GB2475239A

GB2475239A - A continuous flow furnace for heat treating components

Info

Publication number: GB2475239A
Application number: GB0919609A
Authority: GB
Inventors: Sian Guan Teo; Rowland Paul Travis; Steven Hayter; Danny Duggan
Original assignee: Rolls Royce Fuel Cell Systems Ltd
Current assignee: Rolls Royce Fuel Cell Systems Ltd
Priority date: 2009-11-10
Filing date: 2009-11-10
Publication date: 2011-05-18
Also published as: GB0919609D0

Abstract

A continuous flow furnace 110 and associated method of heat treating a component in the continuous flow furnace is disclosed which comprises placing a first component 18 on a first setter member 20 and placing a second component 18 on a second setter 20. The first setter is placed on a transport member 22 and the second setter is placed on the first setter. The first setter member is thermally isolated from the transport member. The transport member is placed on a conveyor 16 for the continuous flow furnace. The transport member and first setter member, second setter member, a first component and a second component are transported on the conveyor into the continuous flow furnace. The first component and the second component are heat treated in the continuous flow furnace. This may be used to heat treat solid oxide fuel cell components at high volumes with consistently high quality.

Description

A METHOD OF HEAT TREATING COMPONENTS IN A

CONTINUOUS FLOW FURNACE AND A CONTINUOUS FLOW

FURNACE

The present invention relates to a method of heat treating components in a continuous flow furnace and a continuous flow furnace and in particular relates to a method of sintering ceramic components, e.g. solid oxide fuel cell components, or solid oxide electrolysis cell components, in a continuous flow furnace.

In a tubular solid oxide fuel cell module the layers of each solid oxide fuel cell are deposited onto an outer surface of a hollow cylindrical ceramic tube and in a planar solid oxide fuel cell module the layers of each solid oxide fuel cell are deposited onto two outer flat surfaces of a hollow tubular ceramic tube. The layers of each solid oxide fuel cell are an anode layer, an electrolyte layer and a cathode layer and there are interconnector layers to connect adjacent solid oxide fuel cells in electrical series. The layers of the solid oxide fuel cell may be deposited by screen printing, tape casting, plasma spraying, CVD and/or PVD.

The layers of the solid oxide fuel cells must be sintered in order to consolidate the ceramic particles to strengthen and/or to densify the layers and the sintering occurs at high temperatures. The sintering of the layers of the solid oxide fuel cells occurs in a continuous flow furnace. It may be necessary to sinter each layer at a particular temperature or it may be that two or more layers may be sintered at the same particular temperature. Thus, a particular layer of the solid oxide fuel cells is deposited onto the hollow ceramic tubes of the solid oxide fuel cell module and then the solid oxide fuel cell module is passed through a continuous flow furnace arranged to sinter that particular layer of the solid oxide fuels. A further layer of the solid oxide fuel cells is deposited onto the hollow ceramic tubes of the solid oxide fuel cell module and then the solid oxide fuel cell module is passed through a further continuous flow furnace arranged to sinter that particular further layer of the solid oxide fuels.

In a continuous flow furnace, e.g. a tunnel furnace or a pusher furnace, components are continuously passed through the furnace to heat the components to any required temperature to heat treat the components, e.g. to sinter ceramic components etc. A continuous flow furnace generally comprises one or more chambers, or zones, arranged in flow series. Each chamber, or zone, in the series of chambers, or zones, is generally at a higher temperature than the preceding chamber, or zone. The continuous flow furnace may comprise conventional radiant heater elements and/or microwave heaters or other types of suitable heaters to provide convective and radiant heating.

A continuous flow furnace generally comprises a continuous belt upon which components are placed to be transported into and through the continuous flow furnace. Alternatively a continuous flow furnace may comprise rollers upon which components are placed to be transported into and through the continuous flow furnace.

Generally each solid oxide fuel cell component is placed upon a respective ceramic setter, which is placed on the continuous belt or rollers of the continuous flow furnace. The setters are placed sequentially on the continuous belt, or rollers, such that a single series of setters and associated components are arranged in flow series in the continuous flow furnace.

It is necessary that the continuous flow furnace produce solid oxide fuel cells at high volumes with consistently high quality.

Accordingly the present invention seeks to provide a novel method of heat treating a component in a continuous flow furnace.

Accordingly the present invention provides a method of heat treating a component in a continuous flow furnace comprising:-a) placing at least one first component on a first setter member and placing at least one second component on a second setter member, b) placing the first setter member on a transport member and placing the second setter member on the first setter member, c) thermally isolating the first setter member from the transport member, d) placing the transport member on a conveyor for the continuous flow furnace, e) transporting the transport member, the first setter member, the second setter member, at least one first component and at least one second component on the conveyor into the continuous flow furnace, f) heat treating the at least one first component and the at least one second component in the continuous flow furnace and g) removing the at least one first component from the first setter member and removing the at least one second component from the second setter member after the at least one first component and the at least one second component have been heat treated in the continuous heat treatment furnace.

Preferably step a) comprises placing at least one third component on a third setter member, step b) comprises placing the third setter member on the second setter member, step f) comprises heat treating the at least one third component in the continuous flow furnace and step g) comprises removing the at least one third component from the third setter member after the at least one third component has been heat treated in the continuous heat treatment furnace.

Step c) may comprise providing a plurality of raised projections on an upper surface of the transport member, the raised projections being spaced apart on the upper surface of the transport member to thermalJy isolate the first setter member from the transport member.

Step c) may comprise providing at least one spacer member between the transport member and the first setter member. The at least one spacer member may comprise a two dimensional polygonal frame and the two dimensional polygonal frame comprises a plurality of spaced apart vertically extending projections. The two dimensional polygonal frame may be a rectangular frame, a triangular frame, a square frame, a hexagonal frame or an octagonal frame. Alternatively the at least one spacer member may comprise a plurality of spacer members and each of the spacer members comprises a plurality of spaced apart vertically extending projections.

Preferably one or more of the at least one first component, the at least one second component and the at least one third component is a ceramic component.

The ceramic component may be a ceramic support structure for solid oxide fuel cells. Preferably the ceramic component comprises magnesium aluminate spinel.

The ceramic component may be a ceramic layer of a solid oxide fuel cell. Preferably the ceramic layer is an electrolyte layer, an anode layer, a cathode layer or an interconnector layer to connect adjacent solid oxide fuel cells in electrical series.

Preferably step f) comprises sintering the at least one component.

The present invention also provides a continuous flow furnace comprising a conveyor and at least one transport member for transporting components into the continuous flow furnace, each transport member carrying a plurality of setter members, the setter members on each transport member being arranged in a stack, each setter member holding at least one component, thermal isolation means being arranged between each transport member and the respective stack of setter members.

Preferably the conveyor comprises a conveyor belt or a plurality of rollers.

The thermal isolation means may comprise a plurality of raised projections on an upper surface of the transport member, the raised projections being spaced apart on the upper surface of the transport member to thermally isolate the first setter member from the transport member.

The thermal isolation means may comprise at least one spacer member between the transport member and the first setter member.

The at least one spacer member may comprise a two dimensional polygonal frame and the two dimensional polygonal frame comprises a plurality of spaced apart vertically extending projections. The two dimensional polygonal frame may be a rectangular frame, a square frame, a triangular frame, a hexagonal frame or an octagonal frame.

The at least one spacer member may comprise a plurality of spacer members and each of the spacer members comprises a plurality of spaced apart vertically extending projections.

The present invention will be more fully described by way of example with reference to the accompanying drawings in which:-Figure 1 shows a continuous flow furnace.

Figure 2 shows a method of heat treating a component in a continuous heat treatment furnace according to the prior art.

Figure 3 shows a proposed method of heat treating components in a continuous heat treatment furnace according to the

prior art.

Figure 4 is a cross-section through a continuous heat treatment furnace shown in figure 3.

Figure 5 is a cross-section through a continuous heat treatment furnace shown in figure 3 showing heat flows within the continuous heat treatment furnace.

Figure 6 shows a method of heat treating components in a continuous heat treatment furnace according to the present invention.

Figure 7 is a cross-section through a continuous heat treatment furnace shown in figure 6.

Figure 8 is a cross-section through a continuous heat treatment furnace shown in figure 6 showing heat flows within the continuous heat treatment furnace.

Figure 9 is perspective view of a transport member for use in a method according to the present invention.

Figure 10 is a perspective view of a spacer member for use in a method according to the present invention.

Figure 11 is a perspective view of alternative spacer members for use in a method according to the present invention.

A continuous flow furnace 10, as shown in figure 1, comprises a plurality of chambers, or zones, 12 arranged in flow series. Each chamber, or zone, 12 in the series of chambers, or zones, 12 is generally at a higher temperature than the preceding chamber, or zone 12. The continuous flow furnace 10 comprises heater elements 14. The heater elements 14 may be electric radiant heaters and/or microwave heaters or other suitable heaters to provide convective and/or radiant heating. The continuous flow furnace 10 may be of the tunnel furnace type or the pusher type.

The continuous flow furnace 10 either comprises a continuous belt 16 upon which components 18 are placed to be transported into and through the continuous flow furnace 10 or a plurality of rollers 16 upon which components 18 are placed to be transported into and through the continuous flow furnace 10.

As mentioned previously in the prior art method of heat treating components 18 in a continuous flow furnace 10, as shown in figure 2, components 18 to be heat treated are placed on a plurality of setter members 20 and each setter member 20 is placed on a respective transport member 22 such that each setter member 20 is arranged to flow sequentially into and through the continuous flow furnace 10 to heat treat the components 18 placed on the respective setter member 20. The setter members 20 act as storage units to transport the components 18 through the continuous flow furnace 10 and in this case a single series of setter members 20 and associated components 18 are arranged to flow in series through the continuous flow furnace 10. This method only transports a single setter member 20, and its associated components 18, on each transport member 22 through the continuous flow furnace 10. Thus, this method does not produce sufficiently high volumes of heat treated components.

In a proposed method of heat treating components 18 in a continuous flow furnace 10, as shown in figure 3, components 18 to be heat treated are placed on a plurality of setter members 20. A plurality of setter members 20 are placed on a respective transport member 22 such that each setter member 20 is arranged to flow sequentially into and through the continuous flow furnace 10 to heat treat the components 18 placed on the respective setter member 20.

The setter members 20 act as storage units to transport the components 18 through the continuous flow furnace 10 and in this case a plurality of series of setter members 20 and associated components 18 are arranged to flow in series through the continuous flow furnace 10. This method transports a plurality of setter members 20, and the associated components 18, on each transport member 22 through the continuous flow furnace 10. Thus, this method produces sufficiently high volumes of heat treated components. In the example three setter members 20 are placed on each transport member 22, but two, three, four or more setter members 20 may be placed on each transport member 22. Thus in the case of three setter members 20 on each transport member 22 the production of heat treated components 18 is trebled. Similarly two setter members 20 on each transport member 22 would double the production of heat treated components 18 and four setter members 20 on each transport member 22 would quadruple the production of heat treated components 18.

Figures 4 and 5 are cross-sections through the continuous flow furnace 10 with a transport member 22 carrying three setter members 20 and associated components 18. The continuous flow furnace 10 comprises two parallel side walls 11 and 13 and a ceiling 15. As mentioned previously the continuous flow furnace 10 has heater elements 14 and the heater elements 14 are provided on the side walls 11 and 13. Figures 4 and 5 also show a transport member 22 resting on the rollers 16 to be transported through the continuous flow furnace 10. The transport member 22 carries three setter members 20 stacked one upon the other and each setter member 20 carries one or more components 18.

Figure 5 shows the major heat transfer mechanisms within the continuous flow furnace 10. The heater elements 14 emit radiation A, which is the major mechanism for heating all the components 18 which pass through the continuous flow furnace 10. The components 18 and setter members 20 emit radiation B and C, which is significant in cooling all the components 18. There is also natural convection D as shown and forced convection, not shown, perpendicular to the plane of the paper, which may be induced by a flow of air through the length of the continuous flow furnace 10.

Conduction occurs within each component 18 and between touching components 18. There is conduction between the components 18 and the associated setter member 20. There is conduction between setter members 20. There is also significant conduction between the bottom setter member 20 and the transport member 22. As a result of a conduction path between the components 18 and the transport member 22 and the limited convection available within the components 18 there are significant temperature differences within components 18 and between components 18.

In particular the components 18 on the bottom setter member 18 take longer to reach their maximum temperature than the components 18 on the middle and top setter members 18 and thus the components 18 on the bottom setter 20 have a shorter time period in the continuous flow furnace at the maximum temperature than the components 18 on the middle and top setter members 20.

The temperature difference between the components 18 is significant in that the bottom setter member 20 is at a lower temperature than the middle and top setter member 20.

In the case of solid oxide fuel cell components 18, the continuous flow furnace 10 heat treats the components 18 so as to sinter the ceramic of the support tube and/or the layers of the solid oxide fuel cells and/or the interconnectors between solid oxide fuel cells. The continuous flow furnace 10 has to heat the solid oxide fuel cell components 18 up to a minimum sintering temperature and maintain the solid oxide fuel cell components 18 at the minimum sintering temperature for a predetermined time. The heat treatment of the solid oxide fuel cell components 18 allows the removal of the solvents and/or binders from the solid oxide fuel cell components 18 at lower temperatures in chambers, or zones, 12 arranged at lower temperatures. The heat treatment of the solid oxide fuel cell components 18 then sinters the solid oxide fuel cell components 18 at higher temperatures in chambers, or zones, 12 arranged at higher temperatures.

Thus, the use of the several setter members 20 on each transport member 22 increases the productivity of sintered solid oxide fuel cell components 18, but there is a significant difference in the time for which the sold oxide fuel cell components 18 have been sintered at temperatures at or above the minimum sintering temperature and this may lead to inconsistent quality.

Figures 6, 7 and 8 show a method of heat treating components 18 in a continuous flow furnace 110 according to the present invention. In the method of heat treating components 18 in a continuous flow furnace 110, as shown in figures 6, 7 and 8, components 18 to be heat treated are placed on a plurality of setter members 20. A plurality of setter members 20 are placed on a respective transport member 22 such that each setter member 20 is arranged to flow sequentially into and through the continuous flow furnace 110 to heat treat the components 18 placed on the respective setter member 20. The setter members 20 act as storage units to transport the components 18 through the continuous flow furnace 110 and in this case a plurality of series of setter members 20 and associated components 18 are arranged to flow in series through the continuous flow furnace 110. This method transports a plurality of setter members 20, and the associated components 18, on each transport member 22 through the continuous flow furnace 110. Thus, this method produces sufficiently high volumes of heat treated components. In the example three setter members 20 are placed on each transport member 22, but two, three, four or more setter members 20 may be placed on each transport member 22.

Thus in the case of three setter members 20 on each transport member 22 the production of heat treated components 18 is trebled.

Similarly two setter members 20 on each transport member 22 would double the production of heat treated components 18 and four setter members 20 on each transport member 22 would quadruple the production of heat treated components 18. The present invention differs in that spacer members 30 are provided to thermally isolate the first, or bottom, setter member 20 from the transport member 22.

Figures 7 and 8 are cross-sections through the continuous flow furnace 10 with a transport member 22 carrying three setter members 20 and associated components 18. The continuous flow furnace 110 comprises two parallel side walls 11 and 13 and a ceiling 15. The continuous flow furnace 110 has heater elements 14 and the heater elements 14 are provided on the side walls 11 and 13.

Figures 7 and 8 also show a transport member 22 resting on the rollers 16 to be transported through the continuous flow furnace 110.

The transport member 22 carries three setter members 20, first, second and third or bottom, middle and top setter members 20, stacked one upon the other and each setter member 20 carries one or more components 18. The first, or bottom, setter member 20 is spaced from the transport member 22 by spacer members 30 to thermally isolate the first, or bottom, setter member 20 from the transport member 22. The second, or middle, setter member 20, rests on the first, or bottom, setter member 20 and the third, or top, setter member 20 rests on the second, or middle, setter member 20.

Figure 8 shows the major heat transfer mechanisms within the continuous flow furnace 110. The heater elements 14 emit radiation A, which is the major mechanism for heating all the components 18 which pass through the continuous flow furnace 110. The components 18 and setter members 20 emit radiation B and C, which is significant in the cooling all the components 18. There is also natural convection G as shown and forced convection, not shown, perpendicular to the plane of the paper, which may be induced by a flow of air through the length of the continuous flow furnace 110.

Conduction occurs within each component 18 and between touching components 18. There is conduction between the components 18 and the associated setter member 20. There is conduction between setter members 20. In the present invention the first, bottom, setter member 20 is raised and thermally isolated from the transport member 22 and thus the first, bottom, setter member 20 does not contact the transport member 22. The spacer members 30 act as thermal conduction barriers between the first, bottom, setter member and the transport member 22 and this significantly reduces conduction between the bottom setter member 20 and the transport member 22. In addition by raising, or spacing, the first, bottom, setter member 20 above the transport member 22 natural convection G is able to flow vertically through the setter members 20 and vertically around the components 18 and forced convection through the continuous flow furnace 110 enables the gases within the continuous flow furnace to mix to enable a more uniform temperature within the stack of setter members 20 and a more uniform temperature within the components 18 carried by the setter members within a stack of setter members 20.

Thus the use of the spacer members 30 in the present invention provides two effects, firstly the first, or bottom, setter member 20 is thermally isolated from the transport member 22 to reduce conductive heat loss from the first setter member 20 to the transport member 22 and secondly the first, or bottom, setter member 20 is raised above the transport member 22 to allow convection vertically through the stack of setter members 20 and components 18 to produce more uniform temperature within the components 18.

Thus temperature differences between the solid oxide fuel cell components 18 are reduced. The time for which the sold oxide fuel cell components 18 have been sintered at temperatures at or above the minimum sintering temperature is more uniform and thus there is more consistency in quality.

To enable the setting up of convection current G vertically through the stack of setter members 20 and components 18 it is necessary for the setter members 20 to be provided with apertures extending vertically there-through. Each setter member 20 is generally a five sided box with an open top and in which the bottom wall is provided with apertures. The components 18 within each setter member 20 are spaced apart horizontally to allow the convection current G vertically through the stack of setter members 20. The setter members preferably comprise a ceramic material.

Figures 9, 10 and 11 show three different embodiments of spacer members according to the present invention.

In figure 9, the transport member 22 is provided with a plurality of spaced apart integral raised projections, or spacer members 30A, which project vertically from an upper surface 23 of the transport member 22.

In figure 10, the spacer member 30B comprises a two dimensional polygonal frame 32 and the two dimensional polygonal frame 32 comprises a plurality of spaced apart vertically extending projections 34. The two dimensional polygonal frame 32 in this example is rectangular or square, but other suitable two dimensional frames may be used e.g. a triangular frame, a hexagonal frame, an octagonal frame etc. Either the two dimensional polygonal frame 32 is placed on the transport member 22 and the first setter member 20 is placed on the projections 34 or the projections 34 are placed on the transport member 22 and the first setter member 20 is placed on the two dimensional polygonal frame 32.

In figure 11, two spacer members 300 are provided and each of the spacer members 30C comprises an elongate member 36 and each elongate member 36 has a plurality of spaced apart vertically extending projections 38. Either the two elongate members 36 are placed on the transport member 22 and the first setter member 20 is placed on the projections 38 or the projections 38 are placed on the transport member 22 and the first setter member 20 is placed on the two elongate members 36. It may be possible to use more than two of the spacer members 300.

The spacer members may produce different separations, or distances between the first, bottom, setter member and the transport member. For example spacer members of 20mm and 38mm have been tried and the 38mm spacer members produced the best results.

In a series of tests the time the solid oxide fuel cell components remained at or above the minimum sintering temperature of 1360°C was compared for a stack of three setters in which the bottom setter member was placed on the transport member and for a stack of three setter members in which a spacer members was placed between the bottom setter member and the transport member. The time for which the solid oxide fuel cell components remained at or above 1360°C on the bottom setter and the middle setter of a stack of three setters in which the bottom setter member was placed on the transport member stack was 56.2 minutes and 79.1 minutes, e.g. a difference of 22.9 minutes. The time for which the solid oxide fuel cell components remained at or above 1360°C on the bottom setter and the middle setter of a stack of three setters in which the spacer member was placed between the bottom setter member and the transport member stack was 80 minutes and 81.9 minutes, a difference of 1.9 minutes. Thus it can be seen that the dwell time above the sintering temperature for the solid oxide fuel cell components in the present invention is more consistent compared to the proposed method without a spacer member between the bottom setter member and the transport member.

Although the present invention has been described with reference to heat treating solid oxide fuel cell components in a continuous flow furnace, the present invention is equally applicable to heat treating, or sintering, of other ceramic components e.g. solar cell components, electronic components, capacitors.

Claims

Claims:- 1. A method of heat treating a component in a continuous flow furnace comprising:-a) placing at least one first component on a first setter member and placing at least one second component on a second setter member, b) placing the first setter member on a transport member and placing the second setter member on the first setter member, c) thermally isolating the first setter member from the transport member, d) placing the transport member on a conveyor for the continuous flow furnace, e) transporting the transport member, the first setter member, the second setter member, at least one first component and at least one second component on the conveyor into the continuous flow furnace, f) heat treating the at least one first component and the at least one second component in the continuous flow furnace and g) removing the at least one first component from the first setter member and removing the at least one second component from the second setter member after the at least one first component and the at least one second component have been heat treated in the continuous heat treatment furnace.
2. A method as claimed in claim 1 wherein step a) comprises placing at least one third component on a third setter member, step b) comprises placing the third setter member on the second setter member, step f) comprises heat treating the at least one third component in the continuous flow furnace and step g) comprises removing the at least one third component from the third setter member after the at least one third component has been heat treated in the continuous heat treatment furnace.
3. A method as claimed in claim 1 or claim 2 wherein step c) comprises providing a plurality of raised projections on an upper surface of the transport member, the raised projections being spaced apart on the upper surface of the transport member to thermally isolate the first setter member from the transport member.
4. A method as claimed in claim I or claim 2 wherein step c) comprises providing at least one spacer member between the transport member and the first setter member.
5. A method as claimed in claim 4 wherein the at least one spacer member comprises a two dimensional polygonal frame and the two dimensional polygonal frame comprises a plurality of spaced apart vertically extending projections.
6. A method as claimed in claim 5 wherein the two dimensional polygonal frame is a rectangular frame.
7. A method as claimed in claim 4 wherein the at least one spacer member comprises a plurality of spacer members and each of the spacer members comprises a plurality of spaced apart vertically extending projections.
8. A method as claimed in any of claims 1 to 7 wherein one or more of the at least one first component, the at least one second component and the at least one third component is a ceramic component.
9. A method as claimed in claim 8 wherein the ceramic component is a ceramic support structure for solid oxide fuel cells.
10. A method as claimed in claim 8 or claim 9 wherein the ceramic component comprises magnesium aluminate spinel.
11. A method as claimed in claim 8 wherein the ceramic component is a ceramic layer of a solid oxide fuel cell.
12. A method as claimed in claim 11 wherein the ceramic layer is an electrolyte layer, an anode layer, a cathode layer or an interconnector layer to connect adjacent solid oxide fuel cells in electrical series.
13. A method as claimed in any of claims 1 to 12 wherein step f) comprises sintering the at least one component.
14. A method of heat treating a component in a continuous flow furnace substantially as hereinbefore described with reference to figure 6 to 11 of the accompanying drawings.
15. A continuous flow furnace comprising a conveyor and at least one transport member for transporting components into the continuous flow furnace, each transport member carrying a plurality of setter members, the setter members on each transport member being arranged in a stack, each setter member holding at least one component, thermal isolation means being arranged between each transport member and the respective stack of setter members.
16. A continuous flow furnace as claimed in claim 15 wherein the conveyor comprises a conveyor belt or a plurality of rollers.
17. A continuous flow furnace as claimed in claim 15 or claim 16 wherein the thermal isolation means comprises a plurality of raised projections on an upper surface of the transport member, the raised projections being spaced apart on the upper surface of the transport member to thermally isolate the first setter member from the transport member.
18. A continuous flow furnace as claimed in claim 15 or claim 16 wherein the thermal isolation means comprises at least one spacer member between the transport member and the first setter member.
19. A continuous flow furnace as claimed in claim 18 wherein the at least one spacer member comprises a two dimensional polygonal frame and the two dimensional polygonal frame comprises a plurality of spaced apart vertically extending projections.
20. A continuous flow furnace as claimed in claim 19 wherein the two dimensional polygonal frame is a rectangular frame.
21. A continuous flow furnace as claimed in claim 18 wherein the at least one spacer member comprises a plurality of spacer members and each of the spacer members comprises a plurality of spaced apart vertically extending projections.
22. A continuous flow furnace substantially as hereinbefore described with reference to and as shown in figures 6 to 11 of the accompanying drawings.