1. A fuel cell system comprising:
a fuel cell assembly comprising a plurality of individual fuel cells, each fuel cell having an electrolyte medium, a cathode and an anode; and,
at least one centrifugal blower system for providing a flow of gaseous medium to the fuel cell assembly, the at least one centrifugal blower system comprising:
a series of blower units, each blower unit in the series comprising a casing having an axial inlet and a radial outlet, an impeller disposed within the casing for drawing a gaseous medium at a first pressure in the axial inlet and expelling gaseous medium at a second higher pressure through the radial outlet, and a motor for driving the impeller; and,
a duct connecting the radial outlet of at least one blower unit in the series of blower units with the axial inlet of at least one successive blower unit in the series of blower units.
2. The fuel cell system of claim 1 wherein the fuel cell assembly is a solid oxide fuel cell assembly.
3. The fuel cell system of claim 2 wherein the solid oxide fuel cell assembly comprises tubular solid oxide fuel cells.
4. The fuel cell system of claim 3 comprising at least two centrifugal blower systems, a first centrifugal blower system for providing a flow of gaseous medium to the anodes of the solid oxide fuel cell assembly and a second centrifugal blower system for providing a flow of gaseous medium comprising an oxidizer gas to the cathodes of the solid oxide fuel cell assembly.
5. The fuel cell system of claim 1 wherein in the at least one centrifugal blower system further comprises:
at least one gaseous medium-directing structure selected from the group consisting of interior walls of the duct configured to be substantially parallel to the trajectory of the gaseous medium expelled from the radial outlet of a blower unit to which the duct is connected, and a gas stream housing for receiving the gas stream from the radial outlet of the last blower unit in the series of blower units, the interior walls of the gas stream housing being configured to be substantially parallel to the trajectory of the gaseous medium expelled from the radial outlet of the last blower unit.
6. The fuel cell system of claim 1 wherein in the at least one centrifugal blower system, the orientation of the radial outlet of one blower unit in the series of blower units to the axial inlet of a successive blower unit in the series of blower units is approximately 0\xb0, 90\xb0, 180\xb0 or 270\xb0.
7. The fuel cell system of claim 1 wherein in the at least one centrifugal blower system, the angle of pitch of the radial outlet of one blower unit in the series of blower units to the axial inlet of a successive blower unit in the series of blower units is approximately 0\xb0, 30\xb0, 60\xb0 or 90\xb0.
8. The fuel cell system of claim 6 wherein in the at least one centrifugal blower system, the angle of pitch of the radial outlet of one blower unit in the series of blower units to the axial inlet of a successive blower unit in the series of blower units is approximately 0\xb0, 30\xb0, 60\xb0 or 90\xb0.
10. The fuel cell system of claim 1 wherein in the at least one centrifugal blower system, at least one blower unit in the series of blower units has greater gas pressure and gas flow capability than another blower unit in the at least one centrifugal blower system.
11. The fuel cell system of claim 1 wherein in the at least one centrifugal blower system, at least one blower unit in the series of blower units is separated from at least one other blower in the at least one centrifugal blower system.
12. The fuel cell system of claim 1 wherein the at least one centrifugal blower system comprises a microprocessor configured to control independently the operation of the blower units in the series of blower units.
13. The fuel cell system of claim 5 wherein the interior walls of the gas stream housing are at an angle \u03b1 of from 12\xb0 to 20\xb0 relative to the radial outlets of the blower units in the series of blower units.
14. The fuel cell system of claim 13 wherein the angle of pitch of the radial outlet of a blower unit in the series of blower units to the axial inlet of the successive blower unit in the series of blower units is approximately 0\xb0.
15. The fuel cell system of claim 1 comprising at least two centrifugal blower systems, a first centrifugal blower system for providing a flow of gaseous medium to the anodes of the fuel cell assembly and a second centrifugal blower system for providing a flow of gaseous medium comprising air to the cathodes of the fuel cell assembly.
16. The fuel cell system of claim 1 wherein the at least one centrifugal blower system comprises a microprocessor configured to control the operation of the series of blower units.
17. The fuel cell system of claim 12 wherein the microprocessor is configured to control independently the operation of the blower units in the series of blower units such that operation of at least one blower unit in the series of blower units of the at least one centrifugal blower system provides from 50% to 90% of the flow of gaseous medium and the operation of at least one other blower unit in the series of blower units of the at least one centrifugal blower system provides the balance of the flow of gaseous medium.
18. The fuel cell system of claim 15 comprising a microprocessor configured to control independently each blower unit in the first centrifugal blower system and the second centrifugal blower system.
19. The fuel cell system of claim 18, wherein the microprocessor is configured to control independently the first centrifugal blower system such that at least one blower unit in the first centrifugal blower system provides from 50% to 90% of the flow of gaseous medium of the first centrifugal blower system and at least one other blower unit in the first centrifugal blower system provides the balance of the flow of gaseous medium of the first centrifugal blower system, and to control the operation of the second centrifugal blower system such that at least one blower unit in the second centrifugal blower system provides from 50% to 90% of the flow of gaseous medium comprising air of the second centrifugal blower system and at least one other blower unit in the second centrifugal blower system provides the balance of the flow of gaseous medium comprising air of the second centrifugal blower system.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
We claim:
1. A method of inducing immunity to pneumonic pasteurellosis in ruminants, comprising the step of:
administering a P. haemolytica bacterium to a ruminant, wherein the P. haemolytica bacterium (a) expresses no biologically active leukotoxin, (b) expresses a form of leukotoxin molecule which is a deletion mutant of about 66 kDa which lacks amino acids 34 to 378 and which induces antibodies which specifically bind to and neutralize biologically active leukotoxin; and (c) contains no foreign DNA, whereby immunity is induced.
2. The method of claim 1 wherein the step of administering is via the oral route.
3. The method of claim 1 wherein the bacterium is top-dressed on the feed of the ruminant.
4. The method of claim 1 wherein the step of administering comprises injecting the bacterium subcutaneously.
5. The method of claim 1 wherein the step of administering comprises injecting the bacterium intradermally.
6. The method of claim 1 wherein the step of administering comprises injecting the bacterium intramuscularly.
7. The method of claim 19 wherein the step of administering is via the nose.
8. A feed for ruminants which comprises a P. haemolytica bacterium to a ruminant, wherein the P. haemolytica bacterium (a) expresses no biologically active leukotoxin, (b) expresses a form of leukotoxin molecule which is a deletion mutant of about 66 kDa which lacks amino acids 34 to 378 and which induces antibodies which specifically bind to and neutralize biologically active leukotoxin; and (c) contains no foreign DNA.
9. A vaccine for reducing morbidity in ruminants, comprising:
a P. haemolytica bacterium (a) expresses no biologically active leukotoxin, (b) expresses a form of leukotoxin molecule which is a deletion mutant of about 66 kDa which lacks amino acids 34 to 378 and which induces antibodies which specifically bind to and neutralize biologically active leukotoxin; and (c) contains no foreign DNA.