Research progress on the effects of CO2 and H2O gasification reactions on coal pyrolysis and char combustion in oxygen-rich atmosphere
Oxy-combustion technology,as a promising CO2 reduction method for coal-fired power plants,holds significant importance for achieving sustainable energy goals.Due to the physical properties and gasification reactions of CO2 and H2O,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 CO2 and H2O.During the combustion of coal or 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 affected the combustion process,especially under pressurized conditions.Regarding gasification reactions,current studies indicate that single CO2 gasification and CO2/H2O 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,CO2 gasifica-tion can promote carbon consumption at high temperatures and low oxygen concentrations,and the addition of H2O further accelerate this process.With rising environmental pressure,the proportion of carbon consumption attributed to CO2 gasification gradually increase,but there is currently limited research on the effects of CO2/H2O co-gasification under pressurized conditions.The pyrolysis and combustion behaviors of coal under CO2 and H2O gasification in the oxy-fuel atmosphere were summarized which provided some theoretical reference for the future development of oxy-combustion technology.
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