Environmental Engineering Reference
In-Depth Information
and the use of FTS has continued there. Since the 1980s, the interest in FTS has been
growing again. Sasol and Shell have commissioned large plants for natural gas-based
FTS in Qatar in 2006 and 2011, respectively. The capacity of the Sasol plant is 34,000
barrels
day
−1
(4,600 t
day
−1
), and that of the Shell plant 140,000 barrels
day
−1
(19,000
day
−1
). Reasons for the renewed interest in the application of FTS to syngas obtained
from coal are that the worldwide coal reserves are much larger than those of oil and gas
and that some countries have a lot of coal, but little or no oil or gas reserves; China is a
prominent example. Finally, also biomass-based FTS has attracted more interest in
recent years. This way of producing biofuel has the advantage that it can rely on
the technology developed for fossil feedstocks and thus is more mature than several
other ways of producing biomass-based transportation fuels.
In the following sections, FTS technology will be presented by its key constituents
in order of an increasing scale: reaction stoichiometry and kinetics, catalyst aspects,
and design and operation of different reactor types.
t
17.2.1 Reaction Stoichiometry and Kinetics
FTS is a way to convert syngas into hydrocarbons at elevated temperature and pres-
sure. It is a complex network of reactions, but the simplified overall reaction scheme is
given as
ð
2
n
+1
Þ
H
2
+
n
CO
!
C
n
H
2
n
+2
+
n
H
2
O
n
=1,2,
…
, > 100
ð
RX
:
17
:
1
Þ
ð
Þ
Þ
−1
Δ
r
H
=
−
170 kJ mol CO
ð
The most widely used kinetics for this reaction is the Yates and Satterfield expression
(Yates and Satterfield, 1991), which follows the Langmuir
-
Hinshelwood model.
It gives the reaction rate based on CO per catalyst mass as
r
=
Fap
CO
p
H
2
1+
bp
CO
ð
Eq
:
17
:
1
Þ
2
ð
Þ
In this equation,
F
is a catalyst activity multiplication factor that accounts for improve-
ments in catalyst activity since publication of the original parameter values in 1991
(Guettel and Turek, 2009; Vervloet et al., 2012),
p
i
is the partial pressure of reactant
i
,
a
is the reaction rate coefficient (per unit mass of catalyst), and
b
is the adsorption
coefficient of CO Equation (17.2), as reported by Maretto and Krishna (1999), which
can be calculated as
;
b
=
b
0
exp
Δ
b
H
R
u
E
a
R
u
1
493
1
T
1
493
1
T
a
=
a
0
exp
15
−
15
−
ð
Eq
:
17
:
2
Þ
:
:
In this expression, R
u
is the universal gas constant and T is the temperature in K. The
other required values are given in Table 17.1. Please note that there is a typo in the
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