Search

Blending coal combustion technology is commonly used in coal-fired power stations, and the combustion interactions (i.e., the ignition promotion and burnout inhibition) during blended coal combustion affect their combustion characteristics. The combustion interactions under conventional air-fuel condition have been well studied. Oxy-fuel firing considerably differs from air-fuel combustion and the combustion interactions of blended coals in O2/CO2 atmospheres have been investigated in our previous research. However, the H2O concentration in actual oxy-fuel condition is relatively high, which may influence the combustion interactions. This study further investigates the effect of H2O on the combustion characteristics and interactions of blended coals in O2/H2O/CO2 atmospheres. The results show that adding H2O into the oxy-fuel atmosphere remarkably affects the combustion characteristics with the more notable ignition delay, faster burnout and better comprehensive combustion characteristics (CCI). In addition, the presence of H2O strengthens the ignition promotion, the burnout inhibition and the comprehensive interactions, resulting in the more obvious non-additive behaviors of CCI. In O2/H2O/CO2 mixtures, enhancing the H2O/CO2 ratio slightly strengthens the ignition promotion, the burnout inhibition, and the comprehensive interactions, which increases the non-additive behaviors of CCI. Furthermore, both of increasing O2/H2O or O2/CO2 ratios significantly weaken the ignition promotion, strengthen the burnout inhibition and the comprehensive interactions, which increases the non-additive behaviors of CCI. The findings shed light on the interaction effects observed during blended coal combustion in O2/H2O/CO2 mixtures, which can provide useful information to improve the combustion characteristics of the blended coals in the real oxy-fuel atmospheres.

Coal blending is an effective method to reduce the slagging tendency. The mineral transformation within blended coal ashes has an important influence on the slagging behaviors, which have been well studied under conventional air-fuel condition. Oxy-fuel combustion is recognized as one of the most promising CO2 reduction technologies. However, the mineral transformation within blended coal ashes in oxy-fuel condition has yet to be fully understood. This work is aimed to comprehensively study the influence of CO2 atmosphere on Ca-containing mineral transformation behaviors during a Ca dominated coal co-firing with a Si/Al dominated coal in O2/CO2 condition by TG-DSC, XRD and HSC simulation. These results show that the atmosphere significantly affects on the transformation of Ca-containing mineral and the final existing form of Ca in the blended coal ashes. When the high content Ca coal is blended with the high content Al/Si coal in the O2/CO2 atmosphere, the CO2 promotes the transformation of Ca into CaCO3 and Ca under low temperature mainly exists in the form of CaCO3 (little CaSO4) in the blended coal ashes. CaCO3 under high temperature is decomposed to produce highly active CaO, and CaO reacts with Al/Si to form the low melting point minerals, which may aggravate the slagging tendency. The present study can provide useful information to reduce the slagging behavior of the blended coals in the O2/CO2 atmosphere.

The combination of oxy-fuel and blended-coal combustion may be one of these effective methods to both reduce CO2 emissions and improve energy utilization efficiency in coal-fired power stations. The aim of this study is to investigate oxy-fuel combustion interactions of blended coals under different conditions using a thermo-gravimetric analyzer. The results show that compared with those in an O2/N2 mixture, the promotive and inhibitive effect and the comprehensive interactions are considerably weaker in an O2/CO2 mixture. In the O2/CO2 mixture, both increasing the O2 concentration and decreasing the particle size result in decreasing the promotive effect but increasing the inhibitive effect and the comprehensive interactions, which increase the non-additive combustion characteristics. Enhancement of the heating rate increases the promotive effect but decreases the inhibitive effect and the comprehensive interactions, which weaken the non-additive combustion characteristics. Of these factors, the effects of the oxygen concentration and heating rate on comprehensive interactions are greater than that of particle size. This study provides useful information for the design and optimization of thermo-chemical conversion systems of coal blends in the O2/CO2 atmosphere.