In addition to the components displayed in Table 5, the sugarcane plant also produces trash; the VSB considers that 140 kg of trash (dry basis) are produced per ton of sugarcane stalks (Seabra et al., 2010). Sugarcane trash composition was fixed as the composition of the bagasse, except for the extractives (which were not included) and water content (assumed as 15%).
3.3 Industrial phase – first generation First generation ethanol production from sugarcane takes place in autonomous distilleries or annexed plants; in the latter a fraction of the sugarcane juice is diverted for sugar production and the remaining fraction along with the molasses (impure solution of sugars that remains after sucrose crystallization) are used for ethanol production. Approximately 70% of the sugarcane processing units in Brazil are annexed plants (BNDES and CGEE, 2008). In the most common scenario annexed plant operates using half of sugarcane juice for sugar production and the other half (plus molasses) is used for bioethanol production. The flexibility of annexed plants to produce more ethanol or more sugar, depending upon the market demands, is part of the reason for the success of bioethanol production in the country. However, the range of operation of an installed plant is somehow limited to the existing design restrictions and available facilities. The sugarcane processing facility is self sufficient on its energy consumption: all the thermal and electric energy required for the production process is produced in combined heat and power (CHP) systems using bagasse as a fuel. If sugarcane trash is recovered from the field, it may also be used as a fuel to produce energy. A scheme of the sugar, ethanol and electricity production process from sugarcane is illustrated in Figure 8. In an autonomous distillery, the unit operations related to the sugar production (left side of Figure 8) are not included in the sugarcane mill.
35