(491a) Modeling and Analysis of Combined Sugar and Ethanol Production Considering Agricultural and Industrial Process Alternatives

We developed an integrated model that describes the inter-connections among the agricultural and industrial processes from sugarcane cultivation to ethanol fermentation. This model clarifies the system-wide implications of process variables on potential contribution of sugarcane-derived ethanol for sustainability.

In the previous studies analyzing the environmental impacts of sugarcane-derived ethanol, its potentials in reduction of greenhouse gas emission have been confirmed. It was also confirmed that the component and conditions of sugarcane have high sensitivities to the result of environmental assessments and process performance. The detailed features of sugarcane are strongly dependent on cultivars, the conditions of climate and soil, and the agricultural operations. It is very difficult to design a practical utilization system because of absence of tools to understand the linkages between the items that influence the component and conditions of sugarcane and the environmental impact reduction, considering the process alternatives in the combined sugar and ethanol production. In this study, we tackle the challenges described above with simulation-based scenario analysis of biomass resource cultivation and utilization.

In the development of agricultural part of the integrated model, the relationship among selected cultivars, farm operation such as fertilization, and the conditions of cultivation area such as climate and soil was modeled based on the results of the existing reports. This model enables the estimation of the yield of sugarcane and its composition. Yield of sugarcane influences the productivity of sugar and ethanol while the composition of sugarcane for the components such as sucrose, glucose, fiber, mineral and water changes the performance of sugar crystallization and ethanol fermentation process. The sugar and ethanol productivities and resources requirement are calculated by the industrial part of the integrated model. For example, sucrose and glucose are the raw material for ethanol fermentation, although glucose is an inhibitor of sugar crystallization. Fiber (bagasse) are not raw materials for sugar and ethanol production, but are used as fuel for these processes. If there can be a surplus in bagasse, it can be used as compost to increase organic soil content in the agricultural field. A case study demonstrates that a scenario in which an appropriate cultivar selection considering the conditions of cultivation area is made and an appropriate process was chosen enables the significantly increase both ethanol and sugar production.

In the integrated model, inter-connections among agricultural and industrial processes were taken into account beyond the mere volume and composition of the raw material. For example, the residues from sugar crystallization and ethanol fermentation contain nitrogen, phosphorous, and potassium (NPK), which are inputted to agricultural area as nutrients. NPK balance with/without reuse of such residues as fertilizers can be analyzed by the developed model. This balance will influence the required input of fertilizers, which may change the potential environmental impacts from a life cycle perspective.

In the long history of sugarcane cultivation for sugar making and ethanol fermentation using sugars, the agricultural and industrial processes have been developing with only very loose interactions. Therefore, the development of technologies took place mainly based on common senses and practices in the respective sectors. In this study, we show that it may be possible to design a better system by intensifying the linkages between the sectors. The results shown by the model can be used to motivate both the farmers and the sugar mills to make a change to increase the profitability and reduce environmental impacts.