Environmental Engineering Reference
In-Depth Information
TABLE 16.1 Possible reactions inside SOFCs when running with syngas
(enthalpy change of reaction given at 25
C and 1 bar)
Dry reforming
Δ
r
H
0
= 247 kJ mol
−1
CH
4
+CO
2
⇄
2CO+2H
2
(RX. 16.4)
Steam reforming
Δ
r
H
0
= 206 kJ mol
−1
CH
4
+H
2
O
⇄
CO + 3H
2
(RX. 16.5)
Δ
r
H
0
= 165 kJ mol
−1
CH
4
+2H
2
O
⇄
CO
2
+4H
2
(RX. 16.6)
Water-gas shift
Δ
r
H
0
= − 41 kJ mol
−1
CO + H
2
O
⇄
CO
2
+H
2
(RX. 16.7)
Carbon formation
Δ
r
H
0
= 75 kJ mol
−1
CH
4
⇄
C+2H
2
(RX. 16.8)
Δ
r
H
0
= − 172 kJ mol
−1
2CO
⇄
C+CO
2
(RX. 16.9)
Δ
r
H
0
= − 131 kJ mol
−1
CO + H
2
⇄
C+H
2
O
(RX. 16.10)
Electrochemical reactions
H
2
+O
2 −
⇄
H
2
O+2e
−
Δ
r
H
0
= − 242 kJ mol
−1
(RX. 16.11)
CO + O
2 −
⇄
CO
2
+2e
−
Δ
r
H
0
= − 283 kJ mol
−1
(RX. 16.12)
C+O
2 −
⇄
CO + 2e
−
Δ
r
H
0
= − 111 kJ mol
−1
(RX. 16.13)
C+2O
2 −
⇄
CO
2
+4e
−
Δ
r
H
0
= − 394 kJ mol
−1
(RX. 16.14)
CH
4
+O
2 −
⇄
CO + 2H
2
+2e
−
Δ
r
H
0
= − 37 kJ mol
−1
(RX. 16.15)
CH
4
+O
2 −
⇄
CO
2
+2H
2
+2e
−
Δ
r
H
0
= − 36 kJ mol
−1
(RX. 16.16)
2
O
2
+2e
−
!O
2−
(RX. 16.17)
1
gas shift reaction (RX. 16.7), while CH
4
may be reformed inside the cell into H
2
and
CO
2
(RX. 16.4, 16.5, and 16.6).
16.3.2 Impact of Biomass-Derived Contaminants and
Gas Cleaning on SOFC Operation
Biosyngas from the biomass gasifier contains various contaminants. These contami-
nants are mainly tar, particulate matter, alkali metal compounds and other halides,
sulfur compounds, and nitrogen compounds. Many of these compounds are likely
to poison the FC anode and must be removed from the gas before it enters the FC.
Understanding the impact of various gaseous components on the anode performance
(Aravind and De Jong, 2012; Aravind et al., 2008; Liu et al., 2013) is essential in the
choice of the most suitable system components, such as the type of gasifier and gas
cleaning system, for smooth FC operation.
16.3.2.1 Tars
Tar can impact the SOFC in several ways, including catalyst deacti-
vation and FC degradation due to anode-side carbon deposits. Tar can also be reformed
and subsequently oxidized, contributing to electricity production. Direct oxidation of
certain tar components cannot be ruled out. It is also possible that tar molecules simply
pass through the anode without exerting any significant influence. The fate of tar on
Search WWH ::
Custom Search