The Effect of Atmosphere on Elemental Mercury Release During Thermal Treatment of Two Bituminous Coals

Abstract

The dynamic release behavior of elemental Hg (Hg 0 ) during thermal treatment of two bituminous coals was studied under N 2 , CO 2 and air atmospheres. The results show that the profiles of Hg 0 released present several peaks during thermal treatment of two bituminous coals. The Hg peak profiles for the same coal are different with the different atmosphere used. The amount of Hg 0 released from the coals is about 92-94, 73-74 and 31-33% under N 2 , CO 2 and air atmosphere, respectively. This indicates that the Hg 0 is the dominant form during thermal treatment of the coals under N 2 atmosphere whereas part of Hg 0 is converted into the oxidized Hg during thermal treatment of the coals under CO 2 and air atmosphere. The total Hg released is promoted by the volatile matter release to some extent while the Hg 0 released is mainly affected by the atmospheres used.

Mercury Release during Thermal Treatment of Two Coal Gangues and Two Coal Slimes under N2 and in Air

“…It is reported that most of the Hg released from coal or coal gangue is in the form of Hg 0 under N 2 , which is very consistent with the result of this study. , Meanwhile, it can be observed that the Hg 2+ RR in air is higher than that in a N 2 atmosphere, especially for the 1# coal gangues. Actually, the air is different from the N 2 atmosphere, because of the existence of oxygen.…”

“…It can be explained that some organic matters in coal gangue are burned under the presence of oxygen, leading to a higher VY under air. However, the HgRR under air atmosphere is lower than that under N 2 . As stated above, it is possibly due to the oxidation of Hg 0 by oxygen in air. , …”

“…Similar to coal gangue or coal, some differences between the VY and HgRR between a N 2 atmosphere and air also can be found. , For example, the VY of two coal slimes under air is higher than that under N 2 , which is likely to be caused by the burned organic matter in coal slimes under air. Meanwhile, the HgRR in air is lower than that under N 2 atmosphere, because of the oxidation effect of oxygen in air. , …”

“…The mercury content in the coal gangues and coal slimes are listed in Table , which shows that the mercury contents of the four samples vary from 289.75 ng/g to 6331.25 ng/g, which are generally higher than the mercury contents of coals. ,− For example, the mercury content in six coals was reported to range from 94 ng/g to 432 ng/g . Among them, 1# coal gangue has the highest mercury content while 2# coal slime has the lowest mercury content.…”

“…In order to provide information for the development of more efficient control technology, it is of great importance to study the mercury release behavior from power plants . Thus, some investigations about the mercury emission from coal-fired power plants have been conducted. , Studies about mercury release during the thermal treatment of coal have also been reported. , Consequently, considerable information focusing on the mercury release from coal has been obtained. − It is generally accepted that the mercury can be transformed to three species with different characters during coal combustion, including particle-bound mercury (Hg p ), elemental mercury (Hg 0 ), and oxidized mercury (Hg 2+ ). Hg p can be easily removed by particulate control devices. , The compounds of Hg 2+ are water-soluble and most of them can be removed by wet flue gas desulfurization units (FGD). ,,− Compared with Hg 2+ , Hg 0 can remain in the atmosphere longer and migrate long distances from the source of emission as a global pollutant. , Therefore, it is harder to be controlled than the other two species.…”