Extraction Process in the Ethanol Production from Sugarcane - A Comparison of Milling and Diffusion

The objective of the extraction process in the ethanol production from sugarcane is to separate the sucrose-containing juice from the remainder of the cane, mainly fibre. The two currents, products of this process, are the juice and the bagasse. The juice is used to produce ethanol and the bagasse is the fuel for the boilers. Two types of devices are employed to perform this operation: mills and diffusers. Each one of them consumes different types of energy: mills consume mechanical energy, diffusers consume basically thermal energy. As both devices utilize an important quantity of energy, their effect in the energy balance of the factory needs to be taken into account. Aiming to discuss and characterize these effects, simulations of the complete ethanol production process, including the cogeneration system, were carried out using the Aspen Plus software, considering both devices. Process integration was also performed targeting to reduce the energy consumption. These results are presented and compared. Considering the integrated ethanol production process, with extraction -condensing steam turbines in cogeneration system, working with mills, it can produce an electricity surplus of 83.4 kWh/t of sugarcane, however, for the same conditions, working with the diffusion extraction process a production of 91.3 kWh/t of cane can be obtained, including also a small increase of 2 % in the ethanol production.