Theheatreleasedinthesyngastomethanestepissufficienttos

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H2
 
 Methan 
 e
steam
 reformer
 2.1.3.
Catalytic
steam
gasification
 CH4,
H2,
 
CO
 H 2
 
 Catalytic
steam
gasification
is
considered
to
be
more
energy‐efficient
than
steam‐oxygen
gasification.
 However,
the
process
is
still
under
development.
In
this
process,
gasification
and
methanation
occur
in
 the
same
reactor
in
the
presence
of
a
catalyst
(Figure
3).
The
energy
required
for
the
gasification
 reaction
is
supplied
by
the
exothermic
methanation
reaction.
CH4
is
separated
from
CO2
and
syngas
(CO
 and
H2);
the
syngas
is
then
recycled
to
the
gasifier.
The
catalytic
reaction
can
take
place
at
a
lower
 temperature
(typically
650°–750°
C).
The
process
was
initially
developed
by
Exxon
in
the
1970s
using
 potassium
carbonate
(K2CO3)
as
a
catalyst,
but
the
process
was
not
commercialized.
 
 The
advantages
of
hydrogasification
and
catalytic
steam
gasification
are
that
they
do
not
require
air
 separation
unit;
hence
there
is
less
energy
penalty
for
the
process.
Furthermore,
the
costs
are
lower,
as
 Climate
Change
Policy
Partnership
 6
 Synthetic
Natural
Gas
(SNG):
Technology,
Environmental
Implications,
and
Economics
 the
gasification
and
methanation
occur
at
a
lower
temperature.
The
disadvantages
of
catalytic
steam
 gasification
are
the
separation
of
catalyst
from
ash/slag
and
the
loss
of
reactivity
of
the
catalyst.
 
 Steam
 
 Steam
 Catalytic
coal
 Coal
+
make‐up
 catalyst
 
 Coal
+
make‐ Catalyst
 up
catalyst
 Particulate,

 tar
removal
 
 Particulates,
tar
 removal
 
 Catalytic
coal
 Ash‐catalyst
 methanation
 separation
 
 
 
 CO2
 Gas
 separator
 Gas
 cleaning
 methanation
 
 CO2
 
 
 Gas
 
 H2,
CO cleaning
 
 
 
 
 Compression
and
 sequestration
(optional)
 SNG
 
 SNG
 CH4
 separation
 
 
 
 
 
 Ash‐catalyst
 Ash
 separation
 

 
 Figure
3.
Catalytic
steam
gasification
process
diagram
 Ash
 
 2.2.
Thermal
Efficiency
of
SNG
Plants
 The
thermal
efficiency
of
an
SNG
plant
employing
the
steam‐oxygen
gasification
process
varies
in
the
 range
of
59%
to
61%.
A
DOE
study
reported
plant
efficiencies
of
60.4%
for
Illinois
#6
(bituminous)
coal
 and
59.4
%
for
Powder
River
Basin
(PRB)
(sub‐bituminous)
coal
(NETL
2007).
A
University
of
Kentucky
 study
calculated
the
efficiency
of
an
SNG
plant
using
bituminous
Kentucky
coal
to
be
60.1%
without
CO2
 capture
a...
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