3.1.4. Calorific value
The high heating value (HHV) of densified biomass showed values
between 19.64 MJ/kg for OL and 17.53 MJ/kg for OW (Table 5). Although
the results were similar, there is a certain alteration due to the
heterogeneity of the raw materials. This increase in the HHV can be
caused by the greater concentration of lignin in this type of biomass
[34], since lignin has a low degree of oxidation and a considerably
high combustion heat [35–37].
The heating values of the olive tree samples analyzed fall between
theHHVof common oak and eucalyptus residues,which showed similar
values to those obtained for OW, while grapevine and branches of cork
oak (19.28 MJ/kg) showed approximately the same HHV as OL [38].
Limits are established for the LHV,which has to reach aminimum of
16.0 MJ/kg to be used in non-industrial furnaces [13]. Although all the
rawmaterials fulfill this requirement,OWwould be classified as category
C, while OL and OP are considered to be within category A1 (Table 1)
in regard to this parameter [13].