Environmental Engineering Reference
In-Depth Information
TABLE 13.1 Average composition of the millable
part of sugarcane according to local data
Component
wt%
Sucrose
13.74
Glucose/fructose
1.70
Minerals
0.62
Other water-soluble components
5.09
Fiber
13.21
Water
65.64
Imbibition water
Wash water
Raw juice to
clarification
Sugarcane
Cleaning
Milling
Bagasse
Used wash water
FIGURE 13.2
Milling of sugarcane.
composition is given in Table 13.1. Sucrose, glucose, and fructose are fermentable to
baker
s yeast.
A representative process for ethanol production from sugarcane is summarized in
Figures 13.2, 13.3, 13.4, 13.5, 13.6, and 13.7. Six parts are distinguished: milling,
clarifying, concentrating, fermenting, purifying, and cogenerating. These parts are
connected in many ways. For simplicity, only material flows are shown and no energy
flows (via steam, cooling water, and electricity). In Table 13.2, a summary of technical
terms in the bioethanol process can be found.
Clearly, there are other outputs besides ethanol. These either result in treatment
costs (vinasse, ash) or can be sold as coproduct (fusel oil, filter cake). The main copro-
duct is the electricity that is produced by cogeneration as shown in Figure 13.7; it is
more than sufficient to cover the plant
'
s requirement. Actually, we are dealing with a
typical biorefinery, where the agricultural feedstock crop, in this case sugarcane, is
separated and converted into various fractions, in which each needs to have a clear
destination. The huge scale would lead to problems even if only a mere 0.1% of
the feedstock had no destination.
The sugar plants are located in areas with cane fields. Transport costs for cane are
minimized in this way and also sugar losses because the cane cells consume sugars
during transport and storage. Calculations show that truck transport in excess of
'
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