Abstract:
The coal resources in China are poorly endowed, with huge reserves of low-quality coal with high water content and high ash content, accounting for about 40% of the original coal reserves. With the promotion of mechanized integrated mining technology, the content of <6 mm fine-grained coal in the raw coal gradually exceeds 50%. The process technology of dewatering and ash removal for synergistic quality improvement was proposed, and the tests of dewatering and drying, dry sorting and quality improvement of fine-grained coal with high water content and low quality were carried out. Firstly, the evolution of the liquid bridge between 6 mm isodiameter particles was investigated. With the increase of the liquid bridge volume
V, the maximum liquid bridge force could reach 825.16 μN, and the maximum liquid bridge fracture distance could reach 1.368 mm, which was due to the increase of the liquid bridge volume caused by the contact angle hysteresis effect in the process of contact angle advance increase of the initial configuration. With the increase of particle separation velocity
v, the maximum liquid bridge force can reach 875.14 μN, and the maximum fracture distance reaches 0.171 mm, which is due to the increase of the advancing volume of the contact angle as well as the slowing down of the backward process of the contact angle produced by the viscosity of the liquid. Secondly, through the hot air drying technology to explore the high moisture content of fine-grained coal before and after drying the law of change of moisture content, the larger the particle size of the longer drying time required, 3–6 mm, 0–3 mm particles at 120 ℃ complete drying time of 60 min and 30 min, respectively, this is because the larger the particle size of the internal migration path of moisture becomes longer penetration into the surface of the coal is limited, the rate of drying process is reduced. When the drying temperature increases from 80 ℃ to 100 ℃, the moisture content can be removed completely from the remaining 7.18% moisture, the increase in drying temperature at the same time to enhance the temperature gradient between the external environment and the coal, the internal moisture mass transfer rate is increased, so the drying rate is faster. Finally, through the vibration composite force field dry sorting technology on the dewatered coal samples to remove the ash and improve the quality of the test, when the vibration frequency f is 42 Hz, the bed surface gas velocity
vA is 7.05 m/s, the material layer in the excitation force and the air flow trailing force under the action of the full loosening, the material density spatial distribution of the material group is ideal, and the upper and lower layers of the ash difference is significant. The vibration frequency has a significant effect on the product recovery rate, when the vibration frequency is 39 Hz, the refined coal recovery rate and yield are 56.56%, 85.28%, the ash content is 12.54%, and the particle mismatch phenomenon is reduced; when the vibration frequency f is 39 Hz and the bed air velocity
vA is 8.97 m/s, the separation effect reaches the best, and the ash dissociation degree SA reaches a maximum of 1.896. This technology is suitable for the high water-scarce areas in the western arid and water-scarce regions. This technology is suitable for the purpose of high-efficiency quality improvement of low-quality fine-grained coal with high water content in the arid and water-scarce areas in the west of China, which has the advantages of no water use, low operation and maintenance cost, and remarkable quality improvement effect, and provides technical reserves for the high-efficiency dewatering and de-ash removal of low-quality fine-grained coal in China.