Effects of Energy Input on the Laboratory Column Flotation of Fine Coal

This study explored the effects of energy input and different energy increase patterns on the separation performance of a laboratory cyclonic–static microbubble flotation column in fine coal flotation. The energy input was changed by adjusting the circulating pump power and pulp residence time. Continuous flotation tests were designed by using five feed rates (i.e., different pulp residence time), which were 53.33, 80.00, 106.40, 133.60, and 160.00 g/min, and various useful power of the circulating pump (22.44, 30.14, 38.50, 46.86, 56.10, and 64.46 W). Results show that concentrate combustible recovery initially increased before reaching saturation distribution with increasing energy input absolute value. An ash content of 10.90% and combustible matter recovery of 92.84% were obtained at the energy input of 10098.00 J which is called the flotation saturation energy Es. Es is the essential condition and guarantee for a complete flotation process. A low ash content of clean coal was obtained with low energy input. With the increase of energy consumption, the additional coals recovered were coarse particles with low ash content and fine particles with high ash content. However, the ash content did not exhibit a significant change with the increase of energy input in this investigation. During the flotation process, a minimum critical flotation time T and critical circulation pump useful power P are required. If the P and T of a variable are less than the critical value, high combustible matter recovery could not be obtained by adding another variable to increase energy input. A reasonable mode of energy input was proposed that the absolute value of the energy input reaches Es; meanwhile, it ensures that each value of the P and T is greater than the critical values.     

Picobubble Enhanced Fine Coal Flotation

Abstract

Froth flotation is widely used in the coal industry to clean ?28 mesh fine coal. A successful recovery of particles by flotation depends on efficient particle‐bubble collision and attachment with minimal subsequent particle detachment from bubble. Flotation is effective in a narrow size range beyond which the flotation efficiency drops drastically. It is now known that the low flotation recovery of particles in the finest size fractions is mainly due to a low probability of bubble‐particle collision while the main reason for poor coarse particle flotation recovery is the high probability of detachment. A fundamental analysis has shown that use of picobubbles can significantly improve the flotation recovery of particles in a wide range of size by increasing the probability of collision and attachment and reducing the probability of detachment.

A specially designed column with a picobubble generator has been developed for enhanced recovery of fine coal particles. Picobubbles were produced based on the hydrodynamic cavitation principle. They are characterized by a size distribution that is mostly below 1 µm and adhere preferentially to the hydrophobic surfaces. The presence of picobubbles increases the probability of collision and attachment and decreases the probability of detachment, thus enhancing flotation recovery. Experimental results with the Coalberg seam coal in West Virginia, U.S.A. have shown that the use of picobubbles in a 2″ column flotation increased fine coal recovery by 10–30%, depending on the feed rate, collector dosage, and other flotation conditions. Picobubbles also acted as a secondary collector and reduced the collector dosage by one third to one half.     

The Limits of Fine and Coarse Particle Flotation

The flotation behaviour of quartz particles was studied over the particle size range from 0.5 µm to 1000 µm and for advancing water contact angles between 0° and 83°. Flotation was performed in a column and in a Rushton turbine cell. Particle contact angle threshold values, below which the particles could not be floated, were identified for the particle size range 0.5–1000 µm, under different hydrodynamic conditions. The flotation response of the particles, either in a column or in a mechanically agitated cell with a similar bubble size, was comparable. Turbulence plays a role, as does bubble‐particle aggregate velocity and bubble size. The stability of the bubble‐particle aggregate controls the maximum floatable particle size of coarse particles. For fine particles, the flotation limit is dictated by the energy required to rupture the intervening liquid film between the particle and bubble. Flotation of very fine and large particles is facilitated with small bubbles and high contact angles. These results greatly extend our earlier observations and theoretical predictions.     

Effect of flotation on the dioxin distribution in size-fractioned fly ash of hospital solid waste incineration

After the flotation of hospital solid waste incinerator (HSWI) fly ash, two types of solid products, froths and tailings, are produced. This paper reports the effect of flotation on the dioxins distribution patterns in different particle size fractions (?25, ?38, +25, ?75, +38, ?106, +75 and +106 µm) of fly ash. The results showed that the froths had a higher small-size particle distribution than that of the raw fly ash. The dioxin content with particle size in the flotation products depended on the partition behavior of powder-activated carbon (PAC). The dioxin content in the fine particles of the froths was higher than that in the coarse particles, and the highest content was in the finest particles (?25 µm). The dominant dibenzo-p-dioxins and dibenzofurans (PCDD/F) congeners in the froths and tailings were similar to those in the raw fly ash. A positive correlation between carbon removal and PCDD/F removal with different size fractions was observed. The carbon removal efficiencies of the fractions of ?25 and ?38, +25 µm were evidently higher than those of the other particle size fractions. Similarly, the PCDD/F removal efficiencies in fractions of ?25 and ?38, +25 µm could reach 156.9% and 115.0%, respectively.     

Flotation of Fine Gold Particles by the Assistance of Coal-Oil Agglomerates

This paper describes the use of coal-oil agglomerates in flotation to increase the gold recovery from an ore containing fine gold particles. The effects of operating parameters on gold flotation recovery such as oil type, particle size of agglomerating material, agglomerate/ore and oil/ore ratios were investigated. The studies showed that petroleum oils are more effective than vegetable oils in oil agglomeration of Kozlu coal and coal-oil assisted gold flotation. Gold recovery can be increased using a higher amount of agglomerates in the process; however, gold grade of the flotation concentrates is reduced significantly. The use of bridging oil at high concentrations in the agglomeration process provides high-grade gold concentrates, but lower recoveries. The utilization of coarser coal particles in the coal-oil agglomeration stage leads to higher selectivity and recovery values for gold particles.     

Optimal conditions for recovering boron from seawater using boron selective resins

We determined the optimal conditions for efficient recovery of boron from seawater using boron selective resins (BSRs). A commercialized BSR named CRB05 was adopted and prepared in two particle sizes: A fine-particulate BSR (effective particle size of 105 μm) and a coarse-particulate BSR (effective particle size of 445 μm). The performance of the two BSRs was compared in terms of boron adsorption, boron desorption, and BSR regeneration and reusability. During boron adsorption, for fine BSR, optimal reaction time, stirring speed and the amount of BSR needed for the adsorption of boron were 30 min, 150 rpm and 1 g-BSR/L respectively, whereas for coarse BSR, values of the above parameters were 300 min, 150 rpm and 3 g-BSR/L. It indicates that the fine BSR can adsorb boron about threetimes more than the coarse BSR. It also shows that the reaction rate of the fine BSR is almost ten-times higher than that of the coarse BSR. During the boron desorption, no significant difference was found between the efficiencies exhibited by the fine and the coarse BSRs. The best desorption performance can be attained with 11.9 mL/mg-B of 0.05 M H₂SO₄ and 15.9mL/mg-B of 0.25M HCl, regardless of the particle size of the BSR. Finally, the boron adsorption efficiency can be maintained at a stable level even after reusing the BSRs over ten times. The present study shows a possibility to recover boron with better efficiency from seawater in short time using the fine BSR, rather than the coarse BSR.     

内蒙某低品位石墨矿选矿工艺研究

内蒙某低品位石墨矿,鳞片微细,为提高石墨精矿的品位并保护石墨鳞片,在采用浮选原则流程的条件下,对原矿粗磨的取舍、再磨段数、精选次数、再磨细度等工艺条件及参数进行了系统的试验分析,结果表明,品位为6.31%的原矿经一段磨矿至-100目占79.17%,采用一粗一扫、两段再磨、五次精选选别后,可获得C固品位为86.55%、回收率为94.20%的石墨精矿。     

Entrainment Rate of Coarse Particles at Different Temperatures in Gas Fluidized Beds

Based on available experimental data, an empirical relationship is developed for the entrainment rate of coarse particles at the exit of gas‐fluidized beds, including the effects of fine particles in the bed, temperature, gas velocity, particle size and density, and column size. It predicts well the influence of fine particles on the entrainment rate of coarse particles, taking into account the momentum of the fine particles and the effect of superficial gas velocity. It also accounts well for the influence of temperature at different solid densities and gas velocities.     

The influence of frother types and concentrations on fine particles’ entrainment using column flotation

Entrainment which is the characteristic feature of fine particles is closely related to water recovery. It is based on the changes depending on the establishment of linear relationship between water recovery and solid recovery. This paper deals with the investigation of the effect of frother types and concentrations on fine particles’ entrainment using column flotation. Entrainment of fine particle using a mixture of artificial ore (celestite:calcite; 1:1) was investigated in column flotation. In a two-phase system (water/air), the variation of bubble diameters and gas hold-up with a superficial air rates using different frother types and concentrations were tested. The results showed that the frother types and concentrations had significant effect on the grade and recovery, superficial air rate, gas hold-up and fine gangue entrainment. Entrainment factors for frother types and concentrations were compared in flotation column. Kirjaveinen^[11] model was used for describing the specific entrained factor (P_i) of hydrophilic particles. It has been found that Kirjaveinen model supports the results of this study.     

Review: An investigation of single particle breakage tests for coal handling system of the gladstone port

Aspects of the literature on single particle breakage test have been reviewed in this article. The test procedures that are commonly used by the researchers in examining and measuring the breakage characteristics of the ore and coal particles are also discussed. It appears that most of the common size distribution function fitting techniques were not suitable for accurate representation of the size distributions obtained from a pendulum breaking process. The single impact test, double impact test (drop weight test, pendulum test) and slow compression test can be used to study the behaviour of the single particle breakage events. The single impact test, slow compression test and drop weight test cannot measure the energy utilization pattern in single particle breakage events, but this can be determined from the pendulum test.The energy utilized for breakage was predominantly dependent upon the size and shape of the specimen, level of input energy and the breakage properties of the specimen. This review highlights that the size distribution curves were linear in the fine particle region and have varying curvature in the coarser region, the gradient of the linear fine particle region of the size distribution curves increases with an increase in the specific comminution energy. The comminution energy increases with input energy at lower levels of input energy but at the higher levels of input energy the comminution energy did not show the same proportional increase. At a given level of input energy, the size distribution resulting from the breakage of the particles by the pendulum apparatus can be represented by a one-parameter family of curves.     

Effect of frothers on removal of unburned carbon from coal-fired power plant fly ash by froth flotation

The effect of single frothers and their blends on bubble size, froth stability, and unburned carbon (UC) flotation performance was studied. Methyl isobutyl carbinol that produces smaller bubbles is efficient in floating ultrafine particles and producing concentrate. DF-250 that gives higher froth stability is effective for recovering coarse particles and improving recovery. The presence of DF-250 in the blend increases bubble size and significantly enhances froth stability, and hence the optimal flotation performance is achieved with 75% DF-250. It indicates that the frother giving high froth stability is better in UC flotation due to the little effect of UC on froth stability.     

磁性灰粒在不同粒级气化灰渣中的分布特性

以气流床煤气化粗渣和细灰为原料,采用筛分和磁选的方法研究了磁性灰粒在不同粒级气化灰渣中的分布特性。结果表明：随着灰渣粒径的减小,在粗渣和细灰中,磁性灰粒的含量均呈现先升高后降低的趋势,磁性灰粒在粗渣中的含量高于细灰。粗渣中,磁性灰粒在0.5~0.25mm粒级中分布最多,该粒级神宁炉和GSP气化炉粗渣在粒度组成中的占比也最高,质量分数分别为38.42%和37.16%,各个粒级中磁性灰粒产率随粒径减小呈递增趋势;细灰中,磁性灰粒在0.074~0.045mm粒级中分布最多,而细灰粒度组成中的占比最高的却是大于0.25mm粒级,磁性灰粒产率在各个粒级都不高,呈现随粒径减小而升高的规律。气化过程中,磁铁矿会更多地富集在凝结团聚且高度玻璃化的大粒径粗渣中,粗渣和细灰中仍有相当量的含铁物相不显磁性。不同粒级煤气化灰渣中磁性灰粒的分布特性可为气化渣分级分质及高值化利用提供基础数据支撑和应用思路。     

Bubble–particle collision and attachment probability on fine particles flotation

Particle size is an important parameter in flotation and has been the focus of flotation research for decades. The difficulty in floating fine particles is attributed to the low probability of bubble–particle collision. In this research, the influence of hydrodynamic parameters on collision probability of fine particles was investigated. Collision probability was obtained using Stokes, intermediate I and intermediate II and potential equations. Maximum collision probability was 5.65% obtained with impeller speed of 1100 rpm, air flow rate of 30 l/h and particle size of 50 μm. Also, attachment probability under Stokes flow, turbulent and potential flow conditions was calculated 100, 99.49 and 81.87% respectively. Maximum attachment probability was obtained with impeller speed of 700 rpm, contact angle of 90°, particle size of 20 μm and air flow rate of 15 l/h. Collision angles were obtained between 60.71° and 60.18° and attachment angles were obtained between 9.15° and 59.83°.     

Flotation behaviour of fine particles with respect to contact angle

The flotation behaviour of methylated quartz particles of different size, but within the size range from 0.2 to 50 μm, and varying contact angle, was probed in a mechanical flotation cell. Results suggest that particles of a given size need to possess a minimum critical contact angle (θ_crit) for flotation to occur. This behaviour is shown not to be solely dependent on fine particles having lower collision efficiency with bubbles, but rather due to a combination of low collision efficiency and particles not having enough kinetic energy at collision with bubbles to form the three phase line of contact and initiate the attachment process. In the particle size range investigated, the critical contact angle increases with a decrease in particle size.     

选粉机颗粒轨迹的非稳态模拟

选粉机颗粒轨迹模拟研究是分析选粉机分级效率与分级精度性能技术指标的重要基础之一。根据计算流体动力学（CFD）理论,运用DPM模型的颗粒运动方程对时间积分求解颗粒运动轨迹,阐述了颗粒的分级过程。对二维平面离散颗粒的捕集和采样结果进行分析,考察了细粉和粗粉的质量流率,并研究了不同工况下细粉颗粒粒径分布情况。对数值模拟相关工况点进行模拟结果的实验分析,结果表明：细粉颗粒质量流率模拟结果与实验结果误差为5.66%;细粉颗粒粒径分布曲线两者较吻合,100 μm颗粒含量相对误差为6.54%。研究结果为分析和预测选粉机不同工况下的成品产量和粒径分布提供了模拟方法。     

Effects of particle dispersion and circulation systems on classification performance

To classify fine powders with particles smaller than 1 μm in diameter, air classifier design must take three factors into consideration: dispersion of feed powders, air flow uniformity in the classification zone, and recovery of fine particles adhering to the coarse fraction. The effects on the classification performance of a centrifugal air classifier using a dispersion nozzle for particle dispersion and a circulation mechanism using channel air jets for the recovery of fine particles are discussed.

By using a dispersion nozzle, the classification sharpness index was improved below 0.8 (D_p/D_p50) and the fine fraction yield was improved by 64% without changing size distribution. The circulation mechanism using channel air improved classification performance by 58% of the classification sharpness index and 65% of the fine fraction yield, although the particle size distribution of the fine fraction became 0.1 μm coarser than that without channel air.     

炭素材料粒度组成控制的理论与实践

简要介绍了Andreassen颗粒堆积理论，并结合生产实践，讨论了实际生产中所用的粒度组成与这一理论的联系与差异。与Andreassen方程所确定的粒度组成相比，实际配方中细颗粒和粗颗粒用量较大，中颗粒用量较小。     

煤泥浮选最佳粒度的探讨

利用大量的生产和实验资料 ,分析了煤泥粒度对浮选的影响、粗煤泥分选的有效设备及细煤泥的分选方法。提出煤泥浮选最佳粒度范围为 0 .2 5～ 0 .0 74mm;+ 0 .2 5mm的煤泥应采用加工费用低的重选设备 ;- 0 .0 74mm细煤泥应根据煤泥特性采用更有效的处理方法     

Flotation Selectivity of Phosphate Ore: Effects of Particle Size and Reagent Concentration

The flotation selectivity of apatite particles from a carbonatite complex was investigated in a flotation column as a function of particle size and reagent concentrations. Experiments were performed according to a factorial experimental design. Fine and coarse particles showed different sensitivities to variations in the concentration of the reagent. Coarser particles showed a higher selectivity ratio and greater sensitivity to the addition of different reagent dosages, providing a more selective separation and a better quality product. Finer particles presented lower selectivity ratios, reflecting the difficulty involved in the concentration process with this particle size.     

Characterization of transverse mixing in a screw mixer by image analysis

Transverse mixing of particles in a screw mixer is investigated by a digitized image analysis method coupled with a solidification technique. The effects of screw rotation speed, filling level, and particle size on the transverse mixing index and mixing rate constant are investigated experimentally. The results show that a decrease in screw rotation speed and filling level results in an increase in the mixing rate. Faster mixing is observed with large particles, and the mixing rate constant of coarse particles is 1.5–2 times higher than that of fine particles. The particle size difference of materials puts the particles at a risk of segregation.