FR2485163A1 - Low nitrous oxides emission combustion process - slows down mixing by blocking air admission all around burner and deflecting fuel away from air - Google Patents

Abstract

The low nitrous oxides emission combustion process is for gaseous or liquid fuels, in industrial usage. It is based on the principle that slowing down the air-fuel mixture rate reduces the amount of nitrous oxides formed. This is achieved by limiting the arc of air admission, with coaxial burners and air casings, to 240 deg. or less, centred on the axis, by blocking part of the flow annulus. The fuel discharge orifice axis is pref. also angled 5-45 deg. to the burner axis, towards the centre of area of the blocked portion. The fuel-air flow ratio may be preset to a value exceeding 0.3. The burner liq. position may be selected for optimum geometrical parameters, depending on the burner type.

Description

 The present invention relates to a method and a combustion device with the minimum emission of nitrogen oxides Ni.

The amount of nitrogen oxides (hereinafter referred to as NOx) which is formed during the combustion of gaseous or liquid fuels without different furnaces or industrial boilers, depends on the combustion conditions, in particular on factors such as the temperature the oxygen concentration and the residence time of the combustion gases in the high temperature zone; the higher the flame temperature and the higher the oxygen concentration, the higher the amount of nitrogen oxides formed
It is common practice in the field of combustion to ensure a uniform mixture of combustion air with the fuel as soon as possible in order to produce a rapid combustion and with the aim of increasing the combustion efficiency. However, such combustion fast raises the flame temperature widens the zone at high temperature in the focus and increases the localized concentration of oxygen in the combustion zone, resulting in the formation of a large amount of nitrogen oxides
NOx. There is therefore an incompatibility between the trend of increasing the maximum combustion efficiency and reducing the environmental pollution to a minimum.
In view of these considerations, the inventors have conducted intensive research to develop a rational means of suppressing the rapid mixing of fuel and air so as to establish a slow or flaky combustion to minimize emission of NOx nitrogen oxides
It has been found that by injecting the combustion air into the furnace so as to produce a flow pattern deviated asymmetrically with respect to the axis of the air injection body or the burner plate, and limiting the deflection of the air flow in a fixed range, it was possible to carry out the combustion by effectively minimizing the formation of nitrogen oxides
NOx while increasing the efficiency of combustion, which is also advantageous from the point of view of energy saving.

The purpose of the invention is therefore to provide a new combustion process with the minimum emission of nitrogen oxides
NOx using gaseous, liquid or solid fuels in different industrial furnaces or boilers, characterized in that the sector or opening angle of a combustion air injection zone to be introduced into a furnace by means of a burner plate or an air injection body is less than 2400, the apex of said angle being placed on the axis of the burner plate or the air injection body of whereby said combustion air is injected into the burner so as to follow a flow path deviated asymmetrically with respect to the axis of the carrier plate or the air injection body
The invention also aims to provide a combustion method as defined above, characterized in that a fuel is injected with deviation using a fuel injection burner whose injection pipe is inclined by a angle of 5 to 450 with respect to the axis of the burner said burner being called "inclined burner"
The invention further aims to provide a combustion method of the type defined above, characterized in that the ratio between the fuel flow rate and the combustion air flow rate is controlled so as to be greater than 0, 3
The invention also aims to provide a combustion method of the type defined above, characterized in that the position of the burner tip is determined so that the ratio (L / D) between the diameter (D) the opening in the inner end surface of the burner plate and the distance (L) separating the burner plate inner end surface from the burner tip is less than 1.3 for the inclined burner and less than 0.8 for the normal type burner.

The invention also aims to provide a combustion method of the type defined above, characterized in that the direction of deflection of the air flow is determined according to the relative positions between the burner and the material to be heated so that the combustion air flow can not arrive directly on said material
The invention further aims to provide a combustion method of the type defined above, characterized in that the fuel is injected with deviation towards the side which is placed opposite the center of gravity of the flow combustion air.

The object of the invention is also to provide a two-stage combustion device that can be used for different industrial furnaces or boilers and characterized in that it is provided, on the outside of a burner plate, which is provided with a burner and a primary combustion air inlet passage surrounding said burner, combustion air inlet passages
secondary, and in that the opening angle of the air injection zone corresponding to said secondary air inlet passages is less than 240, the vertex of said angle being placed on the axis of the plate door-BURNER
The invention further aims to provide a two-stage combustion device, usable with different foci or industrial boilers and characterized in that it is provided on the outside of a plate-burner, provided with a burner and a primary combustion air inlet passage surrounding said burner, secondary combustion air inlet passages and that the opening angle of the air injection zone of each of said primary air and secondary air inlet passages is less than 240, the vertex of said angle being placed on the axis of the bristle plate.

 The invention further aims to provide a combustion device with the minimum emission of NOx oxide oxides comprising a burner placed inside an air injection body and coaxially with respect to the latter, characterized in that said air injection body is provided with combustion air injection holes placed in a limited area so that the combustion air, after having been injected, following a flow path deviated asymmetrically with respect to said axis, said burner being provided with a fuel injection hole which is inclined towards the opposite side to said limited area of said air injection body.

Other advantages and features of the invention will be demonstrated in the following delta description, given by way of non-limiting example, with reference to the appended drawings in which:
Fig.1 (a) is a schematic sectional view showing a concrete example of a burner structure used in the present invention
Fig.1 (b) is a schematic front view of said burner structure,
Fig.2 (a) is a schematic sectional view showing another concrete example of a burner structure;
Fig.2 (b) is a schematic front view of said burner structure;
Fig.3 is a schematic sectional view of a concrete embodiment of an inclined type burner;
Fig.4 is a schematic view showing a combustion model according to the present invention;
Eig.5 is a graph showing the relationship between the deviation of the combustion air flow and the reduction rate of NOx nitrogen oxides;
Fig. 6 is a graph showing the relationship between the deviation of the combustion air flow and the formation of NOx nitrogen oxides;
Figs.7, 8 and 9 are graphs showing the relationship between the air flow rate / fuel flow ratio and NOx nitrogen oxide formation;
Fig.10 is a view showing the installation of a burner in a corresponding area;
Figs. 11 (A), B and 12 (A), (B) are graphs showing the relationship between the burner tip position and the formation of NOX nitrogen oxides;
Fig. 13 is a view showing the directions of fuel injection into a burner,
Fig. 14 (I) to 14 (III) are graphs showing the relationship between fuel injection directions and the formation of NOx nitrogen oxides;
Figs. (I), (II) show a concrete example of embodiment of a combustion device according to the invention;
Figs.16 (I), (II) show another concrete embodiment of a combustion device according to the invention;
Figs.17 (I), (II) are graphs showing the relationship between the formation of nitrogen oxides NOx and the production of smoke
Fig. 1 (a) is a sectional view showing an example of a construction of a burner used to effect combustion in accordance with the present invention. 1 has designated a burner plate and 2 an air injection body which is fixed in a hole in said burner plate. A burner proper 4 is arranged coaxially in a cavity formed in the air injection body 2 and is provided at its front end with a fuel injection hole 3.

The air injection body 2; as shown in Figure 9 (b),
unlike the known body, the entire thick part of which is in the covered state, is closed with the exception of the holes 5 formed in the thick part along an arc whose center is situated on the axis of the body 2. As a result, combustion air is injected into the furnace, not uniformly over the entire circumference, but locally through said holes. As a result, under ordinary conditions or the entire circumference of the body injection is uniformly open, the combustion air follows a symmetrical flow path with respect to
of the air / burner shaft or burner (such a flow of combustion air being called "uniform flow" as when the air flow is located in the open area of the body 2 as shown in the drawings, it is arranged that the air injected into the furnace follows a flow path deviated asymmetrically with respect to the axis of the air injection body or the burner plate. the flow deflection is a function of the magnitude of the aperture angle (or center angle O) formed between two straight lines connecting the opposite sides of the aperture area, If the aperture angle is equal to 360D, the resultant airflow corresponds to the ordinary uniform flow, and it should be noted that the smaller the angle, the greater the deviation of the airflow, in which case the degree of deflection can be controlled optionally by appropriately determining the number and positions of the holes Another means of creating a deflection in the air flow would be to place a screen or other obstructing member in a portion of the opening in the carrier plate. burner so as to locally seal said opening and thereby stop a portion of the air flow passing through the burner plate or the air injection body. Alternatively, it is also possible to install an elbow tube upstream and near the air inlet port of the burner plate to create a flow of air deflected according to hydrodynamic principles. In the present invention, the opening zone for combustion air injection which is defined locally in the burner plate or in the air injection body will be called simply in the following the "zone of combustion". opening "while the angle (or center angle O) formed by said opening area will be called the" opening angle "), this angle serving as a reference to indicate the degree of deflection of the flow In FIG. 1 (b), the holes 5 have been shown as being placed in the lower half of the air injection body to create a deflected air flow in the lower region but as it will be precise in the following, the region or an air flow of It is possible to determine the holes 5 in the upper region or in the right or left region of the injection zone body.
The burner plate or the air injection body used in the present invention may have a rectangular shape, as shown in FIG. 2, in which case also, as in FIG. 1, it is possible to control the degree of deflection by the opening angle O of said opening zone
In accordance with the present invention, the deflected injection of combustion air into a furnace is intended to suppress the rapid mixing of fuel and combustion air, as described above, in order to maintain a slow combustion condition. while ensuring the self-circulation of flue gases. In this rough, the opening angle is limited to a value of about 240 as will be specified in the following
The burner used in the present invention may be between an ordinary burner (hereinafter referred to as "straight burner"), wherein the fuel injection hole in the nozzle is aligned with the burner axis; however, there may be another type of burner such as that shown in FIG. 3, where the fuel injection hole 3 is inclined at a fixed angle i with respect to the axis of the burner
A (this burner being called in the following "inclined type burner").

FIG. 4 schematically represents a combustion model created in a combustion device provided with a burner structure such as that of FIG. 1 (the burner used being an inclined type burner such as that of FIG. 3). In this figure, the combustion air A is injected through an opening zone in the lower region of an air injection body 2 so as to enter the hearth from the lower half of the burner plate 1.The fuel
F is injected on the side where there is less combustion air A, passing through the upper half of the burner plate opening before entering the fireplace. As a result, mixing of the combustion air with the fuel is carried out gradually, so that the combustion proceeds slowly, compared with the case where a uniform flow of combustion air is provided. In addition, in this combustion process, the flue gases G, as indicated, are propelled into the combustion air stream.
A by the living force of the latter and, in addition, it is very effectively occurs what is called a "self-circulation of flue gases".

 According to the method according to the invention, the slow combustion create by the gradual mixing of the fuel and air cooperates with the self-circulation of the flue gases to produce a synergistic effect, which establishes a uniform distribution of the flame temperature without that a localized region occurs at high temperature in the combustion zone. It is thus possible to obtain a significant reduction of nitrogen oxides NOx under satisfactory combustion conditions.

 The reduction effect of NOx nitrogen oxides depends in a large measure on the degree of deflection of the combustion air flow. When it is too big, the opening angle O of the combustion air gap reduces the space with less combustion air near the fuel injection burner so that most of the injected fuel already mixes with the combustion air, which results in a rapid process of combustion and a decrease in the degree of self-circulation of the burnt gases.

To achieve satisfactory combustion with the minimum NOx nitrogen oxide formation, the air must be given the necessary degree of deflection in order to achieve the desirable effects defined above. For this purpose, it is necessary to limit the opening angle O of the air injection zone; about 2400, as will be specified later
FIG. 5 is a graph showing the results of a test carried out to show the influence of the degree of deflection of the combustion air flow on the reduction of NOx nitrogen oxides, which test was carried out using a Experimental combustion chamber 1 m in diameter and 4 m in length, (Burner and a burner plate of the type indicated in Figure 1 were used). The following combustion conditions were adopted in this test:
Fuel: butane gas; burning rate: 40 x 104 kcal / h; firing temperature: 1300-1350 C; fuel / air ratio: 1.15; temperature of preheated combustion air: 3200C; and type of burner: straight type or inclined type (in each case, single-hole burner).

 In FIG. 5, a curve (I) corresponds to the use of the right burner while the curves (II) and (here) correspond to the use of the inclined burner, the angle of inclination being respectively 150 and 300 (elevation angle) .In the ordinates, the percentages of the rate of NOx oxidation formation decrease are taken when the combustion air follows a uniform flow pattern (the amount of of nitrogen oxides NOx formed in the case of a uniform flow pattern being 108 ppm for the straight type burner, 80 ppm for the burner of the type inclined at 15, and 56 ppm for the burner of the type tilted to 30) v As shown in the graph, on which the aperture angle θ has been plotted on the abscissa, the rate of decrease of the NOx nitrogen oxides increases as the aperture angle θ of the zone d air injection is reduced to increase the degree of deflection, regardless of the type of burner; it can be seen that the amount of NOx corresponding to an opening fingernail of about 2400C or less decreases by about 20% or more compared to the amount of NOx oxides produced for uniform airflow (angle opening O = 3600).

It is found that the effect of using an inclined type burner is remarkable, the rate of decrease of the oxides of aote for an opening angle of 12Q reaching a high value of 80%. The function of the sloping type burner is to allow the fuel and air to mix slowly in the initial stages of combustion, by decreasing the maximum flame temperature and allowing the combustion to proceed at a constant temperature. which reduces the degree of formation of nitrogen oxides NOx .This effect of the inclined burner cooperates with the effect created by the controlled deviation of the combustion air to help further reduce the amount of nitrogen oxides NOx formed o In order for the inclined burner to perform its function effectively, the angle of inclination alpha can be chosen; in a range between about 5 and 450, the most advantageous value being about 300
The inclined type burner provides a means of decreasing the formation of NOx nitrogen oxides because its function is to suppress the mixing of fuel and air as described above. Generally, it is found that the nitrogen oxide NOx reduction effect that is obtained by using, in combination, two or more types of NOx reduction techniques does not correspond to the sum of their individual effects.
On the contrary, in the system according to the invention, the use
combination of different techniques for reducing nitrogen oxides
N6x, namely the inclined burner and the control of the deviation of the combustion air flow, creates a synergistic effect resulting in a large decrease in the formation of nitrogen oxides NOx. Such a synergetic effect can also be obtained by the combined use of two or more NOx nitrogen oxide formation reduction techniques which will be described hereinafter. , unlike the generally accepted conventional concept, the combined use of different types of techniques for decreasing the formation of NOx nitrogen oxides further enhances this NOx reducing effect
The NOx nitrogen oxidation reduction effect according to the present invention can be further improved by using, individually or in combination, combustion control means such as burner type, air flow rate, ratio of fuel flow / air flow, the direction of fuel injection and the position of the burner tip, as will be specified in the following
FIG. 6 is a graph showing, in the form of a comparison, the amounts of NOx (with conversion to 11% O 2, which is shown in the following which are produced when using
injection of different burners, the opening angle # of the combustion zone / air being modified in a combustion test machine used with heavy oil (class C). The markings shown on the graph were used to distinguish between different types of burners, as shown in Table 1.

TABLE 1: Combustion Conditions

<tb> Flow <SEP> of <SEP> fuel <SEP> * <SEP> a <SEP> b <SEP> c
<tb><SEP> Right <SEP> O <SEP> o- <SEP> o
<tb> type <SEP> of <SEP> burner <SEP> when100
<tb><SEP> tilted
<tb><SEP> 200
<Tb>
The fuel flow rate varies with the diameter of the injected hole of the burner used, the flows a, b and c being such that b is equal to twice that of a and c is equal to the triple of-a.
The graph shows that, when the opening angle θ is reduced to increase the deviation, the NOx NOx formation decrease effect is magnified, although a certain difference is recorded in correspondence to the type of NOx. burner, and furthermore it is found that the opening angle O of 240 or less is particularly effective in reducing the emission of NOx nitrogen oxides.

Figure 7 is a graph showing the relationship between the fuel flow rate / air flow ratio and the amount of NOx emitted in a combustion test performed using butane gas as the fuel and the degree of flow deflection. combustion air as a parameter o On the graph, the curve (a) corresponds to the case where the air flow is uniform (opening angle = 3600), the curve b corresponds to the case where the opening angle is 1800 and the curve c corresponds to the case where the opening angle is 120. In addition, in each case, the air injection zone is positioned in the lower region of the air injection body and the angle of inclination of the fuel injection hole formed in the burner used is defined. Fig. 8 is a graph showing the result of measurements of amounts of Itx emitted in a combustion test carried out essentially in the same conditions as in Fig. 7, except that it was used as @ ombustible coke oven gas @ @@. However, a value of 15 was given to the angle &alpha;; tilt of the fuel injection hole
As shown in FIGS. 7 and 8, although the amount of NOx varies with the nature of the fuel and the type of the burner, the greater the degree of deflection of the combustion air flow, the greater the amount of NOx formed. low ; it should be noted that, in the case of gaseous fuels, there is a significant reduction in the amount of NOx when the ratio between the fuel flow rate and the air flow rate is greater than or equal to 0.3, in particular being between 0.5 and 2. Moreover, in the case of liquid fuels, this flow ratio has less influence on the formation of NOx.

FIG. 9 is a graph showing the relationship between the fuel flow rate / airflow ratio and the amount of NOx formed for different types of burners, using butane gas as the fuel, the opening angle # of the zone d air injection being 2400. On the graph, the "circle" shaped lairs correspond to a right-type burner, the "triangle" -shaped cores correspond to an inclined burner, with an angle of inclination θ; of 150 (or 10) and the "square" shaped hangers correspond to an inclined burner, the inclination angle &alpha; being 30 (or 20) .The air flow corresponding to the shaded landmarks is approximately equal to twice the flow rate corresponding to the unhatched landmarks. It can be seen that, as described above, by increasing the airflow deflection and increasing the fuel flow / airflow ratio, excellent results can be achieved within a defined range of ratios. flow rates for each type of fuel
As described above, the effect of decreasing nitrogen oxides
NOx is improved by giving a defined degree. by diverting the combustion air flow and using an inclined burner instead of a + burner, the NOx nitrogen oxidation reduction being obtained in FIG. using an inclined type burner whose inclination angle c (is about 300.However, if this inclined type burner corresponding to an inclination angle i of about 300 is directly used in an installation, the very large deflection angle of the injected fuel flow can sometimes cause fuel sticking on the wall of the fireplace or on the wall of the hole in the burner plate, which imposes restrictions on the angle of inclination that it is possible to adopt in practice, which is why angles of between approximately 10 and 200 are used. Moreover, the fact that the injected fuel flow is deviated strongly or not has an influence on the fuel mixture condition e and air, causing a significant change in the mixture. In such circumstances, the control of the ratio of fuel flow to air flow is used as a very effective means of decreasing the amount of NOx oxides formed to a satisfactory extent.
According to the present invention, it is possible to reduce the amount of nitrogen oxides NOx formed, in a stabilized manner, by additional adjustment of the position of the burner tip. The expression burner tip position " As shown in FIG. 10, the distance L separating the end surface (f), turned towards the inside of the furnace, from the burner plate 1 of the nozzle of the burner 4 0 is seen from the point of view of FIG. rapid and uniform mixing of the fuel injected combustion air, early termination of combustion and elimination of damage to the burner nozzle by heat, this burner tip should normally be placed back from the end surface (f) of the burner plate, i.e., in a position of between about 1 and 1.5 with said L / D ratio.

 Fig. 11 is a graph showing the relationship between the burner tip position and the amount of nitrogen oxides NOx formed when the opening angle θ is 1800 and when butane gas is used as the fuel, numerical values indicated on the horizontal axis or abscissas representing the position of the burner tip. (L / D = 0 means that the burner tip is flush with the inner end surface (f) of the burner plate while L / D 90 means that said tip enters the firebox). In FIG. ), the combustion air flow is uniform (the opening angle O of the air-injection zone is equal to 360) whereas, in Figure 11 (B), the air flow is deflected (the opening angle is 180).

Table 2 shows the markings on the graphs to distinguish between burner types (straight type and inclined type) and also between fuel flow rates due to differences in injection hole diameters. fuel
TABLE 2

<tb><SEP> Flow <SEP> of <SEP> fuel <SEP> a '<SEP>b'<SEP> G <SEP> w
<tb><SEP> Right <SEP> C
<tb> type <SEP> of <SEP> burner
<tb><SEP> 15 <SEP>
<tb><SEP> tilted <SEP> 150 <SEP>
<SEP> t <SEP> 2 <SEP> S
<Tb>
* The flow rates a ', b' and and c 'are such that if b' is twice the number of a 'and that is equal to 8 times
As indicated, when the combustion air flow is uniform (Fig. 11A), bringing the burner tip closer to the focus tends, in some cases, to decrease the amount of N6x formed, then in other cases, it has a tendency to increase the amount of NOx formed, which makes it impossible to obtain a definite result. On the contrary, the effective reduction of NOx oxides formed which is obtained by deflecting the combustion air flow in accordance with the present invention is clear and defined independently of the type of burner; in particular, when L / D is close to O (that is to say when the burner tip is flush with the inner end surface (f) of the hearth there is an excellent effect which decreases the amount of NOx formed little by little almost half or below, unlike the conventional process.

 Fig. 12 is a graph showing the relationship between the burner position and the amount of NOx formed for the same test as the combustion test of Fig. 11, but using as fuel coke oven gas. On the graph, the markings shown in Table 3 were used to distinguish between burner types and between fuel injection hole diameters.

TABLE 3

<tb><SEP> *
<tb><SEP> debit <SEP> of <SEP> fuel <SEP> a "<SEP>b"<SEP> c "
<tb><SEP> Right <SEP> 0 <SEP>0a> 8
<tb> type <SEP> of <SEP> burner <SEP> J? <September>
<tb><SEP> tilted
<tb><SEP> 3 &commat;
<Tb>
* The flow rates a ", b", c "and d" are such that b "is twice as much", c "is three times as" and d "is four times as".

 As in the case of Fig. 11, a noticeable decrease in NOx formation was observed, this effect being based on controlling the burner position as the combustion air flow is deflected in accordance with the present invention.

In addition, in the case of Figures 11 and 12, the combustion is outside the optimal range of values of the ratio
combustion rate / fuel airflow (which varies with the nature of the fuel, such as butane gas and coke oven gas, and is determined by taking into account the distribution of temperatures in the hearth). As a result, dreary when using an inclined burner or means to bring this burner closer to the inner end surface of the hearth (particularly in the case of Figure 11 (A) and Figure 12 (A). )), the amount of nitrogen oxide NOX formed is relatively high.In other words, the deflection means of the combustion air flow, when used alone allows to suppress the emission of oxides NOx nitrogen more efficiently than the inclined type burner or the closer of said burner with respect to the interior extreme surface of the hearth, irrespective of the relationship between the flow rates (It is needless to say that X if the flow ratio is regulated in the optimal range of values, the resulting effect is more remarkable).

The deflection means of the combustion air flow is also advantageous from the point of view of the combustion conditions because it expands the said optimum range.

 The reason that the approach of the burner tip to the inner end surface of the firebox is effective in reducing the amount of NOx oxides formed is that the mixing of the fuel and the fuel is prevented. premature air inside the small volume burner losses plate and on the contrary it is allowed a gradual progression of said mixture in a large volume, the resulting jet of combustion air being injected into the hearth with sufficient live force to drive the flue gas, which allows efficient generation of self-circulation of flue gases to the combustion zone.The position where the burner nozzle is to be placed to sufficiently reduce the amount of NOx oxides formed varies with the type of burner and it is necessary that the distance L separating the inner extreme surface (f) from the hearth and the burner tip is not greater than about 0.8 times the right-hand burner D-hole diameter, and not more than about 1.3 times the inclined-type burner D-hole diameter (in each case, positions or the burner tip protrudes into the fireplace); in particular, it is advantageous for the burner tip to be flush with the inner end surface of the hearth (L / D = O). In addition, if the burner tip enters the hearth, it is desirable that the angle of the diverging hole in the burner plate (i.e. angle formed by the inclined hole with the inner wall surface of the burner plate) is less than or equal to 450, in order to achieve satisfactory combustion and to effectively reduce the formation of NOx nitrogen oxides.

The effect of decreasing NOx nitrogen oxide emission, according to the present invention, can be further amplified by adjusting the injection direction of the fuel leaving the burner. The term "fuel injection direction" refers, as shown in Fig. 13 when using an inclined type burner, having a defined angle of inclination &alpha;, to a direction (a) for which the fuel injection makes an elevation angle c (with a horizontal plane H passing through the axis A of the burner plate or the air injection body, to a direction (b) for which it makes a angle α with said horizontal plane1 or with a direction (c) or (d) which is deviated to the left or right of said horizontal plane H. In short, this expression refers to the direction of inclination of the hole fuel injection with respect to the axis A
Figs. 14 (I) - (III) are graphs showing the relationship for the fuel injection direction and the amount of NOx formed when the combustion air flow is deflected
and when the fuel injection direction, when used
An inclined type burner is modified (butane gas has been used as the fuel). The combustion conditions are shown in Table 4 below.
TABLE 4
Angle air injection body
figure
bowed to
N position of the opening angle of its burning
open area- (#)
their (&alpha;)
ture
I high 180 15
II high 120 15
III bass 120 15
In each of these figures, the symbol indicated at the top left indicates the position of the combustion air outlet zone in the air injection body, the hatched portion representing the opening zone and the center angle # defining the opening angle of said opening area. The horizontal axis of each graph represents the fuel direction expressed in angular values (). For example, if said angle is 0 (or 3600), it means that the direction (b), FIG. injection hole makes an angle of elevation &alpha; with the vertical plane V passing through the axis A; an angle of 900 means that the direction (e) is in the horizontal plane H, an angle of 1800 means that the direction (a) is at an angle &alpha; in the vertical plane V while an angle of 270 means that the direction (d) is in the horizontal plane H. On the graph, the untinted marks refer to the case where the position of the burner tip is set so that L / D = 0, while the.

Hue marks refer to the case where said position is set so that the L / D ratio = 1.0 (FIG. 10).

As shown in said figures, when injecting the fuel in a zone other than that in which a deflected combustion air flow is introduced, in particular on the opposite side to said deflected air flow (for example if the lower part of the air injection body is opened and if the deflected combustion air is introduced into said part, the fuel injection hole in the burner is oriented in the direction (a) of FIG. (13), it is possible to obtain a substantial decrease in the amount of NOx oxides formed
With regard to the directions of injection of combustion air and fuel, it is possible to adjust them relatively so that said directions can not coincide with each other. fuel injection is determined taking into account the deflection direction of the combustion air flow, this air can be injected into the upper part, the lower part, the right side part or the left side part the air injection body -or well-in any desired direction. However, when the material to be heated in the furnace or furnace, for example steel, is subjected to the flow of air, it is cooled by it, which presents a disadvantage from the point of view of the Heating efficiency. To overcome this difficulty, it is desirable to determine the deflection of the air flow as a function of the relative positions between the burner and the steel material, so that said air flow does not arrive directly. on steel.

 Other examples will now be described of means making it possible to effectively reduce the quantity of nitrogen oxides NOx emitted.

Fig. 15 (I) - is a sectional view of an embodiment of the combustor according to the invention as shown in Fig. 15
(II) shows the arrangement of the air injection ports in the combustion air inlet passages which are provided on the inner side of a furnace or furnace. A fuel injection burner was designated by a primary burner air inlet passage surrounding the burner, by a burner support plate, by inlet passages, secondary combustion air which are arranged outside of said burner plate and by valves (or registers) for controlling the flow of secondary combustion air. The symbol @ designates the axis of the burner 1 ' or the burner plate 3. ' As indicated, the primary air inlet passage 2 opens around the entire outer periphery of the burner 1 while the opening area of the secondary air inlet passages 4 is defined by a plurality of flow holes 4 'which are distributed in the opening angle #, that is to say an angle at the center # which is delimited by straight lines connecting the opposite sides of the opening zone to the axis of the door plate -burner.

This opening angle # is less than or equal to 240, as will be specified in the following. In FIG. 15 (II), five flow holes are shown, but it goes without saying that the number of holes in the opening angle range can be increased or decreased appropriately. possible to use a single curved hole extending along an arc underlying said angle #.

 In the conventional two-stage combustion apparatus, since the primary air and secondary air inlet passages have mouths which completely surround the burner. is injected into the furnace or furnace is symmetrical with respect to the axis of the burner plate or is uniform. On the other hand, in the device according to the invention, since the opening area of the secondary air inlet passages is limited to a range defined by the opening angle #, the total flow of Combustion air injected from the primary and secondary air inlet passages takes a deflected pattern asymmetrically with respect to the burner axis. The deflection of the airflow is evidently amplified as the opening angle is decreased. Q ## EQU1 ## It is possible to control the amplification of the deflection and the flow of air. only on the opening angle O but also on the diameter, the number and the positions of the flow holes.

 In accordance with the present invention, since the purpose of combustion air injection into the furnace or furnace according to a deviated flow pattern is to avoid premature mixing of fuel and combustion air, as long as this objective is achieved, the position of the mouth of the air passages is not limited to the upper part of the plate corte-burner, as shown in Figure 15but on the contrary these mouths can be located in the lower part or in the right side part or in the left side part of the burner.In the arrangement shown in Figure 16, the secondary air inlet passages 44 are arranged so as to fully urge the l the axis of the burner plate, each air inlet passage being provided with an air flow control valve (or register) 5 "serving to define an opening zone having an angle of desired opening 8, in a desired position circumferentially surrounding the axis of the burner plate by opening and closing the flow passage by the operation of said valves.

According to the process according to the invention, it is possible, while minimizing the emission of nitrogen oxides NOx, as described above, to effectively prevent the emission of fumes in order to produce a satisfactory combustion with minimal heat loss. FIGS. 17 (I) and (II) are graphs showing the relationship between NOx nitrogen oxides and smoke emitted, the results being obtained in combustion tests carried out using different types of burners and also butane gas coiane fuel in (I) and heavy oil (class C) in (II) .On the graphs, markers in the form of
circle correspond to the use of a burner of the right type, while the triangular and square markers correspond
to the use of inclined type burners, having angles
tinting marks correspond to the case where the flow of combustion air is uniform while the tinted marks correspond to the case where there is a degree of deflection defined by an opening angle & alpha of 180). The direction of fuel injection by the inclined type burners was the direction (a) of FIG. 13.

In each case, the opening area for deflecting the combustion air flow was the lower part of the air injection body. As shown in FIG. 17 (I), in the conventional case where the flow of combustion air is not deflected (curve (i)), the quantity of nitrogen oxides NOx emitted. can not be reduced to less than about 50ppm without producing smoke whereas, thanks to the process according to the invention, no smoke is produced even when the quantity of nitrogen oxides NOx emitted is reduced to about 20 ppm. Figure 17 (11) refers to the case where heavy oil (Class C) was used as fuel.

The combustion conditions and the meanings of the different reference marks used are the same as for FIG. 17 (i) except that the angle of inclination &alpha; of the inclined type burner is 10 (triangular shape landmarks is 20 &commat;) (square shaped landmarks) .The smoke emission prevention limit value that is obtained by the conventional process corresponds to ppm NOx, but at beyond this value, it is to be expected to produce smoke (curve) whereas, in accordance with the present invention, it is possible to reduce the emission of nitrogen oxides NOx up to about 50 ppm without generating smoke St while getting a satisfactory combustion
In general, to accommodate the production of smoke, it is necessary to admit a large quantity of combustion air (oxygen), but this increase of the incoming air also results in an increase of the quantity of combustion gas. 'exhaust. As a result, the amount of heat evacuated by the exhaust gas increases, which means an increase in heat losses and an increase in fuel expenditure. As a result, it is desirable to carry out the combustion with a decrease in the amount of fuel. air. According to the invention, since the smoke emission can be effectively prevented by comparison with the conventional method as described above, a stabilized combustion condition requiring a relatively small amount of air is obtained, which is highly advantageous. from the point of view of reducing heat losses and that is what helps to save energy.

 Thus, according to the present invention, a defined degree of deflection of the combustion air flow makes it possible to effectively reduce the quantity of N6x nitrogen oxides emitted and, in combination with other techniques for reducing oxides of nitrogen, it is possible to further reduce this emission. In addition, on the one hand, it obtains a uniform distribution of temperatures in the furnace or furnace and, on the other hand, a uniform distribution of the flame radiation, this characteristic being particularly advantageous in "take" type furnaces.

In addition, a stabilized combustion state is obtained, which makes it possible to perform a very economical combustion, to save fuel, etc.

Claims (6)

 1. Combustion process with a minimum emission of NOx oxides, using gaseous, liquid or solid fuels in different industrial furnaces or boilers, characterized in that the sector or opening angle, a combustion air injection zone which is to be introduced into a furnace by (1) intermediate of a burner plate / or of an air injection body (2) is less than 240, the top of said angle being  @ - the axis of the burner plate or the air injection body, so that said combustion air is injected into the burner (4) so as to follow a flow path deviated asymmetrically with respect to the axis of the burner plate or the air injection body.  2. Combustion method according to claim 1, characterized in that a comb.able is injected with deviation using a fuel injection burner whose injection conduit is inclined at an angle (&alpha;) of 5 at 45 relative to the burner axis, said  burner being called "inclined burner".  3. Combustion method according to claim 1, characterized in that the ratio between the combustion flow rate and the combustion air flow rate is controlled to be greater than 0.3.  4 Combustion method according to claim 1, characterized in that the position of the burner tip is determined so that the ratio (L / D) between the diameter (D) of the opening in the inner end surface of the burner plate (2) and the distance (L) separating the inner end surface of the porle-burner plate from the burner nozzle (4) is less than 1.3 for the inclined burner and less than 0, 8 for the normal type burner  5. Combustion method according to claim 1, characterized in that the deflection direction of the air flow is determined as a function of the relative positions between the burner (4) and the material to be heated so that the flow of The combustion air can not reach directly on the material.  6. Combustion method according to claim 1, characterized in that the fuel is injected with deflection towards the side which is placed opposite the center of gravity of the combustion air flow.  Combustion device with two stages, usable with different furnaces or industrial boilers, characterized in that it is provided, on the outside of a burner plate (1), which is provided with a burner (4) and a primary combustion air inlet passage (2) surrounding said burner, secondary combustion air inlet passages (4), and the opening angle (#) of the zone for injecting air corresponding to said secondary air inlet means is less than 240, with said angle (#) being placed on the axis of the burner plate  8.Dispositif according to claim 7, usable with different furnaces or industrial boilers, characterized in that there is provided, outside a burner plate (1), provided with a burner (3) and a combustion air inlet passage Drimaire (2) surrounding said burner, secondary combustion air inlet passages (4), and in that the opening angle # of the air injection zone of each of said inlet passages primary air and secondary air is less than 240, the top of said angle O being placed on the axis of the burner plate.  Combustion device with a minimum emission of NOx nitrogen oxides, comprising a burner (4) placed inside an air injection body (2) and coaxially pure to that ci, device characterized in Cc that said air injection body (2) is provided with combustion air injection holes (5) placed in a limited area (#) so that the combustion air, after having injected, follows a flow path deflected asymmetrically with respect to said axis, said burner being provided with a filling injection hole (3) which is inclined towards the opposite side to said limited area of said body of air injection