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Publication numberUS3730668 A
Publication typeGrant
Publication dateMay 1, 1973
Filing dateMay 21, 1971
Priority dateMar 3, 1971
Also published asDE2129357A1, DE2129357B2, DE2129357C3
Publication numberUS 3730668 A, US 3730668A, US-A-3730668, US3730668 A, US3730668A
InventorsIida H, Watanabe K
Original AssigneeTokyo Gas Co Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Combustion method of gas burners for suppressing the formation of nitrogen oxides and burner apparatus for practicing said method
US 3730668 A
Abstract
The present invention relates to a novel method for suppressing the formation of nitrogen oxides formed in the combustion of gaseous fuels with air and a novel burner for practicing said method. Said burner comprises a combustion chamber having a converged nozzle portion formed at one end thereof and a draft tube having an upwardly expanding vertical cross-section and spaced ahead of said nozzle portion for guiding the combustion gases exhausted from said combustion chamber.
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Description  (OCR text may contain errors)

[451 May 1,1973

United States Patent 1191 Iida et al.

....43l/l58 X ....43l/l0 X ....43l/l58 X ....43i/352 X mm n n "Um ,S Hu Tamm o k wm mm 0a 0 RCWMC 5084 56545 99999 mmmw 837600 5024 729 5 7 956 .1 23222 Primary Examiner-William F. ODea Assistant Examiner-William C. Anderson Att0rneyWenderoth, Lind & Ponack mh It 30 a ma Hw s r m n e V n Japan [73] Assignee: Tokyo Gas Company Limited,

Tokyo,Japan [57] ABSTRACT The present invention relates to a novel method for 22 Filed: May 21,1971

[2 1 Appl suppressing the formation of nitrogen oxides formed in the combustion of gaseous fuels with air and a novel burner for practicing said method Said burner comprises a combustion chamber having a converged no;-

Mar. 3, 1971 Japan 1207 Z16 Portion formed at one end thereof and a draft tube having an upwardly expanding vertical cross-section [52] U.S. Cl. .......................43l/10,431/12, 431/158 and spaced ahead of said nozzle portion for guiding 51] Int. 3/04 the combustion gases exhausted from i mbustion .431/10, 12, I58 er.

[58] Field of Search..........................

5 Claims, 3 Drawing Figures [56] References Cited UNITED STATES PATENTS 3,048,131 8/1962 Hardgrove........ 1..l 10/72 R Patented May 1', 1973 v 3,730,668

O 4O 6O '80 100 A LO INVENTOREI H53 HIROFUMI llDA KAZUFUM! WATAHABII ATTORNEY 1 COMBUSTION METHOD OF GAS BURNERS FOR SUPPRESSING THE FORMATION OF NITROGEN OXIDES AND BURNER APPARATUS FOR PRACTICING SAID METHOD This invention relates to a method for gas used in boilers, various industrial heating furnaces, dryers, ovens, etc., whereby the amount of nitrogen oxides contained in combustion gases are minimized; and a burner apparatusfor practicing said method.

As the major factors which have influence on the amounts of nitrogen oxides contained in the combustion gases, there are generally considered flame temperature, excess air ratio and cooling velocity of flame. In this regard, various methods have been employed in conventional fixed-type combustion apparatus for suppressing the generation of nitrogen oxides, which are broadly classified into the following two types: Namely, in one type, the combustion gases are recirculated to lower the flame temperature, and in the other type the amount of air required for the com bustion is fed slowly so as to control the combustion rate. However, the former method has disadvantages in that the stability of the flame is low, means must be provided for recycling the combustion gases and thermal efficiency is low. On the other hand, the latter method has the disadvantage that, since the mixing ratio of fuel gas and air tends to be inconsistent, the excess air ratio must be made slightly greater than with the ordinary combustion method, with the result that the formation of nitrogen oxides is further promoted. It has further disadvantages in that means must be provided for supplying the secondary air and in that the combustion flame becomes undesirably long.

The present invention has been achieved based on an entirely novel concept of suppressing the formation of nitrogen oxides in the oxidation of fuels such as hydrocarbons, e.g., natural gas, etc., with air, which as used here, includes air containing more or lessthan the usual amount of oxygen. According tothe invention, the disadvantages of the conventional combustion methods can be completely eliminated and thethermal efficiency can be markedly enhanced.

The present invention will be described in detail hereinafter with reference to the accompanying drawing which illustrate an embodiment of the invention. In the drawings:

FIG. 1 is a vertical cross-sectional view illustrating an embodiment of the burner apparatus according to the present invention;

FIG. 2 is an enlarged-sectional view illustrating another embodiment of the nozzle portion,; and

FIG. 3 is a diagram graphically showing the combustion characteristic of the burner apparatus with respect to the amounts of nitrogen oxides generated during combustion.

in FIG. 1, reference numeral 1 designates a combustion chamber having a converged nozzle portion 2. The cross-sectional area of the combustion chamber 1 is 5 20 times the cross-sectional area of the nozzle portion 2. Reference numeral 3 designates a secondary air passageway formed around the combustion chamber 1. One end of the secondary air passageway 3 is provided secondary air passage holes 4 and the other end thereof is open or closed in the vicinity of the nozzle portion 2. With reference to FIG. 2, in case the secondary air passage 3 is closed in the vicinity of the nozzle portion 2, the secondary air passage holes 11 are formed in chamber 1. In such a case, the cooling air stream 12 is formed on the side of the nozzle portion 2 which cools the nozzle portion 2 made from a metallic material. The quantity of the secondary air passing through the secondary air passageway 3 is 10 40 percent of the theoretical air requirement and determined by the secondary air passage holes 4. Reference numeral S designates a draft tube for drawing the combustion gas in the furnace by the jetting combustion gases stream. The draft tube 5 has an upwardly expanding vertical cross-section so as to enhance the drawing effect of the combustion gases in. the furnace, and is suitably spaced ahead of the nozzle portion 2. The combustion chamber 1, the secondary air passageway 3 and the draft tube 5 are respectively made from a metallic or refractory material. Reference numeral 6 designates an air flow equalizing plate having a large number of primary air passage holes 7 formed therein and connected integrally with a gas feed pipe 8, and 9 designates a pilot burner concentrically mounted in said gas feed pipe 8.

With the construction described above, air required for combustion is supplied through an air inlet port 10 and part of the air, i.e., a quantity of air 60 percent of the theoretical air requirement, is introduced in to the combustion chamber 1 through the primary air passage holes 7 formed in the air flow equalizing plate 6. The remaining part of the air enters the air passageway 3 through the secondary air passage holes 4 and-reaches the. end extremity of the nozzle portion 2 after passing through said airpa'ssageway 3. A fuel gas is fed into the combustion chamber 1 from the fuel gas feed pipe 8, and intensely mixed with the primary air and burned therein. Since the combustion chamber 1 has the converged nozzle portion 2 as stated above, the load in the combustion'chamber reaches as high as about 5,000 10,000-X l0 Kcal/m hr. The cornbustion gases contain some .amount of unburned fuel gas because only the primary airis introduced into the combustion chamber 1, and is exhausted from the nozzle portion 2 to the outside of the combustion chamber at a high velocity of 50 200 m/zsec. The combustion gases ,exhaustedat such ahigh velocityare mixed with the secondary air supply which has cooled the outer wall of the combustion chamber 1, while moving in parallel or at an angle to the secondary air supply, and enter the draft tube5, ahead of the nozzle portion 2, while undergoing secondary combustion. When the combustion gases are mixed with the secondary air supply and are burned, a negative pressure is created around the nozzle portion 2 in accordance with the energy of jetting combustion gases and the combustion gases within the furnace are drawn under the effect of said negative pressure as indicated by the arrows. The jetting combustion gases and the combustion gases in the furnace are mixed so quickly that the high temperature, high velocity combustion gases, containing some amount of unburned fuel gas, are increasingly exhausted and cooled, and the unburned fuel gas contained therein is completely burned. In this case, since the amount of the jetting combustion gases is as large as 10 200 times that of the accompanying gases within the furnace, though variable, depending upon the flow resistance in the furnace, an extremely large amount of combustion gas circulates in the furnace.

Characteristic curve A in the chart of FIG. 3 represents the result of combustion obtained by the method and apparatus of the instant invention. It will be apparent from this characteristic curve that according to the invention, that the amounts of nitrogen oxides can be substantially decreased as compared with the conventional burner apparatus, the characteristic of which is represented by a curve E.

Although in the embodiment described above, the secondary air passageway 3 is formed around the combustion chamber 1 and the draft tube is provided ahead of the nozzle portion 2, the amounts of nitrogen oxides formed can be substantially decreased as compared with the conventional burner E, by employing the combustion chamber 1 only of the construction described without providing said secondary air passageway 3 and said draft tube 5. In this case, the theoretical quantity of air for combustion is introduced into the combustion chamber 1 in its entirety but the cross-sectional area ratio between the nozzle portion 2 and the combustion chamber 1 must be made smaller and the residence time of the air in the combustion chamber 1 must be made shorter than in the case of providing the secondary air passageway 3, so that the combustion may not be completed within said combustion chamber. The combustion gases containing some amount of unburned fuel gas are exhausted from the nozzle portion 2 at a high velocity. The combustion gases jetting from the nozzle portion 2 suck and are mixed with the combustion gases within the furnace, whereby the amount thereof is increased and the temperature thereof is lowered, and the unburned fuel gas contained therein is consumed in the secondary combustion. In such case, the amount of the gases sucked from the furnace is somewhat smaller than in the preceding case because the air is not fed stepwise and the draft tube 5 is not provided. However, as will be obvious from a curve D in FIG. 3, the amounts of nitrogen oxides formed are very much smaller than in case of the conventional burner E. Curve B in FIG. 3 represents the combustion characteristics of a burner apparatus in which the draft tube 5 is provided ahead of the combustion chamber 1 but the secondary air passageway 3 is not provided, similar to the preceding case. In this case, the secondary air is not supplied but, since the amount of the gases withdrawn from the combustion chamber 1 is increased by the existence of the draft tube 5, the effect of suppressing the formation of nitrogen oxides is greater than in the case of the burner apparatus comprising only the combustion chamber 1. Curve C in FIG. 3 represents the combustion characteristics of a burner apparatus in which the secondary air passageway 3 is provided around the combustion chamber 1 but the draft tube 5 is not provided ahead of said combustion chamber. In this case, the amount of the combustion gases withdrawn from the furnace is smaller than in case of the first-mentioned case but, since the secondary air supply is through the secondary air passageway 3 and is used for the secondary combustion, the amounts of nitrogen oxides formed can be substantially decreased.

It will be understood, after all, that the present invention achieves a remarkable effect in suppressing the fonnation of nitrogen oxides, due to a combination of factors including the fact that the primary combustion is a fuel-rich combustion, that the combustion is effected stepwise by the primary and secondary combustions, that the secondary combustion reaction is carried out while the temperature of the fuel gas is being lowered by combustion of the gases in the furnace, that the residence time of the combustion gases within the furnace is long, and that the length of the flame is short. Further, as will be understood from FIG. 2, while in the conventional burner apparatus the amounts of nitrogen oxides formed corresponding to the load factor (the amounts of nitrogen oxide per unit quantity of heat) are substantially constant, in the burner apparatus of the instant invention an increasing load factor results in an increasing velocity of the combustion gases jetting from the nozzle portion 2 and hence in an increasing amount of the gases being withdrawn from the combustion chamber, so that the rate of formation of nitrogen oxides is lowered.

According to the invention, as described above, it is possible not only to substantially decrease the amounts of nitrogen oxides formed, but also to improve the heat transmission rate, to make the temperature distribution within the furnace uniform without providing any special means, and to reduce the size of or eliminate the combustion chamber of a furnace. Thus, by practicing the invention, the general heating apparatus can be simplified.

What is claimed is:

l. A combustion method for suppressing the formation of nitrogen oxides issuing from gas burners, comprising introducing the theoretical quantity of air for combustion into a combustion chamber in its entirety, said combustion chamber being formed with a nozzle portion and said combustion chamber having a crosssectional area 5-20 times that of said nozzle portion, burning -90 percent of a fuel gas in said combustion chamber, exhausting the combustion gases containing unburned fuel gas at a high velocity through said nozzle portion and burning the unburned fuel gas completely outside the burner apparatus by providing means cooperating with said nozzle portion for drawing the combustion gases in the furnace therefrom by said combustion gases jetting from said nozzle portion.

2. A combustion method for suppressing the formation of nitrogen oxides issuing from gas burners, according to claim 1, wherein a secondary air supply in a quantity of 10 40 percent of the theoretical quantity of air for combustion is passed along the outer wall of said combustion chamber and the unburned fuel gas contained in the combustion gases jetting from said nozzle port is completely burned by said secondary air outside the burner apparatus.

3. A burner apparatus so designed as to suppress the formation of nitrogen oxides, comprising a combustion chamber having a converged nozzle portion formed at one end thereof, said combustion chamber having a cross-sectional area 5-20 times that of said nozzle portion and a draft tube having an upwardly expanding vertical cross-section and spaced ahead of said nozzle portion for guiding the combustion gases exhausted from said combustion chamber.

4. A burner apparatus so designed as to suppress the formation of nitrogen oxides, according to claim 3,

wherein one end of the secondary air passage is closed in the vicinity of the nozzle portion and the secondary air passage holes are formed in the combustion chamber in the vicinity of said nozzle portion.

* III

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2451626 *Feb 12, 1945Oct 19, 1948Stewart Warner CorpAir flow regulating valve
US2499207 *Dec 22, 1945Feb 28, 1950Wolfersperger John JPressure-type burner and method of burning fuel
US2577918 *May 8, 1946Dec 11, 1951Kellogg M W CoAir jacketed combustion chamber flame tube
US2665748 *May 27, 1949Jan 12, 1954Cornelius Frank HFuel burner
US3048131 *Jun 18, 1959Aug 7, 1962Babcock & Wilcox CoMethod for burning fuel
US3212553 *Jun 14, 1962Oct 19, 1965Marie Edouard Joseph CathalaMethod and apparatus for burning liquids of low volatility
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3837788 *Oct 5, 1972Sep 24, 1974Aqua Chem IncReduction of gaseous pollutants in combustion fuel gas
US3868211 *Jan 11, 1974Feb 25, 1975Aqua Chem IncPollutant reduction with selective gas stack recirculation
US3905745 *Dec 17, 1973Sep 16, 1975Denyo Kagaku Kogyo KkMethod of preventing formation of harmful combustion gases in combustion furnace
US3914091 *Feb 28, 1974Oct 21, 1975Tokyo Gas Co LtdCombustion method for hydrocarbonic fuels with low emission of nitrogen oxides
US3918834 *Aug 9, 1973Nov 11, 1975Nikolai Alexandrovich GurevichMethod of reducing the concentration of nitrogen oxides in a gaseous effluent from a thermal plant
US3955909 *Jul 12, 1974May 11, 1976Aqua-Chem, Inc.Reduction of gaseous pollutants in combustion flue gas
US4018554 *Jan 14, 1976Apr 19, 1977Institutul Pentru Creatie Stintifica Si Tehnica-IncrestMethod of and apparatus for the combustion of liquid fuels
US4021188 *Aug 21, 1975May 3, 1977Tokyo Gas Company LimitedBurner configurations for staged combustion
US4063870 *Nov 4, 1975Dec 20, 1977Stein IndustrieCombustion of hot gases of low calorific power
US4113417 *Jan 6, 1977Sep 12, 1978Stein IndustrieCombustion of hot gases of low calorific power
US4144017 *Nov 15, 1976Mar 13, 1979The Babcock & Wilcox CompanyPulverized coal combustor
US4204402 *Sep 8, 1977May 27, 1980The United States Of America As Represented By The Administrator Of The National Aeronautics And Space AdministrationReduction of nitric oxide emissions from a combustor
US4232650 *Aug 30, 1977Nov 11, 1980Baffle Stove Company Inc.Baffled stove
US4408982 *Jan 5, 1982Oct 11, 1983Union Carbide CorporationProcess for firing a furnace
US4875850 *Nov 2, 1987Oct 24, 1989Gaz De FranceGas burner of the blown air and premixture type
US5055032 *Oct 12, 1989Oct 8, 1991Ruhrgas AktiengesellschaftA burner with a flame retention device
US5096412 *Jan 28, 1991Mar 17, 1992The United States Of America As Represented By The Secretary Of The ArmyCombustion chamber for multi-fuel fired ovens and griddles
US5269679 *Oct 16, 1992Dec 14, 1993Gas Research InstituteStaged air, recirculating flue gas low NOx burner
US5413477 *Dec 13, 1993May 9, 1995Gas Research InstituteStaged air, low NOX burner with internal recuperative flue gas recirculation
US7771192 *Mar 7, 2006Aug 10, 2010Miura Co., Ltd.Combustion apparatus
DE4336095A1 *Oct 22, 1993Apr 27, 1995Abb Research LtdCombustion method for atmospheric firings and device for carrying out the method
WO2002044617A1 *Nov 27, 2001Jun 6, 2002Messer Griesheim GmbhMethod of combustion and impulse current controlled fuel/oxygen lance
Classifications
U.S. Classification431/10, 431/158, 431/12
International ClassificationF23C9/00, F23C6/00, F23C6/04
Cooperative ClassificationF23C9/006, F23C6/04
European ClassificationF23C6/04, F23C9/00C