IMPROVEMENTS IN FURNACES FOR STEAM GENERATORS FOR BURNING SLACK OR PULVERULENT FUEL
Year: 1884

page_text: 1, OLIVER IMRAY of No. 28 Southampton Buildings, Chancery Lane in the
county of Middlesex Fellow of the Institute of Patent Agents, do hereby declare
the nature of tho said invention for "IMPROVEMENTS IN FURNACES FOR STEAM
GENERATORS FOR BURNING SLACK OR PULVERULENT FUEL to be particularly
described and ascertained in and by the following statement :—
The use of slack or pulverulent fuel in all furnaces and in particular in furnaces
for steam generators, is very limited. Notwithstanding the considerable difference
between the prices of large coal and of coal dust of the same quality, manufacturers
have up to the present time preferred to use large coal instead of sinall coal or coal
dust on furnace grates, because in practice the use of the latter is always attended
with great loss and considerable disadvantages.
This is caused, among others, by the following circumstances:
1, If coal dust is being burnt, and the draught is produced by an ordinary
chimney, the process of combustion is not effectually carried out because the grate
bars, which have to be very close together, become heated so that the slag adberos
theroto and obstructs the passage of air, thus rendering the combustion very
imperfect, in addition to which the furnace bars very rapidly become useless.
Furthermore the quantity of fuel capable of being burnt on each surface unit of the
grate is very limited, so that having regard to the requirements for the proper
production of steam, the use of coal dust with ordinary chimney draught had to be
discontinued for steam boilers.
2, If an increased draught be used for increasing the combustion, all the above
disadvantages remain, with the exception that a larger quantity of coal can be
burnt on the surface unit of the grate. But a great disadvantage arises in that
case, namely that a portion of the fuel is carried by the strong draught up the
chimney, and this to such an extent as to counterbalanco the advantages gained by
the use of the cheaper fuel.
A portion of the above named disadvantages were already obviated by the use of
partially immersed grates, that is to say, grate bars of considerable depth lying

page_text: close together and dipping partly in water, whereby their temperature is kept low
and the adhesion of slag is prevented, so that a freer passage of air is insured, and
the grate bars aro also rendered much more durable. The water for cooling is
contained in a reservoir or closed ashpit on which the bars stand, and which is
contained outside or inside the boiler, according as this is arranged for external or
internal firing. But even with this system it has not been possible to avoid the
main disadvantage, namely the partial carrying off of the fuel dust in consequence
of the increased draught.
The present invention relates to the construction of furnace grates of the kind
above referred to in such manner as to be applicable with advantage for burning
sinall coal or coal dust.
a The transverse bars. The main object of the invention is to prevent the
escape of the fuel dust by the increased draught; for this purpose I arrange the
bara in oblique positions, that is, not parallel to the axis of the hearth. The
direction which is then taken by the air passing between the bars causes the fuel
dust, that would otherwise assume the slanting direction of the air, passing in
longitudinally of the bars, and would thus be carried to the chimney to be, on the
contrary, raised up more or less vertically, thus affording it time to be effectually
burnt before it can be carried off by the draught. In addition to the above, the
more or less oblique position of the bars causes the gases to be retained longer in
the furnace and consequently to burn with greater useful effect.
I claim as novel the use of furnace bars having a more or less oblique position in
all furnaces suitable for the combustion of coal dust or small coal with increased
draught and closed ashpit. I also claim as novel the use, in any system of
firegrates for the combustion of small coal or coal dust with increased draught and
closed ashpit, of openings or passages deviating from a direction parallel with the
axis of the hearth, and having for their object to impart to the air supply a more
or less inclined direction, whereby the carrying away of the fuel is prevented.
The firegrate can also be constructed of a single plate in which are formed more or
less oblique openings or passages, and upon which the fuel is burnt.
b Cooling of the bars or of other forms of firegrates without immersing them
in water. For cooling furnace bars or grates, suitable for burning small coal and
coal dust, I prefer to introduce or generate steam or other gas or a mixture of
liquids and gases in the above mentioned closed ash-pit; the steam may be
produced by raising the temperature of a layer of water at the bottom of the
ash-pit, or it may be introduced by means of a steam pipe.
I claim as novel the production or introduction of steam or of other gases (oxcept
air) or of a mixture of liquid and gas in the ashpit below the furnace grates, of
steam boilers in which the combustion of small coal and coal dust is effected under
increased draught and closed ash pit.
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c Simultaneous double mechanical draught. I also claim the simultaneous use
of an increased or mechanical draught in the chimney or uptake and of air pressure
in the ashpit. If an increased draught already exists in the chimney, as for
instance the draught in a locomotive chimney, and a second increased draught is
produced by air supply under pressuro under the grate, the process of combustion
can be effected much more advantageously than without such combination, as the
products are retained much longer in the furnace, so as to effect the combustion as
completely as possible.
By combining the various above described points desired to bo patented I have
constructed an especial fire grate capable of burning small or pulverulent fuel.
Figs. 1, 2 and 3 of the drawing give an idea of the application of the Ferrando
Grate to any type of Boiler, which in the drawing is shewn with double internal
hearth; the ashpits or ashboxes are hermetically closed and either communicate or
not with each other; in the case of the drawing they communicate. In them the
air supply is compressed which air can only escape through the bar spaces or the
penings that correspond with them. By means of a suitable door the ashes are

page_text: withdrawn from the ashpits. Figs. 1 and 2 shew that the compression of the air
or forced draught is in this particular case effected by means of a steam Injector, it
could howover be effected by other means for instance by a fan, independently of
the steam which in acting for the Blast mixes with the air supply. Another steam
pipe is inserted in the ashpit for the purpose of cooling the bars which, from their
extreme closeness, might otherwise be stopped up by clinkers and burned. The
steam of the blast is of itself insufficient for the cooling, because an increase of
steam in order to effect the cooling, would increase the activity of the draught and
of the combustion, and thus the desired cooling would become illusory. The bars
of the grate are placed in one or more ways laterally or transversely in order to
avoid the conveying of portions of the small fuel into the flues which, when using
a forced draught, could not be avoided if longitudinal bars were employed. In the
drawing fig. 3 shews that they are arranged in two transverse sets..
The furnace, which forms the subject matter of the present invention, consists
therefore in an effective combination of various dispositions of parts, that is to say
bars placed very close together for the purpose of burning small fuel, but placed
more or less transversely as regards the axis of the furnace; very narrow openings
which, in any system whatsoever of grate suitable for burning small coal, should be
more or less transverse to the axis of the grate; cooling of the bars by means of
steam or of any gas, produced or introduced in the ashpits (the air supply excepted):
cooling of the grates by means of jets of liquid or liquid united with gas: jets
thrown into the ash box.
All the arrangements above described refer to grates not immersed in liquids and
must always be combined
1 With a forced draught obtained by steam blast or by other means.
2nd With closed ashpits in which the air supply is compressed.
The simultaneous mechanical draught in the ashpit by forced air supply and in
the chimney or flues of the smoke by artificial exhaust or suction render the
Ferrando Grate applicable even in the most unfavorable cases.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I declare that what
I claim is:
First. The use of more or less oblique fire bars in in respect to the longitudinal
direction of the axis of the furnace in fire grates for burning small coal or
pulverulent fuel with increased draught and closed ashpit.
Second. The use of openings or passages in any construction of fire grates for
the combustion of small coal or pulverulent fuel with increased draught and closed
ashpit, which openings or passages replace the ordinary openings between the bars,
and deviate from the longitudinal direction of the axis of the furnace, and prevent,
by their more or less oblique or sloping position, the carrying off of the fuel, or
retain the gases in the furnace for a greater length of time.
Third. The cooling of the fire bars by means of steam or other gases except air
or by means of mixtures of gases and liquids, in the case of an increased draught
and closed ashpit.
Fourth. The use of a simultaneous double mechanical draught, by suction in the
chimney or the flues and pressure under the fire grate.
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