Normalized boiler efficiency. What is the boiler efficiency? How to increase the efficiency of solid fuel heating equipment

The thermal efficiency of boiler equipment is indicated in the efficiency factor. The efficiency of a gas boiler must be prescribed in the technical documentation. According to manufacturers, for some models of boilers, the coefficient reaches 108-109%, while others operate at the level of 92-98%.

How to calculate the efficiency of a gas heating boiler

η = (Q1/Qri) 100%

In the formula for calculating the efficiency of a gas-fired boiler, the indicated values ​​​​mean:

• Qri is the total amount of thermal energy released during fuel combustion.
• Q1 is the heat that was accumulated and used to heat the room.

An assessment of the error in determining the thermal efficiency is carried out on site. For calculations, another formula is used:

η=100 - (q2 + q3 + q4 + q5 + q6)

Calculations help to analyze, according to the characteristics of a particular heating system. Abbreviations in the formula mean:

• q2 - heat losses in exhaust gases and combustion products.
• q3 - losses associated with incorrect proportions of the gas-air mixture, due to which gas underburning occurs.
• q4 - heat losses associated with the appearance of soot on the burners and heat exchanger, as well as mechanical underburning.
• q5 - heat loss, depending on the outside temperature.
• q6 - heat loss during the cooling of the furnace during its cleaning from slag. The last coefficient refers exclusively to solid fuel units and is not taken into account when calculating the efficiency of equipment running on natural gas.

The flue gas temperature, marked in the formula with the q2 marker, has the strongest effect on the heat efficiency. With a decrease in the intensity of heating of outgoing degrees by 10-15 ° C, the efficiency increases by 1-2%. In this regard, the highest efficiency in condensing boilers belonging to the class of low-temperature heating equipment.

Which gas boiler has the highest efficiency

• Modulating burner used– modern boilers from leading manufacturers, equipped with smoothly two-stage or fully modulating burners. The advantage of the burners is the automatic adjustment to the actual operating parameters of the heating system. The percentage of underburning is reduced to a minimum.
• Heat carrier heating- the optimal boiler is a unit that heats the coolant to a temperature of no more than 70 ° C, while the exhaust gases are heated to no more than 110 ° C, which ensures maximum heat transfer. But, with low-temperature heating of the coolant, there are several disadvantages: insufficient traction force, increased condensation.
  Heat exchangers in gas boilers with the highest efficiency, are made of stainless steel and are equipped with a special condenser unit designed to extract heat from the condensate.
• The temperature of the supply gas and air entering the burner. Boilers closed type, connect . Air enters the combustion chamber through the outer cavity of the two-cavity pipe, preheated, which reduces the required heat consumption by several percent.
  Burners with preliminary preparation of a gas-air mixture also heat the gas before it is fed to the burner.
• Another popular modification- installation of an exhaust gas recirculation system, when the smoke does not immediately enter the combustion chamber, but passes through a broken chimney channel and enters after mixing fresh air, back to the burner.

Maximum efficiency is achieved at the dew point or dew point temperature. Boilers operating under conditions of low-temperature heating are called condensing boilers. They are distinguished by low gas consumption and high thermal efficiency, which is especially noticeable when connected to and.

Condensing boilers are offered by several European manufacturers, including:

• Viessmann.
• Buderus.
• Vaillant.
• Baxi.
• De Dietrich.

In the technical documentation for condensing boilers, it is indicated that the efficiency of devices when connected to low-temperature heating systems is 108-109%.

How to increase the efficiency of a gas boiler

• Changing the principle of coolant circulation- the building warms up faster and more evenly when the circulation pump is connected.
• Installation of room thermostats- modernization of boilers to increase efficiency using sensors that control not the heating of the coolant, but the temperature in the room, an effective method of increasing thermal efficiency.
• An increase in the gas utilization factor in a domestic boiler, by approximately 5-7%, occurs when the burner is replaced. The installation of a modulating burner helps to improve the proportions of the gas-air mixture and, accordingly, reduces the percentage of underburning. The type of burner installed is directly related to the reduction of heat loss.
• Instead of a complete modification of the boiler, a partial redesign and adjustment of the fuel flow may be required. If you change the position of the burners and install them closer to the water circuit, it will be possible to increase the efficiency by another 1-2%. The heat balance of the boiler unit will increase upwards.

The efficiency decreases when the heat exchanger is dirty, due to the fact that scale, consisting of metal salt deposits, has poor thermal conductivity. For this reason, there is a constant increase in gas consumption and subsequently, the boiler completely fails.

There is a slight increase in efficiency during the combustion of liquefied gas, achieved by reducing the rate of fuel supply to the burner, which leads to a decrease in underburning. But, the thermal efficiency increases slightly. Therefore, natural gas continues to be the most economical of all used traditional types fuel.

The heat released during the combustion of fuel cannot be fully used to produce steam or hot water, part 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 states the equality of the amount of heat introduced into the boiler unit and the heat spent on the production of steam or hot water, taking into account losses. In accordance with the "Normative Method" all quantities included in the heat balance are calculated per 1 kg of burned fuel. The input part of the heat balance is called available heat :

where Q-- lower calorific value of fuel, kJ/kg; c T t T - physical heat of the fuel (с t is the heat capacity of the fuel, / t is the temperature of the fuel), kJ/kg; Q B is the heat of the air entering the furnace when it is heated outside the unit, kJ/kg; Qn - heat introduced into the boiler unit with steam used for fuel oil spraying, external blowing of heating surfaces or supply under the grate during layered combustion, kJ/kg.

When using gaseous fuels, the calculation is based on 1 m3 of dry gas under normal conditions.

The physical heat of the fuel plays a significant role only when the fuel is preheated outside the boiler. For example, fuel oil is preheated before being fed to the burners because 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 - theoretically required amount of air, Nm 3 /kg; from to - isobaric heat capacity of air, kJ / (n.m 3 K); / x in - temperature of cold air, ° С; tB- air temperature at the furnace inlet, °С.

Heat introduced with steam, kJDkgfuel):

where Gn- specific consumption of blast steam (approximately 0.3 kg of steam per 1 kg of fuel oil is consumed for spraying fuel oil); / n \u003d 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, take 0 p ~Q? in view of the smallness of the other components of equation (22.2).

The expenditure part of the heat balance consists of the useful heat (production of steam or hot water) of the sum of losses, kJDkgfuel.):

where 0 2 - heat loss with gases leaving the boiler unit;

• 03 - heat loss from chemical incompleteness of fuel combustion;
• 0 4 - heat loss from mechanical incompleteness of fuel combustion;
• 0 5 - heat loss through brickwork to the environment; 0 6 - losses with the physical heat of the 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:

Useful heat in a steam boiler with continuous blowing of the upper drum is determined by the equation, kJDkgfuel.):

where D- boiler steam capacity, kg/s; Dnp- blowdown water consumption kg/s; AT - fuel consumption, kg/s; / p, / p v, / k v - enthalpy of steam, feed and boiler water at pressure in the boiler, respectively, kJ / kg.

Heat loss with flue gases, kJ/(kg fuel):

where from g and from to- isobaric heat capacity of combustion products and air, kJ / (n.m 3 K); d - flue gas temperature, °С; а ux - coefficient of excess air at the outlet of gases from the boiler unit; K 0 G and V0- the theoretical volume of combustion products and the theoretically required amount of air, Nm 3 / (kgfuel).

Vacuum is maintained in the gas ducts of the boiler unit, the volumes of gases during their movement 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 a yx is greater than the coefficient of excess air in the furnace a. It is determined by summing the coefficient of excess air in the furnace and air suction in all gas ducts. 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 combat heat loss.

Thus, the amount of loss Q2 is determined by the temperature of the flue gases and the value of the excess air coefficient а ux. In modern boilers, the temperature of the gases behind the boiler does not fall below 110 °C. A further decrease in temperature leads to the condensation of water vapor contained in the gases and the formation of sulfuric acid during the 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 method of combustion, as well as on the perfect organization of the combustion process. Losses from chemical incomplete combustion in modern furnaces are q 3 = 0.5-5%, from mechanical - q4 = 0-13,5%.

Heat loss to the environment q 5 depend on the power of the boiler. The higher the power, the lower the relative loss q 5 . So, at the steam capacity 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 qb are small and are usually taken into account when compiling the exact heat balance,%:

where a sl = 1 - a un; a un - share of ash in flue gases; with sl and? shl - heat capacity and temperature of the slag; And Mr. ash content of the operating state of the fuel.

Efficiency (efficiency) of the boiler unit called 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 unit efficiency, %:

The efficiency of boiler units significantly depends on the type of fuel, the method of combustion, flue gas temperature and power. steam boilers operating on liquid or gaseous fuels have an efficiency of 90-92%. With layered combustion solid fuel The efficiency is 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. The operation of the boiler unit with steam pressure and less than nominal capacity reduces efficiency. During the operation of the boilers, thermal tests should be periodically carried out in order to determine the losses and the actual efficiency of the boiler, which allows you to make the necessary adjustments to its mode of operation.

Fuel consumption for a steam boiler (kg / s - for solid and liquid fuel; n.m 3 / s - gaseous)

where D- steam capacity of the boiler unit, kg/s; / p, / p v, / k v - enthalpy of steam, feed and boiler water, respectively, kJ / kg; Qp- available heat, kJ / (kg fuel) - for solid and liquid fuels, kJ / (N.m 3) - for gaseous fuels (often taken in calculations Qp~Q- due to their slight difference). P - value continuous purge, % of steam capacity; g| ka - efficiency of the boiler unit, shares.

Fuel consumption for a hot water boiler (kg / s; Nm 3 / s):

where C in - water consumption, kg / s; /, / 2 - initial and final enthalpies of water in the boiler, kJ/kg.

Boiler efficiency gross characterizes the efficiency of using the heat supplied to the boiler and does not take into account the cost of electrical energy to drive draft fans, smoke exhausters, feed pumps and other equipment. When running on gas

h br k \u003d 100 × Q 1 / Q c n. (11.1)

Energy costs for auxiliary needs of the boiler plant are taken into account by the efficiency of the boiler net

h n k \u003d 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 losses for own needs include heat losses with blowing, blowing screens, spraying fuel oil, etc.

The main among them are heat losses with blowdown.

q t \u003d G pr × (h k.v - h p.v) / (B × Q c n) .

Relative electricity consumption for own needs

q el \u003d 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 - the cost of electrical energy to drive the feed pumps, draft fans and smoke exhausters, respectively; h p.n, h d.v, h d.s - efficiency of feed pumps, draft fans and smoke exhausters, respectively.

11.3. Methodology for performing laboratory work
and processing results

Balance tests in laboratory work are carried out for the stationary operation of the boiler when performing the following mandatory conditions:

The duration of the boiler installation from kindling to the start of testing is at least 36 hours,

The duration of maintaining the test load immediately before the test is 3 hours,

Permissible load fluctuations in the interval between two adjacent experiments should not exceed ± 10%.

Measurement of parameter values ​​is carried out using standard instruments installed on the boiler shield. All measurements should be made 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. With a larger relative discrepancy, the measurement result in the third, control experiment is used.

The results of measurements and calculations are recorded in the protocol, the form of which is given in table. 26.

Table 26

Determination of heat losses by the boiler

The end of the table. 26

Table 27

Boiler gross and net efficiency

Analysis of laboratory work results

The value of h br k obtained as a result of the work by the method of direct and reverse balances must be compared with the passport value equal to 92.1%.

Analyzing the influence 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 lowering the flue gas temperature and reducing excess air in the boiler. At the same time, lowering the temperature of gases to the dew point temperature will lead to condensation of water vapor and low-temperature corrosion of heating surfaces. A decrease in the value of the excess air coefficient in the furnace can lead to underburning of the fuel and an increase in losses Q 3 . Therefore, the temperature and excess air must not be below certain values.

Then it is necessary to analyze the impact on the efficiency of the boiler operation of its load, with the growth of which the losses with flue gases increase and the losses Q 3 and Q 5 decrease.

The lab report should conclude on the efficiency level of the boiler.

test questions

1. By what indicators of the boiler operation can a conclusion be made about the efficiency of its operation?
2. What is the heat balance of the boiler? By what methods can it be compiled?
3. What is meant by gross and net boiler efficiency?
4. What heat losses increase during boiler operation?
5. How can q 2 be increased?
6. 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 ratio, boiler load, heat loss, flue gases, chemical incompleteness of fuel combustion, boiler efficiency.

CONCLUSION

In the process of performing a laboratory workshop on the course of boiler plants and steam generators, students get acquainted with the methods for determining the calorific value of liquid fuel, humidity, volatile output and ash content of solid fuel, the design of the DE-10-14GM steam boiler and experimentally investigate the thermal processes occurring in it.

Future specialists study the methods of testing boiler equipment and acquire the necessary practical skills necessary for determining the thermal characteristics of the furnace, compiling the heat balance of the boiler, measuring its efficiency, as well as compiling the salt balance of the boiler and determining the value of the optimal blowdown.

Bibliographic list

1. Khlebnikov V.A. Boiler plant equipment testing:
Laboratory practice. - Yoshkar-Ola: MarGTU, 2005.

2. Sidelkovskii L.N., Yurenev V.N. Boiler plants industrial enterprises: Textbook for universities. – M.: Energoatomizdat, 1988.

3. Trembovlya V.I., Finger E.D., Avdeeva A.A. Thermal engineering tests of boiler installations. - M.: Energoatomizdat, 1991.

4. Alexandrov A.A., Grigoriev B.A. Tables of thermophysical properties of water and steam: a Handbook. Rec. State. standard reference data service. GSSSD R-776-98. – M.: MEI Publishing House, 1999.

5. Lipov Yu.M., Tretyakov Yu.M. Boiler plants 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. Tests of the equipment of the boiler room of the MPEI CHPP. Laboratory workshop: Tutorial on the course "Boiler installations and steam generators". – M.: MPEI Publishing House, 2000.

7. Roddatis K.F., Poltaretsky A.N. Handbook of low-capacity boiler plants / Ed. K.F.Roddatis. – M.: Energoatomizdat, 1989.

8. Yankelevich V.I. Adjustment of oil-gas industrial boiler houses. – M.: Energoatomizdat, 1988.

9. Laboratory works on 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.: MEI Publishing House, 1998.

10. Thermal calculation of boiler units (Normative method) / Ed. N.V. Kuznetsova. - M.: Energy, 1973.

11. SNiP 2.04.14-88. Boiler plants/Gosstroy of Russia. - M .: CITP Gosstroy of Russia, 1988.

Educational edition

KHLEBNIKOV Valery Alekseevich

BOILER INSTALLATIONS
AND STEAM GENERATORS

Laboratory workshop

Editor A.S. Emelyanova

computer set V.V. Khlebnikov

Computer layout V.V. Khlebnikov

Signed for publication on 16.02.08. Format 60x84/16.

Offset paper. Offset printing.

R.l. 4.4. Uch.ed.l. 3.5. Circulation 80 copies.

Order No. 3793. C - 32

Mari State Technical University

424000 Yoshkar-Ola, pl. Lenina, 3

Editorial and publishing center

Mari State Technical University

424006 Yoshkar-Ola, st. Panfilova, 17

In 2020, it is planned to generate 1720-1820 million Gcal.

A milligram equivalent is the amount of a substance in milligrams, numerically equal to the ratio of its molecular weight to the valence in this compound.

There are 2 methods for determining efficiency:

By direct balance;

Reverse balance.

Determining the efficiency of a boiler as the ratio of the useful heat consumed to the available heat of the fuel is its definition according to the direct balance:

The efficiency of the boiler can also be determined by the inverse balance - through heat losses. For the steady thermal state, we obtain

. (4.2)

The efficiency of the boiler, determined by formulas (1) or (2), does not take into account electric energy and heat for own needs. This boiler efficiency is called the gross efficiency and is denoted by or .

If the energy consumption per unit of time for the specified auxiliary equipment is , MJ, and the specific fuel consumption for generating electricity is, kg / MJ, then the efficiency of the boiler plant, taking into account the energy consumption of the auxiliary equipment (net efficiency),%,

. (4.3)

Sometimes referred to as the energy efficiency of a boiler plant.

For boiler installations of industrial enterprises, energy consumption for own needs is about 4% of the generated energy.

Fuel consumption is determined by:

The determination of fuel consumption is associated with a large error, so the direct balance efficiency is characterized by low accuracy. This method used to test an existing boiler.

The reverse balance method is characterized by greater accuracy and is used in the operation and design of the boiler. At the same time, Q 3 and Q 4 are determined according to the recommendation and from reference books. Q 5 is determined by the schedule. Q 6 - is calculated (rarely taken into account), and in essence the determination of the reverse balance is reduced to the determination of Q 2, which depends on the temperature of the flue gases.

The gross efficiency depends on the type and power of the boiler, i.e. performance, type of fuel burned, furnace design. The efficiency is also affected by the mode of operation of the boiler and the cleanliness of the heating surfaces.

In the presence of mechanical underburning, part of the fuel does not burn out (q 4), which means it does not consume air, does not form combustion products and does not release heat, therefore, when calculating the boiler, they use the estimated fuel consumption

. (4.5)

The gross efficiency takes into account only heat losses.

5 DETERMINATION OF HEAT LOSS IN THE BOILER UNIT.

WAYS TO REDUCE HEAT LOSS

5.1 Loss of heat with flue gases

The loss of heat with outgoing gases Q c.g occurs due to the fact that the physical heat (enthalpy) of the gases leaving the boiler exceeds the physical heat of the air and fuel entering the boiler.

If we neglect the low value of the fuel enthalpy, as well as the heat of the ash contained in the exhaust gases, the heat loss with the exhaust gases, MJ / kg, is calculated by the formula:

Q 2 \u003d J h.g - J in; (5.8)

where is the enthalpy of cold air at a=1;

100-q 4 – share of burned fuel;

a c.g is the coefficient of excess air in the exhaust gases.

If the ambient temperature is zero (t x.v \u003d 0), then the heat loss with the outgoing gases is equal to the enthalpy of the outgoing gases Q y.g \u003d J y.g.

The loss of heat with exhaust gases usually occupies the main place among the heat losses of the boiler, amounting to 5-12% of the available heat of the fuel, and is determined by the volume and composition of the combustion products, which significantly depend on the ballast components of the fuel and on the temperature of the exhaust gases:

The ratio characterizing the quality of the fuel shows the relative yield of gaseous combustion products (at a=1) per unit heat of combustion of the fuel and depends on the content of ballast components in it:

- for solid and liquid fuels: moisture W P and ash A P;

– for gaseous fuels: N 2 , CO 2 , O 2 .

With an increase in the content of ballast components in the fuel and, consequently, , the heat loss with the exhaust gases increases accordingly.

One of the possible ways to reduce the loss of heat with flue gases is to reduce the coefficient of excess air in flue gases a c.g., which depends on the air flow coefficient in the furnace a T and ballast air sucked into the boiler gas ducts, which are usually under vacuum

a y.g \u003d a T + Da. (5.10)

There are no air suction in boilers operating under pressure.

With a decrease in a T, the heat loss Q c.g. decreases, however, due to a decrease in the amount of air supplied to the combustion chamber, another loss may occur - from chemical incompleteness of combustion Q 3 .

The optimal value of a T is chosen taking into account the achievement of the minimum value q y.g + q 3 .

The decrease in a T depends on the type of fuel burned and the type of combustion device. Under more favorable conditions for contacting fuel and air, the excess air a T, necessary to achieve the most complete combustion, can be reduced.

The ballast air in the combustion products, in addition to increasing the heat loss Q c.g., also leads to additional energy costs for the smoke exhauster.

The most important factor influencing Q c.g. is the flue gas temperature t c.g. Its reduction is achieved by installing heat-using elements (economizer, air heater) in the tail section of the boiler. The lower the temperature of the flue gases and, accordingly, the lower the temperature difference Dt between the gases and the heated working fluid, the greater the surface area H is required for the same cooling of the gas. An increase in t c.g. leads to an increase in losses with Q c.g. and to additional fuel costs DB. In this regard, the optimal t c.g. is determined on the basis of technical and economic calculations when comparing the annual costs for heat-using elements and fuel for various values ​​of t c.g.

In Fig. 4, one can single out the temperature range (from to ) in which the calculated costs differ insignificantly. This gives reason to choose as the most appropriate temperature at which the initial capital costs will be less.

There are limiting factors in choosing the optimal one:

a) low-temperature corrosion of tail surfaces;

b) when 0 C possible condensation of water vapor and their combination with sulfur oxides;

c) the choice depends on the temperature of the feed water, the temperature of the air at the inlet to the air heater and other factors;

d) contamination of the heating surface. This leads to a decrease in the heat transfer coefficient and to an increase in .

When determining the loss of heat with the exhaust gases, the decrease in the volume of gases is taken into account

. (5.11)

5.2 Heat loss from chemical incomplete combustion

The loss of heat from chemical incompleteness of combustion Q 3 occurs when the fuel is not completely burned within the combustion chamber of the boiler and combustible gaseous components CO, H 2 , CH 4 , C m H n appear in the combustion products ... Afterburning of these combustible gases outside the furnace is almost impossible because due to their relatively low temperatures.

Chemical incompleteness of fuel combustion can be the result of:

- general lack of air;

– poor mixing;

- small size of the combustion chamber;

– low temperature in the combustion chamber;

- high temperature.

With sufficient air quality for complete combustion of the fuel and good mixture formation, q 3 depends on the volume density of heat release in the furnace

The optimal ratio at which the loss q 3 has a minimum value depends on the type of fuel, the method of its combustion and the design of the furnace. For modern furnace devices, the heat loss from q 3 is 0÷2% at q v =0.1÷0.3 MW/m 3 .

To reduce the loss of heat from q 3 in the combustion chamber, they seek to increase the temperature level, using, in particular, air heating, as well as improving the mixing of combustion components in every possible way.

The value is from 0.3 to 3.5% and decreases with increasing boiler power (from 3.5% for boilers with a capacity of 2 t/h to 0.3% for boilers with a capacity of more than 300 t/h).

Loss with physical heat of slag occurs because when burning solid fuel, the slag removed from the furnace has a high temperature: with solid ash removal = 600 ° C, with liquid - = 1400 - 1600 ° C.

Heat losses with physical heat of slags, %, are determined by the formula:

,

where - proportion of slag collection in the combustion chamber; - slag enthalpy, kJ/kg.

With layered combustion of fuels, as well as with chamber combustion with liquid slag removal = 1 - 2% and higher.

For chamber combustion of fuel with solid ash removal, the loss is taken into account only for multi-ash fuels at > 2.5%∙kg/MJ.

Efficiency of the boiler unit (gross and net).

The efficiency of a boiler unit is the ratio of the useful heat used to generate steam (hot water) to the available heat (the heat supplied to the boiler unit). Not all useful heat generated by the boiler is sent to consumers, part of it is spent on own needs (drive of pumps, draft devices, heat consumption for heating water outside the boiler, its deaeration, etc.). In this regard, a distinction is made between the efficiency of the unit in terms of the generated heat (gross efficiency) and the efficiency of the unit in terms of the heat released to the consumer (net efficiency).

Boiler efficiency (gross), %, can be determined by the equation direct balance

,

or equation reverse balance

.

Boiler efficiency (net), %, according to the reverse balance is determined as

where is the relative energy consumption for own needs, %.

Topic 6. Layer furnace devices for burning fuel in a dense and fluidized (fluidized) bed

Furnaces for burning fuel in a dense layer: principle of operation, scope, advantages and disadvantages. Classification of furnaces for burning fuel in a dense layer (non-mechanized, semi-mechanical, mechanical). Fuel dispensers. Mechanical furnaces with moving grates: principle of operation, scope, varieties. Layered furnace devices for fuel combustion in a fluidized bed: principle of operation, scope, advantages and disadvantages.

Layer furnace devices for burning fuel in a dense layer.

Layered furnaces designed for combustion of solid lumpy fuel (from 20 to 30 mm in size) are easy to operate and do not require a complex expensive fuel preparation system.

But since the process of fuel combustion in a dense layer is characterized by a low burning rate, inertia (and, therefore, it is difficult to automate), reduced efficiency (fuel combustion occurs with large losses from mechanical and chemical underburning) and reliability, it is economically feasible to use layer combustion for boilers with steam capacity up to 35 t/h.

Layered furnaces are used for burning anthracites, coals with moderate caking capacity (long-flame, gas, lean), brown coals with low moisture and ash content, as well as lumpy peat.

Classification of layer furnaces.

Maintenance of the furnace, in which the fuel is burned in the layer, is reduced to the following basic operations: fuel supply to the furnace; drilling (mixing) of the fuel layer in order to improve the conditions for supplying the oxidizer; removal of slag from the furnace.

Depending on the degree of mechanization of these operations, layered furnace devices can be divided into non-mechanized (all three operations are performed manually); semi-mechanical (one or two operations are mechanized); mechanical (all three operations are mechanized).

Non-mechanized layer furnaces are furnaces with manual periodic supply of fuel to a fixed grate and manual periodic removal of slag.

semi-mechanical furnace devices are distinguished by the mechanization of the process of supplying fuel to the grate using various casters, as well as the use of special slag removers and rotary or rocking grates.

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