A Closed Drum Carboniser for Converting Ligno-Cellulosic Residues to Biochar Pellets: A Nigerian Study

Abstract

This paper describes an innovative technology that provides an alternative to management of wastes arising from grass cuttings, weeds and agro-forestry residues that are usually discarded unattended. These wastes are now converted into biochar pellets using a newly designed carboniser which is highly economical and can generate employment opportunities to peri-urban and rural low income populations. We used simple spent oil drum with an attached chimney and cassava based starch or clay (e.g. kaolin) as binder to make pellets from the burnt raw materials. This process does not require any moving parts, electricity or any additional fuel to convert the waste into charcoal pellets. We have field tested the carboniser with elephant grass (Pennistum purpureum) as feedstock. Technical performance was evaluated using parameters such as Production Capacity Ratio (PCR), Reliability Ratio (RR) and Efficiency Ratio (ER). Samples of elephant grass, biochar pellets and the ash produced after the biochar used for cooking were analysed for selected chemical characteristics (viz. sulphur, carbon, hydrogen, potassium and calorific value), using standard laboratory procedures. The results obtained gave production capacity and efficiency ratio of 83%; actual production capacity of 25 kg/hour; which is 100% reliable. The differences in the chemical parameters for the three samples were significant. Potassium, carbon and calorific values were observed in increasing order: ash < elephant grass < biochar. Biochar gave lowest values of hydrogen (12.36±0.01%) and sulphur (0.67±0.0%) contents while elephant grass contained highest values of these elements (13.28±.02% and 1.38±0.00%, respectively). This technology will benefit less educated rural and peri-urban populations to develop a small scale or medium scale entrepreneurship with low financial inputs and minimal skills and the product is a good cooking fuel and environment friendly with less or no smoke.