Note: Descriptions are shown in the official language in which they were submitted.
S P E t~ I F ~ C _ _ I O N
~his invent1on relates to the art o:E shaft furnaces and
cupolas, and, more specifically, to a method and means for
maintaining a pilot flame adjacent the charge opening for
igniting burnable gases flowing past the char~e openin~. .
Cupolas or the melting o metal norma~ly consis~ o an
elongated, vertical cylinder having: a charge opening adjacent
~e top through which coke, pieces o metal to be melte~ and
usually flux are feds tuyeres spaced from the lower end fox
injecting combustion air, and. a hearth at the bottom into which
molten meta~ and molten slag can flow to be subseguently
drawn off and in the case o the molten metal, cast into
desirable shapes or in the case of the slag disposed of.
The upper end o~ the cupola commu~icates Pither directly to
alr pollution control devices or throu~h suitable duct wor~
to air preheaters for the combustion air admittect thr~ugh
the tuyeres. In either event, hot gases of c~mbustion are
drawn upwardly through the cupola past the char~e opening
and then out of the top o~ the cupola.
In cupolas, the air is injected thro~gh the tuyeres
unaer pressure and the oxygen thereof combines with incan-
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.;
descent coke ~o form carbon dioxide and produce heat. The
heat melts the metal and the flux. The hot gases of combustion
then ~low upwardly through the cupola preheating the down-
feeding coke and metal. As soon as all of the oxygen opposite
the tuyexes is consumed~ the hot coke above the tuyeres acts
as a reducing agent on the upflowing gases to reduce a portion
of the carbon dioxide to carbon monoxide in an endo~hermic
reac~ion. The amount of carbon monoxide produced and the
ra~io of it to the carbon dioxide is a function of the coke
temperature and the length of time that the gases remain in
contact with the coke at elevated temperature~. In any event,
there are substantial amounts of carbon monoxide ~lowing
vertically upwardly through the furnace and past the charge
opening. It is necessary that this carbon monoxide be burned
lS so that its heat o~ combustion can be recovered i~ the alr
preheaters and/or to prevent the disch~arge of deadly carbon
monoxide into the atmosphereO
In a ~po~a, ~he ~tatic pressur~ he ga~es oppo~i~e
~ the tuyeres is above atmospheric due to the pressure ~n the
- 20 tuyeres and the rapid expansion of the gase~ as they are heated
adjacent the tuyeres. miS st3tic pressure decreases as ~he
gases ~low upwardly due to the resistance of the downfeeding
coke and metal. At the charge openingr which is above the top
of the feed ~toc~, the static pre~sure is normally below
atmospheric due to the draft effect caused by the stack of
the cupola or by suction fans in the ductwork communicatin~
the top of the cupola with the air preheaters~ Thus, there
is normally an inward flow of air through the ~harge openin~
which mixes with the upflowing carbon dioxide and oxygen r
~ormally, by the tim~ the comb~lstion gases have reached
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the charge opening, they have been cooled by the downfeeding
coke and metal ~ufEiciently that they are below the self-
ignition temperature of the carbon m~noxide such that when
the air flows into the cupola through the char~e openi~g, the
carbon monoxide will not ignite.
Heretofore, it has been tle practice to provide a piiot
flam~ adjacent the charge opening such that when the o~ygen
of the air entering through the charge opening comes into
contact with the carbon monoxide, the carbon monoxide will
immedia~ely ignite and be converted to carbon dioxide. mis,
of couxse, results in an exothermic reaction and normally the
heat is recovered through the use of air preheater heat ex- -
changers.
Heretofore, the pilot fLame has been a gas burner
adjacent the charge opening and supplied with a hydrocarbon
fuel such as natural gas. whetl using natural ~as, various
igniting devices are required adjacellt the burner~ ~ddi~ionallyt
safety re~uirements require that there be equipment to sense
whether ~here is a flame pres ent and if not then to shut off
t~e supply of natural yas to the hurner~ Heretofore, it has
been requixed to encase this equipment and the gas hurne~
with refractor~. Because the re~ractory and f~ ame sensing
equipment are frag;le, it has been the practice ~o position
the burner or burners at the side(s) o the ~harge opening
even at the top which are not ~onsidered ~o be desirable
positions for optimum ignition of the C0 gase~.
The present invention contemplates a new and improved -~
cupola pilot flame arrangement and method of operati.ng ~ame
wherein the above referred to di~iculties and others are
overcome and a sel-igniting pilot flame is pro~iaed which
does not require an external supply o~ nat~ral gas,
2~
In accordance with the invention, a standard cupola
having tuyeres spaced from the lower end thereof and a charge
opening in its side wall adjacent the upper end thereof, is
provided with: a gas take-off port positioned above the
tuyeres and below the lower edge of the charge opening and
within the reduciny zone of the cupola through which hot
carbon monoxide gas, at a temperature above its self-ignition
temperature, can be withdrawn from the cupola; a burner
subjacent to the charge opening of the cupola and means for
causing such hot gases to be injected together with a
combustion-supporting gaseous medium through the burner into
the cupola at the charge opening. The take-off port must be
positioned relative to the tuyeres at a location within the
reducing zone of the cupola such that gases have a static
pressure above atmospheric and are at a temperature above the
self-ignition temperature of carbon monoxide so that when
mixed with air at the burner, the carbon monoxide immediately
ignites.
Further in accordance with the invention, means are
provided for supplying a combustion supporting gaseous medium
such as air to the burner along with the carbon monoxide so
that the carbon monoxide will be ignited before it flows so
far into the charge opening that its temperature is reduced ~,
below the self-ignition temperature o the carbon monoxide.
Pre~erably, such means are in the form of an air asplrator at
the burner which air provides some of the oxygen for the hot
carbon monoxide immediately as it exits the burner. There will
be thus formed a continuous pilot flame in the cupola directed
thereinto from the burner at a point adjacent and below the
cupola charge opening and extending upwardly into the cupola
across the charge opening from therebelow so as to ignite any
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4~
carbon monoxide flowing upwardly in the cupola when it is
~nixed with the oxygen of the air flowing inwardly through
the charge opening.
Preferably, the air or other combustion-supporting
gaseous medium which is admixed wi~h the carbon monoxide
gases within the burner i~ preheated to a temperature above
the self-igni~ion temperature of carbon monoxide so that if
for any reason, e.g. start-up or cut-back, the temperature
of the carbon monoxide being supplied to the burner has
dropped below its self-ignition temperature, it will quickly
be raised above this temperature and ignited.
Obviously, a small natural gas or oil pilot burner
and/or an electrical igniter may be provided to take care of
the situation where the carbon monoxide injected through the
burner has been cooled below its self-ignition temperature
although this is undesirable because it involves complying
with certain safety regulations not present when only carbon
monoxide generated internally of the cupola is involved.
Further in accordance with the invention a method of
operating a coke burning cupola having a ch~rge opening and
tuyeres positioned below the opening i5 provided comprised of
the steps of: drawing off carbon monoxide gases from the
cupola above the tuyeres at a temperature above the self~
ignition temperature of carbon monoxide; and, injecting such
hot carbon monoxide into said cupola at a point adjacent the
charge opening and admixed with oxygen whereby to provide a
pilot flame for igniting carbon monoxide gases in the cupola
adjacent said charge opening.
Further in accordance with the invention, the take-off
port or ports for the hot gases is water cooled so that
particles of ash or the like which are entrained in the flowing
gases and impinge on the walls of the poxt do not stick thereto.
A2f~4
Further in accordance with the invention, the above
described conducting tube leads from the lower portion of the
cupola at an angle which is acute with respect to the vertical
axis of the cupola so that paxticulate solids which might be
entrained in the gas stream within the tube will fall by
gravity back into the cupola thereby preventing build-up of
flue dust or like materials within the tube.
In accordance with one broad aspect, the invention
relates to a cupola for the melting of metal having at least
one row of tuyeres therearound located near the base thereof
and a charge opening in the side thereof spaced above the
tuyeres and a burner subjacent the charge opening for
providing a pilot flame directed into the cupola above the
charge material therein and wherein hot carbon monoxide gas is
generated in the cupola in the reducing æone space thereof
between the tuyeres and the charge opening; the improvement
. .. . .
which comprises: means through the walls of said cupola above
said tuyeres for bleeding off from l:he reducing zone space o~
the cupola the hot gases therein at a temperature above the
self-ignition temperature of car~on monoxide and reinjecting
such gases into said cupola through said burner in admixture ~
with a combustion supporting gaseous medium to cause the -
self-ignition and burning of the carbon monoxide present in
~ said gases to produce the said pilot ~lame.
: In accordance with another aspect, the invention relates
to a vertically extending cupola having tuyeres adjacent the ~:
lower end through which combustion air is injected into the
inside of the cupola, a charge opening in the side of the
cupola spaced above said tuyeres and adjacent the upper end of
said cupola through which metal to be melted and coke are fed
into the cupola, means above said charge opening causing a
negative pressure at said charge opening whereby there is an
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2;~4
inflow of air through said charge opening into and upwardlythrough said cupola, and a pilot burner subjacent said charge
opening and directed into the cupola; the improvement which
comprises: a take off port through the walls of said cupola
positioned above said tuyeres in the reducing zone space of
the cupola fcr bleeding off therefrom a portion of the hot gases
therein at temperature above the self~ignition temperature of
carbon monoxide when mixed with airt conduit means communicating
said take-off port with said pilot burner, and means for
injecting a combustion supporting gaseous medium into said
burner whereby to cause the self-ignition and burning of the
carbon monoxide present in the said portion of ~he hot gases
withdrawn from the cupola and provide a pilot flame in the
cupola adjacent said charge opening and extending upwardly
in the cupola across the said charge opening from therebelow.
In accordance with yet cmother aspect, the invention
relates to a method of providing a pilot flame in a cupola
having air injection tuyeres locatecl near the base thereof and
a charge opening located in the side thereof a distance above
said tuyeres and adjacent the upper end of said cupola, said
cupola having means for creating a negative pressure at said :
charge opening and wherein coke is fed downwardly through
said cupola from said charge opening towards and past said
tuyeres, combustion air is injected through said tuyeres to
burn said coke and the gases of combustion move upwardly through
the cupola heating the coke above the tuyeres to an elevated
temperature and the carbon dioxide of combustion of the coke
is reduced to carbon monoxide as it flows upwardly in said
cupola through the reducing zone thereof, said method
comprising the steps of: bleeding o~f a small portion of the
hot gases in said cupola from a point spaced above said tuyeres
in the reducing zone of the cupola where the temperature therein
1~ .
ls above the self-ignition temperature of carbon monoxide
when mixed with air, injecting said withdrawn gases back
into said cupola at a point subjac~nt said charge opening,
and mixing same with air to effect self-ignition and
burning of the carbon monoxide present in said withdrawn hot
gases and produce a pilot flame in the cupola adjacent the
said charge opening and extending upwardly in the cupola
across the said charge opening from therebelow.
It is therefore a principal object of this invention
to eliminate the need for a natural gas fuel pilot flame
for combusting carbon monoxide gas in the upper portions of
a cupola.
It is a further object of this invention to utilize
hot carbon monoxide gas produced within the cupola as the
fuel gas for a pilot flame adjacent: the charge opening, the
hot gas being self-igniting.
It is a further ob~ect oi. the invention to provide
an arrangement for withdrawal of carbon monoxide from a
cupola which avoids the pick-up of flue dust within a conduit
leading from a lower portion of a cupola to an area adjacent
the sill of the charge opening.
These and other objects of the inv~ntion will appear
through the understanding of a more detailed description of
the inveniion which will be described hereinafter as a
preferred embodiment thereof and as illustrated in the
accompanying drawings forming a part of this specification in
which:
FIGURE l is a cross section of a cupola illustrating
a preferred embodiment of the invention;
FIGURE 2 is a cross-sectional view of FIGURE 1 taken
along line 2-2 looking downwardly into th~ cupola;
FIGURE 3 is a cross-sectional view on an enlarged
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scale of FIGURE 2 taken on the line 3-3 showing the preferred
bur~er head used in the present invention; and,
FIGURE 4 is an end view of the burner head taken
on the line 4-4 of FIGURE 3 .
Referring now to the drawings wherein the showings
are for the purpose of illustrating a preferred embodiment
of the invention and not for the purposes of limiting same,
FIGURE 1 shows a cupola A of standard configuration comprised
of vertically extending, cylindrical stee]. outer lining 10
and an inner lining 12 of refractory material or water-cooled
s~eel forming.a vertical cylindrical shaft and a hearth 16.
A molten me~al tap spout 18 leads outwardly from ~he interior
of the shaft at the top of hearth 16. A slag spout 20 is
located slightly above the hearth 16 for drawing off molten
slag material from the cupola.
An air supply conduit 22 leads from blowers (not
shown~ into doughnut shaped wind box 24 encircling the cupola
shaft. Tuyeres 26 lead from wind box 24 to openings 28
located within the cupola above the hearth 16.
A charging platform 30 is located a distance above
the tuyeres 26 for charging material to the cupola through a
charge opening 32 in the side of the cupola, it being
understood that the charge opening may take any form common
in the art depending on the size of the cupola and the type of
mechanism used for charging the cupola. Doors ~not shown) may :.
- be provided. This opening is located above the tuyeres 26 and
below the top of the cupola. The cupola extends above the
charge opening 32 for a sufficient distance as to create an
upward draft through the cupola and past the charge opening
32 and then is exhausted either by venting to the atmosphere
or and more usually the portion above the charge opening 32
communicates to large exhaust fans.
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The cupola interior is charged through charge
opening 32 with alt~rnating layers of metal 36 and coke and
flux 38 extending upwardly to a point immediately below the
sill 40 of charge opening 32.
Static gas pressures within the cupola ~ary from a
maximum above atmospheric adjacent the tuyeres to a minimum
below atmospheric above the upper surface of the feedstock,
past the charge opening to the exhaust fans. In any e~ent,
there is always a negative pressure at the charge opening 32
such that there is a continuous inflow of outside air through
the opening 32 at all times during the operation of the cupola.
To this basic cupola structure which itself
constitutes no portion of the present invention, a take-off
opening 50 is provided in the side of the cupola through outex
shell 10 and refractory lining 12 at a point vertically above
the tuyeres 26 and below charge opening sill 40 and within the
reducing zone of the cupola. This opening is located in a
water cooled conduit 52 extending o~.twardly and upwardly
through the shell 10. Conduit 52 may take a number of different
orms but in the preferred embodiment is comprised of a dou~le
walled tube defining an interior space 59 having a water inlet
57 at the lower end and a water outlet 58 at the upper end.
This water cooling avoids a problem of slag particles impinging
on and sticking to the walls of the conduit 52.
The condu~t 52 in turn communicates to a vertically
extending duct 54 having a refractory, i.e., heat-insulating
liner 56. Duct 54 extends upwardly to an opening 60 through
~ the outside wall 10 and refractory lining 12 of the cupola
: immediately below charge opening sill 40. A combustion chamber62 is formed just in advance of this opening 60 and conduit 54
feeds hot carbon monoxide gases thereto. An air nozzle 66
: extends into chamber 62 and injects a combustion supporting
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gaseous medium such as air, preheated if desired as will
appear, where the carbon monoxide gas ignites to provide a
pilo-t flame in the opening 60 and extending therefrom into
the cupola and upwardly therein adjacent and across the
charge door 32 of the cupola from belowO
Opening 50, in accordance with the invention, is locat~d
at a point above the tuyeres 26 in the reducing zone of the
cupola where the gas mixture within the cupola contains
large amounts o carbon monoxide and the internal temperature
of the cupola under normal operating conditions is at least
above the self-igni~ion temperature of the carbon monoxide
gas in the presence of air; and preferably approximately
1300-1400F. Various sources give slightly different
self-ignition temperatures for carbon monoxide when mixed
with air but they all approximate 1150F. Also, the
take-off opening 50 is located where the static pressures
inside the cupola are a~ove atmospheric. Inasmuch as the
static pressure at the charge opening is below atmospheric,
there will be a ready flow of hot gases through the conduits
52, 54 and burner 62.
The exact vertical location of opening 50 above the
tuyeres and in the reducing zone of the cupola may differ
for different cupolas. Generally it may be located
approximateLy one third of the distance between the tuyeres
28 and the charge opening 32. Here sufficient reduction of
the carbon dioxide has taken place to provide a substantial
percentage of carbon monoxide in the take-off gases and the
gases are still at an elevated temperature. More than one
take-off port may be provided at various vertical positions
and valves may be provided to control the amount ~lowing
through each one.
Thus carbon monoxide above its auto ignition temperature
:~h~
of approximately 1150 flows throug~ opening 50 and gas
conduits 52, 54 to combustion chamber 62 where it mixes
with the oxygen in the combustion air supplied to this
chamber and self-ignites to provide a pilot flame
immediately under charge door 32.
The flow of air and cupola gases in the area adjacent
the charging opening is illustrated in Figure 1. As indicated,
this is an area of reduced pressure due to the stack effect
of the cupola above the opening or exhaust blowers or both.
Thus, there is a large amount of infiltration air thxough
charge opening 32 which flows in the direction of arrows
70 through the charge opening. Gases rising from the lower
portion of the cupola indicated by arrow 72 pass upwardly
and are deflected inwardly by the influx of air at the charge
opening and create an interface 74 therebetween. It is at
this interface 7~ that the hot carbon monoxide gases from
the lower portion of the cupola are reinjected thereinto by
the burner 62 to form a flame ~ront 76 extending along the
inter~ace 74 which is the optimum point for ignition of the
waste gases o~ the cupola. Since burner 62 is made of steel
it may be located below the charge opening sill 40 and will
not be damaged by feed stock materials being charged through
the charge opening and falling onto the charge. This is
contrary to prior art burners which burned natural gas and
: necessitated a refractory shield thereabout and thereby
necessitating a loca~ion away from the optimum interface of
air and cupola gases to avoid being struck with material
being charged through charge opening 32.
It will be appreciated that under start-up or cut-back
conditions of ~he cupola (or even during normal operation of
: the cupola~ the temperature in the cupola adjacent the take-off
opening 50 may be at or fall to temperatures below the self-
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ignition temperature of carbon monoxide. A small natural
gas pilot light of approximately 50 CFH may be employed to
ignite the gases in burner 62 but this defeats one of the
main purposes of the present invention, namely to avoid the
use of any hydrocarbon gases and the attendant complicated
goverNmental regulations controlling the use of such fuels.
Accordingly, means are provided for supplying combustion
air to the burner 62 preheated to a temperature in excess
of the self-ignition temperature of caxbon monoxide which
means may take a number of different forms but in the
embodiment shown include an electric heating element 67 (shown
schematically) installed in the air supply manifold 70 for
nozzles 66. This manifold communicates to a pump or blower P,
capable of supp:Lying 450-600 cubic feet of air per hour.
The heating element 67 has a power rating of approximately
3.5 KW hours per hour and the air i.s heated to a temperature
.
of 1200-1500F. This heating element may run continuously
or only when the temperature of th~ kake-o~f gases as they
reach the chamber 62 fall below a E)redetermined temperature.
The construction of chamber 62 and nozzles 66 form no
part of the present invention. The construction simply acts
as a means for mixing the hot gases from the cupola with
combustion air and injecting the resultant burning mixture
into the cupola in the area immediately below the charge
opening sill 40. The burner includes the nozzles 66 located
within combustion chamber 62 wherein carbon monoxide gas
passing upwardly from the lo~er portion of the cupola is
mixed with the heated air and ignites. The burning mixture
passes outwardly through a reduced diameter opening 82 and a
conical burner head 84 into the cupola itself.
Figure 2 illustrates the optimum positioning of the
opening 60 relative to charge opening sill 40. The opening
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2~fl~
60 is preferably located adjacent one of the vertical
sidewalls 41 of the charge opening 3~ below the sill 40
and offset at an angle of about 15 from t~e center line of
charge opening 32. This allows ~he burner flame to be at
the optimum position for igniting the interface between
incoming air through the charge opening and rising gases
within the cupola.
In the operation of the cupola following the charging
thereof as described above, the coke bed 38 is ignited and
air is injected through tuyere openings 28 to burn the coke
bed 38 to produce heat and carbon dioxide gas. The heat
melts the lowest metal in the column of feed stock and it
flows downwardly through the coke bed and exits as molten
metal through spout 18. The hot carbon dioxide gas produced
now under pressure moves upwardly through the downfeeding
coke bed. This coke is heated by the hot gases and reacts
with the carbon dioxide therein in an endothermic reaction
to produce carbon monoxide gas which continues to pass
upwardly through the feed stock to the area adjacent the
charse opening 32 where the gases are at a considerably lower
temperature due to absorption of heat by both the endothermic
reaction to form carbon monoxide and the absorption of heat
by the feed sto~k. Also the gas pressure is below atmospheric.
This carbon monoxide gas is normally below its auto
ignition temperature or is ~uickly cooked below such
temperature by the large amounts of infusion air passing into
the stack through charge opening 32.
The conduit and burner s~stem of the present in~ention
preferably bleeds off approximately 5% of the total hot carbon
monoxide gas flowing through the cupola and reinjects it at
a temperature of about 1150F. belo~ the charge opening sill
40 through burner 62. The hot gases being at a temperature at
14-
or above the auto ignition tempera-ture of carbon monoxide
when mixed with air, they immediately ignite in the burner
~2 and burn to form a pilot flame in the upper portiQn of
the cupola. If the temperature of the hot gases by-passed
into the burner 62 falls near to or below the self-ignition
temperature of carbon monoxide, the heating element 67 may
be turned on whereby the combustion air injected into the
burner 62 is hot enough to ignite the carbon monoxide.
While there is a slight lowering of the efficiency
of the cupola, this procedure eliminates the necessity for
an external natural gas s`upply to ignite the top gases of
the cupola thereby realizing an extensive savings with regard
to overall fuel cost and efficiency of the cupola system.
While the invention has been described in the more
limited aspects of the preferred embodiment, other
embodiments thereof have been suggested and still others will
occur to those skilled in the art upon a reading and
understanding of the specification. It is intended that all
such embodiments be included within the scope of the present
2a invention as defined in the claims set forth hereinafter.
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