In the residualcoal mining, the retaining and non-mining pillars in the mined area in the past are for resumption of mining.
残煤开采是将过去已开采区留下的煤柱、不可采的煤柱，再进行复采。
2
There exist high gas and serious spontaneous combustion tendency at the same time in many coal mines in china. When the gas is pumped, it is easy to cause the spontaneous combustion of residualcoal.
我国许多煤矿的煤层同时具有高瓦斯和严重自燃倾向，在抽放瓦斯的同时，容易造成采空区遗煤自燃。
3
Murray predicts that energy embodied in the dry solids portion of fecal sludge can be equivalent to coal; in other industries it would replace oil or residual fuel oil.