Effect of steam on the release of arsenic in coal char combustion with low oxygen concentration

The study of trace element emissions has become a new frontier field in coal combustion pollution. Especial- ly some volatile elements or compounds which are discharged into the atmosphere become an important source of envi- ronmental pollution. The most volatile trace element arsenic has attracted wide attention. Qingshuigou char was selected for investigating the effect of steam on the release of arsenic in combustion at 800,1 000 and 1 200 ℃ with 5% oxygen concentration in a customized isothermal combustion system. By changing the residence time,and further exploring the influence of steam on the arsenic release characteristics at different tem-peratures and particle sizes,the variation curve of arsenic release ratio with time during coal char combustion was obtained. The results show that the effect of steam on arsenic release from coal and coal char is synchronous,and the gasification reaction between steam and coke promotes arsenic release from coal char and then affects arsenic release from coal char. 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 com-bustion. The promotion effect decreases with the increase of steam concen- tration. 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 ra- tio of arsenic is. The temperature corre-sponding to the release peak of arsenic will move along the low temperature re- gion 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.