Multi-objective Optimization of a Solar Assisted 1st and 2nd Generation Sugarcane Ethanol Production Plant

Ethanol production sites utilizing sugarcane as feedstock are usually located in regions with high land availability and decent solar radiation. This offers the opportunity to cover parts of the process energy demand with concentrated solar power (CSP) and thereby increase the fuel production and carbon conversion efficiency. A plant is examined that produces 1st and 2nd generation ethanol by fermentation of sugars (from sugarcane) and enzymatic hydrolysis of the lignocellulosic residues (bagasse), respectively. Enzymatic hydrolysis is a promising alternative for 2nd generation biofuels due to its high conversion efficiency and low environmental impact. In conventional ethanol production processes, electrical and thermal power is delivered to the system by burning parts of the feedstock to drive a steam based cogeneration cycle (between 400 and 800K). Introducing high temperature thermal power (at 800K) from a solar trough field coupled with sensible heat storage, for continuous operation, offers the opportunity to replace the heat generated from biomass burning, and thus increase the product yield. In this work, the potential for process integration of a solar trough field coupled with packed bed thermal storage to a 1st and 2nd generation ethanol production site is evaluated by means of pinch analysis. Decision parameters such as the solar fraction, the percentage of bagasse to 2nd generation, and the solar field size are optimized via multi- objective optimization based on evolutionary algorithms to maximize the carbon conversion efficiency and minimize the total annual cost for a plant located in Ribeirao Preto, Brazil.