FINE COAL AND THREE PRODUCT DRY BENEFICIATION WITH VIBRATION AND DOUBLE-DENSITY FLUIDIZED BEDS

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Vibrated fluidized bed air classification of moist raw coal

Vibrated fluidized bed air classification is completely different from traditional screening in principle. It extracts fine coal from moist raw coal by entrainment of an ascending airflow in a vibrated fluidized bed. Pilot tests showed that air classification efficiencies varied from 74.85% to 93.84% at cut-size 6, 4, 3, 2, 1, and 0.5 mm when free moisture of coal is in the range of 1.7% to 9.5%, and ash contents of fine coal products were 2%～3% lower than those of the same size fractions in feed, and 4%～10% lower than those of feeds for most cases because of the density differences between coal and waste, which is beneficial to producing lower ash fine coal from raw coal as fuel of blast furnaces or pulverized coal firing boilers. A commercial unit of 100 t/h has been in smooth operation, and several 300～400 t/h units are in plan or construction.

Combined Removal of Surface Moisture and Dust from Feed Coal for Coal Dry Cleaning with an Air-solid Fluidized Bed

A demonstration plant and a commercial plant employing coal dry cleaning technology with an air-solid fluidized bed were built in China. The operation practice of these two plants shows that the surface moisture and the fines or dust of feed coal must be well controlled as low as possible. For this purpose, a new process of combined removal of surface moisture and dust from feed coal using a vibrated fluidized bed dryer was investigated in a batch test apparatus and a pilot test system. A mathematical model on drying kinetics of coal surface moisture was developed and three empirical formulas of the model coefficient involving the main operating variables were determined based on the test results from the batch test apparatus. The mathematical model shows that the surface moisture retained in coal during drying decreases exponentially with drying time. According to this model, a new divisional heat supply mode, in which the inlet gas of higher temperature was introduced into the fore part of the dryer and the inlet gas of lower temperature into the rear part of the dryer, was employed in the pilot test system. The pilot tests show that 1） the new divisional heat supply mode is effective for lowering down the average temperature and reducing the total heat loss of the outlet gas off the dryer, 2） the moist coal of about 60 g/kg surface moisture contentcan be dried to about 10 g/kg, and simultaneously the fines （〈1mm in diameter） adhering to the surface of coarse coal particles are completely washed off by the gas flow.

Cooling of Granules in Vibrating, Suspended Bed: Engineering Simulation

Here we suggest an algorithm for calculation of the process parameters and design of a vertical cooler with inclined, gas-permeable blades and with a vibrating, suspended layer of granules on them (Vibrating Fluidized Bed—VFB). The algorithm is based on the use of the equations of heat and material balance, taking into account the influx of moisture into the layer with cold air and dust—as a carryover. Mode entrainment of dust particles and moisture from the VFB is described by using empirical formulas and Π-theorem. To calculate the cooling time of granules a model of the dynamics of a variable mass VFB was built, which linked the geometrical and physical process parameters to a single dependency. An example showed that mass flow of granules of 248 kg/h and a volume flow of air of 646 m3/h with temperature of 30℃ to cool the zeolite granules from 110℃ to 42℃ for 49 s required a vertical apparatus of rectangular shape with four chambers and with volume of 0.2 m3. A comparative analysis of technological parameters of the projected cooler with the parameters of typical industrial apparatuses showed that for all indicators: the cooling time of granules, the flow rate of gas (air) and the heat flow, a 4-chambered, vertical apparatus of rectangular shape with VFB was the most effective.

Characteristic research of regeneration process of particulate filter medium in vibrated fluidized bed

The vibrational fluidized bed is innovatively adopted to regenerate the particulate filter medium for the purification of crude syn-thesis gas from the coal gasification process.Characteristic research of vibrated fluidized beds during dust-containing particulate filter medium regeneration has been carried out.The ideal transport model of particulate filter medium on the distributor is estab-lished and verified by using experiments.The mean residence time of the particulate filter medium can be reduced by 72%from 5.5 to 1.5 min with an increase in the working frequency from 50 to 60 Hz.The thickness of the bed layer is linearly increased with the feeding rate of the particulate filter medium under ideal working conditions.The resistance models of the fluidizing air are built up and validated,and they can be used to calculate the pressure drop of the static bed layer of the particulate filter medium on the flu-idizing air distributor,which is the maximum value of the dynamic bed layer with the same thickness.The fluidizing air makes the mean residence time of the particulate filter medium decrease by 50%and reduces the difference in the particulate mean residence time under different feeding-rate conditions.The regeneration effect of dust-containing filter medium particles in a vibrated fluidized bed is evaluated.Fluidizing air with superficial velocity ranging from 0 to 0.6~0.9 m·s-1 makes the regeneration efficiency increase from 29.41%to 70.59~88.24%.This article provides a reference for the industrial application of a vibrated fluidized bed for the par-ticulate filter medium recycling system.

WaveBehaviorofVibratingFluidizedBeds

Experimental data show how vibration energy is imparted to a vibrating fluidized bed (VFB). A new type of sensor was used to measure the wave signals in a VFB. The experimental results show that the vibration energy imparted is through continuous wave propagation in the vibrating fluidized bed. Wave characteristics are affected by the bed properties. A bubble's behavior in the bed is followed by analyzing the wave frequency spectrum.

脉动流化床内青刀豆颗粒的混合特性数值模拟

青刀豆一般采用流化床装置进行速冻。为了解决其床层堵塞和聚集不良的问题,进一步提高青刀豆的混合效率,课题组建立了三维混合脉动流化床模型,将计算流体力学与离散单元法(computational fluid dynamics-discrete element method,CFD-DEM)相结合,探究1,2,4和8 Hz 4种不同频率的脉动进口风速下青刀豆颗粒的流化混合情况。仿真结果表明:脉动流化床对于青刀豆颗粒混合具有一定改善作用,青刀豆颗粒的轴向混合强于径向混合,4 Hz时颗粒混合标准偏差值最小;当进口风速的频率接近颗粒的自主振动频率时,床层膨胀最明显,出现类似“共振”的现象;2 Hz时颗粒径向、轴向混合效果最佳,频率过大或过小对于流态化增强效果不明显。

350 MW超临界等级循环流化床锅炉尾部烟道振动研究

国内多个350 MW超临界等级循环流化床锅炉反馈尾部烟道均出现不同程度的振动。振动发生时,尾部烟道及一定范围内的烟道刚性梁、锅炉平台等均有明显振动,并伴随有低沉的嗡鸣声音。长期频繁振动会造成尾部受热面管排金属疲劳失效,导致受热面泄漏引起机组非停,甚至可能造成安全隐患。以某350 MW超临界循环流化床锅炉为例,结合该项目烟道本身的结构特性和声学特性对烟道系统内振动情况进行分析,找出振动产生的原因并制定相应的改造方案,为其他锅炉尾部烟道系统振动改造提供经验。

Influence of bubbles on the segregated stability of fine coal in a vibrated dense medium gas-solid fluidized bed

In this paper,the variation of bubble size and number in the separation process of vibrated fluidized bed as well as the influence of bubble movement on the axial distribution of fine coal in different positions of the bed were studied.The result revealed that the size and number of bubbles is correlated with the fine coal separation effect in the separation process.When the bed is in a uniform and stable fluidized state,the size of bubbles in the separation process was in the range of 1-2.5 cm and the number of bubbles was reduced by nearly 50%,which is helpful to promote the stratification and segregation of fine coal.Thereby,after separation,the ash content of refined coal products of anthracite and 1/3 coking coal was reduced to 12.1% and 23.7% respectively,and the content of refined coal was up to 42.5% and 68.5% respectively,which show that the vibrated fluidized bed has a good separation performance,and can separate efficiently the coal of size−6+1 mm.

The Influence of an Acoustic Field on the Bed Expansion of Fine Particles

Fine particles are difficult to fluidize due to strong interparticle attraction.An attempt has been made to study the bed expansion of silica gel(dp=25μm) powder in presence of an acoustic field.A 135 mm diameter fluidized bed activated by an acoustic field with sound intensity up to 145 dB and frequency from 90 Hz to 170 Hz was studied.The effects of sound pressure level,sound frequency and particle loading on the bed expansion were investigated.Experimental results showed that,bed expansion was good in presence of acoustic field of particular frequency.In addition,it was observed that in presence of acoustic field the bed collapses slowly.

振动重介质分选流化床流化质量改善机理与细粒煤高效分选

煤炭清洁高效利用是国家重大战略需求。随着我国煤炭工业重心战略西移和综采技术的普及,所开采的原煤尤其是动力煤日趋“贫、细、杂”化,迫切需要细粒煤高效干法分选技术。细粒煤具有迎风面积小、重力效应弱的特点,风力分选时介质密度与分选密度差异大,传统的干法重介质分选时气泡大、返混严重,均无法在有限时间和空间内实现细粒煤有效分离。将简谐振动与上升气流协同输入气固重介质流化床,通过振动能量强化气固接触、抑制气泡兼并、改善流化质量。着重研究了振动能量在床层中的传递过程与床层响应规律,发现床层密度的扰动程度主要取决于上升气流与振动能量的竞争协调结果,气泡引发床层密度的随机性波动,振动能量将颗粒由无规律的随机运动转变为周期性振荡,沿床层轴向挤压破碎气泡;基于经典两相理论,结合床层塌落过程中气泡相与乳化相的逸出规律,计算得到了振动激励下气体在气泡相与乳化相中的分布比例,表明振动能量可以有效驱使气体由气泡相迁移至乳化相,气泡体积减少19.23%,削弱了气泡引起的床层波动,改善了流化质量,形成了均匀稳定的流态化分选环境。建立了振动对流化质量改善效果的量化评价模型,明确了适合细粒煤高效分选的振幅、频率、气速3因素协同操作范围,将新疆黑山矿薄煤层6~1 mm精煤发热量相较于原煤提高了4 571 kJ/kg。

振动分选流化床气泡动态演变与细粒煤分选特性

振动流化床能够有效强化细粒煤的分选提质过程,通过利用二维振动分选流化床,以煤粉和磁铁矿粉混合作为二元复合加重质,采用压力传感器测量床层中的压力信号,结合高速动态摄像机同步捕捉气泡在床层中的演变行为,研究二维振动分选流化床中气泡的动态演变规律,探索气泡行为对细粒煤分选效果的影响。此外,利用塌落试验,研究不同操作条件下床层膨胀高度和气泡体积占比,进而揭示振动气流协同对气泡动态演变行为的抑制作用。研究结果表明,振动能量的引入能够促进颗粒床层均匀流化,在v=16 cm/s,f=20 Hz和A=2 mm条件下,床层压降波动稳定,随振动频率的增大,床层完全流化膨胀高度H_(e)先增加后减小,气泡相体积分数Y先减小后增大。但随着振幅的增加,床层完全流化膨胀高度H_(e)先增加后减小,气泡相体积分数Y逐渐增大。振动与气流的协同作用对床层中的气泡行为具有明显的抑制作用,但随着床层高度的增加,气泡尺寸的瞬时值和平均值均逐渐增大,且在床层中上部,气泡尺寸分布范围较宽。在最佳操作条件下,气泡平均尺寸为1.12~2.45 cm,气固接触效率高,床层介质颗粒呈准散式流化,此时,气泡对细粒煤分选效果的扰动作用弱,细粒煤分选效果最好,选后精煤灰分和产率分别为8.2%和56.1%,矸石的灰分和产率分别为44.5%和43.9%。

Reactive gas-solids flows in large volumes—3D modeling of industrial circulating fluidized bed combustors

A model is presented for the simulation of reactive gas-solids flows in large industrial reactors. Circulating fluidized bed （CFB） combustors with several thousands of cubic meters reaction volume are probably the largest reactors of this type. A semi-empirical modeling approach has been chosen to model the three-dimensional concentration distributions of gas and solids components and temperatures inside the combustion chamber of such boilers. Two industrial CFB boilers are investigated in detail： the 105 MWe Duisburg combustor in Germany and the 235 MWe Turow combustor in Poland. The semi-empirical model approach is described first. Then the model is used to show how the three-dimensional concentration and temperature fields are formed by the interaction of several local phenomena. Good agreement between simulation and measurements has been achieved.

ZLG型振动流化床在硫酸铵生产过程中的应用与改进

文章介绍了ZLG型振动流化床的工作原理,在振动流化床运行过程中通过对进料形式、进风形式、旋风除尘器、清洗方式等进行改进,对进风风压、物料输送速度等关键参数进行调试,并根据生产实际安装测压装置用来监测箱体内的气体压力,取得了较好的效果。

振动参数对流化床分选性能的影响

干法分选对于缺水地区煤炭的加工十分必要,将振动外力场引入普通气固流化床,形成振动重介质流态化,在100 mm×100 mm×220 mm振动流化床装置上,通过分层采样分析,研究了振动及气流参数对分选效果的影响,结果表明:振动强度K对分选效果有显著影响,当K=1.63时,分选效果最佳,可能偏差E为0.07.因振幅改变引起的K的变化对分选效果的影响显著于因振动频率改变引起的K的变化对分选效果的影响.振动方向对分选效果也有较大影响,在分选状态下,垂直振动时的分选效果要优于水平振动.振动流化床的分选性能对气速u较敏感,当u=1.15 cm/s时,分选效果最佳.床层高度H愈低,分选效果愈好,但必须满足足够的分选空间,H应取75 mm.

物料在振动力场流化床中的分离

我国2/3以上的煤炭资源分布在西北等干旱缺水地区,煤炭的高效干法分选技术十分必要,基于振动流化床的分选特性,在80 mm×200 mm×2 000 mm连续式振动流化床分选系统上研究了不同条件下物料在床层中的分离规律及分选效果,结果表明:流化床的似流体特性、水平方向的激振力以及流化床的溢流作用是入选煤在床层中连续分层和移动的动因,在本试验条件下,振动方向α=40°,有效分选带长1 850 mm时,可以发挥振动流化床的最大分选效能,可能偏差E值达0.075,可以实现细粒煤的连续有效分选.

振动波在流化床中的传播行为

在试验基础上，阐述了振动床及振动流化床中振动能的输入方式.对于振动床，振动能输入方式是振动床体对粉体床层的碰撞.对于振动流化床，振动能输入方式是振动波在流化床悬浮体中的连续传播，床层特性影响波的传播特性.通过压力波动的频谱分析，可以考察床层中的气泡行为.

振动流化床的形成机理

研究了振动能量在细颗粒床中的传递以及振动与气流交互作用过程，揭示了振动对气泡的破碎作用机理以及微泡振动流化床的形成机理，并给出了有效抑制气泡生成的临界振动频率计算关联式.试验结果表明：振动流化床密度分布均匀，床层压力波动小，实测值与理论分析结论一致.

振动流化床中浅床层时床层与分布板之间的弹性作用

采用A类颗粒作为实验粉体，通过测量床层对分布板的作用力，分析了振动流化床中分布板与床层的作用机理，提出了振动流化床中在浅床层共振时分布板与床层的弹性作用模型. 实验表明，分布板与床层之间是连续的弹性作用，周期性的机械振动通过分布板与床层之间的弹性作用以波动形式在床层中传播. 该模型计算结果与实验测定结果符合的较好.

振动流化床生产三聚氰酸工艺

在特制的多层立式振动流化床干燥器上,研究了停留时间、加热温度、加热气量、振动频率和振幅等因素对尿素氰酸缩聚反应生产三聚氰酸的影响。结果表明:当加热温度大于220℃时,停留时间是影响反应的主要因素,此时尿素转化率的变化与传统的干燥速率曲线类似。根据实验结果得出相应的经验公式,可用于反应器的设计计算。