the height of the pipe does not exceed 60 m.
This scheme will simplify the process of calculating the main parameters of the pipe for removal of the combustion products of any fuel in the furnaces of the boiler room
Regulatory documents regulating the location and calculation of chimney height, are SNiP41-01-2003, SP 7.13130.2009.
It is also necessary to take into account the recommendations set forth in the instructions for the boiler, in particular, the following requirements:
- From the grate to the top point of the pipe should not be less than 5 m.
- Above a flat roof without a high fence, the pipe should rise not less than 0.5 m.
- In relation to the height of the fence and the ridge of the roof, the pipe should exceed their level by 0.5 m if it is within a m and a half from these structures.
- When the chimney is removed from the parapet and the ridge at a distance of 1.5 to 3 m, its upper point should coincide with their height level.
With an incorrectly calculated chimney height, many problems can arise and the main one is air turbulence or a wind backpressure zone. The fire in the furnace can extinguish strong gusts of wind.
When constructing a chimney, it is necessary to take into account the design of the roof, the thickness of the roofing pie, the distance to the enclosing elements and the ridge, the rules of fire safety (+)
The implementation of fire safety rules is also a prerequisite for the design of the boiler tube. It is necessary to isolate the structures adjacent to the pipe.
So that sparks from the ventilation holes on the pipe do not fall on the roof when it is made of combustible material, the height of the construction increase by 0.5 m. The boiler room pipe should be removed from tall buildings and trees at least 2 m.
The height of the pipe is determined depending on the roof construction. If the roof is multi-level, they take into account height differences, but the base in all cases is the same - ridge height (+)
Since the optimal thrust arises due to the difference between the total density of the gases leaving the chimney and the outside air column equal in height, the calculation is performed according to the formula:
The height of the smoke channel is independently calculated by this formula. All values can be taken from the documentation attached to the heating equipment.
The calculation is quite complicated, it is better if it is performed by experts. Parameters affecting pipe height:
- Coefficient A characterizes the meteorological situation of the region.
- Mi is the mass of flue gases that pass through the pipe per unit of time.
- F - the rate at which the particles formed during combustion settle.
- Spdki and Sfi - indicators of the concentration of various substances in the flue gas.
- V is the volume of gas.
- T is the difference between the temperatures of the air entering and leaving the pipe.
If a boiler room located in the annexe to the house, the latter becomes a hindrance. It is necessary that in this case the tip of the pipe should be located above the zone of the wind backwater. Otherwise, the heating equipment will not function normally.
In order to determine by what amount a pipe should be grown, the highest point on the house is found, a direct angle of 45 degrees is made through it with the surface of the earth. The space below this line is a zone of wind pressure, and the chimney should be located above it.
Pipe diameter calculation
To calculate the diameter of the pipe there is a formula:
S = m / (ρr x w),
Here m is the fuel consumption in 1 hour, w is the speed of movement of the flue gases, ρr is the air density in the working conditions, it is determined by the formula: Where tо is the outside air temperature, pBn is the air density in normal conditions = 1.2932 kg / m3.
The table will help determine the value of air density ρg in the working conditions without performing complex calculations. The value of the density of flue gases to simplify the calculations is assumed to be equal to the density of air (+)
Let 50 kg of solid fuel burn in a boiler in an hour, then in a second it will be 50: 3600 = 0.013888 kg. The speed of movement of flue gases - 2 m per second. At an air temperature of -4 degrees C, the air density is 0.6881 kg per cubic meter. m. Then S = 0.013888: (0.6881 x 2) = 0.01092 square meters. m = 92 square meters. cm. For a round section d = √4 x 92: 3.14 = 10.83 cm.
The diameter of a cylindrical chimney can be calculated using a different formula: d = 1000 / 1.163 x (r x Q√H), where r is a coefficient depending on the type of fuel used. For coal it is 0.03, for firewood 0.045, for gas 0.016, liquid fuel - 0.024.
Conclusions and useful video on the topic
Video with a visual demonstration of the process of calculating the height of the smoke channel for arranging the boiler room:
Here, the author of the video shared his own experience in calculating and installing a chimney for a solid fuel boiler:
Another video to help the amateur designer:
It is not so important on what kind of fuel the boilers in the boiler room work. In any case, do not do without the flue gas removal system. The main requirements that chimney pipes must meet are good traction and throughput, sustained environmental standards.
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