Contact sorption: a method to reduce the moisture content of coal fines

ABSTRACT

This paper introduces contact sorption with ceramic sorbents as a method to reduce the moisture content of coal fines produced by coal processing plants. The proposed method was tested on laboratory scale where ceramic spheres with diameters of 3 mm and 5 mm were combined with wet coal fines of size fractions between 0.25 mm and 2 mm. The coal had an initial moisture content of 0.25 g(Water)/g(Coal and water), and was dewatered using contact sorption to an average moisture content of 0.13 g(Water)/g(Coal and water) after 2.5 minutes and 0.05 g(Water)/g(Coal and water) after 10 minutes, respectively. This paper focuses on identifying the solid phase conditions essential to improving the contact sorption drying technology, proving that contact between the coal and sorbent material is the main driving force behind this technology. Increasing the sorbent to coal mass ratio and using smaller sorbents with a larger surface area resulted in improved contact and consequently improved moisture mass transfer. The final coal moisture content that could be achieved was independent of coal particle size. Current studies show a reliance on thermal drying technologies to dry the saturated sorbent material, whereas this paper proves that drying with high airflow at low temperatures is sufficient to regenerate the sorbent material. The loaded sorbent material could easily be separated from the dried coal product by dry screening, and could be dried and regenerated afterwards in an air-blown packed bed within 10 minutes. The re-use of sorbent material showed no decrease in its dewatering efficiency, and it was shown to be possible to re-use the sorbents for a large number of cycles. Contact sorption can prove to be a cost-effective and efficient drying method to dewater coal fines in the industry.

KEYWORDS:

• Coal beneficiation
• fine coal dewatering
• contact sorption drying

Acknowledgments

This work is based on the research supported by the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa (Chair Grant No: 86880, UID 85643, Grant No: 85632). Any opinion, finding, conclusion or recommendation expressed in this material is that of the author(s) and the NRF does not accept any liability in this regard.