The following brief description of the Babcock & Wilcox boiler will
clearly indicate the manner in which it fulfills the requirements of the
perfect steam boiler already enumerated.
The Babcock & Wilcox boiler is built in two general classes, the
longitudinal drum type and the cross drum type. Either of these designs
may be constructed with vertical or inclined headers, and the headers in
turn may be of wrought steel or cast iron dependent upon the working
pressure for which the boiler is constructed. The headers may be of
different lengths, that is, may connect different numbers of tubes, and
it is by a change in the number of tubes in height per section and the
number of sections in width that the size of the boiler is varied.
The longitudinal drum boiler is the generally accepted standard of
Babcock & Wilcox construction. The cross drum boiler, though originally
designed to meet certain conditions of headroom, has become popular for
numerous classes of work where low headroom is not a requirement which
must be met.
LONGITUDINAL DRUM CONSTRUCTION--The heating surface of this type of
boiler is made up of a drum or drums, depending upon the width of the
boiler extending longitudinally over the other pressure parts. To the
drum or drums there are connected through cross boxes at either end the
sections, which are made up of headers and tubes. At the lower end of
the sections there is a mud drum extending entirely across the setting
and connected to all sections. The connections between all parts are by
short lengths of tubes expanded into bored seats.
[Illustration: Forged-steel Drumhead with Manhole Plate in Position]
The drums are of three sheets, of such thickness as to give the required
factor of safety under the maximum pressure for which the boiler is
constructed. The circular seams are ordinarily single lap riveted though
these may be double lap riveted to meet certain requirements of pressure
or of specifications. The longitudinal seams are properly proportioned
butt and strap or lap riveted joints dependent upon the pressure for
which the boilers are built. Where butt strap joints are used the straps
are bent to the proper radius in an hydraulic press. The courses are
built independently to template and are assembled by an hydraulic
forcing press. All riveted holes are punched one-quarter inch smaller
than the size of rivets as driven and are reamed to full size after the
plates are assembled. All rivets are driven by hydraulic pressure and
held until black.
[Illustration: Forged-steel Drumhead Interior]
The drumheads are hydraulic forged at a single heat, the manhole opening
and stiffening ring being forged in position. Flat raised seats for
water column and feed connections are formed in the forging.
All heads are provided with manholes, the edges of which are turned
true. The manhole plates are of forged steel and turned to fit manhole
opening. These plates are held in position by forged-steel guards and
bolts.
The drum nozzles are of forged steel, faced, and fitted with taper
thread stud bolts.
[Illustration: Forged-steel Drum Nozzle]
Cross boxes by means of which the sections are attached to the drums,
are of forged steel, made from a single sheet.
Where two or more drums are used in one boiler they are connected by a
cross pipe having a flanged outlet for the steam connection.
[Illustration: Forged-steel Cross Box]
The sections are built of 4-inch hot finished seamless open-hearth steel
tubes of No. 10 B. W. G. where the boilers are built for working
pressures up to 210 pounds. Where the working pressure is to be above
this and below 260 pounds, No. 9 B. W. G. tubes are supplied.
[Illustration: Inside Handhole Fittings Wrought-steel Vertical Header]
The tubes are expanded into headers of serpentine or sinuous form, which
dispose the tubes in a staggered position when assembled as a complete
boiler. These headers are of wrought steel or of cast iron, the latter
being ordinarily supplied where the working pressure is not to exceed
160 pounds. The headers may be either vertical or inclined as shown in
the various illustrations of assembled boilers.
[Illustration: Wrought-steel Vertical Header]
Opposite each tube end in the headers there is placed a handhole of
sufficient size to permit the cleaning, removal or renewal of a tube.
These openings in the wrought steel vertical headers are elliptical in
shape, machine faced, and milled to a true plane back from the edge a
sufficient distance to make a seat. The openings are closed by inside
fitting forged plates, shouldered to center in the opening, their
flanged seats milled to a true plane. These plates are held in position
by studs and forged-steel binders and nuts. The joints between plates
and headers are made with a thin gasket.
[Illustration: Inside Handhole Fitting Wrought-steel Inclined Header]
In the wrought-steel inclined headers the handhole openings are either
circular or elliptical, the former being ordinarily supplied. The
circular openings have a raised seat milled to a true plane. The
openings are closed on the outside by forged-steel caps, milled and
ground true, held in position by forged-steel safety clamps and secured
by ball-headed bolts to assure correct alignment. With this style of
fitting, joints are made tight, metal to metal, without packing of any
kind.
[Illustration: Wrought-steel Inclined Header]
Where elliptical handholes are furnished they are faced inside, closed
by inside fitting forged-steel plates, held to their seats by studs and
secured by forged-steel binders and nuts.
The joints between plates and header are made with a thin gasket.
[Illustration: Cast-iron Vertical Header]
The vertical cast-iron headers have elliptical handholes with raised
seats milled to a true plane. These are closed on the outside by
cast-iron caps milled true, held in position by forged-steel safety
clamps, which close the openings from the inside and which are secured
by ball-headed bolts to assure proper alignment. All joints are made
tight, metal to metal, without packing of any kind.
The mud drum to which the sections are attached at the lower end of the
rear headers, is a forged-steel box 7¼ inches square, and of such length
as to be connected to all headers by means of wrought nipples expanded
into counterbored seats. The mud drum is furnished with handholes for
cleaning, these being closed from the inside by forged-steel plates with
studs, and secured on a faced seat in the mud drum by forged-steel
binders and nuts. The joints between the plates and the drum are made
with thin gaskets. The mud drum is tapped for blow-off connection.
All connections between drums and sections and between sections and mud
drum are of hot finished seamless open-hearth steel tubes of No. 9
B. W. G.
Boilers of the longitudinal drum type are suspended front and rear from
wrought-steel supporting frames entirely independent of the brickwork.
This allows for expansion and contraction of the pressure parts without
straining either the boiler or the brickwork, and also allows of
brickwork repair or renewal without in any way disturbing the boiler or
its connections.
[Illustration: Babcock & Wilcox Wrought-steel Vertical Header Cross Drum
Boiler]
CROSS DRUM CONSTRUCTION--The cross drum type of boilers differs from the
longitudinal only in drum construction and method of support. The drum
in this type is placed transversely across the rear of the boiler and is
connected to the sections by means of circulating tubes expanded into
bored seats.
The drums for all pressures are of two sheets of sufficient thickness to
give the required factor of safety. The longitudinal seams are double
riveted butt strapped, the straps being bent to the proper radius in an
hydraulic press. The circulating tubes are expanded into the drums at
the seams, the butt straps serving as tube seats.
The drumheads, drum fittings and features of riveting are the same in
the cross drum as in the longitudinal types. The sections and mud drum
are also the same for the two types.
Cross drum boilers are supported at the rear on the mud drum which rests
on cast-iron foundation plates. They are suspended at the front from a
wrought-iron supporting frame, each section being suspended
independently from the cross members by hook suspension bolts. This
method of support is such as to allow for expansion and contraction
without straining either the boiler or the brickwork and permits of
repair or renewal of the latter without in any way disturbing the boiler
or its connections.
The following features of design and of attachments supplied are the
same for all types.
FRONTS--Ornamental fronts are fitted to the front supporting frame.
These have large doors for access to the front headers and panels above
the fire fronts. The fire fronts where furnished have independent frames
for fire doors which are bolted on, and ashpit doors fitted with blast
catches. The lugs on door frames and on doors are cast solid. The faces
of doors and of frames are planed and the lugs milled. The doors and
frames are placed in their final relative position, clamped, and the
holes for hinge pins drilled while thus held. A perfect alignment of
door and frame is thus assured and the method is representative of the
care taken in small details of manufacture.
The front as a whole is so arranged that any stoker may be applied with
but slight modification wherever boilers are set with sufficient furnace
height.
[Illustration: Cross Drum Boiler Front]
In the vertical header boilers large wrought-iron doors, which give
access to the rear headers, are attached to the rear supporting frame.
[Illustration: Wrought-steel Inclined Header Longitudinal Drum Babcock &
Wilcox Boiler, Equipped with Babcock & Wilcox Superheater]
[Illustration: Automatic Drumhead Stop and Check Valve]
FITTINGS--Each boiler is provided with the following fittings as part of
the standard equipment:
Blow-off connections and valves attached to the mud drum.
Safety valves placed on nozzles on the steam drums.
A water column connected to the front of the drum.
A steam gauge attached to the boiler front.
Feed water connection and valves. A flanged stop and check valve of
heavy pattern is attached directly to each drumhead, closing
automatically in case of a rupture in the feed line.
All valves and fittings are substantially built and are of designs which
by their successful service for many years have become standard with The
Babcock & Wilcox Co.
The fixtures that are supplied with the boilers consist of:
Dead plates and supports, the plates arranged for a fire brick lining.
A full set of grate bars and bearers, the latter fitted with expansion
sockets for side walls.
Flame bridge plates with necessary fastenings, and special fire brick
for lining same.
Bridge wall girder for hanging bridge wall with expansion sockets for
side walls.
A full set of access and cleaning doors through which all portions of
the pressure parts may be reached.
A swing damper and frame with damper operating rig.
There are also supplied with each boiler a wrench for handhole nuts, a
water-driven turbine tube cleaner, a set of fire tools and a metal steam
hose and cleaning pipe equipped with a special nozzle for blowing dust
and soot from the tubes.
Aside from the details of design and construction as covered in the
foregoing description, a study of the illustrations will make clear the
features of the boiler as a whole which have led to its success.
The method of supporting the boiler has been described. This allows it
to be hung at any height that may be necessary to properly handle the
fuel to be burned or to accommodate the stoker to be installed. The
height of the nest of tubes which forms the roof of the furnace is thus
the controlling feature in determining the furnace height, or the
distance from the front headers to the floor line. The sides and front
of the furnace are formed by the side and front boiler walls. The rear
wall of the furnace consists of a bridge wall built from the bottom of
the ashpit to the lower row of tubes. The location of this wall may be
adjusted within limits to give the depth of furnace demanded by the fuel
used. Ordinarily the bridge wall is the determining feature in the
locating of the front baffle. Where a great depth of furnace is
necessary, in which case, if the front baffle were placed at the bridge
wall the front pass of the boiler would be relatively too long, a
patented construction is used which maintains the baffle in what may be
considered its normal position, and a connection made between the baffle
and the bridge wall by means of a tile roof. Such furnace construction
is known as a "Webster" furnace.
[Illustration: Longitudinal Drum Boiler--Front View]
A consideration of this furnace will clearly indicate its adaptability,
by reason of its flexibility, for any fuel and any design of stoker. The
boiler lends itself readily to installation with an extension or Dutch
oven furnace if this be demanded by the fuel to be used, and in general
it may be stated that a satisfactory furnace arrangement may be made in
connection with a Babcock & Wilcox boiler for burning any fuel, solid,
liquid or gaseous.
The gases of combustion evolved in the furnace above described are led
over the heating surfaces by two baffles. These are formed of cast-iron
baffle plates lined with special fire brick and held in position by tube
clamps. The front baffle leads the gases through the forward portion of
the tubes to a chamber beneath the drum or drums. It is in this chamber
that a superheater is installed where such an apparatus is desired. The
gases make a turn over the front baffle, are led downward through the
central portion of the tubes, called the second pass, by means of a
hanging bridge wall of brick and the second baffle, around which they
make a second turn upward, pass through the rear portion of the tubes
and are led to the stack or flue through a damper box in the rear wall,
or around the drums to a damper box placed overhead.
The space beneath the tubes between the bridge wall and the rear boiler
wall forms a pocket into which much of the soot from the gases in their
downward passage through the second pass will be deposited and from
which it may be readily cleaned through doors furnished for the purpose.
The gas passages are ample and are so proportioned that the resistance
offered to the gases is only such as will assure the proper abstraction
of heat from the gases without causing undue friction, requiring
excessive draft.
[Illustration: Partial Vertical Section Showing Method of Introducing
Feed Water]
The method in which the feed water is introduced through the front
drumhead of the boiler is clearly seen by reference to the illustration.
From this point of introduction the water passes to the rear of the
drum, downward through the rear circulating tubes to the sections,
upward through the tubes of the sections to the front headers and
through these headers and front circulating tubes again to the drum
where such water as has not been formed into steam retraces its course.
The steam formed in the passage through the tubes is liberated as the
water reaches the front of the drum. The steam so formed is stored in
the steam space above the water line, from which it is drawn through a
so-called "dry pipe." The dry pipe in the Babcock & Wilcox boiler is
misnamed, as in reality it fulfills none of the functions ordinarily
attributed to such a device. This function is usually to restrict the
flow of steam from a boiler with a view to avoid priming. In the Babcock
& Wilcox boiler its function is simply that of a collecting pipe, and as
the aggregate area of the holes in it is greatly in excess of the area
of the steam outlet from the drum, it is plain that there can be no
restriction through this collecting pipe. It extends nearly the length
of the drum, and draws steam evenly from the whole length of the steam
space.
[Illustration: Cast-iron Vertical Header Longitudinal Drum Babcock &
Wilcox Boiler]
[Illustration:
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