Carbon dioxide separator, fuel cell system including same, and method of operating the fuel cell system

Patent metadata

Field	Value
Publication number	US-2016248111-A1
Application number	US-201615014584-A
Country	US
Kind code	A1
Filing date	Feb 3, 2016
Priority date	Feb 4, 2015
Publication date	Aug 25, 2016
Grant date	—

Abstract

A system and method in which a high temperature fuel cell stack exhaust stream is recycled back into the fuel inlet stream of the high temperature fuel cell stack. The recycled stream may be sent to a carbon dioxide separator that separates carbon dioxide from the fuel exhaust stream. The carbon dioxide separator may include a carbon dioxide separation membrane, an oxygen blocking membrane, and a water blocking membrane.

First claim

1 . A carbon dioxide separator for a fuel cell system, the carbon dioxide separator comprising:
a sweep channel configured to receive a sweep gas; a feed channel configured to receive a fuel exhaust stream of the fuel cell system; a carbon dioxide separation membrane disposed between the sweep channel and the feed channel, the carbon dioxide separation membrane having a higher permeability to carbon dioxide and water than to hydrogen gas, carbon monoxide, and nitrogen gas; and a first blocking layer disposed on a first side of the carbon dioxide separation membrane, the first blocking layer comprising at least one of:
a first oxygen blocking layer disposed between the carbon dioxide separation membrane and the sweep channel, the oxygen blocking layer having a higher permeability to water and carbon dioxide than to oxygen gas and nitrogen gas; and
a first water blocking layer that is hydrophobic.

2 . The carbon dioxide separator of claim 1 , wherein the first blocking layer comprises the oxygen blocking layer.

3 . The carbon dioxide separator of claim 1 , wherein the first blocking layer comprises the first water blocking layer, the first water blocking layer having a higher permeability to carbon dioxide than to water.

4 . The carbon dioxide separator of claim 1 , wherein the first blocking layer comprises the first oxygen blocking layer and the first water blocking layer.

5 . The carbon dioxide separator of claim 4 , wherein:
the first oxygen blocking layer comprises polyethylene oxide (PEO); and the first water blocking layer comprises porous Teflon (PTFE) or a porous polysulfone.

6 . The carbon dioxide separator of claim 1 , wherein the carbon dioxide separator has an oxygen gas permeability ranging from about 0% to about 25%, and a water permeability ranging from about 20% to about 40%.

7 . The carbon dioxide separator of claim 1 , wherein the carbon dioxide separation membrane comprises a (2-aminoisobutyric acid)-potassium salt (AIBA-K) or a glycine-potassium salt (glycine-K).

8 . The carbon dioxide separator of claim 1 , further comprising a second blocking layer disposed on an opposing second side of the carbon dioxide separation membrane and comprising at least one of:
a second oxygen blocking layer that has a higher permeability to water and carbon dioxide than to oxygen gas and nitrogen gas; and a second water blocking layer that is hydrophobic.

9 . The carbon dioxide separator of claim 8 , wherein:
the first blocking layer comprises the first oxygen blocking layer; and the second blocking layer comprises the second water blocking layer.

10 . The carbon dioxide separator of claim 9 , wherein the first side of the carbon dioxide separation membrane faces the sweep channel and the second side of the carbon dioxide separation membrane faces the feed channel.

11 . The carbon dioxide separator of claim 8 , wherein:
the first blocking layer comprises the first oxygen blocking layer and the first water blocking layer; and the second blocking layer comprises the second oxygen blocking layer and the second water blocking layer.

12 . The carbon dioxide separator of claim 11 , wherein:
the first oxygen blocking layer is disposed between the carbon dioxide separation membrane and the first water blocking layer; and the second oxygen blocking layer is disposed between the carbon dioxide separation membrane and the second water blocking layer.

13 . A fuel cell system, comprising:
a fuel cell stack; the carbon dioxide separator of claim 1 , the carbon dioxide separator being configured to remove carbon dioxide from a fuel exhaust stream output from the fuel cell stack and to create a purified recycled fuel exhaust stream by purifying the fuel exhaust stream; a first recycling conduit fluidly connecting a fuel exhaust outlet of the fuel cell stack to the feed channel and configured to provide the recycled fuel exhaust stream to the carbon dioxide separator, by diverting at least a portion of a fuel exhaust stream output by the fuel cell stack; and a second recycling conduit fluidly connecting a feed channel outlet of the carbon dioxide separator to a fuel inlet conduit connected to the fuel cell stack, the second recycling conduit adapted to provide the purified recycled fuel exhaust stream to the fuel inlet conduit.

14 . The fuel cell system of claim 13 , wherein an inlet of the sweep channel and an inlet of the feed channel are disposed on the same side of the carbon dioxide separator, such that the sweep gas and the fuel exhaust stream are configured to flow through the carbon dioxide separator in the same direction.

15 . The fuel cell system of claim 13 , further comprising a sweep gas humidifier fluidly connected to the sweep gas channel.

16 . The fuel cell system of claim 15 , further comprising:
a humidity or dew point detector configured to detect a humidity or dew point of the sweep gas; and a control unit configured to control the sweep gas humidifier in accordance with the detected humidity or dew point.

17 . A method of operating a fuel cell system, comprising:
providing a fuel inlet stream to a fuel cell stack; operating the fuel cell stack to generate a fuel exhaust stream; providing at least a portion of the fuel exhaust stream to a feed channel of a carbon dioxide separator, and separating carbon dioxide from the portion of the fuel exhaust stream in the carbon dioxide separator to generate a purified fuel exhaust stream; providing a sweep gas to a sweep channel of the carbon dioxide separator, to sweep the separated carbon dioxide from the carbon dioxide separator; and recycling the purified fuel exhaust stream to the fuel inlet stream, wherein the carbon dioxide separator comprises:
a carbon dioxide separation membrane disposed between the sweep channel and the feed channel, the carbon dioxide separation membrane having a higher permeability to carbon dioxide and water than to hydrogen gas, carbon monoxide, and nitrogen gas; and
a blocking layer disposed on a first side of the carbon dioxide separation membrane and comprising at least one of:
a first oxygen blocking layer having a higher permeability to water and carbon dioxide than to oxygen gas and nitrogen gas; and
a first water blocking layer that is hydrophobic.

18 . The method of claim 17 , further comprising:
detecting a humidity or dew point of the sweep gas; adjusting water removal rate of the carbon dioxide separator in accordance with the detected humidity or dew point.

19 . The method of claim 18 , wherein the controlling of the water removal rate comprises adjusting, based on the detected humidity or dew point, at least one of:
a flow rate of the sweep gas; a humidity of the sweep gas; a temperature of the carbon dioxide separation membrane; a flow rate of the portion of the fuel exhaust stream; and a humidity of the portion of the fuel exhaust stream.

20 . The method of claim 17 , wherein the carbon dioxide separator is configured to remove at least 50% of the carbon dioxide from the portion of the fuel exhaust stream.

21 . The method of claim 17 , wherein the carbon dioxide separator has an oxygen gas permeability ranging from about 0% to about 25% and a water permeability ranging from about 60% to about 80%.

22 . The method of claim 17 , further comprising controlling water permeation through the carbon dioxide separation membrane, such that an oxygen to carbon ratio of the fuel inlet stream received by the

Assignees

• Bloom Energy Corp
• Ohio State Innovation Foundation

Inventors

• Gasda Michael
• Ballantine Arne
• Karuppaiah Chockkalingam
• Ho W S Winston

Classifications

• H01M8/0687 Primary

  Reactant purification by the use of membranes or filters · CPC title

• H01M8/04492

  Humidity; Ambient humidity; Water content · CPC title

• H01M8/04738

  of auxiliary devices, e.g. reformer, compressor, burner · CPC title

• H01M8/0668 Primary

  Removal of carbon monoxide or carbon dioxide · CPC title

• H01M8/04126

  Humidifying · CPC title