Bioenergy and carbon dioxide sinking in the sugarcane-industry: techno-environmental assessment

Abstract

During the last decades, emissions of carbon dioxide (CO2) have increased exponentially, contributing to global warming. Because of its potential to reduce these emissions, carbon capture and storage (CCS) has become the subject of assiduous study. CCS is a set of technologies that seeks to capture CO2 before it enters the atmosphere, to be transported and stored for a long enough period in an underground geological formation [1].Sugarcane plantations are capable of draining atmospheric CO2 by virtue of a very efficient photosynthetic process. For first-generation bioethanol sugarcane biorefineries, less than 10% of the CO2 coming from sugarcane exits as hydrated ethanol [2], while 90% returns to the atmosphere through cogeneration of energy fueled with bagasse (lignocellulosic residue of sugarcane milling) in steam Rankine cycles. Consequently, a sugarcane biorefinery exports two bioenergy streams —electricity and ethanol—, wasting its enormous biogenic CCS potential.This work evaluates a novel sugarcane biorefinery scheme that drastically increases the percentage of bioenergy carbon capture and storage (BECCS). CO2 emissions from the industry are captured, compressed and transported to geological gas injection fields. Adding to the biorefinery the investment in piping-compression, it is demonstrated that this proposal of plantation-biorefinery-gas injection is technically feasible for the sugarcane sector in the region (Tucumán, Argentina). Furthermore, the environmental sustainability of the bioethanol coupled with BECCS is evaluated environmentally through a Life Cycle Analysis (LCA) and a carbon balance. A cradle-to-gate scope is selected, including the stages of: agriculture, sugar mill and distillery, and CO2 capture and storage. The chosen impact categories are: global warming, scarcity of fossil resources, terrestrial acidification, freshwater eutrophication and stratospheric ozone depletion, to assess any burden shifts. The results are compared with the environmental profile of conventional bioethanol (1 L ethanol as functional unit), providing a distinctive perspective of the sugar-alcohol industry as a carbon sink. In addition, it is shown that the environmental suitably of the implementation of this type of technology strongly depends on the operating conditions of the processes and the category of environmental impact ruling the analysis. The implementation of CCS represents a potential feasible path towards the decarbonization of the mobility and agriculture sector in Argentina through the use of bioethanol as an energy source.