Oven for implementing an endothermic process

Abstract

A furnace for implementing an endothermic process comprising: - a combustion chamber (1) delimited by a wall (2), - at least one tubular reactor (3) positioned in the combustion chamber (1), - at least one burner (4b) arranged in the combustion chamber (1) to supply the tubular reactor (3) with the heat necessary for the endothermic process, - the burner (4b) comprising at least one flame discharge nozzle, the nozzle being oriented along an axis (A'; A'') of the nozzle, characterized in that the chamber (1) has, on at least a portion of an internal surface of the wall (2), an internal profile (7) that is convex and curved in a direction of the axis (A'; A'') of the nozzle, the profile being adjacent to said burner (4b). Abbreviated figure: Fig. 5

Description

Title of the invention: Oven for implementing an endothermic process

[0001] The invention relates to the field of furnaces used in endothermic processes such as the cracking of hydrocarbon feedstocks in externally heated reactors, in particular furnaces for the steam reforming of hydrocarbons, primarily methane. The steam reforming process of hydrocarbons is known by its English acronym SMR for "steam methane reforming".

[0002] The SMR process is essentially based on the methane reforming reaction which, in the presence of steam, leads to a mixture consisting mainly of hydrogen and carbon monoxide. The slow, endothermic reaction requires a catalyst and additional heat input. Generally, the performance of the reforming process is limited not by the reaction kinetics but by heat transfer.

[0003] In practice, an SMR reformer comprises tubular reactors (also called reforming tubes or simply tubes) which are placed in a furnace, which contain catalyst - often in the form of pellets or granules - and are fed with a reaction gaseous mixture of methane (CH4) and water vapor.

[0004] The most common configurations for reforming furnaces are of the vertical downward heating type (heating from the top, vault heating or "top fired" in English), vertical upward heating (heating from the base or hearth of the furnace or "bottom fired" in English), lateral heating or lateral terrace heating.

[0005] Vertically heated furnaces (with burners in the roof or hearth) typically consist of a combustion chamber, most often rectangular in shape, lined with a refractory material and containing several rows of tubes. The heat required for reforming is supplied by burners arranged in rows between the tube rows, except for two rows of burners located between a tube row and an internal lateral surface of the furnace parallel to the tube rows. The burner rows adjacent to two tube rows are called inner rows—their burners are called internal burners—each inner burner row heats the tube rows on either side. The burner rows located between a tube row and the internal lateral surface of the furnace—also called the side wall or adjacent wall—heat only one tube row.The burners in these rows – known as external burners – must therefore have a lower heating power than the internal burners.

[0006] The main objective during the design and operation of the furnace is to maximize heat transfer from the burners to the tubes—from the flames, but also from the furnace wall and the hot flue gases—while respecting the maximum operating temperature constraint for each tube. The maximum operating temperature (or, according to its English acronym, "DTT" for "design tube temperature" or "MOT" for "maximum operating temperature") depends on several factors, in particular the mechanical load on the tube (essentially the feed gas pressure), the mechanical properties of the alloys used for the tubes, and the desired service life for these tubes, which are exposed to the risks of flaring and thermal aging.

[0007] Increasing the heat transferred to the tubes has a direct positive impact, increasing productivity and improving furnace compactness, which is beneficial in terms of capital and operating expenses. However, increasing the heat transferred to the tubes typically means increasing the tube temperatures, thus either reducing their lifespan or requiring the use of more resistant, and therefore much more expensive, alloys.

[0008] Uneven heat distribution within the furnace will cause some tubes to be hotter than others; therefore, tube temperature profiles are critical data both during furnace design and operation. Tube temperature profiles—also known as skin temperature (TST) or tube wall temperature (TWT)—provide crucial information for finding a balance between performance and durability; and a good balance is indeed essential.

[0009] During operation, the furnace performance is limited by the temperature of the hottest tube (also known as the maximum tube temperature or MTT); this temperature must not exceed the MTT. At the same time, the process performance, i.e., the productivity or efficiency of reforming, depends on the average heat fluxes transferred to the tubes and their temperatures. This means that the furnace performance is better when the difference between the temperature of the hottest tube (MTT) and the temperature of the coldest tube is small.

[0010] An inherent consequence of the design constraints of the reforming furnace is the lack of homogeneity in heat transfer between the tube rows within the furnace. One particular reason is the difference between the momentum fluxes generated by the discharge of combustion products between the external and internal burner rows. Indeed, the external burners only need to supply the The heat supplied to tubes located on the same side is generated at a lower heating power than the internal burners—which heat twice as many tubes, distributed on either side—generally between 50% and 80% of the internal burners' heating rate. This difference in heating rate, and therefore in mass flow rate, means that the combustion products discharged by the external burners have a lower momentum flux than those from the internal burners. Consequently, the flames of the external burners are deflected towards the center of the furnace, making it difficult to balance the heat output between the rows of tubes.

[0011] All the proposed solutions to the flame deflection problem share the common characteristic of requiring major modifications to the burners or to the burner combustion product distribution manifolds, making them difficult to apply to existing units. In particular, modifications to the burners themselves are difficult to implement, especially for a pre-existing furnace.

[0012] It is therefore desirable to propose, for a pre-existing furnace, a solution which makes it possible to avoid a phenomenon of deviation of a burner flame and thus to control the homogeneity of the heat transfer to the endothermic reaction.

[0013] In particular, it is desirable to have a furnace which ensures a more uniform heat transfer between the multiple rows of reforming tubes, thus allowing for an efficiency gain in the installation and to adjust the amount of heat transferred to the outer row of tubes so that it corresponds to that received by the inner rows of tubes.

[0014] The invention therefore relates to a furnace for implementing an endothermic process comprising: - a combustion chamber delimited by a wall, - at least one tubular reactor positioned in the combustion chamber, - at least one burner arranged in the combustion chamber to supply the tubular reactor with the heat necessary for the endothermic process, - the burner comprising at least one flame discharge nozzle, the nozzle being oriented along an axis of the nozzle, characterized in that the chamber has, on at least part of an internal wall surface, a convex internal profile curved in a direction of the nozzle axis, the profile being adjacent to said burner and opposite the nozzle axis.

[0015] The fluid flow constituting the flame (or jet) in contact with the internal profile will tend to follow the curvature of the profile rather than continuing to move in a straight line. The phenomenon of flame deflection from the external burners towards the middle of the furnace is thus compensated for, and the heat is transferred more uniformly between the tubes.

[0016] The profile is in particular considered in a cross-sectional plane of the chamber coincident with the nozzle axis.

[0017] According to one embodiment: - the nozzle axis is not intersecting with the internal profile, - a distance between a tangent to the internal profile, parallel to the nozzle axis, and the nozzle axis is a distance P, - an internal dimension of the nozzle at the tip of said nozzle, in a direction in which the distance P is measured, is a dimension D, - a P / D ratio being between 0 and 2.

[0018] Preferably, the P / D ratio is between 0 and 1.15. In particular, the distance P between the tangent and the axis of the nozzle is between 0 and 0.6 m.

[0019] According to an alternative embodiment, the axis of the nozzle is secant with the internal profile and the P / D ratio is between 0 and 0.5. Preferably, the P / D ratio is between 0 and 0.25. In particular, the distance P between the tangent and the axis of the nozzle is between 0 and 0.15 m.

[0020] According to one embodiment, from a point on the tangent touching the internal profile, the internal profile extends over a length L along the tangent, the internal profile moving away from the tangent by a distance R, a ratio R / L being less than 1.1; preferably less than or equal to 1, preferably less than or equal to 0.4; preferably less than or equal to 0.3.

[0021] According to one embodiment: - a distance measured along the axis of the nozzle, between the point of the tangent touching the internal profile and a vertex of the nozzle, is a distance H, - a distance I measured along the axis of the nozzle, between a nozzle apex and an internal wall surface furthest from the nozzle apex, is a distance I, - a ratio H / 1 being less than 1 / 2, preferably less than 1 / 3, preferably less than 1 / 4.

[0022] The distance H is in particular less than 6 meters, preferably less than 2.5 meters.

[0023] According to one embodiment: - a plurality of tubular reactors are positioned in the combustion chamber, - A plurality of burners are arranged in the combustion chamber to supply the tubular reactors with the heat necessary for the endothermic process, - Tubular reactors extend longitudinally between a first internal wall surface and a second internal wall surface, opposite the first; - Tubular reactors are arranged in rows and the burners are mounted on at least one of the first and second internal surfaces, so-called internal burners being arranged between two rows of tubular reactors and so-called external burners being arranged between a row of tubular reactors and a lateral internal surface of the wall, the lateral internal surface connecting the first internal surface and the second internal surface, - each of the external burners comprising at least one flame discharge nozzle, the nozzle being oriented along an axis of the nozzle, - the chamber has, on at least part of the internal lateral surface, a convex profile curved in a direction of the axis of the nozzle of each of the external burners, the profile being adjacent to each of said external burners and opposite the axis of the nozzle of each of the external burners.

[0024] According to one embodiment, the internal profile includes a protrusion that extends continuously over the internal lateral surface, the protrusion being adjacent to a plurality of external burners, the protrusion being opposite the axis of the nozzle of each of the external burners among this plurality of external burners.

[0025] According to an alternative embodiment, the internal profile comprises a plurality of protrusions, each of said protrusions being adjacent to an external burner, each of the protrusions being opposite the axis of the nozzle of the external burner to which it is adjacent.

[0026] According to one embodiment, for at least some or all of the external burners: - the nozzle axis is not intersecting with the internal profile, - a distance between a tangent to the internal profile, parallel to the nozzle axis, and the nozzle axis is a distance P, - an internal dimension of the nozzle at the tip of said nozzle, in a direction in which the distance P is measured, is a dimension D, - a P / D ratio being between 0 and 2.

[0027] Preferably, the P / D ratio is between 0 and 1.15. In particular, the distance P between the tangent and the axis of the nozzle is between 0 and 0.6 m.

[0028] According to one embodiment, for at least one part or each of the external burners, the axis of the nozzle is secant with the internal profile and the D / P ratio is between 0 and 0.5. Preferably, the D / P ratio is between 0 and 0.25. In particular, the distance P between the tangent and the axis of the nozzle is between 0 and 0.15 m.

[0029] According to one embodiment, for each of the external burners, from a point on the tangent touching the internal profile, the internal profile extends over a length L along the tangent, the profile moving away from the tangent by a distance R, a ratio R / L being less than 1.1, preferably less than or equal to 1, preferably less than or equal to 0.4, preferably less than or equal to 0.3.

[0030] According to one embodiment, for each of the external burners: - the external burners are mounted on the first surface, - a distance measured along the axis of the nozzle of each of the external burners, between the point of tangency touching the internal profile and a nozzle apex, is a distance H, - a distance measured along the axis of the nozzle of each of the external burners, between a nozzle apex and the second surface, is a distance I, - a ratio H / 1 being less than 1 / 2, preferably less than 1 / 3, preferably less than 1 / 4.

[0031] The distance H is in particular less than 6 meters, preferably less than 2.5 meters.

[0032] According to one embodiment, the external burners are configured to operate at a power between 45 and 55% of that of the internal burners.

[0033] The invention also relates to a method for modifying a furnace to implement an endothermic process, the furnace comprising: - a combustion chamber delimited by a wall, - at least one tubular reactor positioned in the combustion chamber, - at least one burner arranged in the combustion chamber to supply the tubular reactor with the heat necessary for the endothermic process, - the burner comprising at least one flame discharge nozzle, the nozzle being oriented along an axis of the nozzle, the method comprising a step of modifying a profile of at least a part of an internal wall surface such that the profile is convex and curved in a direction of the nozzle axis, the profile being adjacent to said burner and opposite the nozzle axis.

[0034] The [Fig. 1] represents the configuration of a furnace to implement an endothermic process according to the state of the art; Fig. 2 is a view of one of the burners of a furnace in a prior art configuration; Fig. 3 is a view of one of the burners of a furnace in a configuration according to the invention; Fig. 4 is a view of one of the furnace burners according to the invention in an alternative dimensioning to that of Fig. 3; [Fig.5] is an enlarged view of [Fig.4].

[0035] A furnace according to the prior art for implementing an endothermic process is schematically represented in [Fig.1].

[0036] The furnace includes a combustion chamber 1 (or firebox). The combustion chamber 1 is delimited by a wall 2. From the point of view of the interior of the combustion chamber 1, there is at least one internal surface 5A; 5B; 6 which delimits the internal space of combustion chamber 1.

[0037] Tubular reactors or tubes 3 are arranged in the combustion chamber 1 and extend longitudinally between a first internal surface 5A of the wall 2 and a second internal surface 5B of the wall 2, opposite the first internal surface 5A. In the embodiments shown, the tubular reactors 3 extend vertically (along a vertical axis). The tubes 3 are designed to carry out an endothermic reaction and contain a catalyst for converting a feed gas.

[0038] Burners 4a and 4b are arranged to supply the tubular reactors 3 with the heat required for the endothermic reaction. The burners 4a and 4b comprise a nozzle oriented along a longitudinal axis, which may or may not be the vertical axis. The nozzle is configured to project the combustion gases into the combustion chamber 1 in the direction of the longitudinal axis. The nozzles of the burners 4a and 4b may be oriented along different axes or directions relative to each other.

[0039] In the embodiment of [Fig. 1], the furnace is a vertically heated furnace, and the burners 4a and 4b are mounted in the hearth of the combustion chamber 1 (i.e., the lower internal surface 5A, which forms the floor of the combustion chamber 1). This is referred to as bottom-fired or up-fired vertical heating. In this embodiment, the combustion chamber 1 has a rectangular parallelepiped shape. However, the invention also covers configurations in which the burners are mounted in the roof of the combustion chamber 1 (i.e., the upper internal surface 5B, which forms the ceiling of the combustion chamber 1). This is referred to as top-fired or down-fired heating.

[0040] Internal burners 4a are arranged between two rows of tubes 3. In other words, rows of tubes 3 are arranged on either side of an internal burner 4a. External burners 4b are arranged between a row of tubes 3 and an internal lateral surface 6 of the chamber, connecting the vault to the floor of the chamber. In other words, the internal lateral surface 6 is arranged on one side of an external burner 4b and a row of tubes 3 is arranged on the other side of said external burner 4b.

[0041] For the sake of simplicity, in Figures 2, 3, 4, and 5, the flame of a single external burner 4b is shown in a prior art configuration in [Fig. 2] and according to the invention in the following figures. These views correspond to the area delimited by dashed lines in [Fig. 1], encompassing half of the combustion chamber from the axis of symmetry S. In these embodiments, the burners 4a and 4b are mounted in the hearth.

[0042] The external burners 4b heat only one row of tubes 3 instead of two like the internal burners 4a. The external burners 4b are therefore typically configured to operate at a power between 45 and 55% of that of the internal burners 4a.

[0043] The burner 4b includes a discharge nozzle for a flame emitted by the burner 4b. The nozzle is oriented along an axis represented by line A in [Fig. 2], by line A' in [Fig. 3], and by line A” in Figures 4 and 5. The axis along which a nozzle is oriented passes through the center of said nozzle. In the prior art configuration, a phenomenon of flame deflection towards the middle of the furnace occurs. It is indeed visible in [Fig. 2] that the upper part of the flame deviates from the axis A of the nozzle.

[0044] In the configuration shown in Figures 3, 4, and 5, the chamber has, on an internal lateral surface 6 connecting the roof and the base, a convex internal profile 7. The profile 7 is curved in a direction relative to the axis of the nozzle. The internal profile 7 is adjacent to the external burner and opposite the axis A'; A” of the nozzle of each of the external burners 4b. The internal space of the chamber 1, as delimited by the wall 2, is thus convexly profiled from the point of view of the interior of the chamber and curved on a portion of an internal surface of the wall 2. The profile 7 is considered in a cross-sectional plane of the chamber 1 coinciding with the axis A'; A” of the nozzle, the plane being orthogonal to the internal surface of the wall 2, on an internal surface of the wall 2 (here the internal lateral surface 6), the internal surface being profiled.

[0045] The internal profile 7 includes, for example, at least one protrusion which extends continuously over the internal lateral surface 6, the protrusion being adjacent to a plurality of the external burners 4b (see all external burners 4b), the protrusion being opposite the axis A'; A” of the nozzle of each of the external burners 4b among this plurality of external burners 4b.

[0046] In an alternative embodiment, the internal profile 7 comprises a plurality of protrusions, each of said protrusions being adjacent to one of the external burners 4b, each of the protrusions being opposite the axis A'; A” of the nozzle of the external burner 4b to which it is adjacent.

[0047] By "convex profile", it is understood that a segment connecting any two points of a surface of the profile 7 (the profiled surface) extends exclusively outside the interior space of the combustion chamber 1. The profile is therefore convex from the point of view of the combustion chamber 1 or bulging towards the interior of the chamber 1.

[0048] By "profile adjacent to at least one burner(s)", it should be understood that the burner(s) 4b are in the immediate vicinity of the profile 7, such that no element of the furnace extends or obstructs the flame emitted by said burner 4b and the profile. In other words, the axis of the nozzle is directly opposite the profiled surface. The profile is positioned directly opposite the external burners in the configuration shown in Figures 3 and 4.

[0049] It is possible to define in [Fig. 3] a tangent T' to the profiled surface, tangent T' which is parallel to the axis A' of the nozzle. In a configuration in which the nozzle is oriented vertically and the combustion chamber 1 has a rectangular parallelepiped shape, the tangent is parallel to the internal lateral surface 6. The internal profile 7 has a non-zero curvature with respect to the tangent T', which serves as the reference for the curvature. The tangent T' touches the profiled surface at a point B', without crossing said surface. The profiled surface and the tangent T' thus form a zero angle at point B'. When traversing the profiled surface in the direction of the axis A', the profiled surface moves locally away from the tangent T' (and from the axis A'), which characterizes the curvature in the direction of the axis A'. The curvature is considered on a projection of the axis A' or the tangent T' onto the profiled surface, a projection which forms an arc on the profiled surface.A curved surface is a surface whose tangent changes direction as the surface is traversed, without the surface forming any stops along the path in question.

[0050] The internal profile 7 is arranged adjacent to the external burners 4b so that the flame emitted by an external burner 4b licks the profiled surface: there is a jet line of the flame that reaches the profiled surface tangentially and flows directly along the profile 7. The fluid flow constituting the flame (or jet) in contact with the profile 7 will tend to follow the curvature of the profile 7 (Coanda effect) rather than continuing to move in a straight line or being deflected towards the middle of the furnace as in the prior art. The phenomenon of deflection of the flames from the external burners towards the middle of the furnace is thus compensated for and the heat is transferred more uniformly between the tubes 3.

[0051] A curvature of the internal profile 7 extends from point B' over a length L along the tangent. The length is measured along the tangent T', between point B' and, for example, a point where the profile 7 forms an edge, i.e., ceases to be curved, or to a limit of the convex internal profile 7 (at a point where the internal surface ceases to be convex). Along the considered curvature of the profile 7, it deviates from the tangent T' by a distance R. The distance R thus considered corresponds to the maximum distance of the profile 7 from the tangent T' along its curvature. The distance is measured along a direction perpendicular to the tangent T' and to the axis A'. [Fig. 3] shows an embodiment of the invention in which the ratio of R / L is equal to 0.37.

[0052] Fig. 3 shows a furnace configuration in which the burner 4b and the internal profile 7 are arranged relative to each other in the combustion chamber 1 such that the axis A' of the nozzle does not cut or pass through the profiled surface. We then say that axis A' does not intersect the internal profile 7 (in other words, axis A' does not cross the profiled surface). A distance P between tangent T' and axis A' is, in the embodiments of [Fig. 3], equal to zero. In other words, tangent T' and axis A' coincide. We can define an internal dimension D of the nozzle in the direction in which the distance P is measured. Dimension D is considered at the nozzle tip. The nozzle defines an internal channel for the circulation and projection of combustion gases, and D corresponds to a maximum internal dimension of the nozzle, in the considered direction, within this channel and at the nozzle tip. D serves as the reference dimension. When the nozzle is circular, dimension D corresponds to a diameter of the nozzle.

[0053] The description in the preceding paragraphs applies by analogy to the embodiment shown in Figures 4 and 5, with a tangent T” parallel to axis A” and a point B” where the tangent T’ touches the profiled surface. In this embodiment, the ratio R / L is 0.22. Figure 5 is a zoom of Figure 4 on the area of ​​profile 7 where the dimensions are more visible. Furthermore, a distance P between the tangent T” and axis A” is non-zero and approximately equal to dimension D (P / D = 1). In particular, the distance P is approximately 0.6 meters, and dimension D is also approximately 0.6 meters.

[0054] In the embodiment of [Fig.3], the burner 4b and the profile 7 are arranged relative to each other in such a way that the profile 7 is partly vertical with respect to the burner 4b, some jet lines of a flame emitted by the burner 4b being able to impact the profile 7 in a non-tangential manner.

[0055] In another, unshown arrangement of the burner 4b and the profile 7, the axis A' intersects the profile 7. That is to say, the axis A' cuts or crosses the profiled surface at two points due to the convexity of the profile 7. A P / D ratio is notably between 0 and 0.5. The distance P is notably between 0 and 0.15 meters. Since the emitted flame is typically wider than the nozzle in its dimension D, the profile 7 can thus be positioned directly above the nozzle over most, if not all, of dimension D.

[0056] The distances referred to between the tangent T'; T” ​​and the axis A'; A” in the frame in the invention are expressed in absolute value.

[0057] Preferably, a distance H measured along a direction of the A'; A” axis of the nozzle, between point B'; B” and a nozzle apex, corresponds to less than half of a distance I measured along the direction of the A'; A” axis of the nozzle, between a nozzle apex and the furnace dome, preferably less than one-third of the distance I, preferably less than one-quarter of the distance I, preferably less than one-eighth of the distance I. In other words, point B'; B” is at a height H relative to the nozzle apex. The distance H is, in particular, less than or equal to 6 meters. The distance H measured along the A'; A” axis therefore corresponds to the distance between the projected from point B onto axis A'; A” and the top of the nozzle.

[0058] Point B'; B” is for example located at a height H approximately equal to 6 meters relative to burners 4b and the distance I is approximately equal to 24 meters.

[0059] The configuration according to the invention, shown here for a single external burner 4b, can be extrapolated to a plurality of external burners 4b of the furnace, or even to all external burners 4b.

[0060] The endothermic process is, for example, a reforming process, and the tubular reactors 3 are reforming tubes. The furnace in this case is a reforming furnace, also called a reformer. A steam reforming process of methane can be cited as an example.

[0061] The invention also relates to a method of redesigning (“revamping” in English) a furnace according to the prior art, the method comprising a step of modifying an internal profile 7 of at least a part of an internal surface 6 of the wall 2 such that the profile 7 is convex and curved in a direction of the axis A'; A” of the nozzle of at least one external burner, the profile 7 being adjacent to said external burner 4b and opposite the axis A'; A”.

[0062] The invention thus proposes a flexible solution for adapting an existing oven in order to combat a phenomenon of flame deviation from a burner, a solution which does not require modifying the burner itself.

Claims

Demands

1. Furnace for implementing an endothermic process comprising: - a combustion chamber (1) delimited by a wall (2), - at least one tubular reactor (3) positioned in the combustion chamber (1), - at least one burner (4b) arranged in the combustion chamber (1) to supply the tubular reactor (3) with the heat required for the endothermic process, - the burner (4b) comprising at least one flame discharge nozzle, the nozzle being oriented along a longitudinal axis (A'; A”) of the nozzle, the nozzle being configured to project the combustion gases into the combustion chamber 1 in the direction of the longitudinal axis (A'; A”), characterized in that the chamber (1) has, on at least a part of an internal surface of the wall (2), an internal profile (7) convex and curved in a direction of the axis (A'; A”) of the nozzle, the profile being adjacent to said burner (4b) and opposite the axis (A'; A”).

2. Oven according to the preceding claim, wherein: - the axis (A' ; A”) of the nozzle is not secant with the internal profile (7), - a distance between a tangent (T' ; T”) to the internal profile (7), parallel to the axis (A' ; A”) of the nozzle, and the axis (A' ; A”) of the nozzle is a distance P, - an internal dimension of the nozzle at the tip of said nozzle, in a direction in which the distance P is measured, is a dimension D, - and a ratio P / D is between 0 and 2, preferably between 0 and 1.

15.

3. Oven according to claim 1, wherein: - the axis (A' ; A”) of the nozzle is secant with the internal profile (7), - a distance between a tangent (T' ; T”) to the internal profile (7), parallel to the axis (A' ; A”) of the nozzle, and the axis (A' ; A”) of the nozzle is a distance P, - a dimension of the nozzle at the tip of said nozzle, in a direction in which the distance P is measured is a dimension D, - and a ratio P / D is between 0 and 0.5, preferably between 0 and 0.

25.

4. Oven according to any one of the preceding claims, wherein: - a distance measured along the axis (A'; A") of the nozzle, between the the point of the tangent (T' ; T”) touching the internal profile (7) and a nozzle vertex, is a distance H, - a distance I measured along the axis (A' ; A”) of the nozzle, between a nozzle apex and an internal surface of the wall (2) furthest from the nozzle apex, is a distance I, - an H / I ratio being less than 1 / 2, preferably less than 1 / 3, preferably less than 1 / 4.

5. Oven according to any one of the preceding claims, wherein: - a plurality of tubular reactors (3) are positioned in the combustion chamber (1), - a plurality of burners (4a; 4b) are arranged in the combustion chamber (1) to supply the tubular reactors (3) with the heat necessary for the endothermic process, - the tubular reactors (3) extend longitudinally between a first internal surface (5A) of the wall (2) and a second internal surface (5B) of the wall (2), opposite the first, - the tubular reactors (3) are arranged in rows and the burners (4a; 4b) are mounted on at least one of the first and second internal surfaces (5A; 5B), the so-called internal burners (4a) being arranged between two rows of tubular reactors (3) and the so-called external burners (4b) being arranged between a row of tubular reactors (3) and a lateral internal surface (6) of the wall (2), the lateral internal surface (6) connecting the first internal surface (5A) and the second internal surface (5B), - each of the external burners (4b) comprising at least one flame discharge nozzle, the nozzle being oriented along an axis (A' ; A”) of the nozzle, - the chamber (1) has, on at least a part of the internal lateral surface (6), an internal profile (7) convex and curved in a direction of the axis (A' ; A”) of the nozzle of each of the external burners (4b), the profile being adjacent to each of said external burners (4b) and opposite the axis (A' ; A”) of the nozzle of each of the external burners (4b).

6. A method for modifying a furnace to implement an endothermic process, the furnace comprising: - a combustion chamber (1) delimited by a wall (2), - at least one tubular reactor (3) positioned in the combustion chamber (1), - at least one burner (4b) arranged in the combustion chamber (1) to supply the tubular reactor (3) with the heat necessary for the endothermic process, - the burner (3) comprising at least one flame discharge nozzle, the nozzle being oriented along an axis (A' ; A”) of the nozzle, the method comprising a step of modifying an internal profile (7) of at least a part of an internal surface of the wall (2) such that the profile (7) is convex and curved in a direction of the axis (A' ; A”) of the nozzle, the profile (7) being adjacent to said burner (4b) and opposite the axis (A' ; A”).