Thermo-Economic Optimisation of Integrated Ethanol and Methanol Production in the Sugarcane Industry

The present paper evaluated a sugarcane biorefinery producing ethanol, through the conventional process by sugars fermentation and methanol through bagasse and leaves gasification, hot cleaning and synthesis. The sugarcane biorefinery was modelled using flowsheet modelling software and thermal integration. A thermo-economic model was developed in order to analyze the energy efficiency of the system as well as the total investment. Different configurations are analyzed for the methanol production process. Multi-objective optimization using a genetic algorithm solver is performed, allowing the analysis of several process configurations in terms of conflictive objectives energy efficiency and investment cost. The sugarcane biorefinery is self-sufficient in energy demand after thermal integration with a system energy efficiency increasing when the methanol production is higher, although it also leads to an increase in the total investment. Both Entrained Flow and Circulated Fluidized Bed gasification technologies are modelled and compared for sugarcane residues conversion, showing similar impacts in the system efficiency that can reach more than 55 % (dry biomass input low heating value basis), which is almost two fold higher than the one obtained in the traditional sugarcane ethanol plants currently in use.