Environmental Engineering Reference
In-Depth Information
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World
United States
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Brazil
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China
Europe
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Ye ar
FIGure 21.1 Fuel ethanol production in the world and in selected regions. Ethanol is produced from corn in
the United States and from sugarcane in Brazil. Figures for 2009 and 2010 are projected data. (From Energy
Information Administration, Official energy statistics of the U.S. government, 2009, http:www.eia.doe.gov;
União da Indústria de Cana-de-Açúcar, Statistics of sugarcane sector—Season 2006/2007, 2009, www.unica.
com.br.)
21.9.1 E xtraction , J uicE t rEatmEnt , c oncEntration , and S tErilization
Sugarcane is first cleaned in wet or dry cleaning system, which removes 70% of the dirt, before
entering the mills, in which sugarcane stems are processed and juice and bagasse are obtained. Mill
efficiency is around 96%. Sugarcane juice passes through screens and hydrocyclones that remove
dirt, sand and fibers; then phosphoric acid is added to increase phosphate content, and the mixture
is heated from 30 to 70°C before addition of lime. The limed juice is heated from approximately
70 to 105°C before the flash tank, where air bubbles are removed from the juice. The degasified juice
receives a flocculant polymer and is decanted, aiming at removal of insoluble impurities, including
calcium phosphates formed during the liming step. The mud obtained in the decanters is filtered
(producing filter cake) and the liquid phase returns to the process just after the liming step.
The clarified juice obtained in the decanters goes through multiple effect evaporators (MEE) to
achieve adequate sugars concentration. Only part of the clarified juice must be concentrated. The
final juice is made up of clarified and concentrated juice, and contains about 22 wt % sucrose.
To promote sterilization before fermentation, the juice is heated up to 130°C, cooled down to
28°C and fed to the fermentation reactor.
21.9.2 f ErmEntation
The sterilized juice is added to the fermentor along with the yeast media, which is made up of a
yeast suspension containing about 28% yeast (vol. basis) and comprises 25% of the reactor volume.
Fermentation is carried out at 28°C; ethanol content of the wine can reach 13°GL (approximately
10.5% ethanol on a mass basis, that means around 100 g/L). To achieve this high ethanol content,
batch fermentation may have to be carried out for up to 15 h and alternative cooling methods, such
as a steam jet system or an absorption machine, are necessary to provide water at temperatures low
enough to maintain reactor cooling (Dias et al. 2007), because fermentation is negatively affected by
high temperatures. In an integrated process taking into account hydrolyzed lignocellulosic material
from sugarcane bagasse or straw, the fermentor could be fed with a blend of molasses and hydrolyzed.
The wine obtained in the fermentor is centrifuged for the recovery of yeast cells. The yeast milk
obtained in the second centrifuge contains about 70 vol % yeast, so water is added to this milk to
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