FR3140155A1 - Fixed bed reactor-exchanger provided with at least one hollow bar grid for circulating a heat transfer fluid. - Google Patents

Abstract

Fixed bed reactor-exchanger provided with at least one hollow bar grid for circulating a heat transfer fluid. The invention relates to a fixed bed exchanger reactor (1), intended to carry out a thermochemical conversion reaction, comprising a heat exchange grid whose openings delimited between adjacent bars allow the reagents of the desired thermochemical conversion reaction, the bars being hollow and in fact constitute channels for the circulation of a heat transfer fluid making it possible to evacuate (or provide) the heat of the reaction. Figure for abstract: Fig. 1B

Description

Fixed bed reactor-exchanger provided with at least one hollow bar grid for circulating a heat transfer fluid.

The present invention generally relates to exchanger reactors. More particularly, the present invention relates to the field of catalytic exchanger reactors using a solid catalyst, and in particular a solid catalyst in the form of a fixed bed of powder.

It relates to a catalytic exchange reactor capable of implementing processes for synthesizing exothermic organic compounds. The organic compounds obtained may in particular include synthetic fuels and combustible.

Although described more specifically in relation to exothermic processes, in particular the methanation reaction, the applications envisaged for a reactor according to the invention concern both endothermic and exothermic processes, in particular for which the control of the temperature at the level of the catalyst is critical.

Catalytic reactors using solid catalysts are widely used for the synthesis of organic compounds such as synthetic fuels or fuels including natural gas substitutes, dimethyl ether or even methanol.

These compounds are obtained in particular by the reaction of hydrogen and carbon monoxide in the presence of an appropriate solid catalyst.

However, the chemical reactions relating to the synthesis of these compounds are very exothermic, and consequently release a quantity of heat capable of degrading the solid catalyst. This degradation results in a reduction in the conversion rate of the chemical species present, and a reduction in the selectivity of the reactions involved. Furthermore, the solid catalyst is deactivated under the effect of heat.

Thus, in practice, these reactions can be carried out in a reactor-exchanger of the tube-and-shell type which comprises a plurality of reactive channels each provided with the solid catalyst and continuously cooled by a heat transfer fluid. In this type of reactor, the reactive gases circulate axially in the tubes which contain a catalyst, for example in powder form.

However, despite the implementation of cooling by the heat transfer fluid, this type of reactor remains sensitive to the heat released by the reactions occurring within the reactor.

In particular, a hot spot, generally observed near the inlet of the reactive gases, degrades the solid catalyst, and therefore reduces the performance of the reactor-exchanger.

In order to limit these effects, the following solutions have been proposed:

- a reduction in the volume density of catalyst, in particular by depositing the latter on the walls of the tube or an insert or by diluting it in a non-reactive medium;

- a dilution of the reactive gases with part of the products generated to reduce the activity of the reaction;

- the creation of several injection points of one or more reagents to distribute the hot spot area over a larger surface area;

- a reduction in the dimensions of the tubes or by placing heat-conducting parts in them in order to improve the cooling of the tubes.

However, these solutions are not satisfactory. Indeed, even though they make it possible to reduce the effects of the hot spot, they are complex to implement. Furthermore, their implementation reduces the flexibility of use of the exchanger reactor, and makes the latter less compact.

In order to overcome these drawbacks, an arrangement was then proposed making it possible to distribute the distribution of the reagents over the entire length of the tubes. This solution then makes it possible to obtain better temperature homogeneity over the entire length of the reactor. Thus, patents US3758279, US4374094, EP0560157, IT8021172 and US2997374 propose exchanger reactors implementing distribution of reagents from an annular distribution space. In particular, these exchanger reactors, generally cylindrical in shape, comprise, arranged coaxially and from the outside of the reactor, a tube, the annular distribution space, a catalyst charge and a collection space.

This arrangement is, however, not satisfactory. Indeed, the presence of the annular distribution space around the catalyst charge limits heat transfer from the catalyst to the tube, making the cooling systems generally implemented inefficient. It nevertheless remains possible to insert heat-conducting elements into the reactor. However, such a solution remains incompatible with reactors comprising small diameter tubes.

In order to overcome these drawbacks, the Applicant has proposed in patent EP3827895 B1 a reactor-exchanger with a hollow tube housing a fixed bed of catalytic powder and surrounding a hollow insert whose shape makes it possible to distribute the distribution of the reagents over the entire length of the tube. This solution then makes it possible to obtain better temperature homogeneity over the entire length of the reactor, while obtaining very good thermal control. However, the complexity of the shape of the insert makes its production and therefore that of the reactor-exchanger complicated and expensive. In addition, being able to fill and change the catalyst is not easy. Particularly in the case of a catalyst which has aged poorly and whose flow could be difficult.

Patent application US2004/0141893A1 proposes, to control endothermic or exothermic reactions, to carry out these two reactions simultaneously within the same reactor so that the exothermic reaction directly exchanges its heat with the endothermic reaction. This solution does not make it possible to avoid thermal variations along the reactor channels. Above all, it requires having to carry out two types of reactions simultaneously and at similar temperatures, which is very restrictive in practice.

Patent JP5362553B2 discloses, for its part, a reactor-exchanger with a very complex geometry inside the channels to maximize the exchange surface. This geometry must allow very good heat exchange, but not uniformity of the reaction within the reactor. In addition, the geometry is not easy to achieve by machining.

There is therefore a need to improve exchanger reactors, particularly fixed bed reactors, in particular in order to obtain very good heat exchange and therefore good temperature control in the fixed bed while allowing easy manufacturing and maintenance.

The aim of the invention is to respond at least in part to this need.

To do this, the invention relates to a fixed bed reactor-exchanger, intended to carry out a thermochemical conversion reaction.

• au moins une chambre d’alimentation en gaz réactifs:
• au moins une chambre d’évacuation des gaz produits par la réaction;
• au moins une grille d’échange thermique, agencée entre la chambre d’alimentation et la chambre d’évacuation, la grille d’échange thermique comprenant des barreaux creux adaptés pour faire circuler en leur sein un fluide caloporteur, les ouvertures délimitées entre les barreaux étant dimensionnées pour loger un lit fixe de catalyseur(s) de la réaction et agencées pour déboucher dans la chambre d’évacuation;
• au moins un élément de répartition, agencée entre la chambre d’alimentation et la grille d’échange thermique, les ouvertures de l‘élément de répartition étant dimensionnées pour maintenir le lit fixe de de catalyseur(s) en l’empêchant de s’échapper par gravité et agencées pour laisser passer les gaz réactifs depuis la chambre d’alimentation vers les ouvertures de la grille d’échange thermique logeant le lit fixe de catalyseur(s).

The reactor-exchanger comprises at least one subassembly comprising:

• at least one reactive gas supply chamber:
• at least one chamber for evacuating the gases produced by the reaction;
• at least one heat exchange grid, arranged between the supply chamber and the evacuation chamber, the heat exchange grid comprising hollow bars adapted to circulate a heat transfer fluid within them, the openings delimited between the bars being sized to accommodate a fixed bed of reaction catalyst(s) and arranged to open into the evacuation chamber;
• at least one distribution element, arranged between the supply chamber and the heat exchange grid, the openings of the distribution element being dimensioned to maintain the fixed bed of catalyst(s) by preventing it from moving escape by gravity and arranged to allow the reactive gases to pass from the supply chamber towards the openings of the heat exchange grid housing the fixed bed of catalyst(s).

According to an advantageous embodiment, the distribution element is a grid.

Preferably, the catalyst(s) being in the form of a catalytic powder.

According to an advantageous configuration, the heat exchange grid is attached to the distribution element. According to this configuration, the heat exchange grid is preferably fixed or made integrally with the distribution element.

According to an advantageous embodiment, the reactor-exchanger extends in a first longitudinal direction (X), the hollow bars extending in a second longitudinal direction orthogonal (Y) to the first longitudinal direction (X), the openings of the heat exchange grid and the distribution element extending in a third longitudinal direction (Z) orthogonal to the first and second longitudinal directions.

According to an advantageous alternative embodiment, each of the two ends of the hollow bars is connected to another hollow bar, arranged outside the supply and evacuation chambers, each other hollow bar respectively forming an inlet collector and a heat transfer fluid outlet collector.

The hollow bars can be of rectangular or square cross section, which allow optimal operation. Other sections can be considered, such as a round or oval cross section, particularly for cost reasons.

According to another advantageous embodiment, the reactor-exchanger comprises a first boundary plate delimiting the supply opening and the reactive gas supply chamber and a second boundary plate delimiting the evacuation chamber and the opening evacuation of the gases produced.

According to this mode, and an advantageous configuration, the reactor-exchanger comprises a stack of several sub-assemblies one on top of the other, each supply chamber common to two sub-assemblies opening onto the openings of a distribution element and those of an adjacent heat exchange grid and each evacuation chamber common to two subassemblies opening onto the openings of a heat exchange grid and those of an adjacent distribution element, each first boundary plate delimiting a supply opening and a supply chamber common to two sub-assemblies and each second boundary plate delimiting an evacuation opening and an evacuation chamber common to two sub-assemblies, with the exception of the ends of the stack each delimited by a second delimiting plate delimiting an evacuation opening and an evacuation chamber of a single subassembly.

This reactor configuration with stacking of several subassemblies makes it possible in particular to reduce the production cost (material cost) by removing part of the delimiting plates since the supply and evacuation chambers are pooled without having to delimit them by a dedicated plate. This configuration requires adapting the chambers arranged at the ends of the stack so that they do not have to circulate a flow rate twice as high for the same quantity of catalyst, which could generate a risk of less good thermochemical conversion locally and thermal inhomogeneity. The evacuation chambers of the products obtained being arranged at both ends, the risk of maldistribution of the flow is eliminated at the very least greatly limited.

According to an advantageous assembly variant, each subassembly is an element, one-piece or pre-assembled, consisting of a heat exchange grid, a distribution element and at least one first or second delimiting plate, the stacked subassemblies being assembled together by means of compression tie rods passing through the boundary plates. We can consider producing an element by welding or brazing or welding-diffusion brazing-diffusion of machined plates, in particular by a Hot Isostatic Compression (HIC) technique. We can also consider production by welding with thermocompression of plates. This variant advantageously makes it possible to keep all the sub-assemblies independent of each other, and to maintain the seal between them by means of tie rods which can be screwed in to ensure the desired compression. This makes assembly and disassembly of the reactor easy and facilitates maintenance, particularly with easy access to the catalyst within each distribution element, to remove and replace it.

The invention also relates to the use of a reactor-exchanger as described above, to carry out a catalytic thermochemical, exothermic or endothermic conversion reaction, in particular a methanation reaction.

Thus, the invention essentially consists of producing a fixed bed reactor-exchanger with a heat exchange grid whose openings delimited between adjacent bars allow the reagents of the desired thermochemical conversion reaction to circulate therein, the bars being hollow and in fact constitute circulation channels for a heat transfer fluid making it possible to evacuate (or provide) the heat of the reaction.

The reaction catalyst, preferably in powder form, fills the space between two adjacent bars and is held by an element preferably in the form of a reagent distribution grid.

The reactor-exchanger according to the invention therefore allows a very good exchange between the catalyst (place of the reaction and therefore heat source or sink) and each heat transfer fluid circulation channel formed by the hollow of a bar, which allows to best control the temperature in the catalyst.

• un réacteur-échangeur plus compact ;
• une géométrie de réacteur-échangeur plus simple et donc plus simple à usiner ;
• dans le cas d’une pluralité de grilles indépendantes, alors le démontage et facilité, ce qui permet de changer le catalyseur usagé de façon aisée, même si ce dernier a subi un frittage important.

Ultimately, the invention provides numerous advantages, in particular through the solution according to patent EP3827895 B1, among which we can cite:

• a more compact reactor-exchanger;
• a simpler reactor-exchanger geometry and therefore easier to machine;
• in the case of a plurality of independent grids, then disassembly is made easier, which makes it possible to change the used catalyst easily, even if the latter has undergone significant sintering.

Other advantages and characteristics will become clearer on reading the detailed description, given for illustrative and non-limiting purposes, with reference to the following figures.

there is a schematic view in longitudinal section of a fixed bed reactor-exchanger according to the invention.

there is a schematic top view of the fixed bed reactor-exchanger according to the .

there is a longitudinal sectional view of a reactor-exchanger according to the invention before stacking several sub-assemblies each with a heat exchange grid, a distribution grid and a boundary plate.

there resumes and shows an advantageous variant of assembly by means of compression tie rods.

there is a top view of the .

there illustrates in front view two metal plates used to produce a heat exchange grid of a reactor-exchanger according to the invention.

there schematically illustrates the step of stacking plates according to the for producing by thermocompression a heat exchange grid of a reactor-exchanger according to the invention.

there resumes showing elements of a sizing example.

there is a detailed figure of the showing elements of a sizing example.

there is a schematic view in longitudinal section of a reactor-exchanger according to a stacking embodiment of several sub-assemblies.

detailed description

For the sake of clarity, the same elements are designated by the same numerical references according to the state of the art and according to the invention.

It is specified that throughout the application, the terms “inlet”, “outlet”, “upstream”, “downstream” are to be understood in relation to the direction of circulation of the fluid considered within a reactor-exchanger. according to the invention.

Likewise, the terms “upper”, “lower”, “above”, “below” are to be understood with reference to a reactor-exchanger according to the invention arranged horizontally in its operating configuration.

In Figures 1 and 1A, a fixed bed reactor-exchanger 1 is shown according to one embodiment of the invention, with reference to a methanation reaction that it implements.

This reactor 1 extends in a first longitudinal direction (X) and firstly comprises a supply chamber 2 of reactive gases (CO ₂ , H ₂ ) from a supply opening 20 and an evacuation chamber 3 gases produced by the reaction (CH ₄ , H ₂ O) towards an evacuation opening 30.

A heat exchange grid 4 is arranged between the supply chamber 2 and the evacuation chamber 3. The heat exchange grid 4 according to the invention comprises hollow bars 40 which extend in a second longitudinal direction ( Y) orthogonal to (X) and which are adapted to circulate within them a heat transfer fluid, such as a thermal mineral oil. These hollow bars 40 can be of rectangular or square cross section as in the mode illustrated.

The openings 41 delimited between the bars 40 are dimensioned to accommodate a fixed bed of catalyst(s) (C) of the reaction in powder form. These openings 41 extend in a third longitudinal direction (Z) orthogonal to (X) and (Y) and are arranged to open into the evacuation chamber 3.

The reactor 1 further comprises a distribution grid 5, arranged between the supply chamber 2 and the heat exchange grid 4. The openings 50 of this distribution grid 5 are dimensioned to maintain the fixed bed of catalyst(s). ) by preventing it from escaping by gravity. These openings 50, like the openings 41, extend in a third longitudinal direction (Z) orthogonal to (X) and (Y). These openings 50 are arranged to allow the reactive gases to pass from the supply chamber 2 towards the openings 41 of the heat exchange grid in which the reaction takes place, the products being evacuated into the evacuation chamber 3.

Depending on the configurations, in particular, if the reactor-exchanger must be arranged in an operating position other than a horizontal position, another distribution grid 5 can be arranged between the heat exchange grid 4 and the evacuation chamber 3.

As illustrated in , each of the two ends of the hollow bars 40 is advantageously connected to another hollow bar 42, 43, arranged outside the supply and evacuation chambers, which respectively forms an inlet collector and an outlet collector of the coolant.

To delimit the reactor from the outside, a first delimiting plate 6 delimits the supply opening 20 and the reactive gas supply chamber 2 while a second delimiting plate 7 delimiting the chamber evacuation 3 and the evacuation opening 30 of the gases produced.

The operation of a fixed bed reactor-exchanger 1 according to the invention is as follows.

Reactive gases, CO₂and H₂ in the example of the methanation reaction, enter the reactor 1 through the supply chamber 2 from the supply opening 20. In the example of methanation, the inlet temperature of the gases, and of the The oil can advantageously be between 280 and 320°C and the pressure between 1 and 30 bar.

Due to the pressure loss induced by the openings 50 of the grid 5 and the catalyst in powder form, in the openings 41, the flow of reactive gases is distributed uniformly in the latter, and therefore between the different hollow bars 40 forming the heat transfer fluid circulation channels. Due to the closure of the chamber 2 by the plate 6 opposite the supply opening 20, the entire gas flow can only flow through the openings 41.

At the time of coming into contact with the catalyst C housed in the openings 41, the composition of the gas flow and the temperature are therefore close to being uniform throughout the chamber 2.

In the catalyst C, the speed of the reactive gases is low, the height of the catalytic bed defined by the height of the openings 41 can be optimized as a function of the targeted flow rate so that the contact time between the reactive gases and the catalyst C is sufficient to achieve a high conversion, close to thermodynamic equilibrium.

As the flow rate in the catalyst is low, it is not necessary to have a very long catalytic bed C to have sufficient residence time. Thanks to this short length and the presence of the heat transfer fluid circulation channels delimited by the interior of the hollow bars 40, the heat is distributed as best as possible, which makes it possible to avoid any hot (or cold) spots.

The converted gases and the unconverted reagents open into chamber 3 then are evacuated from the reactor through the evacuation opening 30.

With regard to the construction of a reactor-exchanger 1, a sub-assembly can be constituted beforehand by fixing or integrally producing the heat exchange grid 4 with the distribution grid 5 and advantageously at least one of the boundary plates 6, 7.

As illustrated in , an advantageous embodiment of construction consists of stacking several subassemblies 1.1, 1.2, 1.3 on top of each other, having previously filled the openings 41 with catalytic powder C.

To assemble these different subassemblies 1.1 to 1.3, it is advantageous to use compression tie rods 8 which pass through all of the delimiting plates 6, 7 at the corners of the stack, as illustrated in Figures 3 and 4. These tie rods 8 which is tightened to ensure compression makes it possible to keep the different subassemblies 1.1 to 1.3 independent of each other, and to maintain the seal between them. These assembly means 8 therefore make it possible to guarantee easy assembly/disassembly of the reactor 1 as well as easy access to the catalyst C to remove and replace it, particularly once completely used.

To fully produce the heat exchange grid 4, several manufacturing techniques can be considered, such as extrusion, rolling from rectangular or square section tubes followed by conventional welding, isostatic compression welding at hot (CIC) or by thermocompression.

The choice of manufacturing technique will be made taking into account the dimensions/thicknesses or the size limits achievable.

An example of production using a thermocompression welding technique is illustrated in Figures 5 and 6. It should be noted that on the the dashed L lines designate the cutting lines of the plates for the channel openings once stacking and thermocompression welding have been carried out.

We first produce two types of machined plates 4.1, 4.2 which will be stacked and then assembled together by thermocompression welding to constitute a heat exchange grid 4.

The opening windows 400 of a plate 4.1 will delimit the openings for the passage of reactive gases. Once assembled, plates 4.1 will close the channels 40 of the heat transfer fluid but not those of the reactive gases.

The through windows 410 of a plate 4.2 will delimit the openings for the heat transfer fluid to pass through.

• une plaque 4.1 à une première extrémité,
• un nombre de N plaques 4.2 au centre de l’empilement, le nombre N étant fonction de l’épaisseur des plaques et la hauteur de lit catalytique désirée,
• une plaque 4.1 à une deuxième extrémité opposée à la première extrémité.

The stacking is then carried out as follows:

• a plate 4.1 at a first end,
• a number of N plates 4.2 in the center of the stack, the number N being a function of the thickness of the plates and the desired catalytic bed height,
• a plate 4.1 at a second end opposite the first end.

As illustrated in , we can provide two plates 4.2 between two plates 4.1

As an indication, the materials that can be considered are as follows.

• catalyseur C : poudre de nickel et/ou d’alumine ;
• grille d’échange thermique 4 en acier inoxydable ou en cuivre ;
• plaque de séparation 7 en acier inoxydable 316L

For a methanation reaction:

• catalyst C: nickel and/or alumina powder;
• heat exchange grid 4 in stainless steel or copper;
• separation plate 7 in 316L stainless steel

• catalyseur C en fer, cobalt, ruthénium ou nickel ;
• grille d’échange thermique 4 en acier inoxydable ou en aluminium;

For a Fischer-Tropsch conversion reaction:

• catalyst C in iron, cobalt, ruthenium or nickel;
• heat exchange grid 4 in stainless steel or aluminum;

separation plate 7 in 316L stainless steel or aluminum. The inventor has produced an example of the dimensioning of a reactor-exchanger 1 according to the invention.

The notations of the characteristic dimensions are indicated in Figures 7 and 7A and are evaluated here, in order of magnitude for a methanation reaction.

Table 1 below summarizes the values and results obtained. It should be noted that the Anglo-Saxon acronym GHSV designates “Gas hourly space velocity”, that is to say the hourly space speed of the gas.

Value U nity Rating Dimensions channels/catalyst Length of heat transfer fluid channels delimited by hollow bars 40
0.5 m L.C. Length of bedrooms 2, 3 0.476 m X1 Width of openings 41 housing the catalytic powder C 0.004 m L Channel width 40 2.00E-03 m lc Number of channels 40 60 - Thickness of a bar 20 1.00E-03 m e Height of the catalytic bed C 3.50E-03 m hl Volume of catalyst in an opening 41 7.0E-06 m ³ Reactive gas passage section 0.002 m² Dimensions c rooms Height of a bedroom 2 or 3 3.00E-03 m Pp and Pr Height of a grid 5 1.00E-03 m Plate stacking height 1.05E-02 m Plate volume 2.50E-03 m Reaction conditions Speed in the catalyst 0.005292 m/s Reactive gas flow 0.000011 m ³ /s Temperature 573 K Pressure 8 bar Molar flow of reactive gases entering an opening 41 0.1452 Nm ³ /h Molar flow of reactive gases entering all openings 41 8.56829 Nm ³ /h GHSV 20746.5 h ^-1 Reaction density 3.43E+03 Nm3/h/m3

We see from reading this table that by having set the same GHSV as for a fixed bed tubular reactor, as described in patent application EP3827895, which corresponds to the same performance of the catalyst, the conversion density is increased by approximately 50%, since they are respectively equal to 3400 Nm ³ /h/m ³ and 2300 Nm3/h/m3.

It should be noted that the value of 0.5 m for the total length of the heat transfer channels delimited by the hollow bars 40 was chosen in a purely arbitrary manner. In fact, this value will have to be adapted mainly according to the constraints of the manufacturer of the reactor-exchanger 1. For example, in the case of production using a CIC (Hot Isostatic Compression) technique then, the length of the channels 40 and the length of the Chambers 2, 3 should be limited by the size of the CIC oven used.

We represented at the , an advantageous embodiment of a reactor-exchanger 1 with stacks of several subassemblies 1.1, 1.2, 1.3, 1.4, with sharing of openings 20 and supply chamber 2 as well as openings 30 and chamber 3 d 'evacuation.

Thus, each supply chamber 2 common to two subassemblies opens onto the openings 50 of a distribution grid and the openings 41 of an adjacent heat exchange grid.

The same goes for each evacuation chamber 3 common to two sub-assemblies opening onto the openings 41 of a heat exchange grid and the openings 50 of an adjacent distribution grid.

Each first delimiting plate 6 delimits a supply opening 20 and a supply chamber 20 common to two sub-assemblies and each second delimiting plate 7 delimits an evacuation opening 30 and an evacuation chamber 3 common to two sub-assemblies -sets.

Only the ends of the stack are each delimited by a second delimiting plate 7 delimiting a single evacuation opening 30 and a single evacuation chamber 3 of a single subassembly 1.1 or 1.4.

Other variants and improvements can be considered without departing from the scope of the invention.

For example, the number of subassemblies that are stacked and assembled to produce a reactor-exchanger according to the invention can be adapted as desired depending on the targeted reaction and the desired performances.

As a distribution element, we can consider a porous material in place of a grid 5 whose pores allow the passage of reactive gases while maintaining the fixed bed of the catalyst(s) by preventing it from spreading. escape by gravity.

Claims (12)

Fixed bed exchanger reactor (1), intended to carry out a thermochemical conversion reaction, comprising at least one subassembly (1.1, 1.2, 1.3, 1.4) comprising:

• at least one reactive gas supply chamber (2):
• at least one evacuation chamber (3) of the gases produced by the reaction;
• at least one heat exchange grid (4), arranged between the supply chamber and the evacuation chamber, the heat exchange grid comprising hollow bars (40) adapted to circulate within them a heat transfer fluid, the openings (41) delimited between the bars being dimensioned to accommodate a fixed bed of catalyst(s) (C) of the reaction and arranged to open into the evacuation chamber;
• at least one distribution element (5), arranged between the supply chamber and the heat exchange grid, the openings (50) of the distribution element being dimensioned to maintain the fixed bed of catalyst(s) in preventing it from escaping by gravity and arranged to allow the reactive gases to pass from the supply chamber towards the openings of the heat exchange grid housing the fixed bed of catalyst(s).

Reactor-exchanger according to claim 1, the distribution element being a grid (5). Reactor-exchanger according to claim 1 or 2, the catalyst(s) being in the form of a catalytic powder. Reactor-exchanger according to one of claims 1 to 3, the heat exchange grid being attached to the distribution element. Reactor-exchanger according to claim 4, the heat exchange grid being fixed or produced integrally with the distribution element. Reactor-exchanger according to one of the preceding claims, extending in a first longitudinal direction (X), the hollow bars extending in a second longitudinal direction orthogonal (Y) to the first longitudinal direction (X), the openings of the heat exchange grid and the distribution element extending in a third longitudinal direction (Z) orthogonal to the first and second longitudinal directions. Reactor-exchanger according to one of the preceding claims, each of the two ends of the hollow bars being connected to another hollow bar (42, 43), arranged outside the supply and evacuation chambers, each other hollow bar respectively forming an inlet collector and an outlet collector of the heat transfer fluid. Reactor-exchanger according to one of the preceding claims, the hollow bars being of rectangular or square cross section. Reactor-exchanger according to one of the preceding claims, comprising a first delimiting plate (6) delimiting the supply opening (20) and the reactive gas supply chamber and a second delimiting plate (7) delimiting the evacuation chamber and the evacuation opening (30) of the gases produced. Reactor-exchanger according to claim 9, comprising a stack of several sub-assemblies one on top of the other, each supply chamber common to two sub-assemblies opening onto the openings of a distribution element and those of a grid of adjacent heat exchange and each evacuation chamber common to two subassemblies opening onto the openings of a heat exchange grid and those of an adjacent distribution element, each first boundary plate delimiting a supply opening and a supply chamber common to two sub-assemblies and each second delimiting plate delimiting an evacuation opening and an evacuation chamber common to two sub-assemblies, with the exception of the ends of the stack each delimited by a second boundary plate delimiting an evacuation opening and an evacuation chamber of a single subassembly. Reactor-exchanger according to claim 10, each subassembly being an element, monobloc or preassembled, consisting of a heat exchange grid, a distribution element and at least one first or second delimiting plate, the stacked subassemblies being assembled together by means of compression tie rods passing through the boundary plates. Use of a reactor-exchanger according to one of the preceding claims, to carry out a catalytic thermochemical, exothermic or endothermic conversion reaction, in particular a methanation reaction.