Environmental Engineering Reference
In-Depth Information
Biomethane
combustion
0.5%
Other
0.5%
Biofuel combustion
in ca rs
10%
Manufacture of
auxiliary materials
20%
Feedstock
provision
55%
Residue
combustion
14%
Figure 18. Contributions to the total GHG emissions of the biorefinery system. “Other” includes
wastewater treatment, waste disposal (mainly ashes) and uncontrolled CH
4
emissions from anaerobic
digestion.
Contributions from all the stages to the total GHG emissions of the biorefinery system are
illustrated in Figure 18. More than half of the GHG emissions are due to feedstock provision,
i.e. collection, processing and delivery of wood residue pellets.
Concerning the fossil reference system, the total GHG emissions are mainly due to
gasoline (68%), followed by electricity (12%) and then other products. Detailed information
concerning the contributors to the total GHG emissions of the fossil reference system are
reported in Table 7. The primary energy demand of biorefinery system and fossil reference
system has similar contributions than those of GHG emissions.
Results highlight both the importance of generating high quantities of electricity and the
benefits deriving from an utilization of the process heat produced for achieving high GHG
emission and fossil energy savings. Concerning electricity, the lower the share of electricity
sent to alkaline water electrolysis, the higher the savings. In the determination of the
magnitude of these savings, a fundamental role is played by the fossil reference system
considered. It is assumed that the fossil reference system produces electricity from natural gas
but the savings would be larger if, for instance, electricity from coal or oil is displaced.
Regarding the heat, fundamental is the possibility to use it in an application located in the
surrounded of the biorefinery, maximizing the environmental benefits which can be gained. In
the fossil reference system, heat is assumed to be produced from oil and even in this case,
environmental savings would be larger if coal-derived heat is replaced. The differences
between biorefinery systems with and without process heat utilization are reported in the
