Exergy analysis and parametric improvement of the combined production of sugar, ethanol, and electricity

Abstract

Over the last 500 years, the Brazilian sugarcane industry has evolved from a single product supplier (sugar producer) to an energy enterprise (sugar, alcohol and electricity). Different technological paths were developed in order to improve the energy conversion processes inside the mill. These improvements led mills to first become self-sufficient in energy, and then, sell electricity to the grid. The utilities plant developed were typical steam-based cogeneration systems, using bagasse to produce steam and electricity required by the sugar and alcohol production processes. Hence, considering the mill as a whole, it became a polygeneration plant, using sugarcane to produce sugar, alcohol, and electricity. Yet, many by-products are available (trash, vinasse, filter cake, etc.), and most of them are discarded or used in an inefficient way. This chapter compares, in an exergy basis, current technological paths used in sugarcane mills, with new ones, which can lead to a more renewable use of energy and the by-products of the processes. These technologies aim at converting these low valued by-products into new added value ones. Such technologies include: more efficient steam cycles (such as high pressure and supercritical steam ones) and biomass gasification-based combined cycles.