Regulation of the combustion process (Basic principles of combustion)

For optimal combustion it is necessary to use more air than the theoretical calculation of the chemical reaction (stoichiometric air).

This is due to the need to oxidize all available fuel.

The difference between the actual amount of air and the stoichiometric amount of air is called excess air. As a rule, excess air is in the range from 5% to 50% depending on the type of fuel and burner.

Generally, the more difficult it is to oxidize the fuel, the more excess air is required.

Excess air should not be excessive. Excessive combustion air supply lowers the flue gas temperature and increases the heat loss of the heat source. In addition, at a certain limit of excess air, the flare cools too much and CO and soot begin to form. Conversely, too little air causes incomplete combustion and the same problems mentioned above. Therefore, in order to ensure complete combustion of the fuel and high combustion efficiency, the amount of excess air must be very precisely regulated.

The completeness and efficiency of combustion is checked by measuring the concentration of carbon monoxide CO in the flue gases. If there is no carbon monoxide, then combustion has occurred completely.

Indirectly, the level of excess air can be calculated by measuring the concentration of free oxygen O 2 and/or carbon dioxide CO 2 in flue gases.

The amount of air will be about 5 times greater than the measured amount of carbon in volume percent.

As for CO 2 , its amount in flue gases depends only on the amount of carbon in the fuel, and not on the amount of excess air. Its absolute amount will be constant, and the percentage of the volume will change depending on the amount of excess air in the flue gases. In the absence of excess air, the amount of CO 2 will be maximum, with an increase in the amount of excess air, the volume percentage of CO 2 in the flue gases decreases. Less excess air corresponds to more CO 2 and vice versa, so combustion is more efficient when CO 2 is close to its maximum value.

The composition of flue gases can be displayed on a simple graph using the "combustion triangle" or the Ostwald triangle, which is plotted for each type of fuel.

With this graph, knowing the percentage of CO 2 and O 2 , we can determine the CO content and the amount of excess air.

As an example, in fig. 10 shows the combustion triangle for methane.

Figure 10. Combustion triangle for methane

The X-axis indicates the percentage of O 2 , the Y-axis indicates the percentage of CO 2 . the hypotenuse goes from point A, corresponding to the maximum content of CO 2 (depending on the fuel) at zero content of O 2, to point B, corresponding to zero content of CO 2 and maximum content of O 2 (21%). Point A corresponds to the conditions of stoichiometric combustion, point B corresponds to the absence of combustion. The hypotenuse is the set of points corresponding to ideal combustion without CO.

Straight lines parallel to the hypotenuse correspond to different CO percentages.

Let's assume that our system is running on methane and the flue gas analysis shows that the CO 2 content is 10% and the O 2 content is 3%. From the triangle for methane gas, we find that the CO content is 0 and the excess air content is 15%.

Table 5 shows the maximum CO 2 content for different types fuel and the value that corresponds to optimal combustion. This value is recommended and calculated based on experience. It should be noted that when the maximum value is taken from the central column, it is necessary to measure the emissions, following the procedure described in chapter 4.3.

As you know, heat transfer from flue gases to the walls of chimneys occurs due to friction, which occurs during the movement of these same gases. Under the influence of thrust, the gas velocity decreases and the released energy (that is, heat) passes to the walls. It turns out that the process of transferring the body directly depends on the speed of gas movement through the channels of the source. What then determines the velocity of gases?

There is nothing complicated here - the cross-sectional area of ​​​​smoke channels affects the speed of movement of smoke gases. With a small cross section, the speed increases, while with a larger area, on the contrary, the speed decreases, and the flue gases transfer more energy (heat), while losing their temperature. In addition to the section, the location of the smoke channel also affects the efficiency of heat transfer. For example, in horizontal smoke. channel heat is "absorbed" much more efficiently, faster. This is due to the fact that hot flue gases are lighter and are always higher, effectively transferring heat to the upper walls of the smoke. channel.

Let's look at the types of smoke circulation systems, their features, differences and performance indicators:

Types of smoke

Smoke circuits are a system of special channels inside the furnace (fireplace), connecting the firebox with smoke. pipe. Their main purpose is to remove gases from the furnace furnace and transfer heat to the stove itself. To do this, their inner surface is made smooth and even, which reduces the resistance to the movement of gases. Smoke channels can be long - at stoves, short - at fireplaces, as well as: vertical, horizontal and mixed (lifting / lowering).

According to their design features, smoke circulation systems are divided into:

• channel (subspecies: high- and low-turnover)
• channelless (subspecies: with a system of chambers separated by partitions),
• mixed.

All of them have their differences, and, of course, their pros and cons. The most negative are multi-turn systems with horizontal and vertical arrangement smoke channels, it is generally not advisable to use them in furnaces! But the most acceptable and economical smoke circulation system is considered to be a mixed system with horizontal. channels and vertical domes directly above them. Other systems are also widely used in the construction of furnaces, but here you need to know the nuances of their design. What we will “talk” about further, considering each system separately:

Single turn flue systems

The design of this system involves the exit of flue gases from the firebox into the ascending channel, then their transition to the downstream channel, from the downstream into the upstream channel, and from there into the chimney. This system provides furnaces with a very small heat-absorbing surface, from which gases give off much less heat to the furnace and its efficiency decreases. In addition, due to the very high temperature in the first channel, uneven heating of the furnace mass and cracking of its masonry occur, that is, destruction. And the exhaust gases reach over 200 degrees.

Single-turn smoke circulation system with three downcomers

In this system, the smoke from the firebox passes into the 1st ascending channel, then descends along three descending channels, passes into the lifting channel, and only then exits into the chimney. Its main drawback is the overheating of the 1st ascending channel and the violation of the rule of uniformity of all channel cross-sectional areas. The fact is that the lower channels (there are only 3 of them) form in total such a cross-sectional area, which is already three times greater than the S section in the lift. channels and subvertices, which leads to a decrease in traction in the focus. And this is a significant disadvantage.

In addition to the shortcomings mentioned in the operation of the system with three downs. channels, one more can be distinguished - this is a very poor melting of the furnace after a long break.

Channelless systems

Here, the flue gases begin their journey from the firebox through the hailo (the opening for the exit of smoke gases into the smoke circuits), then they pass into the hood, then up - until the very overlap of the hearth, they cool down, transfer the heat of the furnace, go down and exit into the smoke pipe into bottom area of ​​the oven. Everything seems to be clear and simple, but such a channelless system still has a drawback: it is a very strong heating of the upper region of the furnace (roof), excessive deposits of soot and soot on the walls of the hood, as well as high temperatures of flue gases.

Channelless smoke circulation systems with 2 hoods

The scheme of operation of such a system is as follows: first, smoke gases from the firebox enter the 1st hood, then rise to the ceiling, descend, and then pass into the second bell. Here again they rise to the ceiling, decrease and go down through the channel into the chimney. All this is much more efficient than a single-bell ductless system. With two hoods, much more heat is transferred to the walls, and the temperature of the exhaust gases is also much more noticeably reduced. However, the overheating of the upper area of ​​the furnace and the soot deposits do not change, that is, they do not decrease!

Channelless hood systems - with buttresses on the inside. oven surfaces

In this hood system, the path of smoke is as follows: from the firebox, the transition to the hood, the rise to the ceiling, and the transfer of part of the heat to the ceiling itself, the side walls of the hearth and buttresses. It also has a certain minus - this is an excessive soot deposit (both on the walls of the furnace and on the buttresses), which can cause this soot to ignite and destroy the furnace.

Multi-turn smoke circulation systems with horizontal smoke channels

Here, the smoke from the firebox enters the horizontal channels, passes through them and gives off a lot of heat to the inner surface of the furnace. After that, it goes into the smoke pipe. At the same time, the flue gases are supercooled, the thrust force decreases and the furnace begins to smoke. As a result, soot, soot is deposited, condensation occurs .... and, one might say, the trouble begins. Therefore, before using this system, weigh everything twice.

Multiturn systems with vertical smoke. channels

They differ in that the flue gases from the firebox immediately enter the vertical lifting and lowering smoke channels, also give off heat to the inner surfaces of the hearth, and then go into the chimney. At the same time, the disadvantages of such a system are similar to the previous one, plus one more is added. The first ascending channel (lifting) overheats, from which the outer surfaces of the hearth heat up unevenly and cracking of its brickwork begins.

Mixed smoke circulation systems with horizontal and vertical smoke channels

They differ in that flue gases pass first into horizontal channels, then into vertical lifting, into lowering, and only then into the chimney. The disadvantage of this process is as follows: due to the strong supercooling of the gases, the thrust decreases, it weakens, which leads to excessive deposition of soot on the walls of the channels, the appearance of condensate, and, of course, to the failure of the furnace and to its destruction.

Mixed flue system with free and forced movement of gases

The principle of operation of this system is as follows: when draft is formed during combustion, it pushes smoke gases into horizontal and vertical channels. These gases give off heat to the inner walls of the furnace and go into the chimney. In this case, part of the gases rises into closed vertical channels (caps), which are located above the horizontal. channels. In them, the flue gases cool down, become heavier and go again horizontally. channels. This movement occurs in every cap. The result is smoke. gases transfer all their heat to the maximum, positively influencing the efficiency of the furnace and increasing it up to 89%!!!

But there is one "but"! In this system, heat susceptibility is very developed, because the gases cool very quickly, even supercool, weakening the draft and disrupting the operation of the furnace. In fact, such a furnace could not work, but there is a special device in it that regulates this negative process. These are injection (suction) holes or a system for autoregulating thrust and exhaust gas temperature. To do this, when laying the hearth, holes with a cross section of 15-20 cm2 are made from the firebox and in horizontal channels. When the thrust begins to fall and the temperature of the gases decreases, into the horizon. channels, a vacuum is formed and hot gases are “sucked in” through these holes from the lower smoke channels and from the firebox. The result is an increase in temperature and normalization of thrust. When the draft, pressure and temperature of the smoke are normal, it does not enter the suction channel - this requires a vacuum, a decrease in its draft and temperature.

Experienced stove-makers reducing / increasing the length of the horizontal. channels, the cross section and the number of injection channels regulate the efficiency of the furnace, thereby achieving the best results in its quality, efficiency and increasing the efficiency up to 89%!!!

With such a smoke circulation system, there are practically no drawbacks. They warm up perfectly - from the floor to the very top, and evenly! There are no sudden changes in temperature in the room. If the house is warm, and it is -10 frost outside, then the stove can be heated in 30-48 hours!!! If the street is down to -20, then you will have to heat more often, regularly! It is regular fireboxes that are its disadvantage. Periodic combustion in mixed smoke systems leads to a significant accumulation of soot.

How to optimize a furnace with a multi-turn flue system?

1). Make a suction channel in each horizontally. channel - with a section of 15-20 cm2.

2). Install suction channels every 0.7 m of the channel length.

As a result, your furnace will become much more efficient: it will melt faster, maintain a stable temperature of the outgoing flue gases and accumulate less soot.

Theoretically, the required amount of air for burning generator, blast furnace and coke oven gases and their mixtures is determined by the formula:

V 0 4.762 / 100 * ((% CO 2 +% H 2) / 2 + 2 ⋅ % CH 4 + 3 ⋅ % C 2 H 4 + 1.5 ⋅ % H 2 S -% O 2), nm 3 / nm 3, where% is by volume.

Theoretically required amount of combustion air natural gas:

V 0 4.762/100* (2 ⋅ % CH 4 + 3.5 ⋅ % C 2 H 6 + 5 ⋅ % C 3 H 8 + 6.5 ⋅ % C 4 H 10 + 8 ⋅ % C 5 H 12), nm 3 / nm 3, where% is by volume.

Theoretically required amount of air for burning solid and liquid fuels:

V 0 \u003d 0.0889 ⋅% C P + 0.265 ⋅% H P - 0.0333 ⋅ (% O P -% S P), nm 3 / kg, where% is by weight.

Actual amount of combustion air

The required completeness of combustion when burning fuel with a theoretically required amount of air, i.e. at V 0 (α = 1), can only be achieved if the fuel is completely mixed with the combustion air and is a ready-made hot (stoichiometric) mixture in gaseous form. This is achieved, for example, when burning gaseous fuels using flameless burners and when burning liquid fuels with their preliminary gasification using special burners.

The actual amount of air for fuel combustion is always greater than the theoretically required one, since in practical conditions some excess air is almost always required for complete combustion. The actual amount of air is determined by the formula:

V α \u003d αV 0, nm 3 / kg or nm 3 / nm 3 of fuel,

where α is the coefficient of excess air.

With the flare method of combustion, when the fuel is mixed with air during the combustion process, for gas, fuel oil and pulverized fuel, the excess air coefficient α = 1.05–1.25. When burning gas, previously completely mixed with air, and when burning fuel oil with preliminary gasification and intensive mixing of fuel oil gas with air, α = 1.00–1.05. With the layered method of burning coal, anthracite and peat in mechanical furnaces with continuous fuel supply and ash removal - α = 1.3–1.4. With manual maintenance of furnaces: when burning anthracite α = 1.4, when burning coal α = 1.5–1.6, when burning brown coal α = 1.6–1.8. For semi-gas furnaces α = 1.1–1.2.

Atmospheric air contains a certain amount of moisture - d g / kg of dry air. Therefore, the volume of moist atmospheric air required for combustion will be greater than that calculated using the above formulas:

V B o \u003d (1 + 0.0016d) ⋅ V o, nm 3 / kg or nm 3 / nm 3,

V B α \u003d (1 + 0.0016d) ⋅ V α, nm 3 / kg or nm 3 / nm 3.

Here 0.0016 \u003d 1.293 / (0.804 * 1000) is the conversion factor for weight units of air moisture, expressed in g / kg of dry air, into volume units - nm 3 of water vapor contained in 1 nm 3 of dry air.

Quantity and composition of combustion products

For generator, blast furnace, coke oven gases and their mixtures, the amount of individual products of complete combustion during combustion with an excess air coefficient equal to α:

Amount of carbon dioxide

V CO2 \u003d 0.01 (% CO 2 + % CO + % CH 4 + 2 ⋅% C 2 H 4), nm 3 / nm 3

The amount of sulfur dioxide

V SO2 \u003d 0.01 ⋅% H 2 S nm 3 / nm 3;

The amount of water vapor

V H2O \u003d 0.01 (% H 2 + 2 ⋅ % CH 4 + 2 ⋅ % C 2 H 4 +% H 2 S +% H 2 O + 0.16d ⋅ V α), nm 3 / nm 3,

where 0.16d V Bá nm 3 /nm 3 is the amount of water vapor introduced by moist atmospheric air at its moisture content d g / kg of dry air;

The amount of nitrogen passing from the gas and introduced with air

The amount of free oxygen introduced by excess air

V O2 \u003d 0.21 (α - 1) ⋅ V O, nm 3 / nm 3.

The total amount of combustion products of generator, blast furnace, coke oven gases and their mixtures is equal to the sum of their individual components:

V dg \u003d 0.01 (% CO 2 + % CO + % H 2 + 3 ⋅ % CH 4 + 4 ⋅ % C 2 H 4 + 2 ⋅ % H 2 S + % H 2 O + % N 2) + + V O (α + 0.0016 dα - 0.21), nm 3 / nm 3.

For natural gas, the amount of individual products of complete combustion is determined by the formulas:

V CO2 \u003d 0.01 (% CO 2 +% CH 4 + 2 ⋅ % C 2 H 6 + 3 ⋅ % C 3 H 8 + 4 ⋅ % C 4 H 10 + 5 ⋅ % C 5 H 12) nm 3 / nm 3;

V H2O \u003d 0.01 (2 ⋅ % CH 4 + 3 ⋅ % C 2 H 6 + 4 ⋅ % C 3 H 8 + 5 ⋅ % C 4 H 10 + 6 ⋅ % C 5 H 12 + % H 2 O + 0.0016d V α) nm 3 /nm 3;

V N2 \u003d 0.01 ⋅% N 2 + 0.79 V α, nm 3 / nm 3;

V O2 \u003d 0.21 (α - 1) V O, nm 3 / nm 3.

Total amount of combustion products of natural gas:

V dg \u003d 0.01 (% CO 2 + 3 ⋅ % CH 4 + 5 ⋅ % C 2 H 6 +7 ⋅ % C 3 H 8 + 9 ⋅ % C 4 ⋅ H 10 + 11 ⋅ % C 5 H 12 + %H 2 O + +% N 2) + V O (α + 0.0016dα - 0.21), nm 3 / nm 3.

For solid and liquid fuels, the number of individual products of complete combustion:

V CO2 \u003d 0.01855% C P, nm 3 / kg (hereinafter, % is the percentage of elements in the working gas by mass);

V SO2 \u003d 0.007% S P nm 3 / kg.

For solid and liquid fuels

V H2O CHEM \u003d 0.112 ⋅% H P, nm 3 / kg,

where V H2O CHEM - water vapor formed during the combustion of hydrogen.

V H2O MEX \u003d 0.0124% W P, nm 3 / kg,

where V H2O MEX - water vapor formed during the evaporation of moisture in the working fuel.

If steam is supplied to atomize liquid fuel in the amount of W PAR kg/kg of fuel, then the amount of 1.24 W PAR nm 3 /kg of fuel must be added to the volume of water vapor. The moisture introduced by atmospheric air at a moisture content of d g / kg of dry air is 0.0016 d V á nm 3 / kg of fuel. Therefore, the total amount of water vapor:

V H2O \u003d 0.112 ⋅ % H P + 0.0124 (% W P + 100 ⋅ % W PAR) + 0.0016d V á, nm 3 / kg.

V N2 \u003d 0.79 ⋅ V α + 0.008 ⋅% N P, nm 3 / kg

V O2 \u003d 0.21 (α - 1) V O, nm 3 / kg.

The general formula for determining the products of combustion of solid and liquid fuels:

Vdg \u003d 0.01 + V O (α + + 0.0016 dα - 0.21) nm 3 / kg.

The volume of flue gases during the combustion of fuel with a theoretically required amount of air (V O nm 3 /kg, V O nm 3 / nm 3) is determined by the above calculation formulas with an excess air coefficient equal to 1.0, while oxygen will be absent in the combustion products.

GAS, furnace and flue gas. 1) Flue gases are the products of combustion of fuel in the furnace. Distinguish between complete and incomplete combustion of fuel. In complete combustion, the following reactions take place:

It must be borne in mind that SO 2 - sulfur dioxide - is not, in fact, a product of the complete combustion of sulfur; the latter is also possible according to the equation:

Therefore, when people talk about complete and incomplete combustion of fuel, they mean only carbon and hydrogen fuel. Reactions that sometimes take place during very incomplete combustion are also not noted here, when the combustion products, in addition to carbon monoxide CO, contain hydrocarbons C m H n, hydrogen H 2, carbon C, hydrogen sulfide H 2 S, since such combustion of fuel should not have a place in practice. So, combustion can be practically considered complete if the combustion products do not contain other gases, except for carbon dioxide CO 2, sulfur dioxide SO 2, oxygen O 2, nitrogen N 2 and water vapor H 2 O. If, in addition to these gases, carbon monoxide CO is contained, then combustion is considered incomplete. The presence of smoke and hydrocarbons in the combustion products gives grounds to speak of an unregulated furnace.

Very big role Avogadro's law plays into the calculations (see Atomic theory): equal volumes of gases, both simple and complex, at the same temperatures and pressures, contain the same number of molecules, or, which is the same: the molecules of all gases at equal pressures and temperatures occupy equal volumes. Using this law and knowing the chemical composition of the fuel, it is easy to calculate the amount of K 0 kg of oxygen theoretically necessary for the complete combustion of 1 kg of fuel of a given composition, according to the following formula:

where C, H, S and O express the content of carbon, hydrogen, sulfur and oxygen in % of the weight of the working fuel. The amount G 0 kg of dry air, theoretically required for the oxidation of 1 kg of fuel, is determined by the formula:

Reduced to 0° and 760 mmHg, this amount can be expressed in m 3 by the following formula:

D. I. Mendeleev proposed very simple and practical relationships that give the result with sufficient accuracy for approximate calculations:

where Q is a slave. - the lowest heat output of 1 kg of working fuel. In practice, the air consumption during fuel combustion is higher than theoretically required. The ratio of the amount of air that actually enters the furnace to the amount of air theoretically required is called the excess coefficient and is denoted by the letter α. The value of this coefficient in the furnace α m depends on the design of the furnace, the dimensions of the furnace space, the location of the heating surface relative to the furnace, the nature of the fuel, the attentiveness of the work of the stoker, etc. 2 and more - manual fireboxes for flame fuel without secondary air intake. The composition and amount of flue gases depend on the value of the excess air coefficient in the furnace. When accurately calculating the composition and amount of flue gases, one should also take into account the moisture introduced with the air due to its humidity, and the water vapor consumed by the blast. The first is taken into account by introducing a coefficient, which is the ratio of the weight of water vapor contained in the air to the weight of dry air, and can be. called the coefficient of humidity. The second is taken into account by the value of W f. , which is equal to the amount of steam in kg entering the furnace, related to 1 kg of fuel burned. Using these notations, the composition and amount of flue gases during complete combustion can be determined from the table below.

It is usually customary to take into account H 2 O water vapor separately from dry gases CO 2, SO 2, O 2, N 2 and CO, and the composition of the latter is calculated (or determined experimentally) in% by volume of dry gases.

When calculating new installations, the desired composition of the combustion products CO 2, SO 2, CO, O 2 and N 2, and these values ​​​​are considered: fuel composition (C, O, H, S), excess air coefficient α and loss from chemical incomplete combustion Q3. The last two values ​​are set on the basis of test data from similar installations or are taken by assessment. The greatest losses from chemical incompleteness of combustion are obtained in manual furnaces for fiery fuel, when Q 3 reaches a value of 0.05Q pa. No loss from chemical incomplete combustion (Q 3 = 0) can be obtained in well-functioning manual anthracite, oil and pulverized fuel furnaces, as well as in properly designed mechanical and mine furnaces. In an experimental study of existing furnaces, they resort to gas analysis, and most often they use the Orsa device (see Gas Analysis), which gives the composition of gases in% by volume of dry gases. The first reading on the Orsa device gives the sum of CO 2 + SO 2, since the solution of caustic potash KOH, designed to absorb carbon dioxide, simultaneously absorbs sulfur dioxide SO 2. The second reading, after flushing the gas in the second siphon, where the reagent for oxygen absorption is located, gives the sum of CO 2 +SO 2 +O 2 . Their difference gives the oxygen content O 2 in% of the volume of dry gases. All other quantities are found by jointly solving the above equations. In this case, it must be borne in mind that equation (10) gives the value of Z, which can be. called the characteristic of incomplete combustion. This formula includes the coefficient β determined by formula (8). Since the coefficient β depends only on chemical composition fuel, and the latter in the process of fuel combustion changes all the time due to the gradual coking of the fuel and its non-simultaneous burnout constituent parts, then the value of Z can give a correct picture of the process taking place in the furnace only on condition that the values ​​(CO 2 + SO 2) and (CO 2 + SO 2 + O 2) are the result of the analysis of continuously taken average samples over a certain sufficiently long period of time. It is by no means possible to judge the incompleteness of combustion by individual single samples taken at any arbitrary moment. Knowing the composition of the combustion products and elemental analysis of the fuel, it is possible to determine the volume of combustion products conventionally referred to 0° and 760 mmHg using the following formulas. Denoting by V n.o. total volume of combustion products 1 kg of fuel, V c.g. - the volume of dry gases, a V c.n. - the volume of water vapor, we will have:

combustion products in an arbitrary section of the gas duct, but such a widespread interpretation is incorrect. Based on the Boyle-Marriott-Gay-Lussac law, the volume of combustion products at temperature t and barometric pressure P b. found by the formula:

If we denote by G n.c. weight of combustion products, G c.g. - weight of dry gases, C w.p. is the weight of water vapor, then we will have the following relations:

2) Flue gases. On the way from the furnace to the chimney, air is added to the flue gases, which is sucked in through leaks in the lining of the gas ducts. Therefore, the gases at the entrance to the chimney (called flue gases) have a composition different from the composition of flue gases, since they are a mixture of combustion products of fuel in the furnace and air sucked in the flues along the way from the furnace to the chimney inlet.

The amount of air suction in practice is very different and depends on the design of the masonry, its density and size, on the magnitude of the rarefaction in the gas ducts and many other reasons, fluctuating with good care from 0.1 to 0.7 theoretically necessary. If we designate the coefficient of excess air in the furnace through α m. , and the coefficient of excess air of gases leaving the chimney, through α у. , That

The determination of the composition and amount of flue gases is carried out according to the same formulas as for the determination of flue gases; the difference is only in the numerical value of the excess air coefficient α, on which, of course, the % composition of gases depends. In practice, very often the term "flue gases" is generally understood as combustion products in an arbitrary section of the gas duct, but such a widespread interpretation is incorrect.

Positive traits:

higher than air heat transfer to heat exchange surfaces (due to the greater emissivity of particles of combustion products).

Negative qualities:

Consequences:

The use of flue gases as a heat carrier is possible only when intermediate heat exchangers are used to heat the heat carrier supplied directly to the consumer;

· the utilization (saving and use) of the heat of exhaust flue gases is ensured;

In the presence of substances with high corrosive activity (for example, sulfur compounds), the durability of heat pipes and heat exchange devices is sharply reduced;

· When the flue gases are cooled below the dew point, condensation may occur and, as a result, dampening of structures and the formation of icing in winter.

Classification of heating furnaces:

By heat capacity:

· Non-heat-intensive

I have low thermal inertia. They heat the room only in the process of burning fuel. Designed for short term heating. These ovens include:

1) metal (made of steel or cast iron)

2) ovens made of a small number of bricks (up to 300 pieces),

3) fireplaces (brick niches for open burning of fuel).

· Heat-intensive

They have great thermal inertia. The material of the furnace accumulates heat and after the end of the combustion of the fuel transfers it to the room for a long time (up to 12 hours). Used for continuous space heating.

Heat-intensive furnaces are structurally different in flue gas flow diagram

· ducted . The movement of gases is carried out through internal channels, which can be connected in parallel or in series.

· Channelless (bell-type). The movement of gases is carried out freely, and at the end of the furnace, the furnace does not cool down, since hot flue gases accumulate above the entrance to the chimney. The upper zone is somewhat overheated.

· Combined . Flue gases before entering the hood pass through the channels located below the furnace, which allows you to warm up the lower zone and achieve a more uniform temperature distribution in the room.