Longfei Tang

The Effect of Fine Coal Particles on the Performance of Gas–Solid Fluidized Beds

The distribution of 3 × 1 mm fine coal particles across the fluidized bed was analyzed during beneficiation of coal in a gas–solid fluidized-bed separator. The effect of accumulation of the fine coal on the bed performance was also studied. The experimental results show that as 3 × 1 mm size fine coal content increases in the solid medium the mean density of bed decreases linearly. A mathematical model was developed that can predict the standard deviation of the bed density. The bed density increases sharply as the coal-fines content exceeds 4.5 weight%, at which point the bed becomes unstable and poor fluidization performance takes place. Furthermore, the separation performance of a bed was measured by 50 × 6 mm size tracker balls. The separation performance decreased gradually as the fine coal particles accumulated. When the content of the bed reached 4.5 weight%, the probable error, E, rose from 0.05–0.08 g/cm3. Therefore, to maintain good fluidization and separation performance the 3 × 1 mm fine coal content of the medium should be controlled to less than 4.5% during dry beneficiation processing of coal.

X-ray photoelectron spectroscopy study on the chemical forms of S, C and O in coal before and after microwave desulphurisation

The chemical forms of S, C and O of high-sulphur bituminous coal were analysed before and after microwave desulphurisation by using X-ray photoelectron spectroscopy (XPS). Sulphur existed as 17.908% mercaptan (sulfoether) and 62.160% thiophene before microwave irradiation and decreased to 4.644% mercaptan (sulfoether) and 49.483% thiophene after irradiation with assistance of alkali solution. On the contrary, sulphur that occurred in the chemical form of sulfone (sulfoxide) and sulphates increased from 7.516% and 12.416% to 14.697% and 31.176%, respectively. This increase may be due to the mobility of sulphur-containing species and the oxidisation effect of desulphurisation additive. After irradiation, the relative contents of C-H and C-C groups decreased while C=O and COO-groups in the coal increased. This shows that the organic carbon is oxidised to a higher valence state. These observed changes in functionalities led to a low coking quality of the desulphurised coal. [Received: February 5, 2015; Accepted: December 12, 2015]

Investigation of the relationship between sliding process measurement and induction time test of low rank coal particles in the surfactant solutions

ABSTRACT The induction time or sliding time can be used to characterize the hydrophobicity of mineral particles. In order to investigate the relationship between sliding process and induction time, the Induction Timer and high-speed camera technology were adopted in this study. It was found that the flotation recoveries of low rank coal particles increased with the surfactant concentration increase. Howerer, the analysis results of induction time and slip angle velocity indicated that the flotation performances of low rank coal were depressed by anion SDS surfactant. Therefore, the slip angle velocity results can be adopted to support the induction time measurements.

Effect of particle shape and roughness on the hydrophobicity of low-rank coal surface

ABSTRACT In this paper, a relationship between the roundness, roughness and induction time of low-rank coal particles was investigated. With the increase of grind time from 1 to 5 minutes, the roundness of low-rank coal particles slightly increased. The results of induction time measurements indicated that the particle surface roughness played a significant role in the surface hydrophobicity of low-rank coal particles. Moreover, it was also found that the roundness and roughness of low-rank coal particle surfaces presented a certain degree of change after both grinding and abrasion processes. Contrary to roundness change, during the grinding process, the roughness of low-rank coal particles significantly decreased. It was also observed that the roundnesses of low-rank coal samples after the grinding process significantly increased with the increase of abrading time. However, unlike the roundness increase with the abrading time increase, the roughness of low-rank coal samples significantly decreased. Therefore, the induction times of low-rank coal samples showed an increased trend after the grinding and abrading processes, which may be attributed to the difficult rupture of wetting film on the smooth solid surface. The grinding and abrading processes may result in a further decrease in surface hydrophobicity and adversely impact on the flotation performance of low-rank coal.

Investigation of the induction time of low-rank coal particles on rising bubble surfaces

ABSTRACT In this paper, the back-calculated induction times of low-rank coal particles on the rising bubble with mobile surfaces were back-calculated from the micro-flotation rate constants. The back-calculated induction times slightly increased with the flotation recovery increase or the surfactant concentration decrease. It is because the drainage time accounting for most of the induction time is affected by the force exerted on the wetting film. Moreover, the force exerted on the wetting film is characterized by the Reynolds number. Furthermore, the Reynolds number increased with increasing bubble rising velocity due to an increase in bubble size as a result of decreasing surfactant concentration. Therefore, the back-calculated induction times could reflect the difference in the flotation recoveries at the same surfactant concentration. Meanwhile, it indicated that the hydrodynamic condition in the flotation process had a significant effect on the back-calculated results of induction times. From this investigation, it can be speculated that the back-calculated induction time of particles sliding on the rising bubble with mobile bubble surfaces is greatly influenced by the Reynolds number.