CONICET | Buscador de Institutos y Recursos Humanos

A model is presented for the optimization of the synthesis, design and operation of an Ethanol plant involving batch/semicontinuos operations and recycle streams. In this model, the process variables are optimised simultaneously with the plant structure. The model includes a biomass fermentation - ethanol fermentation superstructure witch permits optimising the number of fermentors and their operation in series or in parallel. The batch items are modeled by discretizing the corresponding Ordinary Differential Equations. The process operates under a zero-wait (ZW) transfer policy. The Ethanol plant produces a non distilled waste called vinasses, which can eventually be recycled to the fermentation stage contributing to the total substrate, to water reuse and to reduce the environmental impact of the process. The substrate concentration of the vinasses was found to be a key variable for the design. The optimization problem is formulated as a Non Linear Program (NLP). Optimal design and operation for different studied cases are shown and a sensitivity analysis is reported. The number, size and operation mode of biomass fermentors and ethanol fermentors, the sugar substrates blending to each biomass and ethanol fermentor, the recycle of vinasses, the number of trays and the reflux ratio of the distillation are optimised in order to minimize the total annual cost of the process. The paper reports optimal plant structures and process variables figures different from industrial practice that may be worth to be explored.