Biofuel and valuable products recovery from Napier grass pre-processing: Process design and economic analysis

Abstract

Utilisation of lignocellulosic materials as alternative sources of clean energy is characterised with high energy consumption during pre-processing. This study presents a novel approach for processing of high moisture content biomass through a steady state process design and economic analysis. The process flow diagram was developed by considering two process scenarios of Napier grass pre-processing down to the final bio-products with and without solid residue drying. A Napier grass stem processing plant (100 kg/h wet basis) with on-site facilities was modelled using ASPEN PLUS® V10. A model-based estimation approach, Aspen Process Economic Analyser (APEA) was used to generate both capital and operating costs estimates, and other investment analysis following first quarter 2016 pricing basis. The results showed that 14.46 kg/h of juice could be produced from fresh Napier grass stem with potential ethanol yield of 9.27 (w/w). About 82% protein relative to the initial protein content in the sample could be recovered in addition to 49 kg/h bagasse (45 wt% moisture), which are important valuable products. The total capital cost of $2.63 M (million USD) and operating cost/year of $0.24 M is required for the process plant with option of solid residue drying while $1.45 M and $ 0.17 M was recorded for the second scenario. The investment analysis at 25-year economic life of the project showed the corresponding net present value (NPV) of $2.93 M and $5.55 M at 7% and 15% internal rate of return (IRR). Consequently, the process scenarios represent alternative on-site pre-processing of Napier grass biomass with potential additional economic value.