Análise da viabilidade técnica e econômica da queima do biogás em uma usina sucroenergética

Abstract

The commitment to curb global warming was set out in the Paris Agreement in 2015. Brazil and the Brazilian sugarcane industry once again have the great opportunity to be the protagonists due to the potential of ethanol production, considered one of the best biofuels in the world. Despite recent problems, this industry continues to improve and develop new technologies, such as the use of straw, second-generation ethanol and anaerobic digestion of vinasse. This last one is not yet widespread, but the current development of anaerobic digestion technology has made this process much more accessible This study consists of a technical and economical evaluation of the application of the most current technologies for anaerobic digestion of vinasse in a sugarcane mill, differing from other similar studies by the use of the existing power generation plant, reducing the initial investment of the project. First, the biogas production potential was calculated using the 2017 production data of a mill that crushes around 4 million tons of sugarcane a year and produces an average of 900 m³ of ethanol per day. The production of vinasse in the period was 320 m³ / h, with organic load of 40,000 mg COD/l, high, due to the use of molasses in the ethanol production process. Internal Circulation (IC) digesters with removal efficiency of 67% were used, resulting in an average volume of 3,688 Nm³/h of biogas, composed of 62% of CH4 and with a Low Heat Value (LHV) of 23,115 kJ/Nm³. The biogas burned in burners installed in an existing watertube boiler, would produce an extra electric power of 6,459 kWh by an existing steam turbine. The project proved to be economically feasible, with a NPV of R$ 16.67 million, IRR of 12,5% and payback of 10 years and 1 months, considering the energy price at R$ 234.92, a minimum rate of return of 7% and the project life cycle of 20 years. The sensitivity analysis assessing the NPV of the project using the free market price fluctuations showed that there are large risks for the investor in this option. Compared to a similar project, burning the biogas in a internal combustion engine, the studied project proved to be more feasible due to the initial investment around 30% lower.