Environmental Engineering Reference
In-Depth Information
5.
C
ONCLUSION
The use of biomass as raw materials for bioenergy and biochemical production is
encouraged by the need for a secure energy supply, a reduction of fossil CO
2
emissions and a
revitalization of rural areas. Biomass energy and material recovery is maximized if a
biorefinery approach is considered, where many technological processes are jointly applied to
different kinds of biomass feedstock for producing a wide range of bioproducts. A lot of
biorefinery pathways, from feedstock to products, can then be established, according to the
different types of feedstock, conversion technologies and products. Biorefinery concept is
analogous to today's petroleum refinery, which produces multiple fuels and products from
petroleum.
Among the different biomass resources, lignocellulosic materials have great potentials for
production of bioenergy and biochemicals in biorefinery, replacing fossil derived products
and services. The LCA depicted in this chapter shows that significant GHG and fossil energy
savings are achievable if a biorefinery system is compared with a fossil reference system. The
investigated biorefinery produces transportation biofuels (bioethanol, MTHF), gaseous
biofuels (biomethane and H
2
), chemicals (furan resins, FUMA and O
2
), electricity and heat
from softwood forest residues, while the fossil reference system produces gasoline as
transportation fuel, natural gas, H
2
from natural gas, conventional O
2
from air processing,
conventional FUMA and epoxy resins from oil refinery, electricity from natural gas and heat
from heavy oil. The biorefinery releases 36.8 kt CO
2
-eq./a and requires 10858 TJ/a of primary
energy, of which 208 TJ/a fossil energy, while the fossil reference system releases 336 kt
CO
2
-eq./a and requires 4772 TJ/a, of which 4736 TJ/a fossil energy. Therefore, 89% of GHG
emissions and 96% of fossil energy can be saved. Even if the biorefinery has higher primary
energy demand than the fossil reference system, it is mainly based on renewable energy (i.e.
the energy content of the processed feedstock): the provision of biomass with sustainable
practices is then a crucial point to ensure a renewable energy supply to biorefineries.
Furthermore, more than half of the total GHG emissions of the biorefinery are originated
from feedstock provision (collection, processing and delivery), followed by manufacture of
auxiliary materials and biomass combustion. Results also show biorefinery system
performances in terms of product yields and mass, energy, exergy and C conversion
efficiencies. Energy and C efficiencies result affected by the fermentation step, where almost
half of the C of the feedstock is loss in the formation of the useless product CO
2
.
In order to share the environmental impacts of the biorefinery among the different
coproducts, several allocation procedures were applied. An attempt to avoid allocation
through system expansion was developed and then allocations based on energy content,
exergy content and economic value of outputs have been carried out. All the findings are
finally compared and the specific GHG emission factors (g CO
2
-eq./unit) of each product are
reported. These factors can be applied in LCA studies of a future biobased society, when
biorefinery products will be widely used by customers and as auxiliary materials in
production processes.
