The effects of water washing temperature and time on coal properties are investigated according to the occurrence mode of alkali metals in Zhundong coal. The experimental results show that Na mainly exists in water soluble form in three typical types of Zhundong coal. Harmful element Na can be effectively removed by water washing
and the removal amount is closely related to washing temperature and time
and the pyrolysis characteristic index number of washed coals reduces. When the temperature gets below 40 ℃
the pyrolysis process of washed coals can be brought forward with more volatile yielded
and coals washed in 60 ℃water vary oppositely. The combustion TG and DTG curves of water washed coals move towards higher temperature zone
while the burnout temperature and the maximum temperature increase
the maximum combustion rate decreases
the burnout time is prolonged
and the combustion performance is deteriorated. The kinetic analysis indicates that water washing facilitates decreasing the pyrolysis apparent activation energy during the first and third stages and increasing it during the second stage. The presence of Na exerts catalytic effect on coal pyrolysis and combustion behaviors. Moreover
there exists an optimal Na content for the strongest catalytic effect.
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