Thermal behavior and kinetic analysis of co-combustion of waste biomass/low rank coal blends

• Co-combustion properties of two kinds of biomass samples and coal were studied.
• Chemical components and physical structures of biomass and coal blends were tested.
• Synergistic effect for combustion of biomass and coal blends was observed.
• Double parallel reactions nth order rate model was built for co-combustion process.

The thermal decomposition behavior of Shenhua bituminous coal (SB), Rice husk (RH), Pine sawdust (PS) and their blend during combustion were investigated by using the thermal analysis method. The apparent kinetic parameters of combustion process were estimated by fitting the experimental data to the double parallel reactions nth order rate model. The results showed that the combustion characteristics of the two kinds of biomass residues with low degree of order are higher than that of bituminous coal. For blend of bituminous coal with biomass residues, the ignition performance could be improved by increasing content of biomass residues, but the comprehensive combustion characteristics first decreases and then increases, with its lowest value occurring at addition content of 60%. Meanwhile, through comparison between theoretically calculated and experimentally measured data, it is concluded that there’s a synergistic effect during combustion process of biomass and coal blend. Through kinetic analysis, it is found that the combustion processes of coal, biomass and their blends could be well represented by the double parallel reactions nth order rate model, and for the two stages in combustion, with an increase of biomass content both activation energies first decrease and then increase. Both stage activation energies of the RH blend have lowest value when RH ratio of 60% (first stage 140.2 kJ/mol, second stage 136.9 kJ/mol), but for the SP blend the first stage lowest activation energies was PS ratio of 20% with a value of 143.1 kJ/mol and the second stage’s was a PS ratio 40% with a value of 143.9 kJ/mol.