# US 8,771,895 B2 · Online anode pressure bias to maximize bleed velocity while meeting emission constraint

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- Number: US 8,771,895 B2
- Document ID: US8771895B2
- Status: Granted
- Kind: B2
- Application number: 12/699,773
- Filed: 2010-02-03
- Published: 2011-08-04
- Granted: 2014-07-08
- Earliest claimed: 2010-02-03
- Assignees: GM Global Technology Operations LLC
- Applicants: Manish Sinha; Seth E. Lerner; Patrick Frost; Victor W. Logan; Balasubramanian Lakshmanan
- Inventors: Manish Sinha; Seth E. Lerner; Patrick Frost; Victor W. Logan; Balasubramanian Lakshmanan
- Web page: https://patentgrep.com/patent/US8771895B2

## CPC

- H01M 8/04: Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M 8/04089: of gaseous reactants
- H01M 8/04097: {with recycling of the reactants (H01M8/04119, H01M8/04104 take precedence)}
- H01M 8/04231: {Purging of the reactants}
- H01M 8/04395: {of cathode reactants at the inlet or inside the fuel cell}
- H01M 8/04402: {of anode exhausts}
- H01M 8/04753: {of fuel cell reactants}
- H01M 8/04761: {of fuel cell exhausts}
- H01M 8/04992: characterised by the implementation of mathematical or computational algorithms, e.g. feedback control loops, fuzzy logic, neural networks or artificial intelligence
- H01M 8/0662: Treatment of gaseous reactants or gaseous residues, e.g. cleaning
- H01M 2008/1095: {Fuel cells with polymeric electrolytes}
- Y02E 60/50: Fuel cells
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

A method that employs a model based approach to determine a maximum anode pressure set-point based on existing airflow in the exhaust gas line. This approach maximizes anode flow channel velocity during bleed events while meeting the hydrogen emission constraint, which in turn increases the amount of water purged from the anode flow channels to increase stack stability.

## Claims

### Claim 1

A method for determining a flow rate of an anode exhaust gas through an anode bleed valve from an anode side of a fuel cell stack, said method comprising:
estimating a bleed flow rate of the anode exhaust gas through the bleed valve that maintains a hydrogen concentration in the anode exhaust gas below a predetermined percentage based on the amount of air in a cathode output from the fuel cell stack, said bled anode exhaust gas being fed into the cathode output from the fuel cell stack;
using a valve orifice model for the bleed valve to estimate an anode side pressure set-point that is necessary to supply the estimated bleed flow rate; and
providing hydrogen to the anode side of the fuel cell stack that maintains the anode side pressure set-point.

### Claim 2 (depends on 1)

The method according to claim 1 wherein the predetermined hydrogen concentration is less than 4%.

### Claim 3 (depends on 2)

The method according to claim 2 wherein the predetermined hydrogen concentration is about 2.5%.

### Claim 4 (depends on 1)

The method according to claim 1 wherein estimating the bleed flow rate includes using the equation:
y
H
⁢
⁢
2
exh
=
y
H
2
·
n
.
H
2
n
.
Air
+
y
H
2
·
n
.
H
2
≤
y
H
⁢
⁢
2
exh
⁢
_
⁢
desired
where, yH2exh—desired is the predetermined hydrogen concentration, yH2exh is the flow rate of hydrogen, yH2 is the hydrogen concentration in the anode, {dot over (n)}Air is the molar flow rate of air in the cathode output and {dot over (n)}H2 is the bleed flow rate.

### Claim 5 (depends on 4)

The method according to claim 4 wherein the valve orifice model is defined as:
k
v
=
4.633
·
n
·
MW
n
·
T
(
p
1
2
-
p
2
2
)
where, kv is an orifice constant, n is the molar flow through the orifice, MWn is the molecular weight of gas, p1 is the pressure at the inlet of the orifice, p2 is the pressure at the outlet of the orifice and T is the temperature of the orifice.

### Claim 6 (depends on 5)

The method according to claim 5 wherein the anode side pressure set-point is determined by rearranging the valve orifice model as:
Δ
P
SP
=
p
2
2
+
(
4.633
·
n
.
H
2
k
v
)
2
·
MW
n
·
T
-
p
2
where the pressure set-point ΔPSP is the inlet pressure of the orifice p1 and the molar flow through the orifice n is the bleed flow rate {dot over (n)}H2.

### Claim 7 (depends on 1)

The method according to claim 1 wherein a portion of the compressor air by-passes the fuel cell stack and is sent directly to the cathode output to be mixed with the anode exhaust gas.

### Claim 8 (depends on 1)

The method according to claim 1 further comprising using excess air flow from a cathode side of the fuel cell stack during freeze conditions to maximize the bleed flow rate during the anode exhaust gas bleed to improve stack stability.

### Claim 9

A method for determining a flow of an anode exhaust gas from an anode side of a fuel cell stack, said method comprising:
providing air from a compressor to a cathode side of the fuel cell stack;
by-passing some of the air from the compressor around the fuel cell stack;
determining how much anode exhaust gas can be output from the fuel cell stack and be mixed with compressor air that is provided to the cathode side and bypassed around the fuel cell stack that will maintain the amount of hydrogen in the mixed anode exhaust gas and air below a predetermined hydrogen concentration; and
providing hydrogen to the anode side of the fuel cell stack that maintains an anode side pressure set-point for the determined amount of anode exhaust gas.

### Claim 10 (depends on 9)

The method according to claim 9 wherein determining how much anode exhaust gas can be output from the fuel cell stack includes estimating a bleed flow rate of the anode exhaust gas through a bleed valve.

### Claim 11 (depends on 10)

The method according to claim 10 wherein determining how much anode exhaust gas can be output from the fuel cell stack includes using a valve orifice model for the bleed valve to determine the anode side pressure set-point that is necessary to supply the estimated bleed flow rate.

### Claim 12 (depends on 11)

The method according to claim 11 wherein estimating the bleed flow rate includes using the equation:
y
H
⁢
⁢
2
exh
=
y
H
2
·
n
.
H
2
n
.
Air
+
y
H
2
·
n
.
H
2
≤
y
H
⁢
⁢
2
exh
⁢
_
⁢
desired
where, yH2exh—desired is the predetermined hydrogen concentration, yH2exh is the flow rate of hydrogen, yH2 is the hydrogen concentration in the anode, {dot over (n)}Air is the molar flow rate of air in the cathode output and {dot over (n)}H2 is the bleed flow rate.

### Claim 13 (depends on 12)

The method according to claim 12 wherein the valve orifice model is defined as:
k
v
=
4.633
·
n
·
MW
n
·
T
(
p
1
2
-
p
2
2
)
where, kv is an orifice constant, n is the molar flow through the orifice, MWn is the molecular weight of gas, p1 is the pressure at the inlet of the orifice, p2 is the pressure at the outlet of the orifice and T is the temperature of the orifice.

### Claim 14 (depends on 13)

The method according to claim 13 wherein the anode side pressure set-point is determined by rearranging the valve orifice model as:
Δ
P
SP
=
p
2
2
+
(
4.633
·
n
.
H
2
k
v
)
2
·
MW
n
·
T
-
p
2
where the pressure set-point ΔPSP is the inlet pressure of the orifice p1 and the molar flow through the orifice n is the bleed flow rate {dot over (n)}H2.

### Claim 15 (depends on 9)

The method according to claim 9 wherein the predetermined hydrogen concentration is less than 4%.

### Claim 16

A system for determining a flow rate of an anode exhaust gas through an anode bleed valve from an anode side of a fuel cell stack, said system comprising:
means for estimating a bleed flow rate of the anode exhaust gas through the bleed valve that maintains a hydrogen concentration in the anode exhaust gas that is bled from the fuel cell stack below a predetermined percentage based on the amount of air in a cathode output from the fuel cell stack, said bled anode exhaust gas being fed into the cathode output from the fuel cell stack;
means for using a valve orifice model for the bleed valve to estimate an anode side pressure set-point that is necessary to supply the estimated bleed flow rate; and
means for providing hydrogen to the anode side of the fuel cell stack that maintains the anode side pressure set-point.

### Claim 17 (depends on 16)

The system according to claim 16 wherein the means for estimating the bleed flow rate uses the equation:
y
H
⁢
⁢
2
exh
=
y
H
2
·
n
.
H
2
n
.
Air
+
y
H
2
·
n
.
H
2
≤
y
H
⁢
⁢
2
exh
⁢
_
⁢
desired
where, yH2exh—desired is the predetermined hydrogen concentration, yH2exh is the flow rate of hydrogen, yH2 is the hydrogen concentration in the anode, {dot over (n)}Air is the molar flow rate of air in the cathode output and {dot over (n)}H2 is the bleed flow rate.

### Claim 18 (depends on 17)

The system according to claim 17 wherein the valve orifice model is defined as:
k
v
=
4.633
·
n
·
MW
n
·
T
(
p
1
2
-
p
2
2
)
where, kv is an orifice constant, n is the molar flow through the orifice, MWn is the molecular weight of gas, p1 is the pressure at the inlet of the orifice, p2 is the pressure at the outlet of the orifice and T is the temperature of the orifice.

### Claim 19 (depends on 18)

The system according to claim 18 wherein the means for providing hydrogen to the anode side of the fuel cell stack determines the anode side pressure set-point by rearranging the valve orifice model as:
Δ
P
SP
=
p
2
2
+
(
4.633
·
n
.
H
2
k
v
)
2
·
MW
n
·
T
-
p
2
where the pressure set-point ΔPSP is the inlet pressure of the orifice p1 and the molar flow through the orifice n is the bleed flow rate {dot over (n)}H2.

### Claim 20 (depends on 16)

The system according to claim 16 further comprising a compressor that provides cathode air, wherein a portion of the compressor air by-passes the fuel cell stack and is sent directly to the cathode output to be mixed with the anode exhaust gas.