Ethanol Production from Sugar Cane: Assessing the Possibilities of Improving Energy Efficiency through Exergetic Cost Analysis

The sugar and ethanol production is one of the most important economical activities in Brazil, mainly due its high efficiency and competitiveness. Ethanol production is done by a series of steps: juice extraction, treatment, fermentation, and distillation. The juice extraction and treatment is a common operation of both the sugar and ethanol industries. The process begins with the sugar cane juice extraction, usually done by mills, where the cane is compressed between large cylinders for the separation of the juice from the bagasse. Recently, a juice extraction system, called a diffuser, was introduced in some sugar and ethanol plants. In diffusers, after the sugar cane preparation stage was completed with knives and shredders, the cane passes through a bed where the juice is separated from bagasse by the addition of imbibition water and steam, resulting in a leaching process. The present study evaluates different possibilities of decreasing the thermal energy consumption through exergetic cost analysis. The base case is a traditional ethanol production plant, for which the unitary exergetic cost of ethanol and electrical energy are determined. In the following cases, two proposals were assessed: the use of the diffuser as an extraction system and the use of pinch technology to perform an energetic integration between distillation and extraction (diffuser) systems. The results of exergetic efficiency, irreversibility generation, and unitary exergetic cost of products of the three cases are analyzed and compared. The results show the feasibility of using diffusers and heat recovery to decrease thermal energy consumption in ethanol production plants.