Improvements in Multitubular High Pressure Steam Boilers.
Year: 1893

page_text: Date of Application, 9th May, 1893-Accepted, 17th June, 1893
COMPLETE SPECIFICATION.
Improvements in Multitubular High Pressure Steam Boilers.
We, ALEXANDRE LAGRAFEL and JULES D'ALLEST, both of 40 Chemin de la
Madrague, Marseilles, in the Republic of France, Engineers, do hereby declare the
nature of this invention 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 on an invention for which a Patent was
granted No. 11160 of 1888, which improvements are hereinafter more fully set out.
In the accompanying drawing,-—
Figure 1 is a cross section; and,
Figure 2 a longitudinal section on line A B of Figure 1 of a boiler constructed
according to our invention:
Figure 3 is a similar view to Figure 1 shewing certain modifications and
additions; and,
Figure 4 is a cross section shewing our improved construction of single boiler.
The body of the boiler is constructed in the manner described in the Specification
of the said former Letters Patent, that is to say, it comprises a number of water
tubes putting into communication two water spaces or prismatic boxes A and B
rigidly connected together and forming the front and rear faces of the boiler;
these water spaces communicate with a cylinder C placed at their upper part in
which the level of the water is maintained and which forms a receptacle for the
steam; the tubes arranged in rectilinear rows are inclined to the horizon sufficiently
to allow the water to circulate through them, the circulation being effected through
the water spaces A and B and the cylinders C.
The grate D is placed beneath the first row of tubes E which is covered with
bricks as shewn in the drawing (Figures 1 and 2) and forms the crown of the
furnace, the gases of combustion produced on the grate D pass over a bridge F
into a combustion chamber or fire-box G formed between the tubes; the flames or
the extinguished gases then return through the cluster of tubes, the top row of
which is also covered with bricks, to the smoke boxes I and thence pass to the
chimpey K after having heated the lower part of the steam cylinder C.
The improvements forming the subject of the present invention relate to the
circulation of the water and the circulation of the gases.
The improvements relating, to the circulation of the water are as follows;
namely:-
1. Reducing the thickness of the rear water space and forming the front water
space conical.
Instead of forming the two water spaces of the same thickness and with parallel
faces we have found in practice that it is advantageous for the rear water space to
be, somewhat smaller than the front one and that the latter should have a section
gradually increasing as shewn in. Figure 2; unless so constructed the steam bubbles
formed in the tubes have a tendency to escape in part through the rear water
space which interferes with the general circulation; the rear water space being
smaller all the steam bubbles formed in the tubes become disengaged in the front
water space where the space gradually grows larger at the same time that the
number of steam bubbles increases.
2. The employment of wing tubes for the lower row and the enclosure of the
fire-box.
According to the Specification of the prior Patent No. 11160 of 1888 the tubes
were all of the ordinary form but we have found in practice that these tubes when
in direct contact with the flame rapidly. became bent and presented a concave
surface at the side nearest the grate, the consequence being that the effective

page_text: operation of the tubes was impaired and the working of the boiler was frequently
interrupted after many and varied trials by means of screens to protect the tubes,
tubes with sliding joints capable of expanding; tubes previously bent so as to be
flexible; tubes of undulated shape in length, crosswise and helically; tubes
provided internally with partitions, etc.; we finally employed tubes having wings
and after working a considerable time such tubes remain perfectly straight and do
not become bent or curved which results not by reason of their being less flexible
but owing to the wings facilitating the passing off of the heat received by the
external surface.
3. Dispensing with the lateral tubes of the furnace and shortening the front
water space.
In the drawings accompanying the Specification of the said former Letters
Patent No. 11160 of 1888 the front. water space is shewn as descending to the level
of the grate but there being no pipes between this level and the crown of the
furnace it resulted that there was no circulation between these parts, whereby
deposits formed and injury was caused to the plates in front of the furnace; further
the tubes placed at the side of the furnace being only heated on one side acted
inefficiently. According to the present improvements the front water space is
sbortened and extends only to just below the first row of tubes whereby deposits
are prevented.
The improvements unladi
1. In the Specification of the said former Letters Patent No. 11160 of 1888 the
hot gases are described as arriving in the fire-box and spreading out to the right
and left into the upper part of the cluster of tubes and escaping into the smoke
boxes I without coming into contact with the lower rows of tubes whence it results
that a large part of the heat surface is not utilized and that the production of
steam per kilogramme of coal is greatly reduced. According to the present
improvements we partly cover the discharge face of the cluster of tubes with a
screen XY leaving below it only a narrow section for the escape of the gases.
Under these conditions the gases which first spread in the upper part of the
cluster of tubes descend as they become cooled and envelope all the tubes and the
vaporization takes place effectively thus this screen is of great importance.
2. In order to ensure an effective distribution of the gases over the whole length
of the tubes we make the fire-bridge exactly parallel with the tubes.
3. In the fire box we place a few tubes immediately beneath those supporting
the upper arch to protect them against the direct action of the flame.
II. ARRANGEMENT OF HORIZONTAL FIRE-BOX (FIGURE 3).
The fire-box formed between the tubes can also be arranged horizontally, as
shewn in Figure 3; this arrangement is generally applicable but is preferably
employed where the space at disposal is less in height than width; it is necessary
to place a few vertical bricks, forming a partition A. B, to prevent the gases passing
directly into the smoke box.
III. SINGLE BOILER WITH CENTRAL FIRE-BOX (FIGURE 4).
In cases where two boilers connected together cannot be employed owing to lack
of space we make use of the arrangement shewn in Figure 4 which. consists of a
single boiler with a vertical or horizontal fire-box formed in the middle of the
cluster of tubes, and a central fire-bridge; two grates separated by the fire-bridge
allow of alternating the charges and of effecting an economical combustion similar
to that obtained with two boilers connected together; this boiler is further provided
with two smoke boxes and screens A B.

page_text: When the space at disposal is still more limited the smoke box may be dispensed
with and replaced by a sheet metal plate applied against the last row of vertical
tubes, in this case the screen A B is placed at A, B and the gases escape through
the part A, A from which the bricks have been previously removed.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. In a steam boiler of the kind hereinbefore referred to forming the rear water
space of a thickness less than the front water space and the latter space conical
substantially as, and for the purpose, herein before described.
2. In a steam boiler of the kind herein before referred to the employment of
winged tubes for the lower row and for enclosing the fire-box, substantially as, and
for the purpose, hereinbefore described.
3. In a steam boiler of the kind herein before referred to dispensing with the use
of lateral tubes and shortening the front water space, substantially as, and for the
purpose, hereinbefore described.
4. In a steam boiler of the kind hereinbefore referred to, the use of a screen for
reducing the space for the exit of the gases, substantially as hereinbefore described
and illustrated in the accompanying drawings.
5. In a steam boiler of the kind hereinbefore referred to arranging the fire-
bridge parallel with the tubes substantially as, and for the purpose, hereinbefore
described.
6. In a steam boiler of the kind herein before referred to, the addition within the
fire-box of a certain number of tubes placed below those supporting the upper arch
substantially as, aud for the purpose, hereinbefore described.
7. In a steam boiler of the kind herein before referred to arranging the fire-box
horizontally instead of vertically substantially as, and for the purpose, hereinbefore
described.
8. A steam boiler arranged and constructed substantially as hereinbefore
described and illustrated in Figure 4 of the accompanying drawings.
9. The improvements in multitubular high pressure steam boilers herein before
described and illustrated in the various figures of the accompanying drawings.
Dad mis
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.