Thermogravimetric investigation of hydrochar-lignite co-combustion

► Hydrochars were produced from coconut fibers and eucalyptus leaves. ► Fuel qualities of the hydrochars were improved compared to parent biomass. ► Co-combustion of the hydrochars with lignite was investigated. ► Synergistic interactions between hydrochar and lignite were observed. ► High combustion efficiency was achieved during hydrochar-lignite co-combustion.