Page 111 - Biofuels for a More Sustainable Future

98 Biofuels for a More Sustainable Future

of fossil fuels by the products produced by the different configurations stud-
ied). Therefore the indicators considered herein for the sustainability analysis
were global efficiency, net productivity per hectare, and avoided CO 2 -eq
emissions. These indicators are presented in details as follows.

15 Sustainability indicators

Global efficiency of the plant (η global ): Defined as the ratio between the useful
energy of the products (ethanol, sugar, cellulosic ethanol, cellulosic butanol,
acetone, diesel, gasoline, waxes, and electricity) and the energy of the inputs
consumed (syrup, bagasse, and straw). η global is calculated by Eq. (4.2).

X

X
_ m product LHV product + Surplus electricity
η (4.2)
Global ¼ X
_ m juice LHV juice + _m bagasse LHV bagasse + _m straw LHV straw
Energy productivity per hectare (σ sugarcane ): Indicates the utilization of sugar-
cane energy per hectare. This parameter indicates the amount of sugarcane
energy that is actually converted into products, such as ethanol, butanol, ace-
tone, sugar, FT liquids, and electricity per hectare. It is determined as a func-
tion of the production of 1 ha of sugarcane crop, as presented in Eq. (4.3).

X
X

_ m product LHV product + Surpluselectricity
σ sugarcane ¼ Ψ (4.3)
_ m sugarcane
ψ represents the sugarcane productivity per hectare and corresponds to
80t sugarcane /ha (Leal et al., 2013b; Rocha, 2015), considering a new sugar-
cane field. The value of σ sugarcane is expressed in GJ/ha, and the values of the
physical properties of the products, such as LHV, density, and so on, are pre-
sented in Table 4.7.
Avoided CO 2-eq emissions (CO 2 eq. ev .): Indicates the amount of CO 2 that is
not emitted due to fuel substitution. Ethanol, for example, is a biofuel that
can substitute other oil-originated fuels such as gasoline. Therefore the emis-
sions of gasoline, when substituted by ethanol, would be avoided, as ethanol
is carbon neutral considering its use as fuel only.
The indicator considers the tonnes of CO 2-eq emissions avoided per
crop. Table 4.8 presents the values of the LHV of these products and the
emissions avoided.