Fuel cell system having thermally integrated, isothermal co-cleansing subsystem

• US 6,485,853 B1
• Filed: 06/27/2000
• Issued: 11/26/2002
• Est. Priority Date: 06/27/2000
• Status: Expired due to Term

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Borup, Rodney Lynn, Pettit, William Henry
• Primary Examiner(s): Chaney, Carol
• Assistant Examiner(s): YUAN, DAH WEI D
• Application Number:
  US09/604,151
• Time in Patent Office: 882 Days
• Field of Search: 429/13, 429/17, 429/26
• US Class Current: 429/412
• CPC Class Codes: H01M 8/0612 from carbon-containing material
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A fuel cell system having a thermally integrated isothermal CO-cleansing subsystem including a water-gas-shift reactor, a preferential oxidation reactor, at least one system heat exchanger, and a closed-loop heat transfer circuit dedicated to that subsystem. The heat transfer circuit utilizes a heat transfer medium which has a high specific heat and is circulated through the circuit at a sufficiently high rate as to thermally dominate the gas stream components communicating with the circuit.

Claims

1. In a PEM fuel cell system comprising (i) a primary reactor for converting a carbon-bound hydrogenous fuel into a fuel gas including H₂ for said fuel cell, said primary reactor comprising a catalyst for catalytically reacting said fuel with steam to form said fuel gas having a first CO concentration and a first H₂ concentration, (ii) at least one water-gas-shift reactor for reacting at least a portion of the CO in said fuel gas exiting said catalyst with steam to reduce the CO concentration in said fuel gas to a second CO concentration below said first CO concentration and increase the H₂ concentration above said first H₂ concentration in said fuel gas, and (iii) a preferential oxidation reactor for selectively reacting at least a portion of the CO in said fuel gas exiting said water-gas-shift reactor with oxygen to reduce the CO concentration in said fuel gas below said second CO concentration and to yield a fuel gas including CO in an amount that is non-toxic to said fuel cell, the improvement comprising:

a. said preferential oxidation reactor being an isothermal reactor having a first catalyst selected to effect said selective oxidation of said CO at a first temperature,

b. said water-gas-shift reactor being an isothermal reactor having a second catalyst selected to effect the water-gas-shift reaction therein at substantially said first temperature;

c. at least one heat exchanger;

d. a closed-loop heat transfer circuit communicating with said water-gas-shift reactor, said preferential oxidation reactor, and a heat exchanger,

e. a heat transfer liquid circulating in said circuit through said water-gas-shift reactor, said preferential oxidation reactor, and a heat exchanger, and

f. a pump adapted to circulate said heat transfer liquid at a rate throughout said circuit as to maintain said water-gas-shift reactor, said preferential oxidation reactor, and said heat exchanger all at substantially said first temperature.

2. In a PEM fuel cell system comprising (i) a primary reactor for converting gasoline into a fuel gas including H₂ for said fuel cell, said primary reactor having a first section for partially oxidizing said gasoline with a substoichiometric amount of oxygen to form a lower-hydrocarbon-containing gas stream having first concentrations of CO and H₂, and a second section downstream of said first section for catalytically reacting said gas stream with steam to form said fuel gas having a second CO concentration less than said first CO concentration and a second H₂ concentration greater than said second H₂ concentration, (ii) at least one water-gas-shift reactor for reacting at least a portion of the Co in said fuel gas exiting said second section with steam to reduce the CO concentration in said fuel gas to a third CO concentration below said second CO concentration and increase the H₂ concentration above said second H₂ concentration in said fuel gas, and (iii) a preferential oxidation reactor for selectively reacting at least a portion of the CO in said fuel gas exiting said water-gas-shift reactor with oxygen to reduce the CO concentration in said fuel gas below said third CO concentration and to yield a fuel gas including CO in an amount that is non-toxic to said fuel cell, the improvement comprising:

a. said preferential oxidation reactor being an isothermal reactor having a first catalyst selected to effect said selective oxidation of said CO at a first temperature;

b. said water-gas-shift reactor being an isothermal reactor having a second catalyst selected to effect the water-gas-shift reaction therein at substantially said first temperature;

c. at least one heat exchanger;

d. a closed-loop heat transfer circuit communicating with said water-gas-shift reactor, said preferential oxidation reactor, and a heat exchanger,

e. a heat transfer liquid circulating in said circuit through said water-gas-shift reactor, said preferential oxidation reactor, and a heat exchanger; and

f. a pump adapted to circulate said heat transfer liquid at a rate throughout said circuit as to maintain said water-gas-shift reactor, said preferential oxidation reactor, and said heat exchanger all at substantially said first temperature.

3. A fuel cell system according to claim 2 wherein a heat exchanger is a vaporizer for vaporizing said gasoline before its introduction into said fuel processor.

4. A fuel cell system according to claim 2 wherein a heat exchanger is a vaporizer for vaporizing said water to form steam before its introduction into said fuel processor.

5. A fuel cell system according to claim 2 wherein a heat exchanger is a vaporizer for vaporizing said water to form steam before its introduction into said water-gas-shift reactor.

6. A fuel cell system according to claim 2 wherein a heat exchanger is a preheater for heating said oxygen before the introduction of the oxygen into said fuel processor.

7. A fuel cell system according to claim 2 wherein a heat exchanger is a cooler for cooling said fuel gas before its introduction into said water-gas-shift reactor.

8. A fuel cell system according to claim 2 wherein a heat exchanger is a cooler for cooling said heat transfer liquid if its temperature is greater than substantially said first temperature.

9. A fuel cell system according to claim 8 including a bypass around said cooler.

10. A fuel cell system according to claim 2 wherein a heat exchanger is a heater for heating said heat transfer liquid if its temperature is less than substantially said first temperature and requires heating.

11. A fuel cell according to claim 2 wherein said heat transfer liquid comprises a hydrocarbon having a specific heat of at least about 2 KJ/Kg·

K.

12. A fuel cell according to claim 11 wherein said hydrocarbon is a paraffin oil.

13. A fuel cell system according to claim 2 comprising a plurality of said heat exchangers including a vaporizer for vaporizing said gasoline before its introduction into said fuel processor, a vaporizer for vaporizing said water to form steam before its introduction into said fuel processor, a vaporizer for vaporizing said water to form steam before its introduction into said water-gas -shift reactor, a preheater for heating said oxygen before the introduction of the oxygen into said fuel processor, a cooler for cooling said fuel gas before the introduction of the fuel gas into said water-gas-shift reactor, a cooler for cooling heat transfer liquid if its temperature is greater than substantially said first temperature, and a heater for heating said heat transfer liquid if its temperature is less than substantially said first temperature.