Page 98 - Biofuels for a More Sustainable Future

88 Biofuels for a More Sustainable Future

• Cases FT (Fischer-Tropsch): Considers the thermochemical route and the
utilization of all the available bagasse available at the syngas production
plant for Fischer-Tropsch synthesis. This process is characterized by the
high demand of energy in the processes that constitute the plant. It was
considered that a BIG-GTCC cycle would meet part of this demand,
using 20% of the syngas produced.
• Case BGT (BIG-GTCC): Considers the thermochemical route for the
production of electricity, using all the available bagasse in the gasification
process. Therefore the produced syngas will be used as fuel for a gas tur-
bine within a BIG-GTCC cycle, and does not require adjustments in its
composition, as occurred indifferently from the FT case.
Each case assumes a sugar and ethanol industry that is energetically self-
sufficient, with electric mills. The self-produced electricity operates equip-
ment such as pumps, agitators, transporters, and lighting.
After the syrup extraction process, bagasse is obtained with a 50% humid-
ity content. For each tonne of sugarcane processed, 280kg on humid basis is
obtained, which corresponds to the available bagasse (Marino, 2014;
Oliv erio, 2014; Hassunai et al., 2005). Straw represents 14% of the sugarcane
available in the field (Marino, 2014; Oliv erio, 2014; Hassunai et al., 2005),
and therefore for each tonne of sugarcane cropped, there is 140kg straw
left in the field. Assuming a plant with a processing capacity of 1200tonnes
of sugarcane per hour, this value corresponds to 86% of the sugarcane avail-
able in the fields, and the remaining 14% refer to straw (equivalent to
195.35tonnes/h).
It is recommended that the maximum amount of straw removed from
the field is 50%, as half of the straw should be left on the soil to reduce ero-
sion, allow the recirculation of nutrients and maintain the humidity levels of
the soil (Marino, 2014; Hassunai et al., 2005). The amount of available straw
(humidity content 15%) for utilization corresponds to 97.68t/h, and herein
the rounded value of 97.60t/h will be considered. Regarding bagasse, part
is mixed with straw and used as fuel for the steam boiler, in a 50%–50%
proportion, as suggested by the manufacturer CALDEMA (Marino,
2014). It is also recommended that a 10% share of the bagasse generated after
syrup extraction is stored (CGEE, 2010), which corresponds to 33.6t/h.
After this separation, there is 204.8t/h of bagasse that can be utilized as a
resource in the biorefinery processes, which contemplates biochemical and
thermochemical conversion routes.
Fig.4.9presentsthegeneralschemeofthebiorefinery,inwhichtheafore-
mentioned processes are integrated within an existing plant. Table 4.2 pre-
sents the operational parameters adopted for the simulation, common to all
study cases. LHV refers to the lower heating value.