Biofuels in Perspective

102 Biofuels
period of a decade. Therefore, it is questionable if the ambitious renewable energy targets
can be met by following this route.
The second and perhaps to be preferred route comprises adapting today’s large-scale
coal-based (entrained flow (EF)) gasification technology, initially by co-firing biomass and
later on construct biomass-based gasifiers. In this way the installed biosyngas capacity can
be increased rapidly, as basic technology is already proven on large scale.
6.3.2 Biomass Feedstock
Approximately 50 % of the biomass globally available for energy purposes (i.e. the technical
potential) is wood or wood residues. A further 20 % is strawlike, which share will increase
to 40 % when strawlike crops are selected as energy crops. 12 Hence, for utilization of the
large amounts of biomass for biosyngas production, it is important to develop technical
routes that are able to utilize both wood and straw materials. Biomass materials like manure
and waste streams will play only a minor role in the biosyngas production, as the absolute
amounts of these streams available for biosyngas production are very low compared to
the required total amounts of biomass. Therefore, they are not of significance for largescale
biosyngas production.
Due to the distributed and global generation of the biomass, large transport distances are
unavoidable. Transport by truck is the major cost driver in biomass transport; therefore,
the transport over land should be minimized. 2 Strawlike materials have a much lower bulk
energy density, which would result in higher transport and transhipment costs. Therefore,
energy densification of straw is desired to reduce transport costs and allow easier handling,
viz. grasses and straw are converted into a bioslurry via flash pyrolysis, 13 as will be discussed
in Sections 6.3.4.4 and 6.3.4.5. Wood, although already relatively high-energy dense, will
preferable also be densified (e.g. by torrefaction discussed in Section 6.3.4.2 or again
pyrolysis, resulting also in simplification of the biomass feeding system of gasification)
before being transported by ship to large centralized conversion facilities.
The transition to green alternatives requires biomass, which should be available in large
quantities. Since wood and grasslike material make up 70–90 % of the total technically
available amount of biomass world-wide, it is reasonable to focus on these biomass fuels
as main renewable energy sources for chemicals and fuels. 14
6.3.3 Syngas Production Technology
In order to produce biosyngas cost-effectively, high biomass-to-syngas yields are required.
This implies that upon gasification of biomass the maximum share of energy contained in
the biomass should be converted into the syngas components H2 and CO.
There are two thermo-chemical ways to produce synthesis gas (H2 and CO) from
biomass: either by applying high temperatures or by using a catalyst at a much lower
temperature Figure 6.4. 15 The first route includes a fluidized bed gasifier and a downstream
catalytic reformer, both operating at approximately 900 ◦ C. In product gas from low
temperature gasification the syngas components H2 and CO typically contain only ∼50 %
of the energy in the gas, while the remainder is contained in CH4 and higher (aromatic)