Boiler Testing

8/16/2019 Boiler Testing

1/342

LAND,^

MRINE,:

;&

-DdGOMOl^iVi:

BRYAN

:P0KKIS, M.

IKST.

G.E,


2/342

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Cornell

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Library

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in

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Cornell

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Library.

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States

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the text.

http://www.archive.org/details/cu319240046074


5/342

THE

HEAT

EFFICIENCY

OF

STEAM

BOILERS


6/342

STANDAR

D

WORKS

FOR

ENGINEERS.

/^AC? rkii ANTr» AID PMrilMP^-

A

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UAS,

UlL,

A1>U

/\1K.

i:il>UIl>E^.

Combustion

Motors

without

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BRYAN

DONKIN, M.Inst.C.E.

Second

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throughout

and

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With numerous additional

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General

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Gas

Engines

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History

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Engine—Chemical

Composition

of

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in

Gas

Engines—

Utilisati

Heat—

Explosion

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Motors

:—

History

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Various Types—Priestman's

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Hot-Air

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BOILERS,

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MUNRO'S

STEAM

BOILERS

:

Their Defects, Management,

and Constructio

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MuNRO,

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FUEL

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: A

Manual for Users of

Steam

and

Water.

By Pr

Fkanz Sohwaokhofek,

of

Vienna,

and

Walter

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Browne,

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late

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A MANUAL

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OTHER

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M.Inst.C.E. Cr

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A

MANUAL

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MARINE

ENGINEERING.

The

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a

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Machinery.

By A. E.

Seaton, M.Inst.C.E.,

M.Inst.

Mech.E.,

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Thirteenth

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MARINE

ENGINEERING

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Engineers,

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Architects, and others. By

A.

E. Seaton,

M.Inst.C.E., and H.

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M.Inst.Mech.E. W

Illustrations. Leather.

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STEAM AND

STEAM

ENGINES

(A

Text-

Book

of).

By Prof. Jamies

M.Inst.C.E.,

M.lnst.E.E.,

F.R.S.E.,

Glasgow and West

of Scotland

Technical College. With

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Twelfth

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8s.

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The

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The Engineer.

JAMIESON'S

ELEMENTARY MANUAL

OF STEAM

AND

THE

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ENGINE.

Fifth

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Quite the

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VALVES

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VALVE-GEARING

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Will prove a VERY

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LOCOMOTIVE

ENGINES:

Their

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A

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8vo. With

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Ravenshear,

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of H.M. Patent

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ENGINE-ROOM

PRACTICE.

A

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Marine. Including

the

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the

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on Board

S

By

John G.

Liveksidge, Engineer,

E.N.,

A.M.lnst.C.E.,

Instructor in Applied

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College,

Greenwich.

With numerous

illustrations

LONDON:

CHARLES

GRIFFIN

&

COMPANY,

LTD.,

EXETER ST., STRAN


7/342


8/342


9/342


10/342


11/342

THE

HEAT

EFFICIENCY

OF

STEAM

BOILERS-

LAND,

MARINE,

AND

LOCOMOTIVE.

WITH

TESTS

AND

EXPERIMENTS

ON

DIFFERENT

TYPES,

HEATING

VALUE OF

FUELS,

ANALYSES

OF GASES,

EVAPORATION,

AND

SUGGESTIONS

FOR

TESTING

BOILERS.

BY

,

BRYAN

pONKIN,

MEMBER

OF

THE

INSTITUTION OF

CIVIL ENGINEERS

;

MEMBER OF

THE

INSTITUTION

OF MECHANICAL

ENGINEERS

;

MEMBER

OF

THE

AMERICAN

SOCIETY OF

MECHANICAL

ENGINEERS

;

MEMBER OF THE

VEREIN

DEUTSCHER ING^NIEURE

;

AUTHOR

OF

A

TEXT-BOOK

OF

GAS, OIL,

AND AIR ENGINES,

ETC.

WITH

NUMEROUS TABLES,

PLATES,

AND ILLUSTRATIONS

IN THE

TEXT.

LONDON:

CHARLES

GRIFFIN &

COMPANY, LIMITED,

EXETER

STREET,

STRAND.

1898.

[All

Rights

Reserved.}


12/342

'ii^b

\-*»\

^')

^.

a^^(J.S'

^


13/342

PREFACE.

In

his professional

career

the

Author

has had

frequent opportunities, during the

twenty-five

years,

of

making

Tests

on

Steam

Boilers.

Some time ago he

began

to

tabulate many

experiments,

and, as

the list

continua

increased, he

considered

that

it

might prove

useful

as a

collection

of

facts, if thrown i

the shape

of

a book. With

this

object

he

has

added

the results

of

various

trials

made

others, as well as chapters on

combustion

and

kindred

subjects. He has

endeavoured

make the

book as practical as possible, and useful

as a

reference for Engineers, and

th

interested

in the

economical production of

steam.

The history

of

Steam

Boilers,

wh

dates

back 100 to 150 years, is not touched upon, as it would be foreign to his purpo

Boiler

tests,

in

his

opinion,

are

useless

and

even

misleading,

unless the

heating value

of

fuel,

analysis

of

gases, evaporation

of

water,

and

boiler efficiency

are given.

Ma

engineers are

satisfied

with recording

only

the

evaporative

results in

lbs.

of

water

per

of

fuel

;

but,

considering

how

largely

fuels

differ

in their heating value and percentage

incombustible

matter,

such tests

cannot

be

regarded

as

satisfactory or exhaustive.

much heat is

given to

a boiler in

the

shape

of fuel,

the

greater part

of

which

is usefu

employed in

evaporating

water,

while a

certain

percentage,

large

or small,

is

wast

Many

manufacturers,

even

in

England,

will now

guarantee a

certain

boiler

effici

with

a

given

fuel. In

other words,

with

coal

of

known

quality and heating

va

(without

economiser)

they

will

guarantee that,

say,

70%

of

the heat shall

be

conver

into

steam

of

a

certain pressure

from

a certain

temperature of feed water,

and so ma

lbs.

of

water

evaporated per

square

foot .

of heating

surface

per

hour.

Boilers

cover

so

large

a

field that

the

Author

has been obliged to

confine

himself

o

to

those

parts of

the

subject

which deal with tests, combustion,

smoke,

etc.,

and

has


14/342

VI

PREFACE.

touched

upon other

questions,

which

are

treated

fully

in

many

books.

On

the

v

important

topic

of

the composition of all

kinds

of fuel,—solid,

liquid,

and

gaseous,

—b

in

England

and elsewhere,

the

reader is referred to

other

works,

especially

those

treat

of

the

analysis

of

combustibles and

their heating value. The

titles

of

some

of

th

books

will

be

found

in

the

Bibliography.

It

is mainly

by

collating and

comparing a large number of

reliable

tests,

that

principles

governing

combustion

and

efficiency in different

types

of

boilers

can be

termined.

The Author hopes,

therefore,

that

his

contribution

to

the

heat

question,

breaking

comparatively

new

ground,

will

lead

the way,

and incite others

to

make mo

complete

collections

of careful boiler experiments,

the

only

mode

in which the

subj

can be thoroughly and practically studied.

Most

of the well-known boiler types made

by leading English

and

foreign

engineers w

be

found represented

in

the Tables of

Tests.

The

trials have been drawn from

trustwor

sources,

such as

The

Proceedings

of

the

Institution

of

Civil

Engineers,

Proceedings

of

Institution

of

Mechanical

Engineers,

of

the

Institution

of

Naval

Architects,

and

of

the

Nort

East

CocLst

Engineers

and Shipbuilders,

as well

as

The Engineer,

Engineering, from Ze

schrift

des

Vereines

deutscher Inginieure,

and

many

other

technical

journals

and

periodica

both

here,

on the Continent, and

in America. Some

Boiler

Insurance

Companies

England and

abroad

now publish in

their

yearly reports

experiments made

by

their o

engineers, and many of

these careful

trials (in which

the

heating

value

of,

the

fuel, analy

of gases,

&c.,

are given)

have

been

selected, especially when made by such compete

authorities

as Mr M.

Longridge

and

others.

It is difficult

to estimate the

number

of steam

boilers of

all

kinds used

in

all

countr

on land. At the end of the last

century

only a few thousand were

working,

and

th

were

no

locomotive or

marine

boilers.

Now

the

number

is

probably

about

three-quart

of

a

million.

This does

not include the number

of

locomotives

in

the

world, which m

be

taken approximately

at

124,000.

On

the Continent

all

boilers must be legally

registered, and marked with

a

Governme

stamp; but

as no such

law

exists in

England,

the number

in

use

is

not

easily

know

Very

large

sums of

money,

representing

many

millions sterling,

have

been

invested

steam boilers, and

thousands

of engineers

are

continually

studying

economy

in

coal. T

question

of

heat

efficiency

is, therefore,

not

a

small

one.

To

generate

steam

a very la

amount of

fuel

is

consumed every

year,

and

much is

wasted. If

10%

or

15%

could

economised, a

very moderate

estimate,

it

would

represent

a great

gain

to

the

world at

lar

The

total

annual

production

of

coal

in

all countries

a few years ago

was

400 millions

tons. We shall

not be far

wrong in

estimating that one-half,

or

200 million

tons,

is

us


15/342

PREFACE.

yearly

for generating

steam.

Putting

the cost

per

ton

at the low

average

price

of

we

get

100

million

pounds

sterhng

as about

the annual

value

of

the

fuel consumed

un

stationary,

semi-portable,

locomotive,

and marine boilers.

The

gradual

increase

in

the

pressures

of

steam is

also very striking.

At

the begin

of

the century

the steam

pressure

was only a

few

lbs. per

square inch

:

now

pressure

150 to 200 lbs.

and

more

are

common.

In

the

Tables

of

Eesults,

English

weights and

measures

have been

used,

although

Author

would

have

much

preferred to

keep

to

the

more

convenient

Metric

System,

but

time

has

hardly

arrived

for its

general

adoption

in

this

country.

Several

gentlemen

have

been

kind

enough,

at

the

Author's

request,

to

make

spe

boiler

tests

for

this book. To his

personal

and

other

engineering friends in Great Brit

the United

States, and on

the

Continent,

who

have helped him

much in

various

ways,

gratefully

acknowledges

his

indebtedness.

The

Donkin

and

Kennedy

series

of 21

t

on

different

types

of

boilers,

all

with

the

same coal, originally published

in Engineeri

have been

incorporated

in

the

Tables.

Mr

C.

J.

Wilson,

the

eminent

chemist,

kin

consented to look through the

chapter on

Combustion,

and

advantage

has been

take

some

of his

valuable

criticisms.

The

Author

will

gratefully receive notice of

any

errors,

and

will

also be glad

to

h

for

insertion

in a future edition, duly signed

particulars of

careful

boiler

tests,

accord

to

the

headings

adopted and

in

the

order

given

in

the

Tables.

At

the

end

of the book a collection of

drawings

of various

types

of

ancient

modern

steam boilers

will

be found.

B.

D

Rbigatb,

May 1898.


16/342


17/342

TABLE

OF

CONTENTS.

CHAPTEK I.

CLASSIFICATION

OF DIFFERENT

TYPES

OF

BOILERS.

Division

I.


18/342

HEAT

EFFICIENCY

OF

STEAM BOILERS.

Chaptbb III.

Tables

of

Experiments

on Boilers

—

contirmed.

Lancashire

—no

smoke

tubes. Hand firing,

,,

Berlin

trials,

—

no

smoke tubes.

Hand

firing,

....

,,

Dlisseldorf

trials,—no

smoke

tubes.

Hand

firing,

....

,,

German trials,

,,

with smoke tubes. Hand firing,

,

,

three flues,

no

smoke

tubes,

Dry back,

with

smoke

tubes,

,,

cold

air,

chimney

draught

(Spenoe),

,,

,,

forced

,,

,,

;) 3} 1i M -J

,

,

hot

forced

draught,

,

Summary,

Spenoe's

experiments, .

Wet

back

with smoke

tubes.

At sea,

Locomotire. Stationary,

>i J)

Agricultural,

Locomotive. Semi-portable,

Locomotive.

Running

on

rails, .

PAGE


19/342

CONTENTS.

CHAPTER

VI.

COMBUSTION

OF

FUEL IN BOILERS.

Conditions

of

combustion,

Admission

of

air, .

Heating

value

of

fuel,

.

,,

,,

formula,

.

Calculation

of

air

required,

.

Chemical

process of

combustion,

Hoadley's

experiments,

Analysis

of

flue

gases,

.

PAGE

133

133

134

134

135

135

135

136

Quantity of air required for

combustion,

Percentage

of

CO2

in escaping

gases,

.

Methods

of

calculation,

.

.

Places

for sampling gases,

Spence's

experiments,

.

Process

of combustion

in practice, .

Methods

of regulating it, . .

CHAPTER

VII.

TRANSMISSION

OF

HEAT

THROUGH

BOILER

PLATES,

AND THEIR

TEMPERATURE.

General remarks,

...

. 142

Plotted results

of

French

locomotive

trials,

143

Examples

of

transmission

of

heat,

143

Blechyndeu's

experiments,

.

145

Results,

.

153

Durston's

experiments,

153

Hirsch's

experiments,

.

Witz's

Kirk's

„

Ti-ansmission

through

Serve tubes,

Hudson

on

heat

transmission,

CHAPTER VIII.

FEED

WATER

HEATERS,

SUPERHEATERS,

FEED

PUMPS,

ETC.

Feed

water heaters,

Efficiency of

economisers,

Economisers. English type.

Green,

Scheurer-Kestner's

trials,

French feed water heaters.

Hale

on economisers,

General

conclusions,

Pimbley's

economiser,

.

Heating

feed

water by exhaust steam,

Trial of an economiser.

Superheating

steam

in boiler

flues,

164

165

165

165

166

166

167

167

168

168

170

Superheaters.

Hicks,

M'Phail

& Simpson,

Schwoerer,

Gehre,

.

Sinclair,

SerpoUet,

Schmidt,

Supply

of feed

water

to boilers.

Table

of superheating

steam,

Injectors,

Longridge

on

feeding

boilers.

CHAPTER

IX.

SMOKE

AND

ITS

PREVENTION.

Smoke from

factories,

.

.

176

I.

Nature of smoke,

. .

. 176

Chemical

combinations,

. .

177

II.

Methods

of

preventing

smoke,

.

178

Conditions

for

good

combustion,.

178

Method of introducing

air, .

179

Spence's experiments,

179

Gaseous

fuel,

. .

. .

180

Down-draught

furnaces,

.

.

180

Powdered coal

firing,....

180

III. Smoke

scales

181

Prussian

smokecommission,

scale adopted

by,

182

III.

IV.

Smoke

scales

continued.

Silence's

experiments.

Precipitation

of soot, .

New

smoke

scale,

Ringelmann's

smoke scale,

Diagi'am of five smoke

scales.

Smoke

commission reports,

.

English

commissions,

Prussian

smoke

commission,

Lewicki's

trials,

Paris

smoke

trials,


20/342

Xll

HEAT EFFICIENCY

OF STEAM

BOILERS.

I.

Sampling and

analysing

gases,

Sampling

—Waller's system,

Analysing,

Orsat

apparatus,

Winkler

,

Bunte

,,

Elliott

Dasymeter,

Eoonometer,

II. Measurement

of temperatures,

Pyrometers,

Ball thermometers,

Anemometers,

U-water

gauge.

CHAPTER X.


21/342

CONTENTS.

X

CHAPTER

XIV.

ON

THE

CHOICE

OF

A

BOILER,

AND

TESTING

OF LAND, MARINE, AND

LOCOMOTIVE

BOILERS.

Choosing

a

boiler.

Heating surface

required.

Notes

for

making

boiler

tests,

Coal,

Fires,

Gases,

Smoke,

.

Feed

water.

Instruments

required,

.

Blank

sheets

for

use in land

boiler

trials,

I'AGE

227


22/342


23/342

LIST

OF

ILLUSTRATIONS.

No.

OP

f

10.

Kg.

40.Bleohyndeii

experimental

boiler,

4jl.Bleehynden

experiments,

Plate

A.

1*187

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.

0'75

0'562

„

0-25

1

Plate

B.

0-468

,,

0-375

0-156'

0-812

4

1-187

0-187

thick,

Plate

C.

„

D.

,,

E.

53.

Durston's

experiments,

No.

1

54.

„

E6.

„

56.

„

57.

Durston's

Expts.

58.

„

„

^.^

,,

„

Fall

of

temperature

of gases,

Hirsch

experimental

boiler.

No.

2,

No.

5,

No.

6,

Small

experimental

boiler

used in

No.

9.

59.

60.

61.

Drawing of

smoke

tubes.

62.

Hirsch's

experiments

plotted, .

63.

Wright's feed

water

heater,

64.

Smoke

diagram.

Wegener

powdered

coal

firing,

65.

Smoke diagram.

Ringelmaun.

No.

0,

66.

„

„

,,

No.

1,

67.

„

,,

,,

No.

2,

'

68.

„

„

„

No.

3,

69.

,,

,,

,,

No.

4,

70.

„

„ „

_

No.

5,

71.

Waller's

gas

sampling

and analysing

apparatus,

72.

U-water gauge,

73.

Fuel calorimeter,

74.

Peabody steam calorimeter,

....

75.

Serve smoke

tubes,

.

. .

.

76.

Babcook

and

Wilcox marine boiler,

....

77.

Graphic

diagram of

boiler

efficiencies

for different

rates

of

evaporation,

78.

,

,

,

,

of

loss

of

heat due

to varying

amounts

of

CO2,

79.

Hoadley's

experiments

with

hot

air for

combustion,

80.

Old

stationary boiler,

1775

(Smeaton),

) „ ,

81.

Modern

Lancashire

boiler—

Two

internal

fires

)

^°

^^™^

^^^^'

82.

Boilers

of steamship

Luoania

I ™

,

83.

Old marine

boiler,

1820

j-lo same

scale,

.

84.

Great

Western Kailway.

Modern

express

locomotive

\

m 1

85.

Old

locomotive,

1825 (Stockton

and

Darlington

Railway)

/^° ^^™

^''*'®'

86. Steamship

Lucania,

general

view

\,^

,

87.

Margate

Steam

Yacht, 1815

'/

^°

^*™^

'^°*^^'

88. Three

flue

marine

boiler with

smoke

tubes, modem,

89.

„

„

,,

,,

back to

back

type,

,,

90.

Howden's

method of

heating air

for

combustion by

hot

gases,

91.

Belleville

water tube

boiler

—

modern,

y^.

,,

,, J J ,,

93.

Watt

stationary boiler,

1788,

94.

Newcomen

stationary boiler,

1772,

95.

Old

stationary

boiler,

1750,

.

.

. .

96.

Old

locomotive

boiler,

1815,

.

...

97.

Lancashire

boiler, showing dirt, soot,

etc.,

as in

an

actual boiler,

98.

,,

,1 ,,

,,

cross section,

99.

Cornish

boiler with

smoke tubes, cross section

(modern),

100.

„ ., 1)

,,

longitudinal

section (modern),

101.

Lancashire

boiler (modern), cross

section,

102.

,,

I)

>i

longitudinal section,

103.

Longitudinal

and

cross

section

of

Cornish

boiler. Special type.

F

•

.

.

.

.

.

.

.

.

To

face

page


24/342

XVI

HEAT EFFICIENCY

OF STEAM

BOILERS.

No. OF Fig.

p

Fig. 104. Cross

section,

Cornish boiler,

.

.

....

105.

Dry

back boiler

with

two furnaces and smoke tubes,

. .

106. Cornish

boiler with

Ferret

grate, longitudinal

section,

.

. .

107.

,,

„ ,,

„

cross section,

.

. .

108.

Lancashire

boiler,

three

flue.

General

view, external,

. .

109.

,,

,,

two flue.

„

,,

„

.

110. Lancashire boiler, front

view

and section,

showing

brick

setting,

. .

111.

Dry

back boiler, two farnace tubes and smoke

tubes,

112. Vertical

boiler

with smoke tubes,

elevation,

.

.

113.

,, ,, ,, ,,

section,

.

114. Vertical boiler with water tubes, section,

. .

115.

Vertical

boiler

with

large water tubes, .

.

116.

„

,,

,,

.

.

117.

Vertical boiler with inclined water

tubes,

118.

„

„

,,

119.

Two-storey

boiler,

longitudinal section,

120.

,,

,,

cross

section,

.

.

121. Thornycroft

water

tube

boiler,

external view,

. . .

122.

,,

,,

,,

showing tubes,

.

123.

,,

,,

,,

general view,

.

124 Yarrow small water tube boiler, .

.

125. Serpollet water tube boiler (two views),

126.

Climax

small

water

tube

boiler

I

,,

.

^ o,

[

three

views,

i^i-

,, ,,

,, )

128.

Water

tube

boiler,

. . .

129.

Cross section of water

tube

boOer,

.

130.

Normand

small water tube boiler, .

.

131.

Clarke

Chapman

small

water

tube

boiler,

2

132. Hornsby

large

water tube boiler,

.

.

2

133.

Babcock

and

Wilcox large

water tube

boiler,

2

134.

Haythorn's small

,,

,,

.

2

135. Vicars'

stoker, cross

section,

.

.

2

136. Hodgkinson's stoker,

elevation,

. .

.

2

137.

Vicars' stoker, general

view with several

boilers,

.

. 2

138.

„

,,

elevation,

.

.

2

139. Green's economiser,

elevation,

3

140.

,, ,,

plan,

.

.

-300

141. Small feed water heater,

copper

coil, .

.

3

142. I

I

^.

/<

Examples

of

joints

between

furnace tubes

and

front

plates

V

. .

3

145;

(

j

146.

Feed

water heater,

small

tubes.

Two

views,

. . .

3

147.

1

)

148.

-j

Examples of

corrugated

furnace

tubes

for internally fired boilers

\

.

3

149.

I

J

*^*

In

each

of the

Tables of

Tests a

small drawing

of the

boiler used is

given, but not

numbered.


25/342

STEAM

BOILERS

AND THEIR

HEAT

EFFICIENCY.

CHAPTEE

I.

Classification

of

Different Types of

Boilers.

Internally Fired

Boilers

—

Cornish,

five types

—

Lancashire,

three types—

Dry

Back—

Wet

Back or

Marine—Lan

shire,

Spence's

Experiments

—

Locomotive—

Two-storey, five

types

—

Externally

Fired

Boilers

—

Cylindrica

Lancashire—

Elephant, four

types

—Two-storey

—

Water

tube

—

Babcock and

Wilcox—

Stirling

—

Thornycrof

Belleville

—

Yarrow

—

Vertical Boilers.

Steam

boilers

may be

divided

into

three

classes,

according

to

the

uses to which they

are

applied,

namely

:

1.

Stationary

boilers

for

mills or

factories,

having

generally

a

fixed

chimney.

2.

Boilers

having

an

iron chimney,

which are

semi-portable

and

often in motion

while

at work,

such as

marine and

locomotives.

3.

Boilers

forming an

intermediate

class

be-

tween

the

two

former, which

are

gener-

ally

at

rest

while

working,

but

portable

on

wheels,

with

a

short iron chimney.

This

type

includes

the large

agricultural

class,

steam

rollers and

traction engines,

road

carriages,

fire

engines,

tramways,

etc.

The

boilers

treated

in

this

book

are

classified

into

two

main

divisions:

I.

Internally

fired,

the

grates

or

furnaces

being

placed inside

the

boiler

and

surrounded by

water

;

and

II. Exter-

nally

fired, or

those

having

their

fires external

to

the

water

of

the

boiler,

and the

grate

and

furnace

underneath,

or

at the front.

In

both

these

two

classes

stoking may

be

carried

on

either

by

hand or

automatically,

by

means

mechanical

stokers, and natural,

forced,

or

duced

draught

may be

used.

Different

Types.

—

In

the following

pa

drawings and

descriptions are

given of

five

ferent

types

of Cornish boilers, both

with

a

without smoke tubes, three kinds of

Lancash

boilers,

the

dry back, wet

back

or marine ty

locomotive

and

agricultural,

running

or

fix

and four

types

of

two-storey

boilers.

All

th

are internally

fired.

Of externally fired boil

the following are described

with

drawings

Several types

of

water tube boilers, three

ty

of

elephant

boilers, two-storey

cylindrical

w

smoke

tubes,

and

various kinds

of

verti

boilers.

DIVISION

I.

INTERNALLY

fired boilers

may

be ag

sub-divided

into

the

following

types

:

li Cornish

boilers,

so caUed because t

were

first

made

in

Cornwall,

and

are

still mu

used there.

They are distinguished

by

hav


26/342

HEAT

EFFICIENCY

OF

STEAM

BOILERS.

Fier.

1.

only

one

furnace

tube, one

grate,

and no

smoke

tubes.

An

example

of

this type

is

shown

in fig.

1.

It

has

generally a

brick-work casing,

three

horizontal

brick

flues,

and

a

horizontal

cylindrical

boiler

shell,

with

a

single

furnace

tube

wholly surrounded by

water,

and

carried

the

whole

length

of

the

boiler.

The

hot

gases

pass

first direct

through

the furnace

tube to the back of

the

boiler, then

return to the front

along

the

bottom

of

the

cylindrical shell, and

divide into

two

streams

on

both

sides, being

thus

carried

horizontally

three

times

the

length

of

the boiler,

from

the grate

to the

chimney.

As

an

alter-

nate

arrangement,

the

gases

after

leaving the

furnace

tube are

sometimes

directed first

through

the

two

side flues

and

then

along the bottom of

the

boiler

to

the

chimney. This type

is

without

any

smoke

tubes, but

has

often a few

conical

water tubes, and

sometimes a corrugated furnace

tube. Twenty-five

experiments on

it

with

coal

or gas coke and

chimney

draught

will be

found

on

pages

21 to 25.

In

these

experiments the

boiler efficiency,

without

economisers,

varies

from

53%

to

81|%.

The

best results were

obtained with an

evaporation

of

from

2J

to

3

lbs.

per square

foot of heating

surface

per

hour,

and

with

10

to

20 lbs. of coal

burnt per

square

foot

of grate

per hour. The

highest efficiencies

were produced

when

evaporating

3

lbs.

of

water

per square

foot

of

heating surface per

hour.

Three

experiments,

all

with

chimney draught,

are added on

page

25,

with

Cornish

externally

fired boilers,

which

should

have been

placed

among the

second

series

of

trials.

The boiler

efficiency

in them

was

from

60%

to

66%.

With

the latter

2j

lbs. water were

evaporated per square foot

of

heating surface

per

hour.

2.

Cornish boiler

with

return smoke tubes

(fig.

2).

—

This

boUer

generally

has

external brick

flues

and

a

cylindrical

shell. The iron

furnace

tube

is

carried

the

whole

length of

the

boiler,

and

the

grate

is placed

inside

it.

The

tube

is

not

in

the

centre

of

the shell, and space is left

on

one

side

for a

series

of

smoke

tubes

running

parallel

with

it

from end

to

end, as shown.

Fig. 2.

The direction of

the hot

gases

is

first

throu

the

fiirnaee tubej

back

through

all

the

smo

tubes,

returning

either

through

the

bottom

side

brick

flues

to chimney.

Xo

experimen

on this type of boiler

are

given in

the

Table

3. Cornish

boiler

with

cylindrical

she

(fig.

3),

central

furnace tube, and

smok

tubes.

—

The

furnace

tube

is

carried

only

part

Fig.

3.

through

the

boiler, and

a

set

of short smo

tiibes are placed

between it and the back,

shown.

A

second

set

surrounding

the furna

tube

run the whole

length of

the

boiler. Th

direction of gases is

through

the furnace tu

and

short

smoke tubes,

then

through

the

lo

smoke

' tubes to

the

front,

and

so

through t

external brick

flues

to

the chimney. No

exper

ments

on

this type

will

be

found in the Tables.

4.

Cornish

boiler

(fig.

4),

with

one

set

short smoke tubes

at

the

end of

the furna

tube.

This

boiler is

somewhat similar

to t

last,

with

external

brick

flues, cylindrical shel


27/342

COENISH AND LANCASHIRE BOILEES.

Fig. 5.

results

seem

to have been obtained with

about

2 lbs.

of water

evaporated per

square

foot

of heat-

ing

surface per

hour,

and

very

inferior results

with

^

lb. per square foot.

All these varieties of Cornish boilers with

internal grates, with and without smoke

tubes,

are common

both here

and

on

the

Continent,

and

are chiefly used

for

stationary purposes.

5. Cornish boiler with smoke tubes

(fig.

5).

—

This type

has

also a

cylindrical

shell

similar

_

to

the

last. Here the

furnace

tube

is

placed

centrally

to

the horizontal

shell,

and

carried

right through,

with

a

series

of

small

smoke

tubes

running along

both sides of

it,

the whole

length

of the

boiler,

as

shown.

The direc-

tion

of

gases is first

through

the

furnace

tube,

then through

the

smoke tubes,

and round

through the external

brick-work flues

to

the chimney as

before.

Four experiments

are given

on page

27 on this

boiler, with

efiiciencies

from

66%

to

81%.

With

the

latter 2 lbs.

of

water were

evaporated per

square

foot of

heating surface

per

hour, with

chimney draught

and no

economiser.

6.

Lancashire

boiler

(fig. 6).—

The

difi'erence

between

this type

and the Cornish

is

that it

has

two furnace tubes,

and

two internal

grates in-

stead of

one.

It

is a

favourite

boiler

in

Lanca-

shire, whence

its name, and is

much

used

in mills,

factories,

and

other large

industrial

works.

It has

a

horizontal

cylindrical

shell

and

furnace

tubes set

in

brick-work

with

external brick

flues.

The

furnace

tubes

are

plain or

corrugated,

and

are

carried

right through

the boiler.

The

direction

of

the

gases

varies

somewhat,

but is

generally as follows

:

—

Through

each

furnace

tube,

then

under bottom

brick

flue to

the front

of

the

boiler,

where

they

divide

and

pass

through

the

two

side

flues

to

chimney.

Sometimes after

leaving

the

furnace tubes

the

gases are

carried

first

through

the two side

flues,

then

unite and

pass

along

the

bottom flue

to

chimney. This

boiler is

very

largely

used in

England

for

stationary

purposes,

and

a

good deal

in

Germany and

Austria.

The

furnace

tube

is

often

provided

with

cross

GaUo-

Tlfr.

6.

way

conical water tubes. In

this

type there

no

smoke

tubes.

The

numerous

experiments on

this boiler

pages

29 to

59 are divided

into machine

and h

stoking trials.

Tests with machine firing or

mechani

stokers.

—Forty-two experiments

are

given

pages

29 to

35,

with

and

without economise

and chiefl.y with

chimney

draught.

About

se

or

eight

difierent types of machine

firing

w

used,

with

different rates of coal burnt per

squ

foot

of grate surface,

and

of evaporation

square foot of heating

surface

per hour. Most

these

experiments

were made in England.

boiler efiiciencies, with different conditions

soot

or

deposit, varied

much,

from

52%

to

7

without

economisers. The

gain

in

effici

with

the

latter

varied from

6%

to

15%,

acco

ing to their area,

condition, dirty or clean,

other

circumstances.

The

total efficiencies

boiler

and

economiser

together

varied

from

6

to

87%.

The best

results with economisers w

obtained

when evaporating

from

4

to

5^

lbs

water

per square foot

of heating

surface

per

ho

The

maximum

lbs. of coal

burnt

per

square

of

grate

per

hour

was

56 lbs., and the minim

9

lbs.

with small

economisers.

Tests

with hand

stoking.

—A

hundred

fourteen

experiments

are given on

pages

37 to

both with

and without

economisers,

and chi

with

chimney draught.

Most of them

w

made

in

England,

but

some on the Contine

The

rates

of

firing,

evaporation,

and

bo

efficiency

vary

much, as

might

be

expect

owing to

the

great variety

of fuels, gra

draughts,

stokers,

temperature

of gases, exc

of

air

in

gases, quantity of soot and deposit,

other

working

conditions. It

is difficult

summarise

such

a

large

number of experimen

Without

economisers

the best results

seem

to

with 3 to

4-|

lbs.

of water evaporated

per

squ

foot

of

heating

surf

ace per hour, and

70%

to

7

boiler efficiency

;

with

economisers the

results

are 4

to

51-

lbs. of water

per

square

of

heating

surface

per

hour,

and

an

efficiency

83%.

From

6%

to

12%

may be added for

efficiency

of

the

economisers alone,

according

their area, etc.

Dusseldorf Exhibition

experiments

(188

—

These,

given

on page

55,

furnish

an

inter

ing

set

of

sixteen

experiments,

all

on the

s

Lancashire boiler,

with the

same

stoker


28/342

HEAT

EFFICIENCY

OF

STEAM

BOILERS.

steam

pressure, but witliout

economiser,

and

burning

eight

different

kinds

of

coal.

Taking

the

set

of

eight

experiments with

cast-iron

grate

bars only,

the

efficiencies varied

from

56J%

to

69%,

the

water

evaporated per square

foot

of

heating

surface

per

hour ranged

from

4

to 4

8

lbs.,

the latter

giving

about the best

results.

The

coal

was

of

good

heating

value.

The

excess

of

air at

the end of

the furnace tube and

at the

damper

is

not given, but

the

difference in

excess

of air

at

these two places, beyond

that

theoretically

required

for

combustion, is

shown, and

proved

that

there

was air leakage

through the brick-

work.

These

experiments are

arranged

in

order of

boiler efficiency.

They

were very

carefully

carried

out, and

the

author

was fortunate

enough

to witness

some of

them.

Prussian

Smoke

Commission.

—

Eight experi-

ments

will

be

found on

page

53 on

the same

Lancashire

boiler,

without

economiser,

made

by

very competent

German engineers,

under

the

auspices

of

the Prussian

Smoke

Commission.

Also

another

set

of

three

experiments

on

another

Lancashire

boiler.

In

the

latter

the

maximum

boiler efficiency was

80%

without economiser, with

an

evaporation of

4^

lbs.

water

per

square

foot

of heatiag surface, and

24

lbs.

fuel

per

square

foot

of grate surface per hour. In

these

good

experi-

ments the gases were

carefully

analysed in

two

different places, at the end both of

the

furnace

tube and of the boiler

flues,

and the

results

always

show

leakage of air

through the

brick-

work,

although

care was taken

to

prevent

any

infiltration.

7.

Lancashire boiler with

short

smoke

tubes

(fig.

7).^

—

-This type has

a

cylindrical

shell

and

two furnace tubes, with internal grates like the

last.

The

furnace tubes, however, are not carried

to the end

of

the boiler, but are followed

by


29/342

DRY

BACK

AND WET BACK BOILERS.

boiler

shell

to

the

chimney.

This

boiler

is used

on

land,

and

is

usually

set

in

brick-work.

Kve

experiments

on

this

type,

with

chimney

draught

and

hand

firing,

and

without

economisers,

will

be

found

on

page

63.. The

water

evaporated per

square

foot

of

heating

surface

per hour

varied

from

3

to

4^

lbs.,

and

15

J to

21|

lbs.

of coal

were

burnt

per

square

foot

of grate

surface per

hour.

The

boiler

eificiency

was

not

high,

varying

from

55%

to

65%.

The

most

economical

rate

of

evaporation

with

this

type

is

about

3J

lbs.

water per

square foot

of

heating

surface

per

hour.

One

experiment

on this

boUer with

mechanical

stoking

and

without

an

economiser

is also

given,

in

which

the

efficiency

was

73^%,

but

this

result

was

obtained with

superheated steam,

when

evaporating

8^

lbs. of

water

per square

foot

of

heating

surface

per

hour

(see also pages

65

to

71

for Spence's

experiments

on

a boiler

of similar type).

10.

Wet

back

or

Fig.

10.

marine

type

(fig.

10).

—

This

boiler

is

similar

to

No.

9,

having

two

Lancashire

furnace

tubes

below, and smoke

tubes above, but^they do not

run the

whole

length of the boiler,

a

water

heat-

ing surface being

left at the back,

hence

the

n

of

wet back.

The

direction of gases

is

thr

the furnace tubes, then

forward

through

the s

smoke

tubes, and thence to

chimney.

This

is

much

used at

sea,

and sometimes

for

statio

purposes.

Pig.

10a shows

two of

these

boil

each

with three

furnace

tubes,

arranged

bac

back

for

steam-ships,

forming

one

boUer

w

six grates and six

firing

doors.

Six

experim

are

given

on

page

73,

five

made

at

sea

and

on

land.

All

are

with

hand

firing, some

forced,

some

with

chimney

draught, none w

economisers. The boiler efficiency

varied f

62%

to

70%,

and the water

evaporated

square

foot of heating

surface

from

2f

to

9f

per hour. Combustion was fairly good, s

times as much as

13%

of

COg by

volume

b

obtained from the

analysis of

the gases.

coal burnt

per

square

foot

of

grate

per

varied

from 19 to

31

lbs.

The best resul

sea was

with

an

evaporation

of

2 7

lbs.

square foot.

Unfortunately

very few

experiments

been or

are

made

on

boilers

at sea.

measurement

of

the

hot feed water

from

surface

condenser

is

rather

troublesome

in

confined and

warm engine-rooms. It

is

a

somewhat tedious

operation to weigh

the

co

baskets

by a spring

balance,

in

all

the dust

dirt between

the

coal bunkers and

the

stoke

floor,

opposite

the

hot boiler furnaces,

especi

if

the weather

is

rough. The

analysis of

g

and

taking

the

temperatures

of

the

funnel

g

in rain,

wind,

and

snow, on deck,

next the

chimney,

is

also not

agreeable, but there

i

real

diificulty.

Care

and

attention

are

necess

and the conditions

work

in

very warm

sp

cannot

be

called

pleas

As one

of

the

memb

of

the

committee,

author

was

present

most of the

marine

t

arranged

by

the Ins

tion

of

Mechanical

En

eers,

and speaks

f

personal

experience.

11. Lancashire bo

with

two inte

furnace

tubes

endin

a

series

of short

smoke tubes, forming

a

tinuation

(fig.

11),

is similar to No.

7.


30/342

G HEAT

EFFICIENCY

OF

STEAM BOILERS.

gases pass in

this

case

direct

from

the

fires

through the smoke tubes,

up the

chimney.

Although

it

resembles the

dry back type, it is

occasionally

used

in ship-yards.

On

pages

65

to 71 will be

found twenty -seven

interesting

experiments made by

Mr Spence

at

Newcastle,

^=?—

^- ^SE^

—

^5 ^


31/342

SPENCE'S

EXPERIMENTS.

hi

SI

Lbs.

oF

Air

per

lb.

of Coal.

^

,

9°

?

^

e,s,7

Lbs.

of

Coal

pef Six.

Ft of Crafe

per

hour.

'

'.

i^'

'

I

'

if

'

—

' ''

'

J.

'

—

I

'

fe

'

Lbs.

of

Water per

lb.

of

Coal

from i

at 212.

Si

Lbs.

of

Wat.er

per

/t>.

of

Coal from

and

at

212

1,2.3

§

to

if

Dl

9

Lbs.

of Air

per

lb.

of

coat

Boil

S:£ffielep

Lbs.ofcoel

perStfFtof'Srate

per^

hour.

Lbs.

of

Water

pcr/b. of

coal

frfm

and

af

3

to

Ss

2/2

-I'S'S-C'M

ED

CD

S

^

Q

31%

rt

(B

ri

cgi^

A6s

o/* Ws/ci

per

lb.

of Coal from

&

af

2/2.'


32/342

8

HEAT

EFFICIENCY

OF

STEAM

BOILERS.

Fig.

12.

at

fifty

to sixty

miles

an

hour

is

not easy

or

agreeable, and

is

seldom

done.

Forty-six experiments

on the

locomotive

type

of

boiler

will be

found

on pages

75

to

83

thirty-five

are on

stationary

or

semi-portable,

and

eleven

on locomotive

boilers

running

on

rails,

at

page 83.

With stationary,

semi-fixed

boilers

feed

water heaters are

sometimes

used,

but

not

economisers.

Pages

75,

77,

and

81

give

the

boiler

efficiency of

twenty-six

stationary

boilers.

In

nearly all of

them

it

is

high,

varying

from

53-7% to

81-J%,

although

there was

no

doubt

some prim-

ing.

The

water per

square foot

of

heat-

ing surface

per hour

ranges from

1

1-

to

8^

lbs.

;

that

evaporated

per

lb.

of

coal

from and

at

212°

is

often

11

lbs.,

sometimes

higher

with

good

coal,

but

the

best

efficiencies

are obtained

when

the

evaporation

is

from 2

to

6

lbs.

of water

per

square

foot

of

heating

surface

per hour.

Page

79

gives

an

interesting

set of

experiments

very

carefully carried out at

Newcastle,

by

the

Royal

AgriculturalSociety's

well-

knownengineers,

on

nine

different

sizes

of stationary

agricultural

boilers,

none

of

them

large, and

all

worked

with

induced

draught.

No

feed water

heaters

were

used.

All the experiments were

made with the

same

coal,

but

with different

stokers. The

boiler

efficiencies

varied

from

59%

to

84%

even

under very similar

conditions.

The

water

evaporated

per

lb. of same

coal,

from and

at

212°

F., varied

from

10 lbs.

to

13

lbs.

;

the lbs.

of

water

per square foot

of

heating

surface

per hour

from

1|

to

5

J,

the

latter

giving the minimum

efficiency

; the best was obtained when not more

than

1^

to 2 lbs. of water were evaporated

per

square foot of heating

surface

per hour. From

9|-

to

30 lbs.

of coal

were

burnt per square foot

of

grate

per hour.

The

maximum

quantity

of

CO2

in

the gases was

15f

%

by

volume.

For

these

boilers,

all

nominally

of

8

HP.,

the

various

makers

supplied

very

different

heating

surfaces,

and it seemed as

if they

had

been constructed

without a

sufficient

number

of

preliminary

tests,

to

.determine

the best proportions for obtaining

the

highest

results. It

is

from

systematic

and

accurate

trials

of

this kind

that a great

deal

can

be

learnt, and

much

exact information obtained.

At page

83,

where

eleven

experiments

three

running

locomotives

are

given,

the

boi

efficiency

varied

between

66%

and

82%.

U

fortunately,

few

accurate

experiments

on

runni

locomotives, in

which

the

water

was

carefu

measured, have

been

published,

nor

is

it

an

e

task

to carry

out

such

trials.

The

best

resu

seem to

be

with

an

evaporation

of

5

to

7

lbs.

water

per

square

foot of

heating

surface

per

ho

With

8 or

9

lbs.

evaporated,

the

results

lower. The

water

per lb.

of

coal

from

and

212°

varied

from

9^

to

12|

lbs.,

but

doubtl

the

boilers

primed

a

little.

13.

Two-storey

boiler

(fig.

13),

Cornish,

wi

short smoke

tubes

and

a

plain

cylind

above.

—

In

this

type

the

lower boiler

has

l-T^

-fcJ-

J^m


33/342

TWO-STOREY

AND

EXTERNALLY

FIRED

CYLINDRICAL

BOILERS.

the

two-storey

type.

They

form,

in

fact,

two

boilers,

one

above the

other,

joined

together,

and

both

producing

steam.

Sometimes

the two

are

alike

in

shape and

diameter,

sometimes

dis-

similar.

They are more

used

abroad

than

in

this

country,

and always

for

stationary

purposes,

with

a

fixed

chimney.

They

give

good

efficiencies

generally,

although

there

is

a

large

external

brick-work

surface

for

radiation.

The

tempera-

ture

of the

escaping

gases

is

generally

low.

14.

Two-storey

boiler,

Cornish

below,

with

smoke

tubes

above

(fig.

14).

—

Here

the

upper

boiler

is

provided

with

smoke

tubes

along its

whole

length.

The

direc-

tion

of

gases is through

the

furnace

tube,

then through

the

smoke tubes,

and

generally

outside

both

cylindri-

cal

shells to the

chimney.

A trial

on

this

boiler,

hand

fired

with

brown

coal,

and

without

econo-

miser,

will

be

found

at page

87,

No.

12. The

boiler

efficiency

was

68%,

with

an

evaporation

of 3

lbs.

water

per

square

foot of

heating

surface

per

hour,

and 35 lbs.

of

coal

were

burnt per

square

foot

of

grate

per

hour.

Considering the poor

quality

of

the

coal

used,

this

is a good

result.

15.

Two-storey

boiler

(fig.

15),

Cornish

below

and

plain

cylindrical

above.

—

In this

type

the lower

boiler

is

Cornish with

a single

furnace

tube and

shell, and

a plain

cylindrical

boiler above,

without

smoke tubes. The

boiler

is

surrounded

with

brick

flues, giving

considerable radiating

surface.

The

direction

of gases

is

usually

through

the

one furnace tube, and

round the

outside brick

flues

surrounding

them,

but

it

is

often

varied

in

dififerent

There are no experiments

on this type

Tables.

Two-storey boiler, Lancashire

below,

tubes above,

with

one water line (flg.

1

6).

This

boiler has two cylinders,

one

above

the

other,

of equal

diameter,

the

lower

one

con-

taining two

Lancashire

furnace

tubes, the

upper

a

series of

smoke

tubes. The

direction of the

gases

is first through

the

furnace tubes, returning

through

the

smoke

tubes

of

the

upper

boiler

and

then

generally

round the

external

brick

flues

of

both shells to chimney.

Three

experiments

on

this

boiler will be

found at

page

85,

seven

on

ways,

in

the

16.

£moke

Fig.

16

page

87,

Nos. 9 and

13 to

18,

and

several

page

89,

both

hand and machine

fired.

M

of

them

were made abroad

with

different kinds of

grates, and no

economisers

were

used.

The

boiler

efiiciency

was

generally

high, rang-

ing

from

61

to

81%.

With

the

latter

only

2

lbs.

water

per

square

foot

of heating

surface

per hour

were

evaporated.

The lbs. fuel

burnt per square

foot of

grate

varied from

13

to

31 lbs.

17.

Two-storey

Lancashire boiler

w

smoke tubes

above

(fig.

17).

—

Similar

to

last,

the only

difference

being

that

there

are

two

water

lines instead

of

one. Two experiments

on

this

type

will

be

found at

page

85,

Nos. 5

and

6,

made

by

the

Vienna

Boiler

Association.

The

efficiencies

varied

from

70

to

71^%,

and the

evapora-

tion per

square

foot of

heating

surface

per

hour was

about

2

lbs.

water

in

both the

experiments.

Another

trial

wUl

be

found

on

page

89,

and

two

on

page

all

without

economisers.

Fig.

1

DIVISION II.

EXTEENALLY

FIRED

BOILERS.—

In

second

division the

grate

is

always

external

to

boiler itself,

and

placed

sometimes

below, so

times at

the end

of

the

cylindrical

shell

conta

ing

the

water.

18.

Plain cylindrical

or

egg-ended boi

(fig. 18).—This is the

simplest

type,

and

lia

horizontal cylindrical

shell, without

either

sm

or

water tubes,

under

which the

grate is

fixed.

An outer brick

casing incloses the grate

and

boiler. The

ends

are generally

hemispherical,

and hence the

name

egg-ended.

The

direction

of gases

is

through

the

furnace

chamber

under the

boiler, then

through

the

brick

flues, round

the external part

of

the surface

to

the

chimney.

This is an

old type, and

only employed

on land for stationary

purpos

It is generally set

in

brick-work

with a f

chimney, and is often used in

collieries.

I

Fig. 18.


34/342

10

HEAT

EFFICIENCY

OF

STEAM BOILERS.

Kg.

19.

not

very

economical,

and

is

only

suitable for

low

pressures;

no

good

experiments on

it

have

been found. Colliery

owners pay little

attention

to their boilers.

Tests are

hardly

ever

made,

and

there

is

often much

waste

of

heat.

19.

Cylindrical

boiler

(fig.

19),

with

return

smoke

tubes

carried through the

water

the whole

length of

the boiler,

as

shown.

This is

a favourite type in

the

United

States, where

it is

largely

used, and considered to be very

economical, an opinion which

seems

to

be

borne

out

by

the tests.

It

is a

cheap boiler to make,

but

is

little used

in

England.

The

direction of gases is

from

the

grate

along

the bottom

of

the

boiler,

returning

through all

the smoke

tubes

to

the

chimney. Sometimes the gases

also

pass round

the

outside

shell.

The

boiler

is

used

on

land

for stationary

purposes,

with a fixed chimney

and natural or forced draught, and is

usually

set

in

brick-work,

and often worked with an econo-

miser.

The

gases escape at a fairly low tempera-

ture.

Eleven experiments on this

boiler

are given at

page

91,

with

heating surfaces

varying from

330

to 1700 square feet. The

diameter of

the

smoke

tubes was

3

in.,

4

in.,

4^

in., 6 in.,

and 10 in.

respectively, the

boiler

efficiency varied

from

56|^%

to

81%.

The temperature of the exit gases

was

rather

low.

From

2

to

9

lbs.

of

water

were

evaporated per

square

foot of heating surface

per

hour.

The best

efficiency was obtained

with

an evaporation

of

2

to

3h

lbs. of water.

The

coal burnt per

square

foot

of

grate

per hour

was

from

10

to

43f

lbs.

Several

tests

were

made

with

the Hawley

down

draught

furnace,

consist-

ing of two grates,

one

above

the

other.

This

ingenious

arrangement

seems

to

give

practically

no smoke,

but requires

a good draught.

20.

Lancashire

boiler

with

external

grate

(fig.

20).

—

This boiler,

generally

set

in

brick-

work,

consists

of

a

oyhndrical

shell

with

two

large

central smoke

tubes and

a

grate

below.

The

direction

of

gases is first round the

shell,

then back through the

tubes to

the

chimney.

Many of these boilers

are used

in Germany,

with

inclined

grates

in front,

or grates in

steps to

burn

poor

coal, such

as brown

coal,

lignite,

and

also

other

fuels containing

much water.

In

some

experiments

there

was

about 50

to

5

moisture

in the coal.

Eight

experiments

this

type, all made in

Germany,

are given

page

93.

The

water

evaporated

per

square foot

of

heating

surface

per

hour varied

from

2 to i^

lbs.;

the

boiler

efficiency

from

53%

to

74%.

The

latter

result

was

obtained

when

evaporating

4

lbs.

of water

per

square

foot

of

heating

surface per

hour.

The

evapora-

tion

per

lb.

of

fuel

is

naturally

very low

with these coals of

small

Fig. 20.

heating

value,

and

varies from

2J

to

5^

l

The

percentage

of

COg

in the

gases

is

genera

very

good, with only a small

excess

of

air.

21, 22,

23. Elephant

boilers

(figs.

21, 22,

a

23).—These three types

and

the

following

fo

a

class

by

themselves, much

used in

France a

elsewhere

on the

Continent.

They

are called

England Elephant

Boilers,

and

in

Fran

Chaudieres

a

Bouilleurs,

houilleurs

being

t

name

applied

in

each

case

to

the

large

low

water

tubes.

No.

21 has only

one

bouille

No.

22 two; and

No.

23 three,

arranged benea

the

central horizontal cylindrical

boiler

she

Fig. 21. Fig.

23.

with which they

are connected.

The

exter

grates are

under the houilleurs, and the

whole

inclosed

in brick flues. The direction

of gase

generally first under the houilleurs, then

forwa

and backwards,

below and

around

the boi

shell, the usual

plan being

to

pass them two

three times

along it, before they

escape to

chimney.

There

are

no

smoke

tubes

in

the three

ty

here

considered.

They are frequently

used

mills

and

for other

stationary

purposes w

brick

setting,

fixed

chimneys,

and natu

draught.

Economisers

are

seldom

applied,

feed

water

heaters

are

very

often added

on

Continent.

These

are

simply horizontal

cylind

cal tubes,

1

or

1

J

feet

in

diameter,

which

act


35/342

ELEPHANT

BOILERS—

TWO-STOREY

B0ILER8.

economisers,

and are

placed

in the

flues;

the

gases

circulate

round

them

after

leaving

the

boiler

on

their

way

to the

chimney.

These

boilers

are in great

favour

on the

Continent,

but

hardly

used in England.

On page

95 will

be

found

ten

experiments

on

this

type,

with two

and

three

bouiUeurs.

The

boiler

efficiency

varies

from

55%

to

65%,

without

feed

water

heaters.

With the

latter

the total

efficiency

is

from

55

to

78%.

With

the

highest

efficiency

5

lbs.

of water were

evaporated

per

square

foot

of

heating

surface

per

hour.

The

best

results

without feed

water

heaters were

obtained with

an

evaporation

of 4

lbs.

of water

per

square foot

per hour.

Ten

to eighteen

lbs.

of coal were

burnt

per square

foot

of

grate

per

hour.

This

type

of

boiler, without

smoke tubes

or

economisers,

does not

seem

to

give

a

very

good

efficiency,

and

the

gases escape

at too

high

a temperature

for

the

best

results.

24,

Elephant boiler

with smoke

tubes

(fig.

24).

—

This boiler

is similar to those

just de-

scribed,

but

is

arranged

with the

external

grate

below the

two

bouiUeurs,

and

a horizontal

cylindrical

boiler

shell

above,

provided

with

a

large

number

of

small

smoke

tubes

running

the

whole

length

of

the

boiler.

The direction

of

gases is

from the

grate under

the

bouiUeurs,

returning through

the

smoke

tubes,

and

outside the

boiler shell

to

the

chimney. Feed water

heaters

are

sometimes used, but are not as

necessary as in some boilers, as

the

temperature of

the gases is already

considerably

reduced

by

the smoke tubes.

Set

in brick-work,

with

natural

draught and fixed

chimney,

this

boiler

is

much in

request for

mill and stationary purposes,

especially in

France.

Eight

experiments are given on

it at

page

97,

in which

the boiler

efficiency

without

feed

water

heaters

varies

from 59

to

70%.

With the

latter

it rises

from

61 to

71%.

The water evaporated per

square

foot

of

heat-

ing

surface

per

hour

is

from 21

to

3|

lbs. The

coal

burnt

per square

foot of grate

per

hour

varies

from

12

to

30 lbs.

These four types

are

practically

two-storied

boilers of

unequal

diameter. If the

water

used

is

bad, they

are

rather difficult

to clean

internally.

25,

26.

Two-storey

boilers

(figs.

25

and

26).

—

The

next two

types

consist

practically of

two

Fig.

24.

boilers,

one

above the other,

connected

as

sho

They

are

heated

by

one

external

grate pla

below.

In

No.

25

the

lower

boiler

is a

p

cylindrical shell, and the upper,

of

the

s

diameter,

is provided with

a

large

num

of

smoke

tubes running

through its

whole length.

The

direction

of

gases

is

underneath the bottom

shell, through the

smoke

tubes, and either

partly

or

wholly

round

both

shells

to

chimney. The arrange-

ment

in

No.

26 is

the

same,

but the

lower

boiler,

although

it

has

a

grate

underneath

it,

is

sha

hke a Cornish, with

one

large

central

sm

tube.

The

direction

of gases

is

first under

bottom

of the

lower boiler,

then

through

large

Cornish

tube,

next

through

all

the

sm

tubes,

and

round

the outside of the two

sh

to the

chimney.

These two types of two-storey boilers,

se

brick-work

and worked with

natural

draug

are

used in factories

and

for

stationary

jDurpo

Feed

water

heaters

are seldom

added, the

h

of

the

gases being almost wholly

absorbed

the

numerous

smoke

tubes

before they

esc

to

the

chimney.

The

boilers are

not of

employed

in

England,

but

largely

on the C

tinent, where

the

author

has often

seen

them

work.

Nine experiments, all made

abroad,

are

gi

on page 99. They

are all

on boilers like

fig.

with smoke

tubes.

None on

the

other type,

26,

with

Cornish tube below,

appear

to

h

been

published. Without

economisers

boiler efficiency varies

from 57 to

79%,

and

evaporation

per square foot of heating

surf

per

hour from

2

Documents

Boiler Testing