A General review of the course of development of China′s coal preparation technologies over the past five decades

Coal will occupy a dominant position in the primary energy structure over a long period of time. Coal preparation constitutes the source and basis for clean and high-efficiency utilization coal. The paper looks back to the course of development of the coal preparation technologies over the past 50-odd years, and presents a summary of the coal cleaning technologies, technological level of process equipment and characteristics of coal cleaning processes in different periods of time, with the focus on the evolution of the equipment applied for major coal washing processes involving, for instance, heavy medium separator, jigging machine, flotation cell and dry separator, as well as the combined coal washing processes. What is introduced first is the course of development of process equipment in different time periods: the jigging machine has made continued development evolving from the Bam jig to the independently developed Batac jig, movable-bed jig, air pulsating jig and the jig for use underground; over the past ten years, the optimum jig structure has been defined through testing with PIV velocity measuring system, and the jig has become more intelligent; the use of the heavy medium separators, such as the inclined lifting wheel and vertical lifting wheel versions, heavy medium vessel and heavy medium cyclone, especially the use of the ϕ1.4 m large-sized H.M. cyclone, signified that the research work on and application of the H.M. cyclone for coal washing stood at the forefront worldwide; the development of flotation machine started from imitation of overseas equipment to manufacture of a series of independently developed versions such as the subaeration-type, jet-type cells and flotation column; in recent years, study has been made on motion pattern of fluid in the cell using computational hydrodynamic technology and numerical simulation method; as for the coal cleaning equipment, following the gradual phasing out of the pneumatic destoning equipment, the self-developed air-medium fluidized-bed separator, triboelectrical separator, and the compound dry separator developed through incorporating the special features of the airless dry cleaning table and air separator made their debut in succession; in recent years, the intelligent dry separator has been gradually shifting its use early for preremoval of gangue to the use for coarse coal separation and underground destoning. Following that, the paper goes to introduce the course of development of coal preparation processes during different periods. Before the 70s of the 20th century, most of the coal preparation plants operated with the jigging and thickened slime flotation combined process; in the 70s, the document for the general design of the 1.8 Mt/a-capacity coal preparation plant was compiled; most of the plants started to use jigging and direct flotation processes to wash mixed raw coal and unthickened slime, respectively, with only a few plants operating with heavy medium separation process; in 1970 the Tianzhuang Plant went into operation. It was an independently designed all heavy medium separation plant operating exclusively with home-made mechanical and electrical equipment, making it the first of its kind in China; in the 80s, advanced overseas equipment were extensively introduced in plants, and some plants become fully automated plants where the main process equipment could be brought under sequential control and monitoring with programmable controller and various up-to-date sensing, measuring and dispatching devices. Among these plants, Antaibao Plant was a most typical one. It was then the only superlarge modern plant in the country operating with the technologies, process equipment and manage mode all introduced from abroad; in the 90s the plants engaging mainly in producing coal for injection in blast furnace, the power coal plants and extralarge plants started to shift to the use of heavy medium separation process, and their washing processes offered the features of being more simplified and modularized. Not long afterward, the first modular plant emerged in China; in 2000—2015 of the 21th century, heavy medium separation process took the place of jigging process become the mainstream washing process. Anjialing Plant, a superlarge modern plant operation with all heavy medium separation system, was independently designed, constructed and managed. Its successful operation marked a new milestone of the country′s ability to design superlarge modern plants; from 2015 onward, the coal washing processes applied in China was approaching the advanced international level, during this period, most of the plants plunged into technical remoulding, capacity expansion, upgrading and regeneration of process equipment, with an aim to turn the plants into automated and intelligent ones. This led to the development of a combined washing process featuring the use of intelligent dry separator for removal of gangue, the superlarge H.M. cyclone, the novel cross-flow filter press for dewatering of flotation concentrate, and ultrahigh-pressure filter press for dewatering of flotation tailing. Lastly, the paper presents the future outlook: the heavy medium separation and flotation will remain the predominant washing processes; the large compound dry separator, coarse coal dry separator, the dry separator for separation and destoning of coal underground, and the new-generation air-heavy medium dry separator will be applied in a more rational manner; for improvement of washing processes, the main efforts should be made directed toward the following aspects — washing feed coal with reduced amount of fine slime or producing no fine slime, rewashing of middling after liberation of intergrown constituents through crushing, and in-depth flotation of slime; the washing equipment should be continuously improved and upgraded, and vigorous endeavors should be made to promote the domestication of process equipment; and research and development and popularization of advanced process equipment through innovation of washing process and methods can help coal preparation plant to become automated, intelligent and informationized.