Coefficient useful action(efficiency) of a boiler unit is defined as the ratio of useful heat used to generate steam (or hot water), to the available heat (heat entering the boiler unit). In practice, not all useful heat selected by the boiler unit is sent to consumers. Part of the heat is spent for its own needs. Depending on this, the efficiency of the unit is distinguished by the heat supplied to the consumer ( Net efficiency).

The difference between the generated and released heat represents the consumption for the boiler house’s own needs. Not only heat is consumed for own needs, but also electrical energy (for example, to drive a smoke exhauster, fan, feed pumps, fuel supply and dust preparation mechanisms, etc.), therefore, consumption for own needs includes the consumption of all types of energy spent on production of steam or hot water.

Gross efficiency boiler unit characterizes the degree of its technical perfection, and the net efficiency characterizes its commercial profitability.

Gross efficiency of the boiler unit ŋ br, %, can be determined using the direct balance equation

ŋ br = 100(Q floor /Q r r)

or according to the reverse balance equation

ŋ br = 100-(q u.g +q h.n +q m.n +q n.o +q f.sh),

Where Q floor useful heat expended to produce steam (or hot water); Q r r- heat available from the boiler unit; q u.g +q h.n +q m.n +q n.o +q f.sh- relative heat losses by heat consumption items.

Net efficiency according to the reverse balance equation is determined as the difference

ŋ net = ŋ br -q s.n,

Where q s.n.- relative energy consumption for own needs, %.

The efficiency according to the direct balance equation is used mainly when preparing reports for a separate period (decade, month), and the efficiency according to the reverse balance equation is used when testing boiler units. Determination of efficiency by reverse balance is much more accurate, since the errors in measuring heat losses are smaller than in determining fuel consumption, especially during combustion solid fuel.

Thus, to improve the efficiency of boiler units, it is not enough to strive to reduce heat losses; it is also necessary to reduce in every possible way the costs of heating and electrical energy for your own needs. Therefore, a comparison of the operating efficiency of various boiler units should ultimately be carried out based on their net efficiency.

In general, the efficiency of a boiler unit varies depending on its load. To construct this relationship, you need to subtract sequentially all losses of the boiler unit from 100%. Sq sweat = q u.g +q x.n +q m.n +q n.o, which depend on the load.

As can be seen from Figure 1.14, the efficiency of the boiler unit at a certain load has a maximum value, i.e., operation of the boiler at this load is the most economical.

Figure 1.14 - Dependence of efficiency boiler from its load: q u.g, q x.n, q m.n., q n.o.,S q sweat- heat losses with exhaust gases, from chemical incomplete combustion, from mechanical incomplete combustion, from external cooling and total losses

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 k.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
Volume flue gases	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
Feed pump efficiency	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.

Control questions

1. Based on what indicators of boiler operation can a conclusion be made about the efficiency of its operation?
2. What is the heat balance of a 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 you increase q 2?
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 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 liquid fuel, humidity, volatile yield 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 methods for testing boiler equipment and gain the necessary practical skills needed in determining the thermal characteristics of the furnace, drawing up the heat balance of the boiler, measuring its efficiency, as well as drawing up the salt balance of the boiler and determining the amount of optimal blowdown.

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 work 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

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 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.

Different types of boilers have different Efficiency range from 85 to 110%. When choosing boiler equipment, many buyers are interested in how efficiency can exceed 100% and how it is calculated.

In the case of electric efficiency boilers really can't be higher than 100%. Only boilers running on combustible fuel can have a higher coefficient.

If you remember the school chemistry course, it turns out that with the complete combustion of any fuel, what remains is CO 2 - carbon and H 2 O - water vapor containing energy. During condensation, the energy of the steam increases, that is, additional energy is generated. Based on this, calorific value fuel is divided into two concepts: higher and lower specific heat of combustion.

Lowest- represents the heat obtained during the combustion of fuel, when water vapor, along with the energy contained in them, enters the external environment.

Higher calorific value is heat taking into account the energy contained in water vapor.

Officially (in any regulatory documents) Efficiency, both in Russia and in Europe, calculated at the lowest specific heat combustion. But if you still use the heat contained in water vapor, and the calculations are based on the lowest specific heat of combustion, then in this case figures appear that exceed 100%.

Boilers that use the heat of condensation of water vapor are called condensation. And they have an efficiency exceeding 100%.

The difference between the lower and higher heating values ​​of fuel combustion is about 11%. This value is the limit by which the efficiency of boilers can differ.

Main settings

Efficiency can be calculated using two parameters. In Europe, efficiency is usually calculated based on the temperature of the exhaust gases. For example, when burning a kilogram of fuel, a certain amount of kilocalories of heat is obtained, provided that the temperature of the exhaust gases and the temperature environment.

By measuring the difference between the ambient temperature and the actual temperature of the exhaust gases, it is possible to calculate the boiler efficiency from it.

Roughly speaking, the waste gases escaping into the chimney are subtracted from 100% to arrive at the actual figure.

Calculate correctly

In the USSR, and later in Russia, a fundamentally different calculation method was adopted - the so-called “ reverse balance method" It consists in the fact that heat consumption is determined by the lower calorific value. Then, a heater is placed on the pipe, and the amount of thermal energy that has gone into it is calculated, that is, the amount of energy loss. To calculate efficiency, energy losses are calculated from the total amount of heat.

This approach when determining efficiency gives more accurate indicators. It was adopted as a calculation method because all the bodies of Russian boilers were very poorly thermally insulated, which is why up to 40% of the energy escaped through the walls of the boiler. According to requirements regulatory documents, in Russia it is still customary to consider efficiency using the reverse balance method. Today, this method can be successfully applied to multi-megawatt boilers operating in thermal power plants whose burners never turn off.

Advantages of modern boilers

But this technique is completely inapplicable to modern boilers, since they have a fundamentally different operating scheme. Since the burners of modern boilers operate in automatic mode: they work for 15 minutes, and then stop for 15 minutes until the generated heat is used. The higher the outside temperature, the longer the burner will “stand” and work less. Naturally, in this case we cannot talk about a reverse balance.

Another difference between modern boilers is the presence of thermal insulation. Large manufacturers produce the highest quality units, with better thermal insulation. Heat loss through the walls of such a boiler is no more than 1.5-2%. Buyers often forget about this, believing that the boiler will also heat the room by releasing heat during operation. When purchasing a modern boiler, it is worth remembering that it is not intended for heating a boiler room, and, if necessary, take care of installing heating radiators.

Modern heat preservation technologies

A good steel boiler always has higher efficiency. This is due to the fact that cast iron boilers, unlike steel ones, always have more technological limitations.

Moreover, thanks to the insulation, modern boilers retain heat perfectly. Even two days after it is turned off, the temperature of the boiler body drops by only 20-25 degrees.

The best examples of imported heating equipment are boiler units in which all requirements are correctly taken into account. Therefore, you should not try to “reinvent the wheel” and assemble a boiler from improvised means. After all, you already have a wide selection of the most modern, diverse and carefully thought-out boiler options that will work for a long time and properly, more than meeting all the expectations placed on them and, what is especially pleasant, saving your costs!

Our specialists will help you choose boiler and related equipment and advise on technical issues!

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All about boiler efficiency

What is boiler efficiency

The efficiency of a heating boiler is the ratio of the useful heat consumed to produce steam (or hot water) to the available heat of the heating boiler. Not all the useful heat generated by the boiler unit is sent to consumers; part of the heat is spent on its own needs. Taking this into account, the efficiency of a heating boiler is distinguished by the heat generated (gross efficiency) and by the heat released (net efficiency).

The difference between the generated and released heat is used to determine the consumption for auxiliary needs. Not only heat is consumed for its own needs, but also electrical energy (for example, to drive a smoke exhauster, fan, feed pumps, fuel supply mechanisms), i.e. consumption for own needs includes the consumption of all types of energy spent on the production of steam or hot water.

* To buy a Unique boiler, go to the appropriate section. And if you need heating boilers wholesale, then go here.

How to calculate boiler efficiency

As a result, the gross efficiency of a heating boiler characterizes the degree of its technical perfection, and the net efficiency characterizes its commercial profitability. For a boiler unit, gross efficiency, %:
according to the direct balance equation:

ηbr = 100 Qpol / Qpp

where Qfloor is the amount of useful heat, MJ/kg; Qрр - available heat, MJ/kg;

according to the reverse balance equation:

ηbr = 100 – (q2 + q3 + q4 + q5 + q6),

where q is heat loss in%:

• q2 - with exhaust gases;
• q3 - because chemical underburning flammable gases (CO, H2, CH4);
• q4 - with mechanical underburning;
• q5 - from external cooling;
• q6 - with physical heat of slag.

Then the net efficiency of the heating boiler according to the reverse balance equation

ηnet = ηbr - qs.n

where qс.н - energy consumption for own needs, %.

The determination of efficiency using the direct balance equation is carried out mainly when reporting for a separate period (decade, month), and using the reverse balance equation - when testing a heating boiler. Calculating the efficiency of a heating boiler using reverse balance is much more accurate, since the errors in measuring heat losses are smaller than in determining fuel consumption.

How to increase the efficiency of a gas boiler with your own hands

Create the right conditions operation gas boiler and thus you can actually increase the efficiency without calling a specialist, that is, with your own hands. What do I need to do?

1. Adjust the blower damper. This can be done experimentally by finding at what position the coolant temperature will be highest. Carry out control using a thermometer installed in the boiler body.
2. Be sure to ensure that the heating system pipes do not become overgrown from the inside, so that scale and dirt deposits do not form on them. WITH plastic pipes Today it has become easier, their quality is known. Still, experts recommend periodically purging the heating system.
3. Monitor the quality of the chimney. Do not allow it to become clogged or soot to stick to the walls. All this leads to a narrowing of the cross-section of the outlet pipe and a decrease in the boiler draft.
4. A prerequisite is cleaning the combustion chamber. Of course, gas does not smoke much like wood or coal, but it is worth washing the firebox at least once every three years to clear it of soot.
5. Experts recommend reducing chimney draft during the coldest time of the year. To do this, you can use a special device - a draft limiter. It is installed at the very top edge of the chimney and regulates the cross-section of the pipe itself.
6. Reduce chemical heat losses. There are two options here to achieve the optimal value: install a draft limiter (this has already been discussed above) and immediately after installing the gas boiler, carry out proper adjustment of the equipment. We recommend entrusting this to a specialist.
7. You can install a turbulator. These are special plates that are installed between the firebox and the heat exchanger. They increase the area of ​​thermal energy extraction.

There are 2 methods for determining efficiency:

By direct balance;

By reverse balance.

Determining boiler efficiency as the ratio of useful heat expended to the available heat of the fuel is determined by direct balance:

The boiler efficiency can also be determined by the reverse balance - through heat losses. For steady thermal state we get

. (4.2)

The boiler efficiency, determined by formulas (1) or (2), does not take into account electrical energy and heat for its own needs. This boiler efficiency is called 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 electricity generation is, kg/MJ, then the efficiency of the boiler plant taking into account energy consumption auxiliary equipment(net efficiency), %,

. (4.3)

Sometimes called the energy efficiency of a boiler plant.

For boiler installations of industrial enterprises, energy costs for their own needs account for about 4% of the generated energy.

Fuel consumption is determined:

Determination of fuel consumption is associated with a large error, so the efficiency by direct balance is characterized by low accuracy. This method is 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. In this case, Q 3 and Q 4 are determined according to recommendations and from reference books. Q 5 is determined from the graph. Q 6 is calculated (rarely taken into account), and essentially the determination by reverse balance comes down 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. productivity, type of fuel burned, firebox design. The efficiency is also affected by the boiler operating mode and the cleanliness of the heating surfaces.

In the presence of mechanical underburning, part of the fuel does not burn (q 4), and therefore does not consume air, does not form combustion products and does not release heat, therefore, when calculating the boiler, the calculated fuel consumption is used

. (4.5)

Gross efficiency only takes into account heat losses.

Figure 4.1 - Change in boiler efficiency with load change

5 DETERMINATION OF HEAT LOSS IN A BOILER UNIT.

WAYS TO REDUCE HEAT LOSS

5.1 Heat loss with flue gases

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

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

Q 2 = J ch.g - J c; (5.8)

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

100-q 4 – proportion of burned fuel;

a у.г – coefficient of excess air in the flue gases.

If the ambient temperature is zero (t x.v = 0), then the heat loss with the exhaust gases is equal to the enthalpy of the exhaust gases Q a.g = J a.g.

Heat loss with flue 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 combustion products, which significantly depend on the ballast components of the fuel and on the temperature of the flue 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 Р and ash А Р;

– for gaseous fuel: N 2, CO 2, O 2.

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

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

a y.g = a T + Da. (5.10)

In boilers operating under pressure, there are no air suctions.

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

The optimal value of a T is selected 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. With more favorable conditions contacting fuel and air, the excess air a T necessary to achieve the most complete combustion, can be reduced.

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

The most important factor influencing Q a.g. is the temperature of the exhaust gases t a.g. Its reduction is achieved by installing heat-using elements (economizer, air heater) in the tail part of the boiler. The lower the temperature of the exhaust gases and, accordingly, the lower the temperature difference Dt between the gases and the heated working fluid, the larger 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 from 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 annual costs for heat-using elements and fuel for different values ​​of t c.g.

In Fig. 4, we can highlight the temperature range (from to ), in which the calculated costs differ slightly. This gives grounds for choosing the most appropriate temperature, at which the initial capital costs will be lower.

There are limiting factors when choosing the optimal one:

a) low-temperature corrosion of tail surfaces;

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

c) the choice depends on the temperature of the feed water, the air temperature 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 an increase.

When determining heat loss with flue gases, the reduction in gas volume is taken into account

. (5.11)

5.2 Heat loss from chemical incomplete combustion

Heat loss from chemical incomplete combustion Q 3 occurs when incomplete combustion fuel within the combustion chamber of the boiler and the appearance in the combustion products of flammable gaseous components CO, H 2 , CH 4 , C m H n ... The afterburning of these combustible gases outside the furnace is practically impossible due to their relatively low temperature.

Chemical incomplete combustion of fuel can result from:

– general lack of air;

– poor mixture formation;

– small size of the combustion chamber;

– low temperature in the combustion chamber;

– high temperature.

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

The optimal ratio at which the loss of 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 combustion devices, the heat loss from q 3 is 0÷2% at q v =0.1÷0.3 MW/m 3.

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