Create a cozy and comfortable atmosphere in country house quite simple - you just need to properly equip the heating system. The main component of an efficient and reliable heating system is the boiler. In the article below we will talk about how to calculate the efficiency of a boiler, what factors influence it and how to increase efficiency heating equipment in the conditions of a particular home.
How to choose a boiler
Of course, in order to determine how efficient a particular hot water boiler will be, it is necessary to determine its efficiency (efficiency factor). This indicator represents the ratio of the heat used to heat the room to the total amount of thermal energy generated.
The formula for calculating efficiency looks like this:
ɳ=(Q 1 ÷Q ri),
where Q 1 is heat used efficiently;
Q ri – total released heat.
What is the relationship between boiler efficiency and load
At first glance it may seem that the more fuel is burned, the better the boiler works. However, this is not quite true. The dependence of the boiler efficiency on the load is just the opposite. The more fuel is burned, the more thermal energy is released. At the same time, the level of heat loss also increases, since chimney highly heated flue gases escape. Consequently, fuel is consumed inefficiently.
The situation develops in a similar way in cases where the heating boiler operates at reduced power. If it falls short of the recommended values by more than 15%, the fuel will not burn completely, and the amount flue gases will increase. As a result, the efficiency of the boiler will drop quite significantly. This is why you should adhere to the recommended boiler power levels - they are designed to operate the equipment as efficiently as possible.
Calculation of efficiency taking into account various factors
The above formula is not entirely suitable for assessing the efficiency of equipment, since it is very difficult to accurately calculate the boiler efficiency taking into account only two indicators. In practice, a different, more complete formula is used during the design process, since not all of the heat generated is used to heat the water in the heating circuit. A certain amount of heat is lost during the operation of the boiler.
A more accurate calculation of boiler efficiency is made using the following formula:
ɳ=100-(q 2 +q 3 +q 4 +q 5 +q 6), in which
q 2 – heat loss from escaping flammable gases;
q 3 – heat loss as a result incomplete combustion combustion products;
q 4 – heat loss due to underburning of fuel and ash precipitation;
q 5 – losses caused by external cooling of the device;
q 6 – heat loss along with slag removed from the furnace.
Heat loss when removing flammable gases
The most significant heat losses occur as a result of the evacuation of flammable gases into the chimney (q 2). The efficiency of the boiler largely depends on the combustion temperature of the fuel. The optimal temperature pressure at the cold end of the water heater is achieved when heated to 70-110 ℃.
When the temperature of the exhaust combustible gases drops by 12-15 ℃, the efficiency of the water heating boiler increases by 1%. However, in order to reduce the temperature of the exhaust combustion products, it is necessary to increase the size of the heated surfaces, and, therefore, the entire structure as a whole. Moreover, when cooling carbon monoxide the risk increases low temperature corrosion.
Among other things, the temperature of carbon monoxide also depends on the quality and type of fuel, as well as the heating of the air entering the firebox. The temperatures of incoming air and exiting combustion products depend on the type of fuel.
To calculate the heat loss rate with flue gases, use the following formula:
Q 2 = (T 1 -T 3) × (A 2 ÷ (21-O 2) + B), where
T 1 – temperature of evacuated flammable gases at the point behind the superheater;
T 3 – temperature of air entering the furnace;
21 – oxygen concentration in the air;
O 2 – amount of oxygen in the exhaust combustion products at the control point;
A 2 and B are coefficients from a special table that depend on the type of fuel.
Chemical underburning as a source of heat loss
Indicator q 3 is used when calculating efficiency gas boiler heating, for example, or in cases where fuel oil is used. For gas boilers, the value of q 3 is 0.1-0.2%. With a slight excess of air during combustion, this figure is 0.15%, and with a significant excess of air it is not taken into account at all. However, when burning a mixture of gases of different temperatures, the value of q 3 = 0.4-0.5%.
If the heating equipment runs on solid fuel, the indicator q 4 is taken into account. In particular, for anthracite coal the value of q 4 = 4-6%, semi-anthracite is characterized by 3-4% heat loss, but when burning hard coal, only 1.5-2% heat loss is formed. For liquid slag removal of burned low-reaction coal, the value of q4 can be considered minimal. But when removing slag in solid form, heat loss will increase to the maximum limit.
Heat loss due to external cooling
Such heat losses q5 usually amount to no more than 0.5%, and as the power of the heating equipment increases, they are reduced even more.
This indicator is related to the calculation of the steam output of the boiler plant:
- Provided the steam output D is within the range of 42-250 kg/s, the value of heat loss q5=(60÷D)×0.5÷lgD;
- If the value of steam production D exceeds 250 kg/s, the level of heat loss is considered equal to 0.2%.
Amount of heat loss from slag removal
The heat loss value q6 is only significant for liquid slag removal. But in cases where slag is removed from the combustion chamber solid fuel, heat loss q6 is taken into account when calculating the efficiency of heating boilers only in cases where they are more than 2.5Q.
How to calculate the efficiency of a solid fuel boiler
Even with an ideally designed design and high-quality fuel, the efficiency of heating boilers cannot reach 100%. Their work is necessarily associated with certain heat losses caused by both the type of fuel burned and the number of external factors and conditions. To understand how calculating the efficiency of a solid fuel boiler looks like in practice, let’s give an example.
For example, heat loss from removing slag from the fuel chamber will be:
q 6 =(A shl ×Z l ×A r)÷Q ri,
where A slag is the relative value of the slag removed from the furnace to the volume of loaded fuel. If the boiler is used correctly, the share of combustion waste in the form of ash is 5-20%, then given value may be equal to 80-95%.
Z l – the thermodynamic potential of ash at a temperature of 600 ℃ under normal conditions is 133.8 kcal/kg.
A p is the ash content of the fuel, which is calculated on total weight fuel. IN various types of fuel, the ash content ranges from 5% to 45%.
Q ri is the minimum amount of thermal energy that is generated during fuel combustion. Depending on the type of fuel, the heat capacity ranges from 2500-5400 kcal/kg.
In this case, taking into account the indicated values, heat loss q 6 will be 0.1-2.3%.
The value of q5 will depend on the power and design performance of the heating boiler. Job modern installations With low power, which are very often used to heat private houses, is usually associated with heat losses of this type in the range of 2.5-3.5%.
Heat loss associated with mechanical underburning of solid fuel q 4 largely depends on its type, as well as on design features boiler They range from 3-11%. This is worth considering if you are looking for a way to make your boiler work more efficiently.
Chemical underburning of fuel usually depends on the concentration of air in the combustible mixture. Such heat losses q 3 are usually equal to 0.5-1%.
The largest percentage of heat loss q 2 is associated with the loss of heat along with flammable gases. This indicator is influenced by the quality and type of fuel, the degree of heating of combustible gases, as well as operating conditions and design of the heating boiler. With an optimal thermal design of 150 ℃, evacuable carbon monoxide should be heated to a temperature of 280 ℃. In this case, this value of heat loss will be equal to 9-22%.
If all the listed loss values are summed up, we get the efficiency value ɳ=100-(9+0.5+3+2.5+0.1)=84.9%.
This means that a modern boiler can only operate at 85-90% power. Everything else goes to ensure the combustion process.
Note that achieving such high values is not easy. To do this, you need to competently approach the selection of fuel and provide equipment with optimal conditions. Manufacturers usually indicate what load the boiler should operate with. In this case, it is desirable that most of the time it is set to an economical load level.
To operate the boiler with maximum efficiency, it must be used taking into account the following rules:
- Periodic cleaning of the boiler is required;
- it is important to control the intensity of combustion and the completeness of fuel combustion;
- it is necessary to calculate the draft taking into account the pressure of the supplied air;
- calculation of the ash fraction is necessary.
The quality of solid fuel combustion is positively affected by the calculation of optimal draft taking into account the air pressure supplied to the boiler and the rate of carbon monoxide evacuation. However, as air pressure increases, more heat is removed into the chimney along with combustion products. But too little pressure and limited access of air into the fuel chamber leads to a decrease in combustion intensity and greater ash formation.
If you have a heating boiler installed at home, pay attention to our recommendations for increasing its efficiency. You can not only save on fuel, but also achieve a comfortable microclimate in your home.
Boiler efficiency gross characterizes the efficiency of using the heat entering the boiler and does not take into account the cost of electrical energy to drive blower fans, smoke exhausters, feed pumps and other equipment. When running on gas
h br k = 100 × Q 1 / Q c n. (11.1)
Energy consumption for the boiler installation’s own needs is taken into account by the boiler efficiency net
h n k = h br k – q t – q e, (11.2)
Where q t, q e– relative costs for own needs of heat and electricity, respectively. Heat consumption for own needs includes heat loss with blowing, for blowing screens, spraying fuel oil, etc.
The main ones are heat losses due to blowing
q t = G pr × (h c.v – h p.v) / (B × Q c n) .
Relative electricity consumption for own needs
q el = 100 × (N p.n /h p.n + N d.v /h d.v + N d.s /h d.s)/(B × Q c n) ,
where N p.n, N d.v, N d.s – electrical energy consumption for driving feed pumps, blower fans and smoke exhausters, respectively; h p.n, h d.v, h d.s - efficiency of feed pumps, blower fans and smoke exhausters, respectively.
11.3. Methodology for performing laboratory work
and processing of results
Balance tests in laboratory work are carried out for the stationary operating mode of the boiler when performing the following mandatory conditions:
The duration of operation of the boiler installation from lighting to the start of testing is at least 36 hours,
The duration of withstanding the test load immediately before the test is 3 hours,
Permissible load fluctuations during the break between two adjacent experiments should not exceed ±10%.
Parameter values are measured using standard instruments installed on the boiler panel. All measurements must be carried out simultaneously at least 3 times with an interval of 15-20 minutes. If the results of two experiments of the same name differ by no more than ±5%, then their arithmetic mean is taken as the measurement result. If the relative discrepancy is greater, the measurement result in the third, control experiment is used.
The results of measurements and calculations are recorded in a protocol, the form of which is given in table. 26.
Table 26
Determination of heat loss from a boiler
| Parameter name | Designation | Unit measured | Experimental results | |||
| №1 | №2 | №3 | Average | |||
| Flue gas volume | V g | m 3 /m 3 | ||||
| Average volumetric heat capacity of flue gases | C g¢ | kJ/ (m 3 K) | ||||
| Flue gas temperature | J | °C | ||||
| Heat loss with flue gases | Q 2 | MJ/m 3 | ||||
| Volume of 3-atomic gases | VRO 2 | m 3 /m 3 | ||||
| Theoretical nitrogen volume | V° N 2 | m 3 /m 3 | ||||
| Excess oxygen in flue gases | a y | --- | ||||
| Theoretical air volume | V° in | m 3 /m 3 | ||||
| Dry gas volume | V сг | m 3 /m 3 | ||||
| Volume of carbon monoxide in flue gases | CO | % | ||||
| Heat of combustion CO | Q CO | MJ/m 3 | ||||
| Volume of hydrogen in flue gases | H 2 | % | ||||
| Heat of combustion H 2 | QH 2 | MJ/m 3 | ||||
| Volume of methane in flue gases | CH 4 | % | ||||
| Heat of combustion CH 4 | Q CH 4 | MJ/m 3 | ||||
| Heat loss from chemical incomplete combustion | Q 3 | MJ/m 3 | ||||
| q 5 | % | |||||
| Heat loss from external cooling | Q 5 | MJ/m 3 |
End of table. 26
Table 27
Boiler efficiency gross and net
| Parameter name | Designation | Unit measured | Experimental results | |||
| №1 | №2 | №3 | Average | |||
| Electrical consumption energy to drive feed pumps | N p.n. | |||||
| Electrical consumption energy for driving blower fans | N d.in | |||||
| Electrical consumption energy for driving smoke exhausters | N d.s | |||||
| Efficiency of feed pumps | h Mon | |||||
| Efficiency of blower fans | h door | |||||
| Efficiency of smoke exhausters | h dm | |||||
| Relative electric consumption energy for own needs | q el | |||||
| Net boiler efficiency | h net k | % |
Analysis of laboratory results
The value of h br k obtained as a result of the work using the method of direct and reverse balances must be compared with the certified value of 92.1%.
Analyzing the effect on the boiler efficiency of the amount of heat loss with flue gases Q 2, it should be noted that an increase in efficiency can be achieved by reducing the temperature of the flue gases and reducing the excess air in the boiler. At the same time, a decrease in gas temperature to the dew point temperature will lead to condensation of water vapor and low-temperature corrosion of heating surfaces. A decrease in the excess air coefficient in the furnace can lead to underburning of fuel and an increase in Q 3 losses. Therefore, the temperature and excess air must not be lower than certain values.
Then it is necessary to analyze the impact of its load on the efficiency of the boiler operation, as the load increases, losses with flue gases increase and losses Q 3 and Q 5 decrease.
The laboratory report should make a conclusion about the level of efficiency of the boiler.
- Based on what indicators of boiler operation can a conclusion be made about the efficiency of its operation?
- What is the heat balance of a boiler? By what methods can it be compiled?
- What is meant by gross and net boiler efficiency?
- What heat losses increase during boiler operation?
- How can you increase q 2?
- What parameters have a significant impact on the boiler efficiency?
Keywords: boiler heat balance, boiler gross and net efficiency, corrosion of heating surfaces, excess air coefficient, boiler load, heat loss, exhaust gases, chemical incomplete combustion of fuel, boiler operating efficiency.
CONCLUSION
In the process of performing a laboratory workshop on the course of boiler plants and steam generators, students become familiar with methods for determining the calorific value of combustion liquid fuel, humidity, volatile yield and ash content of solid fuel, the design of the DE-10-14GM steam boiler and the thermal processes occurring in it are studied experimentally.
Future specialists study methods for testing boiler equipment and gain the necessary practical skills needed in determining the thermal characteristics of the firebox, drawing up heat balance boiler, measuring its efficiency, as well as drawing up the salt balance of the boiler and determining the optimal blowdown value.
Bibliography
1. Khlebnikov V.A. Boiler plant equipment testing:
Laboratory workshop. - Yoshkar-Ola: MarSTU, 2005.
2. Sidelkovsky L.N., Yurenev V.N. Boiler installations industrial enterprises: Textbook for universities. – M.: Energoatomizdat, 1988.
3. Trembovlya V.I., Finger E.D., Avdeeva A.A. Thermal testing of boiler installations. - M.: Energoatomizdat, 1991.
4. Aleksandrov A.A., Grigoriev B.A. Tables of thermophysical properties of water and water vapor: Handbook. Rec. State standard reference data service. GSSSD R-776-98. – M.: Publishing house MPEI, 1999.
5. Lipov Yu.M., Tretyakov Yu.M. Boiler installations and steam generators. – Moscow-Izhevsk: Research Center “Regular and Chaotic Dynamics”, 2005.
6. Lipov Yu.M., Samoilov Yu.F., Tretyakov Yu.M., Smirnov O.K. Testing of equipment in the boiler department of the MPEI CHPP. Laboratory workshop: Tutorial on the course “Boiler installations and steam generators”. – M.: Publishing house MPEI, 2000.
7. Roddatis K.F., Poltaretsky A.N. Handbook of low-capacity boiler installations/Ed. K.F. Roddatis. – M.: Energoatomizdat, 1989.
8. Yankelevich V.I. Adjustment of gas-oil industrial boiler houses. – M.: Energoatomizdat, 1988.
9. Laboratory works in the courses “Heat generating processes and installations”, “Boiler installations of industrial enterprises” / Comp. L.M. Lyubimova, L.N. Sidelkovsky, D.L. Slavin, B.A. Sokolov and others / Ed. L.N. Sidelkovsky. – M.: Publishing house MPEI, 1998.
10. Thermal calculation of boiler units (Normative method)/Ed. N.V. Kuznetsova. – M.: Energia, 1973.
11. SNiP 2.04.14-88. Boiler installations/Gosstroy of Russia. – M.: CITP Gosstroy of Russia, 1988.
Educational edition
KHLEBNIKOV Valery Alekseevich
BOILER UNITS
AND STEAM GENERATORS
Laboratory workshop
Editor A.S. Emelyanova
Computer set V.V.Khlebnikov
Computer layout V.V.Khlebnikov
Signed for publication on 02/16/08. Format 60x84/16.
Offset paper. Offset printing.
Conditional p.l. 4.4. Uch.ed.l. 3.5. Circulation 80 copies.
Order No. 3793. S – 32
Mari State Technical University
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Editorial and Publishing Center
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In 2020, it is planned to produce 1720-1820 million Gcal.
A milligram equivalent is the amount of a substance in milligrams that is numerically equal to the ratio of its molecular weight to the valency in a given compound.
The heat released during fuel combustion cannot be completely used to produce steam or hot water, some of the heat is inevitably lost, dissipating in the environment. The heat balance of a boiler unit is a specific formulation of the law of conservation of energy, which asserts the equality of the amount of heat introduced into the boiler unit and the heat expended on the production of steam or hot water, taking into account losses. In accordance with the “Standard Method”, all values included in the heat balance are calculated per 1 kg of burned fuel. The incoming part of the heat balance is called available heat :
Where Q- - lower heating value of fuel, kJ/kg; c T t T - physical heat of fuel (with t - heat capacity of fuel, / t - fuel temperature), kJ/kg; Q B - heat of air entering the furnace when heated outside the unit, kJ/kg; Q n - heat introduced into the boiler unit with steam used for atomizing fuel oil, external blowing of heating surfaces or supply under the grate during layer combustion, kJ/kg.
When using gaseous fuel, the calculation is performed relative to 1 m 3 of dry gas under normal conditions.
Physical heat of the fuel plays a significant role only when preheating the fuel outside the boiler unit. For example, fuel oil is heated before being supplied to the burners, since it has a high viscosity at low temperatures.
Air heat, kJ/ (kg fuel):
where a t is the coefficient of excess air in the furnace; V 0 H - in theory required amount air, n.m 3 /kg; from to - isobaric heat capacity of air, kJ/(n.m 3 K); / x in - cold air temperature, °C; t B - air temperature at the entrance to the furnace, °C.
Heat introduced with steam, kJDkgfuel):
Where G n - specific consumption blown steam (approximately 0.3 kg of steam per 1 kg of fuel oil is consumed for atomizing fuel oil); / p = 2750 kJ/kg - the approximate value of the enthalpy of water vapor at the temperature of the combustion products leaving the boiler unit (about 130 °C).
In approximate calculations, 0 r is taken ~Q? due to the smallness of the other components of equation (22.2).
The consumption part of the heat balance consists of useful heat (production of steam or hot water) and the amount of losses, kJDkgfuel):
where 0 2 - heat loss with gases leaving the boiler unit;
- 03 - heat loss from chemical incomplete combustion of fuel;
- 0 4 - heat loss from mechanical incomplete combustion of fuel;
- 0 5 - heat loss through the lining in environment; 0 6 - losses with physical heat of slag removed from the boiler unit.
The heat balance equation is written as
As a percentage of available heat, equation (22.6) can be written:
The usefully used heat in a steam boiler with continuous blowing of the upper drum is determined by the equation, kJDkgfuel):
Where D- boiler steam output, kg/s; Dnp- flow rate of purge water kg/s; IN - fuel consumption, kg/s; / p, / p w, / k w - enthalpy of steam, feed and boiler water at pressure in the boiler, respectively, kJ/kg.
Heat loss with flue gases, kJ/(kg fuel):
Where s g And from to- isobaric heat capacity of combustion products and air, kJ/(n.m 3 K); g - flue gas temperature, °C; ax is the coefficient of excess air at the gas outlet from the boiler unit; K 0 G and V 0- theoretical volume of combustion products and theoretically required amount of air, n.m 3 / (kgfuel).
A vacuum is maintained in the gas ducts of the boiler unit; the volumes of gases as they move along the gas path of the boiler increase due to air suction through leaks in the boiler lining. Therefore, the actual coefficient of excess air at the outlet of the boiler unit ax is greater than the coefficient of excess air in the furnace a. It is determined by summing the coefficient of excess air in the firebox and air suction in all flues. In the practice of operating boiler plants, it is necessary to strive to reduce air suction in gas ducts as one of the most effective means combating heat loss.
Thus, the amount of loss Q 2 determined by the temperature of the exhaust gases and the value of the excess air coefficient ax. IN modern boilers the temperature of the gases behind the boiler does not fall below 110 °C. A further decrease in temperature leads to condensation of water vapor contained in gases and the formation of sulfuric acid during combustion of sulfur-containing fuel, which accelerates the corrosion of metal surfaces of the gas path. The minimum losses with flue gases are q 2 ~ 6-7%.
Losses from chemical and mechanical incomplete combustion are characteristics of combustion devices (see clause 21.1). Their value depends on the type of fuel and combustion method, as well as on the perfect organization of the combustion process. Losses from chemical incomplete combustion in modern furnaces amount to q 3 = 0.5-5%, from mechanical - q 4 = 0-13,5%.
Heat loss to the environment q 5 depend on the boiler power. The higher the power, the less relative value losses q 5 . So, with the steam output of the boiler unit D= 1 kg/s losses are 2.8%, with D= 10 kg/s q 5 ~ 1%.
Heat loss with physical heat of slag q b are small and are usually taken into account when drawing up an accurate heat balance,%:
Where a shl = 1 - a un; a un - share of ash in flue gases; with went and? shl - heat capacity and temperature of the slag; A g - ash content of the operating state of the fuel.
Efficiency factor (Efficiency) of the boiler unit is the ratio of the useful heat of combustion of 1 kg of fuel to produce steam in steam boilers or hot water in hot water boilers to the available heat.
Boiler efficiency, %:
The efficiency of boiler units depends significantly on the type of fuel, combustion method, flue gas temperature and power. Steam boilers, operating on liquid or gaseous fuel, have an efficiency of 90-92%. During layer combustion of solid fuel efficiency equals 70-85%. It should be noted that the efficiency of boiler units significantly depends on the quality of operation, especially on the organization of the combustion process. Operating a boiler unit with steam pressure and output less than nominal reduces efficiency. During the operation of boilers, thermal technical tests must be periodically carried out in order to determine losses and the actual efficiency of the boiler, which allows making the necessary adjustments to its operating mode.
Fuel consumption for a steam boiler (kg/s - for solid and liquid fuel; n.m 3 /s - gaseous)
Where D- steam output of the boiler unit, kg/s; / p, / p v, / k v - enthalpy of steam, feed and boiler water, respectively, kJ/kg; Q p - available heat, kJ/(kg fuel) - for solid and liquid fuels, kJ/(N.m 3) - for gaseous fuel (often taken in calculations Q p ~ Q- due to their slight differences); P is the value of continuous blowing, % of steam production; g| ka - efficiency of the cola unit, fraction.
Fuel consumption for hot water boiler (kg/s; n.m 3 /s):
where C in - water consumption, kg/s; /, / 2 - initial and final enthalpies of water in the boiler, kJ/kg.
BOILER EFFICIENCY COEFFICIENT
(Boiler efficiency) - the ratio of the amount of heat transferred to the boiler water to convert it into steam during combustion 1 kg fuel, to the calorific value of the fuel, i.e. the amount of heat that is released during complete combustion 1 kg fuel. The efficiency of boilers reaches values of the order of 0.60-0.85.
Samoilov K. I. Marine dictionary. - M.-L.: State Naval Publishing House of the NKVMF of the USSR, 1941
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Heating equipment that runs on solid fuel is represented today by a whole group of devices. Every solid fuel boiler produced today by domestic and foreign manufacturing companies is a completely new, high-tech heating device. Thanks to the introduction of technical innovations and automatic control devices into the design of heating devices, it was possible to significantly increase efficiency and optimize the operation of solid fuel boilers.
Heating devices of this type use a traditional principle of operation, similar to the variant that is well known to us stove heating. The main action is due to the process of generating thermal energy released during the combustion of coal, coke, firewood and other fuel resources in the boiler furnace, followed by heat transfer to the coolant.
Like other devices that provide energy generation, transmission, boiler equipment has its own efficiency factor. Let us consider in more detail what the efficiency of units operating on solid fuel is. We will try to find answers to questions related to these parameters.
What is the efficiency of heating devices
For any heating unit whose task is to heat the interior space of residential buildings and structures for various purposes, an important component there was, is and remains operational efficiency. The parameter that determines the efficiency of solid fuel boilers is the efficiency factor. Efficiency shows the ratio of the expended thermal energy produced by the boiler during the combustion of solid fuel to the useful heat supplied to the entire heating system.
This ratio is expressed as a percentage. The better the boiler works, the higher the interest. Among modern solid fuel boilers there are models with high efficiency, high-tech, efficient and economical units.
For reference: As a rough example, one should evaluate the thermal effect obtained by sitting near a fire. Emitted when burning wood thermal energy capable of heating limited space and objects around the fire. Most of the heat from a burning fire (up to 50-60%) goes into the atmosphere, providing no benefit other than aesthetic content, while neighboring objects and air receive a limited amount of kilocalories. The efficiency of a fire is minimal.
The efficiency of heating equipment strongly depends on what type of fuel is used and what design features devices. 
For example: when burning coal, wood or pellets, it releases different quantities thermal energy. Efficiency largely depends on the technology of fuel combustion in the combustion chamber and the type of heating system. In other words, every type heating devices(traditional solid fuel boilers, units long burning, pellet boilers and devices operating by pyrolysis), has its own technological features designs that affect efficiency parameters.
Operating conditions and quality of ventilation also affect the efficiency of boilers. Poor ventilation causes a lack of air necessary for the high intensity of the combustion process of the fuel mass. Not only the level of comfort during interior spaces, but also the efficiency of heating equipment, the performance of the entire heating system.
The accompanying documentation for the heating boiler must contain the equipment efficiency declared by the manufacturer. Compliance of real indicators with the declared information is achieved through correct installation device, strapping and subsequent operation.
Operating rules for boiler devices, compliance with which affects the efficiency value
Any kind heating unit has its own parameters for the optimal load, which should be as useful as possible from a technological and economic point of view. The operation process of solid fuel boilers is designed in such a way that most of the time the equipment operates in optimal mode. This operation can be ensured by following the rules of operation of heating equipment operating on solid fuel. In this case, you must adhere to and follow the following points:
- it is necessary to observe acceptable modes of blowing and exhaust operation;
- constant control over the intensity of combustion and completeness of fuel combustion;
- control the amount of entrainment and failure;
- assessment of the condition of surfaces heated during fuel combustion;
- regular boiler cleaning.
The listed points are the necessary minimum which must be adhered to during operation of boiler equipment in heating season. Compliance with simple and understandable rules will allow you to obtain the efficiency of an autonomous boiler stated in the characteristics.
We can say that every little thing, every element of the design of a heating device affects the value of the efficiency factor. A properly designed chimney and ventilation system ensure optimal air flow into the combustion chamber, which significantly affects the quality of combustion of the fuel product. Ventilation performance is assessed by the excess air coefficient. An excessive increase in the volume of incoming air leads to excessive fuel consumption. Heat leaves more intensely through the pipe along with combustion products. When the coefficient decreases, the operation of boilers deteriorates significantly, and there is a high probability of oxygen-limited zones appearing in the furnace. In this situation, soot begins to form and accumulate in large quantities in the firebox.
The intensity and quality of combustion in solid fuel boilers require constant monitoring. The combustion chamber must be loaded evenly, avoiding focal fires.
On a note: coal or firewood is evenly distributed over the grates or grate. Combustion should occur over the entire surface of the layer. Evenly distributed fuel dries quickly and burns over the entire surface, ensuring complete burnout of the solid components of the fuel mass to volatile combustion products. If you have correctly placed fuel in the firebox, the flame when the boilers are operating will be bright yellow, straw-colored.
During combustion, it is important to prevent failure of the fuel resource, otherwise you will have to face significant mechanical losses (underburning) of fuel. If you do not control the position of the fuel in the firebox, large fragments of coal or firewood falling into the ash box can lead to unauthorized combustion of the remaining fuel mass products.
Soot and resin accumulated on the surface of the heat exchanger reduce the degree of heating of the heat exchanger. As a result of all of the above violations of operating conditions, the useful volume of thermal energy required for the normal operation of the heating system decreases. As a result, we can talk about a sharp decrease in the efficiency of heating boilers.
Factors on which boiler efficiency depends
Boilers with a high efficiency value today are represented by the following heating equipment:
- units running on coal and other solid fossil fuels;
- pellet boilers;
- pyrolysis type devices.
The efficiency of heating devices that fire anthracite, coal and peat briquettes is on average 70-80%. Pellet devices have a significantly higher efficiency – up to 85%. Loaded with pellets, heating boilers of this type are distinguished by high efficiency, a huge amount of thermal energy is released during fuel combustion.
On a note: one load is enough to operate the device at optimal modes for up to 12-14 hours.
The absolute leader among solid fuel heating equipment is the pyrolysis boiler. These appliances use firewood or waste wood. The efficiency of such equipment today is 85% or more. The units also belong to highly efficient long-burning devices, but subject to the necessary conditions - fuel moisture content should not exceed 20%.
An important factor for the efficiency value is the type of material from which it is made. heating device. Today on the market there are models of solid fuel boilers made of steel and cast iron.
For reference: The first includes steel products. To reduce market value unit, manufacturing companies use basic structural elements made of steel. For example, the heat exchanger is made of high-strength, heat-resistant black steel with a thickness of 2-5 mm. The heating tubular elements used to heat the main circuit are manufactured in the same way.
The thicker the steel used in the structure, the higher the heat transfer characteristics of the equipment. The efficiency increases accordingly.
In steel devices, an increase in efficiency is achieved through the installation of special internal partitions in the form of pipes - main flow stages and smoke dissipators. Measures are forced and partial, allowing to slightly increase the efficiency of the main device. Among the models of steel solid fuel boilers, you can rarely find devices with an efficiency above 75%. The service life of such products is 10-15 years.
In order to increase the efficiency of steel heating boilers, foreign companies use a bottom combustion process in their models, with 2 or 3 traction flows. The design of the products provides for the installation of tubular heating elements to improve heat transfer. Such equipment has an efficiency of 75-80%, and can last longer, 1.5 times.
Unlike steel units, cast iron solid fuel units are more efficient.
The design of cast iron units uses heat exchangers made of a special grade of cast iron alloy, which has high heat transfer. Such boilers are most often used for open heating systems heating. The products are additionally equipped with grate bars, thanks to which intensive extraction of thermal energy is carried out directly from the burning fuel placed on the grate bar.
The efficiency of such heating devices is 80%. The long service life of cast iron boilers should be taken into account. The service life of such equipment is 30-40 years.
How to increase the efficiency of heating equipment running on solid fuels
Today, many consumers, having at their disposal a solid fuel boiler, try to find the most convenient and practical way how to increase the efficiency of heating equipment. The technological parameters of heating devices laid down by the manufacturer lose their nominal values over time, therefore, to increase the efficiency of boiler equipment, efforts are being made to various ways and funds.
Let's consider one of the most spectacular options, installation of an additional heat exchanger. The task of the new equipment is to remove thermal energy from volatile combustion products.
In the video you can see how to make your own economizer (heat exchanger)
To do this, we first need to know what the temperature of the smoke at the outlet is. You can change it using a multimeter, which is placed directly in the middle of the chimney. Data on how much additional heat can be obtained from evaporating combustion products is necessary to calculate the area of the additional heat exchanger. We do the following:
- we send a certain amount of firewood into the firebox;
- We measure how long it takes for a certain amount of firewood to burn.
For example: firewood, in the amount of 14.2 kg. burn for 3.5 hours. The smoke temperature at the boiler outlet is 460 0 C.
In 1 hour we burned: 14.2/3.5 = 4.05 kg. firewood
To calculate the amount of smoke, we use the generally accepted value of 1 kg. firewood = 5.7 kg. flue gases. Next, we multiply the amount of wood burned in one hour by the amount of smoke produced by burning 1 kg. firewood As a result: 4.05 x 5.7 = 23.08 kg. volatile combustion products. This figure will become Starting point for subsequent calculations of the amount of thermal energy that can be additionally used to heat the second heat exchanger.
Knowing the value of the heat capacity of volatile hot gases as 1.1 kJ/kg, we make a further calculation of the heat flow power if we want to reduce the smoke temperature from 460 0 C to 160 degrees.
Q = 23.08 x 1.1 (460-160) = 8124 kJ thermal energy.
As a result, we obtain the exact value of the additional power provided by volatile combustion products: q = 8124/3600 = 2.25 kW, a large figure that can have a significant impact on increasing the efficiency of heating equipment. Knowing how much energy is wasted, the desire to equip the boiler with an additional heat exchanger is completely justified. Due to the influx of additional thermal energy for heating the coolant, not only the efficiency of the entire heating system increases, but also the efficiency of the heating unit itself increases.
conclusions
Despite the abundance of models of modern heating equipment, solid fuel boilers continue to remain one of the most effective and affordable types of heating equipment. Compared to electric boilers, which have an efficiency of up to 90%, solid fuel units have high economic effect. The increase in efficiency on new models has allowed this type of boiler equipment to come closer to electric and gas boilers.
Modern solid fuel devices are capable of not only operating for a long time using affordable natural fuel resources, but also have high performance characteristics.
