Effect Of Steam On Release Of Arsenic In Coal Combustion With Low Oxygen Concentration

The study of trace element emissions has become a new frontier field in coal combustion pollution.Especially some volatile elements or compounds which are discharged into the atmosphere become an important source of environmental pollution.In this work,the most volatile trace element arsenic in coal is taken as the research object,and the effects of steam on the release characteristics of coal during combustion are systematically studied.Firstly,the effect of steam on coal char combustion at 5% oxygen concentration was studied,by changing the water vapor concentration,reaction temperature and particle size.The results show that with the increase of steam concentration,the peak weight loss rate of coal char increases gradually and the complete combustion time decreases,but it is not linear with steam concentration.At different reaction temperatures,steam can promote the combustion of coal char,and the promotion effect increases gradually with the increase of temperature.The effect of steam on different particle sizes shows the same trend.Then,the effect of steam on the release of arsenic in combustion at 800,1 000 and 1 200℃ with 5% oxygen concentration was investigated.The results show that the presence of steam in the combustion atmosphere can promote the release of arsenic during the coal char combustion.The cause is that the steam reacted with coal char and accelerated the coal combustion.The promotion effect decreases with the increase of steam concentration.The promotion effect of steam on the release of arsenic at 1 000℃ is more obvious than that at 800 and 1 200℃.Under the same temperature and atmosphere,the smaller the particle size is,the greater the final release ratio of arsenic is.The temperature corresponding to the release peak of arsenic will move along the low temperature region with the decrease of particle size.The apparent activation energy and frequency factor of arsenic release with 20% steam are greater than those without steam.Lastly,the volatile combustion and coal char combustion process was divided into two independent parts,effect of steam on the release characteristics of volatile and coal char of arsenic were compared by experiments.Finding that the effect of steam on arsenic release from coal and coal char is synchronous,and steam affect arsenic release from coal by promoting arsenic release from coal char.