Many people think that with biomass like sawdust when compacted it will increase the heat or the heating value, but that is not entirely correct. Densification into pellets or briquettes does raise to solid or density so that the weight or mass is high while the volume is small, for example sawdust when not compacted its density is only about 200 kg / m3 and after solidified (densificated/compacted) into pellet to 650-700 kg / m3 and can be more than 1,000 kg / m3 when briquetted. This makes the biomass efficient for long-distance transport, easier handling, burning and so on.
Indeed before compacted into pellets or briquettes, the solid biomass must have a 5-10% dryness rate that can be compacted. When the biomass is wet or has a high water (moisture) content, then drying it will increase the calorific value. While the biomass initially very dry say with a moisture content of less than 5% then to reach the desired level of dryness (5-10%) then the need for additional water or wetted of course this does not increase the calorific value but instead reduce the calorific value. So the increase in calorific value of biomass can be done by reducing its water content or drying it even down to minimize its volatile matter and increase its carbon content (fix carbon). The pyrolysis process of both torrefaction (mild pyrolysis) and carbonization (slow pyrolysis) is the process of increasing the heating value of the solid biomass.
|Example of pellet fuel types. A photo taken from here|
Well after the increased calorific value through drying up to pyrolysis then followed by the compaction process will be the better quality of fuel is in terms of heating value and volume. For example, when wood charcoal has an 85% fixed carbon with a calorific value of 7500 kcal/kg with a density of 400 kg/m3 and then made into pellet with a density of 650 kg / m3 then in volume 1 m3 has a higher heat content of 3,000,000 kcal in wood charcoal and 4.875.000 kcal on pellet or because its density is higher.