富氧燃烧技术作为一种具有广阔前景的燃煤电站CO2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CO2和H2O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,CO2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CO2和H2O混合气体物性的作用。在煤或焦炭燃烧过程中,CO2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H2O浓度差异的原因,目前对CO2和H2O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,CO2单气化和CO2/H2O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CO2气化在温度较高和氧气浓度较低时可促进燃料碳消耗,H2O的加入则进一步加速了这一过程。随着环境压力的升高,CO2气化反应在燃料碳消耗中占比逐渐增大,但对于加压下CO2/H2O共气化的影响鲜有涉及。本研究总结了富氧气氛中CO2和H2O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 CO2 reduction method for coal-fired power plants, holds significant importance forachieving sustainable energy goals. Due to the physical properties and gasification reactions of CO2 and H2O, the coal conversion processin an oxy-fuel atmosphere may differ significantly from that in an air atmosphere. Through a review of existing literature, it is found thatCO2 impacted the release rate of volatiles and the physical structure and chemical properties of char during coal pyrolysis process. However, few researchers have focused on the role of the physical properties of the mixed gas of CO2 and H2O. During the combustion of coalor char, the high specific heat of CO2 and its low oxygen diffusion rate have a noticeable inhibitory effect on the burning process. However,possibly due to differences in H2O concentration, there is still debate over the mechanism by which the properties of mixed gases affectedthe combustion process, especially under pressurized conditions. Regarding gasification reactions, current studies indicate that singleCO2 gasification and CO2 / H2O co-gasification increase the yield of volatiles during coal pyrolysis, but reduce the yield of char, andthe gasification effect is enhanced at elevated pressure. Furthermore, the reactivity of char increase due to the large surface area from gasification, and its surface functional groups may also change. It is widely accepted that during the combustion of coal or char, CO2 gasification can promote carbon consumption at high temperatures and low oxygen concentrations, and the addition of H2O further accelerate thisprocess. With rising environmental pressure, the proportion of carbon consumption attributed to CO2 gasification gradually increase, butthere is currently limited research on the effects of CO2 / H2O co-gasification under pressurized conditions. The pyrolysis and combustionbehaviors of coal under CO2 and H2O gasification in the oxy-fuel atmosphere were summarized which provided some theoretical referencefor the future development of oxy-combustion technology.

0 引言

1 气体物理性质对煤热解和焦炭燃烧的影响

   1.1 气体物理性质计算及分析

   1.2 气体物性对煤热解的影响

   1.3 气体物性对煤粉和焦炭燃烧的影响

2 CO2和H2O气化对煤热解的影响

   2.1 挥发分析出特性

   2.2 气化对热解焦炭性质的影响

3 CO2和H2O气化对煤粉和焦炭燃烧的影响

   3.1 CO2气化

   3.2 CO2和H2O气化

4 加压条件下气化对煤热解和焦炭燃烧的影响

   4.1 热解特性

   4.2 燃烧特性

5 结语及展望