CO_(2)和H_(2)O气化反应对富氧气氛煤热解和焦炭燃烧影响进展

Research progress on the effects of CO_(2) and H_(2)O gasification reactions on coal pyrolysis and char combustion in oxygen-rich atmosphere

富氧燃烧技术作为一种具有广阔前景的燃煤电站CO_(2)减排技术,对实现可持续发展的能源目标具有重要意义。由于CO_(2)和H_(2)O物理性质和气化反应的影响,煤在富氧气氛中的转化过程可能明显异于空气气氛。通过分析已有文献发现,CO_(2)对煤热解过程中挥发分的析出率和焦炭的物理结构和化学性质有一定影响,但较少学者关注CO_(2)和H_(2)O混合气体物性的作用。在煤或焦炭燃烧过程中,CO_(2)的高比热和低氧扩散速率对燃烧反应有明显抑制作用,但可能是由于H_(2)O浓度差异的原因,目前对CO_(2)和H_(2)O混合气体物性在燃烧过程中的影响机制还有争议,尤其是缺少加压下的数据。对于气化反应的影响,目前研究表明,CO_(2)单气化和CO_(2)/H_(2)O共气化提高了煤热解时挥发分轻质气体的产率,但焦炭产率却有所降低,而压力增加强化了这一影响。此外,气化作用下的煤焦可能由于表面积增加而提高了反应活性,其表面官能团结构也因气化而发生改变。关于煤或焦炭燃烧反应,目前普遍认为CO_(2)气化在温度较高和氧气浓度较低时可促进燃料碳消耗,H_(2)O的加入则进一步加速了这一过程。随着环境压力的升高,CO_(2)气化反应在燃料碳消耗中占比逐渐增大,但对于加压下CO_(2)/H_(2)O共气化的影响鲜有涉及。本研究总结了富氧气氛中CO_(2)和H_(2)O气化作用下的煤热解和焦炭燃烧行为,为今后富氧燃烧技术的发展提供了理论参考。

Oxy-combustion technology,as a promising CO_(2)reduction method for coal-fired power plants,holds significant importance for achieving sustainable energy goals.Due to the physical properties and gasification reactions of CO_(2)and H_(2)O,the coal conversion process in an oxy-fuel atmosphere may differ significantly from that in an air atmosphere.Through a review of existing literature,it is found that CO2 impacted the release rate of volatiles and the physical structure and chemical properties of char during coal pyrolysis process.Howev-er,few researchers have focused on the role of the physical properties of the mixed gas of CO_(2)and H_(2)O.During the combustion of coal or char,the high specific heat of CO_(2)and its low oxygen diffusion rate have a noticeable inhibitory effect on the burning process.However,possibly due to differences in H_(2)O concentration,there is still debate over the mechanism by which the properties of mixed gases affected the combustion process,especially under pressurized conditions.Regarding gasification reactions,current studies indicate that single CO_(2)gasification and CO_(2)/H_(2)O co-gasification increase the yield of volatiles during coal pyrolysis,but reduce the yield of char,and the gasification effect is enhanced at elevated pressure.Furthermore,the reactivity of char increase due to the large surface area from gasi-fication,and its surface functional groups may also change.It is widely accepted that during the combustion of coal or char,CO_(2)gasifica-tion can promote carbon consumption at high temperatures and low oxygen concentrations,and the addition of H_(2)O further accelerate this process.With rising environmental pressure,the proportion of carbon consumption attributed to CO_(2)gasification gradually increase,but there is currently limited research on the effects of CO_(2)/H_(2)O co-gasification under pressurized conditions.The pyrolysis and combustion behaviors of coal under CO_(2)and H_(2)O gasification in the oxy-fuel atmosphere were summarized which provided some theoretical reference for the future development of oxy-combustion technology.