Pressurized oxy-fuel combustion of pulverized coal blended with wheat straw: Thermochemical characterization and synergetic effect

Pressurized oxy-fuel combustion is recognized as the second generation of oxy-fuel combustion technology that can facilitate carbon capture and reduce energy consumption, while coal and biomass combustion is also an effective way to decrease carbon emissions. This study innovatively integrates these two clean combustion technologies and investigates the effects of pressure and blending ratio on the combustion characteristics (ignition, combustion rate, volatile combustion, semi-coke combustion, burnout) of coal, biomass and their blends using an advanced magnetic levitation HPTGA. The results show that pressurization can improve the combustion rate of coal and biomass, but it will cause ignition delay when system pressure exceeds 0.5 MPa. The effect of pressure on combustion characteristics is both facilitative and inhibitive, in terms of reaction kinetics, pressurization can significantly promote combustion but it also plays a role in inhibiting oxygen diffusion, the competition between the two effect leads to an optimum value of pressure in the combustion performance of the blends, which is about 1 MPa. Biomass is more sensitive to pressure than coal, and pressurization changes the ignition mode of biomass. In addition, a new synergy index is defined to quantify the synergistic effect of the whole co-combustion process. Pressurization could suppress both catalytic and non-catalytic mechanisms in the co-combustion process, and different sensitivities of biomass and coal to pressurization lead to more significant differences in combustion time and temperature interval compared with normal pressure, all these factors contribute to negative synergistic effect under pressurization.