Techno-economic evaluations for feasibility of sago-based biorefinery, Part 2: Integrated bioethanol production and energy systems

To reduce reliance on fossil fuel and environmental issues, alternative energy sources such as biomass are vital to be recovered and converted into value-added products. In sago industry, a huge amount of sago biomass (i.e., sago barks and fibres) is generated and discharged to the environment during sago starch extraction process (SSEP). In order to reduce environmental pollutants, the biomass can be utilised as feedstocks for energy, and bioethanol production. Therefore, Part 1 of these articles in series presents a techno-economic analysis to examine the feasibility of sago biomass-based combined heat and power (CHP) system (Wan et al., 2015a); and Part 2 is to examine the feasibility of integrated bioethanol production and energy systems. In this part, a conceptual integrated sago-based biorefinery (SBB) is envisioned and analysed based on the bioethanol plant study conducted by the National Renewable Energy Laboratory (NREL). Besides, techno-economic performance as well as environmental performance of this integrated SBB is evaluated via Aspen Plus software and a spreadsheet based yield prediction model. For the performance evaluation, various feedstocks such as sago fibres, barks and combined biomass (fibres and barks) are considered. In addition, techno-economic and environmental performance of the integrated SBB with on-site and off-site enzyme production as well as the impacts of labour cost on the economic performance of the integrated SBB is also evaluated. Based on the evaluation and analysis, the integrated SBB with combined biomass (fibres and barks) has the highest technical, economic and environmental performance amongst the sago biomass. A total of 4.75 t/d of bioethanol and 252 kW/d of electricity are expected to be produced; and reduction of 16.32 tCO₂ equivalent/d of carbon dioxide emission is expected. In addition, the payback period of the integrated SBB with on-site enzyme production and using current available labour from SSEP is estimated as 6.6 years. Based on the analysis, it is noted that enzyme and labour costs are critical cost contributors to the new development of the integrated SBB and hence, a sensitivity analysis on such parameters is performed.