Boiler room heat supply system calculation

Contents

CONTENTS

1. Introduction

2. Assignment for coursework

1) Calculation of heat loads of industrial and municipal heat consumers

2) Construction of the annual heat load schedule

3) Calculation of the main thermal diagram of the production and heating boiler house

4) Preparation of boiler room heat balance

5) Type and size selection and number of boilers

6) Calculation of theoretical and actual volumes of combustion products

7) Determination of enthalpy of combustion and air products

8) Heat balance of boiler unit

9) Determination of annual fuel consumption

10) Thermal and structural calculation of water economizer

11) Calculation and selection of auxiliary boiler room equipment

12) Boiler room layout

13) Individual assignment. Main fuels

3. Conclusion

4. Literature

Ministry of Agriculture of the Russian Federation

Federal State Educational Institution

higher vocational education

Izhevsk State Agricultural Academy

Department "Electrotechnology of agricultural production"

Coursework

"HEAT SUPPLY SYSTEM CALCULATION"

Introduction

Energy is a system of installations and devices for converting primary energy resources into the types of energy necessary for the national economy and the population, and transferring this energy from its sources of production to objects of use.

Of all the types of energy generated, two types are most widely used - electric energy and heat of low and medium potentials, which currently spend more than 55% of all the country's primary fuel and energy resources used.

The country's thermal economy is developing on the basis of a continuous process of concentration of heat loads in cities and industrial areas.

Heating, which is the most advanced technological method for the production of electric and thermal energy and one of the main ways to reduce fuel consumption for the production of these types of energy, is especially important for the organization of a rational energy supply of the country.

An effective solution to the problem of energy saving in agriculture is possible only if all the features of heat supply are taken into account, as well as modern achievements in the field of energy-saving heat supply systems. The problem of energy conservation is becoming a priority area of ​ ​ state policy. The use of renewable and secondary energy resources is an effective way to save on scarce organic fuels in agriculture.

The rational use of thermal energy, the exploration of unconventional, renewable energy sources, the creation of energy-saving environmentally friendly technologies is becoming one of the main tasks of energy engineers.

The purpose of the course work is to expand and deepen theoretical knowledge in the discipline "Sources and systems of heat supply," acquire practical skills in solving engineering heat engineering problems, familiarize with thermal power systems in agriculture, as well as acquire experience in using regulatory, reference and educational literature.

I) Calculation of heat loads of industrial and municipal heat consumers

A boiler plant is a complex of devices and units designed to produce steam or hot water by burning fuel. By purpose, heating, production and heating-production boiler plants are distinguished. The general case for calculation is heating and production boiler houses, since they work, as a rule, all year round.

The heat load of the boiler house by the nature of the distribution in time is classified into seasonal and year-round. Seasonal (heating and ventilation costs) depends mainly on climatic conditions and has a relatively constant daily and variable annual load schedule. Year-round (heat consumption for hot water supply and technological needs), practically does not depend on the outside air temperature and has a very uneven daily and relatively constant annual schedule of heat consumption.

Design heat load of boiler house of heating and production type is determined separately for cold and warm periods of year. In winter, it consists of the maximum heat consumption for all types of heat consumption

where ΣФот, ΣФв, ΣФг. in ΣФт - the maximum streams of the warmth spent by all consumers of a system of heat supply respectively for heating, ventilation, hot water supply and technological needs, W; kz is a reserve factor that takes into account heat losses in heat networks, heat consumption for the boiler house's own needs and a reserve for a possible increase in heat consumption by the farm, kz = 1.2.

In summer, the boiler house load is the maximum heat consumption for technological needs and hot water supply

Total heat flow rates for all types of heat consumption are determined by approximate formulas.

Heat consumption for heating and ventilation

The maximum flow of heat, W, consumed for heating of residential and public buildings of the village included in the district heat supply system can be determined by enlarged indicators depending on the living area of ​ ​ the premises according to the formulas:

el. = F

F = 20 * 530 = 10600 m2

fr. = 175 * 10600 = 1855 kW

from. obshch = 0.25ot.zh

o.tl = 0.25 * 1855 = 463.75 kW

EMI3.1 Where, is an enlarged index of the maximum specific heat flux consumed for heating 1 m2 of living area, W/m2; F - living area, m2.

The values are determined depending on the estimated winter outside air temperature (tn =30℃,ϕ=175Vt/).

Maximum heat flow, W, consumed for heating of ventilation air of public buildings

Fv.obshch =0.4*463.75=185.5kvt

For individual residential, residential and industrial buildings, the maximum flow of heat, W, spent on heating and heating air in the plenum ventilation system can be determined by their specific thermal characteristics

Phot = qotVn (tvtn) a;

Fot = 0.6 * 10000 * (20 (-30)) * 0.98 = 294 kW

a = 0.54 + 22/( tvtn) = 0.54 + 22/( 20 (-30)) = 0.98

Fv = qVn (tvtn);

Fv = 0.2 * 10000 * (20 (-17) = 74 kW.

Heat consumption for hot water supply

The average flow of heat, W, consumed during the heating period for hot water supply of residential and public buildings is found according to the formula

Fg. century cf. =qg. century of n

where qg. in =320vt - the integrated indicator of an average stream of the warmth, W spent for hot water supply of one person taking into account public buildings of the settlement is accepted depending on the water consumption rate, average for the heating period, at a temperature of 55 wasps on one person of g=105 of l/days:

F.F.W. = 320 * 530 = 169.6 kW

Maximum heat flow, W, consumed for hot water supply of residential and public buildings

Fg.v = 2 * 169.6 = 339.2 kW

The flow of heat, W, consumed for the hot water supply of residential, public and industrial buildings in the summer period with respect to heating decreases and is determined by the following formulas:

for residential and public buildings

II) Construction of the annual heat load schedule

The annual heat consumption for all types of heat consumption can be determined analytically or graphically from the annual heat load schedule. According to the annual schedule, boiler room operation modes are also established throughout the year. Such plot is made depending on duration of action in given area of different external temperatures.

The weighted average calculated internal temperature is determined by the expression:

tf.wd = i = 1nVti = 1nV,

where V - volumes of buildings by external measurement, m3; t - calculated internal temperatures of these buildings, ℃.

Weighted average design internal temperature for residential and public buildings:

tv. cf. =7500*20+4500*16+10000*20+20000*187500+10000+4500+20000=18.6 ℃

First, a schedule of heat consumption for heating residential buildings is built. Point corresponding to maximum heat flow consumed for heating of these buildings at external temperature tH is deposited on ordinate axis. The obtained point is connected straight with a point corresponding to the weighted average design internal temperature tv.W. = 18.6 ° C

(direct 1).

Since the heating season begins at tH = 8 ° C, the line of the graph to this temperature is shown in a dashed line. The heat flow for ventilation is plotted in the form of an inclined straight line up to the design ventilation temperature tn. (direct 3). At lower temperatures, room air is mixed to the supply outside air, i.e. recirculation occurs, and the heat flow rate remains unchanged (the graph runs parallel to the abscissa axis).

Heat costs for hot water supply and technological needs do not depend on tn. A general plot of these types of heat consumption is shown in line 4.

Total plot of heat consumption depending on ambient air temperature is broken line 5 (fracture point corresponds to temperature tH,e), which cuts off a section on the ordinate axis equal to the maximum heat flow consumed for all types of heat consumption.

To the right along the abscissa axis, for each external temperature, the number of hours of the heating season (with an increasing result) is deposited, during which the temperature was kept equal to and lower than the one for which the construction is made, and vertical lines are drawn through these points. Ordinates corresponding to maximum heat flow rates at the same external temperatures are then projected onto these lines from the total heat flow chart. The obtained points are connected by a smooth curve 6, which is a graph of the heat load over the heating period.

Area bounded by coordinate axes, curve 6 and horizontal line 7 showing total summer load expresses annual heat consumption, HJ/year

Qgod = 3.610-6Fmf

where F is the area of the annual heat load schedule, mm2; mf and m scale of heat consumption and boiler room operation time, respectively W/mm and h/mm.

F = 86444.5 mm2

mf = 105 W/mm

Qgod = 3.6106 MJ/year

1 - heat consumption for heating of residential buildings;

2 - for heating public buildings;

3 - for ventilation of public buildings;

4 - for hot water supply and technological needs;

5 is the total heat flow chart;

6 - heat load schedule for the heating period;

7 - summer period load.

III) Calculation of the basic thermal diagram of the production and heating boiler house

Initial data for calculation of boiler room thermal diagram (Fig.20)

Steam for production process needs has the following parameters:

P1 = 1.39 MPa; h1=0.99; DT = 5.65 kg/s.

Raw water temperature tcv = 70C.

Steam pressure after RPA P2 = 0,119 MPa.

Dryness of steam at the exit from the dilator of continuous expulsion h2=0.98.

Steam losses in the boiler house as a percentage of Dcut dut = 5.5%.

Heat water flow rate for continuous blowdown as a percentage of

Dcut dpr = 4.5%.

Heating heat flow Qb = 2.89 MW

Water temperature at the outlet of the network heaters t/1 = 930C.

Temperature in the return line of the heating network t/2 = 430C.

Water temperature before and after HVO tkhvo = 300C.

Condensate temperature at outlet of tkb boiler = 830С.

Condensate return from the consumer is performed by two flows with temperature tk1 = s

The steam flow rate for heating the network water is determined from the equation:

.

From where:

Determination of steam flow rate for heating of mains water and for technological needs.

Heat consumption for technological needs will be:

,

where iko - weighted average enthalpy of condensate from process consumers:

The total flow rate for heating the network water and for technological needs will be:

Steam flow rate for heating of mains water and for technological needs will be:

If there are no network heaters, D0 = DT.

Approximate determination of total fresh steam flow rate.

The total flow rate of acute steam Dg for heating raw water before chemical water treatment and deaeration will be 311% of Dc.

Take Dg=0,03∙D0=0,03∙8,21 = 0.246 kg/s.

Total fresh steam flow:

Calculation of reduction and cooling unit.

The purpose of the ROP is to reduce the steam parameters due to throttling (grab) and cooling it with water introduced into the cooler in a spray state. ROP consists of a reduction valve for reducing steam pressure, a device for lowering steam temperature by injecting water through nozzles located on the section of the steam line behind the reduction valve and a system for automatic control of temperature and pressure of steam throttling.

In the RPA cooler, the main part of the water evaporates, and the other one with boiling temperature is withdrawn to condensing tanks or directly to the deaerator.

We accept in the course design that all water introduced into the ROD is completely evaporated, and the steam at the outlet is dry, saturated.

The supply of cooled water to the ROP of the production boiler houses is usually carried out from the feedwater line after the deaerator.

Thermal calculation of ROE is carried out according to the heat balance.

ROP diagram.

The flow rate of reducing steam Dred with parameters P2, t2, i//2 and flow rate of humidifying water W1 is determined from the equation of RP thermal balance:

from the ROD material balance equation:

We determine the flow rate of humidifying water:

Calculation of continuous blowdown separator.

Continuous blowing of drum boilers is carried out to reduce the salt content of boiler water and obtain steam of proper purity. The amount of blowdown (as a percentage of the capacity of the boilers) depends on the salt content of the feedwater, the type of boilers, etc.

To reduce heat and condensate losses with blowdown water, expander separators are used. Pressure in continuous blowdown expander is taken equal to P2. Steam from the continuous blowdown expanders is usually sent to the deaerators.

The heat of the purge water (from the continuous purge separator) is economically feasible to use when the amount of purge water is more than 0.27 kg/s. This water is typically passed through a raw water preheating heat exchanger. Water from the separator is supplied to a cooler or bubbler, where it is cooled to 4050 0C, and then discharged to the sewer .

Continuous Blowdown Diagram

The flow rate of blowdown water from the boiler unit is determined by its specified dpr value as a percentage of Dcyt.

The amount of steam released from the purge water is determined from the thermal balance equation:

,

and the mass balance of the separator:

.

Continuous purge separator assembly.

We have:

Water flow from expander:

Calculation of chemically purified water flow rate.

The total amount of water added from the chemical water treatment is equal to the sum of the loss of water and steam in the boiler house, in production and in the heat network.

Condensate losses from process consumers:

In case of no condensate return from process loads W2 = (100m )/100DT, kg/s.

W2 = 100-45100· 5.65 = 3.1 kg/s

Blowdown water loss Wp = 0.291 kg/s.

Steam losses inside the boiler room are given as a percentage of D.

Water losses in the heating system WTC = 0.68975 kg/s.

Steam losses with steam from the deaerator can be determined only when calculating the deaerator. Preliminary take Dgp = 0.05 kg/s.

The total amount of chemically purified water is:

To determine the raw water flow rate for chemical water treatment, it is necessary to take into account the amount of water used for cationite decomposition, regeneration, washing and other water treatment needs. They are usually taken into account by the value of the coefficient K = 1.2.

Calculation of the deaerator.

To remove gases dissolved in water, mixing thermal deaerators are used. In general, they can be of atmospheric type with a column pressure of 0.110.13 MPa, elevated pressure and vacuum pressure below atmospheric pressure. In the course design, a mixing thermal deaerator of the atmospheric type (P2 = 0, 119MPa) is used. By thermal deaeration of water is meant the removal of dissolved air in it when heated to a boiling point corresponding to the pressure of the deaerator column. The purpose of deaeration is to remove aggressive gases included in the air that cause corrosion of the metal of the equipment (oxygen and carbonic acid). Water entering the deaerator is heated to saturation temperature by reduced steam (Dg).

The gases emitted by the deaerated water are transferred to the steam stream and the residue of the non-condensed excess steam (vapour) is removed from the deaerator column through the nozzle, and then discharged to the bubbler (sometimes through the vapour cooler). The flow rate of excess steam (Dfp) according to the available experimental data of CKTI is 2 + 4 kg per 1 ton of deaerated water. In the course design, it should be accepted: DGp = 0.003 * Wz, where Wz is the total flow rate of deaerated water.

The enthalpy of steam (vapour) is taken equal to the enthalpy of dry saturated steam at a given pressure (İ2 "). Deaerated water (Wg) from the deaerator tank is supplied by the feed pump (PN) to the boiler unit.

When calculating the deaerator, the steam flow rate to the deaerator (Dg) and the deaerated water flow rate (Wg) are unknown. These values ​ ​ are determined by jointly solving the equations of the mass and thermal balances of the deaerator .

We will refine the previously accepted flow rate Deq. Total flow rate of deaerated water:

Evaporator cooler calculation.

In the evaporator cooler, water from the condensate tank is heated by evaporator steam.

Let's write down the equation of thermal and mass balances:

IV) Preparation of boiler room heat balance

Heat balance of boiler house is made for certain efficiency, estimation of various losses, which makes it possible to estimate economy of proposed thermal scheme.

V) Type and size selection and number of boilers

When selecting the number of installed boilers, we conditionally assume that the maximum boiler room load corresponds to the total capacity and are guided by the following considerations:

It is unacceptable to install one boiler, and their total number should not exceed four to five;

Boilers to be installed shall have the same capacity.

It may be that one of the boilers will not be loaded, in this case it is reserve.

We choose a KE1023 boiler with a steam capacity of 2.78kg/s.

Determine the number of boilers to be installed to cover the entire load:

m = Dob/Dq,

where Dob. - total steam capacity of the boiler house;

Dc is the steam capacity of one boiler.

m=8,175572,78=2,94

Therefore, 3 boilers are required.

VI) Calculation of theoretical and actual volumes of combustion products

The excess air coefficient at the outlet of the combustion chamber is given by: αt = 1.5. The size of prisos of air in the economizer gas flue Δαэ =0.10.

Then the calculation is made for two options: with the installation of the economizer, without the installation of the economizer. Exhaust air excess factor:

VII) Determination of enthalpy of combustion and air products

With the installation of the economizer.

Enthalpy of actual combustion product volumes at tyx1

VIII) Boiler unit heat balance

The heat balance is drawn up to determine the efficiency of the boiler and fuel consumption at the steady-state thermal state of the boiler.

Thermal balance equation:

Qpp = Q1 + Q2 + Q3 + Q4 + Q5 + Q6, kJ/kg.

Take Qpp = Qnr, kJ/kg. Taking the available heat as 100%, you can write in the form:

100% - q1+q2+q3+q4+q5+q6-q1+∑qpot

If heat loss in the boiler is known, its gross efficiency is determined from the expression:

Ηbrka=q=100-∑qpot,%.

Heat losses with exhaust gases are determined by the formula:

Q2 = (I2αuxIxwo) (100q4 )/100, kJ/kg.

q2=Q2/Qpp∙100%

Skhv =1.3 kJ/m3 ℃ - specific capacity 1 m3vozdukha in the range of temperatures 0 - 100 ℃.

Due to the fact that the volumes of combustion products are calculated on the assumption of complete combustion of fuel, the equation is corrected for the value of q4 - mechanical insufficiency of combustion.

q3=0,5; q4=7,0.

For brown coal Qpr = 15.8 MJ/kg.

tkhv=30℃.

Ikhvo=VvotkhvSkhv=4,189∙30∙1,3=163,371 kJ/kg

Heat balance is produced separately for two design options.

With the economizer.

Heat loss with exhaust gases

q5c=1,3 %

Based on the thermal scheme, we have:

Fuel consumption supplied to the furnace:

Consumption of fuel completely burned in the furnace:

No economizer.

Heat loss with exhaust gases

q5b =0.5%

The fuel consumption supplied to the furnace in this embodiment will only change due to the change, therefore

Design fuel consumption

IX) Determination of annual fuel consumption

Annual flow rate of steam generated by one boiler unit

(Dca = 2.78 g/s):

Increment of working medium enthalpy in boiler unit

Annual heat consumption:

Annual fuel consumption for two options:

X) Thermal and structural calculation of water economizer

The water economizer is a surface heat exchanger and serves to heat the feed water before it is supplied to the boiler drum due to the heat of the exhaust gases. At the same time, heat losses with outgoing gases are reduced, but at the same time, heat losses to the environment and air sucks in the gas duct are slightly increased. Air suction in the gas duct not only reduces the cabre, but also causes a significant increase in electricity consumption for their own needs (smoke pump drive).

The initial data for calculating the water economizer are:

Water temperature before economizer tp1, ° C.

Gas temperature upstream of the tyx1 economizer, ° C.

Gas temperature after the tyx2 economizer, ° C.

Calculation determines:

Water temperature at economizer outlet tp2, ° C.

Economizer heating surface No, m2.

The thermal perception of the economizer is determined from the equation of thermal balance:

where φ - heat preservation coefficient.

Then enthalpy of water leaving economizer is determined by formula:

The temperature of the water after the economizer is determined by the corresponding enthalpy of the water ip2.

If the enthalpy of water after the water economizer is less than the enthalpy of water at the boiling point, then the water economizer is non-boiling .

If the enthalpy of water after the economizer is greater than the enthalpy of water at the boiling point, then the water economizer is boiled. In this case, steel coil economizers are used.

After that, water economizer heating surface is determined by formula:

where Ke is the heat transfer coefficient in the economizer, kVt/m2∙K;

Δtэ - a temperature pressure, °C.

In cast iron ribbed economizers, the velocity of combustion products is usually 6-8 m/s. The value of heat transfer coefficients at these rates is 0.0155-0.0215 kVt/m2∙K.

The temperature head in the economizer is determined from the expression:

° С ,

where Δtb is the temperature difference of the heat exchanging media at the end of the heating surface where it is largest, ° C;

Δtn is the temperature difference of the heat exchanging media at the end of the heating surface where it is the smallest, ° С.

At any temperature values, the highest possible temperature head Δte is achieved using a countercurrent circuit and the lowest during direct flow (other things being equal), in connection with which the use of a countercurrent circuit is recommended.

If the degree of steam content is x > 0, but not more than 30%, then the temperature head for economizers is calculated by the formula, but instead of the water temperature at the outlet of the economizer, the conditional water temperature is substituted into this formula.

° С ,

where is the amount of heat spent in the water economizer for steam generation, kJ/kg.

Steam content of water at the economizer outlet is determined by formula:

After determining No, the economizer type is selected or calculated.

Design characteristics of the economizer and its calculation.

In small and medium-capacity steam generators, two types of economizers are used: cast-iron ribbed and steel smooth-tube.

Cast iron ribbed economizers are assembled from standard 1.5-length ribbed pipes; 2,5; 3 m. When choosing the length and number of pipes in the horizontal row, the layout of the economizer in the gas duct is taken into account, as well as the speed of the gases, which should be in the range from 6 to 12 m/s. Total number of pipes is determined by ratio of design heating surface of economizer No to area of heating surface of one pipe from gas side.

Steel smooth-tube economizers are made in the form of horizontal coils from seamless pipes with outer diameter of 28, 32, 38 mm and wall thickness of 33.5 mm.

The main values that should be used in the development of steel economizer structures are as follows:

Outer diameter of pipes dnar, mm 28, 30, 32, 38.

The location of the pipes in the bundle is staggered.

Flue gas velocity at

rated capacity wg, m/s 612 (optimal 810).

Water velocity in pipes wv, m/s:

economizers of non-boiling type 0.4;

economizers of non-boiling type 0.8.

Relative pipe spacing:

across the stroke of gases s1/d 2-3 (optimal 2,32.5)

along the gas flow s2/d 11.5.

Pipe bending radius, m (11.5) dnar.

Pipe pack radius, m 0.9 - 1.2.

The procedure for determining the main structural characteristics of a steel smooth-tube economizer is as follows. Before selecting dimensions of economizer horizontal section, they are linked to dimensions of steam generator gas duct section. Taking into account the above recommendations the relative steps of the pipes across the movement of gases s1, and in the direction of movement s2, the pipes of the economizer are arranged.

If the speed of water in the bundle tubes is less than the recommended values, change the arrangement of the bundle tubes. The increase in the speed of water in the pipes is achieved by reducing the total number of parallel connected pipes Z0 or reducing the diameter dv. In some cases, a decrease in the number of coils leads to an excessive increase in the height economizer.

Temperature head:

XI) Calculation and selection of auxiliary boiler room equipment

Auxiliary equipment includes condensate and feed tanks, condensate and feed pumps, water treatment equipment. They ensure uninterrupted supply of water to boiler units.

Condensate and feed tanks are installed for steam boilers with excess steam pressure above 68.7 kPa. Condensate is pumped from condensate tanks to feed tanks located at a height of 3... 5 m from the floor. Chemically treated water is also supplied to these tanks to compensate for condensate losses. The role of the feed tank can be played by a reservoir of a thermal deaerator, the volume of which is 2/3 V.b. Capacity of condensate tanks, m3, calculated as per

Calculation of water treatment

In order to soften the water in the production and heating boiler houses, precottal treatment of water in sodium cationite filters has become widespread.

XII) Boiler room layout

The layout provides for the correct placement of boiler units and auxiliary equipment in the boiler room.

I choose a boiler room of closed type, since the calculated external temperature for heating tn < 300C (equal to 320C).

The boiler room equipment is arranged in such a way that it can be built from unified prefabricated structures. One end wall shall be free in case of boiler room expansion.

In the boiler room there are two exits located in opposite sides of the room, with doors opening outside.

The distance from the front of the boilers to the opposite wall should be at least 3 m, with mechanized furnaces at least 2 m.

It is allowed to install blast fans, pumps and heat panels before the front of the boilers. At the same time, the width of the free passage along the front is taken to be at least 1.5 m. The passages between the boilers, boilers and boiler walls are left equal to at least 1 m. The clearance between the upper elevation of the boilers and the lower parts of the building coating structures should be at least 2 m.

1-boiler;

2-mains water pumps;

3-heater;

4-deaerated water pump;

5-sodium-cationite filter;

6-tank water level;

7-blast fan;

8-smoke pump;

9-intermediate tank;

a 10-pump for supplying water;

XIII) Literature

Course design in heat engineering: methodological manual/P.L. Lekomtsev, Yu.V. Novokreschenov, L.P. Artamonova, S.A. Kolesnikov. - Izhevsk, IzhGSHA, 2002-95 p.

Calculation of boiler room thermal diagram: Method. Decree ./Yu.V. Novokreschenov, FGOU VPO IzhGSHA. - Izhevsk, 2005 - 54 s.