Improvements in the Combustion of Fuel and Furnace Apparatus therefor.
Year: 1892

page_text: Date of Application, 30th Apr., 1892-Accepted, 4th June, 1892
CORT DELE DOITRATION.
Improvements in the Combustion of Fuel and Furnace Apparatus
therefor.
-
I, ROBERT MARSHALL of Endrick Bank Honor Oak Park in the County of
Surrey Engineer 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 has for its object the more complete combustion of fuel with a
reduced air supply and without the production of smoke.
The weight of air necessary for the combustion of one pound of carbon is about
ten pounds, this weight of air containing about the chemical quantity of oxygen
necessary for the purpose. In ordinary furnaces in which the draught is created by a
chimney it is estimated that from twenty four pounds to thirty pounds of air pass
through for every pound of fuel consumed. The excess of air thus passing through
is stated by authorities to be necessary and is called the air of dilution as it is
supposed to dilute and carry away the products of combustion which if not thus
dealt with are supposed to envelop or surround the surface of the fuel and so impede
or arrest combustion.
The
In furnaces in which the air for combustion is supplied through the agency of a
steam jet in the chimney, a centrifugal fan or other blowing apparatus it has been
found that the combustion of one pound of fuel was effected by eighteen pounds of
air and sometimes by a lesser quantity. This has been accounted for in the
following manner namely:-When a fan or other blowing or exhaust apparatus is
employed the air strikes the fuel with a high velocity carrying away the products
of combustion as soon as formed so that less so called air of dilution is necessary.
less the excess of air over the quantity chemically necessary for the combustion of
fuel the higher the temperature and the greater the efficiency. This has been
found to be the case in locomotive furnaces where usually about eighteen pounds of
air suffice to effect the combustion of each pound of fuel the draught in this case
being induced by a blast pipe in the chimney. Similar results were anticipated by
the introduction of forced draught to marine boiler furnaces but whilst in some
cases economy has been claimed in the majority of instances, no substantial
economy has been effected and no diminution of the excess of the air supply
per pound of fuel.
Now 1 claim to have discovered the true cause of the excessive air supply to fuel
burned in furnaces in which the draught is created by a chimney and also of the
diminution of the excess of air supply when under certain conditions the air is
supplied by a fan or other blowing or exhaust apparatus.
When fuel such as coal or coke is thrown upon the grate of a furnace interstitial
spaces are formed in the mass through which the air supply passes. Through each
of these interstitial spaces there passes a core of air (the before mentioned air of
dilution) which does not come in contact with the fuel. When the pressure of the
air supply is slight as in the case of a draught produced by a chimney the volume
of the core as compared with the volume of the air in contact with the fuel is
relatively large. But as the fuel used in furnaces is porous an increase of the
pressure of the air supply, as when a fan or other blowing or exhaust apparatus is
employed will cause the air to penetrate or saturate such fuel so that the volume
of the core as compared with the air in contact with the fuel is small. The use of
finely divided fuel has been resorted to to effect the relative diminution of air supply
but practically without success as the pressure of the air lifts the light particles of
fuel. In order therefore that penetration of the fuel shall take place and saturation
with air be secured it is necessary to oppose a resistance of a considerable mass of

page_text: fuel to the air pressure and this is evidenced by the diminished relative air supply
with which combustion is effected in a locomotive furnace where a thick fire is
maintained. The form of a marine or circular boiler furnace is ill adapted to carry
a sufficiently thick fire to effect this purpose.
In order to apply my discovery practically I construct a vessel or furnace of a 5
suitable refractory material and of a sufficient height to carry a substantially deep
fire. This vessel or furnace I surmount with a bell hopper box hopper or other
suitable apparatus through which the fuel is fed. The air for combustion controlled
by a valve is supplied on the top of the fuel and passes down through it to the incan-
descent portion at the bottom carrying along with it the gases and distilled products
from the black fuel which are decomposed by the incandescent fuel and practically
complete combustion effected without the production of smoke. The lower portion
of such vessel or furnace I construct with two branches. One of these branches
through which the flames and products of combustion pass, I fit to the furnace flue
of the boiler or other apparatus to be heated. The exterior end of the other 1
branch is fitted with a door by means of which ashes and incombustible matter may
be from time to time removed. The projection of this last branch allows a bank of
fuel and ash to accumulate which not entering actively into combustion protects the
door and its joint. I give to this branch a length proportionate to the quantity of
partly consumed fuel and ash which it is intended to receive this quantity being
determined with reference to the following theoretical considerations. The said
mass of partly consumed fuel and ash is to serve for the protection of the door and
it does this not merely in virtue of its low conductive power but also because a slow
process of distillation continues to take place under the influence of the radiant heat
from the furnace. This radiant heat is thus absorbed more effectively than it could 2
be absorbed by an inert non conductor.
I sometimes construct the said vessel or furnace of cast or wrought iron or steel
and surround it partly or entirely by a water jacket which water jacket I sometimes
connect with a boiler.
I sometimes construct the vessel or furnace of cast or wrought iron or steel 3
and line it with gannister firebrick or other refractory material in which case I
introduce a bridge of fireclay or other refractory material at the bend of the branch
where the products of combustion pass on their way to the furnace flue of the boiler
or other apparatus to be heated.
I sometimes construct this bridge of cast or wrought iron steel copper or other 3
suitable metal which I make hollow and of a circular rectangular or other suitable
section. I cause a current of air or water to be kept circulating through this hollow
bridge to prevent its destruction.
I sometimes make this bridge take the form of part or the whole of the horizontal
section of the vessel or furnace in which case it forms part thereof.
This bridge besides serving to protect the corner against the action of the fire in
a manner that will be obvious has in the furnace of my invention a special purpose
as follows. Without it the fuel would tend to burn away in the part of the furnace
adjacent to the bridge and so to form a channel through which the air would freely
pass. I prevent the formation of such a free passage through the fire by arranging 4
my bridge in such a position as shewn in the accompanying drawings as to deflect
the fuel in its descent through the furnace to this place where combustion takes
place most rapidly.
I sometimes introduce a supply of air regulated by valve in or near the branch
connecting the vessel or furnace with the boiler or other apparatus to be heated.
I sometimes use liquid fuel in conjunction with solid fuel in the said vessel or
furnace directing such liquid fuel in any of the ordinary methods upon or under the
surface of the solid fuel.
4
5
Figures 1. 2 and 4 shew a sectional elevation of a circular vessel or furnace. Fis
the black fuel F" is the incandescent fuel A is the air supply pipe B is the branch 5
fitted with the door and B' is the branch through which the flames and products of
combustion are carried to the boiler or other apparatus to be heated.
H is the

page_text: hopper through which the fuel is fed. J in Figure 1 is the water jacket_and
PP are the pipes sometimes fixed connecting such jacket with a boiler. R in
Figures 2 and 4 is the refractory lining M in Figure 2 is the bridge of fire-
clay or other refractory material M in Figure 4 is the hollow metal bridge
Lin Figure 4 shows one method of using liquid fuel.
Figure 3 is a plan of Figure 2.
Figure 5 is a sectional plan of Figure 4 at X-Y.
Figure 6 is a sectional plan of a circular vessel or furnace with the hollow metal
bridge partially taking the form of the horizontal section of the vessel or furnace.
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. The branch to the vessel or furnace fitted with a door formed substantially
as and for the purposes herein before described.
2. The bridge of fireclay or other refractory material substantially as herein-
before described.
3. The hollow metal bridge substantially as herein before described.
4. In a furnace such as is herein before described the combination of the branch B
and the bridge M substantially as hereinbefore described.
5. The use in a furnace of the kind hereinbefore described and claimed of liquid
fuel supplied and used substantially as described and shewn with reference to
Figure 4.
Dated the Thirtieth day of April 1892.