煤阶是影响煤层饱和状态的参数。煤阶代表了煤化作用中能达到的成熟度的级别，煤阶的改变是由于深埋而增加的温度而改变的。
海拉尔盆地具有多煤阶煤分布。
The coals with different coal ranks occurrence in Hailaer basin.
本文介绍了世界低煤阶煤炭资源及其分类。
The resources of low rank coal in the world have introduced in this paper.
低煤阶煤层气富集成藏具有自身独特的特点。
Enrichment and accumulation of coalbed methane in low rank coal have their own unique characteristics.
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