US3870456A

US3870456A - Burner for the stoichiometric combustion

Info

Publication number: US3870456A
Application number: US359197A
Authority: US
Inventors: Johannes W Graat
Original assignee: Smit Nijmegan BV
Current assignee: Smit Nijmegan BV
Priority date: 1973-05-10
Filing date: 1973-05-10
Publication date: 1975-03-11
Anticipated expiration: 1992-03-11
Also published as: BE840336Q

Abstract

An apparatus and process for combustion of liquid fuel comprises a burner in which the fuel is atomized within a fuel nozzle by a tangential flow into a center bore. An atomizing medium is fed tangentially to a bore and atomized and mixed with the atomized fuel. Combustion air flows through a coaxial cylindrical jacket in the same direction as the mixture of atomized medium and atomized fuel. A conically converging burner mouth contracts the combustion air and atomized medium and fuel for burning in an adjoining burner tube.

Description

United States Patent [191 Graat 1 Mar. 11, 1975 BURNER FOR THE STOllCHIOMETRIC COMBUSTION [75] Inventor: Johannes W. Graat, Overasselt,

Netherlands [73] Assignee: Smit Nymegen B.V., Nymegen,

Netherlands [22] Filed: May 10, 1973 2] Appl. No: 359,197

[52] U.S. Cl 431/8, 239/400, 431/182 [51] Int. Cl. F231) 7/00 [58] Field of Search 239/400, 404; 431/8, 9, 431/182, 185

[56] References Cited UNITED STATES PATENTS 2,530,617 11/1950 Kirk et a1 239/400 2861628 11/1958 Fraser v 239/400 X 3,203,769 8/1965 Sogawa et al..,.. 431/8 X 3,254,846 6/1966 Schretcr et a1. 239/400 1/1968 Davis, Sr. et a1. 239/404 Kawaguchi 239/400 Primary Examiner-Charles J. Myhre Assistant Examiner-William C. Anderson Attorney, Agent, or FirmFitch, Even, Tabin & Luedeka [57] ABSTRACT An apparatus and process for combustion of liquid fuel comprises a burner in which the fuel is atomized within a fuel nozzle by a tangential flow into a center bore. An atomizing medium is fed tangentially to a bore and atomized and mixed with the atomized fuel. Combustion air flows through a coaxial cylindrical jacket in the same direction as the mixture of atomized medium and atomized fuel. A conically converging burner mouth contracts the combustion air and atomized medium and fuel for burning in an adjoining burner tube.

11 Claims, 7 Drawing Figures PATENTED W 1 7 1975 SHEET 1 [IF 5 S? QEWE PATENTED 1 3, 870,456

SHEET 2 or 5 Kg/fi mm. 0707.

BURNER FOR THE STOICHIOMETRIC COMBUSTION The present invention relates to a process for the combustion of liquid fuel, especially fuel oil and Diesel oil, with air, comprising a mechanical atomization of the liquid fuel as the first step and a subsequent supply of the combustion air as a further step. and to a burner for performing the combustion method.

There are already known combustion processes and burners by means of which liquid fuels, especially fuel oils and Diesel oils are burned with air or other oxygen carriers. However, it has been found to be disadvantageous in the conventional burners that they are not adapted to effect a stoichiometric combustion, that is that soot is formed in the combustion of a fuel-air mixture in a stoichiometric ratio. This soot production is of extremely disadvantageous effect because it contaminates the combustion chamber and, in the production of inert gas, e.g., the subsequent washing and cooling plants.

Therefore, in order to avoid the undesired soot formation, the burners were normally operated with an excess of air in order to avoid that the fuel is burnt incompletely. However, this combustion with excess air results in flue gases having a substantial quantity of Thus, combustion processes of this type are unsuitable for the inert gas production.

Further, it is disadvantageous in the known combustion processes that, even in the case of a combustion with an excess of air, a stoichiometric or under-stoichiometric ratio may result due to variations in the properties of the air or of the fuel, with the control being incapable of reacting or responding to these variations in sufficiently rapid manner. Accordingly, even in the case ofa combustion with an excess of air, a temporary soot formation with the detrimental consequences therefrom will be unavoidable.

Accordingly, it is the object of the present invention to provide a process for the combustion of liquid fuels which operates under stoichiometric conditions without soot formation and wherein no soot is formed even at under-stoichiometric conditions, i.e., with an insufficient proportion of air.

Furthermore, the burner for carrying out the process according to the invention should be of simple construction, adapted to be economically manufactured and easily operated, and operable without any additional control means.

According to the present invention, this object is solved by a tangential supply of atomizing medium to the mechanically atomized jet of the fuel within an atomizing chamber and a subsequent coaxial, equidirectional admission of the combustion air to the atomized fuel, and a succeeding contraction of the mixture jet by at least percent.

Further, it has been found to be advantageous that the fuel prior to the mechanical atomization thereof, i.e., prior to its entry into the atomizing chamber and prior to the mixing with the atomizing air, flows tangentially and obliquely to a center bore; additionally, it is extremely advantageous if the atomizing medium represents a very high proportion of the sum of the combustion air and of the atomizing medium. This proportion may amount to between 10 and 50 percent.

Especially for the production of inert gases which should be as free as possible from nitrogen oxides, it has been found to be advantageous to effect an atomization by means of steam which has been superheated by at least about C.

The burner for carrying out the process according to the invention is characterized particularly by an atomizing portion having a mechanically atomizing fuel nozzle, an atomizing passage extending coaxially to the fuel nozzle, and bores for supplying the atomizing medium and opening tangentially into the atomizing passage. Advantageously, the atomizing portion is coaxially surrounded by a cylindricaljacket for the supply of combustion air, which jacket is followed by a conically converging burner mouth and a burner tube adjoined thereto.

Preferably, a contracting wall at the opening of the burner mouth defines an angle of from 20 up to 50 with the direction of flow for the purpose of contracting the flow of the atomizing medium, the combustion air and the oil to the extent of mixing them but not to the extent of causing the oil droplets to settle out onto the contracting wall.

In a manner being absolutely surprising to the expert, it has shown that soot formation does not occur even in the case of under-stoichiometric conditions; rather, only an increased amount of CO is produced. As an outside appearance, the flame produced by the burner according to the invention is not of yellowish color and frayed out, but ratherhas an orange-blue shade with a defined flame region.

In a further embodiment of the invention, in addition to air and steam the atomization of the oil within the atomizing chamber may be effected also by means of inert gas or natural gas. The oil is fed to the fuel nozzle at a pressure of between 1 and I0 kg/cm (atmospheres), and the quantity to be burned is controlled by means of the pressure adjusted upstream of the fuel nozzle.

If air is used as the atomizing medium, a quantity of from 10 and 50 percent of the total amount of air may be fed for the stoichiometric or under-stoichiometric combustion already during the atomizing process; on

the average, the proportion of the atomizing air in the total amount of air will be about 20 percent. Preferably, the pressure of the atomizing medium supplied is selected such that the critical pressure ratio for the maximum speed of flow is adjusted, i.e., that the medium supplied is produced at pressures of above 2.5 kg/cm for the atomization of the oil.

According to the invention, however, satisfactory combustion has been obtained even at lower pressures and lower speeds of flow of the atomizing medium.

Briefly, the combustion process according to the invention proceeds in four steps:

1. The atomization of liquid fuel in a fuel atomizing nozzle, whereby the fuel is supplied to the atomizing orifice through tangential and inclined passages;

2. The supply of atomizing medium through an atomizing passage, whereby the atomizing medium is fed through tangential passages in a plane which extends perpendicularly or obliquely to the axis of the fuel atomizing nozzle;

3. The admixture of combustion air which flows coaxially and in the same direction with the atomized fuels; and

4. The contraction of the mixed flow which results in an improved mixing of the combustion air with the atomized fuel.

In the following, the burner according to the invention is described in an exemplary embodiment by referring to the drawings, and the combustion process according to the invention is explained in greater detail by mean of diagrams. In the FIGS.:

FIG. 1 is a diagram showing the relationship between the quantity of the atomized fuel and the atomizing medium including a range for the combustion according to the invention;

FIG. 2 is a table showing the dimensions of burners according to the invention, wherein the spacing of the atomizing nozzle from the burner mouth and the diameter of the burner are shown in dependency of the fuel flow therethrough;

FIG. 3. is a sectional view through a burner according to the invention;

FIG. 4A is a sectional view through the atomizing nozzle according to the invention;

FIG. 4B is a section along lines 8-8 in 4A;

FIG. A is a sectional view through a pressure atomizer for the liquid fuel; and

FIG. 5B is a section along lines B-B in FIG. 5A.

It can be seen from FIG. 1 that for every given quantity of fuel two boundary ranges for the atomizing medium have to be observed, between which the improved combustion according to the invention takes place. I

The value for a combustion according to the invention must fall within the two solid lines. Thus, obviously the combustion according to the invention depends on the fact that a predetermined quantity by weight of atomizing medium is supplied in relation to the fuel fed in, i.c., that a predetermined minimum impulse in relation to the burnt fuel is spent for the atomization. This impulse is determined by the quantity and the pressure of the fuel supplied.

The present burner proper comprises an atomizing portion 10 which is coaxially surrounded by a cylindrical jacket 11, and the air inlet for the combustion air is defined by an annular passage through a feed line 16.

The cylindrical jacket 11 merges into a conically inwardly converging contracting wall 12 in a plate 25 which contracting wall is designated as the burner mouth and which continues in a burner tube 13 at the smallest cross-section thereof.

The diameter of the burner mouth and its spacing from the atomizing portion 10 can be seen from the table according to FIG. 2.

The contraction interiorly of the burner mouth or the conical shape, respectively, is measured by an angle relative to the burner axis, which angle a has a minimum value of and a maximum value of 50.

The cylindrical jacket 11 has mounted therein a spark plug 18 which provides for an ignition at the startup of combustion. Construction and function of a spark plug of this type are known, so that it can be dispensed with a more detailed description thereof. The cylindrical jacket 11 and the annular passage 15 are provided at the end directed away from the combustion chamber with a plate 19 including a sight glass 17 and with the supply line 20 for the oil or the fuel, respectively, and a supply line 21 for the atomizing air or the atomizing medium, respectively. A connection 14 serves for the monitoring of the flame.

As shown in FIG. 4A, the atomizing portion 10 per se comprises a mechanical pressure atomizing nozzle 1 for the fuel, which nozzle terminates a short distance in front of an atomizing passage 2. Tangential channels or passages 3 open into the atomizing passage with a spacing of at least 2 millimeters from the pressure atomizing nozzle 1, which passages feed the atomizing medium in a plane extending perpendicularly or obliquely to the burner axis.

It has been found to be essential to the invention that the atomizing medium is supplied through these tangential passages, and that the spacing has the abovementioned mimimum dimension. Advantageously, the atomizing passage 2 terminates in a plane 4 which likewise extends perpendicularly to the burner axis.

The supply of the atomizing air or of the atomizing medium is effected, as shown in FIG. 4A, to the bores or passages 3 through an annular passage 9, so that uniform pressurization of the channels 3 is ensured.

The pressure atomizing nozzle 1 for the liquid fuel supplied is shown in FIG. 5. The fuel is likewise passed to an injection bore or orifice 6 via tangential channels 5 inclined relative to the burner axis. whereupon the fuel is atomized into minute droplets at said orifice and is then intimately mixed with the atomizing air or atomizing medium within the atomizing passage 2, whereupon it is burnt after a further admixture with the combustion air.

In view of the fact that both the pressure atomizing nozzle 1 and the atomizing portion 10 in other respects correspond to the general prior art, it can be dispensed with a more detailed description thereof.

Thus, it is obvious to the expert that the structure of the burner according to the invention is of extraordinarily simple nature, that the burner may operate without giving cause to trouble, so that it is the more surprising to the expert that the burner according to the invention provides a soot-free combustion not only at stoichiometric ratios, but also at under-stoichiometric ratios. I

What is claimed is:

1. A method for the combustion of liquid fuel such as fuel oil or diesel oil with air comprising the steps of: mechanically atomizing the liquid fuel, directing the atomized medium tangentially to the mechanically atomized fuel within an atomizing passage, directing combustion air coaxially and in the same direction as the flow of said atomized fuel and medium, and contracting the combustion air and atomized fuel and medium by at least 10 percent before burning on a contracting wall to mix the combustion air and atomized air and atomized fuel and medium without settling of atomized fuel on said contracting wall.

2. A method in accordance with claim 1 including the step of supplying super-heated steam at at least as the atomizing medium.

3. A method in accordance with claim 1 including the step of flowing the fuel tangentially towards a center bore during the step of mechanically atomizing the fuel.

4. A method in accordance with claim 1 including the step of providing air as the atomized medium and supplying the atomized medium air in an amount between 10 to 50 percent of the sum of the combustion air and the atomized medium air.

5. A method in accordance with claim 1 comprising the step of contracting the air and fuel mixture without causing fuel droplets to settle on the wall of the contracting converging surface.

6. An apparatus for the combustion of liquid fuel such as fuel oil or diesel oil with air, said apparatus comprising an atomizing means including a fuel nozzle for mechanically atomizing the fuel into droplets, means defining an atomizing passage extending coaxially to said atomizing fuel nozzle to receive the fuel therefrom, means for conveying an atomizing medium including bores opening tangentially into said atomizing passage. means defining a passage extending coaxially with said atomizing passage for directing combustion air coaxially with said mixture ofatomized fuel and atomizing medium, and a conically converging means including a contracting wall for contracting the combustion air and atomized fuel, and atomizing medium to mix the same without settling of the atomized fuel on said contracting wall.

7. A burner apparatus according to claim 6 in which the spacing between said fuel nozzle and said bores is 2 millimeters.

8. A burner apparatus according to claim 7 in which the center axis of each said atomizing bores extends tangentially to said atomizing passage, said atomizing passage being located coaxially with a central axis for said burner.

9. A burner apparatus in accordance with claim 6 characterized in that said atomizing passage extends in the direction of the flow of the atomized fuel, and in which a surface extending perpendicular to the axis of said passage and direction of fuel flow forms an end for said atomizing passage.

10. A burner apparatus in accordance with claim 6 in which said conically converging surface defines a burner mouth, and in which an adjoining burner tube extends from said burner mouth and said conical surface defines an angle of from 20 to 50 relative to the axis for said burner.

11. A burner apparatus in accordance with claim 6 in which said fuel nozzle comprises a plurality of bores extending tangentially and obliquely relative to the axis of said fuel nozzle.

Claims

2. A method in accordance with claim 1 including the step of supplying super-heated steam at at least 75* as the atomizing medium.

6. An apparatus for the combustion of liquid fuel such as fuel oil or diesel oil with air, said apparatus comprising an atomizing means including a fuel nozzle for mechanically atomizing the fuel into droplets, means defining an atomizing passage extending coaxially to said atomizing fuel nozzle to receive the fuel therefrom, means for conveying an atomizing medium including bores opening tangentially into said atomizing passage, means defining a passage extending coaxially with said atomizing passage for directing combustion air coaxially with said mixture of atomized fuel and atomizing medium, and a conically converging means including a contracting wall for contracting the combustion air and atomized fuel, and atomizing medium to mix the same without settling of the atomized fuel on said contracting wall.

10. A burner apparatus in accordance with claim 6 in which said conically converging Surface defines a burner mouth, and in which an adjoining burner tube extends from said burner mouth and said conical surface defines an angle of from 20* to 50* relative to the axis for said burner.