CA1111244A - Hot cupola gas burner - Google Patents
Hot cupola gas burnerInfo
- Publication number
- CA1111244A CA1111244A CA320,462A CA320462A CA1111244A CA 1111244 A CA1111244 A CA 1111244A CA 320462 A CA320462 A CA 320462A CA 1111244 A CA1111244 A CA 1111244A
- Authority
- CA
- Canada
- Prior art keywords
- cupola
- charge opening
- tuyeres
- carbon monoxide
- air
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Vertical, Hearth, Or Arc Furnaces (AREA)
Abstract
HOT CUPOLA GAS BURNER
ABSTRACT
A pilot flame to be positioned close to the charge opening of a cupola which uses carbon monoxide as a fuel in the presence of a fresh supply of combustion air, such carbon monoxide being drawn off from a position on the cupola where the temperature is above the self-ignition temperature of the carbon monoxide. Air preheated to a temperature above the self-ignition temperature of carbon monoxide may also be supplied.
ABSTRACT
A pilot flame to be positioned close to the charge opening of a cupola which uses carbon monoxide as a fuel in the presence of a fresh supply of combustion air, such carbon monoxide being drawn off from a position on the cupola where the temperature is above the self-ignition temperature of the carbon monoxide. Air preheated to a temperature above the self-ignition temperature of carbon monoxide may also be supplied.
Description
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-- :
.j ~ .
.;
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
~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-- :
.j ~ .
.;
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
2~
~ ~ ASM-6014 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 :~ -4~
^'`" .
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 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 J`~
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.
_9_ ,, : ' ~'~ ' ' ' ~
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 .. ... .. . . . . .. . ... . . . . .. . . .. . ...
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-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
~ ~ ASM-6014 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 :~ -4~
^'`" .
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 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 J`~
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.
_9_ ,, : ' ~'~ ' ' ' ~
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 .. ... .. . . . . .. . ... . . . . .. . . .. . ...
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-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 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 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.
. . .
,
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 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 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.
. . .
,
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In 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 zone 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 the reducing zone space of the cupola the hot gases therein at a temperature above the self-ignition temperature of carbon 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 flame.
2. In 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 inflow of air through said charge opening into and upwardly through 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 for bleeding off therefrom a portion of the hot gases therein at temperatures above the self-ignition temperature of carbon monoxide when mixed with air, 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 the 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.
3. The improvement of claim 2 wherein said burner includes means for preheating said combustion supporting gaseous medium to above the self-ignition temperature of carbon monoxide.
4. The improvement of claim 2 wherein said conduit means is lined with heat insulating means whereby the carbon monoxide passing therethrough loses a minimum amount of heat.
5. The improvement of claim 2 wherein said burner is located below the sill of said charge opening.
6. The improvement of claim 2 wherein the conduit from said take-off port slopes upwardly and outwardly through the walls of said cupola.
7. The improvement of claim 2 wherein the walls of said take-off port are water cooled.
8. A method of providing a pilot flame in a cupola having air injection tuyeres located 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 off 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 is above the self-ignition temperature of carbon monoxide when mixed with air, injecting said withdrawn gases back into said cupola at a point subjacent 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.
9. The method of claim 8 wherein air at a temperature in excess of 1200°F. is injected into said cupola in admixture with said withdrawn hot gases.
10. The improvement of claim 1 wherein the said combustion-supporting gaseous medium admixed with the hot gases reinjected through said burner into the cupola is composed of air pre-heated to a temperature above approximately 1200°F.
11. The improvement of claim 2 wherein the said combustion-supporting gaseous medium injected into said burner is composed of air.
12. The method of claim 8 wherein the said portion of the hot gases withdrawn from said cupola comprises approximately 5% of the said hot gases.
13. The method of claim 8 wherein the said withdrawn gases are injected into the cupola in admixture with the said air.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA320,462A CA1111244A (en) | 1979-01-30 | 1979-01-30 | Hot cupola gas burner |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA320,462A CA1111244A (en) | 1979-01-30 | 1979-01-30 | Hot cupola gas burner |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1111244A true CA1111244A (en) | 1981-10-27 |
Family
ID=4113413
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA320,462A Expired CA1111244A (en) | 1979-01-30 | 1979-01-30 | Hot cupola gas burner |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1111244A (en) |
-
1979
- 1979-01-30 CA CA320,462A patent/CA1111244A/en not_active Expired
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