Method for overheating gases at the inlet of a SOEC/SOFC-type solid oxide stack

Abstract

A system for overheating gases at the inlet of a SOEC/SOFC-type solid oxide stack, the stack including a main body that has first and second zones separated by a median plane, and inflow and outflow conduits, the zones include gas circulation circuits extending in the form of a spiral and communicating by means of a passage passing through the main body. A gas flow to be heated entering the inflow conduit circulates in the first gas circulation circuit and passes through the passage to then circulate in the second gas circulation circuit and in the conduit for the outflow of the reheated gases in order to reach the inlet of the SOEC/SOFC-type solid oxide stack.

Claims

1. A solid-oxide electrolyzer cell/solid-oxide fuel cell (SOEC/SOFC) stack, comprising an assembly comprising: at least one SOEC/SOFC stack inlet gas superheat system, comprising: a main body comprising a first zone for inlet of gases to be heated and a second zone for outlet of heated gases, the first and second zones being separated by a transverse median plane of the main body, at least one inlet duct for the gases to be heated communicating with the first zone of the main body, at least one outlet duct for the heated gases communicating with the second zone of the main body, the first and second zones of the main body comprising respectively a first gas circulation circuit and a second gas circulation circuit, the first gas circulation circuit extending in a spiral from a first outer end to a first inner end, and the second gas circulation circuit extending in a spiral from a second outer end to a second inner end, the first and second inner ends communicating with each other through a through-passage of the main body, formed through the median plane of the main body for fluid communication of the first and second zones, the at least one inlet duct and the at least one outlet duct being in fluid communication with the first and second outer ends, respectively, so that a flow of gas to be heated entering the at least one inlet duct flows into the first gas circulation circuit from the first outer end to the first inner end, and passes through the through-passage and then flows into the second gas circulation circuit, from the second inner end to the second outer end, and then into the at least one outlet duct to reach the inlet of the SOEC/SOFC stack, the at least one inlet duct and the at least one outlet duct extend perpendicular to the median plane of the main body in superposition with respect to each other, and at least one heating element placed in contact with said at least one gas superheat system.

2. The SOEC/SOFC stack according to claim 1, wherein the at least one gas superheat system comprises a first closure plate and a second closure plate, extending on either side of the main body to cover the first and second zones of the main body, respectively, the first gas circulation circuit being located between the median plane and the first closure plate and the second gas circulation circuit being located between the median plane and the second closure plate.

3. The SOEC/SOFC stack according to claim 1, the at least one inlet duct and the at least one outlet duct are separated from each other by a transverse median wall of the main body in which the through-passage is formed.

4. The SOEC/SOFC stack according to claim 1, wherein the main body has a cylindrical shape.

5. The SOEC SOFC stack according to claim 1, the main body has a main portion, comprising the first and second gas circulation circuits, and a lateral portion projecting from the main portion, the at least one inlet duct and the at least one outlet duct are fluidly connected to the main body at the lateral portion.

6. The SOEC/SOFC stack according to claim 1, wherein the main body is made of nickel-based superalloy.

7. The SOEC/SOFC stack according to claim 1, wherein the assembly comprises at least two heating elements arranged on either side of the at least one gas superheat system.

8. The SOEC/SOFC stack according to claim 1, wherein the assembly comprises at least two gas superheat systems in contact with each other and at least two heating elements sandwiching the at least two gas superheat systems.

9. The SOEC/SOFC stack according to claim 1, wherein the at least one heating element has a shape similar to the shape of the at least one gas superheat system.

10. A process for manufacturing the SOEC/SOFC stack according to claim 1, comprising machining the main body to form the first gas circulation circuit and the second gas circulation circuit.

11. The process according to claim 10, further comprising attaching, by a laser transmission welding process, a first closure plate and a second closure plate on either side of the main body to cover the first and second zones of the main body, respectively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention can be better understood by reading the following detailed description, an exemplary non-limiting implementation thereof, and by examining the figures, schematic and partial, of the annexed drawing, on which:

(2) FIG. 1 is a schematic view showing the operating principle of an SOEC,

(3) FIG. 2 is an exploded schematic view of a part of an SOEC comprising interconnects according to the prior art,

(4) FIG. 3 illustrates the principle of the architecture of a furnace on which a high-temperature SOEC or SOFC stack is placed,

(5) FIG. 4 illustrates the principle of an electric gas heater according to the prior art,

(6) FIG. 5 shows, in perspective, an exemplary gas superheat system in conformity with the invention for an SOEC/SOFC stack,

(7) FIG. 6 shows, according to a cross-sectional view, the superheat system in FIG. 5,

(8) FIG. 7 shows, in perspective, the superheat system in FIG. 5, without the presence of closure plates, on the gas inlet side,

(9) FIG. 8 shows, in perspective, the superheat system in FIG. 5, without the presence of closure plates, on the gas outlet side,

(10) FIG. 9 illustrates the transmission welding path to follow for attaching the closure plates to the main body of the superheat system in FIG. 5,

(11) FIG. 10 shows, according to a cross-sectional view, an exemplary SOEC/SOFC stack comprising heating elements on either side of a plurality of superheat systems such as that shown in FIG. 5, and

(12) FIG. 11 illustrates, in perspective, another exemplary SOEC/SOFC stack comprising a heating element in contact with a plurality of superheat systems such as that shown in FIG. 5 for two gas lines.

(13) In all these figures, identical references may refer to identical or similar elements.

(14) In addition, the different parts represented on the figures are not necessarily represented on a uniform scale, to make the figures easier to read.

DETAILED DISCLOSURE OF A PARTICULAR EMBODIMENT

(15) FIGS. 1 to 4 have already been described above in the section on the state of the art and the technical context of the invention. It is specified that, for FIGS. 1 and 2, the symbols and arrows for the supply of steam H.sub.2O, distribution and recovery of hydrogen H.sub.2, oxygen O.sub.2, air and electric current are shown for clarity and precision purposes, to illustrate the operation of the devices shown.

(16) In addition, it should be noted that all the components (anode/electrolyte/cathode) of a given electrochemical cell are preferentially ceramics. The operating temperature of a high-temperature SOEC/SOFC stack is also typically between 600 and 1000° C.

(17) Furthermore, the terms “upper” and “lower”, if used, are to be understood here according to the normal direction of orientation of an SOEC/SOFC stack when in its configuration of use.

(18) FIGS. 5 to 11 illustrate a principle of realization of a superheat system 40 according to the invention. This superheat system 40 heats the inlet gases of an SOEC/SOFC stack 20 associated with a furnace 10, as previously described in reference to FIG. 3.

(19) Among the different heat transfer modes in the zone of the furnace 10, the predominant mode at these temperature levels, between 650 and 800° C., corresponds to radiative exchanges by radiation. The other transfer mode is then thermal conduction, and this is the one that the invention implements because it has the advantage of creating less heat loss to the outside. This is the mode of heat transfer caused by a temperature difference between two regions of the same medium or between two media in contact without appreciable displacement of material. The use of heating plates, as described below, for the superheat system 40 allows the heat conduction to be recovered and the gases to be raised to the correct temperature.

(20) As shown in FIGS. 1 to 8, the superheat system 40 for the gases OG entering the SOEC/SOFC stack 20 first comprises a main body 41 in the form of a central block 41.

(21) This central block 41 forms a compact system which is here in a cylindrical shape of circular cross-section, with a diameter D of about 140 mm and a height H of about 22 mm, as shown in FIG. 5.

(22) This central block 41 is for example made of nickel-based superalloy, particularly Inconel 600.

(23) As shown in FIG. 6, the central block 41 has a first zone Z1, called the lower zone, for the inlet of the gases to be heated IG and a second zone Z2, called the upper zone, for the outlet of the heated gases OG.

(24) These lower Z1 and upper Z2 zones are separated by a transverse median plane M of the central block 41.

(25) Furthermore, the superheat system 40 also comprises an inlet duct 42 for the gases to be heated IG communicating with the lower zone Z1 of the central block 41, and an outlet duct 43 for the heated gases OG communicating with the upper zone Z2 of the central block 41.

(26) As shown in FIG. 6, these first Z1 and second Z2 zones comprise a first gas circulation circuit C1 and a second gas circulation circuit C2, respectively.

(27) Advantageously, each gas circulation circuit C1, C2 extends in the form of a spiral, here circular, respectively from a first outer end P1 to a first inner end I1, and from a second outer end P2 to a second inner end I2.

(28) These first I1 and second I2 inner ends communicate with each other via a through-passage 44 of the central block 41, which is formed through the median plane M for the fluid communication of the first Z1 and second Z2 zones.

(29) In addition, as also shown in FIG. 6, the inlet 42 and outlet 43 ducts are in fluid communication with the first P1 and second P2 outer ends, respectively.

(30) In this way, as illustrated by the course of the arrows in FIGS. 6, 7 and 8, a flow of gas to be heated IG entering the inlet duct 42 flows into the first gas circulation circuit C1, from the first outer end P1 to the first inner end I1, and crosses the through-passage 44 and then flows into the second gas circulation circuit C2, from the second inner end I2 to the second outer end P2, and then into the heated gas OG outlet duct 43 to finally reach the inlet of the SOEC/SOFC stack 20.

(31) In addition, as shown in FIGS. 5 and 6, the superheat system 40 has two closure plates 45 and 46, extending on either side of the central block 41. More precisely, the first gas circulation circuit C1 is located between the median plane M and the closure plate 45 and the second gas circulation circuit C2 is located between the median plane M and the closure plate 46.

(32) Furthermore, the first C1 and second C2 gas circulation circuits are formed by machining, for example by means of a numerically controlled milling machine or other appropriate machining system to obtain a spiral. This machining is carried out in a spiral converging towards the center of the central block 41 at the level of the through-passage 44.

(33) The machining depth f, shown in FIG. 6, is for example about 10 mm, while the machining width W, also shown in FIG. 6, is about 3 mm. Advantageously, the machining section is equivalent to the section covered by the inner diameter of an Inconel 600 tube of diameter 10/12. In general, the cross-section of the spiral formed corresponds preferentially to the quantity of gas required to feed the stack 20.

(34) In addition, as shown in FIGS. 5 to 8, it should be noted that the inlet 42 and outlet 43 ducts extend perpendicular to the median plane M in superposition with respect to each other and are separated from each other by a transverse median wall 47 of the central block 41 in which the through-passage 44 is formed.

(35) Furthermore, the central bock 41 has a main portion 61, comprising the first C1 and second C2 gas circulation circuits, and a lateral portion 62 projecting from the main portion 62 at which the inlet 42 and outlet 43 ducts are fluidly connected to the central block 41.

(36) The inlet gases IG, from heat exchangers, enter the first spiral of the first circuit C1 and converge towards the center of the central block 41 to the through-passage 44 over a total length of about 1.8 m. From there, the gases cross the median plane M through the through-passage 44 and follow an opposite path in the second spiral of the second circuit C2 to travel a total length of about 1.8 m as well.

(37) The closure plates 45 and 46 are preferentially attached by laser transmission welding. The laser welding technique allows the welding of metals by the features of laser technology: with the high energy density and fineness of the laser beam, the targeted areas melt and then are quickly welded by cooling. The result is a solid weld on a small surface.

(38) As shown in FIG. 9, the laser transmission welding should preferentially follow the contour C as shown in order to force the gases to follow the full path.

(39) In addition, it is possible to double the superheat system 40 described above for a plurality of gas lines. Thus, FIGS. 10 and 11 illustrate examples of SOEC/SOFC stacks 20 comprising an assembly 70 of two superheat systems 40 for the inlet gases OG of the stack 20 associated with heating elements 80 in the form of heating plates 80.

(40) More precisely, in FIG. 10, two heating plates 80 are located on either side of two superheat systems 40 so that they are sandwiched by the heating plates 80. These heating plates 80, in contact with the superheat systems 40, allow the gases to be heated by thermal convection before entering the stack 20.

(41) In FIG. 11, the assembly 70 has a heating plate 80 similar in shape to the central block 41.

(42) Of course, the invention is not limited to the exemplary embodiment that has just been described. Various modifications can be made by persons skilled in the art.