Techno-economic analysis of reactor types and biogas utilization schemes in thermophilic anaerobic digestion of sugarcane vinasse

This study conducted a techno-economic analysis to compare two types of thermophilic anaerobic reactors and three biogas utilization schemes in biogas production from vinasse. The reactors studied were the Fixed Bed Reactor (FBR) and Continuous Stirred Tank Reactor (CSTR). The biogas utilization schemes investigated were biogas conversion to electricity compared to direct biogas use for co-firing in the existing boiler and combined uses for co-firing and domestic fuel sale to the nearby households around the plant. The techno-economic calculations were based on experimental data using the prototypes of FBR and CSTR. The fixed and working capital estimations were based on Indonesia's construction industry database. At the same Organic Loading Rate (OLR) of 9.66 g sCOD per litre, 7-day Hydraulic Retention Time (HRT), and 200 m3/day vinasse capacity, FBR produced twice more biogas than CSTR. The economic analysis result indicated that the scheme of co-firing in existing boilers by fuel-oil replacement and partial substitution of coal was economically more attractive than the electricity production at the current electricity pricing in Indonesia. In this recommended scheme, we obtained 17.26% internal rate of return, 4.34 years payback period, and Rp20.94 billion net present value.