US2767785A - Gas burner - Google Patents

Description

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GAS BURNER Original Filed May 9,` 1947 INVENTORS U50/s ASTM/1N 50S; 0. 6?/ ,V5/Q

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United States Patent GAS BURNER Du Bois Eastman, Whittier, Calif., and Leon P. Gaucher, Tuckahoe, N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware Original application May 9, 1947, Serial No. 747,106. and this application April 13, 1951, Serial No.

3 Claims. (Cl. 158-109) This invention relates to a burner for the controlled combustion of gas mixtures, including enriched air or oxygen, characterized by reaction at excessively high combustion temperatures, both local and overall, unless carefully controlled.

In such operations as the preparation of synthesis gas for subsequent synthesis of hydrocarbons, oxygenated compounds and the like, and similar operations, a hydrocarbon such as methane is caused to burn with oxygenenriched air or substantially pure oxygen in a proportion to form principally carbon monoxideand hydrogen. If conducted under perfect conditions as regards mixing and control of the gases, the reaction temperatures would not be in excess of a maximum of about 2400 F. However, such perfect conditions are impossible and with burners of the type proposed and used heretofore, local hot spots and overall temperatures far in excess of this figure have resulted, primarily by reason of poor mixing v such that in spots or for short intervals over the entire reaction zone, the proportionate mixture of the gases is such that the methane is oxidized to Water and carbon dioxide, this reaction producing a much higher temperature. Hence such priorV burners have been unsatisfactory and have been characterized by excessive free carbon Y formation, short lives, poor mixing, and high maintenance costs. With such prior buurners, a high excess of oxygen has been required, a considerable amount of steam being also required to control the reaction temperature and to hold it down to a reasonable level. The problem is further aggravated by the fact that it is desirable to charge the reacting gases to the burner at a high degree of preheat to obtain a maximum yield of product gas.

This application is a division of our co-pending application Serial No. 747,106, led May 9, 1947, now abandoned. l

It is an object of this invention to provide a novel burner particularly adaptable for the burning of such gas mixtures having potential excessively high temperatures Y of reaction, the burner being relatively simple in construction and characterized by sufiiciently good mixing to avoid the aforesaid hot spots and flashes of high temperature, the formation of free carbon being substantially f eliminated. Y

A further object of the invention is the provision of a novel burner assembly for burning such gas mixtures wherein the undesired production of free carbon is substantially eliminated.

Other objects and advantages of the invention will appear from the following description and claims taken in connection with the attached drawing wherein:

Fig. 1 is an axial section through a portion of a burner of this invention, as associated with a refractory housing.

Fig. 2 is an axial section of a modified burner of the invention.

In brief, the burner of the present invention comprises a plurality of concentric feed conduits for the several gases to be reacted, the conduits terminating iny nozzles lice ^ the gases is insured in the proper proportion to hold the temperature down to the desired maximum with the reaction being initiated beyond the burner elements and the hot reaction products being immediately carried away from the burner elements. Furthermore such mixing insures the maintenance of a blanket of non-burning gases immediately adjacent the burner surfaces so that the latter are continuously insulated from the reaction proper oy the entering streams of relatively cool gases. The operation of the burner such that the external gas issues at a higher velocity than the internal gas is contemplated to insure against mixture and combustion adjacent the burner elements with consequent damage thereto and to insure the continuous ow of the gases in the desired paths without the production of eddy currents adjacent the burner elements and consequent Contact of the burning gases therewith. The inner nozzle is preferably in the form of a free unobstructed opening, the external nozzle being in the shape of a surrounding annular space or a surrounding annular collar having a plurality of spaced ports therein.

In describing the invention, reference is made to the preparation of synthesis gas (approximately one part carbon monoxide to two parts hydrogen) from a hydrocarbon consisting principally of methane, such as natural gas and oxygen of -99-5 percent purity.

In Fig. l, which shows only the burner tip, a conduit 11 having a nozzle 12 is positioned concentrically of a surrounding conduit 13 terminating in a nozzle 14, the latter extending beyond nozzle 12 so that an annular space i5 surrounding nozzle 12 is defined by the adjacent surfaces of the two nozzles. Suitable cooling means in the form of a water jacket 16 through which cooling water may be circulated is provided about the burner tip in the manner shown. All elements of the burner are formed from heat resistant metal, preferably also resistant to oxidation.

The respective diameters of the two nozzles and the spacing therebetween is preferably such that the angle A is in the range of 50-80, preferably about 60. The burner is preferably mounted in a refractory tunnel 17, a portion of which is shown diagrammatically about the burner, the tunnel closely surrounding the burner up to the tip thereof and then being flared immediately adjacent and downstream of the tip to provide an enlarged combustion zone. The tip is positioned near the point of ilare of the refractory tunnel so that backward eddy currents cannot be formed and free carbon deposited. The flared portion of the tunnel is arranged to discharge into a combustion zone in a generator proper from which the product gases are removed.

In operation, the oxygen is charged through conduit 11 and the methane through conduit 13, the latter being charged at a pressure in suicient excess of the oxygen so that the methane issues from annular space 1S at a velocity at least 10 percent above that of the oxygen issuing from nozzle 12. This differential in velocities has been found important in securing the flow of the gases in the desired manner, in accomplishing the desired mixing and in protecting the adjacent burner elements from the high temperature of the reaction. The oxygen follows the path generally indicated by broken lines, the vena contracta being located just beyond the end of the burner tip. The methane follows the path generally indicated by the dot and dash lines, the methane joining the oxygen in the region of the vena contracta. By reason of the increased velocity of the oxygen at this point and some increase in the velocity of the methaneby reason of its discharge from opening 1S, the gases are given an impetus which facilitates their substantially uniform mixing, consequent reaction at or below the desired maximum temperature, and the continued movement of the het reacting gases away from the burner elements without backward eddy currents. Furthermore, by reason of this method of mixing the two gases, a relatively quiescent blanket of methane is established around the metal elements of the burner on the faces adjacent the actual burning zone, this blanket functioning to partially insulate and protect the burner elements against the heat of the reaction. By reason of the mixing taking place substantially outside the burner, the danger of any local surface reaction is substantially eliminated. Thus the reaction is controlled so that the temperature is kept to a reasonable level, i. e., not above 7.400" F., and the formation of any local hot spots" of higher temperature is avoided. While in the above example oxygen has been described as the gas charged through the central conduit and methane through the outer conduit, it is to be understood that the gases may be reversed to charge the oxygen through the outer conduit and the methane through the central conduit.

The burner tip shown in Fig. 2 includes a gas conduit 21 terminating in a nozzle 22 and a second concentric gas conduit 23, the end o-f the latter being closed by a metal annulus 24 having a plurality of ports 25 therein. The exterior of the end of conduit 23 is surrounded by a water jacket 26, cast integral with the burner or welded thereto, and connected by a tap 27 to a supply line 23. Two such taps 27 and lines 28 are provided to circulate water through the jacket. The face of nozzle 22, annulus 24, and the end of conduit 23 are preferably faced as shown so that the angle A is in the range of 50-80", preferably about 60.

The method of operation of the burner tip of Fig. 2 is substantially the same as that of Fig. l except that the gas charged through conduit 23 is discharged through ports 25 as a plurality of separate streams whereas the gas discharged through anuuiar opening of Fig. l is in the form of a substantially continuous annulus. The burner tip of Fig. 2 possesses the extra advantage that the mass of metal at the tip of the burner aids in transferring the accumulated heat to the water jacket and thereby permits preheating the oxygen to a high temperature without too rapid oxidation of the burner elements.

In actual operation, the burner tip of the present invention has been found to be superior to those used in prior art burners. In the combustion of methane and oxygen, it has been found possible to reduce the amount of oxygen used without reducing the quality of the product, both because of better mixing and because more preheat is possible, less maintenance has been required, the burner tip has been found to have a longer life than those used in previous burners, there has been a material reduction in the amount of carbon formed, and less burning of the surrounding refractory material. With a burner tip of the type herein described, it has been found possible to operate with a proportion of oxygen only slightly above the theoretical or stoichiometric amount with substantial-ly no formation of free carbon, any requirement for steam being eliminated. Savings are thus realized in oxygen, steam and hydrocarbon as represented by the lack of free carbon. It has also been found possible to increase the degree of preheat of the reacting gases, which further increases the yield of synthesis gas. All the above advantages are believed to be due principally to the manner in which the gases are fed and mixed by the burner structure disclosed.

Obviously many modifications and variations of the invention as above set forth may be made without departing from the spirit and scope thereof and only such lirnitations should be imposed as are indicated in the appended claims.

We claim:

l. In a burner having a tip for discharging and mixing combustible gases in a reaction zone, a first conduit leading to said tip and terminating in a circular discharge orifice normal to the axis thereof, the burner tip having a flared passageway coaxial with and extending outwardly from the periphery of said orifice, said flared passageway -being in the form of the peripheral surface of a frustum ci a cone, the smallest diameter of which coincides with said orifice whereby a stream of combustible gas is directed centrally through said passageway, a second conduit coaxial with and disposed about said first conduit and terminating at said tip and forming an annular passage for a second combustible gas, a plurality of passageways in said tip communicating with said annular passage and terminating in respective outlets disposed about said conical surface of said dared passageway at locations axially spaced from said orifice, said plurality of passageways leading from said annular passage being formed to direct said second combustible gas into intersecting relation with said stream of combustible gas, and means for cooling said tip including a cooling chamber at the outer extremity of said tip disposed about said plurality of passageways, said tip being of substantial mass so that the portions thereof between said plurality of passageways communicating with said annular passage serve as heat bridges between said first conduit carrying a preheated combustible gas at elevated temperatures and said cooling chamber.

2. in a burner having a tip for discharging and mixing gasiform reactants in a combustion zone, a first conduit leading to said tip and terminating in an outlet in the form of a circular discharge orifice normal to the axis of said first conduit, the burner tip having a flared passageway coaxial with and extending from the periphery of said discharge orifice, said liared passageway being in the form of the peripheral surface of a frustum of a cone coinciding at its minimum diameter with said discharge orifice and being coaxial with said first conduit and having an apex angle in the range of about 50 to 80, whereby said discharge orifice directs a stream of gasiform reactant centrally through said flared passageway, a second conduit coaxial with and disposed about said first conduit terminating at said tip and forming an annular passage for a second gasiform reactant, a plurality of passageways in said tip communicating with said annular passage and terminating in outlets disposed on said conical face of said fiared passageway at locations axially spaced from said discharge orifice, said plurality of passageways leading from said annular passage being formed to direct said second gasiform reactant into intersecting relation with said stream of gasiform reactant axially downstream from said outlets and said orifice, said tip being formed with an annular cooling chamber and being of substantial mass whereby the portions thereof between said pluralities of passageways communicating with said annular passage comprise heat bridging means between said first conduit carrying preheated gas at elevated temperatures and said cooling chamber, the flow axes of said first conduit and said plurality of passageways intersecting substantially at the external downstream edge of said burner tip.

3. In a burner having a tip for discharging and mixing reactants in a combustion zone, a first conduit for the provision of a first reactant leading to said tip and terminating in an outlet normal to the axis of said first conduit, the burner tip being formed with a flared passageway coaxial with and extending from the periphery of said outlet, said flared passageway being in the form of the peripheral surface of a frustum of a cone having an apex angle in the range of about 50-80, a second conduit coaxial with and disposed about said first conduit and terminating at said tip and forming an annular passage for the provision of a second reactant, said second conduit being divided into a plurality of passageways in said tip and directing said second reactant into intersecting relation with said rst reactant whereby the columnar stream of reactant delivered by said rst conduit has a minimum cross sectional area downstream from said outlet smaller than the cross sectional area thereof and with its peripheral margin spaced from the conical surface of said flared passageway, and cooling means at the outer extremity of said tip disposed adjacent said plurality of passageways, said tip being of substantial mass with the portions thereof between said plurality of passageways dividing said annular passage comprising heat transfer bridges between said rst conduit carrying preheated gas at elevated temperatures and said cooling means, the ow axes of the reactants provided through said first conduit and said second conduit and its plurality of passagewaysy intersecting substantially at the downstream edge and external of said burner tip.

References Cited in the file of this patent UNITED STATES PATENTS 536,945 Auery Apr. 2, 1895 1,407,871 Knudsen Feb. 28, 1922 2,247,548 Forster July l, 1941 2,532,711 Goddard Dec. 5, 1950 2,582,938 Eastman et al Jan. 15, 1952 FOREIGN PATENTS 917,802 France Sept. 23, 1946

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