Significance of separation and enrichment of organic coal macerals and status quo of related research work

Traditional coal cleaning operations are proceeded with the stress centered on sulfur removal and ash reduction, and the technologies applied are quite mature in the current stage. With an aim to explore the new techno-economical growth point in coal preparation, the paper presents general survey of the different properties of macerals required by different sectors to illustrate the significance in making separation and enrichment of coal macerals. The technical survey is made based on the difference of macerals in color, form, elementary composition, molecular structure, hardness, frangibility, density, surface property, etc. It is noted that for the coking sector, the use of the separated and enriched tellinite, which is in mass occurrence in low-rank bituminous coal, as a coking blend can greatly expanded the sources of coking coal materials, and hence reduce the reliance on supply of the materials from external sources; for the coal liquefaction sector, the effective enrichment of the tellinite and liptinite which can yield a higher conversion rate and oil recovery than tellinite can undoubtedly play a significant role in promoting the direct liquefaction of coal and the whole coal liquefaction sector; and in the case of using macerals as fuel or for making carbon, the separation and enrichment of macerals is also of vital importance because it is prerequisite for utilization of the macerals according to well-defined quality standards. The research and development of the macerals separation and enrichment technologies is of particularly paramount importance. The methods commonly used include handpicking, image identification, heavy-medium separation, flotation and electrical concentration, out of which the heavy-medium separation and flotation methods are more matured in technology. The research work is currently made, however, with excessive stress on degree of liberation of intergrown constituents, causing as a result the difficulty and high cost of the subsequent processing links in treating a material with a much reduced size, which is unfavorable for the utilization of the products of the follow-up processes. Analysis shows importance needs to be placed on the right way of using the image identification method and the selection of the material to be separated. An overall maceral separation idea of making stepwise liberation and stepwise enrichment is proposed. While ensuring the separation efficiency, the use of the proposed method can lead to reduction of operating cost and help promote the development of the organic macerals separation and enrichment undertakings.