Characterization of rice husk varieties in Uganda for biofuels and their techno-economic feasibility in gasification

• Published in: Chemical engineering research & design 2016-03, Vol.107, p.63-72
• Main Authors: Olupot, P.W., Candia, A., Menya, E., Walozi, R.
• Format: Article
• Language: English
• Subjects: Biochemical; Energy; Gasification; Rice husks; Thermo-chemical
• ISSN: 0263-8762
• DOI: 10.1016/j.cherd.2015.11.010

•Low bulk densities and lignin necessitate use of binders for husk densification.•The C/N ratios are higher than required for either biogas production or composting.•Ash and non concentration of husk generation suit downdraft gasification systems.•Electricity production cost using 250kW rice-husk gasifier system is US$0.22/kWh.•Electricity production cost using 250kW diesel engine system is US$0.36/kWh. This study set out to investigate the properties of husks from ten selected rice varieties in Uganda. Rice samples were collected from one geographical region, identically milled, and the husks ground for analysis. Characterization involved physical, proximate, ultimate, thermal, lignin, hemicellulose and cellulose composition analyses. The samples exhibited bulk density of 88.8–124.3kgm−3, moisture contents 9.2–11.2%wb, volatile matter contents 58.8–66.4%wb, ash contents 15.9–25.6%db, fixed carbon 14.8–17.8%db, carbon contents 30–34.5%db and carbon to nitrogen ratios of 55:1–87:1. The higher heating values (HHV) ranged between 12.8 and 14.5MJ/kg, lignin 10.6–13.5%db, hemicelluloses 11.4–20%db and cellulose 31–37%db. The low bulk densities and lignin contents necessitate that the husks should be densified in the presence of binders. The C/N ratios are higher than required for either biogas production or composting. The HHV, ash content and non-concentration of rice husk generation offer prospects for converting rice husk fuel into energy using downdraft gasification for systems capable of 30–500kW. Results demonstrate that a gasifier generator system of 250kW operating for 8h a day for 350 days in year requires 5.8t of husk per day to produce 700MWh/year. This results in annual electricity production cost saving of US$98,000 when compared to equivalent diesel plant, with payback period of 2.5 years.