Environmental Engineering Reference
In-Depth Information
producers and users. Nevertheless, the biomass feedstock can effectively be turned
into syngas (without the need of any microorganisms) and subsequently into
bioalcohols [3]. Compared to bioalcohols produced by biological conversion, this
protocol avoids issues such as the inefficient degradation of biomass to fermentable
sugars as well as dealing with the processing of the pentoses (C5) generated in the
hydrolysis of biomass.
8.4.1.3 Biogas
Biogas might be of relevance in renewable energy markets both for transport and
for generation of electricity. It is also a realistic alternative to the accumulation of
waste in landfill as new sites can be specially configured to optimise gas output (as
high as 1000 m
3
/h biogas. However, LCA studies have identified an impact to GHG
in its production, associated to the generation and emission of CO
2
and N
2
Ointhe
process [126, 127].
8.4.1.4 Biohydrogen
Biohydrogen is believed to be one of the biofuels for the future, combining its abil-
ity to potentially reduce the dependence of foreign oil and contribute to lower the
GHG emissions from the transportation sector. However, storage (biohydrogen has
to be compressed, liquefied, or stored in metal hydrides), transportation and use (fuel
cell vehicles are not commercially available yet and a distribution infrastructure for
hydrogen cannot be realised in the short term) as well as the technological advances
needed for its successful implementation limit bio-hydrogen only as a longer-term
option for the transport sector.
8.4.1.5 Bio-SNG
Bio-SNG has various advantages but also a number of challenges for the future. Its
octane number is very high, but the cetane number is very low, which means that
bio-SNG has to be used in spark ignition engines, which need to be adapted for its
use. Storage is also a challenge for the future as bio-SNG is also a gas at room tem-
perature so it needs to be compressed or liquefied to be used as an automotive fuel.
Furthermore, larger storage and fuel tanks are needed due to the lower volumetric
energy content of the fuel.
The supercritical water low-temperature gasification technology may overcome
some of the main technological barriers in the process. Nevertheless, gas clean-
ing (especially tar removal) and catalyst development are important technological
issues, although if active and selective catalysts are used (e.g. Ru/C), no signifi-
cant quantities of tars or char have been reported to form. However, the cost of the
supercritical water production of bio-SNG is several times higher than that of the
conventional gasification process [89].
