BIOCHEMICAL CONVERSION: BIOFUELS BY INDUSTRIAL FERMENTATION - Biomass as a Sustainable Energy Source for the Future - page 425

This process configuration can be extended to simultaneous saccharification and
cofermentation of pentose and hexose sugars. Another possibility is consolidated
bioprocessing, where the fermenting microorganism produces the enzymes necessary
to hydrolyze cellulose and hemicelluloses. Besides simplifying the process by per-
forming everything in one step, synergism between enzyme and microbe has been
reported, although the microorganisms are not efficient yet for tests at industrial scale.

13.3.6 Case Study: Production of Ethanol from Bagasse

The transition toward lignocellulosic feedstocks will have an impact on the process
scheme; the mass, energy, and waste streams in the process; and the equipment used.
Consequently, it will also have an impact on the economic performance of the process.
In a similar way as described Section 13.2, a conceptual study for a plant located in
Brazil was performed (Efe et al., 2007). In this case, however, the plant produces both
sugar and ethanol. Nevertheless, the process steps required for ethanol production are
similar to those already described. Table 13.10 shows a summary of the input and
output flows for the first-generation scenario of the combined sugar and ethanol plant.
Just as for the plant producing ethanol only (Section 13.2), the process requires large
amounts of sugarcane, water, and air.
In this case, 9 kg sugarcane results in 1 kg of product (both sugar and ethanol). In
other words, about 13 kg sugarcane is required for producing 1 kg sugar and 0.4 kg
ethanol. In the first-generation scenario, the sugarcane bagasse is used for cogenera-
tion (in the same way as shown in Figure 13.7). In the second-generation scenario, all
bagasse is pretreated so that it can also be used as feedstock for the fermentation.
A simplified block scheme is shown in Figure 13.11.

TABLE 13.10 Input and output flows for a first-generation
sugar and ethanol plant a
Input flow

kg.s -1 kg.s -1

Output flow

Sugarcane 332.58833 Ethanol 11.03899
Imbibition water 93.12473 Sugar 24.63819
(Recycle) water 174.02778 Carbon dioxide 11.31399
Air 407.43717 (Waste) water 308.87555
Lime 0.30309 Exhaust gas 488.09758
Flocculant 0.00069 Ash 1.240000
Sulfuric acid 0.14199 Filter cake 15.27793
Sulfur 0.10809 Vinasse 16.99999
Fusel oil 113.29699
Yeast 3.51859
Exhaust air 13.43279
Total in 1007.73187 Total out 1007.73059
a The plant capacity is determined by the feedstock supply (5 million tonnes per year of
sugarcane). The plant operates 174 days per year (4176 h per year).