This work describes a methodology which combines conceptual design and process simulation to determine the main variables and steps involved in an anhydrous ethanol production unit. Ethanol is produced from biomass by sugar fermentation process. First, the sugar cane juice is pretreated with acid and enzyme to produce sugar. The sugar is then fermented into ethanol. The ethanol produced still contains a significant amount of water, which is removed by using a fractional distillation process composed by several columns that finally allow obtaining azeotropic ethanol. Then, ethanol dehydration step is simulated using two different technologies: extractive distillation and molecular sieves adsorption; in order to compare them and conclude about its energy consumptions and costs.
The simulation program Aspen Plus 2006 was used to construct the process model and simulations were performed to investigate different conditions for the plant. The input data for the ethanol production were based on information provided by a typical ethanol distillation plant located in Colombia that produces 300.000 liters per day of anhydrous ethanol. In particular, fermentation process was simulated using an adjusted kinetic expression reported in the literature. The conceptual design of extractive distillation column was based on the residue curve map and it allowed determination of feasible separation scheme and maximization of the concentration of ethanol in the stream top of the distillation column. Simulation of the process has allowed determining the operating variables and design parameters for the fermentors and the distillation columns. Finally, a summary with the most important quantities of steam, water and power are presented for each step of the process, concluding that fermentation has high water consumption, distillation has high steam consumption and the ethanol dehydration using molecular sieves utilizes large quantities of power to operate at higher and lower pressures.
Regarding the process models, there are improvements to be made. The solubility of carbon dioxide in the wine streams obtained from the fermentation step should be adjusted in order to calculate more exactly the carbon dioxide stripper. The stillage recovery through multieffect evaporation system should be included to perform energetic integration studies. But the process models constructed are good enough to be used for simulations of overall plants with other conditions.