A study on densification and CO2 gasification of biocarbon

Biocarbon is a promising alternative to fossil reductants for reducing greenhouse gas emissions and increasing sustainability of the metallurgical industry. In comparison to conventional reductants (i.e., petroleum coke and coal), biocarbon has low density, poor mechanical strength and high reactivity. Densification is an efficient way to upgrade biocarbon and improve its undesirable properties. In this study, woody biocarbon was compressed into briquettes using two different binders, starch and lignin. The biocarbon densification process, basic fuel properties, mechanical strength and moisture uptake of the biocarbon briquettes were studied. Effects of type and amount of binder on properties of the briquettes were evaluated. The CO2 gasification behaviours of the biocarbon briquettes were investigated by performing thermogravimetric analyses. The results showed that high mechanical compressing force was required for producing biocarbon briquettes with addition of binder. The biocarbon briquettes produced with addition of starch achieved higher mechanical strength compared to those with addition of lignin. In addition, the mechanical strength of the biocarbon briquettes increased with increasing starch content. For all biocarbon briquettes produced with and without binder addition, there was no moisture uptake after stored for 4 weeks at 35 °C and 98% relative humidity. The saturated moisture content of all briquettes densified with addition of binder were higher than those produced with only biocarbon. Compared to biocarbon powder, conversion of the biocarbon briquettes with and without binder addition took significantly longer time according to thermogravimetric CO2 gasification tests. The results of the present work indicate that densification of biocarbon is a promising measure to improve biocarbon properties for further handling, logistics and storage and also for final utilization as reductant in metallurgical industries.