1.2 Definition of the System Under Study

The comparative analysis presented in this chapter is based on a reference case defined as follows: bioethanol is produced from wheat in a facility with a capacity of 40,000 t/yr (i. e.,

134,0 t/yr of wheat). The corresponding agricultural area is of the order of 20,900 ha located in the region surrounding the ethanol plant. Beside fuel ethanol, the plant also produces about 48,600 t/yr of DDGS. Fuel ethanol is distributed over an average distance of 250 km (100 km by lorry and 150 km by train). The cultivation of wheat is carried out under the usual practice in Switzerland, with an average yield of 6.425 t/ha of grains (fresh matter at 15% wt. moisture) and 3.915 t/ha of straw (fresh matter at 15% wt. mois­ture). The grains are sent to the plant over a distance of 50 km (10 km by tractor and 40 km by lorry).

A simplified flow diagram of bioethanol production is presented in Figure 4. The stages common to both bioethanol and DDGS are shown in block A and include grinding,

liquefaction, saccharification, fermentation, and distillation. Block B represents the stillage treatment, specific to DDGS. Block C is the dehydration stage, specific to bioethanol. When applicable, the allocation of impacts between bioethanol and DDGS is performed at the point of separation, after the distillation stage in this case (i. e., between hydrated ethanol and stillage). Allocation therefore applies to block A only (incl. production and delivery of wheat). The impacts associated to blocks B and C are fully allocated to DDGS and bioethanol, respectively.

Regarding the utilization phase, various blends are considered in this chapter. Each of these fuel blends has a specific performance (expressed in terms of fuel consumption per 100 km). The vehicle considered is a standard EURO 3 light-duty vehicle.