IMPROVEMENTS IN FURNACES FOR THE PREVENTION OF SMOKE
Year: 1873

page_text: LETTERS PATENT to George Nimmo, of the City of Glasgow, in the
County of Lanark, North Britain, Steel Maker, for the Invention
PROVISIONAL SPECIFICATION left by the said George Nimmo at the
Office of the Commissioners of Patents, with his Petition, on the
21st November 1873.
I, GEORGE NIMMO, of the City of Glasgow, in the County of Lanark,
North Britain, Steel Maker, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN FURNACES FOR THE PREVENTION OF SMOKE,"
to be as follows:-
My said Invention has reference to certain improvements in the con-
struction of furnaces for the prevention or consumption of black or
visible smoke, and I believe the effecting of a saving in fuel also, which
improvements are so simple that they are applicable with little cost or
alteration to most ordinary forms of steam boilers and furnaces generally

page_text: in use, which burn dross and small coal fired in the usual way and noted
for giving much black smoke.
And the nature and novelty of the Invention consists in having the
plate or hearth of the firing door or doors some inches (as from three to
twelve) higher than the front of the furnace bars and fire on them,
varying according to the depth or thickness of fire or incandescent fuel
kept on top of furnace bars, and such that sufficient air is allowed to
enter this new open mouth or space (left below the under back edge of
the front plate) and so close over the fire as to ignite and consume all
the inflammable gases produced, especially after and from each charge of
fresh dross, coal, or other fuel, in addition to the usual air admitted
below the furnace bars. The fuel is charged into the furnaces as usual
through the ordinary doors which are preferred to be kept quite close,
and the new orifice for admitting the air is preferred to have a per-
forated or close door hinged near it in front at the top to the under
back edge of the ordinary front plate to insure the admission of the air
under the lower edge of this hanging door and close to the fire and
having a notched or other hand rod, or it might be an automatic spring
or other cateract arrangement to regulate its opening and time of
closing when the dark gases or smoke had passed off from each fresh
charge of fuel.
For these improvements the furnace bars may be of any ordinary
form and construction although I prefer them to be highest behind, that
is, the front bearer and bars may in most cases be lowered a little to
assist in giving the said new air space in front.
The improved form of bar I make in carrying out this Invention is to
make the wide parts of the furnace bars, where they form the narrow
space between them for the admission of air and the escape of the small
ashes, considerably further down, and bevel or angle them up on each
side to a ridge in the centre all along, which leaves a V shaped channel
between the bars open below for the fine ashes to pass through and so
that when clinkers form over the bars they can be easily removed by a
pronged poker or other equivalent.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said George Nimmo in the Great Seal Patent Office
on the 2nd May 1874.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GEORGE
NIMMO, of the City of Glasgow, in the County of Lanark, North
Britain, Steel Maker, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-first day of November, in the
year of our Lord One thousand eight hundred and seventy-three, in the
thirty-seventh year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto me, the said George Nimmo, Her special
licence that I, the said George Nimmo, my executors, administrators,
and assigns, or such others as I, the said George Nimmo, my executors,
administrators, and assigns, should at any time agree with, and no others,
from time to time and at all times thereafter during the term therein
expressed, should and lawfully might make, use, exercise, and vend,
within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN FURNACES
FOR THE PREVENTION OF SMOKE," upon the condition (amongst others)
that I, the said George Nimmo, my executors, or administrators, by an
instrument in writing under my, or their, or one of their hands and
seals, should particularly describe and ascertain the nature of the said
Invention and in what manner the same was to be performed, and .
cause the same to be filed in the Great Seal Patent Office within six.
calendar months next and immediately after the date of the said Letters
Patent.
NOW KNOW YE, that I, the said George Nimmo, do hereby .
declare the nature of my said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in
and by the following statement in writing, reference being had to the.
accompanying Sheet of Drawings and to the letters and numerals
marked thereon, that is to say :-
My said Invention has reference to certain improvements in the con-
struction of furnaces for the prevention or consumption of smoke, and
I believe having also the effect of saving fuel, which improvements are
so simple that they are applicable with little cost or alteration to most '

page_text: ordinary forms and constructions of steam boiler furnaces in use, which
even burn dross or small coal fired in the usual manner in a thick layer
and noted for giving much black smoke heretofore.
And in order that the nature, novelty, and mode of performing
my said Invention may be properly understood I shall now proceed to
describe the several Figures on the Sheet of Drawings which I have
hereunto appended for the purpose of showing the best modes and
means I am at present aware of for putting the same into effect or
practice, the same letters and numerals indicating the same or like-parts
in all the Figures where seen, while the black arrows indicate the :
direction of the in-flowing current of air to the furnaces, and the red
arrows the course and egress of the flames and heated gases or products
of combustion through the flues of the steam boiler and its building in
all the Figures.
Figures 1 and 2 are a longitudinal vertical section and a sectional :
front end view of a circular or cylindrical horizontal double flue steam
boiler A (of the Cornish class), with a grate furnace C formed with
the front end B¹ of each boiler flue B, and both corresponding to each
other and sectioned through one flue B and fire C, and fitted with and
illustrative of one modification of my said Invention or improvements.
Figures 3 and 4 are a longitudinal vertical section and a front
elevation, both corresponding to each other of a similar double flue
boiler A, B, but having only one fire-grate C constructed or built
within the brickwork D below the front end of the boiler A, and fitted
with and illustrative of my said Invention or improvements.
Referring to these Figures 1 to 4 generally, the nature and mode of
performing my said Invention as applied thereto consists all as follows:
-In having the "dumb" plate a or front hearth of the firing door or
doors 6 some inches (as from three to twelve inches) higher than the
front ends c¹ of the furnace bars c and fire Z on them, varying according
to the depth or thickness of fire or incandescent fuel kept on top of
furnace bars c, and such that sufficient air is admitted by this new open
mouth or space 1 (left below the under back edge a¹ of the front or
"dumb" plate a), and conducted inwards so close down to and over the
fire Z at z as to heat the air, and ignite and consume all the inflammable
gases as they are produced, especially after and from each fresh charge
of dross or "tripping" coal or other fuel, simultaneous with and in

page_text: addition to the usual air admitted below and up through the furnace
bars c. The fuel Z is charged into the furnaces C as usual through the
ordinary doors B¹, 6, which are preferred to be kept quite close.
篇
This-
new duct or orifice 1 for admitting the air above the front of the fire Z
may when desired have a perforated or close door 3, preferably hinged at
the top edge and to the near or entering front end c", of the duct 1, and
under side of the ordinary front plate a to insure the admission of the air
under the lower edge of this hanging door 3, so as to be conducted close
to and over the fire z by the plate a, a', and having in some cases an
ordinary cataract or other equivalent arrangement to automatically.
regulate the opening 1 and time of closing it, and the door or valve 3 to
suit the time when the black smoke and gases would pass off from each
fresh charge of fuel. The arrangement of regulator shown in Figures
3 and 4 for this purpose is a simple small close air bellows box 4, such
as that used for accordions or for small portable smith's fires, fixed by
its lower close end to the floor at the one side of the ash-pit, and having
a large flap leather valve opening inwards in the upper moveable end 5,
and a small outlet tap 6, and a light connecting rod 7, connecting this
movable end 5 with the lateral arm 3¹ of the new air door 3 of the
furnace C, all so that when the fireman charges the furnace with fresh.
fuel, he pulls up the rod 7. and upper end of the bellows 4 filling it with
air through its inlet valve, and leaves the door 3 the desired distance
open, which will slowly and automatically close by its own weight, and
that of the rod 7 and upper end 5 of the bellows 4 as the air escapes
through the small tap 6, which may be set more or less open to regulate
the time the air door 3 will take to close to suit the amount and
duration of the black smoke evolved after each charge. And although
only an air regulator 4 is herein shown, it will be understood that any
other ordinary automatic fan, water, or spring regulator used for other
purposes may be used instead of it, or otherwise when this nicety of
regulation is not desired a notched or other hand rod or segment and
latch as 3, shown in Figures 5 and 6 might be used to hold the valve
or door 3 in any desired open position, it is set to by the fireman to
admit the required amount of air to suit the particular furnace, and
charge of green or fresh fuel put into the furnace at each time to con-
sume the gases and smoke evolved.
:

page_text: highest behind, as I prefer them, especially where the furnace mouths
and doors B', b, are formed low enough for conveniently charging the
furnace, and with the ordinary hearth plate a so high that the new air-
admitting duct 1 can only be conveniently formed by lowering the front
ends c¹ of the bars c, in which case (as shown in Figures 1 and 2) I
insert a new front bearing bar, plate, or box 2, some inches below the
old hearth plate a, a³, so as to form the new open entering air duct 1
below this plate a, a', which conducts the air forward to impinge on the
front part of the burning fuel at z, so as to be heated, and enter, and
mingle with the hydrocarbon or smoke, and so ignite with them, and
thus prevent the formation of or burn the black smoke.
Referring to Figures 3 and 4, where the furnace. bars c are formed
quite low enough below the boiler already, a good. plan for obtaining
room for the new air supplying duct 1 is to raise the whole furnace
mouth and doors B¹, b, with the hearth plate a, a, six inches or so, and
insert a new bearing plate 2 near the place, or a little lower than the
old hearth a, a¹, so as to form the air duct 1 between them as shown,
leaving the furnace bars c at nearly their old angle, but a little further
forward, so that the back end a¹ of the old hearth will be able to conduct
the air quite back to the burning fuel at z, Figure 3.
In some cases (as shown in Figures 5 and 6, which are a longitudinal
section and a front end view of the furnace of a steam boiler, analogous
to that shown in Figures 3 and 4) where the arch B" of the furnace
mouth B¹ is found to be high above the ordinary bearing and hearth
plate a of the furnace bars c, I prefer to form the new air duct 1 by the
insertion of a new box or plate 1, 2, (with sides) and placed horizontally
some inches above the hearth plate a, with its back open end at c¹ the
full width of the furnace, and with its front end narrowed to open into
the lower end of a new or improved vertical air duct or box 2", formed
on the back of the door 6, and opening up with it when the furnace has
to be charged through the furnace mouth B¹, B¹¹, over the new plate 2¹,
which in this case conducts the air to the front z of the burning fuel
from the top of the box 2" (when it and the door 6 are closed up to it
and the furnace mouth), and where the air enters through the door or
valve 31, set at any open position by the latch and quadrant, as 3", after
every charge, to suit the state of the fire and gases or smoke.
Referring to Figures 7 and 8 (which are a longitudinal vertical section
and front end view of the furnace part of a steam boiler, somewhat

page_text: analogous to Figures 1 and 2), where the furnace doors b, b, are nearly
the full width of the furnace C, the said new or improved horizontal
and vertical entering air duct 1, 2¹, and 2", may both be formed on or
attached to the door & quite within the furnace mouth, so as both to open
out with the door, and fire as usual over the ordinary hearth plate a;
the air being admitted when the door 6 is shut by long ports 3 in it,
fitted with regulating doors or valves 31 swivelling on end journals, and
set open by the fireman as desired, to regulate the admission of air
required to consume the gases or smoke, and conducted forward to the
burning fuel at z, as explained in reference to the other Figures, by the
new or improved duct and plate, 1 and 2¹, or other equivalents therefor;
and when desired, this guiding plate as a, a¹, Figures 1 to 4, and 2¹,
Figures 5 to 8, forming the top of the new duct 1 for guiding the air
for igniting and burning the smoke, may be made loose or with a loose
piece at its inner end z, to slide out and in, or oscillate up and down, to
enable it to be set to regulate and conduct the air close to or within a
few inches of the front burning fuel at z, instead of regulating the
height and distance of the burning fuel from the back edge of this plate
a, a, 2¹, as is required to some extent from it when it is in a fixed
position, as shown in the several Figures.
As before explained, the depth of the new air duct 1 depends on the
depth of the front part of the fire on the grate bars, near the inner end ≈
of the conducting plate for leading the air to this part, leaving at least.
in the smallest furnaces room for a thin layer or current of air of an inch
or so to pass below the end of the plate on to and close over the burning
fire and fuel and gases evolved; and when light fires are used, and this
new duct 1 is only two or three inches in depth, the waste ashes and
clinkers may be easily drawn or raked out over the top of the dumb.
plate a, and through the charging mouth B¹, b, Figures 1 and 2 or 5
and 6, in which latter Figures a grating or perforated plate d is shown.
to assist this, and keep the fire from coming too far forward below the
air conducting plate a, a¹, and 2¹, and which yet allows the air to pass
in a thin layer and impinge on the front of the fire z, although I prefer
and find the open form shown in Figures 1 to 4 to answer fully as well
with the front burning fuel coming forward a little under the plate a, a¹,
and 2, to heat the air thoroughly. Where this opening 1 is wide, as in
the two latter Figures 3 and 4, the ashes and clinkers are easily taken
out through it, and when the conducting plate 2' is fixed on the back of t
.

page_text: the door with an opening in the bottom of the door for admitting the air,
as shown in Figures 7 and 8, the fires can be cleaned and clinkers
removed over the ordinary hearth plate a.
It is to be understood that any ordinary form or construction of
furnace bars in use, and modes of fitting and supporting them may be
used and are suitable for these improvements, although I prefer the
improved form and construction shown in the Drawings, and seen more
particularly in reference to the enlarged transverse section of three bars
shown in Figure 2A; and referring to this Figure I make the broadest
part ff, of each furnace bar F, where they form the narrow spaces g
between them, for the admission of air and the escape of the small ashes,
considerably further down below the highest bearing part f¹, and bevel
or angle them up on each side to this ridged central part f¹ all along,
which leaves a V shaped chamber h between the bars above the open
slits or spaces g below, for the air to pass up and the fine ashes to pass
down through, all so that when clinkers form over the bars they can be
more easily removed by a pronged poker or other equivalent, and thus
admit of the fire being more quickly cleaned than heretofore.
Although only one form of steam boiler, with ordinary construction
of furnaces within its flues or below it, has been shown and described, it
is to be understood that my said improvements are equally applicable to
all other forms and constructions of these, and I consider this sufficient
to show engineers and furnace builders the full nature of the Invention,
and mode of applying it to any other ordinary construction of horizontal
or vertical steam boilers and their furnaces in use.
Having thus particularly described the nature of my said Invention,
and the manner in which the same is or may be performed, I have to
state that I do not restrict myself to the precise details herein described
and delineated, but what I believe to be novel and original, and therefore
claim as the Invention secured to me by the herein-before in part recited
Letters Patent is,―
First. The construction and arrangement of steam boiler furnaces
with a new or improved duct or channel 1, and a plate above it for
conducting air direct on to and across the whole front of the burning
fuel and fire to support its combustion and that of the gases evolved, to
prevent the production in or emission of black smoke from furnaces so
fitted, all substantially as herein described and shown in the accompanying
Drawings, or any mere modification thereof.

page_text: Second. The application and use of a duct and top plate, either open
or fitted with a regulating door or valve, for conducting air to and
across the whole front of the burning fuel and gases produced in steam
boiler furnaces, all for preventing the production in and emission of
black smoke from these, all substantially as herein described.
Third. The new or improved construction of furnace bars with angled
bearing ridges along their central part, so as to leave V shaped channels
between them, with the open air spaces or slits below, all substantially
as herein described and shown in the accompanying Drawings.
In witness whereof, I, the said George Nimmo, have hereunto set
my hand and seal, this First day of May, in the year of our Lord
One thousand eight hundred and seventy-four.
Witness,
W. R. M. THOMSON,
Patent Agent,
Glasgow.
GEORGE NIMMO. (L.S.)