Modeling and techno-economic analysis of a hybrid sugarcane plant fed by vinasse biogas and bagasse surplus for electricity generation

Abstract

The growing demand for electricity from renewable energy sources has motivated sugarcane producers to improve the power generation capacity of their plants. In this regard, the present work aims to contribute to the energy recovery process from two sugarcane byproducts: bagasse and vinasse. A novel hybrid combined cycle is devised to use the bagasse surplus generated during the sugarcane season to produce high enthalpy steam for a dedicated condensing turbine. A gas turbine, fed by vinasse biogas vinasse, is used to provide thermal energy to the steam bottoming cycle. Concomitantly, steam for the sugar and ethanol is produced by the existing sugarcane cogeneration system. This approach allows to increase the plant's electricity generation. From a prescribed milling capacity, a conventional sugarcane plant is modeled and validated at steady-state regime. Then, a hybrid plant, designed to consume the bagasse surplus and the vinasse biogas, is presented, and compared to the conventional plant. During the off-season, in the absence of vinasse and biogas, an off-design option is proposed to keep the system running full-time. Results showed that the hybrid plant electricity generation (kWhel) is 7.2–41.5% higher than the conventional plant. The economic feasibility of retrofitting a typical sugarcane plant (live steam parameters at 68 bar/480 °C, for example), by means of a hybrid combined cycle, points to an internal rate of return of around 22.3% and payback period of 5 years. A parametric analysis was carried out showing that, for a process steam consumption below 540kg of steam per tons of sugarcane milled, there will always be leftover bagasse of the season, regardless of the conventional plant steam profile. The production of vinasse required for the hybrid system ranges from 310 to 375 L by tons of sugarcane milled (TC), values within the range of existing sugarcane plants (156–910 L/TC). In addition, the plant operating time can be extended in the off-season, from 200 to 330 days per year, with electrical efficiency achieving around of 27% in this period. In conclusion, the proposed system moves towards the advancement of clean and sustainable electricity generation in the sugarcane industry.