For micro-algae conversion into a secondary bio-energy carrier,
the efficiency and cost of final conversion are calculated. All selected
conversion options are taken into account as stand-alone
options: the conversion efficiency and costs include energy inputs
for pre-treatment or during conversion. Considered options are
both existing and expected future technologies for biomass conversion,
see Table 11. Biomass combustion for heat production is
a well established technology for woody biomass. Conversion efficiencies
between 70% and 90% are common for modern furnaces
[52]. Dry feedstock for combustion is preferred, we thus assumed
that algae are dried to 85% dry solids before combustion. Gasification
of biomass including electricity production with combined cycle
reached the demonstration phase around 2006 [52].
Conventional gasification requires relatively dry feedstock (above
80% dry solids) to produce gas under elevated temperatures. Product
gas can be converted to electricity or Fischer–Tropsch liquids,
the latter require a larger scale operation in order to be economically
viable. Supercritical Water Gasification (or hydrothermal gasification)
is a newly developed process for the conversion of wet
feedstock (