Title : Approach to carbon neutral electricity and heat in a bioethanol biorefinery
Abstract:
The environmental benefits of biogas technology are often highlighted as a valid and sustainable alternative to fossil fuels. Together with the reduction of greenhouse gas (GHG) emissions, biogas can improve energy security, thanks to its high energy potential. As a renewable energy source. Three biogas plants (BG1, CGY y BG2) integrated into a cornstarch bioethanol biorefinery located in the province of Córdoba, Argentina, which receive manure from a feedlot and other agro-industrial residues from the dairy industry and recovered cooking oil were studied. For the calculation of energy emissions, the methodology present in Annex VI of the European Directive RED II “rules for the calculation of greenhouse gas emissions from fuels from biomass and its reference fossil fuels”was used as a guide and provides the opportunity to be certified in the future. A proprietary methodology was used to calculate the digestate emissions. A credit of 45 gCO2/Mw was granted to plants that receive manure from the feedlot in accordance with the provisions of European regulations. Fugitive emissions were estimated according to the ISCC at 1%. The total annual production of the complex reached 24,137,469 m3 of biogas, 57,202 MWh of electricity injected into the national grid and 26,316 MWh as thermal energy used in the biorefinery. A total of 320,000 m3 of digestate were produced and used in fertigation in surrounding fields and partly reinjected into the biorefinery. The input that presents the highest emission in the three units considered is ferric chloride by a wide margin, representing 74% of the emissions in the industrial stage.The incorporation of vinasse from BIO4 represents a great reduction in emissions, taking into account that it is a "waste" and therefore has no associated carbon footprint and that it is the main input of the biodigestion process in the three plants, representing between 80% and 90% of the total raw materials that enter the biodigesters. An average emission of 8,29 gCO2eq/kWhelectric and 0,82 gCO2/MJthermal were obtained, with an average reduction of 99 % compared to the Argentine electric interconnected grid (338,52 gCO2eq/kWh). Comparing thermal energy production, the reduction was more than 98,9 %, very close to carbon neutrality. Emissions associated with digestate, which consider transport, application and fertilization, reached 1.57 kgCO2eq/m3. The impact over the bioethanol plant considering the bioethanol carbon footprint as en indicator was very important, reducing it in 23 %. The future inclusion of undergoing studies on fossil fertilizer reduction, yield increase and possible carbon capture on the fertiirrigated fields may result in carbon negative emissions for the complex.
