S E C T I O N III.

BOILERS

LESSON 6

BOILER DESIGN
The boiler is the heart of a steam power plant. It is a device
for converting the chemical energy contained in fuel to
heat energy in the steam. There is a burner which mixes air
and fuel for combustion, a metal surface for transferring
heat from the hot gases to the water, and water for conver -
sion into steam.
Steam bubbles are formed on the inside surface of the
boiler, released from this surface and passed upward through
the water. Because the steam bubbles are released from the
boiling surface at the bottom of the boiler and the voids are
replenished by water from the upper colder portion, we
have a natural circulation boiler. That is no mechanical
means are used to cause the steam to pass upward and the
water to pass downward.
Every boiler must convert the chemical energy contained
in the fuel to heat energy in steam. In order to do this the
boiler must cool the hot combustion gases to the minimum
possible temperature to recover as much of the heat energy
in the gases as possible, and the circulating steam and water
must cool the metal tubing in the boiler effectively.
Fig. 6 shows a modern water-tube boiler. Burners are
located in front of the furnace. The furnace is like a large
box enclosed on three sides, the roof, and the floor by
panels of steel tubing. All of the tubes (furnace wall
floor, and roof tubes) are connected through a system of
headers and piping to both the upper and lower drums.
The fourth side of the furnace is enclosed by a row of screen
tubes which are widely spaced. The first row is backed by
several more rows of tubing also spaced widely. This
section of the boiler is called the boiler tube bank. All of
these tubes are also connected to the upper and lower
drums.
All of the tubing surrounding the furnace is called ra-
diant heat transfer surface because flames emit radiant
heat energy and these tubes absorb the radiated energy.
 The tubes behind the first row in the boiler tube bank
are not exposed to radiant energy from the flame. These
tubes are considered convection heat transfer surface because
they absorb heat from the hot gases by means of convection
heat transfer.
boiler tube
banks

water
walls
radiant surface
Surface

downcomers

economizer

Superheater
roof ' first pass

burners boiler tube

bank
furnace •superheater
second pass
water wall lower water
header drum
floor

SECTIONAL ELEVATION Fig.6.

Marine water-tube boiler.
The gases that pass from the furnace and through the
boiler tube bank are still very hot. In order to obtain more
of the thermal energy from the gases, additional convection
heat transfer surface is provided. Superheater tubing is
used to further cool the gases. No boiling takes place in these
tubes; they are fed with saturated steam from the top of the
upper boiler drum and as the gases are cooled the steam is
superheated. The figure shows that the superheater is divided
into two sections.
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 After the superheater an economizer is provided to cool
the gases further. No boiling occurs in the economizer. The
economizer receives feed water at one end, and the heated
water at the other end is fed directly to the boiler feed pipe
located in the upper drum.
The figure does not show a gas air heater. Air heaters are
used to heat combustion air and to recover more of the heat
energy from the exhaust gases before they are sent to the
stack.
Words to be Known
design [di'zain] конструкция to call [ ko:l] называть to
steam power plant паросиловая surround окружать radiant
установка радиационный flame пламя to
to convert превращать emit излучать to absorb
steam nap поглощать to expose открывать
burner ['Ьэ-.nэ] форсунка to consider рассматривать, счи-
combustion горение тать
surface I'sэ:fis] поверхность to obtain получать thermal
bubbles пузырьки energy тепловая энергия
inside внутренний additional дополнительный to
to release высвобождать provide обеспечивать
voids пустоты superheater пароперегреватель
to replenish пополнять further [ 'fэ;зэ] дальнейший
to cause заставлять boiling кипение to feed (fed;
in order to для того чтобы fed) питаться saturated
to recover восстанавливать, по- насыщенный to divide делить,
лучать обратно разделять economizer
tubing трубы экономайзер to occur
effectively эффективно происходить to receive
furnace l'fэ:nis] топка получать feed water
enclosed закрытый питательная вода directly
roof подволок (топки) непосредственно feed pipe
floor [flо:] под (топки) питательная труба air heater
to connect соединять воздухоподогреватель to use
header ['hedэ] коллектор применять, использовать
piping трубопровод; трубы exhaust [ig'zo:st] выход, выхлоп
row Irou] ряд to send (sent; sent) посылать
screen экран stack дымовая труба
widely широко
to space размещать
 Notes
natural circulation boiler котел с естественной циркуляцией
mechanical means механические средства hot combustion
gases горячие продукты сгорания row of screen tubes ряд
экранных трубок water-tube boiler водотрубный котел boiler
tube bank пучок котельных трубок
radiant heat transfer surface радиационная теплопередающая поверхность
convection heat transfer surface конвективная теплопередающая поверх-
ность
61
superheated steam перегретый пар
exhaust gases уходящие газы
upper boiler drum верхний котельный барабан (пароводяной)
gas air heater газовый воздухоподогреватель
rows of tubing ряды трубок
sectional elevation разрез продольный
floor под (топки)
water wall header коллектор водяного экра-
на
furnace burners топка
superheater first pass форсунки
первая секция паропере-
boiler tube bank гревателя
superheater second pass пучок котельных трубок
вторая секция паропере-
lower water drum гревателя
sectional plan нижний (водяной) барабан
radiant surface поперечный разрез
water walls радиационная поверхность
downcomers водяные стенки, экраны
convection surface нисходящие трубки
roof конвективная поверхность
feed pipe подволок, покрытие топки
dry pipe питательная труба
upper drum заборник сухого пара
economizer верхний барабан
экономайзер
 THE FURNACE

A furnace provides steady burning of fuel. It is restricted

by surfaces forming combustion space.
The chief function of a combustion process is to obtain
a thorough mixture of fuel and air and burn it in suspension.
Hence large furnace volumes are required. In modern boil-
66
ers the furnace front wall is exposed and formed from re-
fractory fire brick backed with high temperature insulation.
The furnace side, rear wall and roof are fully water cooled
and these areas are lined with insulation.
To provide the efficient combustion process of burning
oil fuel, a certain set of conditions is necessary: maintenance
of high furnace temperature, provision of continuous oil-
fuel and air supply and removing products of combustion.
Different types of burners have been designed for burning
liquid fuel. Mechanical oil burners and steam-assisted ones
a) mechanical oil burner b) rotary cup atomizer
 Vane

nozzle
fuel supply
burner
diffuser

Fig. 7. Fuel burning equipment.

are employed to obtain efficient atomization. Mechanical

atomizing oil burners may be classified according to their
method of atomization as centrifugal atomizers and rotary
cup atomizers.
Oil-fuel burning equipment consists of atomizer proper
and air registers, controlling the air supply. The air regis -
ter has vanes and a diffuser. The latter is for the flame pro-
tection and a better mixing of oil with air.
The oil is given rapid whirling motion in the burner inner
chamber and then discharged through a nozzle as a cone-
shaped spray. Air for combustion is supplied at the burner.
It passes through vanes, which give it a whirling motion.
This results in thorough mixing of oil fuel and air at the
atomizer nozzle. The oil fuel supplied to such atomizers
should be heated, as heating decreases oil viscosity.
As to atomization quality and reliability in operation,
rotary cup atomizers have proved reliable in marine prac -
tice. They may be either electrically or steam-turbine driv-
 Words to be Known
steady ['stedi] устойчивый proper собственно
thorough тщательный to burn air register воздушный регистр
] (burnt; burned) vane лопасть
жечь, сжигать diffuser диффузор
hence отсюда flame пламя
fire brick огнеупорный кирпич chamber камера
insulation изоляция rear wall inner внутренний
тыловая, задняя стенка to discharge выбрасывать
maintenance поддержание nozzle сопло
provision обеспечение continuous cone-shaped конусообразный
непрерывный fuel supply spray струя
подача топлива air supply to decrease уменьшать
подача воздуха removing oil viscosity вязкость топлива
удаление atomization quality ['kwoliti] качество
распыление centrifugal reliability надежность
центробежный equipment to prove зд. оказываться
оборудование

Notes
furnace volume объем топки
fully water-cooled furnace полностью экранированная топка
set of conditions комплекс условий
products of combustion продукты сгорания
mechanical oil burner механическая форсунка
stearn-assisted burner паромеханическая форсунка
rotary cup atomizer ротационная форсунка с распылительным стаканом
burning equipment топочное оборудование
whirling motion вихревое движение
inner chamber внутренняя камера (завихрения)
marine practice морская практика
electrically driven, steam-turbine driven приводимый в движение (от)
 BOILER PARTS THE
SUPERHEATER

The use of superheated steam has become common practice.

This steam can be transmitted over great distances with very
little heat loss, results in decreased steam rates, and has
reduced turbine-blade erosion to a minimum.
Steam heated above the temperature of saturation cor-
responding to the pressure is said to be superheated. Super-
heating surface is all surface exposed to steam on one side
and hot gases on the other. In some installations when it is
desired to reheat or resuperheat steam after it has been used,
reheater superheaters are employed. These may be of the
separately fired type or they may be included in the main
boiler setting. When saturated or only slightly superheated
steam is required for the auxiliaries from a high pressure
unit, a desuperheater is usually placed in the steam drum
to supply desuperheated steam. The function of the desuper-
heater is to maintain uniform steam flow through the super-
heater and provide cooled and sometimes saturated steam
as it is required.
There are two general types of superheaters: radiant and
convection. The former is placed in the furnace. The con-
vection type is more generally used on ships. These are
placed in one of the gas passages of the boiler where the heat
is transmitted by convection.
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 The convection type superheater usually consists of two
headers into which seamless steel tubes are rolled. The
tubes are connected to the steam inlet header and to the su-
perheater outlet header. Steam from the boiler circulates
through these tubes. Access to the tubes is had by caps. Su-
perheater tubes range from 1 to 2 in. in diameter; the temper-
ature rarely ever exceeds 550 deg. C, as the tensile strength
of most metals decreases rapidly after passing 350 CC.
The boiler drums or shells are designed for a certain max-
imum operating pressure. When for any reason the steam
pressure gets above the safe maximum, the safety valve
should open and steam discharged.

Words to be Known
superheated steam перегретый uniform steam flow равномерный
пар поток пара
heat loss потеря тепла radiant superheater радиацион-
decreased steam rates уменьшен- ный пароперегреватель
ный расход пара convection конвективный
saturated steam насыщенный gas passages газоходы
пар seamless steel tubes бесшовные
superheating surface поверхность трубы
перегрева to roll развальцовывать
reheater superheater промежу- access ['aeksis] подход
точный пароперегреватель to exceed превышать
to employ использовать tensile strength предел прочности
desuperheater пароохладитель shell корпус, кожух
desuperheated steam охлажден- safety valve предохранительный
ный пар клапан
to maintain поддерживать to discharge стравливать