MILLIMETER-SCALE EXCHANGER-REACTOR FOR HYDROGEN PRODUCTION OF LESS THAN 10 Nm3/h

Abstract

Reactor-exchanger comprising at least 3 stages with, on each stage, at least one area promoting the heat exchanges and at least one distribution area upstream and/or downstream of the area promoting the heat exchanges, characterized in that the area promoting the heat exchanges comprises cylindrical millimetric channels, there being 1 to 1000 of said channels with a length of between 10 mm and 500 mm.

Claims

1.-16. (canceled)

17. A reactor-exchanger comprising at least 3 stages with, on each stage, at least one area promoting heat exchange and at least one distribution area upstream and/or downstream of the area promoting the heat exchanges, wherein the area promoting heat exchange comprises cylindrical millimetric channels, wherein there are between 1 and about 1000 of said channels, each channel comprising a length of between about 10 mm and about 500 mm.

18. The reactor-exchanger according to claim 17, wherein the at least one distribution area comprises cylindrical millimetric channels which correspond to a continuous extension of the channels of the area promoting heat exchange.

19. The reactor-exchanger according claim 17, wherein the cylindrical millimetric channels the same stage are separated by walls with a thickness of less than 2 mm.

20. The reactor-exchanger according to claim 17, wherein the cylindrical millimetric channels have a hydraulic diameter of between about 0.5 and about 3 mm.

21. The reactor-exchanger according to claim 17, wherein the cylindrical millimetric channels have a length of between about 50 and about 400 mm.

22. The reactor-exchanger according to claim 17, wherein said exchanger-reactor comprises: a reaction stage whose channels are configured to promote a reaction by allowing the circulation of a reagent gaseous flow, a return stage whose channels are configured to allow the circulation of a product gaseous flow, a heat top up stage whose channels are configured to allow the circulation of a heat-transfer fluid.

23. The reactor-exchanger according to claim 22, wherein the number of channels at the reaction stage is between about 100 and about 700.

24. The reactor-exchanger according to claim 22, wherein the number of channels at the return stage is between about 100 and about 700.

25. The reactor-exchanger according to claim 22, wherein the number of channels at the heat top up stage is between about 100 and about 700.

26. The reactor-exchanger according to claim 22, wherein the reaction stage is surrounded by a heat top up level and a return level.

27. The reactor-exchanger according to claim 22, wherein the channels of the reaction stage and the channels of the return stage have, over at least a part of their internal walls, a protective coating against corrosion.

28. The reactor-exchanger according to claim 22, wherein the channels of the reaction stage have, over at least a part of their internal walls, a catalyst.

29. A method for steam reforming a hydrocarbon charge implementing a reactor-exchanger according to claim 17.

30. The steam-reforming method according to claim 29, comprising a production of hydrogen exhibiting a flow rate of between 0.1 and 10 Nm.sup.3/h.

Description

[0021] Whatever the machining method used to manufacture the millimetre-scale exchanger or exchanger-reactors, channels are obtained of semi-circular section in the case of the chemical machining (FIG. 1) and which are made up of two right angles or of rectangular section in the case of the traditional machining and which are made up of four right angles. This plurality of angles is prejudicial to obtaining a uniform protective coating over all the section. In effect, the phenomena of geometrical discontinuities such as angles increase the probability of generating non-uniform depositions, which will inevitably lead to the initiation of phenomena of degradation of the surface condition of the die that has to be guarded against such as, for example, phenomena of corrosion, of carburation or of nitriding.

[0022] The angular channel sections obtained by the chemical machining or traditional machining techniques do not make it possible to optimize the mechanical strength of such an assembly. In effect, the calculations for dimensioning such sections for pressure withstand strength result in an increase in the thickness of the channel walls and the bottom, the equipment thus losing its compactness but also its efficiency in terms of heat transfer.

[0023] Furthermore, the chemical machining imposes limitations in terms of geometrical forms such that it is not possible to have a channel having a height greater than or equal to its width, which leads to limitations of the surface/volume ratio resulting in optimization limitations.

[0024] The assembly of the etched plates by diffusion welding is obtained by the application of a high uni-axial strain (typically of the order of 2 to 5 MPa) on the die consisting of a stacking of etched plates and exerted by a high-temperature press for a holding time of several hours. The implementation of this technique is compatible with the manufacturing of apparatuses of small dimensions such as for example apparatuses contained in a volume 400 mm600 mm. Beyond these dimensions, the force to be applied to maintain a constant strain becomes too high to be implemented by a high-temperature press.

[0025] Some manufacturers using the diffusion welding method mitigate the difficulties of implementation of a high strain by the use of a so-called self-clamping rig. This technique does not make it possible to effectively control the strain applied to the equipment which results in channels being crushed.

[0026] The assembly of the etched plates by diffusion brazing is obtained by the application of a low uni-axial strain (typically of the order of 0.2 MPa) exerted by a press or a self-clamping rig at high temperature and for a holding time of several hours with the die made up of the etched plates. Between each of the plates, a brazing filler metal is deposited according to industrial deposition methods which do not make it possible to guarantee the perfect control of this deposition. The purpose of this filler metal is to diffuse in the die during the brazing operation so as to produce the mechanical join between the plates.

[0027] Furthermore, while the equipment is being held at temperature during manufacturing, the diffusion of the brazing metal cannot be controlled, which can lead to discontinuous brazed joints resulting in a degradation of the mechanical withstand strength of the equipment. As an example, the equipment manufactured according to the diffusion brazing method and dimensioned according to ASME section VIII div.1 appendix 13.9 in HR120 that we have produced did not withstand the application of a pressure of 840 bar during the burst test. To mitigate this degradation, the thickness of the walls and the geometry of the distribution area were adapted in order to increase the contact surface between each plate. This causes the surface/volume ratio to be limited, the head loss to be increased and poor distribution in the channels of the equipment.

[0028] Furthermore, the ASME code section VIII div.1 appendix 13.9 used for the dimensioning of this type of brazed equipment does not allow the use of the diffusion brazing technology for equipment implementing fluids containing a lethal gas such as carbon monoxide for example. Thus, an apparatus assembled by diffusion brazing cannot be used for the production of Syngas.

[0029] The equipment manufactured by diffusion brazing ultimately consists of a stacking of etched plates between which brazed joints are arranged. Because of this, any welding operation on the faces of this equipment leads in most cases to the destruction of the brazed joints in the area affected thermally by the welding operation. This phenomenon is propagated along the brazed joints and leads in most cases to the rupture of the assembly. To mitigate this problem, it is sometimes proposed to add thick reinforcing plates at the time of assembly of the brazed die so as to offer a support of frame type for the welding of the connectors which has no brazed joint.

[0030] From a method intensification point of view, the assembling together of the etched plates means that the equipment has to be designed with a two-dimensional approach which limits the thermal and fluidic optimization in the exchanger or exchanger-reactor by requiring the designers of this type of equipment to limit themselves to a fluid distribution stage approach.

[0031] From an eco-manufacturing point of view, all these manufacturing steps being carried out by different trades are generally performed by various subcontractors located at different geographic locations. This causes lengthy production delays and numerous part transportations. Starting from there, one problem which arises is how to provide an improved reactor-exchanger that does not have at least some of the drawbacks cited above.

[0032] One solution of the present invention is a reactor-exchanger comprising at least 3 stages with, on each stage, at least one area promoting the heat exchanges and at least one distribution area upstream and/or downstream of the area promoting the heat exchanges, characterized in that the area promoting the heat exchanges comprises cylindrical millimetric channels, there being 1 to 1000 of said channels with a length of between 10 mm and 500 mm.

[0033] Depending on the case, the reactor-exchanger according to the invention can have one or more of the following features: [0034] the distribution area comprises millimetric channels which correspond to the continuous extension of the channels of the area promoting the heat exchanges, [0035] the channels of one and the same stage are separated by walls with a thickness of less than 2 mm, [0036] the channels have a hydraulic diameter of between 0.5 and 3 mm, [0037] the channels have a length of between 50 and 400 mm, preferably between 100 and 300 mm, [0038] said exchanger-reactor comprises a reaction stage whose channels are capable of promoting a reaction by notably allowing the circulation of reagent gaseous flows, a return stage whose channels allow the circulation of product gaseous flows, a heat top up stage whose channels allow the circulation of a heat transfer fluid. [0039] the number of channels at the reaction stage is between 100 and 700, preferably between 200 and 500, [0040] the number of channels at the return stage is between 100 and 700, preferably between 200 and 500, [0041] the number of channels at the heat top up stage is between 100 and 700, preferably between 200 and 500, [0042] the reaction stage is surrounded by a heat top up level and a return level, [0043] the channels of the reaction stage and the channels of the return stage have, over at least a part of their internal walls, a protective coating against corrosion, [0044] the channels of the reaction stage have, over at least a part of their internal walls, a catalyst.

[0045] Note that the protective coating and the catalyst are preferably deposited by liquid means. Another subject of the present invention is the manufacturing of the reactor-exchanger according to the invention. An additive manufacturing method is preferably used to manufacture a reactor-exchanger according to the invention. Preferably, the additive manufacturing method implements, as base material, at least one metal powder of micrometric size.

[0046] The additive manufacturing method can implement metal powders of micrometric size which are melted by one or more lasers in order to manufacture finished parts of complex forms in three dimensions. The part is constructed layer by layer, the layers are of the order of 50 m, depending on the accuracy of the forms required and the desired rate of deposition. The metal to be melted can be provided either by powder bed or by a spray nozzle. The lasers used to locally melt the powder are either YAG, fibre or CO2 lasers and the melting of the powders is performed under inert gas (argon, helium, etc.). The present invention is not limited to a single additive manufacturing technique but it applies to all the known techniques.

[0047] Unlike chemical machining or traditional machining techniques, the additive manufacturing method makes it possible to produce channels of cylindrical section with the following advantages (FIG. 4): (i) of offering a better pressure withstand strength and thus allowing a significant reduction of the thickness of the walls of the channels and (ii) of allowing the use of pressure apparatus dimensioning rules which do not require the performance of a burst test to prove the efficiency of the design as is the case for section VIII div.1 appendix 13.9 of the ASME code.

[0048] In effect, the design of an exchanger or of an exchanger-reactor produced by additive manufacturing, making it possible to produce channels with cylindrical section (FIG. 5), relies on standard pressure apparatus dimensioning rules which are applied to the dimensioning of the channels, of the distributors and of the manifolds with cylindrical sections that make up the millimetre-scale exchanger-reactor or exchanger. As an example, the dimensioning of the wall of straight channels with rectangular section (value t.sub.3 on FIG. 2) of a reactor-exchanger made of nickel alloy (HR 120), dimensioned according to the ASME (American Society of Mechanical Engineers) section VIII div.1 appendix 13.9, is 1.2 mm. By using channels with cylindrical section, this wall value calculated by the ASME section VIII div.1 is no more than 0.3 mm, i.e. a fourfold reduction of the wall thickness necessary for the pressure withstand strength.

[0049] The reduction of the volume of material associated with this gain makes it possible (i) either to reduce the bulk of the apparatus with identical production capacity by the fact that the number of channels necessary to achieve the targeted production capacity is lesser and thus occupies less space, (ii) or to increase the production capacity of the apparatus by retaining the bulk thereof which makes it possible to position more channels and thus handle a greater flow rate of reagents.

[0050] Furthermore, in the case of millimetre-scale exchanger-reactor or exchanger produced in noble alloy with a strong nickel charge, the reduction of material needed is in line with an eco-design beneficial to the environment while reducing the cost in raw materials.

[0051] The additive manufacturing techniques ultimately make it possible to obtain so-called bulk parts, which, contrary to the assembly techniques such as diffusion brazing or diffusion welding, have no assembly interfaces between each etched plate. This property supports the mechanical withstand strength of the apparatus by eliminating, by construction, the presence of embrittlement lines and by thereby eliminating a potential source of defect.

[0052] The obtaining of bulk parts by additive manufacturing and the elimination of the diffusion brazing or welding interfaces makes it possible to envisage numerous design possibilities without being limited to wall geometries designed to limit the impact of any assembly faults such as discontinuities in the brazed joints or in the welded-diffused interfaces.

[0053] Additive manufacturing makes it possible to produce forms that cannot be envisaged by the traditional manufacturing methods and thus the manufacturing of the connectors of the millimetre-scale exchangers-reactors or exchangers can be done in continuity with the manufacturing of the body of the apparatuses. This then makes it possible to not perform an operation of welding of the connectors to the body and thus eliminate a source of damage to the structural integrity of the equipment.

[0054] The control of the geometry of the channels by additive manufacturing allows the production of channels with circular section which, in addition to the good pressure withstand strength that this form provides, makes it possible also to have a channel form that is optimal for the deposition of protective coatings and of catalysts which are thus uniform all along the channels. By using this additive manufacturing technology, the productivity gain aspect is also made possible by the reduction of the number of manufacturing steps. In effect, the steps of producing a reactor by incorporating additive manufacturing change from seven to four (FIG. 6). The critical steps, potentially resulting in a scrapping of a complete apparatus or of the plates forming the reactor, of which there are four when using the conventional manufacturing technique by assembly of chemically etched plates, change to two with the adoption of additive manufacturing. Thus, the only remaining steps are the additive manufacturing step and the step of deposition of coatings and of catalysts.

[0055] To sum up, the advantages of additive manufacturing over a conventional solution of diffusion brazing or welding of chemically etched plates are: [0056] a greater intensification of the method (integration of the channels, compactness) [0057] a reduction of the weight of the reactor or increase in the volume useful to the catalytic reaction [0058] a reduction of the number of manufacturing steps and of parties involved located on different sites [0059] improved manufacturing quality by ensuring perfect reproducibility [0060] possible monitoring of the method during manufacturing, which will reduce the quantity of parts scrapped [0061] simplification of the design validation according to the ASME construction code.

[0062] The exchanger-reactor according to the invention is particularly suitable for use in a steam reforming method, preferably for the production of hydrogen with a flow rate of between 0.1 and 10 Nm.sup.3/h, preferably between 1 and 5 Nm.sup.3/h.

[0063] In the context of hydrogen production less than 5 Nm.sup.3/h, we can take the example of an exchanger-reactor made of Inconel 625 for the production of 0.6 Nm.sup.3/h of hydrogen intended to supply a fuel cell to produce electricity and hot water in a dwelling. The dimensional characteristics for this reactor-exchanger would be as follows: [0064] Nickel-based materials (Inconel 601-625-617-690) [0065] Channels 1.14 mm in diameter [0066] 0.4 mm wall [0067] Effective length of the channels 150 mm [0068] Number of reagent channels 232 [0069] Number of return channels 116 [0070] Number of heat top up channels 174 [0071] Width of the exchanger-reactor 49 mm [0072] Overall length of the exchanger-reactor 202 mm [0073] Height of the exchanger-reactor 25.4 mm [0074] The reagent channels and the return channels are protection coated against corrosion [0075] The reagent channels are coated with catalyst

[0076] From the following input conditions:

TABLE-US-00001 Reagent gas Fumes Flow rate Nm.sup.3/h 0.70 2.01 Temperature C. 368.5 900 Pressure bar 1.1 1.1 Composition CH.sub.4 0.2050 0.0000 C2 0.0000 0.0000 H.sub.2O 0.6149 0.1149 O.sub.2 0.0000 CO.sub.2 0.0439 0.0307 H.sub.2 0.1357 0.0000 CO 0.0005 0.0000 N.sub.2 0.0000 0.7213

[0077] The equipment described previously makes it possible to achieve the following performance levels:

TABLE-US-00002 Gas produced Fumes Flow rate Nm.sup.3/h 0.97 2.01 Temperature C. 439 460 Pressure bar 1.1 1.1 Composition (mol basis) CH.sub.4 0.01 0.0000 C2 0.0000 0.0000 H.sub.2O 0.31 0.1149 O.sub.2 0.0000 0.1331 CO.sub.2 0.030 0.0307 H.sub.2 0.51 0.0000 CO 0.14 0.0000 N.sub.2 0.0000 0.7213 Head loss mbar 6.19 10.76