APPARATUS FOR GENERATING HYDROGEN, PARTICULARLY FOR SUPPLYING FUELL CELLS

Technical Field

The present invention relates to an apparatus for generating hydrogen, particularly for supplying fuel cells or the like.

As is known, hydrogen intended in particular to supply fuel cells or other similar devices is generated by using apparatuses which allow to provide a so-called "steam reforming" process, which substantially consists in reacting, in the presence of a catalyst and by applying heat, methane and water vapor to obtain hydrogen (H ₂ ), carbon dioxide (CO ₂ ) and, in small amounts, carbon monoxide (CO) as reaction products.

Typically, the products obtained from the steam reforming process are then further processed to reduce the amount of CO, which is harmful for fuel cells, possibly obtaining higher quantities of hydrogen.

For this purpose, the gases obtained from the steam reforming reaction are generally sent to a first apparatus, which performs an exothermic process known as "water gas shift", which consists in practice in introducing water vapor into the gases to be treated, keeping the temperature at a preset value by means of a cooling fluid which is fed to the water gas shift apparatus, and then to a second apparatus, which in turn allows to perform an additional exothermic process which is known in technical jargon as "prox" and consists instead in introducing oxygen in the gases being processed at a preset temperature, which is also kept constant by means of a suitable cooling fluid.

Currently commercially available steam reforming apparatuses are generally constituted by an outer enclosure which defines a heat exchange region, into which a high-temperature hot gas is sent in order to supply the heat required for the steam reforming reaction and in which there are reaction ducts constituted by a plurality of tubular elements which have a

flattened transverse cross-section and a rectilinear axis and accommodate internally a catalyst which is capable of facilitating the reforming reaction and are connected by means of their input to a source of methane and water vapor and, by means of their output, to a discharge for the reaction products. Although steam reforming apparatuses structured as described above are valid in principle, they suffer however some drawbacks, including certainly the fact of having considerable production complexity, which also entails high manufacturing costs.

The tubular elements arranged inside the heat exchange region are in fact fixed at their opposite ends to respective supporting tube plates by means of a butt weld which is difficult to perform due to the flattened shape of the passage section of such tubular elements.

Another drawback observed in currently known reforming apparatuses is constituted by their poor reliability over time. The tubular elements, at the high temperatures to which they are subjected in order to promote the steam reforming reaction, are in fact subjected to considerable mechanical stresses, which may cause the onset of cracks or ruptures in the regions where such tubular elements are welded to the tube plates, with the risk that the flue gases used for heating might mix with the reagents and the reaction products, consequently compromising the correct operation of the apparatus.

Another drawback of currently available steam reforming apparatuses is that they are rather bulky since, in order to facilitate the substantially complete reaction of the methane and water vapor, the tubular elements must have a considerable length and a very large lateral heat exchange surface.

DiscIosHre of the Invention

The aim of the present invention is to provide a valid solution to the drawbacks cited above by providing an apparatus for generating hydrogen particularly for supplying fuel cells or the like which has an extremely

simplified structure, so that it can be manufactured at very low cost.

Within this aim, an object of the invention is to provide an apparatus which, thanks to its particular constructive characteristics, is capable of offering the greatest assurances of reliability and safety in operation. Another object of the invention is to provide an apparatus which can be used to perform a steam reforming process or a water gas shift process or a prox process.

Another object of the present invention is to provide an apparatus for generating hydrogen which allows to modify easily its operating conditions to adapt, it to the different contingent requirements, by acting very simply only on some of its constructive characteristics.

Still another object of the present invention is to provide an apparatus for generating hydrogen which is structurally very compact and has small dimensions. This aim and these and other objects, which will become better apparent hereinafter, are achieved by an apparatus for generating hydrogen, particularly for supplying fuel cells or the like, according to the invention, comprising an enclosure which defines a heat exchange region which can be supplied with a heat exchange fluid and is crossed by at least one reaction duct which accommodates a catalyst and has an inlet for the inflow of the reagents and an outlet for the discharge of the reaction products and is characterized in that said at least one reaction duct has a cylindrical spiral shape. Brief Description of the Drawings Further characteristics and advantages of the invention will become better apparent from the description of some preferred but not exclusive embodiments of the apparatus according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a schematic longitudinal sectional view of the apparatus according to the invention in an embodiment adapted to perform a steam

reforming process;

Figure 2 is a schematic longitudinal sectional view, taken to illustrate the interior, of a reaction duct of the apparatus according to the invention, the duct being shown, for the sake of simplicity in illustration, as if it were straight, and being further shown in the specific case of the first embodiment of the invention of Figure 1 ;

Figure 3 is a schematic longitudinal sectional view of three apparatuses according to the invention arranged in series to each other, each designed to perform a different process for obtaining hydrogen. Ways of carrying out the Invention

With reference to the figures, the apparatus according to the invention, designated by the reference numerals Ia, Ib and Ic in the different embodiments, generally comprises an enclosure 2, which defines a heat exchange region 3 which is crossed by at least one reaction duct 4 inside which a catalyst agent 5 is arranged.

The reaction duct 4 has in particular an inlet 4a for the inflow of the reagents and an outlet 4b for the discharge of the reaction products.

The heat exchange region 3 is supplied with a heat exchange fluid, which is designed to exchange heat with the products which flow inside the reaction duct 4.

The peculiar aspect of the invention consists in that the reaction duct. 4 has, along at least one of its portions arranged inside the heat exchange region 3, a preferably cylindrical spiral shape, so as to provide in practice a coil. In greater detail, the heat exchange region 3 is conveniently provided by a substantially cylindrical containment chamber 6 inside which the reaction duct 4 is positioned.

The containment chamber 6 can be obtained for example by providing the enclosure 2 by means of a cylindrical side wall 2a, which is closed at its opposite ends by two opposite end walls 2b.

Advantageously, the reaction duct 4 lies, with its cylindrical spiral portion, substantially coaxially with respect to the containment chamber 6.

It should be noted that it is also optionally possible to provide, along the reaction duct 4, one or more auxiliary inlets 4c, through which it is possible to introduce in the reaction duct 4 additional quantities of the reaction products, so as to facilitate the reaction processes.

As shown in Figure 2, the catalyst 5 is provided by means of at least one elongated plate-like element 7 which is arranged along at least one portion of the longitudinal extension of the reaction duct 4 and supports a catalyst agent, which can vary as a function of the type of reaction to be performed inside the reaction duct 4.

The plate-like element 7 conveniently comprises at least one grid-like portion 7a, preferably made of a material which is inert with respect to the reaction that occurs inside the reaction duct 4 and more preferably is made of a heat-resistant metallic material, such as for example an AISI 316 L, AISI 309 S, AISI 304, AISI 430, AISI 310 S steel and the like or an unalloyed carbon steel.

In particular, the catalyst agent is deposited onto at least one face of the grid-like portion 7a by means of a process which depends on the materials used.

According to an important aspect of the invention, the plate-like element 7 is folded in a helix along its longitudinal extension, so as to define inside the reaction duct 4 at least one substantially helical path for the reagents which forces such reagents to affect the surfaces of the plate-like element 7.

Moreover, with the helical shape of the plate-like element 7, one achieves in practice a greater possibility of crossing of the grid-like portion

7a on the part of the reagents which flow along the reaction duct 4 and accordingly a higher possibility of contact of the reagents with the catalyst agent.

It should be noted that the plate-like element 7 can have a helix with a constant pitch or advantageously with a pitch which varies along its longitudinal extension.

It is optionally also possible for the catalyst 5 to be constituted by a plurality of small bodies, such as for example spheroidal elements or pellets, on the outer surface of which the catalyst agent is applied. Advantageously, such bodies provide, inside the reaction duct 4, a loose system which is permeable to the flow of the reagents, so as to create a large surface of contact between the catalyst agent and the reagents. It should be noted that it is also possible to provide for the combined use of the different types of catalysts 5 described above.

With reference to the first embodiment, shown in particular in Figure 1, the apparatus Ia allows to perform a steam reforming process.

In this case, the reagents introduced in the reaction duct 4 at its inlet 4a comprise water vapor and at least, one hydrocarbon preferably in gaseous form, such as for example methane or other natural gas, whereas at the outlet 4b of the reaction duct 4 it is possible to obtain a mixture of gases containing hydrogen and carbon dioxide with the optional presence of carbon monoxide. In the first embodiment, therefore, it is possible to introduce through the auxiliary inlets 4c which may be present along the reaction duct 4 additional amounts of water vapor and/or methane to control the quantities of the various reaction products obtained.

It should also be noted that in the case of the apparatus 1 a, the heat exchange fluid fed to the heat exchange region 3 is constituted by the hot combustion flue gases generated by a burner 8 which is functionally associated with said heat exchange region 3.

As shown in Figure 1 , the burner 8 is conveniently arranged coaxially with respect to the spiral formed by the reaction duct 4 and is advantageously arranged at a first axial end 6a of the containment chamber

6, which at its axial end 6b which lies opposite the first end 6a is connected to a port 10 for the discharge of the combustion flue gases, in order to allow their evacuation into the external environment.

As can be deduced easily, with this configuration the flow of combustion flue gases can cross the containment chamber 6 longitudinally from its end 6a to the opposite end 6b.

In order to ensure effective transfer of the heat from the combustion flue gases to the reagents which transit in the heat exchange region 3 through the reaction duct 4, conveniently inside the containment chamber 6 there is at least one baffle for the combustion flue gases which allows to create a convoluted path for the combustion flue gases which pass through the containment chamber 6.

As in the illustrated example, the baffle can be provided by means of at least one disk 1 1 made of heat resistant material, which is arranged coaxially to the spiral formed by the reaction duct 4 and is arranged in practice between the inlet 4a and the outlet 4b of the reaction duct 4.

Again with the purpose of optimizing heat exchange between the combustion flue gases and the reagents and consequently facilitating the reaction occurring inside the reaction duct 4, the inlet 4a of the reaction duct 4 is advantageously positioned proximate to the first end 6a of the containment chamber 6 and therefore of the burner 8, while its outlet 4b is arranged proximate to the opposite end 6b of the containment chamber 6 and therefore proximate to the combustion flue gas discharge port 10.

It should be noted that it is also possible to provide for reversal of the position of the inlet 4a and of the outlet 4b with respect to the arrangement described above, so as to be able to obtain an exchange in countercurrent, instead of in equi current, between the reagents and the combustion flue gases, which can have an even more positive effect on the chemical reaction that occurs inside the reaction duct 4. By way of example, in the first embodiment the catalyst agent can be

constituted by a layer of platinum which is applied by electrolytic deposition to the grid-like portion 7a of the plate-like element 7, conveniently made of AISI 304, AISI 316, AISI 310 S or AISI 309 S steel.

The second embodiment of the invention, shown in Figure 2, allows to provide a water gas shift process, particularly on the reaction products obtained in output from the apparatus Ia, in order to eliminate or at least reduce the amount of carbon monoxide generated by the steam reforming reaction performed by the apparatus 1 a.

More specifically, the reaction duct 4 of the apparatus Ib is connected, by means of its inlet 4a, to the outlet 4b of the reaction duct of the apparatus Ia and to a water vapor source, so as to receive in input, as reagents, a mixture in gaseous form which contains hydrogen, carbon dioxide and carbon monoxide, and a preset quantity of water vapor.

Moreover, it is possible to add, through optional auxiliary inlets 4c, additional amounts of water vapor to the reagents that transit along the path of the reaction duct 4 of the apparatus Ib, so as to be able to control effectively the reaction products obtained in output.

In this case, the catalyst agent is constituted for example by platinum, palladium, rhodium, chromium, nickel, iron oxides and noble metals. Since the water gas shift reaction is exothermic, the heat exchange region 3, and more particularly the chamber 6 for containing the apparatus Ib, is fed with a cooling fluid, which is constituted in particular by a diathermic fluid, such as for example water, in order to maintain the temperature inside the reaction duct 4 at a substantially constant value which is adapted to ensure activation of the catalyst 5. By way of example, the temperature inside the reaction duct 4 of the apparatus Ib is generally kept from 300 to 500 ⁰ C.

Conveniently, the cooling fluid is introduced in the containment chamber 6 of the apparatus Ib by means of an inlet 12, which is connected to a line 12a for delivering the cooling fluid and is discharged from the

containment chamber 6 by means of an outlet 13 which leads to a line 13a for drawing the cooling fluid.

More particularly, the delivery line 12a and the withdrawal line 13a of the cooling fluid are preferably both connected, respectively through the inlet 12 and the outlet 13, to the same end 6a of the containment chamber 6, in the proximity to which the inlet 4a of the reaction duct 4 is conveniently positioned.

In the third embodiment, the apparatus I c allows to perform a prox process, which allows to further reduce the amount of carbon monoxide which may be present as a residue after the steam reforming and water gas shift process.

In particular, the reaction products obtained in output from the apparatus Ib are introduced through the inlet 4a into the reaction duct 4 of the apparatus 1 c and receive the addition of a preset amount of air or oxygen which is dispensed by an appropriately provided source, not shown, which is also connected to the inlet 4a of the reaction duct 4.

It is optionally possible to add, along the path of the reagents through the reaction duct 4, other quantities of air or oxygen by means of the auxiliary inlets 4c. Analyzing the third embodiment more particularly, it can be seen that the apparatus Ic has a structure which is substantially similar to the structure of the apparatus Ib.

More specifically, since the prox reaction is exothermic like the water gas shift reaction, the heat exchange region 3 of the apparatus Ic also is supplied with a cooling fluid, which allows to keep the temperature in the reaction duct 4 at a substantially constant level, preferably ranging from 100 to 300 ⁰ C.

In a manner similar to the apparatus Ib, in the case of the apparatus

I c also, the cooling fluid is preferably introduced in the containment chamber 6 by means of an inlet 12 which is connected to a line 12a for the

delivery of the cooling fluid and is arranged at the same end 6a of the containment chamber 6 at which an outlet 13 is opened which reaches a line 13a for drawing the cooling fluid.

It should be noted that the delivery line 12a and the withdrawal line 13a connected to the apparatus I c may be the same ones that feed the heat exchange region of the apparatus Ib or may also be different.

Advantageously, in the apparatus Ic as well, the inlet 4a of the reaction duct 4 is positioned proximate to the end 6a of the containment chamber 6. For the sake of completeness, it must be added that the catalyst agent used in the apparatus I c can be constituted for example by platinum, palladium, rhodium, chromium, nickel, iron oxides and noble metals, copper, silver.

As mentioned above and as shown in Figure 3, the apparatuses Ia, Ib and Ic may be arranged so that their corresponding reaction ducts 4 are connected in series to each other, so as to provide a complete hydrogen generation process.

It should also be added that in all the embodiments it is optionally possible to provide, inside the reaction region, even two or more reaction ducts 4, each of which has, along at least one portion, a cylindrical spiral shape.

In this case, the reaction ducts 4 are preferably arranged substantially coaxially to each other and so that the turns of one of the reaction ducts 4 are interleaved between the turns of the others. It should also be specified that in all the embodiments each reaction duct 4 is preferably made of stainless steel.

Operation of the apparatus according to the invention is as follows. With reference to the first embodiment and to Figure 1 , a mixture of water vapor and methane, preferably at a temperature substantially ranging from 0 to 200 ⁰ C, is introduced through the inlet 4a into the reaction duct 4,

] 1 inside which it comes into contact with the catalyst 5, which allows the activation of the steam reforming reaction.

At the same time, the burner 8 is operated so as to generate inside the containment chamber 6 combustion flue gases at a temperature which ranges substantially from 300 to 1000 ⁰ C, in order to transmit to the reagents which transit through the reaction duct 4 the heat required to perform the steam reforming reaction.

In particular, the flow of the combustion flue gases is diverted, with the aid of the disk 1 1, toward the coils of the reaction duct 4, through which it flows, striking externally the reaction duct 4, until it reaches the end 6b of the containment chamber 6, from which it exits by means of the discharge port 10.

The reaction products, constituted by hydrogen, carbon dioxide and optionally carbon monoxide, obtained from the steam reforming reaction exit from the reaction duct 4 at its outlet 4b and are drawn in order to be sent directly to a fuel cell or optionally to an additional treatment step.

With reference to Figure 3, in this last case the reaction products extracted from the apparatus Ia are sent to the apparatus Ib, in which they undergo a water gas shift process and more specifically are introduced in the reaction duct 4 of the apparatus 1 b by means of the corresponding inlet 4a, to which a stream of water vapor is also fed which, by reacting with the carbon monoxide, allows to obtain additional quantities of hydrogen and carbon dioxide.

The optimum temperature conditions for performing this reaction are maintained by introducing in the heat exchange region 3 of the apparatus Ib the cooling fluid dispensed by the delivery line 12a through the inlet 12 and making it exit toward the withdrawal line 13a by means of the outlet 13.

The reaction products obtained in output from the reaction duct 4 of the apparatus Ib can be used to supply a fuel cell or, if there are still unwanted residues of carbon monoxide, they can be sent to the apparatus Ic,

in which they are treated with a prox process.

Again with reference to Figure 3, the inlet 4a of the reaction duct 4 of the apparatus I c can thus be connected to the outlet 4b of the reaction duct 4 of the apparatus Ib and to a source of oxygen or air. Due to the circulation of the cooling fluid inside the heat exchange region 3 of the apparatus Ic, performed by introducing it through the inlet 12 and extracting it through the outlet 13, the reagents which transit along the reaction duct 4 of the apparatus Ic are kept at a substantially constant temperature, preferably ranging from 100 to 300 ⁰ C. With these temperature conditions and by means of the action of the catalyst 5, the reaction between the carbon monoxide and the oxygen introduced in input occurs in the reaction duct 4 of the apparatus Ic, consequently obtaining carbon dioxide.

In practice it has been found that invention achieves, in all of its embodiments, the intended aim and objects and in particular the fact is stressed that the cylindrical spiral structure of the reaction duct allows to achieve extremely uniform temperatures along the entire reaction duct itself, so as to ensure the optimum reaction conditions for the reagents along its entire extension. Moreover, in the particular case of the first embodiment, the spiral structure of the reaction duct allows to bring the reagents that transit inside it to extremely high temperatures, so as to achieve ideal conditions for triggering the steam reforming reaction on the part of the catalyst.

Another advantage of the invention consists in that by using the reaction duct arranged in a spiral, the welds exposed to contact with the combustion flue gases are eliminated, overcoming the limitations that occur in the background art.

Another advantage of the invention resides in that due to its spiral shape the time for which the reaction duct is crossed by the reagents can be very long, allowing the complete development of the reactions which lead to

the formation of hydrogen.

It should also be noted that the apparatus according to the invention, structured in the manner described above, is capable of having an extremely low thermal inertia, which makes it very flexible to the variable load required by fuel cells.

It should also be added to the above that by changing the position of the disk or disks made of heat-resistant material inside the spiral formed by the reaction duct, by varying the distance between one turn and the next of the spiral formed by the reaction duct, by varying the diameter of the spiral formed by the reaction duct, by varying the number of reaction ducts, by varying the density, type and characteristics of the catalyst elements contained inside the or each reaction duct, and finally by varying the linear extension of the reaction duct, it is possible to achieve different conditions of heat transmission between the heat exchange fluid that is used and the reagents that transit within said reaction duct.

All the characteristics of the invention indicated above as advantageous, convenient or the like may also be omitted or be replaced with equivalents.

The individual characteristics presented with reference to general teachings or particular embodiments may all be present in other embodiments or may replace characteristics in these embodiments.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. In practice, the materials used, so long as they are compatible with the specific use, as well as the shapes and dimensions, may be any according to requirements.

Moreover, all the details may be replaced with other technically equivalent elements. The disclosures in Italian Patent Application No. VR2006A000186

from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.