Optimisation of the production of pyrolysed corn stover briquettes and its techno‑economic analysis

Abstract

Renewable energy sources such as biomass wastes serve as potential alternatives for traditional fossil fuel sources. This study investigated the conversion of corn stover (CS) waste into an eco-friendly solid fuel (briquettes) with high carbon content and high calorific value (HHV) to meet the increasing energy demand in South Africa through slow pyrolysis and densification processes. Biochar and char briquettes were characterised using ultimate and proximate analyses. Central composite design (CCD) was used to optimise the production of briquettes, in terms of HHV, compaction pressure, durability, and density. The optimised conditions were used to develop a process design and economic evaluation of a briquette production scale-up plant. The results indicated that the HHV (25.5–28.81 MJ/kg) of the briquettes was influenced by binder concentration. Whereas the compressive strength (3.45–6.11 N/mm2) and density (420–788 kg/m3) of the briquettes were both influenced by compaction pressure and binder concentration. All 3 factors influenced the durability (97–100%) of the briquettes. At these optimised conditions (40 MPa, 8.74% and 21.6 °C), HHV, compressive strength, density and durability as predicted by the respective developed models are 27.32 MJ/kg, 5.48 N/mm2, 770.40 m3/kg and 98.87% respectively. Techno-economic analysis of the CS briquetting plant showed that it was able to generate 300 kg/h of dry briquettes. The economic evaluation of this study showed that with a total capital investment (TCI) of $518,791, the plant was economically feasible with a discounted payback period (DPBP) of < 4 years and discounted cash flow rate of return (DCFROR) of > 30%.