Personnel engaged in coal-to-oil production. Coal-to-liquid producers refer to those who are engaged in the control of coal-to-liquid production process and the operation, maintenance and overhaul of equipment. Their main tasks are to operate coal-to-liquid production devices, produce refined oil and operate public works equipment. Coal-to-liquid, also known as coal liquefaction, is a coal chemical technology that uses coal as raw material to produce liquid fuel and chemical raw materials through chemical processing. Coal-to-oil has the advantages of high calorific value, little pollution and long service life.