62
open-air fire on the field, which brings advantages in terms of diesel consumption.
Nevertheless, driven by other environmental (urban air pollution due to PM, NO x ,
and SO x pollutants) and social concerns, manual harvest technique planned to be
phased out by 2014–2017 (Goldemberg et al. 2008). In the simulation period (2030),
besides the phaseout of the open-air burning, changes of sugarcane farming practices are related to the boost of sugarcane productivity, the increase of application of
agrochemicals, and the rising consumption of diesel (due to a higher rate of harvest
mechanization). Additionally, with the introduction of mechanical harvest, straw
(initially burned in the field) could be recovered to supply the ethanol refining
process.
The ethanol processing stage was modeled assuming a conventional autonomous
ethanol refining unit, where only ethanol is produced, through conventional mechanical and biochemical processes. First, harvested sugarcane passes through a cleaning unit to remove impurities, followed by an extraction system, where sugarcane is
chopped, and shredded, and juice with high content of sugar is separated and
cleaned. Bagasse and filter cake are also generated as coproducts. Following juice
extraction, the mixture is fermented by yeasts (commonly the Saccharomyces cerevisiae). Finally, the resulting wine is purified through fractional and azeotropic distillation processes. Besides the final product anhydrous ethanol, vinasse is also
generated. As this coproduct has a high nutrient content (N, P, K), it is commonly
recovered and used for ferti-irrigation. One tone of vinasse recovers 0.36 kg of
N-fertilizer (Donzelli 2007).
The ethanol processing consumes energy for activating pumps, fans, and milling
equipment, as well as thermal energy for the juice concentration and distillation
processes. The process is assumed to be energy self-sufficient, i.e., the consumed
energy is entirely powered by bagasse and straw (from mechanically harvested
fields), in combined heat and power (CHP) units. Currently, CHP systems are generating steam at low pressure (~22 bar), which results in limited electricity generation. However, old boilers are being replaced by efficient high-pressure steam
boilers (~65 to 90 bar, 480 °C) that increase the amount of surplus electricity
(Macedo et al. 2008; Seabra et al. 2010). Thus, in the baseline scenario, forecasts up
to a 2030 horizon were modeled taking into consideration the shift to high-pressure
steam boilers and penetration of more efficient processes in ethanol production.
Alternatively, the cellulosic ethanol route (scenario B) considers the integration
of an adjacent plant next to the principal ethanol distillery unit that produced cellulosic ethanol (the so-called second-generation ethanol) sourced by disposed
bagasse and sugarcane straw. Prior to the fermentation and purification stages, the
pretreatment processes are applied. Acid or enzymatic hydrolysis is done in order to
separate degradable cellulose and hemicellulose compounds from the nondegradable
lignin compounds. Accordingly, bagasse and straw biomass are pretreated via
diluted sulfuric acid, followed by enzymatic hydrolysis with co-fermentation. The
product is recovered, and purification follows common processes of the sugarcanederived ethanol. Thus, an extra 46.3 l per ton of sugarcane is expected to be generated from the cellulose coproducts.
K. Hanaki and J. Portugal-Pereira
open-air fire on the field, which brings advantages in terms of diesel consumption.
Nevertheless, driven by other environmental (urban air pollution due to PM, NO x ,
and SO x pollutants) and social concerns, manual harvest technique planned to be
phased out by 2014–2017 (Goldemberg et al. 2008). In the simulation period (2030),
besides the phaseout of the open-air burning, changes of sugarcane farming practices are related to the boost of sugarcane productivity, the increase of application of
agrochemicals, and the rising consumption of diesel (due to a higher rate of harvest
mechanization). Additionally, with the introduction of mechanical harvest, straw
(initially burned in the field) could be recovered to supply the ethanol refining
process.
The ethanol processing stage was modeled assuming a conventional autonomous
ethanol refining unit, where only ethanol is produced, through conventional mechanical and biochemical processes. First, harvested sugarcane passes through a cleaning unit to remove impurities, followed by an extraction system, where sugarcane is
chopped, and shredded, and juice with high content of sugar is separated and
cleaned. Bagasse and filter cake are also generated as coproducts. Following juice
extraction, the mixture is fermented by yeasts (commonly the Saccharomyces cerevisiae). Finally, the resulting wine is purified through fractional and azeotropic distillation processes. Besides the final product anhydrous ethanol, vinasse is also
generated. As this coproduct has a high nutrient content (N, P, K), it is commonly
recovered and used for ferti-irrigation. One tone of vinasse recovers 0.36 kg of
N-fertilizer (Donzelli 2007).
The ethanol processing consumes energy for activating pumps, fans, and milling
equipment, as well as thermal energy for the juice concentration and distillation
processes. The process is assumed to be energy self-sufficient, i.e., the consumed
energy is entirely powered by bagasse and straw (from mechanically harvested
fields), in combined heat and power (CHP) units. Currently, CHP systems are generating steam at low pressure (~22 bar), which results in limited electricity generation. However, old boilers are being replaced by efficient high-pressure steam
boilers (~65 to 90 bar, 480 °C) that increase the amount of surplus electricity
(Macedo et al. 2008; Seabra et al. 2010). Thus, in the baseline scenario, forecasts up
to a 2030 horizon were modeled taking into consideration the shift to high-pressure
steam boilers and penetration of more efficient processes in ethanol production.
Alternatively, the cellulosic ethanol route (scenario B) considers the integration
of an adjacent plant next to the principal ethanol distillery unit that produced cellulosic ethanol (the so-called second-generation ethanol) sourced by disposed
bagasse and sugarcane straw. Prior to the fermentation and purification stages, the
pretreatment processes are applied. Acid or enzymatic hydrolysis is done in order to
separate degradable cellulose and hemicellulose compounds from the nondegradable
lignin compounds. Accordingly, bagasse and straw biomass are pretreated via
diluted sulfuric acid, followed by enzymatic hydrolysis with co-fermentation. The
product is recovered, and purification follows common processes of the sugarcanederived ethanol. Thus, an extra 46.3 l per ton of sugarcane is expected to be generated from the cellulose coproducts.
K. Hanaki and J. Portugal-Pereira