FR2615595A1 - AIR DISTRIBUTION DEVICE FOR SUPPLY AIR BURNER - Google Patents

Abstract

The device is of the type comprising, downstream of a turbine (5) arranged laterally in relation to the burner, a given number of longitudinal slots (30) distributed over a cylindrical surface (29) arranged axially in relation to the burner and a plug (31) capable of being operated in the axial direction in order to close partially said slots with a view to regulating the admission of air, characterised in that the passage cross-section of said slots (30) increases progressively as the distance from the flow of air generated by the turbine (5) increases.

Description

the position of distribution. for air burner souttle The present

  The invention relates to an air distribution device for a blast air burner, of the type comprising, downstream of a turbine disposed laterally with respect to the burner, a certain number of longitudinal tents distributed over a cylindrical surface disposed axially with respect to the burner and a valve capable of being actuated in the axial direction in order to close off

  partially said slots for adjusting the air intake.

  In blast air burners, operating on fuel oil, natural gas, or other fuels, the air-fuel, or more generally oxidant-fuel, mixture is produced in a flame tube comprising a flame holder whose purpose is to rotate an air mass. In addition, the intimate air-fuel mixture must be as homogeneous as possible in order to obtain complete combustion. An excess of air is therefore expected, but for reasons of efficiency, this should be as small as possible. However, to avoid traces of incomplete combustion products, no area of the

  mixture, therefore of the flame, must not be locally lacking air.

  In addition, the combustion air which passes through the flame tube divides

  generally in a so-called primary air flow, rotated by the grip

  flame, which mixes directly with the fuel, and a so-called secondary air flow, passing around the flame holder and which has the function of

  "pinch" the flame and ventilate its perimeter.

  It is therefore obvious that it is very important to obtain a

  homogeneity of the air velocities in the flame tube, in front of the grip

  flame. In addition, a burner is designed to respond to a certain range of power between a maximum power and a minimum power. Consequently, since the quality of combustion must be maintained over the entire power range, it is necessary, once the calorific flow rate has been fixed, to adjust the

air flow at fair value.

  However, the air distribution devices known until now do not ensure, whatever the air flow, a perfectly homogeneous distribution. Generally, there is a decrease in the quality of the mixture when the power decreases and this is particularly noticeable when the fuel used is fuel oil and the power reaches the bottom of

  range of domestic heating powers, approximately 10 to 15 kW.

  The main object of the present invention is therefore to remedy these drawbacks and, to do this, it relates to a dispensing device.

2615 5 9 5

  -2- air of the aforementioned type which is essentially characterized in that the passage section of said slots increases progressively as

  that we are further from the air flow generated by the turbine.

  Thanks to this arrangement, it is possible to equalize the flow rates according to the general direction of the air flow and therefore to obtain a more

  great homogeneity in the flame tube.

  Preferably, the slots have a point-shaped profile and are oriented with respect to the plug so that the point corresponds to the flow rate.

lowest air.

  This gives an almost constant adjustment precision over all

the burner power range.

  In a particular embodiment of the invention, the profile of the slots is designed so that the variation in passage cross section between the different slots varies as a function of the axial position of the plug. Preferably, the variation is practically zero for low air flow rates,

  increasing for medium flows and constant for large flows.

  In fact, for low flow rates, equilibrium takes place automatically, since the pressure drop is significant, while for large flows

  debits, we are mainly looking for the maximum opening.

  An embodiment of the invention is described below by way of example, with reference to the accompanying drawings in which: - Figure 1 is a longitudinal sectional view of an oil burner fitted with a distribution of supply air in accordance with the invention; - Figure 2 is an end view of the cover of the combustion head; - Figure 3 is a sectional view along line III-III of Figure 2; Figure 4 is a view from the inside of the cover of the combustion head; - Figure 5 is a sectional view along the line V-V of Figure 4; and - Figure 6 is a developed view of the slots provided on the cover

of the combustion head.

  The burner shown in FIG. 1 firstly comprises, in a manner known per se, a flame tube or barrel 1 inside which a fuel injector 2 is disposed. The flame tube 1 is fixed on a cylindrical casing 3 into which a sheath 4 opens out laterally equipped with a turbine --3- intended to blow air inside the burner. On the other side, the housing is closed by a cover 6, commonly known as the cover of

combustion head.

  The fuel injector 2 is centered inside the flame tube 1 by means of a sliding sleeve 7 on which are fixed four wings 8 which come to bear on the inner wall of the tube. The injector ends with a nozzle 9 and in front of the nozzle is arranged a flame catcher 10 provided in its center with stamped cutouts 11. The flame catcher is fixed on the front end of the wings 8 and is supported at its periphery on six fins 12 integral with the wall of the flame tube 1. The air blown inside the burner by the turbine 5 is thus divided into a primary flow rotated by the cutouts 11 and a secondary flow which passes around the flame holder 10. The position of the flame holder relative to the nozzle 9 can be adjusted by means of a fixing screw 13 intended to make the sliding sleeve 7

secured to the injector.

  At the rear, the injector is extended by a tube 14 d. Supplied with fuel, for example fuel oil, which passes axially through the cover 6 via an opening 15. An adjustment knob 16, accessible from outside and cooperating with a threaded part of the tube 14, makes it possible to adjust the position of the assembly injector / flame holder inside the flame tube 1. The rotation of this assembly is prevented by a tongue 17, in solidarity with

  tube 14 and engaging in a slot 18 provided on the cover 6.

  On the injector 2 is also provided an electric fuel preheater 19, the power cable 20 of which passes through the cover 6 by

  through an opening 21.

  The ignition of the burner is carried out by means of two electrodes such as 22, each supported by an electrode holder 23 and whose power cable

  high-voltage 24 passes through the cover via an opening 25.

  As can be seen more clearly in Figures 2 and 3, the cover 6 further comprises an inspection eyelet 26 and an opening 27 for the establishment of a photoresist cell 28 for detecting

the presence of the flame.

  Furthermore, the cover 6 is provided on its internal wall with a cylindrical surface 29, disposed axially with respect to the burner and in which a number of longitudinal slots 30 are formed through which the air blown by the turbine 5 gets inside the

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  4- burner. The passage section of these slots 30 is controlled by means of a cylindrical plug 31, placed inside the cylindrical surface 29 and which is capable of moving axially under the action of a system of screws 32 and nut 33. The screw 32 is rotatably mounted in an opening 34 of the cover 6 so as to be accessible from the outside, while the nut 33 is made integral with the plug 31 by means of a tongue 35. In addition, this tongue 35 projects outside through a slit 36 of the cover, thus forming a strip 37 which is advantageously provided with graduations

  to control the position of the plug.

  According to the present invention, the passage section of the different slots 30 is not identical over the entire periphery of the surface 29, but gradually increases as one is further from the air flow generated by the turbine 5. In other words, the slots formed in the cylindrical surface 29 are smaller on the side of the turbine 5 than on the opposite side, this in order to equalize the air flows as a function of the

general direction of flow.

  In the particular embodiment described here and as can be seen more clearly in Figures 4 to 6, six slots 30, delimited by projections 38, have been provided in the cylindrical surface 29. In addition, these slots are distributed in pairs on either side of the axis of symmetry 39 of the flow generated by the turbine. The two smallest slots 301 are located opposite the air flow, the two medium slots 302 are located laterally and

  the two larger slots 303 are located at the rear.

  In reality and as is very clear from FIG. 6, each slot is double due to the presence in the center of a symmetrical triangular tooth with double slope 40. The passage section of the slot thus depends on

  both the total height of the tooth and the height of the slope change.

  Thanks to this arrangement, the variation in passage cross-section, or asymmetry, between the different slots, changes as a function of the axial position of the

bushel 31.

  For low air flows, corresponding to a low burner output, the slots are almost entirely masked. Only the bottom of the slots remains open and this bottom has a pointed shape allowing high precision of adjustment to be obtained. It will also be noted that up to a height h corresponding to the change in slope of the smallest tooth 40, the variation in the passage section between the different slots is practically zero. Indeed, for 2 6 1.s 5 9 5 -5- low flow rates, the pressure drop is significant and the balance is restored

  automatically at the air inlets.

  On the contrary, beyond a height H corresponding to the total height of the largest tooth 40, the variation in cross section between the different slots is constant. Indeed, for large air flows, the

  The most significant pressure drop occurs at the flame holder 10.

  The air flow is sufficient to distribute itself and the objective is then

  to give the largest cross section possible.

  In the median zone between the heights h and H, the asymmetry between the different slits takes all its importance. It gradually increases and thus allows a perfectly homogeneous distribution to be obtained

  air in the flame tube, regardless of the flow rate.

Claims (4)

  1. Air distribution device for blast air burner, of the type comprising, downstream of a turbine (5) disposed laterally with respect to the burner, a certain number of longitudinal slots (30) distributed over a cylindrical surface (29 ) arranged axially with respect to the burner and a plug (31) capable of being actuated in the axial direction in order to partially close said slots for the purpose of adjusting the air intake, characterized in that the passage section of said slots (30) gradually increases as one is further from the air flow generated by the turbine (5).   2. Device according to claim 1, characterized in that the slots (30) have a point-shaped profile and are oriented relative to the plug   so that the tip corresponds to the lowest air flow.   3. Device according to claim 1 or 2, characterized in that the profile of the slots (30) is designed so that the variation in passage section between the different slots varies as a function of the axial position of the bushel (31).   4. Device according to claim 3, characterized in that the variation is practically zero for low air flows, increasing for   average and constant flows for large flows.