Lignite is a kind of low-grade coal, which is formed by peat diagenetic formation of humic coal, it’s the lowest degree of coalification, always present brown, dark brown, dim or asphalt luster color, no cohesive. Its physical and chemical properties are between peat and bituminous coal. High water content, high volatile, low density, containing humic acid, oxygen content up to 15 ~ 30%, easy to fragmentation, spontaneous combustion in the air. According to China's coal classification standards, they are divided into two categories: light transmittance PM 30 ~ 50% of the old lignite and PM less than or equal to 30% of the young lignite. Chinese and Indonesian lignite are mostly old lignite.