O_2/CO_2气氛下CO_2和H_2O气化反应对煤及煤焦燃烧特性的影响

Effect of CO_2 and H_2O gasification on the combustion characteristics of coal and char under O_2/CO_2 atmosphere

利用热天平对比研究了大同煤及煤焦在O_2/N_2、O_2/CO_2和O_2/H_2O/CO_2中的燃烧行为,探讨CO_2和H_2O气化反应对其富氧燃烧特性的影响。结果表明,在5%氧气浓度下,煤粉在O_2/N_2、O_2/CO_2和O_2/H_2O/CO_2中的燃烧速率按顺序依次降低。氧气浓度降低到2%,由于CO_2和H_2O气化反应的作用,煤粉在高温区的整体反应速率按顺序依次增大。当氧气浓度为5%时,煤焦在O_2/CO_2中的燃烧速率要低于O_2/N_2中的燃烧速率,但燃烧反应推迟后气化反应的参与使得煤焦在O_2/H_2O/CO_2中的整体反应速率显著升高。当氧气浓度降低到2%后,随着温度的升高,在CO_2气化反应的作用下,煤焦在O_2/CO_2中的整体反应速率逐渐高于O_2/N_2中的燃烧速率。在O_2/H_2O/CO_2中,由于H_2O在共气化中起主要作用,煤焦在O_2/H_2O/CO_2高温区的整体反应速率进一步升高。动力学分析表明,在5%氧浓度时,煤焦在O_2/N_2、O_2/CO_2和O_2/H_2O/CO_2中的表观活化能依次升高。随着氧气浓度的降低在不同反应气氛中的表观活化能均有所下降。

The burning behaviors of Datong coal and char under O2/N2 , O2/CO2 and O2/H2 O/CO2 atmosphere were comparatively investigated by thermogravimetric analyzer. The influence of CO2 and H2 O gasification on the oxy-fuel combustion characteristics of coal and char were mainly studied. The results indicate that at 5%oxygen concentration the burning rate of pulverized coal in each atmosphere decreases in the order of O2/N2 , O2/CO2 and O2/H2 O/CO2 . When the oxygen concentration reduces to 2%, owing to the CO2 and H2 O gasification, the overall reaction rate of pulverized coal increases in the same order at high temperatures. The burning rate of char is slower in O2/CO2 than that in O2/N2 at 5% oxygen concentration, but as the burning process is delayed, the overall reaction rate of char in O2/H2 O/CO2 rises significantly due to the action of gasification. At 2% oxygen concentration, the overall reaction rate of char in O2/CO2 is higher than the burning rate of char in O2/N2 with the rise in temperature. The overall reaction rate of char in O2/H2 O/CO2 further increases because the H2 O gasification plays a major role in CO2 and H2 O co-gasification. The kinetic analysis shows that at 5% oxygen concentration the apparent activation energy in the atmosphere increases in the order of O2/N2 , O2/CO2 and O2/H2 O/CO2 . However, the apparent activation energy of different atmospheres declines with the decrease of oxygen concentration.