Through process simulation, the yield of an ethanol production facility from cas­sava can be assessed. This acquires greater importance considering the lack of information published about this type of process. In a previous work (Cardona et al., 2005a), the performance of two processes for bioethanol production employing two different starchy feedstocks using a commercial simulation package (Aspen Plus) and especially developed models were compared. For this, a SSF was con­templated in both processes. For corn, dry-milling technology and an organiza­tion of streams, such as that shown in Figure 11.7, was considered. This flowsheet allows the production of a valuable co-product, the DDGS. In the case of cas­sava, the utilization of fresh roots was considered. This implies the generation of a fibrous residue.

The comparison results are summarized in Table 11.10. Presented data show that the higher yields correspond to the corn due to its higher starch content mea­sured in wet basis. These data are close to ethanol yields from corn and cassava reported by the FAO (for instance, these data were published by Observatorio Agrocadenas Colombia, 2006). The production and protein content of the material to be used as a protein supplement in animal feed in the corn case (DDGS) are higher than in the case of cassava (fibrous residue) due to its low protein content. On the other hand, the high moisture content of the cassava implies that the con­densates of the stillage evaporation step cannot be recycled to the cooking step. In fact, this explains the need for employing a higher amount of feedstock to achieve the same starting starch mass as in the case of corn. However, for some countries, cassava represents a better option considering the high agronomic yields com­pared to corn. For instance, the cassava yield in Colombia reaches 20 ton/ha while average corn yield only reaches 6 ton/ha (Observatorio Agrocadenas Colombia, 2006). This situation would represent ethanol yields per hectare of 3,336 L EtOH/ ha cassava and 2,105 L EtOH/ha corn. These estimations clearly favor the utiliza­tion of the tuber especially if the agroecological conditions of this country are taken into account.

Note: The mass flowrate of starch in each process is 30,675 kg/h. a Solids equivalent to DDGS.