Improvements in Firegrates for Combined Forced and Natural Draught.
Year: 1895

page_text: Date of Application, 19th Sept., 1895-Accepted, 7th Dec., 1895
COMPLETE SPECIFICATION.
Improvements in Firegrates for Combined Forced and Natural
Draught.
I, PETER CARL HOMBURG, of Barmen, Oberdirnerstrasse, No. 70-70 Rhenish
Prussia, Germany, Manufacturer 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:-
My invention relates to improvements in firegrates allowing the combined appli-
cation of forced draught and of natural draught simultaneously, to the fire-grate and
'furnace, by which means not only the detrimental effects of forced under-draught
are obviated but also a complete and smokeless combustion of fuel is attained, as it
allows the regulated admission of heated air into the fuel on the grate between and
through the firebars as well as to the furnace gases behind the firebridge.
The introduction of forced draught taking place through a hollow dead-plate and
the hollow firebars, the latter are provided with holes or longitudinal slots in their
upper face for the passage of the air blast; these firebars are therefore cooled in
the best way, having at the same time their exterior sides cooled by the passage of
natural draught through the interstices between the bars and so duration and con-
servation in proper state of the firebars is increased. Part of the forced draught
and also the natural draught may be directed into a hollow firebridge containing
tubes in the direction of the flames for the sake of heating the air passing through
it and cooling the firebridge at the same time. The air taking its way through the
interior of the hollow firebridge escapes through holes in the rear wall of the same
and is blown into the mixed products of combustion and the smoke and flames
passing over the fire-bridge into the flues, there mixing itself thoroughly in hot
state with these products of combustion, produces, a complete consumption of
smoke.
The new firegrate-arrangement prevents also the formation of slag and cinders
on the bars by the constant cooling of the latter, is easily worked and kept in order;
it allows the use of inferior quality of fuel without formation of smoke. This
excellent combustion and the easy regulation of the re, added to the increased
duration of the firebars, which remain so cool that a hand may touch them without
harm, secure a most. economic service of the furnace.
I preferably arrange my firegrate as a common plane grate which is the most
solid form, but it may be carried out in different other styles.
The drawing accompanying this Specification, shows such a firegrate arranged in
the flue of a Cornish boiler, and
Fig. 1 is a vertical longitudinal section of the boiler-furnace.
Fig. 2 is partly a front view and partly a cross section along I---I of Fig. 1.
Fig. 3 is partly a horizontal section above the grate and partly through the
hollow firebars.
Fig. 4 is a cross section of a single grate-bar.
Fig. 5 is a part of the lower side of the fire bridge.
The boiler-furnace shown is one with two lengths of bars, but it is clearly under-
stood, that without modifying in any way the principle, the arrangement can be as
well made with a single, or more than two lengths of bars.
Three main parts compose, as usual, the furnace grate, but they are all of a special
arrangement in order to carry out the invention, the dead-plate, the bars, and the
fire-bridge.
The fire-plate or dead plate c is a hollow casting with a front tubular extension d,
a front cross-opening e with cover e' under the fire-door a, fitted as usual to the

page_text: fire-door-plate b, and another cross-opening ƒ, inside the fire-box, below the upper
surface of the plate c.
The front cross-opening e is for introducing a fire-iron into the interior of the
hollow firebars and further into the back-end box, for cleaning it from ashes and
dust; the back cross-opening f takes in the front ends or heads of the hollow fire-
bars; the tubular elbow d is for the connection to a suitable source of air under
pressure, as to a jet-blower or fan.
Below this hollow plate e the front of the furnace is open and gives access to the
ash-pit and it serves for the entrance of the natural draught of air under the grate
and to the fire-bridge. The middle part of the boiler-furnace is formed of a set of
hollow fire-bars g with open ends, laid in a horizontal row with air spaces between
them the front ends resting in the cross-opening f, the rear ends upon the cross-
bar, or in the case of a single length of grate-bars, in the front cross-opening of
the hollow box of the fire-bridge-supporting plate k; the open ends of the fire-
bars facing each other, in the case of several lengths being used, upon the cross
bars i, represent one through channel extending from front to rear, so that the
forced draught being blown into the hollow dead-plate, divides itself through all
of the bars in the whole length, and by longitudinal apertures or slots g' in the
upper face of the bars, or through equivalent holes, this air enters into the fuel
spread over the grate-surface h.
The rear part of the furnace consists of a firebridge-supporting plate k with an
opening taking up the open ends of the hollow fire-bars, whilst the rear opening
is covered by a damper or register o with hinges p, serving to regulate the flow of
the forced draught under and through the hollow firebridge, by a rod 9 extending
to the front of the furnace.
The fire bridge-supporting plate & has at its lower side an opening covered by a
hinged damper or register connected to a rod s extending also to the furnace front
in order to regulate by it the admission of natural draught coming through the
ashpit, and in order to allow cleaning of the space under the fire-bridge from ashes
and dust.
row of
On the top of this supporting plate k, being arranged with an angle-plate.
extending horizontally to the rear with a large opening k¹, is put the hollow.fire-
bridget, composed of a lower part t' open underneath, the open part corresponding
to the opening k¹, and crossed by a horizontal row of half-round channels t³ in
the longitudinal direction of the boiler-flue, and a top part t' having a corresponding
row of half round tubes in its under part and a covered top v, and a
round or other convenient holes w above the rear ends of the half-round channels
in the vertical wall of the fire-bridge. The two parts t¹ and t being put one above
the other, so that the rows of half round channels form a row of horizontal
longitudinal tubes open at both ends, constitute the hollow fire bridge and rest
with the lower front edge upon the top-rib k² of the angle-plate extension, which
by and a rib u' is sitting upon the top of a firebrick masonry u separating the ash-
room from the rest of the boiler flue.
The row of horizontal tubes t³ serves for the passage of flames and combustion
gases through the firebridge, and the forced draught coming from the hollow dead-
plate and passing through the bars, chamber and damper o into the firebridge, is
strongly heated by passing between and around the fire-tubes to and by contact
with the hot walls of the firebridge, cooling them in this way and the tubes t.
It then flows out through the holes w, and mixing intimately with the products of
combustion behind the firebridge, produces almost complete smoke-consumption.
The service of firing this grate and the effects of it are the following:
The fire is got up in the ordinary way and if the boiler is cold yet, and no source
of artificial blowing at hand, that is in the case, that the boiler has to furnish the
blowing power, the natural chimney-draught alone is used, and the dampers or
registers o and remain closed, but the cover e' of the furnace front opening e may
be opened to allow air to be drawn through the slots g' of the hollow firebars into
the fuel on the grate. If another source of forced draught independent from the

page_text: boiler in question, is at hand, the firing up may be accelerated by coupling it to
the air-tube d, and closing door e¹. When the boiler has got up steam of little
pressure only, a jet blower will give sufficient forced draught for accelerating the
firing.
The natural draught will pass by the free spaces between the bars partly, and
partly it may be directed by the regulating register under the fire bridge and
through it and the holes w, to cool the firebridge, taking up heat from it
and mixing up with the hot furnace gases, in order to contribute to smokeless
combustion.
The artificial draught or air under pressure introduced into the hollow dead-
plate c will flow through all the open ends into the hollow grate bars, where it is.
partly heated by contact with the metal of the bars, entering then into the fire,.
increasing the energy of combustion. Part of it will also flow through the
regulating damper o under the hollow fire bridge where it mixes with the natural
draught entering from register r, and assists in cooling the walls of the firebridge t
and its flame-tubes t³, heating itself and discharging through holes w into the
furnace-gases behind the firebridge, causing complete smoke-consumption and at
the same time preserving the firebridge from the destructive effects of the fire.
The cooling of the grate bars by the forced draught flowing through their
interior has the beneficial effect of preventing any settling of scale and slag upon
them taking in account the additional cooling of the natural draught going through
the free spaces between the bars, and therefore the necessity of cleaning the fire is
a rare occurence, in consequence of which the excellent state of conservation of the
bars increases their durability.
The equally distributed access of air to the whole fire in consequence of the clean
bars and edges of slots in them render the uniform stoking an easy task, and this
is the case even with fuel of inferior quality.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :
1. In firegrates for boiler heating and other purposes the use of combined natural
and artificial or forced draught in such a manner that the natural draught as usual
is passing through the free spaces left between the gratebars and that the greater
part or the whole of forced draught is blown into the hollow firebars used and
passing out into the fuel by suitable holes in the upper side of the bars and that
part of the forced draught is blown out at the open ends of the hollow gratebars—
(the openings being made adjustable)-into the furnace gases behind the fire
bridge.
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2. In a firegrate-arrangement for combined natural and artificial draught used
at the same time, the hollow dead-plate c having a tubular projection d for con-
necting a wind-pipe, an opening e and a cover e in combination with a set or sets
of hollow firebars g open at both ends and having slots or holes g' at their upper
side, a firebridge-carrying plate receiving in an opening the rear ends of the
firebars, said opening being closed by an adjustable damper o suspended in hinges p,
a rod for regulating said damper and an opening below the grate in plate
provided with an adjustable cover r and rods; a hollow firebridge t placed on the
horizontal wing of plate k and being provided with passages for the flame and
furnace gases and hollow spaces with outlets to at the rear end. The whole as
described and illustrated and for the purpose specified.
Deted this 17th day of September 1895.
PETER CARL HUMBURG,
Per Karl J. Mayer,
Agent.