1078, a large iron mine (a mine run by the imperial court) in Li Guojian, Xuzhou used coal to make iron. There is no doubt that although West Asians first started smelting iron, China people first started using coal to make iron. The disadvantage of using coal to make iron is that the product has high sulfur content, but because the combustion value of coal is higher than that of charcoal, a lot of charcoal can be saved. With the increase of population, the increase of iron output and the increasing shortage of wood, coal has increasingly become the basic fuel for ironmaking. During the Northern Song Dynasty, there was also a workshop in Kaifeng City to refine "fierce fire oil", which was the processing and utilization of oil.