Production of solid biofuel granules from drum granulation of bio-waste with silicate-based binders

Herein compost was selected as a model bio-waste substrate to make solid biofuel granules using wet drum granulation and a sodium silicate binder. Using a laboratory-scale drum granulator (300 g/batch), spherical compost granules within the targeted size range (3.35 - 14 mm) could be produced with a good compressive strength in good to excellent yields. The effects of compost moisture content, process parameters (drum speed, granulation time) and binder parameters (binder concentration, binder to compost ratio) on the properties of the resulting granules (size distribution, bulk density, compressive strength, water resistance, gross calorific value, ash content) were investigated. The optimal conditions for producing granules as a solid biofuel with competitive properties when compared with woody biomass fuels were achieved by applying a drum rotational speed of 32 - 37 rpm, granulation time of 15 min, sodium silicate solution 1 - 3 wt% and binder to solid ratio 0.77 - 0.90.