An energy optimization model comparing the use of sugarcane bagasse for power or ethanol production

Abstract

This work addresses the energy balance of producing ethanol from sugarcane bagasse and using lignin from the bagasse as a source of electrical power through Rankine cycle and oxy-combustion. On ethanol 2 G (second generation) proposed plant, lignin is obtained from the concentration and filtration of vinasse which yields a fuel with good calorific value to be used for power generation. The energy balance for 2 G ethanol production including electric power is calculated based on parameters of a typical operational sugarcane plant, coupled with a 2 G plant whose production was assessed by means of global chemical reactions and conversion coefficients obtained from literature. These reactions permit to calculate ethanol production and electricity generation in terms of a virtually infinite number of scenarios characterized by two controlled variables (burning bagasse and straw mass flow rates) and several uncontrolled variables (biomass composition, cellulose, hemicelluloses and lignin yields, fermentation efficiencies, etc.). Results reveal that when the option for carbon capture and storage is used, net power become available when all tops and leaves plus 10 t/h of bagasse are burned. In this condition availability of ethanol is by and large unaffected, yielding a production about 60 m3/h. The application of carbon capture and storage produces a significant impact on power balance that comes from oxy-combustion use (air split unity) and CO2 compression. Another interesting result concerns biomass composition: for both bagasse and straw, higher lignin contents favor simultaneously 2 G ethanol and electricity.