Chao Ni

A Design of an Inclined Froth Zone in Column Flotation Device to Reduce Ash Content in Clean Coal

A modified column flotation was designed based on the cyclonic microbubble flotation column (FCMC). In the modified flotation column, the froth zone was designed with an inclined arrangement to enhance the gravity settling of coarse middling particles, which were collected as a third product. The modified flotation column was referred as S-FCMC. In this study, the effects of process parameters (collector dosage, frother dosage, superficial gas velocity, and froth layer height) on the performance of the S-FCMC were investigated. For comparison purposes, tests were also conducted using the standard FCMC. The results showed that clean coal obtained using the S-FCMC had lower ash content than that obtained with the FCMC. Under the optimized operating conditions, the decrease in clean coal ash content and clean coal yield was 1.29% and 3.93%, respectively. The increase in tailings ash content and flotation efficiency index was 6.77% and 1.57%, respectively. About 64.55% of the settled (third) product in the inclined zone consisted of −0.045 mm sized particles and the ash content of this size fraction was 58.04%.

Effective Flotation of Lignite Using a Mixture of Dodecane and 4-Dodecylphenol (DDP) as a Collector

ABSTRACT Lignite is difficult to float using common oily collectors, for example, diesel and kerosene. In this investigation, a mixture of dodecane and 4-dodecylphenol (DDP) was used as a collector. The flotation performance using the mixture of dodecane and DDP as a collector is much better than that using dodecane or DDP solely. The concentrate yield using the mixture as a collector is much higher than that using dodecane or DDP solely. However, concentrate ash is lower than that using dodecane or DDP solely. The mixture of dodecane and DDP was proven to be an effective collector for lignite flotation. FTIR was used to indicate the changes in surface properties of lignite before and after the adsorption of different collectors. The improvements in flotation performance of lignite by the mixture are discussed and the adsorption mechanism of the dodecane and DDP on lignite surface was also obtained. Using the mixture of DDP and dodecane as the collector, the dodecane primarily covers the hydrophobic sites on the lignite surface while the DDP primarily covers the hydrophilic sites on the lignite surface.

The Order of Kinetic Models in Coal Fines Flotation

ABSTRACT The purpose of this article is to investigate the order of kinetic models in coal fines flotation. Six kinetic models with different orders were used for flotation tests using fine coals with different average particle sizes, 375, 188, 100, and 37 μm, respectively. Statistical techniques were employed to evaluate the models, and a nonlinear regression was used to calculate the model parameters by MatLab software. The results indicated that the first-order kinetic model with a rectangular distribution of floatabilities gave the best fit to the experimental data under the average particle size of 375 and 37 μm. Furthermore, the nonintegral-order equation fit the test data of fine coal in average particle sizes of 188 and 100 μm. The order of flotation process of moderate particles (188 and 100 μm in average particle size) and coarse/fine particles (375 and 37 μm in average particle size) were nonintegral order and first order, respectively. Likewise, a nonlinear relationship existed between the order of the flotation process and the average particle diameter.

Improving the Recovery of Coarse-Coal Particles by Adding Premineralization Prior to Column Flotation

ABSTRACT A premineralization process, a pipe flow mineralization method adopted by adding a self-aspirated bubble generator in the feed pipe, was developed to improve the recovery of coarse-coal particles using a flotation column. The recoveries of various size fractions, including -700+600, -600+500, -500+250, -250+74, and -74 μm, using a conventional column (CC), a premineralization column (PMC), and a conventional column combined with the premineralization process (PM-CC) were investigated. According to the results, the CC showed a good performance in recovering coal particles with sizes below 250 μm, but a poor recovery of particles of sizes above 250 μm. The PM-CC presented advantages in recovering coal particles in contrast with the CC, especially coarse coal particles. Compared with the CC, the combustible recovery of -700+600, -600+500, -500+250, -250+74, and -74 μm size fractions obtained with the PM-CC was increased by 17.69, 17.15, 10.37, 0.58, and 4.07 percentage points, respectively, and the combustible recovery of the clean coal increased by 9.29 percentage points. The ash content of clean coal obtained with the PM-CC was almost identical to that of the CC. It was an effective way that adding the premineralization process prior to column flotation to strengthen the recovery of coarse-coal particles.

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.

Overview of Typical Coal Flotation Flowsheets in China’s Coal Preparation Plants

The entrainment of high-ash fine slime severely contaminates clean coal product of traditional flotation cell, leading to serious technical problems such as high ash in clean coal, low recovery, and the sacrifice of the yield of gravity separation to lower the ash content of final product. In order to solve those issues, the performance of FCMC series cyclonic microbubble flotation column and traditional flotation cell were compared. Several typical flowsheets for the separation of coal flotation in China’s coal preparation plants (CPPs) were extensively reviewed and deeply explored. Results show that FCMC flotation column is especially suitable for the beneficiation of fine and non-selective coal slime downstream the heavy medium separation. The mixed (one-stage) flotation process utilizing the combination of flotation column and clean coal quick-operating pressure filter is recommended in newly built and retrofitted CPPs. As for those utilizing one-stage flotation flowsheet equipped with traditional flotation cell and pressurized filter, either classified flotation process or secondary flotation for the filtrate of pressurized filter using flotation column and clean coal quick-operating pressure filter is recommended in their technical modifications.