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.     

PLC变频调速在空气重介质流化床中的应用

空气重介质流化床干法选煤是适用于缺水地区煤炭加工的一种方法．阐述了流化床床高和密度对分选过程的影响和重要性,针对其特定的工艺特点提出利用PLC对空气重介质流化床叶轮给料器进行变频调速,使流化床床高和密度保持均匀、稳定．     

Effect of agitation on the characteristics of air dense medium fluidization

In order to study the effect of agitation on the characteristics of air dense medium fluidization, we designed and constructed an agitation device. Analyses were then conducted on the fluidization characteristics curves, the bed density stability and the average bubble rise velocity Uaunder different agitation conditions. The results indicated that a lower bed pressure drop(without considering lower gas velocity in a fixed bed stage) and higher minimum fluidized velocity are achieved with increasing agitation speed.The height d(distance between the lower blades and air distribution plate) at which the agitation paddle was located had a considerable effect on the stability of the bed density at 9.36 cm/s U 10.70 cm/s. The higher the value of d, the better the stability, and the standard deviation of the bed density fluctuation r dropped to 0.0364 g/cm~3 at the ideal condition of d = 40 mm. The agitation speed also had a significant influence on the fluidization performance, and r was only 0.0286 g/cm~3 at an agitation speed of N = 75 r/min. The average bubble rise velocity decreased significantly with increasing agitation speed under the operating condition of 1.50 cm/s U–U_(mf) 3.50 cm/s. This shows that appropriate agitation contributes to a significant improvement in the fluidization quality in a fluidized bed, and enhances the separation performance of a fluidized bed.     

空气重介质流化床中入料颗粒的受力特性

入料颗粒在空气重介质流化床中所受合力是决定颗粒运动行为与分离特性的关键.在理论分析的基础上,建立了入料颗粒在流化床中运动时的受力平衡方程.采用自行研制的颗粒受力测量装置,对不同粒径示踪颗粒在流化床中的受力变化进行了准确测量,结果表明:对粒径为8～10mm、密度为7 850kg/m3的球形颗粒,在以0.3～0.1mm高密度磁铁矿粉作为加重质形成的稳定流化床中,其受力稳定,并与理论计算符合良好.     

Characteristics of fluidization and dry-beneficiation of a wide-size-range medium-solids fluidized bed

Wide-size-range medium-solids are used in a modularized coal beneficiation demonstration system with a gas-solid fluidized bed. The characteristics of fluidization and dry-beneficiation of the medium solids were studied. The numerical simulation results show that 0.15–0.06 mm fine magnetite powder can decrease the disturbances caused by the bubbles. This is beneficial to the uniformity of the gas-solid interactions and thus to the uniformity and stability of the bed density and height. The experimental results show that, with an increase in the fine coal content in medium solids, both the fluidization quality and the beneficiation performance of the bed decreased gradually. When the fine coal content was no more than 13%, a relatively high superficial gas velocity increased the beneficiation efficiency. When the content was more than 13%, part of the fine coal was separated, leading to product layers. The separation efficiency was therefore gradually decreased. The models for predicting the bed density standard deviation and the probable error, E, value were both proposed. The E value can reach to 0.04–0.07 g/cm~3 under the optimized experimental parameters. This work provides a foundation for the adjustment of the bed density and the separation performance of the modularized 40–60 ton per hour dry coalbeneficiation industrial system.     

空气重介流化床干法选分配曲线数学模型研究

借鉴湿法选分配曲线数学模型，研制出空气重介流化床干法选分配曲线的最佳数学模型——复合ＬＯＧＩＳＴＩＣ－ＧＯＭＰＥＲＴＺ模型，通过大量的计算机模拟工作，验证了该模型的可行性。     

采用空气重介流化床选煤技术分选高密度无烟煤的研究

针对高密度老年无烟煤的煤质特征与分选要求，本文从理论分析和实验研究两个方面论述了采用空气重介流化床干法选煤技术分选高密度老年无烟煤的结果。     

流化床垃圾焚烧炉物料混合特性试验研究

采用焚烧方法进行城市生活垃圾处理时,由于国内垃圾混合收集的特点,大量尺寸较大的物料如建筑垃圾等都入炉燃烧,如不及时排出将影响床内物料的流化质量．针对这一问题,研究开发了异重流化床垃圾焚烧技术,采用倾斜布风板、导向风帽将这些惰性物料有效地排出炉外,依据这一技术,成功投运了一台150t／d处理量的垃圾焚烧炉,对水平布风板和倾斜布风板在使用普通风帽和导向风帽时的物料混合特性进行了对比研究．     

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.     

脉冲鼓泡床内鼓泡和颗粒混合特性的CFD-DEM数值模拟

基于FLUENT软件信息传递模式的MPI(message passing interface)并行计算平台,通过用户自定义函数(user-defined functions, UDFs)文件发展一种拟三维颗粒的计算流体力学(computational fluid dynamics, CFD)-离散单元法(discrete element method, DEM)耦合并行算法。采用该算法数值模拟了脉冲鼓泡床内气固两相流动,揭示了气相鼓泡特性和颗粒混合机制。数值模拟结果表明:该算法具有随计算节点数增加的良好扩展性能和加速性能;在鼓泡过程中,主流两侧的小尺度气流涡逐渐发展为双主涡;单气泡通过床层后,颗粒混合仅局限于射流触及区域;数值模拟结果与相关试验和数值模拟结果吻合较好,表明该并行算法能够较好的模拟稠密颗粒气固两相流中鼓泡和颗粒混合特性,为其在大规模并行集群上的应用奠定基础。     

Mechanism and application of coal dry beneficiation with air-dense medium fluidized bed

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宽筛分颗粒高压热态最小流化速度的实验研究

在内径80 mm的加压热态流化床实验台上,以4种不同平均粒径的宽筛分颗粒为实验物料,研究了在压力(0.1～4.5 MPa)和温度(20～800℃)范围内实验物料的最小流化速度。实验结果表明:在相同的温度下,最小流化速度随压力的增加而减小。而在相同的压力下,温度对最小流化速度的影响随床料的种类的不同而有明显的差别。基于Ergun方程和床层受力分析,得到了最小流化速度的计算式,给出了高温高压宽筛分颗粒流化床最小流化速度合理计算步骤,并与其他研究者的关联式和实验结果进行了对比,结果表明本文提出的预测方法与实验结果吻合较好,相对误差在10%以内,为增压流化床反应器的设计和运行提供较可靠的参考依据。     

流化床造粒过程层式生长的实验研究

通过在流化床中将碳酸钾溶液雾化后喷涂在处于流化状态的玻璃珠上，研究了流化床造粒过程的层式生长机理。考察了床层温度、流化气速及溶液浓度等对涂覆率的影响。结果表明在实验范围内，造粒过程为典型的层式生长过程，造粒时间对涂覆率影响较小。床层温度对涂覆率影响显著、流化气速及溶液浓度对涂覆率也有较大影响，而且均是非单调的。     

接触式风水共冷对流化床灰渣的活化作用研究

提出了接触式风水共冷的灰渣冷却方式,研究了这种冷却方式对流化床灰渣的活化作用机理.在冷渣器中通入冷却风使高温灰渣处于流化状态,通过雾化喷嘴将冷却水喷入床内与灰渣直接接触.采用分峰法对冷却后灰渣样品的X衍射图谱进行非晶态含量分析,用国家标准方法测定了灰渣的活性指标--抗压强度比.试验结果表明,这种冷却方式与堆积自然冷却、风冷、喷雾冷却等相比,冷却速率提高5倍以上;对灰渣颗粒表面具有较强的腐蚀作用,有效增加了灰渣中的非晶态矿物含量,使灰渣得以活化;灰渣的抗压强度比提高了5%～10%.     

Effect of geogrid reinforcement on soft and medium dense soils

The field tests were carried out to examine the reinforcement effect of a geogrid on various conditions of embankment height, the number of passages of vibratory roller, the number of reinforced layer of geogrid, and soil properties. The test results of the dynamic earth pressure indicate that the soil reinforced by geogrid is very effective to increase the stiffness of soil, especially in soft soil. The dynamic earth pressure ratio, which is defined as the ratio of dynamic earth pressure to self weight of soils, exponentially decreases as the embankment height increases. The dynamic earth pressure ratio increases up to 80% for soft soils reinforced by both one layer of geogrid in place of no reinforced soils and two layers in place of a single layer of geogrid.     

中低品位磷矿重介质选矿试验

对宜昌丁东磷矿进行重介质选矿试验.当分离密度为2.96 g/cm^3时,沉物P2O5品位达30.86%,回收率55.61%,MgO为0.95%,可获得合格精矿;当分离密度为2.70 g/cm^3时,浮物可抛去17.35%左右的尾矿,可作中低品位胶磷矿预选作业,若再用浮选,即可获得优质精矿.     

在流化床中热解废旧塑料的实验研究

对高密度聚乙烯(HDPE)、低密度聚乙烯(LDPE)、聚丙烯(PP)、聚苯乙烯(PS)和聚氯乙稀(PVC)等5种单组分废旧塑料在流化床中进行了热解实验,得到了在实验条件下,热解温度对各种单组分废旧塑料热解产物成分和产率的影响规律,为开发废旧塑料热解制油、制气工业装置提供了基本的工艺参数.     

液固流化床中物料属性对固体混合物分布的影响

利用窄粒度和窄密度分布的石英砂和细粒煤作为实验物料,在液固流化床中进行了两种物料混合物的流化实验研究.结果表明,轻物料的自由沉降速度大于重物料的自由沉降速度是颗粒群发生完全混合和反分层的必要条件,提出了双物料混合物能否发生完全混合的判据;在双物料混合物中,当两种物料的有效密度比与粒度比的比值(ρe1/ρe2)/(d2/d1)大于1.5时,两种物料才能发生完全混合,并且该比值越大,完全混合越容易发生.     

流化床油页岩流化特性的数值模拟研究

应用CFD软件Fluent对流化床内油页岩的流动特性进行了冷态流场模拟,并研究不同时刻、不同粒径以及不同弹性恢复系数对流化床内流化状态的影响。最终模拟结果表明：随着时间的推移流化现象越来越明显,同时颗粒粒径越小,弹性恢复系数越小更容易使气流稳定,有益于物料的正常流化。