Biofuels in Perspective

64 Biofuels
completely eliminated, with almost no impact in the sugarcane plant. Due to the lower
costs, in some regions up to 90 % of sugarcane is mechanically harvested. It is estimated
that with mechanized harvesting costs can be reduced 30 %, but investments required are
still very high.
In the years to come, and mainly due to environmental constraints, a gradual growth
on green cane harvesting is forecast, i.e. mechanized harvesting without previous field
burning. Green cane harvesting will allow the recovery of sugarcane trash (leaves and tops
of the plant) and a significant increase in biomass availability (about 30 % in mass basis
and about 50 % in energy basis, considering that 50 % of the trash can be transported to
the mill). In the state of São Paulo legislation obliges a gradual growth on mechanized
harvesting and full mechanization will be reached just in 2017. On the other hand, in
most of the Northeast region mechanized harvesting cannot be extensively applied due to
topographic conditions.
Green cane harvesting requires the development of more adequate machines, considering
local topography and the way sugarcane is planted. The main aspects to be observed are
high performance in sugarcane recovery, lower costs, reduction of the amount of soil
transported and low level of sugar losses. 25 Appropriate harvesting machines have been
developed in Brazil.
Gains on productivity and cost reductions were also achieved due to the introduction
of operation research techniques in agricultural management and to the use of satellite
images for varieties identification in planting areas. Similar tools have been used in
decision-making regarding harvesting, planting and application rates for herbicides and
fertilizers.
On the other hand, regarding the industrial process of ethanol production different
priorities were defined along the years. 26 In a first moment the focus was put on increasing
equipment productivity, eventually with reducing conversion efficiencies. The size of
Brazilian mills also increased and nowadays milling capacity is 2–5 times higher than
25–30 years ago; 23 the current standard mill has crushing capacity of 2–3 million tonnes
of sugarcane per year. In a second moment the focus was moved to improvements on conversion
efficiencies, effort that still continues. Since mid-1980s the conversion efficiency
at the industry has grown from 73 to 85/t of sugarcane processed, or 1.6 to 1.9 GJ/t (based
on the LHV of anhydrous ethanol – 22.3 MJ/liter). It is expected that conversion efficiency
can reach 91/t in 8 years and 92.5/t in 18 years. Finally, during the last 15 years the focus
has been on better management of the processing units.
A summary of the main technological improvements in the industrial process is presented
in Table 4.2.
Due to the technological developments achieved both on the agriculture and on industry
sides, average production yields have grown from 3000 liters/ha.year (67 GJ/ha/yr) in
early 1980s to 6500 liters/ha.year (145 GJ/ha/yr) in 2005. 9 Production yields based on
conventional process can reach 8000 liters/ha.year (178 GJ/ha/yr) in about 8 years or even
9000 liters/ha.year (about 200 GJ/ha/yr) in case ethanol production from hydrolysis of
sugarcane bagasse reaches a commercial stage.
Sugarcane bagasse is a prime candidate for ethanol production via hydrolysis because of
its low opportunity cost (below 1 Euro/GJ) and the fact that the existing mill infrastructure
can be used. Brazilian companies have an R&D program aiming at developing ethanol
production through acid hydrolysis (ethanol and diluted acid as solvent). 3