US2941587A - Combustion chamber burner - Google Patents

Description

June 21, 1960 J. D. HAGY ETAL 2,941,587

COMBUSTION CHAMBER BURNER Filed July 14, 1955 OXYGEN CHANNELS oxmma mmmfiim IN TORS F E JAMES HA HARRY A. WAUGH L ATTOR/VE United States Patent 2,941,587 COMBUSTION CHAMBER BURNER James D. Hagy, Alhambra, and Harry Waughtal, Tulsa, Okla, assignors to Pan American Petroleum Corporation, a corporation of Delaware Filed July 14, 1955, Ser. No. 522,022

4 Claims. (Cl. 158-99) Our invention relates to an improved gas burner design. More particularly, it pertains to a novel burner design especially adapted for use at relatively high temperatures over extended periods of time. Burners of the design hereincontemplated find application in combustion chambers of the type employed for the partial oxidation of light hydrocarbons such as, for example, methane, to synthesis gas utilized in the production of synthetic liquid fuels.

In the preparation of hydrocarbon synthesis gas by direct combustion of methane or natural gas at elevated temperatures and pressures, rather severe requirements are placed on the thermal characteristics of the combustion chamber employed for the production of such gas and particularly on the burner utilized in the operation. Thus, at the pressures employed, i.e., 250 to 350 p.s.i., it usual to have temperature zones of from 2200 F. to 3500 F. throughout the chamber.

.-The conversion of methane to synthesis gas by combustion with oxygen may take place in successive steps. In the first step, methane may combine with oxygen in a ratio of 1:1 in accordance With the following equation:

This reaction is highly exothermic and raises the temperature of the products to about 3500 F. If additional methane is available, i.e., if the feed-ratio of oxygen to methane is less than 1:1, the excess methane may then be reformed by the steam and carbon-dioxide in the product gases in accordance with either or both of the following equations:

Both of these reactions are endothermic and will cause the temperature of the products to drop to an equilbrium value. 4 The relative proportions of C0, C0 H and H 0 in the'products are set by the water gas shift reaction. Thus, as the final temperature of the methane conversion reactions reaches equilibrium the CO and CO will adjust to equilibrium proportions in accordance with the following equation: 1

Prior to our invention, a number of different types of burners were employed in combustion chambers used to prepare synthesis gas. However, much difliculty was experienced in attempts to operate these combustion chambers for long periods. The problems encountered in previous attempts to produce synthesis gas and to obtain adequate burner performance were concerned chiefly with proper mixing of the preheated gas, suitable oxygen to methane ratio in the feed gas, procurement of adequate cooling of the critical burning areas, and prevention of burner failure due to the fusion of the gas and/ or cooling channels.

One particular type of burner previously proposed for 2,941,587 Patented June 21, 1960 use in combustion chambers of the aforesaid type, consisted of two concentric metal tubes, the end of the inner tube being recessed slightly within the outer tube. The latter curved inwardly at the end to form with the inner tube what was considered to be the correct annulus area. In the operation of this burner, the methane was heated to a temperature of from about 400 to 600 F. higher than the oxygen and hence, when the preheated methane was supplied through the outer tube, the latter expanded lengthwise causing an increase in the annulus area. This reduced the velocity of the methane and resulted in internal burning and flame erosion, causing the burner to fail. When methane was supplied through the inner tube the latter expanded, closing off the flow of oxygen through the outer tube. Another disadvantage of this design resided in the fact that the flame produced during operation was in contact with the burner tip or face, thus placing considerable stress on the burner structure. The accumulation of heat under such. circumstances often contributed to fusion of the burner tip and subsequent failure thereof.

Other burner designs employed a series of small channels through which methane was introduced and thereafter combined with oxygen flowing through a recessed centrally spaced channel. The preheated methane frequently carried small particles of carbon which had a tendency to plug one or more of the gas channels, causing the burner flame to be deflected and resulting in the erosion of the burner face. Also welding on the face of burners previously employed was subject to cracking and carburization while in service.

Still another type of burner used where high temperatures were not required and demands upon effiiciency of operation were not too great is described in French Patent No. 917,802. This particular burner had a relatively large central gas channel surrounded by a plurality of air or oxygen channels terminating at the face of the burner. A coolant, for example, water or air, was circulated around the gas conduit through a jacket sur rounding said conduit. In this structure, however, adequate cooling could not be supplied because of the manner in which the air channels slanted inwardly toward the central large gas channel at the point where the air and gas channels touched. Presumably, at the hottest portion of the burner, there was very little surface from which the circulated coolant could extract heat. Moreover, the burner face of such a design is extremely diflicult to cool. Even if the base of the flame produced in a burner of the above-described design could be maintained above the face thereof, the heat absorbed by the latter due to radiation is so intense during, for example, the partial oxidation of methane, to produce synthesis gas, that the burner slots of the jets become fused unless proper precautions are taken to cool the burner face.

A further equally serious difficulty with the abovementioned burner design or with any design in which the central gas channel comprises so much more area than the total area of the surrounding air or oxygen channels is that the gas (methane) flowing through the central channel of relatively large diameter tends to penetrate the space above the burner surface a substantial distance without achieving proper mixing with the air or oxygen, thus resulting in temperatures and other conditions favoring cracking of the methane to carbon. This follows from the fact it is well known that the distance a jet of gas penetrates a still mass of another gas is proportional to the diameter of the jet. Otherwise expressed, the greater the diameter of the stream of gas being jetted into the still body of gas, the greater will be the penetration of the former into the latter. The relatively small air jets surrounding the larger body of methane emanating from the central channel, as in the case of the burner design of the French patent referred to above, do nottend to retard the larger methane stream sufliciently for a rapid partial combustion of the latter.

It is an object of our invention to provide asuitable combustion chamber burner capable of operatingfor extended periods of time under severe operating conditions without mechanical failure or excessive carbon formation during operation thereof. It is a further object of our invention to provide a burner in which the parts thereof exposed to the flame or to the radiant zone of the combustion chamber are internally cooled in a manner such that safe metal temperatures are assured during operation. It is a still further object of our invention to provide a combustion chamber burner having aflat burning face thereby eliminating the undesirable flame erosion caused as a result of the" combustion of turbulent burner effluent gases. It is another object of our invention to provide a burner having a minimum of welded areas exposed to the radiant zone. It is a further object to provide a burner of a design such that during operation thereof the flame is maintained well above the burner face. It is still another object of our invention to provide a convenient and economical method for the preparation of synthesis gas in which a burner of the aforesaid type may be employed.

In order for a better understanding. of our invention, reference is made to the accompanying drawings inwhich Figure 1 represents a sectional view of a burner body contemplated by our invention. Figure 2 is a plan view of a cross section taken along line A--A of Figure 1 showing the internal cooling system and gas channels; while Figure 3 represents a sectional plan view also taken along line A-A of the burner design shown in Figure 1, modified to the extent that the passageways" through which oxygen is introduced are in the form of circularly spaced slots rather than round channels as shown in Figure 2.

In the burner design shown in Figures 1 and 2, methane channel 2 is spaced centrally of burner 4. Pipe 6 conducts oxygen into a chamber 8 and then through channels 10, geometrically spaced as shown in Figure 2. The exit ends of both channel 2 and channels 10 are flush with burner face 12. An annular passageway 14 adjacent burning face 12 communicates with channel 16 through which a suitable coolant, such as water, is introduced. The coolant as it enters passageway 14 is forced to flow in the direction indicated in Figure 2, because of barrier 18 placed just back of channel 16 and in front of opening 20 which communicates with annular slot 22. Thus, the coolant enters channel 16, flows around circularpassageway 14 till it comes to opening 20, passes upwardly through annular slot 22 and out through pipe 24. Although methane introduced through channel 2 is heated from about 400 to 600 F. higher than the oxygen em ployed, the coolant in annulus 22 prevents the oxygen from becoming hotenough to burn or react with the metal surface of the burner.

Figure 3 is a modification of the burner shown in Figures 1 and 2, in which symmetrically spaced openings or slots 26, are substituted for round conduits or channelsand for the purpose of this description may be considered the equivalentof channels 10. The dimensions of these slots or openings may vary; however, they preferably should be of such a size as to allow the" required amount of oxygen to be passed therethrough at essential ly the same velocity as the methane forced through channel 2. Generally speaking, the velocity of the oxygen stream may range from a velocity equal to that of the gas to' one which is only about one-third the gas velocity.

In the burner design shown in Figures 1 and 2, channels 10 may vary in number from about 4 to about 1-2 and from about A to about A" I.D. While the arrangement of channels 10 about channel 2 need not follow any particular pattern; they should be evenly or symmetrically spaced about channel 2, so" that theresulting:

flame will not be deflected from its vertical axis. The extended axes of channels 10 should intersect at a common point on the extended vertical axis of channel 2 and define an angle therewith which may vary from about 5 to about 30 in order to secure adequate mixing of oxygen with the gas. The distance between the channels 10 and channel 2 should be such that the vertex formed by the intersection of the two streams is approximately 0.5 to about 6" and preferably from about 0.5" to about 3.5" from the face of the burner.

One particular advantage of the burner design of our invention lies in the selection of gas and oxygen channels which give a range of area ratios corresponding to the range set forth herein. With gas channels having a large diameter and employing oxygen channels in combination therewith of insufiicient diameter, difliculty in proper mixing of the gases leading to cracking, carbon formation, etc., as previously described, is encountered. With gas channels smaller than about .3, a definite possibility of plugging the gas channel exists. This may be caused from corrosion and subsequent scaling of the channel or from the accumulation of entrained particles in the gas stream due to cracking resulting frompreheati'ngthe gas; The presence ofsuch solid material (carbon, etc.) in the gas channels causes deflection of the flame which inevitably results in severe erosion ultimately causing the burne'r to fail.

For satisfactory operation, the diameter of the oxygen channels and the diameter of the gas channels should be such that the ratio of the gas channel area to the total area of the oxygen channels lies within a range of from 1:1- to about 3:1 and preferably within a range of from about 1.75: 1 to about 2.5: 1. Typically, the oxygen channel diameter (I.D.) may range from a minimum of .06 to about 0.3, while the gas or' methane channel may vary from about 0.3" to about 1''. Satisfactory combinations of gas and oxygen channel diameters using eight oxygen channels are: oxygen channel diameters of- 0.14 and 0.2", and methane channel diameters of 0.62" and 0.75, respectively.

The lower limit of the oxygen channel diameter, i.e., 0.06, is likewise considered important because of possible corrosion problems which might occur during operation of the burner. The tendency of the oxygen chan nels to scale or corrode is not generally considered to be as great as that-of the gas channel. However, owing to the high temperatures to which the oxygen may be preheated, i.e., to about 600 F., the presence of most any foreign materialsysuch as welding flux, would readily react under such conditions and tend to cause a plugging of the oxygen channels if they were smaller than about .06. In fact, for that reason, we ordinarily prefer to employ'oxygen channel diameters ranging from about .15 to about .20".

Inpilot plant operations employing a hollow, unobstructed combustion chamber, burners of the design herein described have been successfully operated for periods of 2500 to 2800 hours, producing a gas consisting chiefly of carbon monoxide and hydrogen with not more than about 5 mol per cent carbon. In such burners the individual diameters of the geometrically spaced oxygen channels were 4 and the angle defined by the intersection of a line parallel with channel 2 and .a line parallel with channels 10 was approximately 10. Gas channel 2 had an ID. of 0.336". Burners having the; abovedimensions are designed for a gas velocity of about 200 feetper second, although gas velocities in gen-' eral may vary from about to about 300 or 400 feet per second. Velocities in the lower range are determinedby the degree of mixing that can be obtained while the higher velocities are limited by the pressure drop produced with gas or oxygen ports of a given diameter. Attemperatures of the order of about 2400 to 2600? F., pressures of about 300 or 400 p.s'.i;, and with a feed gas having: an" oxygen to" methane ratio of about 0.6; a burner having the aforesaid dimensions produced only 5 pounds of carbon per million cubic feet of gas consumed.

In addition to the foregoing burner design, the com position of the combustion chamber feed gas is an important factor in the production of a gas suitable for use in hydrocarbon synthesis. We have found that with combustion chamber feed gases having an oxygen to methane ratio below 0.58, the increase in carbon production is very rapid. Accordingly, we prefer to employ feeds having an oxygen to methane ratio of from about 0.6 to about 0.7 for maximum output of synthesis gas with a minimum of carbon formation.

It is likewise very desirable and important to preheat both the oxygen and methane. The former may be heated up to temperatures of 600 F., while the latter should be preheated up to about l000 to about i200 F. Preheating of the oxygen and/or methane increases the methane conversion.

Pilot plant tests of the maximum methane preheat temperatures have indicated that temperatures as high as 1200 F. may be employed without adverse effects from coking.

From the foregoing description, it will be apparent to those skilled in the art to which the present invention relates that numerous modifications thereof exist and may be employed without departing from the scope of said invention. In general, it may be said that our invention comprises an internally cooled burner having a fiat burning face with a central gas channel within a plurality of symmetrically spaced oxygen channels or slots, the feed gas channels and said oxygen channels terminating flush with said burning face and the axes of said channels and the axis of said gas channel intersecting at a point above the burner face ranging from about 0.5" to about 6".

This application is a continuation-in-part of our copending application, U.S. Serial No. 241,232, filed August 10, 1951, now abandoned.

We claim:

1. In a burner the combination comprising a burner body having a generally flat burning face, said body having therein the following elements: a channel extending through said body and terminating at the center of said burning face, a first cooling means surrounding said channel, a chamber surrounding said first cooling means, a

plurality of channels extending from said chamber to said burning face, said plurality of chamielsbeing symmetrically spaced about said channel, the extended axes of said plurality of channels intersecting at a common point on the extended axis of said channel, a second cooling means adjacent said face surrounding said symmetrically spaced channels, an inlet port ofi? said face communicating directly with said second cooling means, a passageway adjacent said face connecting said first and second cooling means, and a fluid tight barrier in said secand cooling means adjacent said face and said passageway between said inlet port and said passageway.

2. The burner of claim 1 in which the extended axes of channels (2) intersect the extended vertical axis of channel (1) to define an angle at the point of intersection with said axis of about 5 to about. 30.

3. In a burner the combination comprising a burner body having a generally flat burning face, said body having therein the following elements: a channel extending through said body and terminating at the center of said burning face, a first cooling means surrounding said channel, a chamber surrounding said first cooling means, a plurality of arcuately spaced slots extending from said chamber to said buring face, said slots being symmetrically spaced about said channel, the extending axes of said slots intersecting at a common point on the extended axis of said channel, a second cooling means adjacent said face surrounding said slots, an inlet port off said face communicating directly with said second cooling means, a passageway adjacent said face connecting said first and second cooling means, and a fluid tight barrier in said second cooling means adjacent said face and said passageway between said inlet port and said passageway.

4. In a burner the combination comprising a burner body having a generally flat burning face, said body having therein the following elements: a channel extending through said body and terminating at the center of said burning face, a first cooling means surrounding said channel and running substantially the entire length of said channel, a chamber surrounding said first cooling means, a plurality of channels extending from said chamher to said burning face, said plurality of channels being spaced about said channel, the extended axes of said plurality of channels intersecting at a common point on the extended axis of said channel, a second cooling means adjacent said face surrounding said plurality of channels, an inlet port off said face communicating directly with said second cooling means, a passageway adjacent said face connecting said first and second cooling means, and a fluid tight barrier in said second cooling means adjacent said face and said passageway between said inlet port and said passageway.

References Cited in the file of this patent UNITED STATES PATENTS 2,145,649 Fox Jan. 31, 1939 2,408,282 Wolf Sept. 24, 1946 2,582,938 Eastman et a1. Ian. 15, 1952 2,594,094 Todd Apr. 22, 1952 2,725,933 Gaucher Dec. 6, 1955 FOREIGN PATENTS 749,423 France May 8, 1933 917,802 France Sept. 23, 1946

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