Fuel cell system and method of reprocessing off-gas
A fuel cell system including a fuel cell, an off-gas reprocessing unit that is provided downstream of the fuel cell and that at least partially removes at least one of steam or carbon dioxide from an off-gas discharged from the fuel cell, a flow passage that is provided downstream of the off-gas reprocessing unit and that allows a reprocessed off-gas discharged from the off-gas reprocessing unit to flow therethrough, and a controlling unit that modulates the reaction constant K pa of a reaction A with respect to the reprocessed off-gas discharged from the off-gas reprocessing unit, to 1.22 or more.
1. A fuel cell system comprising
a fuel cell including an anode and a cathode in which the anode is supplied with a fuel gas,
a fuel gas supply passage that is connected with the anode and is provided upstream of the fuel cell and allows the fuel gas to flow therethrough,
an off-gas reprocessing unit that is provided downstream of the fuel cell and that at least partially removes at least one of steam or carbon dioxide from an off-gas discharged from the fuel cell, wherein reprocessing corresponds to at least partially separating at least one of carbon dioxide or steam from the off-gas in the off-gas reprocessing unit,
a flow passage that is provided downstream of the off-gas reprocessing unit and that allows a reprocessed off-gas discharged from the off-gas reprocessing unit to flow therethrough, and
a controlling unit that modulates a reaction constant K pa of the following reaction A with respect to the reprocessed off-gas discharged from the off-gas reprocessing unit, to 1.22 or more by modulating at least one of a rate of removal of steam or a rate of removal of carbon dioxide in the off-gas reprocessing unit, wherein the flow passage is connected between the off-gas reprocessing unit and the fuel gas supply passage to supply the anode via the fuel gas supply passage with the reprocessed off-gas:
Reaction A: CO+H 2 ↔H 2 O+C (Solid)
Reaction constant of Reaction A: K pa ═P(H 2 O)/[P(CO) x P(H 2 )]
wherein P(H 2 O), P(CO), and P(H 2 ) represent respective partial pressures of H 2 O, CO, and H 2 in the reprocessed off-gas.
2. The fuel cell system according to claim 1 , wherein the controlling unit modulates a reaction constant K pb of the following reaction B with respect to the reprocessed off-gas discharged from the off-gas reprocessing unit, to 0.57 or more:
Reaction B: 2CO↔CO 2 +C (Solid)
Reaction constant of Reaction B: K pb ═P(CO 2 )/[P(CO)] 2
wherein P(CO 2 ) and P(CO) represent respective partial pressures of CO 2 and CO in the reprocessed off-gas.
3. The fuel cell system according to claim 2 , wherein the controlling unit modulates the K pb to 0.57 or more by modulating at least one of the rate of removal of steam or the rate of removal of carbon dioxide in the off-gas reprocessing unit.
4. The fuel cell system according to claim 1 , wherein the off-gas reprocessing unit comprises a condenser that removes steam of the off-gas by condensation.
5. The fuel cell system according to claim 4 , wherein the controlling unit is capable of modulating at least one of a condensation temperature of the condenser or a pressure in the condenser.
6. The fuel cell system according to claim 1 , wherein
the fuel cell is a first fuel cell, and
the fuel cell system further comprises a second fuel cell to which the reprocessed off-gas flowing through the flow passage is supplied.
7. The fuel cell system according to claim 1 , wherein the reprocessed off-gas flowing through the flow passage is supplied to the fuel cell.
8. The fuel cell system according to claim 1 , wherein the fuel cell system further comprises a reformer that reforms a raw material gas and generates a fuel gas, or the raw material gas is reformed in the fuel cell, thereby generating a fuel gas.
9. The fuel cell system according to claim 1 , wherein the fuel cell system satisfies the following (1) or (2):
(1) the fuel cell system further comprises a reformer that reforms a raw material gas and generates a fuel gas, and at least one of a reforming temperature of the reformer or a fuel utilization of the fuel cell is controlled; or
(2) the controlling unit controls the fuel utilization of the fuel cell.
10. A method of reprocessing an off-gas, comprising using a fuel cell system comprising
a fuel cell including an anode and a cathode in which the anode is supplied with a fuel gas,
a fuel gas supply passage that is connected with the anode and is provided upstream of the fuel cell and allows the fuel gas to flow therethrough,
an off-gas reprocessing unit that is provided downstream of the fuel cell and that at least partially removes at least one of steam or carbon dioxide from an off-gas discharged from the fuel cell, wherein reprocessing corresponds to a process for at least partially separating at least one of carbon dioxide or steam from the off-gas in the off-gas reprocessing unit, and
a flow passage that is provided downstream of the off-gas reprocessing unit and that allows a reprocessed off-gas discharged from the off-gas reprocessing unit to flow therethrough,
wherein the flow passage is connected between the off-gas reprocessing unit and the fuel gas supply passage to supply the anode via the fuel gas supply passage with the reprocessed off-gas,
the method comprising a step of removing at least one of steam or carbon dioxide from the off-gas in the off-gas reprocessing unit, wherein by the step, a reaction constant K pa of the following reaction A with respect to the reprocessed off-gas discharged from the off-gas reprocessing unit is modulated to 1.22 or more:
Reaction A: CO+H 2 ↔H 2 O+C (Solid)
Reaction constant of Reaction A: K pa ═P(H 2 O)/[P(CO) x P(H 2 )]
wherein P(H 2 O), P(CO), and P(H 2 ) represent respective partial pressures of H 2 O, CO, and H 2 in the reprocessed off-gas.
11. The method of reprocessing an off-gas according to claim 10 , wherein a reaction constant K pb of the following reaction B with respect to the reprocessed off-gas discharged from the off-gas reprocessing unit, is modulated to 0.57 or more by removing at least one of steam or carbon dioxide from the off-gas in the off-gas reprocessing unit to modulate at least one of a rate of removal of steam or a rate of removal of carbon dioxide in the off-gas reprocessing unit:
Reaction B: 2CO↔CO 2 +C (Solid)
Reaction constant of Reaction B: K pb ═P(CO 2 )/[P(CO)] 2
wherein P(CO 2 ) and P(CO) represent respective partial pressures of CO 2 and CO in the reprocessed off-gas.
12. The fuel cell system according to claim 2 , wherein the controlling unit modulates the K pa to 1.22 or more by modulating at least one of the rate of removal of steam or the rate of removal of carbon dioxide in the off-gas reprocessing unit.
13. The fuel cell system according to claim 3 , wherein the controlling unit modulates the K pa to 1.22 or more by modulating at least one of the rate of removal of steam or the rate of removal of carbon dioxide in the off-gas reprocessing unit.
14. The fuel cell system according to claim 2 , wherein the off-gas reprocessing unit comprises a condenser that removes steam of the off-gas by condensation.
15. The fuel cell system according to claim 3 , wherein the off-gas reprocessing unit comprises a condenser that removes steam of the off-gas by condensation.
16. The fuel cell system according to claim 14 , wherein the controlling unit is capable of modulating at least one of a condensation temperature of the condenser or a pressure in the condenser.
17. The fuel cell system according to claim 15 , wherein the controlling unit is capable of modulating at least one of a condensation temperature of the condenser or a pressure in the condenser.