The energy balance of the dry and wet route is shown in Fig. 2.
The energy demand is presented in two manners: the upper bar re-
flects the energy consumption without allocations, while the lower
bar allocates the energy demand into electricity and heat. Fig. 2a
shows the fossil energy demand and energy production associated
with production and processing of 1 ton of dry microalgae via the
dry route. For both the standard-N and the low-N scenario, a positive
energy balance (the energy output is higher than the fossil energy
input) is achieved. From Fig. 2a it can be concluded that the
energy consumption for culturing, dewatering and lipid conversion
are dominating the dry route. At standard-N conditions, the dewatering
process requires the highest energy input, followed by culturing
and lipid conversion. At low-N conditions, the lipid
conversion process consumes more energy than the culturing process
caused by the higher methanol input. From the distribution of
the products, one finds that at standard-N conditions, pyrolysis oil
is the main product which contains 48.4% of the output energy.
Low-N conditions result in bio-diesel as the main product with
62.7% of the output energy. This is caused by the higher lipid content
achieved at the low-N condition (Lardon et al., 2009). The latter
case (low-N) is more attractive because bio-diesel, in contrast to pyrolysis oil, can directly be applied in engines for transportation.
The FER improved to 1.50 at low-N conditions from 1.23 at
standard-N conditions.