EP0117201A1 - Electric resistance heater for heating a gaseous mixture - Google Patents

Abstract

The electric heater allows a gas mixture to be heated to temperatures and pressures up to 900 ° C and 60 bar, respectively. This device comprises a central duct (5) which connects the inlet (3) and the outlet (4) of the gas mixture and is constituted by several superimposed and removable modules (6a, .. 61) each comprising several electrically resistant elements constituted by metal strips arranged one beside the other, a peripheral zone (8) containing the electrical supply conductors of the resistive elements, passages made between the central duct (5) and the peripheral zone (8) to allow a proportion reduced gas flow from passing into the peripheral area. Use in particular for heating gas mixtures comprising hydrocarbons.

Description

The present invention relates to an electric heating device by direct Joule effect, of high power, for heating a gas mixture at temperatures and pressures which can reach respectively 900 ° C. and 50 bars.

• . le reformage du naphta en présence d'un catalyseur à base de platine pour l'obtention des essences;
• . la désulfuration des hydrocarbures par l'hydrogène.

The invention relates in particular, but not limitatively, to an electric heating device intended to equip the following installations:

• . reforming naphtha in the presence of a platinum-based catalyst to obtain gasolines;
• . desulfurization of hydrocarbons with hydrogen.

In such heating installations, it is sought to replace traditional ovens consuming a fuel of fossil origin, by electric ovens having a markedly improved thermal efficiency and allowing much easier and precise temperature regulation.

Several types of electric ovens are known.

These electric ovens are generally of limited power, significantly lower than the power required (of the order of 10 MW) in the installations mentioned above.

Furthermore, known electric ovens generally include sheathed electrical resistors.

These sheathed electrical resistors limit the power dissipated per unit area. Thus, if the power of such an oven were brought to a value of the order of 10 MW, its size would be prohibitive, all the more so since the electrical resistances, the cross section of which is greatly increased by the insulator, must be arranged at sufficient distances so as not to cause an excessive pressure drop during the passage of the gas stream to be heated.

In addition, these electrical resistors are difficult to use for heating at high temperatures up to 900 ° C.

Electric ovens are also known comprising electrical resistances embedded in a fluidized bed of particles. Nor can such ovens be used in applications where it is necessary to heat a gas at high temperature and under high pressure, because of the risks of entrainment of the particles of the fluidized bed and of reaction between these and the gas.

Furthermore, the production of an electric furnace for heating a gas at high temperature and pressure such as a mixture of hydrocarbons and hydrogen, poses numerous problems of sealing, thermal expansion, sealed passage for the conductors. resistance, thermal resistance and corrosion, which have not found a satisfactory solution so far.

The object of the present invention is to remedy the shortcomings of known electric ovens, by creating a high power electric heating device capable of heating gas mixtures, such as a mixture of hydrocarbons and hydrogen at temperatures and pressures. can reach respectively 900 ° C and 60 bars, this device having an excellent thermal efficiency, a relatively small size and causing during the passage of the gas mixture a very reduced pressure drop.

The heating device targeted by the invention comprises an enclosure comprising an inlet and an outlet for the gaseous mixture and which contains bare electrical resistors and the electrical supply conductors of these resistors.

According to the invention, this device is characterized in that it comprises a central duct which connects the inlet and the outlet of the gas mixture, consisting of several superimposed modules, removable and independent of each other, each comprising several electrically resistant elements constituted by sheets of metal strips arranged one next to the other, a peripheral zone containing the electrical supply conductors of the modules which contain the resistive elements, passages being provided between the central duct and the peripheral zone allowing a reduced proportion of the gas flow to pass into the peripheral zone.

During the operation of the heating device according to the invention, the gas flow passes through the central duct formed by several removable and superimposed modules. All of these modules can expand freely independently of the connections and the external envelope without causing harmful constraints.

The fact that the electrical resistors are lamellae placed one beside the other, makes it possible to obtain a large dissipated power per unit of resistance area and consequently a relatively small size. In addition, these strip resistances which offer practically no resistance with respect to the gas flow, make it possible to obtain a very reduced pressure drop.

In addition, the supply conductors electric resistors which are arranged in the peripheral zone are cooled by a small part of the gas flow which enters the enclosure of the device, so that the problem of the thermal behavior of these conductors is effectively resolved.

In addition, since the modules are removable, it is possible to replace a defective element without interfering with the other elements.

In addition, this principle makes it possible to adapt the power required for each oven by varying the number of stacked modules, only the length of the external envelope being modified.

On the other hand, these modules supplied separately by regulated electrical sources make it possible to obtain a temperature profile, between the input and the output of the device, perfectly adapted to the optimal conditions desired.

According to an advantageous version of the invention, the enclosure comprises in the lower part a bottom bowl comprising an inlet pipe of the gas mixture on which is removably mounted a thermally insulated vertical ferrule constituting the envelope and carrying at its upper part an outlet pipe for the gas mixture. The modules comprising the electrical resistors are arranged one above the other along the axis of the shell and are supported by the bottom cup, being free relative to the side wall and the upper wall of the shell. The bottom bowl has in its wall passages for the arrivals of the electrical supply conductors of the resistant elements.

Furthermore, the watertight junction between this ferrule and the rest of the device is limited to a simple seal between the latter and the bottom bowl, which limits the risk of leaks caused by the high pressure of the gas passing inside the device.

According to a preferred version of the invention, the modules consist of parallelepipedal sheet metal boxes, closed laterally, removably fixed on the general internal framework (framework), one above the other, in the extension of their faces. lateral, each box containing several layers of resistant sheet metal lamellae arranged parallel to each other, the faces of these lamellae being parallel to the axis of the shell. The resistant strips are preferably made of expanded metal sheet.

The realization of these modules is both simple and leads to a minimal space requirement. The use of expanded metal strips makes it possible to obtain an ohmic value per unit of high surface area, with a good temperature distribution due to the fact of the turbulence caused by the offset of the strips of expanded metal.

Preferably, the electrical supply conductors of the modules are metal tubes rising parallel to the axis of the ferrule in the peripheral zone, these tubes being connected by flexible metal braids to the resistant elements of the modules.

Thus the electrical conductors, while being cooled in the peripheral zone, can expand freely without repercussion of constraints on the connection pads of the resistors.

Other features and advantages of the invention will appear in the description below.

• . la figure 1 est une vue en élévation avec arrachements d'un dispositif de chauffage électrique conforme à l'invention;
• . la figure 2 est une vue en plan à plus grande échelle avec arrachement du dessus du dispositif;
• . la figure 3 est une vue en groupe à plus grande échelle suivant le plan III-III de la figure 1;
• . la figure 4 est une vue en coupe à plus grande échelle suivant le plan de jonction entre cuvette et virole;
• . la figure 5 est une vue en coupe longitu- di-nale' à plus grande échelle du détail V de la figure 1;
• . la figure 6 est une vue en coupe longitudinale à grande échelle du détail VI de la figure 1;
• . la figure 7 est une vue partielle d'une lame résistante du dispositif;
• . la figure 8 est une vue suivant la flèche VIII de la figure 6;
• . la figure 9 est une vue en coupe transversale partielle à grande échelle du dispositif montrant le raccordement entre les conducteurs d'alimentation et les résistances électriques;
• . la figure 10 est une vue analogue à la figure 9 montrant un autre mode de raccordement entre les conducteurs et les résistances, permettant la répartition périphérique des conducteurs;
• . la figure 11 est une vue en coupe à plus grande échelle suivant le plan IV-IV de la figure 1, montrant les arrivées des conducteurs électriques d'alimentation des résistances du dispositif conforme à l'invention;
• . la figure 12 est une vue en coupe longitudinale partielle à grande échelle de la cuvette de fond du dispositif, montrant les arrivées des conducteurs électriques d'alimentation des résistances;
• . la figure 13 est un schéma montrant le raccordement électrique entre les différents modules superposés;
• . la figure 14 est un schéma électrique montrant un mode de raccordement entre les conducteurs et les résistances d'un module courant;
• . la figure 15 est un schéma électrique montrant un mode de raccordement entre les conducteurs et les résistances d'un module haute performance.

In the appended drawings, given by way of nonlimiting examples:

• . Figure 1 is an elevational view with cutaway of an electric heating device according to the invention;
• . Figure 2 is a plan view on a larger scale with cutaway of the top of the device;
• . Figure 3 is an enlarged group view along the plane III-III of Figure 1;
• . Figure 4 is a sectional view on a larger scale along the junction plane between bowl and ferrule;
• . Figure 5 is a longitudinal sectional view 'on a larger scale of the detail V of Figure 1;
• . Figure 6 is a longitudinal sectional view on a large scale of the detail VI of Figure 1;
• . Figure 7 is a partial view of a resistant blade of the device;
• . Figure 8 is a view along arrow VIII of Figure 6;
• . Figure 9 is a partial cross-sectional view on a large scale of the device showing the connection between the supply conductors and the electrical resistances;
• . Figure 10 is a view similar to Figure 9 showing another mode of connection between the conductors and the resistors, allowing the peripheral distribution of the conductors;
• . Figure 11 is a sectional view on a larger scale along the plane IV-IV of Figure 1, showing the arrivals of electrical conductors supplying the resistors of the device according to the invention;
• . Figure 12 is a partial longitudinal sectional view on a large scale of the bottom bowl of the device, showing the arrivals of conductors electric resistors supply;
• . FIG. 13 is a diagram showing the electrical connection between the various superimposed modules;
• . FIG. 14 is an electrical diagram showing a method of connection between the conductors and the resistors of a current module;
• . FIG. 15 is an electrical diagram showing a method of connection between the conductors and the resistors of a high performance module.

In the embodiment of FIGS. 1 to 4, there is shown an electric heating device by direct Joule effect, of great power for heating a gas mixture at temperatures and pressures which can reach respectively 900 ° C. and 60 bars.

This device comprises a vertical envelope 1 of generally cylindrical shape comprising a heat-insulating coating 2 which is only partially shown in the internal or external case in FIG. 1. This envelope 1 comprises at its lower part a tank with a tube 3 of inlet and at its upper part a ferrule with an outlet pipe 4 for the gas mixture to be heated.

This enclosure 1 comprises a central duct 5 shown in dotted lines in FIG. 1 which connects the inlet 3 and the outlet 4 of the gas mixture and which contains several identical modules 6a, 6b, 6c, 6d, ... 6k, 61) superimposed and removable.

These modules 6a, ... 61 each comprise several layers of resistant elements, coupled in series and in parallel.

It can be seen in FIGS. 2 and 3 and more clearly in FIGS. 6, 7, 9 and 10 that these resistant elements consist of metal strips 7 arranged one next to the other. These resistant strips 7 are made of bare expanded metal sheet (see Figure 7) and are arranged parallel to the vertical axis of the device. These lamellae have a thickness of a few tenths of a millimeter and are spaced from each other for example by insulating refractory rings (for example made of alumina). The spacing between the resistant lamellae 7 is determined in order to obtain an optimal heat exchange between these lamellae and the gas to be heated and to achieve a minimum space requirement, while being however sufficient for the pressure drops to be negligible. In practice, the resistant strips 7 are spaced from one to two centimeters for electrical insulation between the blades at different potentials.

The central conduit 5, constituted by the superimposed modules 6a, ... 61 is surrounded by a peripheral zone 8 (see FIGS. 1, 2, 3, 6 and 8 to 10) containing the conductors 9 of the electrical supply of the modules 6a, ... 6), which contain the resistant lamellae 7.

Furthermore, as can be seen in FIG. 6, passages 9a are provided between the central duct 5 and the peripheral zone 8 to allow a reduced proportion of the gas flow to pass into the peripheral zone 8 to cool the tubes and balance the pressures between conduit and peripheral zone.

As indicated in FIGS. 1, 4, 11 and 12, the enclosure 1 comprises a bottom bowl 10 comprising the tube 3 for entering the gas mixture. On this bottom bowl 10 is removably and tightly mounted a vertical ferrule 11 which carries at its upper part the tube 4 for the outlet of the gas mixture to be heated.

The superimposed modules 6a, ... 61 contained in the shell 11 are placed one on the other along the vertical axis of this shell. They communicate with the inlet pipe 3 via a connection sleeve 12 flared upwards (see FIG. 1). Furthermore, these modules 6a, ... 61 are free relative to the side wall and the upper part of the shell 11.

As can be seen in FIGS. 2, 3, 6, 9 and 10, the modules 6a, ... 61 are constituted by parallelepipedal sheet metal boxes closed laterally and fixed in a removable manner one above the other in the extension of their side faces.

All the modules 6a ... 61 rest on a lower plate 13 (see FIG. 5) which is itself supported by an internal shoulder 13a of the bottom bowl 10.

Each module 6a, ... 61 (see figures 1,6,9 and 10) is supported by a peripheral plate which extends over almost the entire width of the peripheral zone, plate itself fixed on the framework general internal 16. The small clearance e formed between the outer edge of these plates 14 and the wall of the shell 11 is calculated so that these plates 14 can expand under the effect of the heat given off by the electrical resistances contained in the modules 6a, ... 61 without these plates touching the wall of the shell 11.

These plates 14 have openings in which are engaged rings 15 of insulating material surrounding the electrical conductors 9 supplying the modules 6a, ... 61 (see FIGS. 6 and 8 to 10).

All of these modules 6a, ... 61 is laterally fixed to vertical profiles 16 (of H section for example) which extend in the peripheral zone 8 (see Figures 2, 3, 9 and 10) and provide support for internal equipment.

The electrical conductors 9 supplying the modules 6a, ... 61 are metal tubes which extend (see FIGS. 6, 8 to 10) parallel to the axis of the ferrule 11 in the peripheral zone 8. These metal tubes 9 are connected by flexible metal braids 16a to the electrically resistant strips 7 contained in the modules 6a, ... 61.

In the embodiment shown (see FIG. 6), each module 6a,... 61 includes two superimposed sets of sheets of resistant lamellae 7. In this FIG. 6, it can also be seen that each module communicates with the peripheral zone 8 adjacent by a slot 9a a few millimeters wide formed between the upper edge 17 of the side wall of a module and the lower plate 14 supporting the upper module.

In FIGS. 11 and 12, it can be seen that the lower bottom bowl 10 has in its side wall 18 radial passages 19 arranged for the arrivals of the conductive tubes 9 for the electrical supply of the modules 6a, ... 61.

These passages 19 are closed by metal lids 20 crossed by insulating rings 21 which surround the metal tubes 9. These pass horizontally through the passages 19 then extend vertically into the lower compartment 10 and pass through the support plate 13 of the modules.

In the example of Figure 11, we see that the bottom bowl 10 has five passages 19 which are each traversed by three conductors 9 and a sixth passage which is left in reserve; the number of penetrations fitted being a function of the power and the number of modules.

Figures 13 to 15 show the principle of the electrical supply of the resistant modules of the device according to the invention.

In FIG. 13, the various modules superimposed according to four levels A, B, C, D are shown diagrammatically, each level comprising three modules. The upper levels B, C, D are each supplied by three conductors 9 in the manner shown diagrammatically in FIG. 14. In this figure, each single-phase element such as a, b, represents a module for example 6e which is supplied with single-phase. A level such as B-C or D is made up of three single-phase modules and corresponds to a power between 2 and 3 MW.

Each single-phase element such as a, b is composed of two layers of twice twenty seven resistant lamellas 7.

The lower level A is supplied by a pair of three conductors 9, as can be seen more clearly in FIG. 15. According to this supply mode, the power reaches 4 to 5 MW.

The electric heating device which has just been described has numerous advantages compared to the previous solutions.

On the one hand, the device is easily removable when it is desired, for example, to repair it. For this purpose, it suffices to remove the ferrule 11 which covers all of the modules. This operation is particularly simple since this shell 11 is completely free relative to the modules and their electrical supply conductors.

Furthermore, the power supply conductors 9 of the modules are effectively cooled by a small part of the gas flow which passes through the peripheral zone 8, which guarantees their good resistance over time.

In addition, the delicate problems posed by the thermal expansion of the heating elements have been overcome in a simple and effective manner since the set of modules can freely expand towards the upper part of the shell 11.

In addition, thanks to the thinness of the resistant lamellae 7, despite the great power dissipated by a unit volume of the device, a very reduced pressure drop is obtained, which considerably reduces the power of the compressors and pumps used to compress and conveying the gas to be heated through the heater.

Since the levels are supplied separately, the heating power delivered by each element can be adjusted independently of the other levels.

Thus it is possible to obtain between the input and the output of the device an optimal temperature profile with respect to the desired heating conditions in the case of a specific application.

In addition, the device according to the invention is perfectly suited for heating a gas at pressures reaching or exceeding 60 bars, in particular because the ferrule 11 is connected to the lower part 10 of the device by a single gasket. sealing and has no connection for the passage of electrical conductors or other organs, which considerably limits the risk of gas leakage.

Of course, the invention is not limited to the example which has just been described and many modifications can be made to it without departing from the scope of the invention.

Thus the modules 6a, ... 61 instead of being parallelepipedic could be cylindrical or have any other tubular shape.

Furthermore, the resistant strips 7 instead of being made of expanded metal could be produced in another way, the main thing being that these strips have cutouts which make it possible to increase their resistance per unit area, without affecting free passage. gas to be heated between these strips.

Of course, this example provided with a three-phase alternating current supply is not limiting and the device of the present invention can be supplied by all kinds of electric currents, in particular direct current.

The electric oven described in the present application can be used advantageously in the process described in the French patent application N ° 8302764 filed on 21.2.1983, in the names of the applicants and which is entitled "Installation for the chemical transformation of a gaseous mixture containing hydrogen and hydrocarbons ".

Claims (9)

1. An electric heating device by direct Joule effect, of high power, for heating a gas mixture at temperatures and pressures which can reach respectively 900 ° C. and 60 bars, comprising an enclosure (1) comprising an inlet (3) and a outlet (4) of the gas mixture and which contains bare electrical resistors (7) and conductors (9) for supplying these resistors, characterized in that it comprises a central conduit (5) which connects the inlet ( 3) and the outlet (4) of the gaseous mixture and constituted by several modules (5a ... 61) superimposed and removable from each other, each comprising several electrically resistant elements (7) constituted by metal strips arranged one next to the other others, a peripheral zone (8) containing the conductors (9) of electrical supply of the resistive elements (7), and passages (9a) formed between the central duct (5) and the peripheral zone (8) to allow a reduced proportion of u gas flow passing through the central duct to pass into the peripheral zone. 2. Device according to claim 1, characterized in that the enclosure (1) comprises a bottom bowl (10) comprising an inlet pipe (3) of the gaseous mixture, on which a vertical ferrule is removably mounted (11) insulated carrying at its upper part a tube (4) for the outlet of the gas mixture, in that the modules (6a ... 61) comprising the resistive elements (7), extend one above the other along the axis of the ferrule, are supported by the general framework (16) resting on the bottom bowl (10) and are free relative to the side wall and the upper part of the ferrule (11) and in that the bowl of bottom (10) comprises in its wall passages (19) for the arrivals of the conductors (9) of electrical supply of the modules (6a, ... 61) containing the resistant elements (7). 3. Device according to any one of claims 1 or 2, characterized in that the modules (6a, ... 61) are constituted by parallelepipedal sheet metal boxes closed laterally removably fixed one above the other in the extension of their lateral faces. 4. Device according to claim 3, characterized in that each box (6a, ... 61) contains several layers of lamellae (7) made of resistant sheet metal arranged parallel to each other, the faces of these lamellae being parallel to the axis of the ferrule (11). 5. Device according to claim 4, characterized in that the blades (7) are made of expanded metal sheet. 6. Device according to any one of claims 2 to 5, characterized in that the set of modules (6a, ... 61) rests on plates (13) fixed to a general framework (16) which is it - even supported by the bottom bowl (10). 7. Device according to any one of claims 2 to 6, characterized in that each plate (14) module support (6a, ... 61) extends over almost the entire width of the shell (11 ), these plates comprising openings provided with insulating rings (15) for the passage of the conductors (9) of electrical supply of the modules. 8. Device according to any one of claims 1 to 7, characterized in that the conductors (9) of electrical supply of the modules (6a ... 61) are metal tubes extending parallel to the axis of the ferrule (11) in said zone peripheral (8), these tubes being connected by flexible metal braids (16a) to the resistant elements (7) of the modules. 9. Device according to any one of claims 7 to 8, characterized in that each module (6a ... 61) communicates with an adjacent peripheral zone (8) by a passage (9a) formed between the upper part (17 ) of a module and the lower plate (14) supporting the upper module and in that the peripheral zones (8) communicate with each other by passages formed between the outer edge of the plates (14) and the wall of the ferrule (11 ).

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