SOLID OXIDE CELL STACK WITH A PRESSURE DIFFERENCE BETWEEN ANODE AND CATHODE COMPARTMENTS

Abstract

A SOC stack has interconnects with a maximum distance between the contact points which are designed to compensate for pressure difference between one side of the interconnect to the other side.

Claims

1. Solid Oxide Cell stack comprising a plurality of stacked cell units, each unit comprises a solid oxide cell in a cell layer and an interconnect in an interconnect layer, wherein one interconnect layer separates one cell layer from the adjacent cell layer in the cell stack, each interconnect comprises one or more protruding contact areas on a first side and one or more protruding contact areas on a second side of the interconnect adapted to provide mechanical and electrical contact between interconnects and solid oxide cells, wherein each solid oxide cell has a high-pressure side facing the first side of an adjacent interconnect and a low-pressure side facing a second side of an adjacent interconnect and wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 2.5 mm.

2. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 2.0 mm.

3. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 1.8 mm.

4. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 1.5 mm.

5. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 1.2 mm.

6. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 1.0 mm.

7. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 0.9 mm.

8. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 0.8 mm.

9. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 0.7 mm.

10. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 0.6 mm.

11. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 0.5 mm.

12. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 0.4 mm.

13. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects is 0.3 mm.

14. Solid Oxide Cell stack according to claim 1, wherein the maximum distance between two adjacent edges of the contact areas on the first side of the interconnects is the same or larger than the maximum distance between two adjacent edges of the contact areas on the second side of the interconnects.

15. Solid Oxide Cell stack according to claim 1, wherein the area of each of the interconnects is between 15 cm.sup.2 and 10000 cm.sup.2, preferably between 64 and 500 cm.sup.2.

16. Solid Oxide Cell stack according to claim 1, wherein the solid oxide cells are ceramic cells.

17. Solid Oxide Cell stack according to claim 1, wherein the interconnects comprise one or more intermediate contact enhancing layers.

18. Solid Oxide Cell stack according to claim 1, wherein the Solid Oxide Cell stack is a Solid Oxide Electrolysis cell stack.

19. Solid Oxide Cell stack according to claim 1, wherein the pressure difference between the high-pressure side and the low-pressure side is minimum 300 mBar.

20. Solid Oxide Cell stack according to claim 1, wherein the pressure difference between the high-pressure side and the low-pressure side is minimum 1 Bar, preferably minimum 5 Bar, preferably minimum 15 Bar.

21. Solid Oxide Cell stack according to claim 1, wherein the high-pressure side is a fuel-side.

Description

DRAWING

[0041] In the following an embodiment of the invention will be explained with reference to FIG. 1, which shows a partial principle side cut of a part of an SOC stack according to an embodiment of the invention.

[0042] A part of an Solid Oxide Cell (SOC) 101 is shown with a high pressure side, H and a low pressure side L. It is to be understood that several SOCs are stacked in layers in the SOC stack, with Interconnects, 102 separating each SOC from the next in the cell stack. An SOC and one interconnect each forming a cell unit 103. The high pressure side of the SOC faces a first side of an interconnect and the low pressure side of the SOC faces a second side of the interconnect. The interconnects comprise protruding contact areas on both the first and the second side of the interconnect. According to the invention, the maximum distance between two adjacent edges of the contact areas on the second side of each interconnect M1, is adapted be 2.5 mm, to support the cell unit. The distance M2 between two adjacent edges of the contact areas on the first side of each interconnect may in an embodiment of the invention be larger than M1, since the high pressure side of the SOC needs less support than the low pressure side. In a further embodiment of the invention, the high pressure side of the SOC is the fuel side of the SOC.

EXAMPLES

[0043] The design of the invention was tested in two short SOC stacks containing 9 single repeat cell units. The distance between the contact points/ribs on the low pressure oxy side was 1.3 mm, and the fuel side was pressurized up to 1.75 bara yielding a pressure difference from fuel to oxy side of up to 750 mbar.

[0044] The first test was performed in electrolysis mode, with fuel containing 5% hydrogen in steam. The oxy side was flushed with air and kept at ambient pressure (1.013 bara) throughout the test. The inlet gases were heated to 750° C. and the stack was installed in a furnace keeping the temperature around the stack stable at 750° C. The stack was run at a current density of approximately 0.75 A/cm2. Below is a table showing the average cell voltage at the chosen operating point with increasing fuel side pressure.

TABLE-US-00001 Fuel side pressure Pressure difference Average cell voltage [bara] [mbar] [mV] 1.02 8 1255 1.26 250 1253 1.51 495 1248 1.76 742 1241

[0045] As seen from the table, the average voltage of the cells decreases as the fuel side pressure increases, which in SOEC mode corresponds to improved performance. The increased performance at this operating point corresponds to a reduced power consumption of a little more than 1%.

[0046] The second test was performed in SOFC mode on a fuel of 60% hydrogen and 40% nitrogen. Again, the oxy side was flushed with air and kept at ambient pressure (1.013 bara) throughout the test. The inlet gases were heated to 700° C. and the SOC stack was installed in a furnace keeping the temperature around the SOC stack stable at 700° C. The SOC stack was run at a current density of approximately 0.28 A/cm2. Below is a table showing the average cell voltage at the chosen operating point with increasing fuel side pressure.

TABLE-US-00002 Fuel side pressure Pressure difference Average cell voltage [bara] [mbar] [mV] 1.01 0 874.7 1.26 243 877.2 1.51 492 878.5 1.75 740 879.5

[0047] As seen from the table, the average voltage of the cells increases as the fuel side pressure increases, which in SOFC mode corresponds to improved performance. The increased performance at this operating point corresponds to an increase in power output of roughly 0.6%.