This study considers the anode gas flow rate is 0.00621-0.0621 mol s, the cathode gas flow rate is 0.0263-0.1841 mol s, the inlet temperature of anode gas and cathode gas are 858K and 867 K, the operation pressure is 3.5 atm, the operation voltage is 0.8 V, and the deviation of the non-uniform profile is 0.5. Figure 3-3 shows that the current density distribution in pattern A and pattern B when the anode gas and cathode gas flow rate is 0.0621mol s and 0.1841 mol s, respectively. In this figure, the profile with bold line is the current density distribution in uniform pattern, and the profile with color represents current density distribution in pattern A or pattern B. Examining the current density distribution in uniform pattern indicates that the current density mainly decreases along the anode gas flow direction from 1842A m to 1315 ⋅ −2 A m . In the cathode gas flow direction, the current density ⋅ −2 slightly rises because of the decrease of total resistance in Eq.X(3.15)X. In Fig. 3-3(a), the current density has more severe reduction in the corner of the anode gas exit and
the cathode gas inlet. In this corner, the hydrogen concentration becomes lower because the progressively increasing anode gas profile induces less anode gas flowing through this area. Oppositely, the area with apparent current drop happens in the corner of the anode gas exit and the cathode gas exit, because the anode gas non-uniform profile is progressively decreasing. Comparing the Fig. 3-3(a) and 3-3(b) indicates that the current density drop in the corner of Fig. 3-3(b) is slightly larger than that of Fig. 3-3(a).
Figure 3-4 shows that the current density distribution in pattern A and pattern B when the anode gas and cathode gas flow rate is 0.01242mol s and 0.0526 mol s, respectively. In this figure, the profile with bold line is the current density distribution in uniform pattern, and the profile with color represents current density distribution in pattern A or pattern B. Examining the current density distribution in uniform pattern indicates that the current density mainly decreases along the anode gas flow direction from 1846A m to 347 ⋅ −2 A m . This current density range is ⋅ −2 clearly lower than that in Fig. 3-3. Because both the anode gas and cathode gas molar flow rate reduces in Fig. 3-4, the current density becomes lower due to the less hydrogen and oxygen concentration. In Fig. 3-4(a), the current density has a reduction in the corner of the anode gas exit and the cathode gas inlet. In this corner, the current density rapidly decreases from 1848A m to 138 ⋅ −2 A m . This means ⋅ −2 the region is close to a non-reaction area. The less anode gas flow rate and non-uniform inlet flow induces the anode gas molar flow rate is fewer in this area, so
the hydrogen is almost used up and the current density becomes near zero. Similarly, the current density severely drops in the corner of the anode gas exit and the cathode gas exit in Fig. 3-4(b), and this corner occur the non-reaction situation.
Figure 3-5 shows that the current density distribution in pattern A and pattern B when the anode gas and cathode gas flow rate is 0.00621mol s and 0.0263 mol s, respectively. The non-reaction area of Fig. 3-5(a) is apparently larger than the same area of Fig. 3-4(a), because the anode gas molar flow rate is the least in this study.
Even in uniform pattern, the current density distribution happen a severe drop in the anode gas exit, as shown in the bold line. This means the anode gas is almost used up when the anode gas flows out the cell reaction in uniform pattern. Examining the average current density over the reaction area shows that it is the lowest one in Figs.
3-3 to 3-5. When the inlet flow is non-uniform, the current density in the corner of the anode gas exit of Fig. 3-5(a) and 3-5(b) drops to zero because of the progressively increasing and decreasing profile of the anode gas inlet molar flow rate.
Promoting the anode gas utilization in an anode gas cell is more economical, but the global current density will drop with an increase in anode gas consumption and decrease the power of a anode gas cell. Moreover, the non-reaction area will happen and more deteriorate the global current density when the anode gas inlet molar flow rate becomes less and the non-uniform inlet profile is considered. Table 3-1 lists the average current density and anode gas utilization in all cases of this study. In this
table, it is clear that the average current density and anode gas utilization decreases and increases with a decrease in the molar flow rate, respectively. Furthermore, Pattern B has the lowest average current density and anode gas utilization when the molar flow rate is unchanged, because the happening of non-reaction area in the corner of the anode gas exit and the cathode gas exit. Figure 3-6 depict the histogram of relative change of average current density in non-uniform pattern related to that in uniform pattern. In this figure, the relative change is below –2% when the anode gas molar flow rate is 0.0621 and 0.00621 mol s, and the anode gas utilization is near 30% and 90%, respectively. The minus represents the average current density becomes lower when the inlet profile is non-uniform. Once the anode gas molar flow rate decreases, the anode gas utilization will increase accompanying the flow rate decrease. The effect of non-uniform inlet flow on the average current density becomes more apparent when the anode gas utilization is close to 73%, and then becomes slighter along the increase of gas utilization. In this figure, the relative change of average current density raise to –4% in Pattern B.
3.4.
19BConclusions
This study investigates the effect of non-uniform inlet flow on the electrical performance of a MCFC unit. This work employed a software package to solve the simultaneous mass, energy, and electrochemistry equations. With considering three flow patterns and three molar flow rates, this research analyzed the current density
distributions at different conditions. The results show that the anode gas utilization increases with a decrease in the molar flow rate, and the average current density decreases with the decrease in the molar flow rate. In addition, non-uniform Pattern A and B will induce a happening of non-reaction area in the corner of the anode gas exit. This non-reaction area deteriorates the average current density and deteriorates the electrical performance to –4% when the anode gas molar flow rate is 0.01242mol s and anode gas utilization is 73%.
Table 3.1 Average current density and anode gas utilization at different inlet molar flow rate and patterns
Uniform PatternA PatternB
1655 25 1636 25 1626 23
nf=0.01242
Inter-connector Cell
Air Fuel
Fig 3.1. Schematic diagram of a unit of molten carbonate anode gas cell in cross-flow.
Fig 3.2. Arrangements of non-uniform inlet flow patterns in this chapter.
Fig 3.3. Current density distribution in Pattern A and B when n =0.0621 and f
n =0.1841 mol/s. a
(a) Pattern A
(b) Pattern B
Fig 3.4. Current density distribution in Pattern A and B when n =0.01242 and f
n =0.0526 mol/s a
(a) Pattern A
(b) Pattern B
Fig 3.5. Current density distribution in Pattern A and B when n =0.00621 and f
n =0.0263 mol/s. a
(a) Pattern A
(b) Pattern B
uniform uniform
i i
i
−
-0.04 -0.03 -0.02 -0.01 0
nf=0.0621 nf=0.01242 nf=0.00621
Pattern A Pattern B
Fig 3.6. Relative change of average current density in non-uniform pattern.