Occurrence characteristics of mercury in high-mercury coal and distribution rule of mercury in products of an air dense medium fluidized bed

Mercury emitted from direct combustion of high-mercury coal does great harm to the environment. To make good use of high-mercury coal, it is necessary to study the occurrence characteristics of mercury in coal and high-efficient methods of mercury removal. In this paper, high-mercury coal of Guizhou Province of China was taken as an object to study the nature of mercury in coal and the rule of mercury removal by dry preparation method. Mercury mainly distributes in the medium and high density fractions, and has a good affinity with silicon, aluminum, iron, titanium, potassium, calcium, zinc, sodium and magnesium. It exists in minerals formed by these elements and presents significant correlation with ash in coal. After the high-mercury coal is separated by air dense medium fluidized bed, mercury content of clean coal is reduced to 1/10 of raw coal, while mercury content of gangue is increased to 3 times that of raw coal. This indicates that mercury in raw coal is rejected greatly by ADMFB and enriched in highdensity fractions. The rates of ash removal and mercury removal decrease with the density and present a very high correlation.

MECHANISM AND APPLICATION OF COAL DRY BENEFICIATION WITH AIR-DENSE MEDIUM FLUIDIZED BED

The mechanism of beneficiation with air dense fluidized bed has been theoretically studied in the paper. Focusing attention on the misplacing resources in separation process, the misplacing effects are divided into two parts called respectively as misplacing effect of viscosity and misplacing effect of motion. The proposed separation theory can reasonably explain the results of separation in different fluidization states. Experimental results in pilot and commercial plants showed that the air dense medium fluidized bed is a high efficiency dry cleaning technique. The dynamic stability of fluidized bed density is directly affected by the variation of fine coal content in fluidized bed and can be controlled in expected range through measurement of fluidized bed density and adjusting of split flow rate. With air dense medium fluidized bed, various coals of size 50—6 mm can be efficiently beneficiated. The separation density can be adjusted between 1.2—2.2 g/cm 3, and the probable error E p value is about 0.06.

The Forming-Mechanism and Role of Creativity Thinking in Dry Coal Beneficiation of Coal with Air-Dense Medium Fluidized Bed

In this paper, the authors point out that the Creativity is an inevitable request in solving engineering and technological problems and that the coal beneficiation technology with air dense medium fluidized bed is a result of reversal thinking, and its forming mechanism is the use of other things for reference and the transplantation.

Analysis and evaluation on pressure fluctuations in air dense medium fluidized bed

Pressure fluctuations contribute to the instability of separation process in air dense medium fluidized bed, which provides a high motivation for further study of underlying mechanisms. Reasons for generation and propagation of pressure fluctuations in the air dense medium fluidized bed have been discussed.Drift rate and collision rate of particles were employed to deduce the correlation between voidage and pressure fluctuations. Simultaneously, a dynamic pressure fluctuation measuring and analysis system was established. Based on frequency domain analysis and wavelet analysis, collected signals were disassembled and analyzed. Results show gradually intensive motion of particles increases magnitudes of signal components with lower frequencies. As a result of violent particle motion, the magnitude of real pressure signal's frequency experienced an increase as air velocity increased moderately. Wavelet analysis keeps edge features of the real signal and eliminates the noise efficaciously. The frequency of denoised signal is closed to that of pressure signal identified in frequency domain analysis.

Numerical simulation and experimental verification of bubble size distribution in an air dense medium fluidized bed

Bubble size distribution is the basic apparent performance and obvious characteristics in the air dense medium fluidized bed (ADMFB). The approaches of numerical simulation and experimental verification were combined to conduct the further research on the bubble generation and movement behavior. The results show that ADMFB could display favorable expanded characteristics after steady fluidization. With different particle size distributions of magnetite powder as medium solids, we selected an appropriate prediction model for the mean bubble diameter in ADMFB. The comparison results indicate that the mean bubble diameters along the bed heights are 35 mm < D b < 66 mm and 40 mm < D b < 69 mm with the magnetite powder of 0.3 mm+0.15mm and 0.15mm+0.074mm, respectively. The prediction model provides good agreements with the experimental and simulation data. Based on the optimal operating gas velocity distribution, the mixture of magnetite powder and <1mm fine coal as medium solids were utilized to carry out the separation experiment on 6-50mm raw coal. The results show that an optimal separation density d P of 1.73g/cm 3 with a probable error E of 0.07g/cm 3 and a recovery efficiency of 99.97% is achieved, which indicates good separation performance by applying ADMFB.

RESEARCH ON DENSITY STABILITY OF AIRDENSE MEDIUM FLUIDIZED BED

In this paper on the basis of studying the distribution of fine Coal in the dense medAn fluidised bed. the optimai size range of fine coal, which constitutes a fluidized bed together with the dense medium, has been found. In the separating process the fine coal will continuously aeeumulate in fluidized bed, thus inevitably reducing the density of the bed.In order to keep bed density stable, the authors adopted such measures as split-now of used medium and complement of fresb dense medium.The experiment results in both lab and pilot systems of the air-dense medium fluidized bed show that these measures are effective and satisfactory. Then authors also have estabinbed some relative dynamic mathematical models for it.

DRY CLEANING OF COAL WITH AIR DENSE MEDIUM FLUIDIZED BED

This paper deals with the experimental study of dry cleaning of coal with air dense medium fluidized bed. This technique opens up an efficient way of coal separation for vast areas in the country where water resources are in short supply or coals tend to slime seriously in wet process. Tests show that it can separate any kind of coal (6--50mm) efficiently. The probable error E, can reach 0.05--0.08. The separating density can be adjusted in the range of 1.0--2.0 g/cm^3. This technique brings about enormous economic benifits.

Fluidization stability and periodic fluctuations in gas–solid separation fluidized bed using Geldart A dense medium

Gas–solid separation fluidized bed is a typical method for coal separation without water utilization.Geldart A particles is also considered as the ideal dense medium to strengthen separation efficiency.Fluidization stability reflects the bed pressure fluctuations and the distribution of bubble and emulsion phases,affecting the separation performance.And the main frequency of pressure fluctuations can directly reflect the degree of pressure fluctuations.Therefore,the detailed fluidization stability is analyzed combined the method of standard deviation of pressure fluctuations,power spectral density,etc.,for Geldart A particles.The results showed that maintaining an appropriate gas velocity resulted in an average bed pressure of around 2000 Pa.The main frequency is mainly concentrated around 1–1.5 Hz.Finally,a prediction model of the main frequency of pressure fluctuations is established,and the error can be controlled within±0.15.The investigation further proved the stable fluidization of Geldart A particles and provides a method for predicting the main frequency of pressure fluctuations in the gas–solid separation fluidized bed.

基于Euler-Euler模型的空气重介质流化床密度分布特性

以Geldart B类磁铁矿粉为主体加重质,采用试验测量与基于Euler-Euler多相流模型的数值计算相结合的方法,考察流化床沿床层高度方向和轴向的密度分布特性。结果表明:当操作气速控制在1.50Umf≤U≤2.20Umf时,床层密度沿床层高度方向与轴向位置的分布范围分别为1.95～2.10 g/cm3与2.00～2.10 g/cm3,两者的密度标准差均小于0.20 g/cm3。其中,轴向密度稳定性要高于床高方向密度稳定性,因此在实际分选过程中要侧重保持沿床高方向的密度波动性最小,进而提高流化床三维空间内的密度均匀稳定性,试验测量与数值模拟结果基本吻合。

-0.5mm煤粉对空气重介质流化床流化特性的影响

为研究-0.5 mm煤粉在空气重介质流化床中的分布规律与影响效果,采用煤粉含量分布标准差、煤粉灰分分布标准差以及在稳定区间内的压降波动标准差3个指标分析了煤粉在分选流化床中的流化质量及分选性能。结果表明:-0.5 mm煤粉对流化质量有显著影响,少量-0.5 mm煤粉能促进形成密度均匀稳定的分选流化床,过多煤粉含量对流化床密度稳定不利,试验条件下最佳的-0.5 mm含量为6%;同时揭示了-0.5 mm煤粉在流化床中的分布规律,为空气重介质流化床的分选稳定控制提供了依据。

基于机器学习的Geldart A类加重质流化床的床层膨胀特性研究

为了预测Geldart A类加重质的膨胀特征,通过床层塌落试验,研究了床层流化过程中的气泡相和乳化相的组成与操作因素之间的关联,构建了操作气速、静止床高以及床层膨胀高度的数据集,进行了数据统计分布和相关性分析,利用具有最佳超参数的GBDT模型成功模拟了膨胀高度和影响变量之间的非线性关系,分析了特征变量的敏感性。结果表明,随着气速的逐渐增加,乳化相与气泡相的膨胀呈现先增加并略有减小的规律。对于不同的初始床高与床层膨胀高度,气泡相组成不受其变化的影响且组成比例相对稳定。操作气速的重要性得分是0.68,是膨胀高度最敏感的变量。而静止床高的重要得分仅为0.32,表明此变量对床层膨胀的影响较小。此外,由部分相关性分析可知,床层的膨胀高度对操作气速的依赖性具有一定的敏感性区间。

干法重介质流化床中加重质颗粒与煤表面碰撞黏附特性研究

【目的】流态化干法分选技术是气固两相理论在选煤领域的拓展延伸。使用干法重介质流化床对原煤进行分选时,煤炭的表面水分便随着气流携带、颗粒运动等因素在床层中运移扩散,导致加重质发生颗粒团聚现象。颗粒聚团是由于流体作用以及颗粒间耗散作用形成的颗粒富集,是一种不均匀的介尺度结构。颗粒聚团可降低流化质量,导致床层失稳,床层内部密度分布不均,产品质量变差。【方法】以颗粒碰撞黏附过程为切入点,探究潮湿条件下加重质颗粒与煤表面之间的碰撞黏附特性。【结果】结果表明,随着碰撞速度的增加,颗粒法向碰撞恢复系数呈上升趋势;相同湿度条件下,碰撞速度相同时,恢复系数随着颗粒粒径的增加而呈上升趋势;潮湿条件下流化床中颗粒间碰撞的主要能量损失为颗粒表面黏弹性损失及液桥黏附能损失,随着相对湿度的增加,液桥力引起的黏附能损失逐渐增大,颗粒恢复系数显著降低。【结论】揭示了颗粒聚团碰撞黏附机理,这为实现分选流化床中颗粒聚团的调控、维持床层稳定流化、提高流化床分选效果提供理论依据。

空气重介质流化床中细粒煤的流化与分选特性

3~1 mm粒级细粒煤介于煤粉与传统空气重介质流化床分选所适用的粒度之间,其在空气重介质流化床中被分选的同时对自身分选与流化特性产生重要影响。利用高速动态摄影等手段详细研究了空气重介质流化床分选3~1 mm细粒煤过程中不同流化数下床层的流化特性、压降波动、煤粒分离混合规律以及流化床中不同高度处的密度分布,阐释了气泡在分选过程中的作用机理。结果表明,加入一定量细粒煤后床层密度降低,流化效果发生了一定程度的改变。随着气速的增加,煤粒在流化床中先后经历了分离与混合两种状态,流化床各高度的密度也随之改变。当流化数在1.8~2.0时煤粒达到较好的分离效果。随着气速增大煤粒受气流影响增大,不再严格按照流化床密度分离。

CFB密相区大颗粒横向扩散系数的CPFD模拟

运用一种离散单元法(DEM)计算颗粒流体力学(CPFD)对尺寸为900 mm×100 mm×1200 mm的准三维流化床的密相区大颗粒扩散行为进行研究。模拟之前,依照前人实验研究对CPFD方法进行验证,模拟结果与实验结果符合较好,证明了CPFD方法模拟的有效性。模拟中通过注入示踪粒子的方法来研究大颗粒在密相区中的横向扩散系数,研究了流化风速、颗粒直径对颗粒横向扩散系数的影响。模拟结果显示,气泡是引起密相区内颗粒混合的主要因素;随着流化风速增加,颗粒横向扩散系数变大;随着颗粒直径增大,颗粒横向扩散系数减小。

新型干法分选机分选过程影响因素分析

设计了一种新型空气重介质流化床,利用振动反倾角工作面替代刮板排出矸石。采用正交法对影响新型干法分选机分选和输送效果的主要因素进行了实验研究和方差分析,结果表明:风量和振动频率对分选效果有高度显著的影响,风量、振动频率以及实验时间对输送效率都有高度显著的影响,风量Q=160 m3/h、振动频率f=16.6 Hz、实验时间T=40 s时,可能偏差Ep=0.055 g/cm3、输送效率90%,取得了理想的分选和输送效果。

空气重介质振动流化床入料特性与操作参数的协同研究

入料物性直接影响空气重介质流化床的分选效果,为此进行了不同粒度和不同可选性煤样的分选特性研究,考察了抛射强度、风量与入料特性的协同作用。结果表明：粒级对分选精度的影响显著,随粒级减小,Ep值变大,50～25,25～13和13～6 mm粒级难选煤最小Ep值分别为0.06,0.07和0.11 g/cm3;可选性对Ep值略有影响,50～25 mm粒级不同可选性煤样,易选、中等可选和较难选煤样最小Ep值分别为0.035,0.040和0.045 g/cm3。通过优化风量和抛射强度,分选精度明显提高,不同粒级或可选性煤样优化后的风量和抛射强度相近,均分别在140 m3/h和1.46左右。分析了气泡生成频率与床体振动频率的关系,揭示了振动改善流态化分选的作用机理。

空气重介流化床介质流动和床层密度分布研究

建立了空气重介质流化床的多相流体力学模型 ,基于选矿实验室的二维床 ( 60 cm× 1 .2cm)求解了介质速度和密度的分布 .结果表明 :模拟结果和实验结果符合性很好 .磁性介质在流化床内部呈现出中心上升边壁下降的流动趋势 .固体颗粒的运动速度很小 ,在床内的大部分区域其速度在 - 40～ 40 mm/ s之间 .在气体的表观速度为 0 .1 5 7m/ s时 ,床层密度值为 1 .96± 0 .0 3。

空气重介流化床粗粒物料分选机理的研究

对空气重介流化床的分选过程进行了试验和理论研究，针对物料分选产生错配的根源，将错配效应分成了“粘性错配效应”和“运动错配效应”两个部分。提出的流化床中粗粒物料的分选理论能够满意地解释不同流化状态下的分选试验结果。

潮湿褐煤干法分选实验研究

为提高空气重介质流化床对入料煤水分的适应性，以热气代替常温空气改善流化床对褐煤的分选效果。采用可能偏差 E p为评价指标，研究了热态空气重介质流化床的干燥温度、干燥时间和风量对褐煤分选效果的影响。结果表明：干燥温度为30~50℃时，干燥温度越高，Ep越低；干燥时间为1~5 min 时，干燥时间越长，Ep越低，超过3 min 后，Ep降低缓慢；风量为8~12 m3/ h 时，风量增大，Ep先降低后升高。煤样表面水分越高，干燥温度、干燥时间和风量变化对 E p影响越显著。表面水分1％的褐煤，干燥温度50℃、干燥时间5 min、风量10 m3/ h 时，褐煤分选效果最好，Ep 可达到0.022 g / cm3。实验证明热态空气重介质流化床可用于分选潮湿褐煤。

空气重介流化床选煤过程中介质动态平衡的研究

通过对空气重介流化床选煤过程中介质动态平衡的研究，建立了流化床密度与介质中煤粉含量的关系模型，给出了分流量的计算方法，同时建立了分流量与流化床密度的数学模型，为流化床密度的在线测控提供了基础，试验研究表明，通过调节介质分流量，保持介质动态平衡和产品数质量指标，可能偏差Ｅｐ值达０．０３８～０．０６，取得了良好的结果。