Thermogravimetric analysis and process simulation of oxy-fuel combustion of blended fuels including oil shale, semicoke, and biomass

Oxy-fuel (OF) combustion is considered as one of the promising carbon capture and storage technologies for reducing CO2 emissions from power plants. In the current work, the thermal behaviour of Estonian oil shale (EOS) and its semicoke (SC), pine saw dust, and their blends were studied comparatively under model air (21%O-2/79%Ar) and OF (30%O-2/70%CO2) conditions using thermogravimetric analysis. Mass spectrometry analysis was applied to monitor the evolved gases. The effect of SC and pine saw dust addition on different combustion stages was analysed using kinetic analysis methods. In addition, different co-firing cases were simulated using the ASPEN PLUS V8.6 (APV86) software tool to evaluate the effects of blending EOS with different biomass fuels of low and high moisture contents. The specific boiler temperatures of each simulated case with the same adjusted thermal fuel input were calculated while applying the operation conditions of air and OF combustion. According to the experiment and process simulation results, the low heating value and high carbonate content of SC brings along endothermic decomposition of carbonates, which negatively affects the heat balance during the conventional co-combustion of EOS with SC. Instead, firing of EOS with SC and biomass in OF process can be an effective solution to reduce the environmental impact in terms of the reduction of CO2 emissions and ash. Furthermore, the sensible heat from SC can positively affect the energy balance of the system as the endothermic effect of decomposition of CaCO3 (for both EOS and SC) can be avoided in OF combustion.