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The Factors Affecting the Moisture of Coal from Coarse Coal Centrifuge

Abstract:The coarse and fine coal centrifuges are widely used in coal preparation plants, it is characterized by large handling capacity, low production cost and easy maintenance. However, the coal preparation plant usually cannot control it well for the first time, which may makes the higher moisture of product or even causes the coal preparation plant out of production normally. This paper introduced the working conditions of the coarse coal centrifuge, hope it can be helpful to the coal preparation plants that applied the same type centrifuge.

Application of coarse coal centrifuge

The coarse coal centrifuge is a widely used dewatering equipment in coal preparation plant. HOT Mining's customers of centrifuge are mainly in China and Russia, where the centrifuges have been widely used in China's coal preparation industry. According to the application of several coal preparation plants in China, the product moisture is about 12%, so that coarse coal centrifuge is an ideal equipment for dewatering coarse coal slime. The application of the coarse coal centrifuge can improve the working condition of the coal slurry treatment system and reduce the product moisture. Because of its small size, it is also suitable for the improvement of existing coal preparation plant.
However, the operation of the coarse coal centrifuge is not as simple as described in the product specification, as long as the slime water through the concentration classification, so that the concentration of 50 % ~ 60 %, can achieve the desired effect.
In fact, most of the selling engineers did not describe in detail the conditions the centrifuge were used to, nor did they promise to meet any moisture targets. Because the product moisture is not unchanged, with the change of feed concentration and particle size composition, product moisture will change greatly, up to more than 30%, so that cause out of production.

Problems with coarse coal centrifuges

In July 2015, the coarse coal centrifuge was put into production test operation in the technical renovation project of a coal preparation plant in Inner Mongolia, China. During the commissioning, the biggest problem encountered was the unstable production of the coarse slime recovery system, the product moisture was higher, sometimes as high as 30%, the product was mushy and could not meet the product moisture index required by the design. See figure 1 for the dewatering process used in the coarse coal slime recovery system of the preparation plant.


The coal slurry is graded by cyclone, then it is further dehydrated and graded by sieve bend screen, and finally dehydrated in coarse coal centrifuge. From the technical characteristics of the coarse coal centrifuge and the requirements of the operating instructions, the system meets the technical requirements of the coarse coal centrifuge, the generated materials basically meet the equipment to adapt to the feeding conditions (feeding concentration of 50% ~ 60%), so that it should be able to obtain the ideal product moisture. But, in the commissioning, the water content of the product from centrifuge is up to more than 30%, a long-term adjustment cannot solve this problem. To that end, HOT Mining's engineers visited a coal preparation plant in Huainan, China, that had earlier used coarse coal centrifuges. When Huainan coal preparation plant was put into operation, the recovery system of coarse coal slime was not normal, and the product moisture was very high. After many years of transformation, the product can achieve satisfactory moisture index. From this point of view, the plants which operated coarse coal centrifuge for the first time encountered the same trouble, is the product moisture is high.

Factors of higher moisture in coarse coal centrifuge products
It is found from the production transformation of Huainan coal preparation plant for many years that the product moisture of the coarse coal centrifuge is closely related to the particle size composition of the feed. Under the condition of constant feed concentration, when the fine slime content of <80 mesh in the feed is about 10% (maximum cannot exceed 15%), the product moisture can be controlled at about 12%. With the content of < 80 mesh fine slime increased, the product moisture increased greatly. Therefore, controlling the fine slime content of <80 mesh in the feed is the key to controlling the moisture of the product. In view of the above problems, we carried out a screening test on the coarse coal slime in the Inner Mongolia coal preparation plant, and the test results are shown in table 1.


It can be seen from Table 1 that the content of fine slime of <80 mesh up screen is as high as 31167%. Based on the production experience of Huainan coal preparation plant, it can be concluded that the high content of fine slime cause high product moisture.

The method reduces the moisture of the product from coarse coal centrifuge
The main reason for the high content of < 80 mesh fine slime is bad grading effect obviously. The solution to this problem is to improve the efficiency of classification equipment. Based on the production experience of Xinjiyi coal preparation plant, we adjusted the coarse coal slime classification system as following:
Changed the production system from intermittent production to continuous production, which ensured the feeding stability of cyclone and improved the classification efficiency of cyclone.
Changed the screen mesh of sieve bend screen from 0.135mm to 0.15mm, which improved the secondary grading effect. Thus, the overall grading efficiency of the grading system was improved.
The result of the transformation was that the moisture of the coarse coal centrifuge fell down and basically reached the expected water content. The product is loose.



Through the investigation on the commissioning of coal preparation plant in Inner Mongolia and the application of the coarse centrifuge in the coal preparation plant in Huainan, it can be determined that the working conditions for the coarse coal centrifuge are not only the feed concentration, but also the fine slime content < 80 mesh in the feed.
In the actual operation of the coal preparation plant, it is necessary to control the two indicators of the concentration and the fine slime content <80 mesh in the feed, especially the fine slime content, which is preferably controlled at about 10%. However, the instruction manual of the coarse coal centrifuge only requires controlling the feed concentration (50% ~ 60%), and there is no requirement for the particle size composition of the feed, which results in that the user cannot control the product moisture well for the first time and waste a lot of manpower and material for transformation. I hope this article can be helpful to you who will use coarse coal centrifuge in the future.

Any more information about coal washing plant or centrifuge, can contact us:

Kira Zhang, International Business Manager


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Teresa Zheng, International Business Manager  


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Tari Wang, Mineral Process Engineer & Centrifuge Products Manager


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