Environmental Engineering Reference
In-Depth Information
TABLE 13.11 Input and output flows for a second-generation sugar
and ethanol plant
Input flow
kg.s
-1
kg.s
-1
Output flow
Sugarcane
332.58833
Ethanol
26.39900
Imbibition water
93.12473
Sugar
24.63849
(Recycle) water
500.72025
Carbon dioxide
26.92400
Air
236.91997
(Waste)water
546.81902
Lime
0.92509
Exhaust gas
281.63719
Flocculant
0.00069
Ash, gypsum, soil
6.36579
Sulfuric acid
0.93759
Fusel oil
239.54099
Sulfur
0.10809
Exhaust air
13.43740
Cellulase
0.36579
Natural gas
0.05189
Total in
1165.74240
Total out
1165.76190
For the fermentation and given the rapid developments that are being made,
recombinant yeast able to ferment C
5
and C
6
sugars has been considered. For the
calculations, a future scenario is assumed in which such microorganism has a perfor-
mance similar to current yeast. After the fermentation, the downstream process has the
same structure as the first-generation scenario. Table 13.11 shows a summary of the
input and output flows for the second-generation scenario.
From this table, it can be seen that, for the same sugarcane input as in the first-
generation scenario, more ethanol can be produced. In fact, roughly 13 kg sugarcane
is now required for producing 1 kg sugar and 1 kg ethanol. Other important differ-
ences are:
Increase in input flows associated with the bagasse pretreatment
: More sulfuric
acid for the steam explosion, more lime for detoxification, and commercial
cellulase for hydrolysis.
Less waste streams
: As an alternative to bagasse, other organic waste streams are
sent to cogeneration, namely, filter cake, vinasse, and yeast. The solids from the
furnace (ash, gypsum, and dirt) are sent to landfill.
Less steam and electricity generation
: Since the bagasse is now directed to
fermentation, the excess electricity demand is met by purchasing it from the grid.
For the same reason,
less air but more natural gas is now required for
cogeneration.
The main economic figures for both scenarios are shown in Table 13.12.
Although somewhat dated, these values are still valuable for comparison
purposes. Despite the increase in investment costs due to the additional pretreatment
line and an increase in energy consumption, the plant revenues in the second-
generation scenario are 60% higher, resulting in a significant reduction in ethanol
production costs.
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