Process simulation of renewable electricity from sugarcane straw: Techno-economic assessment of retrofit scenarios in Brazil

Abstract Approximately 7% of Brazilian electricity is generated from sugarcane biomass. Although this scenario is relatively optimistic when compared to the fossil-based energy matrix of other nations, there is a clear opportunity of expanding bioelectricity production in the country even more. Recent changes in the environmental legislation are progressively prohibiting burning before sugarcane harvesting in Brazilian Center-South region. Consequently, straw (i.e., sugarcane tops, dry and green leaves) has become available in most of the sugarcane fields. When considering the low availability of capital to invest in large-scale greenfield projects currently in Brazil, this paper focuses on retrofit investments, i.e., those related to existing sugarcane mills aiming to increase electricity production with incremental investments. This study is based on the Virtual Sugarcane Biorefinery framework that is developed in the Brazilian Biorenewables National Laboratory (LNBR/CNPEM). This simulation framework integrates both agricultural and industrial models to anticipate the impacts of biorefineries on different sustainability aspects. In this paper, process-based models are used to represent incremental changes caused by sugarcane straw recovery adopting the integral harvesting system. The techno-economic analysis shows that the internal rates of return (IRRs) of different alternatives depend on the conditions assumed in the sensitivity analysis. The main parameters assessed in the sensitivity are related to industrial plant scale, straw transport distance, industrial operating period, dry-cleaning system (DCS) efficiency and electricity prices. In the best incremental scenarios (operation during the offseason), IRRs ranged from 35 to 69%, 44–83%, and 54–99% per year when recovering straw in mills with original crushing capacities of 2, 4 and 8 million tons of sugarcane per year, respectively. This analysis ratifies that the economic feasibility increases as much as industrial scale increases; also, the system benefits from shorter straw transport distances. In general, higher DCS efficiencies can improve the economic viability, although some non-linear effects can be observed under specific conditions of the industrial operation. From all variables tested in the simulation, electricity price is one of the most sensitive parameters affecting the economic viability of straw recovery projects.