EP0180098B1 - Combustion chamber - Google Patents

Description

The invention relates to a combustion chamber, in particular for use in connection with high-speed burners.

Such combustion chambers are mainly used in heat treatment, heating and annealing furnaces in the mechanical engineering industry and in the iron and metal industry.

The ceramic combustion chambers used primarily in high-speed burners have only a limited service life due to the high operating temperatures and the strong heat exchange, particularly in the case of pulse-controlled burners, and therefore have to be replaced accordingly frequently. Replacing the combustion chamber requires long downtimes and high repair costs.

To reduce the material and repair costs, it is known to provide the burner chamber with a nozzle insert designed as a hollow body, which is fastened in the burner housing and encloses the nozzle opening. The insert is preferably made of a more heat-resistant material than the other parts of the combustion chamber.

A combustion chamber known from US Pat. No. 3,320,999 consists of a housing and a hollow insert made of ceramic material, which are arranged in a metal housing. The hollow insert is permanently installed in the burner housing together with the combustion chamber housing. To replace the insert, the entire burner with the combustion chamber must be removed from the system. This leads to long downtimes and correspondingly high repair costs. Due to the fixed installation of the ceramic combustion chamber in the metal housing, there is a risk that the combustion chamber will be mechanically overloaded and break at high temperatures due to thermal expansion of the chamber.

From GB-PS-2 069 683 a burner chamber with a housing made of refractory stone with an axial tunnel is known, which tapers towards the entrance and is widened in the central section. An insert is installed at the outlet end, which forms a tapered outlet nozzle. The insert is aligned with the tunnel axis and connected to the tunnel housing by fire-resistant material. During operation of this known combustion chamber, the connection between the insert and the housing can come loose under the action of high temperatures and as a result of heat exchange. The consequence of this is that the insert is pushed out of its use position following the tunnel in the event of overpressure in the combustion chamber and / or due to vibrations of the system and falls out. This deficiency has been observed repeatedly in burners whose combustion chambers have inserts aligned symmetrically with the housing axis. The risk of the insert being ejected is increased when the burner is operated in a pulse-controlled manner (the burner is switched on and off in pulses). The ejection of the insert from the tunnel of the combustion chamber not only leads to long downtimes of the furnace and high repair costs for the combustion chamber, but also to interruptions in the heat treatment of the annealing material with the corresponding consequential damage.

The invention is therefore based on the object of equipping a combustion chamber with an insert such that the insert is reliably fixed in the combustion chamber housing and can nevertheless be replaced quickly and inexpensively.

Starting from a combustion chamber with a housing defining an axial tunnel and an insert held in the housing and designed as a hollow body, which surrounds a nozzle opening which is adjacent to the tunnel and is coaxial to the housing axis and is delimited by end faces perpendicular to the housing axis, the invention provides for the solution of this task that the insert is aligned on a longitudinal axis which is inclined to the two end faces and inclined at an acute angle to the housing axis.

The design of the combustion chamber according to the invention ensures that the insert is securely anchored in the housing. The insert is held wedged by gravity on the one hand and by operating tilting moments on the other in the seat in the housing. It is not absolutely necessary to use a fire-resistant fixing agent to fasten the insert in the housing. Therefore, the insert in the combustion camera according to the invention can be exchanged particularly easily. As a result, the invention achieves a longer operating time of the combustion chamber, a reduction in operating costs and an increase in the performance of the system due to shorter downtimes when repairing or replacing the combustion chamber.

According to a preferred development of the invention it is provided that the insert is arranged in the housing such that its longitudinal axis intersects the housing axis at a point which is spaced from the inner end face of the insert against the flow direction of the combustion products. This leads to an increase in the tilting moment by which the insert is held in its seat in the housing. Even with small angles of inclination of the axis of the insert in relation to the housing axis, the tilting moment is sufficient to reliably fix the insert in the burner housing. As a result, the dimensions and the use of materials in the combustion chamber can also be reduced.

The insert is preferably arranged in the housing in such a way that its axis extends at an acute angle between 3 and 30 ° to the axis of the housing. Within this angular range, a secure attachment of the insert in the housing with reasonable housing dimensions is guaranteed.

The intersection of the axis of the insert and the housing should preferably be shifted relative to the inner face by an amount whose ratio to the maximum diameter of the inner face of the insert is in the range from 1.9 to 0.17. This also ensures better anchoring of the insert by a favorable ratio between the dimensions of the insert and those of the housing of the combustion chamber.

The insert can also be arranged in the housing so that the intersection of its axis with that of the housing lies in the plane of the inner end face of the insert.

• Fig. 1 einen schematischen Längsschnitt durch eine Brennkammer gemäß der Erfindung;
• Fig. 2 einen Schnitt entlang der Linie 11-11 in Fig. 1:
• Fig. 3 einen Schnitt entlang der Linie III―III in Fig. 1;
• Fig. 4 einen Längsschnitt durch ein Ausführungsbeispiel eines Einsatzstückes; und
• Fig. 5 einen Längsschnitt durch ein abgewandeltes Ausführungsbeispiel eines Einsatzstücks mit Darstellung der auf das Einsatzstück im Betrieb einwirkenden Drücke und Kräfte.

The invention is explained in more detail below on the basis of exemplary embodiments shown schematically in the drawing. The drawing shows:

• Figure 1 is a schematic longitudinal section through a combustion chamber according to the invention.
• 2 shows a section along the line 11-11 in Fig. 1:
• 3 shows a section along the line III ― III in Fig. 1.
• 4 shows a longitudinal section through an embodiment of an insert; and
• Fig. 5 is a longitudinal section through a modified embodiment of an insert showing the pressures and forces acting on the insert during operation.

In Figure 1, the combustion chamber 1 is shown in longitudinal section with a housing 2 in which an axial tunnel 3 runs. In an end section of the housing 2 there is an insert 4 designed as a hollow body with a nozzle opening 5 which is arranged coaxially to the longitudinal axis 11 of the housing 2. The insert 4 has an essentially cylindrical lateral surface (section III ― III according to FIG. 3), the cylinder axis 14 of which is inclined at an acute angle against the housing axis 11. An inner end face 6 and an outer end face 7 of the insert 4 lie in planes running perpendicular to the housing axis 11; the end faces 6 and 7 therefore have an elliptical shape (section 11-11 according to FIG. 2) and run obliquely to the longitudinal axis of the insert. In the illustration according to FIG. 1, the insert 4 is installed in the housing 2 such that its axis 14 intersects the housing axis 11 approximately in the plane of the inner end face 6 (upstream of the combustion products) of the insert at an acute angle a.

In a modified embodiment shown in FIG. 4, the axis 14 of the insert 4 is shifted upward by a dimension "e", the intersection of the axis 14 of the insert 4 with the axis 11 of the housing 2 against the flow direction of the combustion products relative to the end face 6 is moved. As can be seen from FIG. 4, the material mass of the insert above the nozzle opening 5, which is coaxial with the housing axis 11, is thereby substantially larger than the material mass below the nozzle opening 5.

When the burner is operating, an overpressure arises in the interior of the combustion chamber. If the adhesive connection between the housing 2 (FIG. 1) and the insert 4 is missing or is lost, the pressures and forces shown in FIG. 5 act on the insert. P denotes the pressure in the combustion chamber and P ₂ the pressure in the system. Because of the asymmetrical shape of the insert 4, the pressure front acting on the insert causes a tilting moment M = Pa; where P is an equivalent pressure force and a is the force arm of the force P. In addition, an axial force P ₃ acts on the insert 4 in the direction of the longitudinal axis 11 of the combustion chamber 1. This force can be applied to the force component P ₄ acting along the inclined axis 14 of the insert ₄ and be divided into the force component P ₅ directed at right angles, the latter pressing the insert 4 against the housing 2.

The tilting moment M presses the insert 4 against the complementary seat in the housing 2 and is effective in the clockwise direction. In addition, the force component P ₅ counteracts slipping of the insert 4 out of the housing 2. If it slipped out of the housing seat, the insert 4 would have to perform an upward movement, so that gravity would have to be overcome in addition to the frictional force.

• D = große Achse der elliptischen Stirnfläche des Einsatzstücks 4
• d, = Durchmesser des Tunnels 3
• d₂ = Austrittsdurchmesser der Düsenöffnung 5
• 1 = Länge des Einsatzstücks 4

The maximum angle of inclination a _{max of} the insert 4 to the combustion chamber axis 11 can be determined geometrically by the intersection of the lower surface line of the insert 4 with its outer end face 7 at point C (FIG. 1). With the practically permissible ratios D / d _i = 1.4 to 1.5; d ₂ / d _j = 0.45 to 0.55; and 1 / d ₂ = 1.2 to 1.3, the maximum angle of inclination a _max = 27 to 30 °. Here mean:

• D = major axis of the elliptical end face of the insert 4
• d, = diameter of the tunnel 3
• d ₂ = outlet diameter of the nozzle opening 5
• 1 = length of insert 4

When choosing the angle of inclination a of the axis 14 of the insert 4 to the axis 11 of the combustion chamber 1, the following must be taken into account: the smaller the angle a, the smaller the tilting moment M and the stroke movement of the insert 4 when moving. The hold of the insert in the seat opening of the housing 2 is correspondingly smaller. On the other hand, if the angle α is larger, the hold of the insert 4 in the seat opening is also larger. However, in this case the material thickness of the housing 2 must be increased to maintain the permissible dimensions L, and L ₂ , so that the housing 2 cannot tear open at the thinnest points. When the angle of inclination is increased, the stress in the acute-angled transition region B of the housing 2 also increases. In addition, difficulties arise in the shaping of the insert 4 when the angle a is increased. Studies have shown that a sufficiently favorable effect on one Angle a = 3 ° is guaranteed. An optimal effect is achieved in an angle range of a between 5 and 15 °.

As can be seen from FIG. 4, the axis 14 of the insert 4 can be shifted to the tunnel axis 11 by the size e / D: -5 (1-d, / D): 2. Here e = displacement of the axis of the insert 4 upwards. However, at an extreme value of e / D, the thickness of the wall of the insert 4 in the lower part becomes almost zero. Therefore, this value should be considered as a limit. In practice, with the ratio D / d _i : 5 1.4 to 1.5, the limit value for the shift e / d = 0.15. However, in order to be able to adhere to the permissible minimum thickness of 20 to 25 mm of the wall of the lower part of the insert 4, the ratio e / D ≤ 0.1. At an angle of inclination a = 3 to 30 °, the displacement b extends against the flow of the combustion products to the longer axis D of the insert 4: b / D = 1 / D. ctg a = 1.9 to 0.17. The optimal result can be achieved by a longitudinal displacement b at an angle of inclination a = 5 to 15 ° and b / D = 1.14 to 0.37.

Due to the asymmetrical shape of the insert 4, an additional tilting moment is created by moving the insert axis 14 upward, which fixes the insert in the seat opening of the housing during operation of the burner. Therefore, if one simultaneously tilts and shifts the axis 14 of the insert piece, one can achieve the result corresponding to the description above with smaller tilting and shifting angles.

As shown in FIGS. 2 and 3, the insert 4 and the complementary seat in the housing 2 are flattened on one side in order to prevent the insert 4 from rotating about its axis 14.

Claims (5)

1. A combustion chamber, particularly for use with high-velocity burners comprising a body bounding an axial tunnel and an insert held by said body, of the type of a hollow body with a substantially cylindrical surface, said insert surrounding a nozzle port coaxial with the body centerline adjoining said tunnel and being limited by faces intersecting said body centerline at right angles characterized in that said insert (4) is centered on a longitudinal axis (14) which is inclined with respect to said two faces (6, 7) and intersects said body centerline (11) at an acute angle (a).

2. A combustion chamber according to claim 1 characterized in that said insert (4) is arranged inside said body (2) so that its longitudinal axis (14) intersects said body centerline (11) at a point spaced relative to the plane of the inner face (6) in the direction opposite to the direction of combustion product flow.

3. A combustion chamber according to claim 2 characterized in that the point of intersection of said axis (14) of said insert (4) and said centerline (11) of said body (2) is displaced with respect to said inner face (6) by a distance (b), the ratio of said distance (b) and the maximum diameter (D) of said inner face (6) of said insert (4) being in the range between 1.9 and 0.17.

4. A combustion chamber according to claim 1 characterized in that said insert (4) is arranged inside said body (2) so that the point of intersection of its axis (14) and the centerline (11) of said body (2) is situated in the plane of said inner face (6) of said insert (4).

5. A combustion chamber according to any one of claims 1 through 4 characterized in that said insert (4) is arranged inside said body (2) so that its axis (14) and the centerline (11) of said body (2) enclose an acute angle (a) between 3° and 30°.

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