Effects of critical extrusion factors on quality of high-density briquettes produced from sawdust admixture

Abstract

Successful briquette production is largely dependent on several process-dominant variables that influences the physical, mechanical and combustion characteristics of the final product. Critical among these variables are: machine factors, feedstock material factors and machine operating conditions. The effects of these three dominant factors and its derivatives on the quality of briquettes produced from sawdust admixture using a single-screw extruder was investigated in this work. Three units of extruder heads were utilized to produce briquettes from sawdust admixtures at three particle moistures of 12%,10%, and 8% respectively. The results showed that rough barrel and die surfaces, die lengths below 90 mm, shaft taper angles in excess of 5° and barrel-screw clearance in excess of 5 mm adversely affect extruder performance. Particle moisture and sizes are dominant material factors in producing good quality briquettes. Briquettes produced at particle moistures lower than 10%, have good qualities, however, above 12% particle moisture, briquettes produced are weak and brittle. Particle sizes influences the density of briquettes. Oversized particle sizes produced less dense briquettes while fine particle sizes produced higher density briquettes. Short material dwell time (<2–3 min) within the compression/transition zone produced weak and unstable briquettes, longer dwell time (3–5 min) produces strong, well-formed carbonated briquettes. Operating temperatures<200 °C are not suitable for good quality briquetting, temperature range between 200 °C and 290 °C is considered transition temperature for briquetting depending on other favourable production factors. Temperatures in the range 290 °C to 310 °C are suitable for good quality briquetting. Temperatures above 310 °C often adversely affect the quality and economic viability of briquette production. Beyond this range, heating cost increases without significant improvement in briquette quality. Barrel and die surface finishing, shaft-screw-barrel clearance and machining precisions significantly contributed to extrusion performance and products quality.