Zhenfu Luo

Separation characteristics for fine coal of the magnetically fluidized bed

Dry beneficiation technology with an air dense medium fluidized bed is briefly introduced. Systems for the dry separation of fine coal consisting of a magnetically fluidized bed (MFB) as separation medium are described. The magnetic stabilization produces homogeneity and stability of the fluidized bed and thus enhances the separation efficiency by preventing remixing of the feedstock to be separated. Experiments have been conducted in a 100-mm inner diameter cylinder and results show that a uniform and stable MFB can be formed and fine coal (<6 mm size) can be separated efficiently.

Progress in Dry Coal Cleaning Using Air-Dense Medium Fluidized Beds

A commercial dry coal cleaning plant (50 2 6 mm feed) using an air-dense medium fluidized bed has been established in China. It is an important clean coal technology (CCT) due to insufficient water resources in China and abroad. This article studies the fluidization performance and bed density homogeneity of a vibrated fluidized bed and a double-density fluidized bed. The experimental results obtained with a 2000 mm 2 80 mm 2 200 mm model apparatus showed that the vibrated fluidized bed can efficiently separate <6 mm fine coal with an E p value of 0.07 and a lower separation limit of 0.5 mm. A double-density fluidized bed was formed by specially designing the bed structure with a pyramidal part. It can produce three products in a fluidized cascade at aseparation density of 1.49 g/cm 3 with an E p value of 0.06 and a separation density of 1.85 g/cm 3 with an E p value of 0.07.

Utilizing an Air-Dense Medium Fluidized Bed Dry Separating System for Preparing a Low-Ash Coal

An industrial-scale air-dense medium fluidized bed was used to prepare a low-ash coal from a feed coal that was difficult to wash. The low-ash coal provided raw material for preparing low-ash activated carbon. A new fluidized bed density control method for preparing a low-ash coal was proposed, which effectively reduced bed density fluctuation, thus maintaining the uniformity and stability of the bed density. A separation density of 1.42 g/cm3 was maintained in the air-dense medium fluidized bed to produce a clean coal with an ash content of 3.71%, with an E P value of 0.055. Results showed that the air-dense medium fluidized bed system is an efficient dry separation method for difficult-to-wash coal.

Low Density Dry Coal Beneficiation Using an Air Dense Medium Fluidized Bed

Abstract For the production of low ash content clean coal, separation at low density is required for some raw coals. Based on analyzing the fluidizing characteristics of magnetic pearls with a specific size distribution and formation mechanism of a microbubble fluidized bed, optimal technological and operating parameters suitable for low density coal separation were determined. The experimental results show that an air dense medium fluidized bed with low density can be formed using magnetic pearls as medium solids, which can efficiently beneficiate coal of 6–50 mm size with a probable error E p value of 0.05 at a separating density of 1.44 g/cm 3 .

Fine coal (6-1 mm) separation in magnetically stabilized fluidized beds

Abstract Air-dense medium fluidized beds for separating 50–6 mm coal have been used successfully in commercial applications in China. In this study, the authors studied magnetically stabilized fluidized beds for separating fine coal (6–1 mm). The magnetic stabilization enhances the separation by preventing back mixing of the feed solids. This paper discusses the principle of coal separation in magnetically stabilized fluidized beds, the experimental system, and the separation results.

Fundamentals of a Magnetically Stabilized Fluidized Bed for Coal Separation

The performance of a magnetically stabilized fluidized bed is strongly affected by the properties of the air-fluidized dense medium, especially for the dry fine coal separation. The successful design and operation of a magnetically stabilized fluidized bed system for dry coal separation depend on the ability to accurately predict the fundamental properties of the fluidized bed, particularly the fluidized beds rheological properties and density. These properties are controlled and modified by magnetic field intensity and medium composition. The composition variables include medium density, magnetite particle size distribution, particle shape, and level of contamination. Some of these fundamentals of a magnetically stabilized fluidized bed for dry coal separation are described in this paper.

Fluidization Characteristics of a Gas-Paigeite-Powder Bed to be Utilized for Dry Coal Beneficiation

The physical properties of paigeite powder were investigated and the characteristics of a gas-solid fluidized bed using the powder were studied. The intent was to expand the choice of medium solids appropriate for fluidized bed dry coal beneficiation. Experimental results show that paigeite powder has a low density, a high saturation magnetization, and a small coercivity. Under suitable technical and operating conditions the fluidization performance of paigeite powder with either a narrow, or a specified wide, size range is good. A gas-paigeite fluidized bed, formed from 0.074–0.3 mm paigeite, was used to separate 6–13 mm, hard-to-wash coal at a separating density of 1.5 g/cm3. The ash content of this coal was reduced from 22.37% to 9.88%, with a clean coal recovery of 60.64% and a probable error, E, value of 0.075 g/cm3. This indicates good separation performance of the fluidized bed.

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.

Nanobubble generation and its applications in froth flotation (part III): specially designed laboratory scale column flotation of phosphate

Abstract Froth flotation is used widely for upgrading raw phosphate. The flotation recovery of coarse phosphate (−1.18+0.425 mm) is much lower than that achieved on the −0.425+0.15 mm size fraction. Enhanced recovery of coarse phosphate particles is of great economic and environmental importance for phosphate industry. In this investigation, four different phosphate samples were aquired, characterized and tested in a specially designed laboratory-scale flotation column. Significant recovery improvement of coarse phosphate flotation was achieved using cavitation-generated nanobubble though its effects differ among the four testing phosphate samples. The laboratory-scale flotation column test results indicate that nanobubble increased P2O5 recovery by up to 10%∼30% for a given Acid Insoluble (A.I.) rejection, depending on the characteristic of phosphate samples. The improvement effect of nanobubble on the hard-to-float particles was more significant than that on easy-to-float particles, especially at lower collector dosages. Nanobubbles reduced the collector dosage by 1/3 to 1/2. Nanobubbles almost doubled the coarse phosphate flotation rate constant and increased the flotation selectivity index by up to 25%.

Separation lower limit in a magnetically gas–solid two-phase fluidized bed

Abstract The magnetically stabilized fluidized bed has the characteristics of a dispersion gas–solid two-phase flow. The essential condition by which the feedstock was separated by bed density was determined through studying the composition and action of dense medium (gas–solid fluidized bed) on feedstock. The forces exerted on a separated feed with sizes close to the lower limit of separation were analyzed. The correlative formula of the lower limit of separation was obtained theoretically. Experimental results in a 100-mm magnetically fluidized bed model show that the coal can be separated efficiently under a good fluidization state with Ep values of 0.05–0.08. The lower limit of separation is about 0.5 mm.