Energy generation from thin stillage anaerobic digestion in stand-alone corn ethanol mills

Abstract

The potential applications of by-products from corn ethanol mills are still at an early stage of development in Brazil. Therefore, research on technological perspectives, strategic production and analysis of bioenergy potential are fields to be improved in the next few years. The present study analyses a corn ethanol mill located in the State of Mato Grosso in Brazil and analyzes the thin stillage anaerobic digestion (AD) potential for thermal and electric energy generation from biogas combustion. Thin stillage is a by-product derived from corn ethanol production. The potential energy generation from thin stillage AD was assessed to examine new renewable energy sources to supply the stand-alone corn mill energy requirement. In addition, mass balances are presented based on the partial inlet and outlet flows of each of the main stages of ethanol processing. Simulation results based on the mass flow rate of thin stillage and its chemical oxygen demand show that it can produce a large quantity of biogas containing 65 % methane. The combustion of the biogas produced by thin stillage AD is sufficient to meet 12 % of the thermal requirement of the whole mill. Alternatively, the biogas could be used in a Combined Heat and Power system to generate 53 % of the total stand-alone corn-ethanol facility electricity and about 6 % of the thermal energy requirements. Moreover, for the specificities of Brazilian corn industrial crops and corn-ethanol production, the thin stillage AD would be a win-win alternative technological route for stand-alone corn-ethanol mills toward the circular economy approach.