Environmental Engineering Reference
In-Depth Information
(1)
+
1.08 H
2
CH
1.49
O
0.67
(s)
0.33 H
2
O(g)
CO
+
1.56 H
2
(2)
+
0.52 CH
4
+
0.52 H
2
O(g)
0.52 CO
0.48 H
2
O(g)
0.48 CO
2
(3)
0.48 CO
+
+
0.48 H
2
(4)
CH
1.49
O
0.67
(s)
0.29 H
2
O(g)
0.52 CH
4
+
0.48 CO
2
+
Fig. 8.9
Reactions involved in the conventional gasification of biomass
disintegrates in supercritical water forming a mixture of carbon dioxide, carbon
monoxide and methane (SNG). The technology is expected to be especially suitable
for wet (polluted) biomass and has higher efficiency than the conventional gasi-
fication process at lower temperature [86]. Bio-SNG can also be produced from
biogas.
Various projects in the Netherlands, including the largest existing bio-SNG
plant located in Buggenum, currently produce bio-SNG from the co-gasification
of biomass with coal at different proportions [88].
Bioalcohols
Biomethanol
. Biomethanol can be produced from synthesis gas [89] via conven-
tional gasification of biomass (partial oxidation) at high temperatures (800-1000
◦
C)
and subsequent catalytic synthesis of the CO+H
2
-in a 1:2 ratio-under high pressures
(4-10 MPa) [89-91].
The biofuel can be blended with petrol up to 10-20% without the need of any
engine modifications [90, 91]. Several feedstocks including bark, woodchips, bam-
boo, waste wood and pulp [89-91] and even glycerol [92] have been reported to be
used in the process.
There are a few biomethanol pilot plants under development, mainly in the US
(e.g. North Shore Energy Technologies, 40 MMgy plant) and Japan (e.g. Norin
Green no1, MAFF and Mitsubishi heavy industries) [90].
Bioethanol
. Bioethanol can be also obtained via conventional thermal gasifica-
tion of biomass to syngas combined with catalytic processes in similar way to those
for the production of biomethanol (Fig. 8.11, left side) [3].
Alternatively, following biomass gasification, the syngas can be directly fer-
mented to ethanol using anaerobic bacteria (Fig. 8.11) [93]. This eliminates the
need of the hydrolysis step to break up the cellulose and hemicellulose fractions
of the biomass. The lignin fraction can also be converted into ethanol. The process
has been reported at lab scale and is still under development [3, 93]. However, the
efficient delivery of the syngas to the microorganisms still remains a challenge [3].
There are some examples of ongoing industrial processes. An operating lig-
nocellulosic bioethanol production plant is located in Ottawa (Canada), run by
the IOGEN Corporation [94]. The demonstration plant produces up to 3 million
litres of bioethanol per year. The feedstocks employed are wheat, oat and barley
