Wencheng Xia

Effect of middle-temperature pyrolysis on the surface hydrophobicity of sub-bituminous coal

ABSTRACT Middle-temperature pyrolysis is widely used to convert sub-bituminous coal into gas/liquid products and the coal char, which benefits the utilization of low rank coal resources. However, the coal char usually contains high-ash content because the volatile components in coal release from coal particle forming gas/liquid products while most of high-ash mineral components remain in the coal char. Therefore, the upgrading of the coal char is usually required to meet the requirement of calorific value for burning. It is necessary to find out the effect of middle-temperature pyrolysis on the surface hydrophobicity of coal. In this study, the effects of pyrolysis temperature (700, 800, and 900°C) and pyrolysis time (30 and 90 min) on the surface hydrophobicity of sub-bituminous coal were comprehensively investigated. X-ray photoelectron spectroscopy (XPS), attachment time, and flotation tests were used to reveal the changes of surface hydrophobicity and floatability of sub-bituminous coal before and after middle-temperature pyrolysis. The XPS results indicated the content of hydrophilic oxygen-containing functional groups was reduced while the content of hydrophobic functional groups on coal surface was increased after the pyrolysis. The attachment time of coal particle-bubble was reduced while the flotation recovery of coal was increased after the pyrolysis. The surface hydrophobicity and floatability of sub-bituminous coal were enhanced by middle-temperature pyrolysis, which makes the upgrading of the coal char feasible.

Effects of Fine Coal Particles on the Recovery of Coarse Coal in Collectorless Coal Flotation

The effects of fine coal ( 1.8xa0g/cm3, on the recovery of coarse coal (−500xa0+xa0250xa0μm) in collectorless flotation were studied in...

Comparative Study of Separation Performance of a Spiral and Dense-medium Cyclone on Cleaning Coal

Spiral separators and dense-medium cyclones (DMCs) are widely used for separation of −1 + 0.125 mm fine coal. In this study, testing was carried out using −1 + 0.125 mm fine coal with low near dens...

Effects of high-temperature oxygen-deficient oxidation on the surface properties of sub-bituminous coal

ABSTRACT The air oxidation of coal releases heat which increases coal temperature, as a result, the spontaneous combustion of coal happens. Generally, coal spontaneous combustion needs to be prevented artificially, however, most of the coal particles still suffer a high-temperature heating process under the oxygen-deficient condition. This paper aims to investigate the effect of high temperature (500°C, 600°C, and 700°C) oxygen-deficient (3% oxygen and 97% nitrogen) oxidation on the surface properties of sub-bituminous coal. SEM and XPS were applied to show the changes of surface properties of sub-bituminous coal. SEM results showed the number of pores and cracks on coal surface increased with the increasing heating temperature, and XPS results showed the content of hydrophobic functional groups on coal surface reduced whereas the content of hydrophilic oxygen-containing functional groups increased after the oxygen-deficient oxidation.

Effect of ultrasound on the true flotation of lignite and its entrainment behavior

ABSTRACT In this study, the ultrasound was fixed in the pulp zone of flotation cell and its effect on the true flotation of lignite was analyzed. Flotation results indicated that the simultaneous ultrasound treatment increased the concentrate yield and decreased the concentrate ash content. Screening analysis of flotation products revealed that the ultrasound could crush coarse coal to fine coal and scanning electron microscopy (SEM) tests indicated that the ultrasound could reduce the coverage of high-ash coal fines on the coarse particle surface. Thus, the flotation recovery of coarse lignite particle was increased. In addition, the true flotation and entrainment of −0.074 mm fine particles were studied by the sink-float test and the method of Trahar. It was found the ultrasound significantly enhanced the true flotation of fine particles and improved the overall water recovery in lignite flotation.

Influence of Inclined Plates in the Froth Zone on the Flotation Performance of a Flotation Column

ABSTRACT In this study, the influence of installing a set of inclined plates within the froth zone (IFC) on flotation performance of a flotation column (FC) was investigated. The inclined plates were tilted from the center of the column to the periphery. For a comparison, a conventional FC was tested in parallel. It was found that the recovery of fine slimes particles obtained with the IFC decreased by 3.16% compared with the FC. Furthermore, the clean coal ash of the IFC was lower than that of the FC, while the flotation efficiency index of the IFC was significantly higher than that of the FC under the suitable aeration flow. Both the recovery of fine slime particles and clean coal ash reduced since the arrangement of the inclined plates in the froth zone enhanced the drainage behavior of the froth layer, and reduced the water entrainment of the fine slime particles. A FC within the built-in inclined plates in the froth zone presented advantages in reducing the entrainment of fine slime particles, thereby upgrading the concentrate grade.