CA1085616A - Reducing gas generator - Google Patents

Abstract

Abstract Apparatus for heating and mixing industrial tail gases with a reducing gas by burning n mixture of fuel, air, and steam in a combustion chamber having a small outlet opening at the end of the chamber. A jacket surrounds the combustion chamber. She industrial gases are circulated around the combustion chamber inside the jacket, heat being transferred from the combustion chamber to the industrial gas.
It is then mixed with the combustion products from the outlet of the combustion chamber to form a high temperature mixture of an industrial gas and a reducing gas for subsequent processing.

Description

. . . ' :~8S6~6 REDUCING GAS --GENER~TOR
Field o~ the Invention This invention relates to a method and apparatus for processing industrial tail gases, and more particularly, is concerned with a heater assembly for generating a reducing gas by combustion of a fuel in an oxygen limited atmosphere, and mixing the reducing gas and industrial gas.
Background of the Inven*ion I~ U.S. Patent No. 3,752,877, for example, there is described a process for the reduction of compounds, such as sulfur, nitrogen oxides and the like, occurring in industrial gases, such as the tail gases from Claus plant, or the like.
In the patented process, the tail gases are first heated to an elevated temperature by a conventional burner through a heat exchanger that prevents mixing of the products of combustion with the tail gases. ~fter heating, the tail gases are mixed with a reducing gas containing hydrogen and carbon monoxide.
The reducing gas is produced by ~urning air and fuel in the presence of steam in a sub-stoichiometric combustion reaction.
When hydrocarbon i5 burned stoichiometrically or sub-stoichiometrically, it is difficult to avoid formation of free carbon or soot, which is harm~ul to subsequent process steps.
It is also di~ficult to insure complete consumption of free oxygen, which of course is not wanted in the reducing gas.
suhlmary of the Invehtion In accordance with the present invention there is provided ~':

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Apparatus for generating hot gas free of molecular oxygen and soot by combustion of hydrocarbon fuel and mixing the hot ga3 with industrial gas, comprising (a~ a cylindrical combustion chamber providing an in~ernal refractory surface and havIng at one end an elongated inlet opening forming a throat axially aligned with an outlet opening in an opposing end wall of the chamber, which wall provides a refractory surface, each opening being of a smaller cross-.
sectional area than the axial cross-section~l area of the combustion chamber, the end containing the outlet opening forming a portion of a first radiating surface;
(b~ a concentric cylindrical jacket enclosing the outlet end and having a second planar radiating end refractory surface facing the outlet opening of the combustion chamber, a portion of the jacket surrounding the cylindrical portion of the combustion chamber to form an annular passage therebetween, said concentric cylindrical jacket extending beyond the end of the combustion : chamber having the outlet,to form a mixing zone;
(c~ a windbox for introduction of an oxygen-containing gas enclosing the inlet opening of the combustion chamber;
(d) means for directing the oxygen-containing gas into the windbox tangentially to the axis of the combustion chamber, whereby the gas has a rotating motion in passing through the throat;
(e) means at the throat for ~orming a plurality of jets of fuel and steam directed into the combustion chamber through the throat simultaneously with passage of the rotating motion oxygen-: containing gas through the throat; and . - 2 r ;

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(f) an inlet communicating with the annular passage for introduction of the industrial gas to the jacket and an outlet in the jacket adjacent the second radiating end surface for exhaust of the industrial gas and products of combustion from the ~: 5 combustion chamber.
Also in accordance ~ith the invention there is provided Apparatus for heating an industrial gas by mixing the industrial gas with a combustion gas free of molecular oxygen and soot, and formed by combustion of a hydrocarbon fuel,for u~e in an industrial gas recovery process or the like, comprising:
(a) an elongated combustion chamber providing an internal refractory surface and having an inlet opening at one end forming an elongated throat and an outlet opening in a planar wall providing a portion of the internal refractory surface~ ;
at the other end, the area of the openings being up to 50% of the axial cross-sectional area of the combustlon chamber, means for directing a plurality of jets of fuel and steam into the inlet opening of the combustion chamber;
(b) means, rearward of the means for directing fuel 2Q and steam into the combustion chamber, for directing a s:~ream of gas containing oxygen through the inlet opening, said last-named means generating a rotating component of motion to the stream of gas to provide a vortex in the combu~tion chamber;
; (c) an annular chamber surrounding the combustion chamber to form an annular passage therebetween and enclosing the outlet : end of the combustion chamber to form a mixing zone, said chamber providing a planar refractory surface facing the outlet opening of the combustion chamber;

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(d) means directing the industrial gas into the annular chamber in a direction transverse to the longitudinal axis of the combustion chamber on one side of the annular chamber, and (e) means for directîng gase~ out of the annular chamber adjacent the outlet end of the combustion chamber.
Further in accordance ~ith the invention there is provided apparatus for heating an industrial gas by mixing the industrial gas with a combustion gas free of molecular oxygen and formed by combustion of a hydrocarbon fuel~for use in an industrial gas recovery process or the like, comprising:
(a) an elongated combustion chamber having a length to diameter ratio of 2 to 1 and providing an internal refractory surface and having an inlet opening at one end axially aligned with an outlet opening at the other énd in a planar wall providing part of the refractory surface, the openings being smaller than the axial cross-sectional area of the combustion chamber, said inlet opening forming a constricted throat and said outlet opening formed by a first radiating end wall having an area up to 50~ of the area of the end wall;
2a (b) annular means directing a hydrocarbon fuel in : admixture with steam through a plurality of holes in the annular means into the combustion chamber;
(c) means for directing a stream of gas containing oxygen through the inlet opening, said last-named means generating a rotating component of motion to the stream of an oxygen containing ga~ to provide a vortex in the combustion chamber by passing the gas flow tangentially to the inner surface of the combustion chamber;

~: :: . .: '. . . : ' `:, ' ,:. ' ' .: ',:: ,. : .. ,:,.: . '' " :., ' ' ' . ',': ', ' ', ', . . :'` ' 1~l356~6 (d) an annular chamber surrounding the combustion chamber to form an annular passage therebetween and enclosing the outlet end of the combustion chamber, said annular chamber having a second planar radiating wall providing a refractory 3 surface parallel to the first radiating end wall of the combustion chamber and spaced therefrom;

(e) inlet means for introducing industrial gas into the annular chamber, said inlet means associated with baffles to direct gas flow transverse to the longitudinal axis of the combustion chamber on one side of the chamber, and (fj outlet means for dlrecting gases out of the annular chamber adjacent the outlet end o the combustion chamber.

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Further in accordance with the invention there is provideA
a method for preheating industrial gases which comprises:
(a) introducing into a ~indbox associated with a combustion chamber an oxygen bearing gas, a rotational velocity from about S0 to about 150 ft. per second;
(b~ mixing a hydrocarbon ~uel with the oxygen bearing gas;
(c) passing the oxygen ~earing gas and the hydro-carbon fuel into a throat leading to a combustion chamber, the velocity of the oxygen bearing gas being rotational and from about 100 to abou* 300 ft. per second;
(d~ combusting the fuel into a cylindrical combustion cham~er adjacent the throat in the presence of the oxygen bearing gaS, the rotational flow of the oxygen bearing gas in the throat causing the products of combustion to pass rotation-ally along the wall surfaces of the combustion chamber, and ~ e1 passing the products of combustion through an orifice po~ition at the end of the cylindrical combustion chamber opposite the throat and com~ining the products of combustion with the industrial gas, said industrial gas being preheated by rotational passage ~hrough an annular passageway surrounding the com~ustion chamber.
Further in accordance wi~h the invention there is provided a method fox heating an industrial gas in which an oxygen cont~ining gaæ is mixed w~th ~uel and com~usted in a ,. ~
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combustion chamber, the combustion products ~ravelling along the walls of the combustîon chamber to transfer heat to an industrial gas stream passing along an annular passageway surrounding the combustion cham~er and wherein final heating S occurs by combining the products of combustion with the industrial gas external of the combustion chamber, the improvement which.comprises premixing steam with the fuel gas in an amount up to about 5 pounds per pound o~ fuel prior to combining the mixture ~ith an oxygen containing gas to prevent formation of carbon during com~ustion of the fuel gas.

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i~856~6 The present invention is directed to an improved method and apparat~s for generating a reducing gas and at the same time using the heat generated by the produc~ion of the reducing gas to preheat the industrial gas, and then mixing the industrial gas with the reducing gas. In the past, high operating temperature in the reducing gas generator has presen~ed cooling problems since operating temperatures generally exceed working temperatures of common metals. The present invention provides improved.eficiency by utilizing the industrial gas as a cooling agent for the walls of the combustion cham~er. In brief, the apparatus of the present invention includes a combustion chamber comprising a refractory lined elongated metal cylinder preferably having a length to a diameter ratio of 2 to l surrounded by a concentric outer cylinder forming an annulus through which the industrial gas flo~s.
The combustion chamber terminates in a radiant end wall havin~ an exit orifice o~ an area up to about 50% of the end wa1l.~ Fuel ga~ preferably premixed with steam i~

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10 5~6~ 6 1 dircctcd into ~hc combustion chaml)cr throu~h a burner ring with mul'ciple outlct holes. Air or oxygen is ~dmitced into the combustion zone through a wind box positioned rearward o the burning into which a source of oxygen, typically air S is in~roduced tangentially to form a vortex flow within the combusEion cham~er, Relatively high rotary velocity is imparted by a cons~cric~ed throa~c section at the entrance to the combustion chamber. Preferably, the constricted throat doubles the velocity of the gas in ~he wind ~ox which is in the range of about 50 to 150 ft./sec. The products of combustion are mixed with the industrial gas after the .
products o~ combustion pass through a ~lame exit ori~ice.

Brief Description of the Drawin~s .
For a more complete understanding of the invention, reference should bo made to the accompanying dra~ings, wherein:
. FIG. 1 is a side elevational view of the apparatus of the present invention;
i FIG. 2 is an end view of the apparatus;
FIG~ 3 is a sectional view taken substantially on the line 3-3 vf FIG. 2;
~IG. 4 is a partial sec~ional view taken on the line 4-4 o ~G. 3; and . FIG. S is a fragmentary view showing the burner.
Detailed Descripti.on :
Referring to the drawings in detail, tlie numeral 10 indicates generally the combustion and mixing apparatus which : includes an inner metal cylinder 12~ having an inner lining 14 of refrac~ory ma~erial orming a combustion cllamber 16. A

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1 me~:al inner wall 18 havi~ n openill~, 20 is lined wit:h re~ractory material 22 surroun~ g t:he opening 20 to orm a res~rictcd thro~t at the inlet end of the combustion chamber 16 . The other end 24 o the combus tion chamber is onned o 5 refractory material havin~ an outlet openin~ 26 therethrou~h forming a flame exit ori~ice.
An annular burner 28 surrounds the outside of the : opening 20 in the metal wall 18. As shown in detail in FIG. 5, the burner ring is formed of a hollow pipe having a 10 plurality of equally spaced holes 30 around the inner periphery thereof for directing uel gas into the combustion chamber. An inlet pipe 32 is connected ~o the ~urner 28 and extends through a 90 elbow 34 out~"ardly through the metal cylinder 12. The pipe 32 connects through a T-connection 36 to a source o~ a gaseous or liquid fuel which is hydrocarbon, such as natural gas, methane or the Like, a fuel gas containing hydrogen, carbon monoxide~ or mix~ures thereof, normally liquid hydrocarbons and the like. The T-connection 36 also connects to a source o~ steam, the T-connection mixing 201 ~he steam and fuel together before the'mixture is directed : into the combustion chamber through the burner 28.
¦ The inle~ end o~ the metal cylinder 1~ is provided with a ~lange 38 to which is bol~ed or otherwise secured an end pLate 40. The space within the cylinder 12 between the end plate 40 and inner wall 18 provides a wind box 42. Air, oxygen, ox o~her oxygen-containing gas is connec'ted into the wind box through an inlet pipe 44. As best seen in FIG. 2, the inlet pipe 44 is positioned o~ cenker, so that the flow o~ air into the wind box is tangen~ial to the cylindrical wall 120 Thus a rotary mo~ion is imparted to'the air w~thin the wind box 42 by the ~low o~ air out of the pipe 44.
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1 Mle air from the wind box en~crs thc coml~ustion cham~er ~hrou~h the opcnin~ 20 where it mixcs Witll the fuel and s~eam ~rom the burner ring 28. The mixture is i~nited by suitable means, such as a pilo~ 1ame, an electrical spark or S the like.
In order to produce high t~rbulance in the throat zone illdicated at 48, formed by the openin~ through the refractory Inaterial 22, air is introduced through the pipe at a velocity in the range o~ 50 to 150 ft. per second, thus maintaining a high rotary velocity ~n the wind box and a still higher velocity in the throat 48 preferably in the range o~
about 100 to about 300 ~t. per second or double the velocity in the wind bo~. The constriction formed by the throat 48 is pre~erably less than hal~ the diameter o~ the combustion chamber 16.
To pro~ide cooling for the combustion chamber, and at the same time to provide preheating of the industrial or : tail gases, the combustion chamber is provided with a - cylindrical shell or Jacket 50. The jacket 50 is supported from an end ring 5~ which surrounds and is welded to the cylinder 12 in the same plane as the inner wall 18. ~he ~acket 50 is provided with an annular flange 54 which is bolted or otherwise secured to the end ring 52~
The outer jacket 50 extends substantially beyond the ori~iced reractory end wall 24 o~ the combustion chamber and ter~inates in an end walL 56, which is welded or otherwise secured and sealed to the end of the iacket 50.
The area o the orifice is up to about one-hal~ the area of the end wall to maximize back radiation without impeding ~as ~lowu The industrial gases are dirccted into the annular . ,.
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~-' ~l0~56~L6 1 spacc be~ween tlle cylindcr 12 of the combustion chambcr and the ~acket 50 through an inlet pipe section 5~. As best seen in FIG. 4, the pipe section 58 has its axis of center from the axis o~ ro~ation o~ the cylinder 12 and jacket 50. In addition, a series of ba~fle plates 60, 62, and 64 are positioned inside the inlet pipe section 58 adjacent the opening into the annular space with;n the ~acket 50 so as to direc~ the industrial gas in a 10w directi~n ~ .
which is tangential ~o the cylinder 12. Thus a rotary component of motion to the ~low of industrial gas along the outside of the combustion chamber is provided.
As the indus~rial gases move longitudinaLly off the : combustion chamber they enter the region between the end o~
the combustion chamber and the end wall 56 where they mix with the products of combustion ~rom the combustion chamber which pass out through the fLame exit ori~ice 26. This mixture is directed out through an outlet pipe 66. Because the gas from the combustion chamber ente~s the mixing region ~ at a relatively high temperature, the outlet 66 and the jacket :~ 20 50 are lined with a layer o re~ractory material 68 which also serves to radiate heat back to the combustion chamber.
The re~ractory material extends back along the jacket 50 to a point where ~he temperature o~ the jacket is maintained at a safe level by the cooling efect of the industrial gases flowing in the annular space between the jacket and the . cylindricaL wall 12.
: In operation, the addition of steam to the fuel gas :-has been found to provide substantially soot-~ree combustion~
The presence o~ steam wi~h the hy~rocarbon gas has thc e~ect of reducing any thermal re~ction or cracking process in which l2 ~ . " ' ,:
: ' 1~ ( 1 08 56~ 6 1 frcc c~rbon is relea3cd ~rom the hydxoc~rbon moleculc~s. Even though some craclcing o the hydrocarbon moleculcs may stilL
take place in the combustion chambcr, the ~ntimate mixture o water molecules cnhances the reaction of the released carbon with oxygen to orm carbon monoxide and carbon dioxidc.
Typically, up to about 5 pounds of steam is mixed with each pound of fuel.
The combination of greatex turbulance to provide improved mixing of the ~uel gas and airl the high temperature wi~hin the combustion chamber, the radiating end wall 24 o refractory material for re-radiating energy into the combus-tion chamber, and the addition of s~eam to the fuel gas combine ~o insure more complete oxidation thereby removing all free oxygen from the reducing gas produced b~ the combustion operation. The combustion chamber preferab~y has a length to diameter ratio of about 2 to 1 to provide a voLume equivalent to a gas residence time of 0.1 to 1 second. A
residence time of about 0.5 second is preferred when the fuPl gas containes 10% or more of propane and heavier hydrocarbon molecules. With fuel gases lean in propane or heavier components, very little steam need be premixed with ~he fuel gas. About one pound of s~eam ~or each pound of uel is preerred. With fuel gases having heavier co~ponen~s or wi~h liquid fuels, the ratio of steam may be increased to as much as five pounds of steam per pounds of fuel. I a liquid ~uel is used, a steam atomizing spray nozzle is substituted for the burner ring for injecting the uel into the combustion chamber.
While the combustion process has been described as generating a reducing ~as, the same apparatus may be used ; 30 wllere a neu~ral gas is re~uired. This of course depends only on the amo~nt o~ oxygcn supplicd in relation to the ~uel ~as '":
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Claims (18)

WE CLAIM:

1. Apparatus for generating hot gas free of molecular oxygen and soot by combustion of hydrocarbon fuel and mixing the hot gas with industrial gas, comprising:
(a) a cylindrical combustion chamber providing an internal refractory surface and having at one end an elongated inlet opening forming a throat axially aligned with an outlet opening in an opposing end wall of the chamber, which wall provides a refractory surface, each opening being of a smaller cross-sectional area than the axial cross-sectional area of the combustion chamber, the end containing the outlet opening forming a portion of a first radiating surface;
(b) a concentric cylindrical jacket enclosing the outlet end and having a second planar radiating end refractory surface facing the outlet opening of the combustion chamber, a portion of the jacket surrounding the cylindrical portion of the combustion chamber to form an annular passage therebetween, said concentric cylindrical jacket extending beyond the end of the combustion chamber having the outlet, to form a mixing zone;
(c) a windbox for introduction of an oxygen-containing gas enclosing the inlet opening of the combustion chamber;
(d) means for directing the oxygen-containing gas into the windbox tangentially to the axis of the combustion chamber, whereby the gas has a rotating motion in passing through the throat;
(e) means at the throat for forming a plurality of jets of fuel and steam directed into the combustion chamber through the throat simultaneously with passage of the rotating motion oxygen-containing gas through the throat; and (f) an inlet communicating with the annular passage for introduction of the industrial gas to the jacket and an outlet in the jacket adjacent the second radiating end surface for exhaust of the industrial gas and products of combustion from the combustion chamber.

2. Apparatus of claim 1 wherein said means directing the oxygen-containing gas into the windbox produces rotating velocities of 100 to 300 ft./sec.

3. Apparatus of claim 2 wherein the throat at least doubles the rotating velocity in the window.

4. Apparatus of claim 1 wherein said means forming jets of fuel includes an annular tube in the windbox extending around the inlet opening of the combustion chamber, the tube having a plurality of openings through which fuel passes into the throat.

5. Apparatus of claim 4 further including means connecting a premixed mixture of steam and fuel to the annulus tube.

6. Apparatus of claim 1 wherein the inlet extends tangentially to the cylindrical jacket whereby the industrial gas passes circumferentially around the annulus between the combustion chamber and the jacket.

7. Apparatus of claim 1 wherein the outlet opening in the opposing end wall of the cylindrical combustion chamber has an area up to 50% of the cross-sectional area of the combustion chamber.

8. Apparatus for heating an industrial gas by mixing the industrial gas with a combustion gas free of molecular oxygen and soot, and formed by combustion of a hydrocarbon fuel, for use in an industrial gas recovery process or the like, comprising:
(a) an elongated combustion chamber providing an internal refractory surface and having an inlet opening at one end forming an elongated throat and an outlet opening in a planar wall providing a portion of the internal refractory surface at the other end, the area of the openings being up to 50% of the axial cross-sectional area of the combustion chamber, means for directing a plurality of jets of fuel and steam into the inlet opening of the combustion chamber;
(b) means, rearward of the means for directing fuel and steam into the combustion chamber, for directing a stream of gas containing oxygen through the inlet opening, said last-named means generating a rotating component of motion to the stream of gas to provide a vortex in the combustion chamber;
(c) an annular chamber surrounding the combustion chamber to form an annular passage therebetween and enclosing the outlet.
end of the combustion chamber to form a mixing zone, said chamber providing a planar refractory surface facing the outlet opening of the combustion chamber;
(d) means directing the industrial gas into the annular chamber in a direction transverse to the longitudinal axis of the combustion chamber on one side of the annular chamber, and (e) means for directing gases out of the annular chamber adjacent the outlet end of the combustion chamber.

9. Apparatus of claim 8 further including means for mixing steam with the fuel before it is directed into the combustion chamber.

10. Apparatus for heating an industrial gas by mixing the industrial gas with a combustion gas free of molecular oxygen and formed by combustion of a hydrocarbon fuel, for use in an industrial gas recovery process Or the like, comprising:
(a) an elongated combustion chamber having a length to diameter ratio of 2 to 1 and providing an internal refractory surface and having an inlet opening at one end axially aligned with an outlet opening at the other end in a planar wall providing part of the refractory surface, the openings being smaller than the axial cross-sectional area of the combustion chamber, said inlet opening forming a constricted throat and said outlet opening formed by a first radiating end wall having an area up to 50% of the area of the end wall;
(b) annular means directing a hydrocarbon fuel in admixture with steam through a plurality of holes in the annular means into the combustion chamber;
(c) means for directing a stream of gas containing oxygen through the inlet opening, said last-named means generating a rotating component of motion to the stream of an oxygen containing gas to provide a vortex in the combustion chamber by passing the gas flow tangentially to the inner surface of the combustion chamber;
(d) an annular chamber surrounding the combustion chamber to form an annular passage therebetween and enclosing the outlet end of the combustion chamber, said annular chamber having a second planar radiating wall providing a refractory surface parallel to the first radiating end wall of the combustion chamber and spaced therefrom;

(e) inlet means for introducing industrial gas into the annular chamber, said inlet means associated with baffles to direct gas flow transverse to the longitudinal axis of the combustion chamber on one side of the chamber, and (f) outlet means for directing gases out of the annular chamber adjacent the outlet end of the combustion chamber.

11. A method for preheating industrial gases which comprises:
(a) introducing into a windbox associated with a combustion chamber an oxygen bearing gas, a rotational velocity from about 50 to about 150 ft. per second;
(b) mixing a hydrocarbon fuel with the oxygen bearing gas;
(c) passing the oxygen bearing gas and the hydro-carbon fuel into a throat leading to a combustion chamber, the velocity of the oxygen bearing gas being rotational and from about 100 to about 30% ft. per second;
(d) combusting the fuel into a cylindrical combustion chamber adjacent the throat in the presence of the oxygen bearing gas, the rotational flow of the oxygen bearing gas in the throat causing the products of combustion to pass rotationally along the wall surfaces of the combustion chamber, and (e) passing the products of combustion through an orifice position at the end of the cylindrical combustion chamber opposite the throat and combining the products of combustion with the industrial gas, said industrial gas being preheated by rotational passage through an annular passageway surrounding the combustion chamber.

12. A method as claimed in claim 11 in which the amount of oxygen containing gas fed to the windbox in an amount insufficient to combust all of the fuel to form a reducing gas stream.

13. A method as claimed in claim 11 in which steam is premixed with the fuel in an amount up to about 5 pounds per pound of fuel prior to combining the fuel with the oxygen bearing gas to prevent soot formation during combustion.

14. A method as claimed in claim 12 in which steam is premixed with the fuel in an amount up to about 5 pounds per pound of fuel prior to combining the fuel with the oxygen bearing gas to prevent soot formation during combustion.

15. A method as claimed in claim 7 in which the fuel is atomized when mixed with the oxygen containing gas.

16. A method as claimed in claim 13 in which the mixture of fuel and steam are atomized when mixed with the oxygen containing gas.

17. In a method for heating an industrial gas in which an oxygen containing gas is mixed with fuel and combusted in a combustion chamber, the combustion products traveling along the walls of the combustion chamber to transfer heat to an industrial gas stream passing along an annular passageway surrounding the combustion chamber and wherein final heating occurs by combining the products of combustion with the industrial gas external of the combustion chamber, the improvement which comprises premixing steam with the fuel gas in an amount up to about 5 pounds per pound of fuel prior to combining the mixture with the oxygen containing gas to prevent formation of carbon during combustion of the fuel gas.

18. A method as claimed in claim 17 in which the steam is premixed with the fuel gas in an amount of about 1 pound per pound of fuel gas.