Improvements in Multitubular Steam Generators.
Year: 1894

page_text: Date of Application, 2nd Feb., 1894-Accepted, 7th Apr., 1894
COMPLETE SPECIFICATION.
Improvements in Multitubular Steam Generators.
1 JAMES YATE JOHNSON, of 47 Lincoln's Inn Fields, in the County of Middlesex,
Gentleman, do hereby declare the nature of this invention (which has been
communicated to me from abroad by La Société Augustin Normand & Cie. of
67 Rue du Perrey, Havre, in the Republic of France) and in what manner the
same is to be performed to be particularly described and ascertained in and by the
following statement :-
This invention relates to improvements in steam generators or boilers of the
class in which an upper chamber or upper chambers is or are connected to a lower
chamber or lower chambers by two systems of tubes, one system being composed
of a large number of tubes of small diameter giving a large superficial area and
exposed to the action of the fire and the other system being composed of a small
number of tubes of larger diameter which are situated outside of the furnace and
which serve to conduct the water previously conveyed to the upper chamber or
chambers by the small tubes and which has not been converted into steam, back
again into the lower chamber or chambers, an object of the invention being to
provide an increased heating surface and to arrange the chimney at the front end
of the generator whereby a group of boilers may be connected together by one
chimney.
In most steam generators of this kind the flames and hot products of combustion
rise vertically towards a chimney situated about the middle of the boiler crossing
on their way the group of tubes. This gives a large volume of hot gases coming
in contact with a relatively small heating surface only, a condition which utilises
only to a very small extent the heat contained in the products, while some of the
tubes are not acted upon by the gases which pass up the chimney without their
heat being properly abstracted and sometimes in a state of combustion.
In a more improved form of generator forming the subject matter of an
invention for which Letters Patent were granted to my correspondents dated
7th January 1890 No. 203008 by the Republic of France this disadvantage is
obviated, the gases taking a horizontal course before reaching the chimney which
is situated at the extreme end of the boiler remote from the firing space or
stoke-hold.
In the boiler or steam generator forming the object of the present invention
this advantage is retained whilst a return passage of the gases and flames is
effected. That is to say, the gases take a horizontal course, but after having
reached the end of the boiler remote from the stoke-hold, return in an opposite
direction across the groups of tubes to the smoke box and chimney situated at the
front of the boiler.
And in order that the said invention may be fully understood I shall now
proceed more particularly to describe the same and for that purpose shall refer to
the several figures on the annexed sheets of drawings the same letters of reference
indicating corresponding parts in all the figures.
Figures 1, 2, 3 and 4 of the drawings represent views of one form of boiler
constructed according to this invention, Figure 1 being a transverse section on the
lines 1, 1 and 2, 2 of Figure 2, Figure 2 being a central longitudinal section,
Figure 3 a half transverse section on the line 3, 3 and a half front elevation
(Figure 2), and Figure 4 a transverse section on the line X Y (Figure 1).
Figures 5, 6 and 7 represent similar views of a modified form of boiler con-
structed according to this invention, Figure 5 being a transverse section on the

page_text: lines 4, 4 and 5, 5 (Figure 6), Figure 6 a central longitudinal section and
Figure 7 a half front elevation and a half transverse section on the line 6, 6
(Figure 6).
Figures 8, 9 and 10 shew the arrangement of a group of four generators con-
structed according to the present invention, and arranged suitably for a steamship,
Figure 8 shews a longitudinal section through two of the boilers, Figure 9 a part
transverse section and part front elevation of a pair of the boilers, and Figure 10
a general plan of the group of boilers.
Referring to Figures 1 to 4 the upper drum or chamber A, which is partially
filled with water, communicates with the lower drums or chambers B by tubes C
of large diameter situated outside of the furnace and by rigid stay tubes D, the
heat of which tubes is limited to that derived from the water and which are
situated at the opposite end to the tubes C. Horizontal stays E at either end
also serve to form a rigid connection between the lower drums or chambers B, the
three chambers thus forming a whole sufficiently rigid to withstand the steam
pressure and the stresses due to the distortion of the heating tubes.
The said heating tubes are arched or curved so as to be able to expand and
contract freely. They are secured in the upper drum A below the water level
and are composed of three systems or groups longitudinally with the boiler. The
two first groups F G form a kind of vault or arch, the first or inner rows of
tubes of each of these groups being arranged in the same plane and so form a kind
of screen, the impermeability or tightness of which is obtained either by arranging
the tubes in such a manner that they form an unbroken surface, or by allowing a
slight space between the said tubes which may be filled with some material such
for example as woven or fibrous asbestos which, being in-contact with these heating
tubes which are always full of water, will last for a considerable time. The space
situated below this arch forms the combustion chamber and the gases cannot
escape vertically or at least, such small volumes as may escape between the tubes
will be so small as to be quite inconsiderable in the working of the boiler. The
screen is completed by a central longitudinal line of bricks H at the top and by
brickwork I and a lining of asbestos or the like to cover the spaces at the lower
ends of the tubes.
Beyond the bridge J is a second group of tubes K, made up of tubes spaced
some distance apart so as not to extinguish the gases not yet consumed. These
gases are then diverted to the right and left returning in an opposite direction,
namely towards the front of the boiler through the two groups of tubes F G.
The tubes of the outer row of each of the three bunches or groups are placed
close together so as to form a screen as far as the opening to the chimney, where
they separate at the top so as to give a free passage for a portion of the gases.
The remaining portion of the gases deflected by the inverted bridge M continues
its horizontal movement finally being discharged into the smoke box N. The said
box N is preferably constructed so as to reach down to the lower drums B, so that
the draught caused by the chimney forces a part of the gases into the box to heat
the lower parts of the tubes in front of the generator. The bunched tubes are
enclosed by a thin sheet iron casing made as tight as possible to prevent the
admission of air which would tend to destroy the draught. The admission of air
into the furnace and above the grate after the said air has been raised in
temperature by contact with the outer casing may also be applied to this generator
in the same manner as this is effected in an earlier boiler constructed by my
correspondents.
The heating tubes are preferably expanded into the drums or chambers and may
be of steel, iron, copper or any other suitable metal and they may be say of from
20 to 40 millimetres internal diameter. The lower drums or chambers B, are
preferably cylindrical and of an internal diameter sufficiently large to admit a child
or a slender adult, a diameter of say about 16 inches being sufficient for this
purpose.
Instead of having a steam dome as shown in Figures 1 and 2 the diameter of the

page_text: upper drums or chambers may be increased as in the arrangement shown in
Figures 8, 9 and 10 of the drawings so as to give an increased steam space.
One of the principal advantages of the boiler constructed as hereinbefore
described consists in that the heated gases do not penetrate immediately into the
groups of tubes and being caused to travel a distance of sufficient length under the
vault or archway formed by the tubes the height of the said tubes above the grate
surface may be diminished and their number be increased. In the accompanying
drawings the tubes are shewn as being of uniform diameter but the tubes may also
have two different diameters except those in the rows which form the screens.
In the slightly modified arrangement of the boiler Figures 5, 6 and 7 the fire
grate extends the whole length of the groups of tubes F. G. K. the groups F. G,
as in the boiler hereinbefore described, having each of their innermost rows of
tubes arranged close together to form a practically continuous surface, but the
group K which is most remote from the front of the generator having its inner
row openly arranged so as to permit of the free passage of the gases, the number of
tubes of different curvatures in the said groups being as few as possible. The
same system of reducing the number of different curvatures of the tubes forming
the group situated behind the fire-bridge J may be applied in the arrangement of
generator hereinbefore described with reference to Figures 1, 2, 3 and 4.
By placing the chimney at the front end of the generator the grouping of
generators is facilitated and diminishes the number of chimneys necessary on board
steam-ships. In Figures 8, 9 and 10 for example four generators are shown with
but a single chimney.
In this arrangement the stokehold is shown common to all the four boilers. If
the boiler room be considered too long by this arrangement, necessitating a
partition or bulkhead between the two pairs of boilers, this only tends to encumber
the firing space, communication between the two holds can however be easily
made.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed 1 declare that what I
claim is :-
1. Steam generators of the multitubular type in which the circulation of the
water is effected by a number of tubes connecting an upper chamber or upper
chambers and a lower chamber or lower chambers, and in which the circulation
of the water is effected on the one hand by means of tubes heated by the furnace,
of which tubes the upper ends are for the greater part situated below the water
level, and on the other hand by pipes or conduits outside of the furnace, leading
the water which has not been converted into steam from the upper chamber or
chambers to the lower one or ones, arranging the group or groups of tubes so as
to form an arch or vault and screen as impervious to the gases as possible, arranged
above the fire grate for preventing the gases from rising vertically and causing
them to pass horizontally to the back of the boiler and thence after penetrating a
group of tubes not forming a screen to return amongst the tubes to a chimney
placed near the front of the generator substantially as herein before described with
reference to the accompanying drawings.
2. The several arrangements of steam generators substantially as hereinbefore
described and shewn respectively in Figures 1, 2, 3 and 4 Figures 5, 6 and 7 and
Figures 8, 9 and 10 of the accompanying drawings.
Dated this 2nd day of February 1894.
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.